mechanical recycling of consumer electronic...
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LICENTIATE T H E S I S
Luleå University of TechnologyDepartment of Chemical Engineering and Geosciences, Division of Mineral Processing
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Mechanical Recycling of Consumer Electronic Scrap
Jirang Cui
Mechanical Recycling of Consumer Electronic Scrap
Jirang Cui
Division of Mineral Processing Department of Chemical Engineering and Geosciences
Luleå University of Technology,SE-971 87, Luleå, Sweden
May 2005
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ABSTRACT
Consumer electronic equipment (brown goods), such as television sets, radio sets, and video recorders, are most common. However, recycling of consumer electronic scrap is only beginning.
Characterization of TV scrap was carried out by using a variety of methods, such as chemical analysis, particle size and shape analysis, liberation degree analysis, thermogravimetric analysis, sink-float test, and IR spectrometer. A comparison of TV scrap, personal computer scrap, and printed circuit boards scrap shows that the content of non-ferrous metals and precious metals in TV scrap is much lower than in personal computer scrap or printed circuit boards scrap. It is expected that recycling of TV scrap will not be cost-effective by utilizing conventional manual disassembly. The result of particle shape analysis indicates that the non-ferrous metals particles in TV scrap formed as a variety of shapes, it is much more heterogeneous than for plastics and printed circuit boards. The results of sink-float tests demonstrate that a high recovery of copper could be produced by an effective gravity separation process. Identification of plastics shows that the major plastic in TV scrap is high impact polystyrene. Gravity separation of plastics may encounter some challenges in separation of plastics from TV scrap because of specific density variations.
Furthermore, Mechanical recycling of TV scrap oriented to recovery of non-ferrous metals is highlighted by using several techniques, such as air table, eddy current separation, and optical sorting. The separation results reveal that air table separation is an effective technology to recover metals from consumer electronic scraps. By using a DGS table, approximately 90% of non-ferrous metals were recovered in the heavy product with a purity of 40%. Printed circuit boards and cables in TV scrap cause metals loss due to the fact that metals in printed circuit boards and cables are not liberated from plastics and ceramic materials. The study shows that eddy current separation and optical (metal) sorting process provide alternatives to recover metals from TV scraps.
At last, new developments of eddy current separation, such as wet eddy current separation and Magnus separation are discussed in the thesis. A comparison of eddy current separation and Magnus separation on aluminum recovery shows that wet eddy current separation is more effective for recovery of fine non-ferrous particles.
Keywords: WEEE; Consumer electronic scrap; Recycling; Characterization; Mechanical separation; Materials recovery; Eddy current separation; Air table separation; Optical sorting; Magnus separation
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ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to my supervisor, Professor Eric Forssberg for his guidance, encouragement and invaluable discussions. I am very grateful to Dr. Peter Rem at Faculty of Civil Engineering and Geosciences, Delft University of Technology (TU Delft), the Netherlands, for his creative instructions on eddy current separation. I also thank Professor M.A. Reuter at Faculty of Civil Engineering and Geosciences, TU Delft for providing an opportunity of doing three-month research work at TU Delft.
I would very much like to express my deep gratitude to Professor Shouci Lu at University of Science and Technology Beijing for his encouragement, help and discussions concerning work and life in the past ten years.
I am also indebted to Professor Bo Bjökman, Director of the Minerals and Metals Recycling Research Centre (MiMeR) for providing me an opportunity to conduct this subject. Thanks also go to staff and colleagues at the Department of Chemical Engineering and Geosciences, Lulea University of Technology (LTU), for a friendly and cooperative academic environment, particularly Dr. Yanmin Wang for his suggestions on my experimental work, Dr. Bertil Pålsson for his prompt assistance to solve computer problems and an introduction of the image process system, Dr. Nourreddine Menad for his conducting TGA analysis and invaluable comments on my papers, Dr. Hamid-Reza Manouchehri for his conducting optical sorting experiments, Ms. Siv T. Berhan and Lic. Eng. Mia Tossavainen for their care and help.
I would like to appreciate invaluable contributions from Ms. Lenka Muchova and Mr. Bo Zhou at Faculty of Civil Engineering and Geosciences, TU Delft for their support and help during my stay in TU Delft.
I am very grateful to Mr. Sverker Sjölin at Stena Technoworld AB for providing the TV scrap sample and the identification of plastics, Mr. Johan Petersson at Draka Kabel Sverige AB for supplying the cable samples, Mr. Istvan Lukacs, OVAKO Steel AB for the chemical analysis of samples. Financial support from MiMeR. LTU, Sweden is gratefully acknowledged.
Thanks go to all Chinese friends for their help, particularly Dr. Qixing Yang for the translation of Swedish mails, Lic. Eng. Mingzhao He for his suggestions of my work, and Dr. Hongyuan Liu for his help.
Last but not least, I thank my Rong’er, parents, grandmother, brother and sister for there love, continuous encouragement, patience and support.
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LIST OF PAPERS
This thesis is based on five papers referred to in the text by roman numbers:
I. Mechanical recycling of waste electric and electronic equipment: a review Jirang Cui, Eric Forssberg Journal of Hazardous Materials, B99 (2003) 243-263
II. Characterization of consumer electronic scrap oriented to materials recoveryJirang Cui, Eric Forssberg submitted to Waste Management
III. Mechanical separation of consumer electronic scrap Jirang Cui, Eric Forssberg, Hamid-Reza Manouchehri to be submitted to Waste Management
IV. Eddy current separation for fine particles Jirang Cui, Eric Forssberg to be submitted to Journal of Hazardous Materials
V. A comparison of Magnus separation and wet eddy current separation Jirang Cui, Lenka Muchova, Peter Rem, Eric Forssberg to be submitted to Resources Conservation and Recycling
Paper related to, but not included in the thesis:
Recycling of consumer electronic scrap Jirang Cui, Eric Forssberg Accepted by the 4th Colloquium of SORTING: Innovations and Applications,Berlin, Germany, October 2005
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CONTENTS
1. Introduction......................................................................................................11.1. Management of waste electric and electronic equipment ........................................ 11.2. Mechanical recycling processes............................................................................... 21.3. Objectives of the present work................................................................................. 4
2. Materials and methods ....................................................................................52.1. Materials................................................................................................................... 52.2. Methods.................................................................................................................... 6
3. Characterization of consumer electronic scrap ..........................................113.1. Chemical analysis .................................................................................................. 113.2. Size and metal distribution of TV scrap................................................................. 113.3. Particle shapes of materials in TV scrap ................................................................ 123.4. Liberation degree of copper ................................................................................... 133.5. Sink-float test ......................................................................................................... 133.6. Quantification of plastics by thermogravimetric analysis...................................... 163.7. Identification of plastics by FT-IR spectrometer ................................................... 17
4. Mechanical separation of consumer electronic scrap.................................214.1. Ferromagnetics recovery........................................................................................ 214.2. DGS Table separation ............................................................................................ 214.3. Eddy current separation ......................................................................................... 224.4. Optical sorting........................................................................................................ 22
5. New developments of eddy current separation for fine particles ..............255.1. Theory .................................................................................................................... 255.2. Traditional eddy current separation for fine particles ............................................ 285.3. Preliminary study of Magnus separation and wet eddy current separation............ 29
6. Conclusions.....................................................................................................35
References:..................................................................................................................37
Paper I- V
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1. Introduction
1.1. Management of waste electric and electronic equipment
The production of electric and electronic equipment (EEE) is increasing worldwide. Both technological innovation and market expansion continue to accelerate the replacement of equipment leading to a significant increase of waste electric and electronic equipment (WEEE). In west Europe, 6 million tonnes of WEEE were generated in 1998, the amount of WEEE is expected to increase by at least 3-5% per annum (European Commission, 2000).
Due to their hazardous material contents, WEEE may cause environmental problems during the waste management phase if it is not properly pre-treated. Many countries have drafted legislation to improve the reuse, recycling and other forms of recovery of such wastes so as to reduce disposal (European Parliament and Council, 2003; Silicon Valley Toxic Coalition, 2002).
Recycling of WEEE is an important subject not only from the point of waste treatment but also from the recovery aspect of valuable materials. The U.S. Environmental Protection Agency (EPA) has identified seven major benefits when scrap iron and steel are used instead of virgin materials. Using recycled materials in place of virgin materials results in significant energy savings (as shown in Table 1 and 2) (ISRI, 1996).
Table 1 Recycled materials energy savings over virgin materials
Materials Aluminum Copper Iron and steel Lead Zinc Paper Plastics
Energy savings, %
95 85 74 65 60 64 >80
Table 2 Recycled materials energy savings over virgin materials
Materials Aluminum Copper Iron and steel Lead Zinc Paper Plastics
Energy savings, %
95 85 74 65 60 64 >80
Currently, recycling of WEEE can be broadly divided into three major stages: Disassembly (dismantling): Selective disassembly, targeting on singling out hazardous or valuable components, is an indispensable process. Upgrading: Using mechanical/physical processing and/or metallurgical processing to upgrade desirable materials content, i.e. preparing materials for refining process. Refining: In the last stage, recovered materials return to their Life Cycle.
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Consumer electronic equipment (brown goods), such as television sets, radio sets, and video recorders, are most common. However, recent work on recycling of waste electric and electronic equipment primarily focused on personal computer and printed circuit boards scraps (Zhang et al., 2000; Macauley et al. 2003; Li et al., 2004; Veit et al., 2005).
The European Directive (2002/96/EC) on waste electric and electronic equipment (WEEE) has to be implemented into national legislation by 13 August 2004 (European Parliament and Council, 2003). According to the WEEE directive, member states shall ensure that, by 31 December 2006, producers meet the following targets:
The rate of recovery for consumer electronic equipment shall be increased to a minimum of 75% by an average weight per appliance; Component, material and substance reuse and recycling for consumer electronic equipment shall be increased to a minimum of 65% by an average weight per appliance.
In order to meet the above targets, disassembly and mechanical recycling of consumer electronic scraps are of concern in European member states due to the fact that they are oriented to towards full materials recovery including plastics (Zhang and Forssberg, 1997; Langerak, 1997; Matsuto et al., 2004). In the practice of recycling of WEEE, selective disassembly (dismantling) is an indispensable process because it aims to remove hazardous or high value components (Stuart and Christina, 2003; Basdere and Seliger, 2003; Torres et al., 2004). However, a study of potential future disassembly of electronic scraps indicated that full automation disassembly of consumer electronic scraps will not be economically attractive by 2020 (Boks and Tempelman, 1998). As a consequence, a mechanical process is of interest for upgrading metal content of consumer electronic scraps because it can yield high material recovery.
1.2. Mechanical recycling processes
1.2.1. Magnetic separation Magnetic separators, in particular, low-intensity drum separators are widely used for the recovery of ferromagnetic metals from non-ferrous metals and other non-magnetic wastes. Over the past decade, there have been many advances in the design and operation of high-intensity magnetic separators, mainly as a result of the introduction of rare earth alloy permanent magnets capable of providing very high field strengths and gradients (Schubert, 1991).
1.2.2. Density-based separation Several different methods are employed to separate heavier materials from lighter ones. The difference in density of the components is the basis of separation. Gravity concentration separates materials of different specific gravity by their relative movement in response to the force of gravity and one or more other forces, the latter often being the resistance to motion offered by a fluid, such as water or air (Wills, 1988). The motion of a particle in a fluid is dependent not only on the particle’s density, but also on its size and shape, large particles being affected more than smaller ones. In practice, close size control of feeds to gravity processes is required in order to reduce the size effect and make the relative motion of the particle specific gravity dependent.
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The use of air to separate materials of differing density has long been known and is typified by the winnowing of grain using an air current to remove the chaff. Air tables have been used to eliminate a host of small problems in the food industry and in applications such as separating abrasive grains in the cleaning of foundry sand and removing metals from crushed slag (Fuerstenau and Han, 2003). In recent years, it also has been developed and implemented in a few electronic scrap recycling plants.
1.2.3. Electric conductivity-based separation Electric conductivity-based separation separates materials of different electric conductivity (or resistivity). There are three typical electric conductivity-based separation techniques: (1) eddy current separation, (2) corona electrostatic separation, and (3) triboelectric separation (Meier-Staude and Koehnlechner, 2000; Schubert and Warlitz, 1994; Higashiyama and Asano, 1998; van Der Valk et al., 1982; Stahl and Beier, 1997).
In the past decade, one of the most significant developments in the recycling industry was the introduction of eddy current separators whose operability is based on the use of rare earth permanent magnets. When a conductive particle is exposed to an alternating magnetic field, eddy currents will be induced in that object, generating a magnetic field to oppose the magnetic field. The interactions between the magnetic field and the induced eddy currents lead to the appearance of electrodynamic actions upon conductive non-ferrous particles and are responsible for the separation process. The separators were initially developed to recover non-ferrous metals from shredded automobile scrap or for treatment of municipal solid waste (Wilson et al., 1994; Dalmijn and van Houwelingen, 1995; Gesing et al., 1998; Norrgran and Wernham, 1991), but is now widely used for other purposes including foundry casting sand, polyester polyethylene terephthalate (PET), electronic scrap, glass cullet, shredder fluff, and spent potliner (Hoberg, 1993; Dalmijn and van Houwelingen, 1996; Meyer et al., 1995; Wernham et al., 1993; Schubert, 1994; Mathieu et al., 1990). Currently, eddy current separators are almost exclusively used for waste reclamation where they are particularly suited to handling the relatively coarse sized feeds. However, the number of waste streams containing fine metal particles is foreseen to grow substantially in the near future (Rem et al. 2000). In recent years, there have been some developments of eddy current separation processed designed to separate small particles (Zhang et al. 1999, Rem et al. 2000).
1.2.4. Optical sorting process With the fast development of Charge-Coupled Device (CCD) sensor, computing, and software technology, optical sorting process has been developed in both recycling and mineral processing industry (Kattentidt et al. 2003; Harbeck, 2001; Sötemann, 2000)). In addition, recording more and better data with sensors improves the separation performance of automated sorting equipment. The measuring of particle properties like color, texture, morphology, conductivity and others allows high quality sorting of mixed materials into almost pure fractions. Multi-sensor systems by using two or more different sensors were of concern in the past years (Kattentidt et al. 2003).
An automatic sorting device named “CombiSense 1200” was developed by Separation Systems Engineering (SSE), Wedel, Germany (Schäfer et al. 2003). This type of sorting is a combined opto-electronical system which is operating with a belt width of
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600 mm or 1200 mm. It combines the special characteristics of an optical system incorporating a high speed camera with a 1 billion colors recognition and a special conductivity sensor permitting the identification of a variety of metals. The CombiSense can handle mass streams of up to 10 tons/h for instance in the size classes 5-50 or 10-100 mm.
1.3. Objectives of the present work As discussed above, recycling of waste electric and electronic equipment is an important subject not only from the point of waste treatment but also from the recovery aspect of valuable materials. However, recent work on recycling of waste electric and electronic equipment primarily focused on personal computer and printed circuit boards scraps. Recycling of consumer electronic scrap is only beginning.
It is of great importance to characterize consumer electronic scrap in order to develop a cost effective and environmentally friendly recycling system. In the present study, one of the major objectives is to investigate the characteristics of television scrap by using a variety of methods, such as chemical analysis, particle size and shape analysis, liberation degree analysis, thermogravimetric analysis, sink-float test, and IR spectrometer. Mechanical processing technology has been widely utilized in recycling industry. As a consequence, it is also the objective to develop an improved separation system to separate valuable materials. Since eddy current separation plays a critical role in recovery of non-ferrous metals from waste steams, an investigation of new developments of eddy current separation is another objective.
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2. Materials and methods
2.1. Materials
2.1.1. TV scrap sample Television scrap sample was provided by Stena Technoworld AB, Bräkne-Hoby, an electronic recycling corporation in Sweden. End-of-life TVs of any model and brand with plastic houses that were collected primarily from Sweden were pre-dismantling to remove the cathode ray tubes, CRTs. Then the scraps were shredded into -12 mm particles. An approximately 30 kg of the TV scrap sample was procured and packed for the laboratory study. A detailed description of the sample preparation was given in paper 2.
A powdered sample was prepared by means of a turborotor grinder developed by Görgens Engineering GmbH, Germany, which is capable of grinding metallic materials and plastics. Before the grinding, ferrous metals were removed by a magnetic separator. This powdered sample was used for thermogravimetric analysis (TGA). The size distribution of the powdered sample analyzed by a Cilas 1064 Liquid instrument was shown in paper 2.
2.1.2. Pure material samples A wide range of materials, such as copper, aluminum, plastics, glass, and stone was produced by cutting or grinding pure materials. Copper wires were provided by Draka Kabel Sverige AB, Sweden. The dimensions and shapes of materials to be investigated are presented in Table 3.
Table 3. Dimension and shape of test materials
Dimension and shape
L W T (mm) (sheet)
T S (mm) (cylinder)
Size range, (mm) (Granulated Particles)
Material
14 14 220 10 240 5 2
Al
3 3 234 0.512 1.58 2.53 6
Cu
5 5 2 Cu, PVC
2-6 Al, Glass, Stone
L: length, W: width, T: thickness, S: section area, PVC: polyvinyl chloride
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2.2. Methods
2.2.1. Sampling standard deviation In order to find out whether or not the test results are consistent, the weight of each specimen amounts up to 1.5 kg, and 2 or 3 specimens were analyzed for the chemical analysis and particle size analysis. The sample standard deviation, S is defined as followings (Montgomery, 2001):
2/12
1
_))1/())((( nyyS
n
ii (1)
where, S denotes sample standard deviation, n is the number of samples to be studied, yi represents a sample, y indicates the sample mean.
2.2.2. Chemical analysis Chemical analyses were carried out in the laboratory of OVAKO Steel AB, Hofors, Sweden. Samples were ground to powder and treated with aqua regia for dissolution of the metal. The plastic was then filtrated and the remaining solution analyzed with ICP/AES (inductively coupled plasma/ atomic emission spectroscopy) and ICP/MS (inductively coupled plasma/mass spectroscopy).
2.2.3. Particle size analysis The specimens prepared for size analysis were initially dried up at 105 C for 12 hours. Subsequently, the samples were screened by employing an ASTM Retsch testing sieve series with square openings that were shaken off by a RO-TAP testing sieve shaker for 30 minutes.
2.2.4. Particle shape analysis An image process system, produced by Kronton Elektronik GmbH, Germany, was utilized for particle shape analysis. The quantitative criterion is expressed in terms of FCIRCLE defined as follows (KRONTON, 1991):
FCIRCLE=4 AREA/PERIM2 (2) PERIM=PERIMX+PERIMY+PERIMXY 2 (3)
where AREA, is defined as the number of pixels multiplied by the scaled pixel area, PERIM is the perimeter of the object, PERIMX, PERIMY is the length of perimeter in x and y direction, respectively, PERIMXY is the length of perimeter having direction of 45 and 135 degrees to x-axis. In this case, holes in the object will contribute to the perimeter.
Eq. (2) shows that the values of circularity shape factor, FCIRCLE range between close to 0 for very elongated or rough objects and 1 for circular objects.
2.2.5. Liberation degree analysis Liberation degree can be simply expressed as:
LD=Nf/(Nf+Nl) (4)
where, LD is liberation degree, Nf represents the number of free particles of the desired material, and Nl indicates the number of locked particles of the same material.
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In the present study, up to 2 kg sample was analyzed and the liberation degree of copper was calculated by Eq. (4).
2.2.6. Sink-float test Sink-float test is an effective method to determine the density of characteristics sample. The heavy liquids that were used in the laboratory test were presented in Table 4.
Table 4 Heavy liquids and their densities employed in the sink-float test
Heavyliquids
H2O NaCl+ H2O
NaCl+H2O
NaCl+H2O
CaCl2+H2O
CaCl2+H2O
Acetone+TBE
Acetone+TBE
Tetrabrome-ethane (TBE)
Density,g/cm3
1.0 1.02 1.06 1.13 1.23 1.41 2.00 2.44 2.97
The densities of the liquids were detected by using a 25 ml volumetric flask and following equation:
D=(Wt-Wf)/25.00 (5)
where D denotes the density of liquid, Wt is the total weight of liquid and the volumetric flask, Wf is the weight of the volumetric flask.
2.2.7. Quantification and identification of plastics Thermogravimetric analyses (TGA) were performed by using NETZSCH STA 409 in both argon and air atmosphere to quantify the amount of plastics in TV scrap. In this test, the samples of 100 mg were heated linearly at a heating rate of 10 C/min from 25 C to 1200 C with a gas flow rate of 100 ml/min.
Identification of plastics in the products of sink-float test was carried out by using the Perkin Elmer System 2000 FT-IR spectrometer, coupled with one FT-IR microscope. Plastics pieces from sink-float test were also identified by using an industry-scale online infrared technique in Stena Technoworld AB, Sweden.
2.2.8. Magnetic separation A low intensity drum magnetic separator, Mörsell Separator, was employed for removing ferrous metals from the sample (as shown in Fig. 1). In the present study, the drum peripheral speed is 2 m/s.
2.2.9. DGS Table separation Air table separation was carried out by using a DGS-Sort 300D in MinPro AB, Stråssa, Sweden. The separator was developed by Fren Erschliessungs-und Bergbau GesmbH, Austria.
2.2.10.Eddy current separation The eddy current separation experiments were conducted with a rotating drum eddy current separator, BM 29.710/18, developed by Bakker Magnetics, the Netherlands. The BM 29.710/18 rotor has 9 pairs magnetic poles, the magnetic induction at the belt surface is 0.32 T, and the dimension of the magnetic rotor is 300 mm.
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Fig. 1. Flowsheet of magnetic separation
The separability of pure material sample was characterized by their distribution in an array of the collectors that were placed in front of the conveyor belt pulley (as shown in Fig. 2). Twelve collectors, each with dimensions of 500 85 100(length width height) mm, were used. The material distribution was analyzed by its percent weight in each collectors such that:
%100)/()(12
1jijijij WWPW (6)
where (PW)ij is the percent weight of the ith material in the jth collector, and Wij is the weight of the ith material in the jth collector.
Fig. 2. Illustration of rotating eddy current separation A: Magnetic drum rotates in a Forward mode
B: Magnetic drum rotates in a Backward mode
No.12 ... No.1 Collectors
BeltFeed
Non-ferrous metals
A B
Scrap sample
Ferrous metals Non-ferrous metals and non-metals
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2.2.11.Optical (metal) sorting The optical (metal) sorting process was performed by a Clara All-metal Separator (Scan & Sort GmbH, Wedel, Germany). As demonstrated in Fig. 3, the optical (metal) sorting appliance consisting of electromagnetic sensors and/or color line-cameras identifies the material on the belt and transmits the corresponding information to a high performance computer in milliseconds. A pneumatic ejection system with up to 256 valves shoots the selected material out of the product stream by air pressure.
Fig. 3. Demonstration of optical (metal) sorting system
2.2.12.Magnus separation The Magnus separator (Fig. 4) was developed by Delft University of Technology, the Netherlands. At the present study, the magnetic rotor speed is 1000 rad/s for the dipole rotor.
Fig. 4. Schematic draws of the Magnus separator
Water lever
Non-ferrous metals
Feeder
Splitter
Non-metals
Magnetic rotor
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2.2.13.Hand picking Hand picking method was used in the evaluation of separation for qualitative and quantitative analysis of products. Approximately 1 kg of each product sample was separated by a chute riffling for hand picking. Subsequently, metals, printed circuit boards and cables (PCBs), and plastics were separated from each other by hand.
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3. Characterization of consumer electronic scrap
3.1. Chemical analysis Table 5 shows the multi-element analysis result of TV scrap sample. From the result, it can be seen that TV scrap contains very low-grade of non-ferrous metals and precious metals, 1.2% Al, 3.4% Cu, 7 ppm gold, 20 ppm silver, and less than 6 ppm platinum and palladium. A comparison of TV scrap, personal computer scrap (Legarth et al., 1995), and printed circuit boards scrap (Zhang and Forssberg, 1997) is given in Table 6. It is apparent that the content of non-ferrous metals and precious metals in TV scrap is much lower than that of in personal computer or printed circuit boards scrap. From the point of view of recycling industry, the major economic drive force to process those scraps is recovery of non-ferrous metals and precious metals. Therefore, it is expected that recycling of TV scrap will not be economically viable by using conventional manual dismantling. Mechanical processing techniques may provide an alternative to separate copper and different plastics.
Table 5 Multi-element analysis of TV scrap samples
Al Cu Pb Zn Cr Mo Ni V Ag Au Pt Pd
% ppm
Assay 1.2 3.4 0.2 0.3 90 13 380 7 20 <10 <2 <2
Note: These results are the average obtained from two samples.
Table 6 Comparison of TV scrap, personal computer scrap, and printed circuit boards scrap
Al Cu Pb Zn Ni Ag Au
% ppm
TV scrap 1.2 3.4 0.2 0.3 0.038 20 <10
PC scrapa 2.8 14.3 2.2 0.4 1.1 639 566 Assay
PCBs scrapb 7.0 10.0 1.2 1.6 0.85 280 110 a data source: Legarth et al. (1995), b data source: Zhang and Forssberg (1997)
3.2. Size and metal distribution of TV scrap Fig. 5 gives the size cumulative distribution of TV scrap sample. From the figure, it can be seen that approx. 90% of particles is present in +5 mm size range; median size of the sample (d50) is about 9 mm.
A cumulative oversize distribution of copper for TV scrap sample is presented in Figure 6. We can see that approximately 90% of Cu is widely distributed in +2.36mm fraction. This indicates that mechanical processing techniques, such as eddy current separation, air table, jigging, and sink-float separation, may be employed in this size range to recover copper. But this wide size range (2mm to 15mm) is also a challenge for those mechanical separation techniques.
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Particle size, mm
Cum
ulat
ive
unde
rsiz
e, %
0.1 1 10 1000
20
40
60
80
100
Fig. 5. Size cumulative weight of TV scrap sample
0
10
20
30
40
50
60
70
80
90
100
1 10 100
Size range, mm
Fig. 6. Cu distribution in screening products
3.3. Particle shapes of materials in TV scrap Fig. 7 shows images of non-ferrous metals (a), plastics (b), and printed circuit boards (PCBs) (c) separated from TV scrap sample. It is evident that non-ferrous metals are extremely heterogeneous, formed as wide variety of particle shapes such as, straight and bent bars, bent plates, cable and wire bundles. Furthermore, it can be seen that almost all of the plastics in TV scrap is black in color (Fig. 7 (b)). Therefore, with the
Cum
ulat
ive
dist
ribut
ion
of C
u, %
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fast development of CCD (Charge-Coupled Device) sensor technology, optical sorting process may provide a good choice to separate black plastics.
An image process system introduced by Kronton Elektronik was used to quantify particle shape factor, FCIRCLE (as shown in Figure 8). It is obvious from Figure 8 that the frequency distribution of FCIRCLE for non-ferrous particles varies to a large range (0.1-0.9); the frequency distributions of FCIRCLE for plastics and PCBs are mainly in the range of 0.6 to 0.9. This result indicates that non-ferrous metals particles in TV scrap sample form in a variety of shapes, much more different than that of plastics and printed circuit boards. The separation processes will be significantly influenced by the particle shape for recovery of non-ferrous metals.
It should be pointed out that shape separation techniques, primarily developed to control properties of particles in powder industry provide an alternative to separate non-ferrous metals from TV scrap (Cui and Forssberg, 2003). Shape separation by tilted plate and sieves is the most basic method that has been utilized in recycling industry. An inclined conveyor and inclined vibrating plate were used as a particle shape separator to recover copper from electric cable waste (Koyanaka et al., 1997).
3.4. Liberation degree of copper It is well-known that the liberation of values in scraps is of primary importance for mechanical processing. The liberation degree of copper in TV scrap was quantified (as shown in Table 7). From the result, we can see that it is difficult to achieve complete liberation, since in this particle size copper in printed circuit boards and cables is almost impossible to liberate. This result indicates that printed circuit boards and cables in TV scrap may cause copper loss or low quality of copper product in mechanical processing.
Table 7 Liberation degrees of Copper in TV scrap
3.5. Sink-float test The result of the sink-float test is given in Fig. 9 and Fig. 10. It is obvious that a high recovery of copper is obtained by using a sink-float process. For +1.4 g/cm3 fraction, the recovery of Cu is up to 88.4% with an assay of 42.4%. In addition, it must be pointed out that approximately 18% of the copper is distributed in –2.0+1.23 g/cm3
fraction with an assay of only 7%. As discussed in the liberation degree section, this is because copper in printed circuit boards is not liberated from plastics and ceramic materials.
Size range, mm Weight, % Liberation degree of Cu, %
+12.5 22.9 0.0 +9.5 25.7 0.0 -9.5+6.7 27.6 36.4 -6.7+4.75 14.3 54.3 -4.75+3.35 3.1 74.4 -3.35+2.36 3.5 73.4 -2.36+1.65 1.5 51.1 -1.65 1.4 n.d.
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Fig. 7. Images of non-ferrous metals (a), plastics (b), and printed circuit boards (c) separated from TV scrap sample (+2.36mm)
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Fig. 8. FCIRCLE analysis of non-ferrous metals (a), plastics (b), and printed circuit boards (c) separated from TV scrap sample (+2.36mm)
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0
20
40
60
80
100
1,0 1,2 1,4 1,6 1,8 2,0 2,2 2,4 2,6 2,8 3,0
Density, g/cm3
Cum
ulat
ive
wei
ght o
f sin
ks, %
Fig. 9. Cumulative weight of sinks versus specific density for TV scrap (-9.5+1.65mm)
0
20
40
60
80
100
0,5 1 1,5 2 2,5 3
Density, g/cm3
Cum
ulat
ive
assa
y, %
assaydistribution
Fig. 10. Cumulative data of copper for sinks versus specific density for TV scrap (-9.5+1.65mm)
3.6. Quantification of plastics by thermogravimetric analysis
In the present study, the sink-float test is oriented not only to evaluate the separability of copper but also to estimate the separability of different plastics. The plastics employed in TV set are primarily HIPS (high impact polystyrene), ABS (acrylonitrile butadiene styrene), PC (polycarbonate), and POM (Polyoxymethylene) with densities of 1.03-1.17, 1.03, 1.15-1.22, and 1.4, respectively (Menad et al., 1998; APC, 2000; APME, 2001).
17
Thermogravimetric analysis (TGA) is widely utilized to quantify and identify plastics (Menad et al, 1998; Jakab, 2003; Braun and Schartel, 2004; Levchik et al., 2000; Wang et al., 2003). In the present test, a HIPS particle from TV scrap was also analyzed in air atmosphere as a reference. Fig. 11 gives the TG/DTG/DTA curves of powdered TV scrap sample in air atmosphere (a), powdered TV scrap sample in argon atmosphere (b), and HIPS sample in air atmosphere (c). It can be seen from the curves that:
The apparent reaction of powdered TV scrap occurs starting at the temperature of about 210 C in both air (Fig. 11 (a)) and argon (Fig. 11. (b)) atmosphere. The complete degradation of TV scrap sample takes place at approx. 924 C. At this temperature, the weight losses of samples are 86% and 78%, respectively. The difference of weight loss between air and argon atmosphere is because part of char is oxidized by oxygen at air atmosphere. Thermal decomposition of powdered TV scrap (Fig. 11 (a)) is much more complicated than that of pure HIPS (Fig. 11 (c)). From the DTA/DTG curves of Fig. 11 (a), we can see that at least three steps of decomposition of powdered TV scrap sample undergo with characteristic decomposition temperature of 268 C, 432 C, and 590 C, respectively. Otherwise, HIPS sample decompose in one major step with characteristic decomposition temperature of 440 C (Fig. 11 (c)).
Flame retardants are widely used in plastics to prevent or delay a developing fire in electronic equipment (Levchik et al., 2000; Braun and Schartel, 2004; Jakab et al., 2003; Hamm et al., 2001; Imai et al., 2003; Yamawaki, 2003; Riess et al., 2000). A detailed discussion of Flame retardants in electronic scrap is shown in paper 2.
3.7. Identification of plastics by FT-IR spectrometer In order to evaluate the separability of plastics in TV scrap using density-based processes, plastics pieces in products of sink-float test were identified by a FT-IR spectrometer. Fig. 12 shows the spectra of plastics with the density range of –1.02+1.0 g/cm3, -1.06+1.02 g/cm3, -1.23+1.13 g/cm3, respectively.
It is obvious that similar spectra are obtained for plastic samples, which are distributed in various density ranges. In comparison with the spectrum of a commercial HIPS (as shown in Fig. 13) (Sidwell, 1997), the absorption bands at
3010, 2956, 1600, 1500, 1458, and 758cm-1, are indications of HIPS contributed by aromatic ring and -CH2-. The absorption bands at 1739 cm-1 can be recognized as characteristic absorption of ester that is common as flame retardants additive in plastics (Braun and Schartel, 2004; Carlsson et al., 2000; Imai et al., 2003; Levchik et al., 2000; Sjödin et al., 2001).
In addition, identification of plastics in products from the sink-float test also carried out by using an industry scale infrared instrument in Stena Technoworld AB, Sweden. From the results (Table 8) we can see that plastic in this scrap sample primarily is HIPS, besides some ABS, PC, and POM. It can be seen that HIPS is widely present from –1.0g/cm3 fraction to –1.23g/cm3 fraction. This specific density variation of the same material is due to variations of additives of plastic and from enclosed cavities and inclusions of other materials. Gravity separation of plastics may encounter some challenges because of specific density variation of same material.
18
Fig. 11. Thermogravimetric analysis of a) powdered TV scrap in air atmosphere, b) powdered TV scrap in argon atmosphere, c) HIPS in air atmosphere
c)
b)
a)
590 C
19
Fig. 12. FT-IR spectra of plastics from the products of sink-float test
Table 8 Identification of plastics for the products of sink-float test (size range –9.5+1.65mm)
Specific density, g/cm3
-1.0 -1.02 +1.0
-1.06 +1.02
-1.13 +1.06
-1.23 +1.13
-1.41 +1.23
+1.41
Identification of plastics
HIPS HIPS HIPS HIPS, SAN HIPS PC, POM -
20
Fig. 13. Infrared spectrum of a commercial HIPS
21
4. Mechanical separation of consumer electronic scrap
4.1. Ferromagnetics recovery Table 9 shows the chemical assay of ferromagnetics from the TV scrap. It is clear that a high grade of ferromagnetics product can be produced by employing a low intensity magnetic separator. It must be pointed out that due to the high contamination levels of Cu, Al, and Pb, this ferromagnetics fraction may not correspond to the requirements of iron and steel smelters.
Table 9 Chemical assay of ferromagnetics from the TV scrap
Chemical Assay, % Weight, %
Fe Cu Al Ni Pb Ag Au
Ferromagnetics 22.1 90.10 5.70 0.900 2.000 0.960 0.000 0.000
4.2. DGS Table separation Fig. 14 gives the separation results of DGS table separation. It can be seen that 70% to 90% of metals are recovered in the heavy product with metal content between 40% and 60%. In addition, printed circuit boards and cables in the sample are difficult to separate from plastics by the DGS table. The result indicates that DGS table separation is effective and efficient for recovery of metals from consumer electronic scraps. Printed circuit boards and cables should be dismantled before further mechanical separation. A number of parameters must be optimized on DGS table separation. Paper 3 gives a detailed discussion of those parameters.
0
10
20
30
40
50
60
70
60 70 80 90 100
Recovery, %
Gra
de, %
Metals
0
10
20
30
40
10 20 30 40
Recovery, %
Gra
de, %
PCBs
Fig. 14. Grade-Recovery of metal and printed circuit boards in the heavy product from the DGS table separation
22
4.3. Eddy current separation The separation of non-ferrous metals from the -9.5+6.7 mm fraction and -3.35+1.65 mm fraction of shredded TV scrap performed after an optimization of the operating conditions by using a rotating drum eddy current separator. As shown in Table 10, more than 75% of non-ferrous metals were recovered, while maintaining a purity of 27% in a single pass for the large particle size fraction. However, only 45% of non-ferrous metals can be separated for the small particle size fraction. This result indicates that application of traditional eddy current separation in recycling of consumer electronic scraps may encounter a problem because the limitation of particle size. New development of eddy current separation for recovery of fine particles is required.
Table 10 Eddy current separation result of TV scrap
Particle size, mm Products Weight, % Metal content, % Recovery, %
Non-ferrous metals 34 27 77
-9.5+6.7 Waste 66 4 23
Total 100 12 100
Non-ferrous metals 19 39 45
-3.35+1.65 Waste 81 11 55
Total 100 16 100
4.4. Optical sorting The optical (metal) sorting experiments by using color and/or metal sensors were carried out in Scan & Sort GmbH, Wedel, Germany. Two samples with particle size of +9.5 mm and -9.5+4.6 mm, were processed respectively (as shown in Fig. 15). Table 11 and 12 give the results of optical (metal) sorting of TV scrap. It is evident that 90% of metals can be recovered in metallic product by utilizing optical sorting system.
Table 11 Optical sorting result of TV scrap (+9.5mm) Weight, % Metal content, % Recovery, %
White fraction 37 75 60
Metallic product from dark fraction
32 40 32
Non-metallic product from dark fraction
31 1 8
Total 100 41 100
23
Table 12 Optical sorting result of TV scrap (-9.5+4.6 mm) Weight, % Metal content, % Recovery, %
Metallic product 55 47 90
Non-metallic product 45 6 10
Total 100 29 100
Fig. 15. Flowsheet of optical (metal) sorting process of TV scraps
White product
TV scraps (+9.5 mm)
Color sorting
Dark product
Non-metallic product Metallic product
Metal sorting
Non-metallic product Metallic product
TV scraps (-9.5+4.6 mm)
Color sorting
White product Dark product
Metal sorting Metal sorting
Metallic product
25
5. New developments of eddy current separation for fine particles
5.1. Theory
5.1.1. Magnetic interaction A magnet rotor with k pairs of magnet poles and a magnetic induction bm at the radius Rm of the outer shell surface produces a magnetic induction outside the shell (r>Rm):
B=)(sin)(cos1
tktk
rRb
BB
m
mk
mm
r (7)
where (r, ) are cylindrical coordinates with respect to the axis of the rotor, t is time and m is the angular velocity of the rotor.
The expression shows that a stationary particle at some point (r, ) experiences a magnetic induction of constant magnitude B bm(Rm/r)k+1 revolving at angular velocity -k m (Fig. 16.). If the particle itself is spinning with some angular velocity ,it perceives a field of the same size as a stationary particle but now rotating at an apparent angular velocity -k m- . The magnetic torque makes the particle spin in the same direction as the magnetic field.
Fig. 16. Magnet rotor (left) produces a rotating magnetic field B inducing eddy currents in a particle (right) resulting in a particle magnetic moment M.
For particles of simple geometries, such as spheres, thin disks and long cylinders, with a size that is small with respect to the magnetic wavelength 2 Rm/(k+1) of the rotor, the theory of eddy current separation (Rem, 1999) provides an expression for the particle magnetic dipole moment M in a rotating magnetic field:
M=r
mr
m BB
dkIBB
dkRV ))(())(( 20
20
0
(8)
N
NN
NS
S
S
S MB
26
where V and are the volume of the particle and its electrical conductivity, respectively, and R( ) and I( ) are dimensionless functions, for which approximations in terms of rational functions are tabulated in Table 13 (Rem et al., 2002; Fraunholcz et al., 2002).
Table 13. Parameters defining the magnetic interaction for particles of several shapes and parallel ( ) or perpendicular ( ) orientations of their axis of symmetry with respect to the axis of the rotor
Shape (R( ), I( )) D cm
Sphere 21( 2, 42 )/20(1764+ 2) D 1/40
Cylinder 3( 2, 24 )/2(576+ 2) D 1/16
Cylinder 9( 2, 24 )/8(576+ 2) D 3/64
Disk ( 2, 12 )/(144+ 2) 1/12
Disk (0.6 2/D, 16 )/4(256+(0.6 )2 2/D2) D 1/64
D: diameter, : thickness.
As a consequence, the torque Tm on the particle from its magnetic moment is given by (Rem et al., 2002; Fraunholcz et al., 2002):
Tm=M B= )(0
2
IVB ez (9)
the direct magnetic force Fm can be written by:
Fm=M B=)()()1(
0
2
IR
rVBk (10)
For conductive particles with d less than 10 mm, the factor I in Tm reduces to a linear function of m:
VdBkcT mmm22)( (11)
where, the coefficient cm depends on the shape and orientation of the particles (Table 13).
5.1.2. Magnus effect It is known that a spinning particle moving through a fluid experiences a force perpendicular both to its direction of motion and to the axis of rotation. This phenomenon is called the Magnus effect (Massey, 1989).
As shown in Fig. 17, the trajectory of a spinning particle falling in a fluid can be analyzed to the forces of drag, lift and drag torque (Reynolds number Re>300) (Rem et al., 2002; Fraunholcz et al., 2002):
27
FL
FD
VGravity-buoyancy
Fig. 17. Force diagram for a particle that rotates at an angular velocity while settling with a linear velocity v with respect to a fluid
FD=cD v2A/2 (12)
FL=cL v2A/2 (13)
5DcT Td (14)
where cD , cL, and cT represent the coefficients that depend on the shape and orientation of the particle (Table 14), is the density of fluid, v is the particle velocity, A is the characteristic area of the particle, D is the characteristic dimension of the particle, is the angular velocity of the particle (assuming that is always perpendicular to v).
The speed of rotation of the conductive particles in a Magnus separation is found by integration of the balance of angular momentum:
J =Tm-Td (15)
Eq. (15) implies that within the size ranges indicated, the particle spin in a Magnus separation does not depend on the particle size, but only on its shape and orientation, since J, Tm, and Td are all proportional to the fifth power of the particle size.
Table 14 Measured valuesor the drag torque coefficient for particles of several shapes
Particle definition cT
Rough sphere (Re=300-700) 0.007
Smooth sphere (Re=3 106) 0.0008
Rough cylinder (Re=500-700, L/D=3) 0.008 L/D
Smooth cylinder (Re=2 106, L/D=5) 0.0012 L/D
Disk (Re=300-30000, D/ =3.5-4) 0.03
28
D
rh
5.1.3. Wet eddy current separation In order to simplify the calculation, we assume a spherical particle with diameter Dthat is connected to a surface by a cylindrical mass of water (as shown in Fig. 18). For a completely wettable solid particle, the adhesion work Wa between particle and water is much higher than the cohesion work of water, WC (Lu et al., 2005). As a result, the energy between a wettable solid particle and water can be written by:
E=2 rhWC (16)
where r and h are the radius and height of the water cylinder. Geometrical analysis shows that radius r= DhhDh )( (h<<D). Additionally, the work of cohesion WC is expressed as:
WC=2 gl (17)
here, the surface tension of water gl=73 10-3 J/m2.
By putting the Eq. (17) to Eq. (16), the force gluing the particle to the belt surface is given as:
DhdhdEF gl6/ (18)
For instance, if D=3 mm and h=0.2 mm, the force F=1.1 10-3 N, which is about the same order as the gravity force on a stone particle with a same particle size.
Fig. 18. Geometry of wet bond
Although the adhesive force is strong enough to keep most of the non-metal particles glued to the belt surface, the eddy current torque can easily provide the force to break the water bond for the non-ferrous metal particles. As discussed above, the magnetic torque is expressed as Eq. (11). The non-ferrous metal particle is able to break loose if the torque is of the order FD/2. For a typical water layer, h=0.2 mm, and on a traditional rotating drum eddy current separator, B=0.3 T, =150 rad/s, this criterion is met for well-conducting metals if D>1 mm, whereas for metals like solder and lead it is realized for D>2 mm (Table 15).
5.2. Traditional eddy current separation for fine particles Fig. 19 demonstrates the material distribution for large particle size. It is obvious from Fig. 19. a) that, when the eddy current separator run in the forward mode, almost all the aluminum particles is distributed in the collectors of No. 1 to No. 4, otherwise PVC particles are distributed in the collectors of No. 6 to No. 8. Analysis of the
29
material distribution indicates that it is easy to separate large aluminum particles from non-metals, when the magnetic drum rotates in the forward mode. It can be seen from Fig. 19. b) that, when the eddy current separator run in the backward mode, aluminum particles are widely distributed in collectors of No. 1 to No. 10. This result indicates that it is difficult to separate large non-ferrous metals from non-metals when the magnetic drum rotates in the backward mode.
Table 15 Electrical conductivity of some metals and alloys
Alloy Conductivity , (1/ m)
Aluminum 3003 27 106
Copper 56 106
Zinc 17 106
Yellow brass 15 106
Lead 5 106
Solder 50-50 7 106
Fig. 19 also shows the effect of particle shape on eddy current separation. It is clear that, in the forward mode, the deflections of square plates of Al are larger than those of the rectangular sheets since a square plate is more conducive to eddy-current induction than a rectangular sheet.
The material distribution for fine particles is presented in Fig. 20. It can be seen that fine conducting particles like copper are either mixed up with the non-metals ones or distributed in the collectors that are closer to the magnetic drum. The results indicate that it is difficult to separate fine non-ferrous metals from non-metals selectively, when the magnetic drum rotates in the forward mode. It has been found that if the magnetic drum rotates in the backward mode, separation of fine conducting particles from non-conducting ones is improved drastically. It is shown in Fig 20 that more than 80% of copper particles are distributed in the collectors of No. 1 to No. 6. Separation of copper wires demonstrated in Fig. 20 shows that fine copper cable and wires can be recovered by traditional rotating drum eddy current separator in a backward mode.
5.3. Preliminary study of Magnus separation and wet eddy current separation
5.3.1. Effect of splitter position The effect of splitter position on wet eddy current separation of aluminum is demonstrated in Fig 21. It is observed that the recovery of Al is decreasing slowly, as the splitter moving from 300 mm to 335 mm. In the meanwhile, the grade of Al product increases from 26% to 63%. In order to ensure maximum the aluminum recovery, the splitter position for the rest test was set to 335 mm horizontally away (x) from the axis of the rotor.
30
12
34
56
78
910
1112
40*5
*2
20*1
0*2
14*1
4*2PV
C
0
20
40
60
80
100
Wei
ght,
%
collectror No.
Particle size, mm
a)
12
34
56
78
910
1112
40*5*220*10*2
14*14*2PVC
0
10
20
30
40
50
60
70
80
90
Wei
ght,
%
collectror No.
Particle size, mm
b)
Fig. 19. Material distribution for large particle size (volume of Al particle=400 mm3, a) forward mode, b) backward mode)
31
12
34
56
78
910
1112
3*3*23*6
8*2.512*1.5
34*0.5PVC
0
20
40
60
80
100
Wei
ght,
%
collectror No.
Particle size, mm
a)
1
23
45
67
89
1011
12
3*3*23*6
8*2.512*1.5
34*0.5PVC
0
10
20
30
40
50
60
70
80
90
Wei
ght,
%
collectror No.
Particle size, mm
b)
Fig. 20. Material distribution for fine particle size (volume of Cu particle=18 mm3, a) forward mode, b) backward mode)
32
5.3.2. Effect of rotor speed The effect of rotor speed on wet eddy current separation of aluminum is exhibited in Fig. 22. As can be seen in Fig.22, the grade of Al product is slightly decreasing as the rotor speed increasing from 1000 rpm to 1500 rpm due to a drastic particle-particle interaction. However, the rotor speed from 1000 to 2000 rpm insignificantly influences the recovery of aluminum. It indicates that a high rotor speed that is widely used in traditional rotating drum eddy current separation is dispensable in wet eddy current separation. This result is sufficiently consistent with the preliminary study by Settimo et al. (2004).
0
20
40
60
80
100
250 300 350 400 450
Splitter position, mm
%
GradeRecovery
Fig. 21. Effect of splitter position on eddy current separation of Al (rotor speed=1500 rpm, belt speed=1 m/s, moisture content=10%, particle size=4-6 mm).
0
20
40
60
80
100
500 1000 1500 2000 2500
Rotor speed, rpm
%
GradeRecovery
Fig. 22. Effect of rotor speed on eddy current separation of Al (belt speed=1 m/s, moisture content=10%, particle size=4-6 mm).
33
5.3.3. Effect of moisture content of the feed Table 16 gives the effect of moisture content of the feed on wet eddy current separation of aluminum. It is clear that the moisture content of the feed has significant effect on the grade of Al product. The Al grade increases from 63% to 84% as the moisture content of the feed increase from 10% to 15%. This result shows that a 15% of moisture content of feed is needed to provide an effective water layer on the belt surface so as to glue the large stone particles.
Table 16 The effect of moisture content of the feed on wet eddy current separation of Al (rotor speed=1500 rpm, belt speed=1 m/s, particle size=4-6 mm)
Weight, % Grade, % Recovery, %
Moisture content, % 10 15 10 15 10 15
Al product 14 11 63 84 96 95
Tailings 86 89 0.4 0.5 4 5
Feed 100 100 9 9 100 100
5.3.4. Effect of particle size The effect of particle size on wet eddy current separation of aluminum is shown in Table 17. It can be seen that the grade of aluminum product for particle size of 2-4 mm is much better than that of 4-6 mm. As discussed above, this is due to the fact that the adhesive force gluing a particle to the belt surface of large particles, e.g., 6 mm is much lower than the gravity force on the same particle size.
Table 17 The effect of particle size on wet eddy current separation of Al (rotor speed=1500 rpm, moisture content=15%, belt speed=1 m/s)
Weight, % Grade, % Recovery, %
Size range, mm 4-6 2-4 4-6 2-4 4-6 2-4
Al product 11 7 84 97 95 96
Tailings 89 93 0.5 0.3 5 4
Feed 100 100 9 4 100 100
5.3.5. Magnus separation The primary study of Magnus separation by one of the authors (Rem et al. 2002) shows that Magnus separation as a novel type of eddy current separation can recover fine non-ferrous metal particles from solid wastes. As a comparison of wet eddy current separation by using a traditional drum eddy current separator, a new design of
34
industry Magnus separator was utilized in our test. Experiments were carried out with the same artificial sample as in the wet eddy current separation. Table 18 gives the separation results of Magnus separation. It can be seen that a grade of 80% with an Al recovery of 60% can be obtained by using Magnus separation.
Table 18 Magnus separation of artificial Al sample (rotor speed=10000 rpm)
Weight, % Grade, % Recovery, %
Size range, mm 4-6 2-4 4-6 2-4 4-6 2-4
Al product 7.5 4.5 80 75 61 37
Tailings 92.5 95.5 4 6 39 63
Feed 100.0 100.0 10 9 100 100
35
6. Conclusions The study of mechanical recycling of consumer electronic scrap yields the following major findings:
1. The comparison of TV scrap, personal computer scrap, and printed circuit boards scrap shows that non-ferrous metals and precious metals content in TV scrap is much lower than that of in personal computer scrap or printed circuit boards scrap. From the point of view of recycling industry, it is expected that recycling of TV scrap will not be economically viable by using conventional manual disassembly.
2. The images of plastics show that optical sorting processes may provide a good choice to separate black plastic because almost all of the plastics in TV scrap are black in color. In addition, the result of FCIRCLE shows that non-ferrous metals particles in TV scrap sample form as a variety of shapes that is much more different than that of plastics and printed circuit boards. The result indicates that the separation processes will be significantly influenced by the particle shape for recovery of non-ferrous metals.
3. A high recovery of copper could be produced by utilizing an effective gravity separation technique. For +1.4 g/cm3 density fraction in sink-float test, the recovery of Cu is up to 88.4% with an assay of 42.4%. Additionally, approx. 18% of the copper is distributed in the –2.0+1.23 g/cm3 density fraction with an assay of only 7%. This is because copper in printed circuit boards is not liberated from plastics and ceramic materials. Identification of plastics shows that the major plastic in TV scrap is HIPS. It is widely presented in the –1.23 g/cm3 density fraction. Gravity separation of plastics may encounter some challenges in separation of plastics from TV scrap because of specific density variations.
4. DGS table separation is an effective and efficient separation technique for consumer electronic scrap. The separation results show that approximately 70% to 90% of non-ferrous metals are recovered in the heavy product with purity 40% to 60%. It can be revealed that better separation results of DGS table separation can be expected by optimizing separation parameters such as particle size, shape, and feeding rate. Eddy current separation and optical sorting process provide alternatives to recover non-ferrous metals from consumer electronic scrap.
5. The preliminary study of traditional rotating drum eddy current separation shows that large non-ferrous metal particles can be separated effectively by using Bakker eddy current separator when the magnetic drum rotates in the forward mode; fine non-ferrous metal particles can only be separated by eddy current separator in backward mode. Separation of copper wires shows that fine copper cable and wires can be possible recovered by traditional rotating drum eddy current separator in a backward mode. A comparison of eddy current separation and Magnus separation on aluminum recovery shows that wet eddy current separation is more effective for recovery of fine non-ferrous particles.
37
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Paper I
Mechanical recycling of waste electric and electronic equipment: a review
Journal of Hazardous Materials, B99 (2003) 243-263
Journal of Hazardous Materials B99 (2003) 243–263
Mechanical recycling of waste electric andelectronic equipment: a review
Jirang Cui∗, Eric ForssbergDivision of Mineral Processing, Luleå University of Technology, SE-971 87 Luleå, Sweden
Received 16 August 2002; received in revised form 12 February 2003; accepted 13 February 2003
Abstract
The production of electric and electronic equipment (EEE) is one of the fastest growing areas.This development has resulted in an increase of waste electric and electronic equipment (WEEE).In view of the environmental problems involved in the management of WEEE, many counties andorganizations have drafted national legislation to improve the reuse, recycling and other forms ofrecovery of such wastes so as to reduce disposal. Recycling of WEEE is an important subject notonly from the point of waste treatment but also from the recovery of valuable materials.
WEEE is diverse and complex, in terms of materials and components makeup as well as theoriginal equipment’s manufacturing processes. Characterization of this waste stream is of paramountimportance for developing a cost-effective and environmentally friendly recycling system. In thispaper, the physical and particle properties of WEEE are presented. Selective disassembly, targetingon singling out hazardous and/or valuable components, is an indispensable process in the practiceof recycling of WEEE. Disassembly process planning and innovation of disassembly facilitiesare most active research areas. Mechanical/physical processing, based on the characterization ofWEEE, provides an alternative means of recovering valuable materials. Mechanical processes,such as screening, shape separation, magnetic separation, Eddy current separation, electrostaticseparation, and jigging have been widely utilized in recycling industry. However, recycling ofWEEE is only beginning.
For maximum separation of materials, WEEE should be shredded to small, even fine particles,generally below 5 or 10 mm. Therefore, a discussion of mechanical separation processes for fineparticles is highlighted in this paper.
Consumer electronic equipment (brown goods), such as television sets, video recorders, are mostcommon. It is very costly to perform manual dismantling of those products, due to the fact thatbrown goods contain very low-grade precious metals and copper. It is expected that a mechanicalrecycling process will be developed for the upgrading of low metal content scraps.© 2003 Elsevier Science B.V. All rights reserved.
Keywords: Recycling; Electronic scrap; Waste treatment; Material recovery
∗ Corresponding author. Tel.: +46-920-492064; fax: +46-920-97364.E-mail address: [email protected] (J. Cui).
0304-3894/03/$ – see front matter © 2003 Elsevier Science B.V. All rights reserved.doi:10.1016/S0304-3894(03)00061-X
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1. Introduction
The production of electric and electronic equipment (EEE) is increasing worldwide.Both technological innovation and market expansion continue to accelerate the replacementof equipment leading to a significant increase of waste electric and electronic equipment(WEEE). In west Europe, 6 million tonnes of WEEE were generated in 1998, the amount ofWEEE is expected to increase by at least 3–5% per annum [1]. In the USA, a recent studypredicted that over 315 million computers would be at end of their life by the year 2004[2].
Due to their hazardous material contents, WEEE may cause environmental problemsduring the waste management phase if it is not properly pre-treated. Many countries havedrafted legislation to improve the reuse, recycling and other forms of recovery of suchwastes so as to reduce disposal [1,2].
Recycling of WEEE is an important subject not only from the point of waste treatmentbut also from the recovery aspect of valuable materials. The US Environmental ProtectionAgency (EPA) has identified seven major benefits when scrap iron and steel are used insteadof virgin materials. Using recycled materials in place of virgin materials results in significantenergy savings (as shown in Tables 1 and 2) [3].
Currently, recycling of WEEE can be broadly divided into three major stages:
• Disassembly (dismantling): selective disassembly, targeting on singling out hazardousor valuable components, is an indispensable process.
Table 1Benefits of using scrap iron and steel
Benefits Percentage
Savings in energy 74Savings in virgin materials use 90Reduction in air pollution 86Reduction in water use 40Reduction in water pollution 76Reduction in mining wastes 97Reduction in consumer wastes generated 105
Table 2Recycled materials energy savings over virgin materials
Materials Energy savings (%)
Aluminum 95Copper 85Iron and steel 74Lead 65Zinc 60Paper 64Plastics >80
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• Upgrading: using mechanical/physical processing and/or metallurgical processing to up-grade desirable materials content, i.e. preparing materials for refining process.
• Refining: in the last stage, recovered materials return to their life cycle.
Consumer electronic equipment (brown goods), such as television sets, radio sets, andvideo recorders, are most common. However, it is very costly to perform manual dismantlingof those products, due to the fact that brown goods contain very low-grade precious metalsand copper. A mechanical process is interest for upgrading recycling of WEEE because itcan yield full material recovery including plastics. It is expected that a mechanical recyclingprocess will be developed for the upgrading of low metal content scraps.
2. Characteristics of WEEE
Waste electric and electronic equipment is non-homogeneous and complex in termsof materials and components. In order to develop a cost-effective and environmentallyfriendly recycling system, it is important to identify and quantify valuable materials andhazardous substances, and further, to understand the physical characteristics of this wastestream.
2.1. Hazardous substances and components
WEEE consists of a large number of components of various sizes and shapes, some ofwhich contain hazardous components that need be removed for separate treatment. Majorcategories of hazardous materials and components of WEEE that have to be selectivelytreated are shown in Table 3 [1].
2.2. Materials composition
Waste electric and electronic equipment is a complex material containing various frac-tions. The Association of Plastics Manufactures in Europe (APME) released figures on ma-terials consumption in electric and electronic equipment in western Europe 1995 (Table 4[5]). In general, printed circuit boards scrap contains approximately 40% metals, 30% plas-tics, and 30% ceramics [4,6–9].
The main economic driving force for the recycling of electronic scrap is the recovery ofprecious metals. However, the content of precious metals in WEEE is steadily decreasing[6,10,11].
2.3. Physical characteristics of WEEE
Waste electric and electronic equipment, being a mixture of various materials, can beregarded as a resource of metals, such as copper, aluminum and gold, and plastics. Effectiveseparation of these materials based on the differences on their physical characteristics is thekey for developing a mechanical recycling system. Therefore, an in-depth characterizationof this specific material stream is imperative.
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Table 3Major hazardous components in waste electric and electronic equipment
Materials and components Description
Batteries Heavy metals such as lead, mercury and cadmium arepresent in batteries
Cathode ray tubes (CRTs) Lead in the cone glass and fluorescent coating cover theinside of panel glass
Mercury containing components, such as switches Mercury is used in thermostats, sensors, relays andswitches (e.g. on printed circuit boards and inmeasuring equipment and discharge lamps); it is alsoused in medical equipment, data transmission,telecommunication, and mobile phones
Asbestos waste Asbestos waste has to be treated selectivelyToner cartridges, liquid and pasty, as well as
color tonerToner and toner cartridges have to be removed from anyseparately collected WEEE
Printed circuit boards In printed circuit boards, cadmium occurs in certaincomponents, such as SMD chip resistors, infrareddetectors and semiconductors
Polychlorinated biphenyl (PCB) containingcapacitors
PCB-containing capacitors have to be removed for safedestruction
Liquid crystal displays (LCDs) LCDs of a surface greater them 100 cm2 have to beremoved from WEEE
Plastics containing halogenated flame retardants During incineration/combustion of the plasticshalogenated flame retardants can produce toxiccomponents
Equipment containing CRC HCFC or HFCs CFCs present in the foam and the refrigerating circuitmust be properly extracted and destroyed; HCFC orCFCs present in the foam and refrigerating circuit mustbe properly extracted and destroyed or recycled
Gas discharge lamps Mercury has to be removed
2.3.1. Magnetic, density and electric conductivity propertiesThe magnetic susceptibilities, density, and electric conductivity of some materials used
in electric and electronic equipment are given in Tables 5–7 [12–14].
2.3.2. Particle size, shape and liberation propertiesParticle size, shape and liberation degree play crucial roles in mechanical recycling pro-
cesses. Almost all the mechanical recycling processes have a certain effective size range.
Table 4Main materials found in EEE
Material Percentage
Ferrous 38Non-ferrous 28Plastics 19Glass 4Wood 1Other 10
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Table 5Magnetic susceptibilities of copper alloys used in EEE (data basis: magnetic field intensity, 325 kA/m)
Materials Fe content (%) Mass susceptibility, χ (×10−7 m3 kg−1)
Aluminum-multi-compound bronze 2–4 6.5–11.5Manganese-multi-compound bronze 1.5–3 0.7–2.4Special brass 0.7–1.2 1.3–5.8Brass (Fe-free) <0.2 <0.1Tin and lead bronze <0.2 <0.1
Table 6Magnetic susceptibility, density and electric conductivity of metals used in EEE
Materials Density, ρ (×103 kg m−3) Electric conductivity, σ (×106 m−1 �−1)
Copper 8.93 59.0Cu–Zn alloy (Ms 58) 8.4 1.9Aluminum 2.70 35.0Magnesium 1.74 23.0Silver 10.49 68.0Zinc 6.92 17.4Gold 19.32 41.0Brass (Fe-free) 8.40 15.0–26.0Nickel 8.90 12.5Tin 7.29 8.8Lead 11.34 5.0Alloy steel 7.7 0.7
Characterization of personal computers (PC) scrap and printed circuit boards (PCB) scrapshows, after secondary shredding by a laboratory scale hammer mill, that the main metalspresent are in the −5 mm fraction for both PC and PCB scrap and show excellent liberation(ca. 99% [6]). Additionally, industry scale tests showed that after two stages comminution,the liberation of −5 mm fraction is between 96.5 and 99.5% [15].
Fig. 1 shows the metal distribution as a function of size range for PC scrap [6]. In thisfigure, we can see that aluminum is mainly distributed in the coarse fractions (+6.7 mm),
Table 7Volume resistivity and specific gravity of plastics used in EEE
Plastics Volume resistivity, � m Specific gravity (×103 kg m−3)
Polyvinyl chloride (PVC) 109–2 × 1012 1.16–1.38Polyethylene (PE) 1014 0.91–0.96Acrylonitrile butadienestyrene (ABS) 1014 1.04Polystyrene (PS) 1014 1.04Polypropylene (PP) 1015 0.90Nylon and polyamide (PA) 1012 1.14Ployesters (PET and PBT) 1–1.4 × 1013 1.31–1.39Polycarbonates (PC) 8.2 × 1014 1.22Elastomer (neoprene, SBR, silicone etc.) 109–1015 0.85–1.25
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Fig. 1. Metals distribution as a function of size range for PC scrap.
but other metals are mainly distributed in the fine fractions (−5 mm). To know particlesize properties is essential for choosing an effective separation technique. In addition, it iscommon to upgrade metals content by a screening process.
It is well known that diversified particle shapes have a significant impact on materialprocessing, both comminution and separation. On the other hand, differences in particleshape have been utilized in shape sorting technique.
Koyanaka et al. investigated the particle shape properties of copper milled by a swing-hammer-type impact mill [16]. Copper plate and PCB scrap were used as samples. Theeffects of mill operating conditions, i.e. hammer circumferential speed (vc) and screenaperture size (diameter, ds), on shape and size distribution of milled products were examined.
Fig. 2 shows the effect of hammer circumferential speed on anisometry KI and spacefilling factor φc of milled copper plate (ds = 1 mm). KI and φc were defined by the following
Fig. 2. Anisometry KI and space filling factor φc of milled copper plate.
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equations:
KI = A
B(≤ 1) (1)
φc = πD2
4s(2)
where A and B are the short and long principal axes of an ellipse of inertia equivalent toparticle projection, D the maximum diameter in particle projection, and s the projected areaof the particle.
In Fig. 2, it is apparent that hammer circumferential speed influences the particle shape ofmilled copper. At the same time, the effects of milling conditions on the separation efficiencybetween copper and non-copper components of PCB scrap using an inclined vibrated plate(IVP) were also studied.
3. Disassembly of WEEE
Disassembly is a systematic approach that allows removal of a component or a part,or a group of parts or a subassembly from a product (i.e. partial disassembly); or sep-arating a product into all of its parts (i.e. complete disassembly) for a given purpose[17].
The areas of disassembly that are being pursued by researchers are focused on disassemblyprocess planning (DPP) and innovation of disassembly facilities.
3.1. Disassembly process planning
The objective of disassembly process planning is to develop, procedures and softwaretools for forming disassembly strategies and configuring disassembly systems [18]. Thefollowing phases for developing a disassembly process plan have been proposed[17–23]:
• Input and output product analysis: In this phase, reusable, valuable, and hazardous com-ponents and materials are defined. After preliminary cost analysis, optimal disassemblyis identified.
• Assembly analysis: In the second phase, joining elements, component hierarchy andformer assembly sequences are analyzed.
• Uncertainty issues analysis: Uncertainty of disassembly comes from defective parts orjoints in the incoming product, upgrading/downgrading of the product during consumeruse, and disassembly damage.
• Determination of dismantling strategy: In the final phase, it is decided whether to usenon-destructive or destructive disassembly.
Research on disassembly process planning has been an active area in the last decade.Hundreds of papers have been written on this subject. A detailed survey of disassembly waspresented by Gungor and Gupta [19].
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3.2. Innovations of disassembly tools
In addition to generating a good disassembly process plan, the implementation of disas-sembly needs highly efficient and flexible tools. Several patented disassembly tools werehighlighted in the paper by Feldmann et al. [24].
The most attractive research on disassembly process is the use of robots. The automatedassembly of electronic equipment is well advanced. Unfortunately, full (semi) applicationof automation disassembly for recycling of electronic equipment is full of frustration. Cur-rently, there are only a few pilot projects for automated disassembly of keyboards, monitorsand printed circuit board, and there is no (semi-) automated solution for the PC itself [25,26].
3.3. Disassembly in practice
In the practice of recycling of waste electric and electronic equipment, selective disas-sembly (dismantling) is an indispensable process since: (1) the reuse of components hasfirst priority, (2) dismantling the hazardous components is essential, (3) it is also commonto dismantle highly valuable components and high grade materials such as printed circuitboards, cables, and engineering plastics in order to simplify the subsequent recovery ofmaterials.
Most of the recycle plants utilize manual dismantling. Ragn-Sells ElektronikåtervinningAB in Sweden is a typical electronics recycling operation. Fig. 3 illustrates the currentdisassembly process that they utilize [27]. A variety of tools is involved in the disman-tling process for removing hazardous components and recovery of reusable or valuablecomponents and materials.
A study of potential future disassembly and recycling technologies for the electronics andthe automotive industry was carried out by Boks and Tempelman between November 1996and March 1997 [28]. The results reflect the opinions of a panel of approximately 70 spe-cialists pre-selected by the authors. Concerning the technical feasibility of full automation
Fig. 3. Recycling process developed by Ragn-Sells Elektronikåtervinning AB.
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(90–100%) disassembly of electronic equipment, 65% of the panel members thought abreakthrough in automated disassembly will occur by 2010; and 57% of the panel thoughtit will be in Germany, while only 35% of the German panel members agree. In addition,32% of the panel thought full automation disassembly of both brown goods (e.g. TVs,audio and video equipment) and white goods (e.g. freezers, washing machines) will notbe economically attractive by 2020. In their opinion, the main obstacles preventing auto-mated disassembly from becoming a commercially successful activity are: (1) too manydifferent types of products, (2) the amount of products of the same type is small, (3) gen-eral disassembly-unfriendly product design, (4) general problems in return logistics and (5)variations in returned amounts of products to be disassembled.
Fortunately, research in the field of product design for disassembly has gained momen-tum in the past decade. One good idea is self-disassembly which is called active disas-sembly using smart materials (ADSM). Chiodo [29] reported the application of shapememory polymer (SMP) technology to the active disassembly of modern mobile phones.The smart material SMP of polyurethane (PU) composition was employed in the experi-ments. This method provides a potential dismantling scenario for the removal of all com-ponents if this material was to be developed for surface mount components. Research intousing ADSM in other small electronics also has been done to handle units such as tele-phones, cell phones, PCB/component assemblies, cameras, battery chargers, photocopiercartridges, CRTs, computer casings, mice, keyboards, game machines and stereo equipment[29].
4. Mechanical/physical recycling process
4.1. Screening
Screening has not only been utilized to prepare a uniformly sized feed to certain me-chanical process, but also to upgrade metals contents. Screening is necessary because theparticle size and shape properties of metals are different from that of plastics and ceramics.
The primary method of screening in metals recovery uses the rotating screen, or trommel,a unit which is widely used in both automobile scrap and municipal solid waste process-ing. This unit has a high resistance to blinding, which is important with the diverse arrayof particle shapes and sizes encountered in waste. Vibratory screening is also commonlyused, in particular at non-ferrous recovery sites, but wire blinding is a marked problem[30].
4.2. Shape separation
Shape separation techniques have been mainly developed to control properties of particlesin the powder industry [31–34]. The separation methods were classified into four groupsby Furuuchi [31]. The principles underlying this process makes use of the difference: (1)the particle velocity on a tilted solid wall, (2) the time the particles take to pass through amesh aperture, (3) the particle’s cohesive force to a solid wall, and (4) the particle settlingvelocity in a liquid.
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Shape separation by tilted plate and sieves is the most basic method that has beenused in recycling industry [17,35]. An inclined conveyor and inclined vibrating platewere used as a particle shape separator to recover copper from electric cable waste [35],printed circuit board scrap [17], and waste television and personal computers in Japan[36].
4.3. Magnetic separation
Magnetic separators, in particular, low-intensity drum separators are widely used forthe recovery of ferromagnetic metals from non-ferrous metals and other non-magneticwastes. Over the past decade, there have been many advances in the design and op-eration of high-intensity magnetic separators, mainly as a result of the introduction ofrare earth alloy permanent magnets capable of providing very high field strengths andgradients.
In Table 5, we can see that the use of high-intensity separators makes it possible to separatecopper alloys from the waste matrix. An intense field magnetic separation is achievable atleast for the following three alloy groups [14]:
• copper alloys with relatively high mass susceptibility (Al multi-compound bronze);• copper alloys with medium mass susceptibility (Mn multi-compound bronze, special
brass);• copper alloys with low mass susceptibility and/or diamagnetic material behavior (Sn
and Sn multi-compound bronze, Pb and Pb multi-compound bronze, brass with low Fecontent).
4.4. Electric conductivity-based separation
Electric conductivity-based separation separates materials of different electric conduc-tivity (or resistivity) (Tables 6 and 7). As shown in Table 8, there are three typical electricconductivity-based separation techniques: (1) Eddy current separation, (2) corona electro-static separation, and (3) triboelectric separation [37–41].
In the past decade, one of the most significant developments in the recycling indus-try was the introduction of Eddy current separators whose operability is based on theuse of rare earth permanent magnets. The separators were initially developed to recovernon-ferrous metals from shredded automobile scrap or for treatment of municipal solidwaste [30,42–44], but is now widely used for other purposes including foundry casting sand,polyester polyethylene terephthalate (PET), electronic scrap, glass cullet, shredder fluff, andspent potliner [45–50]. Currently, Eddy current separators are almost exclusively used forwaste reclamation where they are particularly suited to handling the relatively coarse sizedfeeds.
The rotor-type electrostatic separator, using corona charging, is utilized to separate rawmaterials into conductive and non-conductive fractions. The extreme difference in the elec-tric conductivity or specific electric resistance between metals and non-metals suppliesan excellent condition for the successful implementation of a corona electrostatic separa-tion in recycling of waste. To date, electrostatic separation has been mainly utilized for
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Table 8Mechanical separation processes based on electric characteristics of materials
Processes Separation criteria Principles of separation Sorting task Workableparticle sizeranges
Eddy currentseparation
Electric conductivityand density
Repulsive forces exerted inthe electricly conductiveparticles due to theinteraction between thealternative magnetic fieldand the Eddy currentsinduces by the magneticfield (Lorentz force)
Non-ferrousmetal/non-metalseparation
>5 mm
Coronaelectrostaticseparation
Electric conductivity Corona charge anddifferentiated dischargelead to different charges ofparticles and this to actionof different forces(particularly, image forces)
Metal/non-metalseparation
0.1–5 mm(10 mm forlaminarparticles)
Triboelectricseparation
Dielectric constant Tribo-charge withdifferent charges (+ or −)of the components causedifferent force directions
Separation ofplastics(non-conductors)
<5 (10) mm
the recovery of copper or aluminum from chopped electric wires and cables [37,38,51–54],more specifically the recovery of copper and precious metals from printed circuit board scrap[37–39,55].
Triboelectric separation makes it is possible to sort plastics depending on thedifference in their electric properties (Table 7). For the processing of plastics waste, re-search has shown many obvious advantages of triboelectric electrostatic separation, suchas independence of particle shape, low energy consumption, and high throughput[41].
4.5. Density-based separation
Several different methods are employed to separate heavier materials from lighter ones.The difference in density of the components is the basis of separation. Table 9 shows thatdensity-based separation processes have found widespread application in non-metal/metalseparation [56].
Gravity concentration separates materials of different specific gravity by their relativemovement in response to the force of gravity and one or more other forces, the latter oftenbeing the resistance to motion offered by a fluid, such as water or air [57]. The motion ofa particle in a fluid is dependent not only on the particle’s density, but also on its size andshape, large particles being affected more than smaller ones. In practice, close size controlof feeds to gravity processes is required in order to reduce the size effect and make therelative motion of the particle specific gravity dependent.
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Table 9Density separation processes utilized for non-metal/metal separation
Density separationprocess
Workable piecesizes (mm)
Utilized for following sorting tasks
Plasticswaste
Aluminumscrap
Leadbatteryscrap
Cablescrap
Electronicscrap
Lightsteelscrap
Sink-float separationIn liquids + + + +In heavy media
Gravity separator 5–150 + + + +Hydrocyclone <50 +
In aerosuspensionsIn aero-chutes 0.7–3 +In fluidized bedtrough separators
0.7–5 +
Sorting by jiggingHydraulic jigs 2–20 +Pneumatic jigs <3 +
Sorting in chutes and on tablesAero-chutes 0.6–2 +Aero-tables <4 +
Up-stream separationUp-stream hydraulic
separation5–150 + + +
Up-stream pneumaticseparation
<300 +
5. Mechanical recycling process for fine particles
The number of waste streams containing fine metal particles is foreseen to grow sub-stantially in the near future [59], due to: (1) more stringent legislation, (2) more costlylandfilling for metal-containing waste, (3) continuing increased production of diversifiedwaste streams, particularly the arising of portable EEE, and (4) ever-growing environmentalawareness. It is predicted that an economic and technically viable separation technology torecover fine particles from waste will be in great demand in the near future.
5.1. New developments of the ECS for small particles
The rotating Eddy current separators have been successfully utilized in several non-ferrousmetals sorting and recovery operations, most common is the sorting of non-ferrous metalsfrom shredded automobile scrap and municipal solid waste [42,58,60]. Nevertheless, inrecycling of WEEE, the use of the traditional Eddy current separator is limited, due to thesize of feed required. Particles greater than 5 mm in size or, even 10 mm are needed [61].
In recent years, there have been some development of Eddy current separation processesdesigned to separate small particles [44,59–64]. Understanding the interaction between the
J. Cui, E. Forssberg / Journal of Hazardous Materials B99 (2003) 243–263 255
separator field and conductive particles is essential to provide a theoretical foundation forthis novel design.
Before the 1990s, intensive theoretical work was carried out by Schlömann [65,66] andvan der Valk et al. [56,67,68]. A theoretical model was developed to calculate the magni-tude of the forces exerted on small block-shaped particles in magnetic fields with periodicalvariations. The separators involved in the study were ramp Eddy-current separator (RECS),vertical Eddy-current separator (VECS), and rotating disc separator (RDS). This model hasbeen used to design separators with different field distributions and mechanical construc-tions. The validity of this model was tested by deflection measurements in a VECS and byforce measurements in two different RDS prototypes. The deflection measurements werecarried out with copper particles extracted from granulated power cables. These particlesare pieces of wire with diameters between 0.2 and 4 mm and with lengths mainly between3 and 10 mm. The particles sizes by screening and calculation correspond with each other,as the size range does not exceed 3 mm.
In the early 1990s, theoretical work was done by Fletcher et al. [63,69–72]. In thesestudies, three kinds of theoretical models were used to represent the profile of the magneticfield at the boundary of a single boundary Eddy current separator. In the first model, themagnetic field profile at the boundary of ECS was represented by an idealized single fieldstep of height �Bz, which equals the flux density change between the point of elementvelocity measurement and the point where maximum flux density is first reached. Thismodel is satisfactory for large conductors with medium vy (velocity of particle in y-axisdirection). In the second model, a multi-step staircase field that follows the measured profilewas used for representing the magnetic field of ECS. This model was presented in paper[71]. The last model was developed for small conducting particles. A single rising linearramp was used as a theoretical representation of the profile of the magnetic field at theboundary of a single boundary ECS. Fletcher et al. [63] discussed the limitations of singleboundary ECS for small particles. A theoretical model was developed and tested using abench top single boundary ECS. Two sizes of aluminum laminar discs with 5.1 mm ×2 mmand 10.2 mm × 1.5 mm were used in the test. The results of this model were reasonablyconsistent with experimental observation. In addition, Fletcher predicted that if a 2T rampof length 10 mm was possible and was used with a deep-set splitter, the limit of particle sizeis reduced to 0.6 mm.
An important work involving the separation of small particles using the ECS method wascarried out by Rem and co-workers [59–62,73,74]. A model was developed for small andmedium-sized particles in both symmetric and asymmetric fields by treating the particles asmagnetic dipoles. The theory was expanded in Rem’s paper [60] for a rotary drum separator,sliding ramp, and vertical Eddy current separator. Zhang et al. [61] presented the resultsof their investigation of the separability of various materials smaller than 5 mm using arotating type ECS. The study shows that the magnetic drum should rotate backwards forsorting small non-ferrous metal particles. They concluded that the “backward phenomenon”results from the competition between the tangential Eddy current force and the dynamicfrictional force crested by the electromagnetic torque.
Based on the analysis of separation mechanisms, proposals were made to improve theseparation selectivity of small particles. A number of novel design concepts of ECS werehighlighted by Rem et al. [59]. The redesigned Delft vertical ECS (VECS), the prototype
256 J. Cui, E. Forssberg / Journal of Hazardous Materials B99 (2003) 243–263
TNO ECS and a laboratory wet ECS (WECS) were used in their investigation. The newVECS was redesigned based on the one developed by van der Valk et al. [68]. In this study,the magnets were more powerful than the ones used earlier. The separation results of binarymixtures by Delft VECS were presented in the article.
The prototype designed by The Netherlands Organization (TNO for Applied ScientificResearch) combines a small pole width of approximately 20 mm with a narrow gap betweenmagnet surface and feed, and a high rotor speed of up to 4000 rpm. Theoretical analysisshowed that the tangential Eddy current force of TNO ECS is six times that of the rotarybelted-drum ECS. The idea of a wet ECS comes from converting the effects of the elec-tromagnetic torque to a separating effect. It is well known that a spinning particle movingthrough a fluid experiences a force perpendicular both to its direction of motion and to theaxis of rotation. This is the Magnus effect. The experimental results of WECS have shownto be promising. A critical comparison of the four types ECS was given by Rem et al. [59](Table 10).
Norrgran [44] discussed the application of an Eriez rotating belted-drum ECS in the ben-eficiation of fine sized metals, such as aluminum slags, brass foundry sands, and electronicscrap. Typical customer applications that have resulted in effective separations are given inhis article (Table 11).
A vertical Eddy current rotating separator, designed to increase the separation efficiencyand to reduce the cost of the separation equipment, was proposed by Schlett et al. [64]. In theseparator, the magnetic drum with NeFeB permanent magnets was driven by a dc electricmotor that was placed under the magnetic drum. A mixture of copper wire and plasticparticles with the average diameter of 4 mm and length of 5 mm was used to simulateelectronic wastes in a laboratory-scale experiment.
5.2. Corona electrostatic separation
Corona electrostatic separation is an important technique suitable for fine particles withthe size range of 0.1–5 mm [37–39]. This process has been investigated extensively inthe minerals processing industry. There are also some applications in recycling of ca-ble scraps. The utilization of corona electrostatic separators in material recovery fromwaste electric and electronic equipment for a recycling purpose is only in its infancy.Some industrial applications for the corona drum separator are shown in Table 12[75].
In corona electrostatic separation, electrode system, rotor speed, moisture content, andparticle size have the greatest effect in determining the separation results. Both fundamentaland practical aspects concerning the design of new electrode system have been investi-gated and developed by Iuga et al. [51–53,76]. An experimental study was carried out onthe influence of material superficial moisture on insulation-metal electrostatic separation[54].
Comparing the foregoing processes with the mineral processing industry processes, onefinds that larger liberated particles with 5–8 mm are usually encountered in recycling ofWEEE, although they are generally called fine particles. In electrostatic separation, coarseparticles collect small specific charges and hence small electric forces, while having rela-tively large centrifugal forces. Optimization of the electrode system, enhancing electrode
J. Cui, E. Forssberg / Journal of Hazardous Materials B99 (2003) 243–263 257
Tabl
e10
Cri
tical
com
pari
son
ofE
CS
with
vari
ous
desi
gnco
ncep
tsfo
rsm
allp
artic
les
Des
ign
conc
ept
Thr
ough
put
Sepa
ratio
nse
lect
ivity
Ope
ratin
gdi
fficu
lty(s
ensi
tivity
toth
em
agne
tics)
Mai
nten
ance
Num
ber
ofno
n-fe
rrou
spr
oduc
tsat
one
step
Inve
stm
ent
cost
for
1t/h
Fina
lres
ults
Dry R
otat
ing
drum
type
+++
00
00
+++
VE
CS
00
−+
−−
−T
NO
EC
S+
++−
−0
+++
Wet R
otat
ing
drum
WE
CS
+++
++
−+
−++
++N
ote
that
“0”,
“−”,
and
“+”
deno
teba
se,n
egat
ive
and
posi
tive,
resp
ectiv
ely.
258 J. Cui, E. Forssberg / Journal of Hazardous Materials B99 (2003) 243–263
Table 11Typical applications of the Eddy current separator in waste treatment industry
Sample description Feed rate,tpha
Weight percent of feed (%)
Magnetics Conductor Non-conductor
Aluminum cans and PET bottles 1 – 49 51Shredded PET bottles and aluminum caps 1 – 2 98Mixed aluminum and PVC 1 – 33 67Auto scrap (unscreened) 3 60 33 7Auto scrap (7 × 1/2 in.) 3 30 35 35Auto scrap (−1/2 in.) 3 27 24 49Mixed ferrous and non-ferrous scrap (−3/4 in.) 3 53 43 4RDF bottom ash (3 × 5/8 in.) 6 3 3 94RDF bottom ash (−5/8 in.) 3 10 3 87Glass cullet with aluminum caps 3 1 9 90Glass cullet (crushed light bulbs) 1 4 14 82Electronic scrap, coarse 2 5 48 47Electronic scrap, fine 1 67 14 19Mixed Fe, Al, Zn 4 10 55 35Mixed Fe, Al, Cu, Pb, Zn 6 28 30 42Brass foundry casting sand 3 – 12 88Aluminum foundry casting sand 6 – 5 95High grade aluminum slag 3 7 81 12Low grade aluminum slags 1 2 5 93Aluminum dross and cryolite 4 – 26 74
a Unit capacity of tph/ft of rotor width.
Table 12Applications of the corona drum separator in waste treatment industry
Materials Waste origin Liberationmethod
Particlesize
Achievable gradesof products
Remarks
Cu Cable scrap Cutting mill 0.5/5 mm Cu 90–99%PVC/PE Plastics up to 99%
Al Skeleton wastee.g. milk cans
Cutting mill 6/12 mm Al up to 100%
PS PS 99%
Al Compound materialse.g. tetra brick
Cryogenicgrinding
50/500 �m Al 95%
Plastics Plastics 95%
Cu Bare PC boards Hammer mill 0.2/2 mm Cu 99%Epoxy resin Resin 99.5%
PE Car tanks Cutting mill 3/5 mm PE 95% Separation ofnon-conductorEOVH EVOH 90%
J. Cui, E. Forssberg / Journal of Hazardous Materials B99 (2003) 243–263 259
voltage, and lowering down the rotor speed can maximize the adhering of non-conductiveparticles.
One of the advantages of electrostatic separation in cable recycling is to obtain a metal-freeproduct. However, in some cases, the specific resistance of certain types of flexible PVC andrubber used to make cables falls below 4×1010 � m. Hence, corona electrostatic separationis difficult because the discharge time constant of the non-conductor may fall below 1 s [37].
5.3. Jigging
Jigging, one of the oldest methods of gravity concentrations, is widely utilized in themineral processing industry to concentrate relatively coarse materials. If the feed is fairlyuniformly sized (e.g. 3–10 mm), it is not difficult to achieve good separation of a narrowspecific gravity range in minerals in the feed [57].
Thus, the jigging process provides a good solution for sorting small pieces of metalsby density separation. Advantages of wet jigs are their robustness, high capacity per unitsurface, low operating costs and suitability to process large amounts of small particles.According to de Jong and Dalmijin [77], in the processing of car scrap, the 4–16 mmnon-ferrous fraction can be separated by wet jigging. The light product mainly consists ofaluminum, glass, and stone; the heavy product consists of metals, such as copper, lead, brass,and stainless steel etc. A recyclable intermediate fraction, continuously added to the feedof the jig was introduced to on-screen jigging. In this study, the principles of jigging and ofthe intermediate layer are discussed first. Then the optimum properties of the intermediatelayer and metal distribution in the jig bed are described.
One of the important applications of the jig in recycling industry is separation of lightand heavy products in recycling demolition rubble. Wet jigging enables a high-grade heavyproduct to be achieved. Plant-scale testes were carried out at Groot B.V., a Dutch companyin Heilo The Netherlands. The test was designed to reduce the light product content of therecycle stream to at least a maximum of 0.1% by weight [78]. A pulsator jig was used in thestudy. The results show that wet processing of demolition rubble with a pulsator jig enablesa product quality not possible with air classifiers to be achieved.
Before the 1990s, this process had also been utilized for sorting of non-ferrous met-als pro-concentrated of light steel scrap processing (hydraulic jigs) and from cable scrap(pneumatic jigs). Recently, Schmelzer [79] discussed the separation of non-ferrous metal
Table 13Mass recovery and density composition of light and heavy product fractions of jig process treating non-ferrousmetal mixtures
Size fraction (mm) Product Recovery (%) Density distribution of products (g/cm3)
<2.4 2.4–2.7 2.7–3.0 3.0–3.3 >3.3
10–4 Light 75.3 48.4 51.6 – – –Heavy 24.7 – – 0.2 0.9 98.9
4–0.5 Light 76.7 42.1 56.1 1.8 – −97.9Heavy 13.3 – – 1.0 1.1
260 J. Cui, E. Forssberg / Journal of Hazardous Materials B99 (2003) 243–263
mixtures with particle size ranges of 4–10 and 0.5–4 mm, using a discontinuous U-tube jig.Table 13 shows the separation results.
Significant heterogeneity and high complexity of WEEE make it difficult to operate ajigging process. Complicated scrap pieces, particularly wiry materials impede the separationprocess considerably and can prevent a separation into layers [56].
6. Conclusions
(1) Waste electric and electronic equipment has been taken into consideration not onlyby the government but also by the public. With the climate change being of concern,mechanical/physical processing will play an essential role in upgrading of WEEE.
(2) Characterization of WEEE provides a sound and solid foundation for developing effec-tive separation techniques. However, WEEE is significantly heterogeneous and complexin terms of the type, size, and shape of components and materials. Therefore, an in-depthstudy should be done with a goal of clearly understanding this special waste stream.
(3) In order to be separated, WEEE must be shredded to small even fine-sized particles,usually below 10 mm or even 5 mm. Mechanical separation of fine particles is neededin the recycling of WEEE.
(4) Eddy current separation, corona electrostatic separation, and jigging are three importantprocesses that have been developed in recycling of automobile scrap, waste cables, andbuilding materials, respectively. For sorting fine WEEE, the foregoing also providealternative approaches to current systems.
(5) In recycling of WEEE, investigations to date have mainly focused on the recovery ofprecious metals from personal computer scrap and printed circuit boards scrap. How-ever, it is important that recycling of the electronic scrap that contains very low-gradeprecious metals, such as brown goods, should be investigated.
Acknowledgements
The authors are grateful for financial support and approval of publication for this paperfrom the Minerals and Metals Recycling Research Center (MiMeR), Sweden.
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Paper II
Characterization of consumer electronic scrap oriented to materials recovery
submitted to Waste Management
1
CHARACTERIZATION OF CONSUMER ELECTRONIC SCRAP ORIENTED TO MATERIALS RECOVERY
Jirang Cui*, Eric Forssberg
Division of Mineral Processing, Luleå University of Technology, SE-971 87, Luleå, Sweden
*Corresponding author. Tel.: +46 920 492064; fax: +46 920 97364. E-mail address: [email protected] (J. Cui).
Abstract
Consumer electronic equipment (brown goods), such as television sets, radio sets,
and video recorders, are most common. In the context, characterization of TV scrap
was carried out by using a variety of methods, such as chemical analysis, particle size
and shape analysis, liberation degree analysis, thermogravimetric analysis, sink-float
test, and IR spectrometer. A comparison of TV scrap, personal computer scrap, and
printed circuit boards scrap shows that the content of non-ferrous metals and precious
metals in TV scrap is much lower than that of in personal computer scrap or printed
circuit boards scrap. It is expected that recycling of TV scrap will not be cost-effective
by utilizing conventional manual disassembly. The result of particle shape analysis
indicates that the non-ferrous metals particles in TV scrap formed as a variety of
shapes, it is much more heterogeneous than that of plastics and printed circuit boards.
Furthermore, separability of TV scrap by using density-based techniques was evaluated
by sink-float test. The result demonstrates that a high recovery of copper could be
obtained by using an effective gravity separation process. Identification of plastics
shows that major plastic in TV scrap is high impact polystyrene. Gravity separation of
plastics may encounter some challenges in separation of plastics from TV scrap
because of specific density variations.
Keywords: Characteristics; Recycling; Electronic scrap; Mechanical separation; Material recovery
2
1. Introduction
The amount of electronic scrap in the world is growing rapidly (Silicon Valley
Toxic Coalition, 2002). Due to their hazardous material contents, electronic scrap may
cause environmental problems during the waste management phase if not properly pre-
treated (Cui and Forssberg, 2003). Many countries have presented legislation on the
management of this special waste stream (European Parliament and Council, 2003).
Recycling of electronic scrap is a significant subject not only from the point of waste
treatment but also from the recovery aspect of valuable materials. Using recycled
materials in place of virgin materials results in significant energy savings (as shown in
Table 1) (ISRI, 1996).
Consumer electronic equipment (brown goods), such as television sets, radio sets,
and video recorders, are most common. However, recent work on recycling of waste
electric and electronic equipment primarily focused on personal computer and printed
circuit boards scraps (Zhang et al., 2000; Macauley et al. 2003; Yamagiwa et al., 2000;
Li et al., 2004; Jang and Townsend, 2003; Torres, 2004; Veit et al., 2005).
The European Directive (2002/96/EC) on waste electric and electronic equipment
(WEEE) has to be implemented into national legislation by 13 August 2004 (European
Parliament and Council, 2003). According to the WEEE directive, member states shall
ensure that, by 31 December 2006, producers meet the following targets:
1. The rate of recovery for consumer electronic equipment shall be increased to a
minimum of 75% by an average weight per appliance;
2. Component, material and substance reuse and recycling for consumer electronic
equipment shall be increased to a minimum of 65% by an average weight per
appliance.
3
In order to meet the above targets, disassembly and mechanical recycling of
consumer electronic scraps are of concern in European member states due to the fact
that they are oriented to towards full materials recovery including plastics (Zhang and
Forssberg, 1997; Langerak, 1997; Matsuto et al., 2004). In the practice of recycling of
WEEE, selective disassembly (dismantling) is an indispensable process because it aims
to remove hazardous or high value components (Cui and Forssberg, 2003; Stuart and
Christina, 2003; Basdere and Seliger, 2003; Torres et al., 2004). However, a study of
potential future disassembly of electronic scraps indicated that full automation
disassembly of consumer electronic scraps will not be economically attractive by 2020
(Boks and Tempelman, 1998).
It is of great importance to characterize consumer electronic equipment in order to
develop a cost effective and environmentally friendly recycling system (Zhang and
Forssberg, 1997). In the present study, characterization of television scrap with the
cathode ray tubes removed was carried out oriented to materials recovery.
2. Materials and methods
2.1. Materials
Television scrap sample was provided by Stena Technoworld AB, Bräkne-Hoby, an
electronic recycling corporation in Sweden. End-of-life TVs of any model and brand
with plastic houses that were collected primarily from Sweden were pre-dismantling to
remove the cathode ray tubes, CRTs. Then the scraps were shredded into -12 mm
particles. An approximately 30 kg of the TV scrap sample was procured and packed for
the laboratory study.
Coning and quartering method was used in the sampling process to get a standby
sample and a test sample. Then, the test sample was subsequently riffled by a rotary
4
sampler with each sample up to 1.5 kg for further analyses. The sampling procedure is
shown in Fig. 1.
A powdered sample was prepared by means of a turborotor grinder developed by
Görgens Engineering GmbH, Germany, which is capable of grinding metallic materials
and plastics. Before the grinding, ferrous metals were removed by a magnetic separator.
This powdered sample was used for thermogravimetric analysis (TGA). The size
distribution of the powdered sample was analyzed by a Cilas 1064 Liquid instrument
(as shown in Fig. 2).
2.2. Sampling standard deviation
In order to find out whether or not the test results are consistent, the weight of each
specimen amounts up to 1.5 kg, and 2 or 3 specimens were analyzed for the chemical
analysis and particle size analysis. The sample standard deviation, S is defined as
followings (Montgomery, 2001):
2/12
1
_))1/())((( nyyS
n
ii (1)
Where, S denotes sample standard deviation, n is the number of samples to be
studied, yi represents a sample, y indicates the sample mean.
2.3. Chemical analysis
Chemical analyses were carried out in the laboratory of OVAKO Steel AB, Hofors,
Sweden. Samples were ground to powder and treated with aqua regia for dissolution of
the metal. The plastic was then filtrated and the remaining solution analyzed with
5
ICP/AES (inductively coupled plasma/ atomic emission spectroscopy) and ICP/MS
(inductively coupled plasma/mass spectroscopy).
2.4. Particle size analysis
The specimens prepared for size analysis were initially dried up at 105 C for 12
hours. Subsequently, the samples were screened by employing an ASTM Retsch testing
sieve series with square openings that were shaken off by a RO-TAP testing sieve
shaker for 30 minutes.
2.5. Particle shape analysis
An image process system, produced by Kronton Elektronik GmbH, Germany, was
utilized for particle shape analysis. The quantitative criterion is expressed in terms of
FCIRCLE defined as follows (KRONTON, 1991):
FCIRCLE=4 AREA/PERIM2 (2)
PERIM=PERIMX+PERIMY+PERIMXY 2 (3)
Where AREA, is defined as the number of pixels multiplied by the scaled pixel area,
PERIM is the perimeter of the object, PERIMX, PERIMY is the length of perimeter in x
and y direction, respectively, PERIMXY is the length of perimeter having direction of
45 and 135 degrees to x-axis. In this case, holes in the object will contribute to the
perimeter.
Eq. (2) shows that the values of circularity shape factor, FCIRCLE range between
close to 0 for very elongated or rough objects and 1 for circular objects.
6
2.6. Liberation degree analysis
Liberation degree can be simply expressed as:
LD=Nf/(Nf+Nl) (4)
Where, LD is liberation degree, Nf represents the number of free particles of the
desired material, and Nl indicates the number of locked particles of the same material.
In the present study, up to 2 kg sample was analyzed and the liberation degree of
copper was calculated by Eq. (4).
2.7. Sink-float test
Sink-float test is an effective method to determine the density of characteristics
sample. The heavy liquids that were used in the laboratory test were presented in Table
2.
The densities of the liquids were detected by using a 25 ml volumetric flask and
following equation:
D=(Wt-Wf)/25.00 (5)
Where D denotes the density of liquid, Wt is the total weight of liquid and the
volumetric flask, Wf is the weight of the volumetric flask.
2.8. Quantification and identification of plastics
Thermogravimetric analyses (TGA) were performed by using NETZSCH STA 409
in both argon and air atmosphere to quantify the amount of plastics in TV scrap. In this
test, the samples of 100 mg were heated linearly at a heating rate of 10 C/min from 25
C to 1200 C with a gas flow rate of 100 ml/min.
7
Identification of plastics in the products of sink-float test was carried out by using
the Perkin Elmer System 2000 FT-IR spectrometer, coupled with one FT-IR
microscope. Plastics pieces from sink-float test were also identified by using an
industry-scale online infrared technique in Stena Technoworld AB, Sweden.
3. Results and discussion 3.1. Chemical analysis
Table 3 shows the multi-element analysis result of TV scrap sample. From the
result, it can be seen that TV scrap contains very low-grade of non-ferrous metals and
precious metals, 1.2% Al, 3.4% Cu, 7 ppm gold, 20 ppm silver, and less than 6 ppm
platinum and palladium. A comparison of TV scrap, personal computer scrap (Legarth
et al., 1995), and printed circuit boards scrap (Zhang and Forssberg, 1997) is given in
Table 4. It is apparent that the content of non-ferrous metals and precious metals in TV
scrap is much lower than that of in personal computer or printed circuit boards scrap.
From the point of view of recycling industry, the major economic drive force to process
those scraps is recovery of non-ferrous metals and precious metals. Therefore, it is
expected that recycling of TV scrap will not be economically viable by using
conventional manual dismantling. Mechanical processing techniques may provide an
alternative to separate copper and different plastics.
3.2. Size and metal distribution of TV scrap
Fig. 3 gives the size cumulative distribution of TV scrap sample. From the figure, it
can be seen that approx. 90% of particles is present in +5 mm size range; median size
of the sample (d50) is about 9 mm.
8
A cumulative oversize distribution of copper for TV scrap sample is presented in
Figure 4. We can see that approximately 90% of Cu is widely distributed in +2.36mm
fraction. This indicates that mechanical processing techniques, such as eddy current
separation, air table, jigging, and sink-float separation, may be employed in this size
range to recover copper. But this wide size range (2mm to 15mm) is also a challenge
for those mechanical separation techniques.
3.3. Particle shapes of materials in TV scrap
Undoubtedly, heterogeneous shapes have a significant impact on materials recovery
by mechanical processing. Schubert (1991) noticed that particularly wiry, complicated
scrap pieces (above all longer copper wires) impede the jigging separation process
considerably and can prevent a separation into layers. Zhang et al. (1998) investigated
the effect of particle shape on a rotating drum type eddy current separator. The results
showed that the deflections of the conducting particles were significantly dependent on
their shapes. In addition, it was mentioned that the shape influence was more
significant as the particle size increases.
Fig. 5 shows images of non-ferrous metals (a), plastics (b), and printed circuit
boards (PCBs) (c) separated from TV scrap sample. It is evident that non-ferrous
metals are extremely heterogeneous, formed as wide variety of particle shapes such as,
straight and bent bars, bent plates, cable and wire bundles. Furthermore, it can be seen
that almost all of the plastics in TV scrap is black in color (Fig. 5 (b)). Therefore, with
the fast development of CCD (Charge-Coupled Device) sensor technology, optical
sorting process may provide a good choice to separate black plastics.
9
An image process system introduced by Kronton Elektronik was used to quantify
particle shape factor, FCIRCLE (as shown in Figure 6). It is obvious from Figure 6 that
the frequency distribution of FCIRCLE for non-ferrous particles varies to a large range
(0.1-0.9); the frequency distributions of FCIRCLE for plastics and PCBs are mainly in
the range of 0.6 to 0.9. This result indicates that non-ferrous metals particles in TV
scrap sample form in a variety of shapes, much more different than that of plastics and
printed circuit boards. The separation processes will be significantly influenced by the
particle shape for recovery of non-ferrous metals.
It should be pointed out that shape separation techniques, primarily developed to
control properties of particles in powder industry provide an alternative to separate
non-ferrous metals from TV scrap (Cui and Forssberg, 2003). Shape separation by
tilted plate and sieves is the most basic method that has been utilized in recycling
industry. An inclined conveyor and inclined vibrating plate were used as a particle
shape separator to recover copper from electric cable waste (Koyanaka et al., 1997).
3.4. Liberation degree of copper
It is well-known that the liberation of values in scraps is of primary importance for
mechanical processing. The liberation degree of copper in TV scrap was quantified (as
shown in Table 5). From the result, we can see that it is difficult to achieve complete
liberation, since in this particle size copper in printed circuit boards and cables is
almost impossible to liberate. This result indicates that printed circuit boards and cables
in TV scrap may cause copper loss or low quality of copper product in mechanical
processing.
10
3.5. Sink-float test
Gravity concentration separates materials of different specific gravity by their
relative movement in response to the force of gravity and one or more other forces
(Wills, 1988). Table 6 shows that the density-based separation processes have found
widespread application in non-metal/metal separation (Schubert, 1991). Sink-float tests
are widely utilized to evaluate separability of minerals by means of gravity separation
techniques.
The result of the sink-float test is given in Fig. 7 and Fig. 8. It is obvious that a high
recovery of copper is obtained by using a sink-float process. For +1.4 g/cm3 fraction,
the recovery of Cu is up to 88.4% with an assay of 42.4%. In addition, it must be
pointed out that approximately 18% of the copper is distributed in –2.0+1.23 g/cm3
fraction with an assay of only 7%. As discussed in the liberation degree section, this is
because copper in printed circuit boards is not liberated from plastics and ceramic
materials.
3.6. Quantification of plastics by thermogravimetric analysis
In the present study, the sink-float test is oriented not only to evaluate the
separability of copper but also to estimate the separability of different plastics. The
plastics employed in TV set are primarily HIPS (high impact polystyrene), ABS
(acrylonitrile butadiene styrene), PC (polycarbonate), and POM (Polyoxymethylene)
with densities of 1.03-1.17, 1.03, 1.15-1.22, and 1.4, respectively (Menad et al., 1998;
APC, 2000; APME, 2001).
Thermogravimetric analysis (TGA) is widely utilized to quantify and identify
plastics (Menad et al, 1998; Jakab, 2003; Braun and Schartel, 2004; Levchik et al.,
11
2000; Wang et al., 2003). In the present test, a HIPS particle from TV scrap was also
analyzed in air atmosphere as a reference. Fig. 9 gives the TG/DTG/DTA curves of
powdered TV scrap sample in air atmosphere (a), powdered TV scrap sample in argon
atmosphere (b), and HIPS sample in air atmosphere (c). It can be seen from the curves
that:
1. The apparent reaction of powdered TV scrap occurs starting at the temperature
of about 210 C in both air (Fig. 9 (a)) and argon (Fig. 9. (b)) atmosphere. The
complete degradation of TV scrap sample takes place at approx. 924 C. At this
temperature, the weight losses of samples are 86% and 78%, respectively. The
difference of weight loss between air and argon atmosphere is because part of
char is oxidized by oxygen at air atmosphere.
2. Thermal decomposition of powdered TV scrap (Fig. 9 (a)) is much more
complicated than that of pure HIPS (Fig. 9 (c)). From the DTA/DTG curves of
Fig. 9 (a), we can see that at least three steps of decomposition of powdered TV
scrap sample undergo with characteristic decomposition temperature of 268 C,
432 C, and 590 C, respectively. Otherwise, HIPS sample decompose in one
major step with characteristic decomposition temperature of 440 C (Fig. 9 (c)).
Flame retardants are widely used in plastics to prevent or delay a developing fire in
electronic equipment (Levchik et al., 2000; Braun and Schartel, 2004; Jakab et al.,
2003; Hamm et al., 2001; Imai et al., 2003; Yamawaki, 2003; Riess et al., 2000).
According to the report from the Association of Plastics Manufactures in Europe
(2001), about 12% of all plastics used in the electric and electronic equipment contains
flame retardants, mainly television housing, computer monitors and cases. In consumer
electronic equipment sector, up to 55% of plastics is treated with flame retardants.
12
In practice, Polybrominated diphenyl ethers (PBDEs) and organophosphate esters
are widely used in HIPS as flame retardants additives (Vehlow et al., 2000; Braun and
Schartel, 2004; Jakab et al., 2003; Hamm et al., 2001; Imai et al., 2003; Yamawaki,
2003; Riess et al., 2000; Sjödin et al., 2001). Unfortunately, additives may leak out into
the environment during the lifetime or destruction of the product because those are not
chemically bound to the polymer matrix (Carlsson et al., 2000; Sjödin et al., 2001;
Lemieux et al., 2000; Wolf et al., 2000; Riess et al., 2000). It must be pointed out that
flame retardants exposure at the workplace during recycling or recovery should be
taken into attention. A recent research work by Sjödin et al. (2001) demonstrated that
brominated and phosphorus- containing additives to plastic materials are emitted to the
indoor work environment in connection with recycling. Eight PBDE congeners
including decabromodiphenyl ether (BDE-209), decabromobiphenyl (BB-209), 1,2-
bis(2,4,6-tribromophenyxy)ethane (BTBPE), Tetrabromobisphenol A (TBBPA), and
five arylated and six alkylated organophosphate esters were identified and quantitated
in the air samples from dismantling hall and shredder room of a Swedish electronics
recycling plant. In air from the dismantling plant the corresponding concentration of
triphenyl phosphate (TPP) was 1-2 orders of magnitude higher, hepta- to deca-BDE,
BTBPE and TBBPA were several orders of magnitude higher than those observed in
any of the other work environments investigated such as assembly of circuit boards,
office with computers, computer repair facility. Therefore, dismantling of electronic
scrap may encounter a challenge due to the fact that the potential threat of these
chemicals to human health must be considered carefully.
3.7. Identification of plastics by FT-IR spectrometer
13
In order to evaluate the separability of plastics in TV scrap using density-based
processes, plastics pieces in products of sink-float test were identified by a FT-IR
spectrometer. Figure 10 shows the spectra of plastics with the density range of –
1.02+1.0 g/cm3, -1.06+1.02 g/cm3, -1.23+1.13 g/cm3, respectively.
It is obvious that similar spectra are obtained for plastic samples, which are
distributed in various density ranges. In comparison with the spectrum of a commercial
HIPS (as shown in Figure 11) (Sidwell, 1997), the absorption bands at 3010, 2956,
1600, 1500, 1458, and 758cm-1, are indications of HIPS contributed by aromatic
ring and -CH2-. The absorption bands at 1739 cm-1 can be recognized as characteristic
absorption of ester that is common as flame retardants additive in plastics (Braun and
Schartel, 2004; Carlsson et al., 2000; Imai et al., 2003; Levchik et al., 2000; Sjödin et
al., 2001).
In addition, identification of plastics in products from the sink-float test also carried
out by using an industry scale infrared instrument in Stena Technoworld AB, Sweden.
From the results (Table 7) we can see that plastic in this scrap sample primarily is
HIPS, besides some ABS, PC, and POM. It can be seen that HIPS is widely present
from –1.0g/cm3 fraction to –1.23g/cm3 fraction. This specific density variation of the
same material is due to variations of additives of plastic and from enclosed cavities and
inclusions of other materials. Gravity separation of plastics may encounter some
challenges because of specific density variation of same material.
4. Conclusions
1). The comparison of TV scrap, personal computer scrap, and printed circuit boards
scrap shows that non-ferrous metals and precious metals content in TV scrap is much
lower than that of in personal computer scrap or printed circuit boards scrap. From the
14
point of view of recycling industry, it is expected that recycling of TV scrap will not be
economically viable by using conventional manual disassembly. Mechanical recycling
provide an alternative to separate copper and different plastics.
2). Images of plastics shows that optical sorting processes may provide a good
choice to separate black plastic because almost all of the plastics in TV scrap are black
in color. In addition, the result of FCIRCLE indicates that non-ferrous metals particles
in TV scrap sample form as a variety of shapes that is much more different than that of
plastics and printed circuit boards. Therefore, it can be expected that the separation
processes will be significantly influenced by the particle shape for recovery of non-
ferrous metals.
3). A high recovery of copper could be obtained by utilizing an effective gravity
separation technique. For +1.4 g/cm3 density fraction in sink-float test, the recovery of
Cu is up to 88.4% with an assay of 42.4%. In addition, approx. 18% of the copper is
distributed in the –2.0+1.23 g/cm3 density fraction with an assay of only 7%. This is
because copper in printed circuit boards is not liberated from plastics and ceramic
materials.
4). Identification of plastics shows that the major plastic in TV scrap is HIPS. It is
widely presented in the –1.23 g/cm3 density fraction. Gravity separation of plastics may
encounter some challenges in separation of plastics from TV scrap because of specific
density variations.
Acknowledgements
The authors are grateful for financial support and approval of publication for this
paper from the Minerals and Metals Recycling Research Center (MiMeR), Sweden.
Thanks are also extended to the OVAKO Steel AB for the chemical analysis, Stena
15
Technoworld AB for providing the scrap sample and identification of plastics, and Dr.
Nourredine Menad for his helpful comments.
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Sidwell, J.A., 1997. Rapra Collection of Infrared Spectra of Rubbers, Plastics, and Thermoplastic
Elastomers. 2nd edn., Rapra Technology Limited, 54-57.
Silicon Valley Toxic Coalition, 2002. Just Say No to E-waste: Background Document on Hazards and
Waste from Computers.
Sjödin, Andreas, Håkan Carlsson, Kaj Thuresson, Sverker Sjölin, Åke Bergman, and Conny Östman,
2001. Flame Retardants in Indoor Air at an Electronic Recycling Plant and at Other Work
Environments, Environmental Science & Technology 35, 448-454.
Stuart, Julie Ann, Vivi Christina, 2003. New Metrics and Scheduling Rules for Disassembly and Bulk
Recycling. IEEE Transactions on Electronics Packaging Manufacturing 26, 133-140.
Torres, F., P. Gil, S. T. Puente, J. Pomares, R. Aracil, 2004. Automatic PC Disassembly for Component
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18
Wolf, M., M. Riess, D. Heitmann, M. Schreiner, H. Thoma, O. Vierle, R. van Eldik, 2000. Application of
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19
Table 1 Recycled materials energy savings over virgin materials
Materials Aluminum Copper Iron and steel Lead Zinc Paper Plastics
Energysavings, %
95 85 74 65 60 64 >80
Table 2 Heavy liquids and their densities employed in the sink-float test
Heavyliquids
H2O NaCl+ H2O
NaCl+H2O
NaCl+H2O
CaCl2+H2O
CaCl2+H2O
Acetone+TBE
Acetone+TBE
Tetrabrome-ethane (TBE)
Density, g/cm3
1.0 1.02 1.06 1.13 1.23 1.41 2.00 2.44 2.97
Table 3 Multi-element analysis of TV scrap samples
Al Cu Pb Zn Cr Mo Ni V Ag Au Pt Pd
% ppm
Assay 1.2 3.4 0.2 0.3 90 13 380 7 20 <10 <2 <2
Note: These results are the average obtained from two samples.
20
Table 4 Comparison of TV scrap, personal computer (PC) scrap, and printed circuit boards (PCBs) scrap
Al Cu Pb Zn Ni Ag Au
% ppm
TV scrap 1.2 3.4 0.2 0.3 0.038 20 <10
PC scrapa 2.8 14.3 2.2 0.4 1.1 639 566 Assay
PCBs scrapb 7.0 10.0 1.2 1.6 0.85 280 110 a data source: Legarth et al. (1995), b data source: Zhang and Forssberg (1997)
Table 5 Liberation degrees of Copper in TV scrap
Size range, mm Weight, % Liberation degree of Cu, %
+12.5 22.9 0.0 +9.5 25.7 0.0 -9.5+6.7 27.6 36.4 -6.7+4.75 14.3 54.3 -4.75+3.35 3.1 74.4 -3.35+2.36 3.5 73.4 -2.36+1.65 1.5 51.1 -1.65 1.4 n.d.
21
Table 6 Density separation processes applied for non-metal/metal separation
Utilized for following sorting tasks
Density separation process Workable PieceSizes, mm Plastics
wasteAluminum scrap
Leadbattery scrap
Cable scrap
Electronicscrap
Light steelscrap
Sink-float separation In liquids In heavy media
Gravity separator Hydrocyclone
In aerosuspensions In aero-chutes In fluidized bed trough separators
5-150 <50
0.7-3 0.7-5
+
+
+
+
+
++
+
+
++
Sorting by jigging Hydraulic jigs Pneumatic jigs
2-20 <3
++
Sorting in chutes and on tables
Aero-chutes Aero-tables
0.6-2 <4
++
Up-stream separation Up-stream hydraulic separation Up-stream pneumatic separation
5-150
<300
+ +
+
+
Table 7 Identification of plastics for the products of sink-float test (size range –9.5+1.65mm)
Specific density, g/cm3
-1.0 -1.02 +1.0
-1.06 +1.02
-1.13 +1.06
-1.23 +1.13
-1.41 +1.23
+1.41
Identification of plastics
HIPS HIPS HIPS HIPS, SAN HIPS PC, POM -
22
cum
ulat
ive
unde
rsiz
e, %
0
20
40
60
80
100
0.01 0.1 1 10 100 1000diameter, um
Fig. 2. Particle size distribution of powdered TV scrap sample
Standby sample
End-of-life TVs
Cathode Ray Tubes TV scrap sample
Coning and quartering
…
Rotary riffling
Size, shape and liberation degree
analysis
Shredding
Dismantling
Separation tests Sink-float test
Plastic identification
Chemical analysis
Fig. 1. Procedure of sample preparing for TV scraps
23
Particle size, mm
Cum
ulat
ive
unde
rsiz
e, %
0.1 1 10 1000
20
40
60
80
100
Fig. 3. Size cumulative weight of TV scrap sample
0
10
20
30
40
50
60
70
80
90
100
1 10 100
Size range, mm
Fig. 4. Cu distribution in screening products
Cum
ulat
ive
dist
ribut
ion
of C
u, %
24
Fig. 5. Images of non-ferrous metals (a), plastics (b), and printed circuit boards (c)
separated from TV scrap sample (+2.36mm)
25
Fig. 6. FCIRCLE analysis of non-ferrous metals (a), plastics (b), and printed circuit
boards (c) separated from TV scrap sample (+2.36mm)
26
0
20
40
60
80
100
1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0
Density, g/cm3
Cum
ulat
ive
wei
ght o
f sin
ks, %
Fig. 7. Cumulative weight of sinks versus specific density for TV scrap (-9.5+1.65mm)
0
20
40
60
80
100
0.5 1 1.5 2 2.5 3
Density, g/cm3
Cum
ulat
ive
assa
y, %
assaydistribution
Fig. 8. Cumulative data of copper for sinks versus specific density for TV scrap (-9.5+1.65mm)
27
Fig. 9. Thermogravimetric analysis of a) powdered TV scrap in air atmosphere, b) powdered TV scrap in argon atmosphere, c) HIPS in air atmosphere
c)
b)
a)
590 C
28
Fig. 10. FT-IR spectra of plastics from the products of sink-float test
29
Fig. 11. Infrared spectrum of a commercial HIPS
Paper III
Mechanical separation of consumer electronic scrap
to be submitted to Waste Management
1
MECHANICAL SEPARATION OF CONSUMER ELECTRONIC SCRAP
Jirang Cui*, Eric Forssberg, Hamid-Reza Manouchehri
Division of Mineral Processing, Luleå University of Technology, SE-971 87, Luleå, Sweden
*Corresponding author. Tel.: +46 920 492064; fax: +46 920 97364. E-mail address: [email protected] (J. Cui).
Abstract
Consumer electronic equipment (brown goods), such as television sets (TV), radio
sets, and video recorders, are most common. However, recycling of consumer
electronic scraps is only beginning. Based on a detailed characterization study of
consumer electronic scrap, mechanical recycling of TV scrap oriented to recovery of
metals is highlighted by utilizing several techniques, such as air table, eddy current
separation, and optical (metal) sorting process. The separation results reveal that air
table separation is an effective technology to recover metals from consumer electronic
scraps. By using a DGS table, approximately 90% of non-ferrous metals were
recovered in the heavy product with a purity of 40%. Printed circuit boards and cables
in TV scrap cause metals loss due to the fact that metals in printed circuit boards and
cables are not liberated from plastics and ceramic materials. The study shows that
eddy current separation and optical (metal) sorting process provide alternatives to
recover metals from TV scraps.
Keywords: Recycling; Electronic scrap; Waste treatment; Metal recovery; Eddy
current separation; Air table separation; Optical sorting
2
1. Introduction
The production of electric and electronic equipment (EEE) is one of the fastest
growing domains of the production industry in the world. Both technological
innovation and market expansion continue to accelerate the replacement process. New
applications of EEE are increasing significantly. This development leads to an
important increase of waste electric and electronic equipment (WEEE). In west
Europe, 6 million tonnes of WEEE were generated in 1998, the amount of WEEE is
expected to increase by at least 3-5% per annum (Cui and Forssberg, 2003).
Due to their hazardous material contents, electronic scrap may cause environmental
problems during the waste management phase if not properly pre-treated. Many
countries have presented legislation on the management of this waste stream
(European Parliament and Council, 2003).
Consumer electronic equipment (brown goods), such as television sets (TV), radio
sets, and video recorders, are most common. However, work on recycling of WEEE
primarily focused on personal computer and printed circuit boards scraps (Zhang et al.
2000). According to the European Directive on waste electrical and electronic
equipment (European Parliament and Council, 2003), member states shall ensure that,
by 31 December 2006, producers meet the following targets:
the rate of recovery for consumer electronic equipment shall be increased to a
minimum of 75% by an average weight per appliance and
3
component, material and substance reuse and recycling for consumer
electronic equipment shall be increased to a minimum of 65% by an average
weight per appliance.
However, it is very costly to perform conventional manual dismantling of those
products since brown goods contain very low-grade precious metals and copper. A
mechanical process is of interest for upgrading metal content of consumer electronic
scraps because it can yield high material recovery.
Based on the results of our sink-float test, it is expected that effective gravity
separation may provide an alternative for upgrading metal content of TV scraps (Cui
and Forssberg, 2005). The use of air to separate materials of differing density has long
been known and is typified by the winnowing of grain using an air current to remove
the chaff. Air tables have been used to eliminate a host of small problems in the food
industry and in applications such as separating abrasive grains in the cleaning of
foundry sand and removing metals from crushed slag. In recent years, it also has been
developed and implemented in a few electronic scrap recycling plants. In addition,
eddy current separation, introduced in 1889 for the extraction of gold from sand
deposits has been widely applied in recycling of automobile industry for recovery of
non-ferrous metals. A growing interest in recovering non-ferrous metals from a wide
variety of wastes is the major impetus for the development of eddy current separators.
As a consequent, it is expected that eddy current separation will be introduced in the
recycling of consumer electronic scraps. Characterization of consumer electronic
scraps shows that almost all of the plastics in TV scraps are black in color (Cui and
Forssberg, 2005). With the fast development of Charge-Coupled Device (CCD)
4
sensor technology, optical sorting process also provides a good choice to remove
black plastics from TV scraps.
The objective of this work is to investigate the separability of consumer electronic
scraps by using mechanical separation processes, such as air table, eddy current
separation, and optical sorting.
2. Material and methods
2.1. Material
The television scrap sample was provided by Stena Technoworld AB, Bräkne-Hoby,
an electronic recycling corporation in Sweden. End-of-life TVs of any model and
brand with plastic houses that were collected primarily from Sweden were pre-
dismantled manually to remove the cathode ray tubes. Then the scraps were shredded
into -16 mm particles. An approximately 30 kg of the TV scrap sample was procured
and packed up for the laboratory study.
2.2. Methods
2.2.1. Magnetic separation
A low intensity drum magnetic separator, Mörsell Separator, was employed for
removing ferrous metals from the sample (as shown in Fig. 1). In the present study,
the drum peripheral speed is 2 m/s.
2.2.2. DGS Table separation
Air table separation was carried out by using a DGS-Sort 300D in MinPro AB,
Stråssa, Sweden. The separator (Fig. 2) was developed by Fren Erschliessungs-und
Bergbau GesmbH, Austria.
5
The operation principle of the DGS table is illustrated in Fig. 3. The table consists
essentially of an inclined porous slab which can vibrate and through which air is
blown upwards. The heavy particles are transported upwards by the vibration forces
and are discharged at the upper end of the separation slab. The light particles are kept
in suspension by the regulated air upstream, floating downwards due to the adjustable
incline, discharging at the lower end of the separation slab.
2.2.3. Eddy current separation
The eddy current separation experiments were conducted with a rotating drum eddy
current separator, BM 29.710/18, developed by Bakker Magnetics, the Netherlands, at
a belt speed of 1.25 m/s and a rotor speed of 2500 rpm. In industrial applications of
eddy current separation, the belt speed is typically between 1.0 m/s to 2.0 m/s, and the
rotor speed is between 2000 rpm and 3000 rpm. The BM 29.710/18 rotor has 9 pairs
magnetic poles, the magnetic induction at the belt surface is 0.32 T, and the
dimension of the magnetic rotor is 300 mm.
Fig. 4 illustrates the mechanism of rotating drum eddy current separator. When a non-
ferrous metal particle is exposed to an alternating magnetic field, eddy currents will
be induced in that object, generating a magnetic field to oppose the magnetic field.
The interactions between the magnetic field and the induced eddy currents lead to the
appearance of electrodynamic actions upon conductive non-ferrous particles and are
responsible for the separation process.
2.2.4. Optical (metal) sorting
The optical (metal) sorting process was performed by a Clara All-metal Separator
(Scan & Sort GmbH, Wedel, Germany). As demonstrated in Fig. 5, the optical (metal)
6
sorting appliance consisting of electromagnetic sensors and/or colour line-cameras
identifies the material on the belt and transmits the corresponding information to a
high performance computer in milliseconds. A pneumatic ejection system with up to
256 valves shoots the selected material out of the product stream by air pressure.
2.2.5. Hand picking
Hand picking method was used in the evaluation of separation for qualitative and
quantitative analysis of products. Approximately 1 kg of each product sample was
separated by a chute riffling for hand picking. Subsequently, metals, printed circuit
boards and cables (PCBs), and plastics were separated from each other by hand.
2.2.6. Chemical analysis
Chemical analyses were carried out in the laboratory of OVAKO Steel AB, Hofors,
Sweden. Up to 600 g sample was ground to powder and treated with "Aqua Regina"
(2/3 of HCl and 1/3 HNO3), which will force the metals in the sample to a solution.
The plastic was then filtrated and the remaining solution analyzed with ICP
(Inductively coupled plasma) technique.
3. Results and discussion
3.1. Ferromagnetics recovery
Table 1 shows the chemical assay of ferromagnetics from the TV scrap. It is clear that
a high grade of ferromagnetics product can be produced by employing a low intensity
magnetic separator. It must be pointed out that due to the high contamination levels of
Cu, Al, and Pb, this ferromagnetics fraction may not correspond to the requirements
of iron and steel smelters.
7
3.2. DGS Table separation
Fig. 6 gives the separation results of DGS table separation. It can be seen that 70% to
90% of metals are recovered in the heavy product with metal content between 40%
and 60%. In addition, printed circuit boards and cables in the sample are difficult to
separate from plastics by the DGS table. The result indicates that DGS table
separation is effective and efficient for recovery of metals from consumer electronic
scraps. Printed circuit boards and cables should be dismantled before further
mechanical separation.
A number of parameters must be optimized on DGS table separation. Those
parameters that related to both the feed material and the machine can be classified as
follows:
(1) Particle size and shape
In DGS table separation, large bars that are driven by vibration forces tend to be in the
heavy product, and small spheres tend to be in light product. In this case, a narrow
particle size range is helpful for separation. Fig. 7 gives the images of the products
from the DGS table separation. It can be seen that the major pure plastics in the heavy
product are formed as large bars, and the metals in the light products are copper wires
and aluminum. Therefore, it is expected that a better separation result may be obtained
if the sample is classified into two different size ranges before the DGS table
separation.
(2) Feeding rate
Compared with wet gravity separation techniques, low throughput is the primary
drawback for air table separation. In our study, there is not big difference between a
feeding rate of 93 kg/h and that of 165 kg/h. Therefore, feeding rate of 500 kg/h to
8
800 kg/h can be expected for industry machine with a width of separation slab up to
1.5 m.
(3) Table incline and air velocity
Table incline and air velocity are important and very sensitive variables on the
separation. Once one variable is changed, the other must be correspondingly
coordinated and adjusted in such a way as to maintain an efficient separation. An
increase of table incline gives a rise to the material shift towards the lower end. In
addition, the air velocity must be adjusted in such a way that the light particles are
kept in suspension.
3.3. Eddy current separation
The separation of non-ferrous metals from the -9.5+6.7 mm fraction and -3.35+1.65
mm fraction of shredded TV scrap performed after an optimization of the operating
conditions by using a rotating drum eddy current separator. As shown in Table 2,
more than 75% of non-ferrous metals were recovered, while maintaining a purity of
27% in a single pass for the large particle size fraction. However, only 45% of non-
ferrous metals can be separated for the small particle size fraction. This result
indicates that application of traditional eddy current separation in recycling of
consumer electronic scraps may encounter a problem because the limitation of particle
size. New development of eddy current separation for recovery of fine particles is
required.
3.4. Optical sorting
The optical (metal) sorting experiments by using color and/or metal sensors were
carried out in Scan & Sort GmbH, Wedel, Germany. Two samples with particle size
9
of +9.5 mm and -9.5+4.6 mm, were processed respectively (as shown in Fig 8). Table
3 and 4 give the results of optical (metal) sorting of TV scrap. It is evident that 90%
of metals can be recovered in metallic product by utilizing optical sorting system.
4. Conclusions
The study of mechanical separation of consumer electronic scrap by utilizing air table,
eddy current separation, and optical sorting process yields the following major
findings:
(1) DGS table separation is an effective and efficient separation technique for
consumer electronic scrap. The separation results show that approximately
70% to 90% of non-ferrous metals are recovered in the heavy product with
purity 40% to 60%.
(2) It can be revealed that better separation results of DGS table separation can be
expected by optimizing separation parameters such as particle size, shape, and
feeding rate.
(3) Printed circuit boards and cables in TV scrap cause problems in recovery of
metals because metals in printed circuit boards are not liberated from plastics
and ceramic materials.
(4) Eddy current separation provides an alternative to recover non-ferrous metals
from consumer electronic scrap, but it caused an unacceptable level of loss of
non-ferrous metals for fine particle size fraction.
(5) The results of optical (metal) sorting process show that 90% of metals can be
recovered in metallic product.
10
Acknowledgements
The authors are grateful for financial support and approval of publication for this
paper from the Minerals and Metals Recycling Research Center (MiMeR), Sweden.
Thanks are also extended to Mr. Per Nordenfelt, MinPro AB for the help of DGS
Table test, the OVAKO Steel AB for the chemical analysis, and Stena Technoworld
AB for providing the scrap sample.
References:
Cui, Jirang and Forssberg, Eric, 2003. Mechanical recycling of waste electric and
electronic equipment: a review, Journal of Hazardous Materials B99 243-263
Cui, Jirang and Forssberg, Eric, 2005. Characterization of consumer electronic scrap
oriented to materials recovery, submitted to Waste Management
the European Parliament and the Council of the European Union, 2003. Directive
2002/96/EC of the European Parliament and of the Council of 27 January 2003
on waste electrical and electronic equipment (WEEE), Official Journal of the
European Union, L37/24-L37/38
Zhang, Shunli, Eric Forssberg, Jan van Houwelingen, Peter Rem, and Liu-Ying Wei,
2000. End-of-life Electric and Electronic Equipment Management Towards the
21st Century, Waste Management & Research 18, 73-85.
11
Table 1 Chemical assay of ferromagnetics from the TV scrap
Chemical Assay, % Weight, %
Fe Cu Al Ni Pb Ag Au
Ferromagnetics 22.1 90.10 5.70 0.900 2.000 0.960 0.000 0.000
Table 2 Eddy current separation result of TV scrap Particle size, mm Products Weight, % Metal content, % Recovery, %
Non-ferrous metals 34 27 77
-9.5+6.7 Waste 66 4 23
Total 100 12 100
Non-ferrous metals 19 39 45
-3.35+1.65 Waste 81 11 55
Total 100 16 100
12
Table 3 Optical sorting result of TV scrap (+9.5mm) Weight, % Metal content, % Recovery, %
White fraction 37 75 60
Metallic product from dark fraction
32 40 32
Non-metallic product from dark fraction
31 1 8
Total 100 41 100
Table 4 Optical sorting result of TV scrap (-9.5+4.6 mm) Weight, % Metal content, % Recovery, %
Metallic product 55 47 90
Non-metallic product 45 6 10
Total 100 29 100
13
Fig. 1. Flowsheet of magnetic separation
Fig. 2. DGS-Sort 300D Separator
Scrap sample
Ferrous metals Non-ferrous metals and non-metals
14
Fig. 3. Schematic diagram illustrating the principle of DGS table separation
Fig. 4. Illustration of rotating eddy current separation
Separation slab
Feed
Light product
Heavyproduct
VIBRATION AIR UPSTREAM
BeltFeed
Non-ferrous metals
Non-metals
Splitter Magneticrotor
Non-ferrous metals
15
Fig. 5. Demonstration of optical (metal) sorting system
0
10
20
30
40
50
60
70
60 70 80 90 100
Recovery, %
Gra
de, %
Metals
0
10
20
30
40
10 20 30 40
Recovery, %
Gra
de, %
PCBs
Fig. 6. Grade-Recovery of metal and printed circuit boards in the heavy product from the DGS table separation
16
a). Heavy product of the DGS table separation b). Light product of the DGS table separation
c). Plastics picked out from the heavy product d). Metals and printed circuit boards in the light product
Fig. 7. Images of the products from the DGS table separation
17
Fig. 8. Flowsheet of optical (metal) sorting process of TV scraps
White product
TV scraps (+9.5 mm)
Color sorting
Dark product
Non-metallic product Metallic product
Metal sorting
Non-metallic product Metallic product
TV scraps (-9.5+4.6 mm)
Color sorting
White product Dark product
Metal sorting Metal sorting
Metallic product
Paper IV
Eddy current separation for fine particles
to be submitted to Journal of Hazardous Materials
1
EDDY CURRENT SEPARATION FOR FINE PARTICLES
Jirang Cui*, Eric Forssberg
Division of Mineral Processing, Luleå University of Technology, SE-971 87, Luleå, Sweden
*Corresponding author. Tel.: +46 920 492064; fax: +46 920 97364. E-mail address: [email protected] (J. Cui).
Abstract
A comparison of eddy current separation in both “forward mode” and “backward
mode” is discussed in the paper. The preliminary results show that large non-ferrous
metal particles can be separated effectively by using Bakker eddy current separator
when the magnetic drum rotates in the forward mode; fine non-ferrous metal particles
can only be separated by eddy current separator in the backward mode. Separation of
copper wires shows that fine copper cable and wires can be possible recovered by
traditional rotating drum eddy current separator in a backward mode.
Keywords: Eddy current separator; Fine particles; Non-ferrous metal; Recycling:
Metal recovery
1. Introduction
In the past decade, one of the most significant developments in recycling industry was the
introduction of eddy current separators based on the use of rare earth permanent magnets.
When a conductive particle is exposed to an alternating magnetic field, eddy currents will be
induced in that object, generating a magnetic field to oppose the magnetic field. The
interactions between the magnetic field and the induced eddy currents lead to the appearance
of electrodynamic actions upon conductive non-ferrous particles and are responsible for the
separation process.
2
Now, eddy current separators are almost exclusively used for waste reclamation
where they are particularly suited to treating the relatively coarse sized feeds.
However, the number of waste streams containing fine metal particles is foreseen to
grow substantially in the near future (Rem et al. 2000). In recent years, there have
been some developments of eddy current separation processed designed to separate
small particles (Zhang et al. 1999, Rem et al. 2000). A preliminary work (Zhang et al.
1999) shows that the belted-drum eddy current separation is effective for separating
non-ferrous metals below 5 mm if the magnetic drum rotates in an opposite direction
to the conveyor belt. It was called as “backward phenomenon”. The aim of
experiments described here is to compare the results of eddy current separation in
both “forward mode” and “backward mode” so as to find best parameter conditions
for recovery of fine particles.
2. Theory
A magnet rotor with k pairs of magnet poles and a magnetic induction bm at the radius Rm of
the outer shell surface produces a magnetic induction outside the shell (r>Rm):
B=)(sin)(cos1
tktk
rRb
BB
m
mk
mm
r (1)
where (r, ) are cylindrical coordinates with respect to the axis of the rotor, t is time and m is
the angular velocity of the rotor.
The expression shows that a stationary particle at some point (r, ) experiences a magnetic
induction of constant magnitude B bm(Rm/r)k+1 revolving at angular velocity -k m (Fig. 1.).
If the particle itself is spinning with some angular velocity , it perceives a field of the same
3
size as a stationary particle but now rotating at an apparent angular velocity -k m- . The
magnetic torque makes the particle spin in the same direction as the magnetic field.
For particles of simple geometries, such as spheres, thin disks and long cylinders, with a size
that is small with respect to the magnetic wavelength 2 Rm/(k+1) of the rotor, the theory of
eddy current separation (Rem, 1999) provides an expression for the particle magnetic dipole
moment M in a rotating magnetic field:
M=r
mr
m BB
dkIBB
dkRV ))(())(( 20
20
0
(2)
where V and are the volume of the particle and its electrical conductivity, respectively, and
R( ) and I( ) are dimensionless functions, for which approximations in terms of rational
functions are tabulated in Table 1.
As a consequence, the torque Tm on the particle from its magnetic moment is given by:
Tm=M B= )(0
2
IVBez (3)
the direct magnetic force Fm can be written by:
Fm=M B=)()()1(
0
2
IR
rVBk
(4)
For conductive particles with d less than 10 mm, the factor I in Tm reduces to a linear function
of m:
VdBkcT mmm22)( (5)
where, the coefficient cm depends on the shape and orientation of the particles (Table 1).
4
3. Materials and method
3.1. Materials
A wide range of materials, such as copper, aluminum, and plastics was produced by cutting
pure materials with a semi-automatic cutting machine. Copper wires were provided by Draka
Kabel Sverige AB, Sweden. The dimensions and shapes of materials to be investigated are
presented in Table 2.
3.2. Method
The eddy current separation experiments were conducted with a rotating drum eddy
current separator, BM 29.710/18, developed by Bakker Magnetics, the Netherlands.
The BM 29.710/18 rotor has 9-pair magnetic poles, and the magnetic induction at the
belt surface is 0.32 T.
The separability of materials was characterized by their distribution in an array of the
collectors that were placed in front of the conveyor belt pulley (as shown in Fig 2).
Twelve collectors, each with dimensions of 500 85 100 (length width height) mm,
were used. The material distribution was analyzed by its percent weight in each
collectors such that:
%100)/()(12
1jijijij WWPW (6)
where (PW)ij is the percent weight of the ith material in the jth collector, and Wij is the
weight of the ith material in the jth collector.
4. Results
Fig. 3 demonstrates the material distribution for large particle size. It is obvious from
Fig. 3. a) that, when the eddy current separator run in the forward mode, almost all the
5
aluminum particles is distributed in the collectors of No. 1 to No. 4, otherwise PVC
particles are distributed in the collectors of No. 6 to No. 8. Analysis of the material
distribution indicates that it is easy to separate large aluminum particles from non-
metals, when the magnetic drum rotates in the forward mode. It can be seen from Fig.
3. b) that, when the eddy current separator run in the backward mode, aluminum
particles are widely distributed in collectors of No. 1 to No. 10. This result indicates
that it is difficult to separate large non-ferrous metals from non-metals when the
magnetic drum rotates in the backward mode.
Fig. 3 also shows the effect of particle shape on eddy current separation. It is clear
that, in the forward mode, the deflections of square plates of Al are larger than those
of the rectangular sheets since a square plate is more conducive to eddy-current
induction than a rectangular sheet.
The material distribution for fine particles is presented in Fig. 4. It can be seen that
fine conducting particles like copper are either mixed up with the non-metals ones or
distributed in the collectors that are closer to the magnetic drum. The results indicate
that it is difficult to separate fine non-ferrous metals from non-metals selectively,
when the magnetic drum rotates in the forward mode. It has been found that if the
magnetic drum rotates in the backward mode, separation of fine conducting particles
from non-conducting ones is improved drastically. It is shown in Fig 4. that more than
80% of copper particles is distributed in the collectors of No. 1 to No. 6. Separation of
copper wires demonstrated in Fig. 4 shows that fine copper cable and wires can be
recovered by traditional rotating drum eddy current separator in a backward mode.
6
5. Conclusions
The preliminary study indicates that large non-ferrous metal particles can be separated
effectively by using Bakker eddy current separator when the magnetic drum rotates in
the forward mode; fine non-ferrous metal particles can only be separated by eddy
current separator in backward mode. Separation of copper wires shows that fine
copper cable and wires can be possible recovered by traditional rotating drum eddy
current separator in a backward mode.
Acknowledgements
The authors are grateful for financial support and approval of publication for this
paper from the Minerals and Metals Recycling Research Center (MiMeR), Sweden.
Thanks are also extended to Draka Kabel Sverige AB, Sweden for providing the
experiment samples.
References:
Rem, P.C., Eddy Current Separation, Eburon, 1999, Delft, ISBN 90-5166-702-8
Rem, P.C., Zhang, S., Forssberg, E. and De Jong, T.P.R., The investigation on
separability of particles smaller than 5 mm by eddy current separation
technology - Part II: Novel design concepts, Magnetic and Electrical Separation
10 (2000) 85-105
S. Zhang, P.C. Rem, E. Forssberg, Investigation of separability of particles smaller
than 5 mm by eddy current separation technology Part I: rotating type eddy
current separators, Magnetic and Electric Separation 9 (1999) 233-251
7
Table 1. Parameters defining the magnetic interaction for particles of several shapes and parallel ( ) or perpendicular ( ) orientations of their axis of symmetry with respect to the axis of the rotor
Shape (R( ), I( )) D cm
Sphere 21( 2, 42 )/20(1764+ 2) D 1/40
Cylinder 3( 2, 24 )/2(576+ 2) D 1/16
Cylinder 9( 2, 24 )/8(576+ 2) D 3/64
Disk ( 2, 12 )/(144+ 2) 1/12
Disk (0.6 2/D, 16 )/4(256+(0.6 )2 2/D2) D 1/64
D: diameter, : thickness.
Table 2. Dimension and shape of test materials
Dimension and shape
L W T (mm) (sheet)
T S (mm) (cylinder)
Material
14 14 220 10 240 5 2
Al
3 3 234 0.512 1.58 2.53 6
Cu
5 5 2 Cu, PVC L: length, W: width, T: thickness, S: section area, PVC: polyvinyl chloride
8
Fig. 1. Magnet rotor (left) produces a rotating magnetic field B inducing eddy currents in a
particle (right) resulting in a particle magnetic moment M.
Fig. 2. Illustration of rotating eddy current separation A: Magnetic drum rotates in a Forward mode
B: Magnetic drum rotates in a Backward mode
N
NN
NS
S
S
S MB
No.12 ... No.1 Collectors
BeltFeed
Non-ferrous metals
A B
9
12
34
56
78
910
1112
40*5
*2
20*1
0*2
14*1
4*2PV
C
0
20
40
60
80
100
Wei
ght,
%
collectror No.
Particle size, mm
a)
12
34
56
78
910
1112
40*5*220*10*2
14*14*2PVC
0
10
20
30
40
50
60
70
80
90
Wei
ght,
%
collectror No.
Particle size, mm
b)
Fig. 3. Material distribution for large particle size (volume of Al particle=400 mm3, a) forward mode, b) backward mode)
10
12
34
56
78
910
1112
3*3*23*6
8*2.512*1.5
34*0.5PVC
0
20
40
60
80
100
Wei
ght,
%
collectror No.
Particle size, mm
a)
1
23
45
67
89
1011
12
3*3*23*6
8*2.512*1.5
34*0.5PVC
0
10
20
30
40
50
60
70
80
90
Wei
ght,
%
collectror No.
Particle size, mm
b)
Fig. 4. Material distribution for fine particle size (volume of Cu particle=18 mm3, a) forward mode, b) backward mode)
Paper V
A comparison of Magnus separation and wet eddy current separation
to be submitted to Resources Conservation and Recycling
1
A COMPARISON OF MAGNUS SEPARATION AND WET EDDY CURRENT SEPARATION
JIRANG CUI+, LENKA MUCHOVA* PETER REM* AND ERIC FORSSBERG+
+ Division of Mineral Processing, Lulea University of Technology, SE-971 87 Lulea, Sweden *Delft University of Technology, Mijnbouwstraat 120, 2628 RX Delft, the Netherlands
Abstract:
Fine non-ferrous metals (with particle sizes below 5 mm) can be concentrated directly from wet waste streams by Magnus separation as well as by a wet variant of eddy current separation. The present study gives a careful comparison of the results of both techniques on aluminum concentrates from bottom ash.
Keywords: Non-ferrous metals, wet separation, eddy current, small particles
INTRODUCTION
It is well known that, when a conductive particle is exposed to an alternating magnetic field, eddy
currents will be induced in that object, generating a magnetic field to oppose the magnetic field.
The interactions between the magnetic field and the induced eddy currents lead to the appearance
of electrodynamic actions upon conductive non-ferrous particles and are responsible for the
separation process.
The fine fractions of non-ferrous concentrates, e.g. deriving from electronics scrap, car scrap or
household waste, are increasingly treated by wet concentration techniques. Previous work showed
that it is relatively easy to separate heavy non-ferrous metals and organics from such streams by
separation on terminal velocity in water. The separation of small (say < 5 mm) aluminum particles
from the resulting wet streams can be realized both by a process called Magnus separation and by a
wet variant of eddy current separation described earlier. The aim of experiments described here is
to compare the results of both techniques on aluminum concentrates from bottom ash. Both
2
Magnus separation and wet eddy current separation use the effect that small non-ferrous particles
start to spin in a rotating magnetic field.
Magnetic interaction
A magnet rotor with k pairs of magnet poles and a magnetic induction bm at the radius Rm of the
outer shell surface produces a magnetic induction outside the shell (r>Rm):
B=)(sin)(cos1
tktk
rRb
BB
m
mk
mm
r (1)
where (r, ) are cylindrical coordinates with respect to the axis of the rotor, t is time and m is the
angular velocity of the rotor.
The expression shows that a stationary particle at some point (r, ) experiences a magnetic
induction of constant magnitude B bm(Rm/r)k+1 revolving at angular velocity -k m (Fig. 1.). If the
particle itself is spinning with some angular velocity , it perceives a field of the same size as a
stationary particle but now rotating at an apparent angular velocity -k m- . The magnetic torque
makes the particle spin in the same direction as the magnetic field.
For particles of simple geometries, such as spheres, thin disks and long cylinders, with a size that is
small with respect to the magnetic wavelength 2 Rm/(k+1) of the rotor, the theory of eddy current
separation (Rem, 1999) provides an expression for the particle magnetic dipole moment M in a
rotating magnetic field:
M=r
mr
m BB
dkIBB
dkRV ))(())(( 20
20
0
(2)
3
Fig. 1. Magnet rotor (left) produces a rotating magnetic field B inducing eddy currents in a particle (right)
resulting in a particle magnetic moment M.
where V and are the volume of the particle and its electrical conductivity, respectively, and R( )
and I( ) are dimensionless functions, for which approximations in terms of rational functions are
tabulated in Table 1.
As a consequence, the torque Tm on the particle from its magnetic moment is given by:
Tm=M B= )(0
2
IVB ez (3)
the direct magnetic force Fm can be written by:
Fm=M B=)()()1(
0
2
IR
rVBk (4)
For conductive particles with d less than 10 mm, the factor I in Tm reduces to a linear function of
m:
VdBkcT mmm22)( (5)
where, the coefficient cm depends on the shape and orientation of the particles (Table 1).
N
NN
NS
S
S
S MB
4
FL
FD
VGravity-buoyancy
Table 1. Parameters defining the magnetic interaction for particles of several shapes and parallel ( ) or perpendicular ( ) orientations of their axis of symmetry with respect to the axis of the rotor
Shape (R( ), I( )) D cm
Sphere 21( 2, 42 )/20(1764+ 2) D 1/40
Cylinder 3( 2, 24 )/2(576+ 2) D 1/16
Cylinder 9( 2, 24 )/8(576+ 2) D 3/64
Disk ( 2, 12 )/(144+ 2) 1/12
Disk (0.6 2/D, 16 )/4(256+(0.6 )2 2/D2) D 1/64
D: diameter, : thickness.
Magnus effect
It is known that a spinning particle moving through a fluid experiences a force perpendicular both
to its direction of motion and to the axis of rotation. This phenomenon is called the Magnus effect
(Massey, 1989).
Fig. 2. Force diagram for a particle that rotates at an angular velocity while settling with a linear velocity v
with respect to a fluid
As shown in Fig. 2, the trajectory of a spinning particle falling in a fluid can be analyzed to the
forces of drag, lift and drag torque (Reynolds number Re>300) (Rem et al., 2002):
5
FD=cD v2A/2 (6)
FL=cL v2A/2 (7)
5DcT Td (8)
where cD , cL, and cT represent the coefficients that depend on the shape and orientation of the
particle (Table 2), is the density of fluid, v is the particle velocity, A is the characteristic area of
the particle, D is the characteristic dimension of the particle, is the angular velocity of the
particle (assuming that is always perpendicular to v).
The speed of rotation of the conductive particles in a Magnus separation is found by integration
of the balance of angular momentum:
J =Tm-Td (9)
Eq. (9) implies that within the size ranges indicated, the particle spin in a Magnus separation does
not depend on the particle size, but only on its shape and orientation, since J, Tm, and Td are all
proportional to the fifth power of the particle size.
Table 2 Measured values for the drag torque coefficient for particles of several shapes
Particle definition cT
Rough sphere (Re=300-700) 0.007
Smooth sphere (Re=3 106) 0.0008
Rough cylinder (Re=500-700, L/D=3) 0.008 L/D
Smooth cylinder (Re=2 106, L/D=5) 0.0012 L/D
Disk (Re=300-30000, D/ =3.5-4) 0.03
6
Wet eddy current separation
The aim of adding water to the feed of eddy current separation is to glue all the particles to the belt
surface. For small particles, typically below 5 mm, this adhesive force is of the same order of
magnitude as gravity. The rotating magnetic field makes the conductive particles spin, with the
effect that the water bonds between these particles and the belt are broken.
In order to simplify the calculation, we assume a spherical particle with diameter D that is
connected to a surface by a cylindrical mass of water (as shown in Fig. 3.). For a completely
wettable solid particle, the adhesion work Wa between particle and water is much higher than the
cohesion work of water, WC (Lu et al., 2005). As a result, the energy between a wettable solid
particle and water can be written by:
E=2 rhWC (10)
where r and h are the radius and height of the water cylinder. Geometrical analysis shows that
radius r= )( hDh . Additionally, the work of cohesion WC is expressed as:
WC=2 gl (11)
here, the surface tension of water gl=73 10-3 J/m2.
By putting the Eq. (11) to Eq. (10), the force gluing the particle to the belt surface is given as:
)(4/ hDhdhdEF gl (12)
For instance, if D=3 mm and h=0.2 mm, the force F=0.7 10-3 N, which is about the same order as
the gravity force on a stone particle with a same particle size.
Although the adhesive force is strong enough to keep most of the non-metal particles glued to the
belt surface, the eddy current torque can easily provide the force to break the water bond for the
non-ferrous metal particles. As discussed above, the magnetic torque is expressed as Eq. (5). The
7
D
rh
non-ferrous metal particle is able to break loose if the torque is of the order FD/2. For a typical
water layer, h=0.2 mm, and on a traditional rotating drum eddy current separator, B=0.3 T, =150
rad/s, this criterion is met for well-conducting metals if D>1 mm, whereas for metals like solder
and lead it is realized for D>2 mm (Table 3).
Fig. 3. Geometry of wet bond
Table 3 Electrical conductivity of some metals and alloys
Alloy Conductivity , (1/ m)
Aluminum 3003 27 106
Copper 56 106
Zinc 17 106
Yellow brass 15 106
Lead 5 106
Solder 50-50 7 106
EXPERIMENTAL RESULTS
Separation results of wet eddy current separation
Effect of splitter position The effect of splitter position on wet eddy current separation of aluminum is demonstrated in Fig 4.
It is observed that the recovery of Al is decreasing slowly, as the splitter moving from 300 mm to
335 mm. In the meanwhile, the grade of Al product increases from 26% to 63%. In order to ensure
maximum the aluminum recovery, the splitter position for the rest test was set to 335 mm
horizontally away (x) from the axis of the rotor.
8
0
20
40
60
80
100
250 300 350 400 450
Splitter position, mm
%
GradeRecovery
Fig. 4. Effect of splitter position on eddy current separation of Al (rotor speed=1500 rpm, belt speed=1 m/s, moisture content=10%, particle size=4-6 mm).
Effect of rotor speed The effect of rotor speed on wet eddy current separation of aluminum is exhibited in Fig. 5. As can
be seen in Fig. 5, the grade of Al product is slightly decreasing as the rotor speed increasing from
1000 rpm to 1500 rpm due to a drastic particle-particle interaction. However, the rotor speed from
1000 to 2000 rpm insignificantly influences the recovery of aluminum. It indicates that a high rotor
speed that is widely used in traditional rotating drum eddy current separation is dispensable in wet
eddy current separation. This result is sufficiently consistent with the preliminary study by Settimo
et al. (2004).
Effect of moisture content of the feed Table 4 gives the effect of moisture content of the feed on wet eddy current separation of
aluminum. It is clear that the moisture content of the feed has significant effect on the grade of Al
product. The Al grade increases from 63% to 84% as the moisture content of the feed increase from
10% to 15%. This result shows that a 15% of moisture content of feed is needed to provide an
effective water layer on the belt surface so as to glue the large stone particles.
9
0
20
40
60
80
100
500 1000 1500 2000 2500
Rotor speed, rpm
%GradeRecovery
Fig. 5. Effect of rotor speed on eddy current separation of Al (belt speed=1 m/s, moisture content=10%, particle size=4-6 mm).
Table 4 The effect of moisture content of the feed on wet eddy current separation of Al (rotor speed=1500 rpm, belt speed=1 m/s, particle size=4-6 mm)
Weight, % Grade, % Recovery, %
Moisturecontent, % 10 15 10 15 10 15
Al product 14 11 63 84 96 95
Tailings 86 89 0.4 0.5 4 5
Feed 100 100 9 9 100 100
Effect of particle size The effect of particle size on wet eddy current separation of aluminum is shown in Table 5. It can
be seen that the grade of aluminum product for particle size of 2-4 mm is much better than that of
4-6 mm. As discussed above, this is due to the fact that the adhesive force gluing a particle to the
belt surface of large particles, e.g., 6 mm is much lower than the gravity force on the same particle
size.
10
Table 5 The effect of particle size on wet eddy current separation of Al (rotor speed=1500 rpm, moisture content=15%, belt speed=1 m/s)
Weight, % Grade, % Recovery, %
Size range, mm 4-6 2-4 4-6 2-4 4-6 2-4
Al product 11 7 84 97 95 96
Tailings 89 93 0.5 0.3 5 4
Feed 100 100 9 4 100 100
Magnus separation
The primary study of Magnus separation by one of the authors (Rem et al. 2002) shows that
Magnus separation as a novel type of eddy current separation can recover fine non-ferrous metal
particles from solid wastes. As a comparison of wet eddy current separation by using a traditional
drum eddy current separator, a new design of industry Magnus separator was utilized in our test.
Experiments were carried out with the same artificial sample as in the wet eddy current separation.
Table 6 gives the separation results of Magnus separation. It can be seen that a grade of 80% with
an Al recovery of 60% can be obtained by using Magnus separtion.
Table 6 Magnus separation of artificial Al sample (rotor speed=10000 rpm)
Weight, % Grade, % Recovery, %
Size range, mm 4-6 2-4 4-6 2-4 4-6 2-4
Al product 7.5 4.5 80 75 61 37
Tailings 92.5 95.5 4 6 39 63
Feed 100.0 100.0 10 9 100 100
11
CONCLUSIONS
The preliminary study indicates that fine non-ferrous metal particles can be separated effectively by
wet eddy current separation as well as Magnus separation. Comparing with Magnus separation, a
better separation result can be obtained by using wet eddy current separation.
REFERENCES
Fraunholcz, N., Rem, P.C., and Haeser, P.A.C.M., Dry Magnus Separation, Minerals Engineering 15 (2002) 45-51.
Köhnlechner, R., Schlett, Z., Lungu, M. and Caizer, C., A new wet Eddy-current separator, Resources, Conservation and Recycling, Volume 37, Issue 1, December 2002, Pages 55-60
Lu, S., Pugh, R.J., Forssberg, E., Interfacial Separation of Particles, Elsevier, 2005, Amsterdam, ISBN 0-444-51606-9, 50-55
Massey, B., Mechanics of fluids (sixth edition), Van Nostrand Reinhold Co. Ltd, London, 334-335.
Rem, P.C., Eddy Current Separation, Eburon, 1999, Delft, ISBN 90-5166-702-8
Rem, P.C., Zhang, S., Forssberg, E. and De Jong, T.P.R., The investigation on separability of particles smaller than 5 mm by eddy current separation technology - Part II: Novel design concepts, Magnetic and Electrical Separation 10 (2000) 85-105
Rem, P.C., Fraunholcz, N., and Schokker, E.A., Magnus Separation, Separation Science and Technology 37 (2002) 3647-3660.
Rem, P.C., De Vries, C., van Kooy, L.A., Bevilacqua, P., Reuter, M.A., The Amsterdam Pilot on Bottom Ash, Minerals Engineering 17 (2004) 363-365
Settimo, F., Bevilacqua, P., Rem, P.C., Eddy current separation of fine non-ferrous particles from bulk streams, Physical Separation in Science and Engineering, 2004 - 13 - 15 – 23
van Kooy, L.A., Mooij, M., Rem, P.C., Kinetic gravity separation, Physical Separation in Science and Engineering, 2004 - 13 - 1 – 25
