Development of Manufacturing Technology for Direct RecyclingCemented Carbide (WC-Co) Tool Scraps

Saharat Wongsisa+, Panya Srichandr and Nuchthana Poolthong

Integrated Product Design and Manufacturing Programme, Division of Materials Technology, School of Energy,Environment and Materials, King Mongkut’s University of Technology Thonburi, Bangkok, Thailand

The objective of this research was to develop a sustainable industry manufacturing method for direct recycling cemented carbide toolscraps combining a hydrothermal and electrolysis process (CHEP). The research methodology was performed by studying the current recyclingcarbide tools, scrap industry and associated recycling technologies. A tungsten carbides (WC) recycling technology was designed by using anelectrochemical cell comprising of a titanium cathode, titanium anode and hydrochloric acid (HCl) electrolyte under controlled temperature.Finally, the speed of binder phase removal, key process variables, WC leached and recovered WC purity rates were examined and identified. Theresults of this research indicated that this recycling process was effective in recycling cemented carbide from industrial cutting tools scraps. Thistechnology can be used to purify the recovered WC rate to near virgin material, resulting in a more environmentally friendly process andreducing natural tungsten material usage. [doi:10.2320/matertrans.M2014213]

(Received June 11, 2014; Accepted August 28, 2014; Published December 25, 2014)

Keywords: recycling oriented materials, sustainable manufacturing, tungsten carbide, electrolysis

1. Introduction

Cemented tungsten carbides are currently used extensivelyin various industries, especially in manufacturing industrieswhere WC is used to make a variety of hard metals. Forexample, cemented tungsten carbides are commonly used inthe production of cutting tools for machining processes, wearresistant parts, and similar industrial uses. As the globalpopulation increases, the need for manufactured goods willalso increase, and the consumption of tungsten carbide willgrow.1,2) However, tungsten is a finite natural resource, andeffective recycling is the only solution to the problem oftungsten depletion. In addition to natural resource conserva-tion, recycling would also yield other benefits such as,reduction in the use of energy and chemicals in extractingtungsten and manufacturing of tungsten carbide, as well asreduction of waste.3,4) Indeed, recycling is widely considered tobe one of the three R’s of environmental friendliness, waste theother two being reduce and reuse. It is envisaged that recyclingof tungsten carbide will considerably grow in the futurebecause of the reasons mentioned above.2,3) In order to meetsuch a challenge, it is imperative that the recycling processshould be efficient, environmentally friendly, and econom-ically viable. The resulting products must also be as good or atleast comparable to those manufactured from virgin materials.

Tungsten recycling today can be considered from fourstandpoints: preservation of natural tungsten ore reserves,minimization of environmental pollution, the economy, andtungsten pricing policy.3) Numerous studies have beenconducted examining the efficacy of various recyclingapproaches. Kieffer and Lassner discussed and comparedthe future of direct and indirect recycling processes and therecycling of WC by zinc processes;3) which consumes lowenergy, but is dependent on the size of scrap input.Venkateswaran et al. researched recycling through the useof melting baths for W-heavy metal scraps.6) Lin et al.;7)

Human and Exner;12) and Sutthiruangwong et al.;14) have

researched recycling of WC by electrochemical processes forWC purity. Kellner et al. discussed the corrosion behavior ofWC-Co in alkaline solutions.10) Human and Exner researchedthe behavior of W-carbide hard metal in electrochemicalprocesses.16) Kojima et al. researched recycling of WC-Coby hydrothermal treatments and examined the propertiesof re-sintering hard metals.17) Byrappa and Adschiri haveexamined modern hydrothermal technologies, not justconfined to crystal growth, but covering other categoriesused in different contexts and scientific approaches.18) Zhangand Hideaki researched the extraction of metals frommunicipal solid waste,19) with HCl is the most effectiveextraction reagent. Edtmaier et al. researched the selectiveremoval of the cobalt binder from cemented WC/Co base byacetic acid leaching,20) and associated recycling capacitiesthat are economically and ecologically viable.

The Zinc process uses Zinc as a catalyst for melting awaycobalt binder at 900°C or higher, followed by vacuumdistillation under a controlled Ar/N2 atmosphere and acidleaching for Zinc removal.3,5) However, further refining byelectrochemical processes is required to obtain a higherpurity of WC product.

In the melt bath process,6) cemented carbide scraps areheated at a temperature higher than the melting point ofthe binder metal in a controlled atmosphere, followed bycrushing and acid leaching, consecutively. The resultingproduct is a WC powder with more than 90% purity. If higherpurity is required, the powder is further refined by employingan electrochemical process.

Better carbide recovery rates (the ratio between the amountof recovered WC and scrap used in the recycling process)from recycling can be achieved by using electrolysis.8,10,12­15)

Both WC and Co binder phase can be recovered. The mainlimitation of this method is that the process is very slow,requiring a long time and relatively a lot of energy for a unitof carbide recovery. This makes the process relativelyinefficient and expensive compared to the thermal process.The main advantage of this method is the direct recyclingprocess that yields high purity WC and Co outputs.+Corresponding author, E-mail: saharat_w@hotmail.com

Materials Transactions, Vol. 56, No. 1 (2015) pp. 70 to 77©2014 The Japan Institute of Metals and Materials

In the hydrothermal treatment process,11,17­20) cobaltbinder phase is leached out from cemented carbide byheating the carbide scrap in concentrated HCl. The speed ofthis process is faster than that of the electrolysis process. Therecovered WC has a purity sufficiently high to be used as rawmaterial for making commercial cemented carbide products,depending on the particle sizes of the WC powder, Copowder28,29) and grain structure of hard metals.23,25­27)

Each of these processes has its advantages and limitations.The thermal process, for example, is highly efficient, andtherefore capable of being employed for large scale recycling.However, this method consumes a large amount of energy,and the high temperature for required treatment couldpotentially affect the structure of the recovered WC, and bedetrimental to its mechanical properties. Contamination isalso a potential problem in thermal-based recycling. Theelectrolysis process, while yielding high purity WC and Co,is a very slow but expensive method, and therefore noteconomically viable for commercial purposes. The hydro-thermal method yields better productivity than the electrol-ysis process, but the use of concentrated acid and hightemperature could lead to loss of WC (causing low recoveryrates) and pose serious environmental problems.22) A lotof work is thus still required to improve and develop newprocesses for cement carbide recycling in order to overcomefuture challenges.

The present study explores the possibilities of utilizinga new cemented carbide recycling approach, a combinedhydrothermal and electrolytic process (CHEP), by developingreaction tools at the anode and cathode to create the oxidationreaction for binder recovery under different temperatures.The objective of CHEP is to exploit the advantages ofboth processes while minimizing their limitations. Specificobjectives of the present work are: (1) To determine whetherit is feasible to use the combined hydrothermal andelectrolysis process for recycling cemented tungsten carbide;and (2) If it is feasible, to determine performance and outputcharacteristics in terms of process efficiency, environmentalfriendliness, and product characteristics.

2. Experimental Procedure

2.1 Cemented carbide tools scrapsCemented WC-Co scraps require dimensions 12.75 ©

12.75 © 3.75mm. For the recycling experiment in this study,indexable insert tool scraps as illustrated in Fig. 1 wereselected from used cemented tungsten carbide scraps.

The cemented carbide scraps contained tungsten carbide94mass% and cobalt 6mass%, with an average measurementof approximately 1.0 µm. The scraps were produced bycompact pressure at 350MPa and a sintering process at1450°C, and had a hardness of approximately 1550 HV (R.S.carbides Co., Thailand). After being processed in a metalremoval process, cemented tungsten carbide scraps were leftas waste and were no longer viable for further removalprocesses. The overall recycling process in the present studyis depicted schematically in Fig. 1.

2.2 Extraction and removal of binder phaseCemented carbide scraps were first washed and then

cleaned to remove dirt and other contaminants. The cleanedscraps were then dried in an oven before being put in thebinder phase removal apparatus (autoclave). The output ofthe autoclave after binder removal was tungsten carbide mud.The WC mud was then crushed and washed to removeresidue and contaminants. After washing the powder, theproduct was then ball milled and dried in an oven to obtainthe final recycled WC powder.

The heart of the recycling process in this study was thebinder removal operation, which was achieved through theuse of the binder removal apparatus, or autoclave. Theoperating function of the apparatus was to employ anelectrolytic process to remove the binder phase at a slightelevated temperature. Cemented carbide scraps were sub-merged in an electrolyte in contact with a cathode and ananode to form an electrolysis, or electrochemical cell. Theelectrolyte can be heated to a desired temperature. Schematicrepresentation of the design of the binder removal apparatusis shown in Fig. 2.

The removal apparatus consisted of a barrel, made fromTeflon for acid electrolyte resistance, in which the cementedcarbide scraps were placed. Several holes were drilledthrough the wall of the barrel so that the electrolyte couldflow through it without any difficulty. The cathode employedwere curved titanium plates as shown in Fig. 2, and the anodewas titanium rods in the center of the barrel. The barrel,the cathode, the anode, and the electrolyte (hydrochloricacid)17,19) were housed in a Teflon-clad stainless steel tank.The electrolyte was circulated in a continuous basis in orderto maintain the pH level of the electrolyte and current densityof the cell. The pressure of the electrolyte in the tank wasmaintained at one bar.11,20) The temperature of the electrolytewas controlled by a heater. During the binder phase removaloperation, the barrel containing the scrap rotated and tumbledto maximize contact between the scrap and the electrolyte toenhance binder phase removal activity. Once the binder phasewas removed, the recovered carbides dropped through theholes in the barrel to the bottom of the tank, and eventuallysettled in a container in the form of WC mud through anorifice at the bottom of the tank. The WC skeleton had beensufficiently crushed into WC particles.

The WC mud, was further crushed, washed and ballmilled28) before it was dried in an oven. The recoveredWC powder was then characterized using scanning electronmicroscopy (SEM) and transmission electron microscopy(TEM). Particle size, particle size distribution, and the purityof the recovered WC powder were determined usingrespective X-ray diffractometry (XRD), X-ray fluorescence(XRF) and energy dispersive X-ray spectroscopy (EDS).

In order to identify key process characteristics in terms ofperformance, three process variables were initially studied inthis experiment; the concentration of electrolyte (HCl), tem-perature, and operating potential. The concentrations of theHCl electrolyte employed in this experiment were 1N, 3N, 5Nand 7N. The treatment temperatures used were room temper-ature (30°C), 60°C and 80°C. The operating potentials studiedwere 0.2V, 0.6V, 1.0V, and 1.4V. Barrel rotational speed wasfixed at 15 rpm with the pressure of one bar. The cementedcarbide scraps used were standard sized WC+6mass%Coindexable inserts, and the amount used for each test was 5 kg.

Development of Manufacturing Technology for Direct Recycling Cemented Carbide (WC-Co) Tool Scraps 71

The autoclave in this experiment functioned mentioned,the internal processes of the autoclave were designed tofacilitate consistent to extract the Co binder phase from thecemented tungsten carbide scraps and remove the binderphase from the grain structure of the cemented carbide. Inaddition to the application of the factors previously oxidationreactions of the anode with the increasing binder recoveryvis-a-vis the shape and size of the cathode metal sheet, asdependent on the positioning to cover the barrel, as shown inFig. 2.

The functions of the autoclave are to extract and removethe cobalt binder from the grain structure of the cementedcarbide. With continuous extraction, it will gradually reduceto skeletons and particles, that is, a significant amount ofWC skeletons will be extracted to particles. The process ofwashing and filtering the mud with ethanol to clean andpurify it, and then drying the material at 100°C, as illustratedin Fig. 3. This is performed to examine the amount ofresulting metal powder by weighing and comparing it withthe original, pre-process tungsten carbide powder.

This is performed to examine the amount of resulting metalpowder by weighing and comparing it with the original, pre-process tungsten carbide powder. The analysis of metalpowder characteristics can be applied with XRD, XRF, SEM,TEM. EDS and particle size distribution, which can beperformed with the tools available in the Operating Labsof the National Metal and Materials Technology Center(MTEC) and Thailand Institute of Scientific and Techno-logical Research (TISTR) in Thailand.

2.3 Characterization of product re-sinteringRe-sintering of the cemented WC-Co was conducted from

the recovered WC powder. Preparation of the WC powderwas done by ball milling28­30) for particles with an averagesize of approximately 1.0 µm, and a mixture of WC powder-6mass% Co powder and paraffin wax 3mass%, with a ballmilling time of 24 h.24,36) Green-formed production toIndexable insert tools (standard sized SNMG120408) byClod isostatic press (CIP) and sintering was performed at

Fig. 2 Schematic representation of the design of the binder phase removal apparatus.

Fig. 3 Flow sheet direct recycling of cemented WC-Co.

Fig. 1 Schematic diagram of the direct recycling process in employed the present study.

S. Wongsisa, P. Srichandr and N. Poolthong72

1,450°C for 60min. The final Indexable insert tool wasproduced by the grinding machine with a nose radius of0.80mm. The basic property characteristic tests of Indexableinsert tools include hardness, microstructure and dry, turn-ing21,30­34) with AISI 1045 steels35) pre-machined andannealed for stress relief. Testing conditions included acutting speed of 100m/min, feed rate of 0.10mm/rev, depthwas cut at 1.00mm and cutting length of 3,000mm.

3. Results and Discussions

3.1 Results3.1.1 The effectiveness of the CHEP process

It was determined that the CHEP process can besuccessfully used for recycling cemented tungsten carbide.The sequence of the binder removal process is shown inFig. 4. The process parameters employed in this case were anelectrolyte concentration of 7N, temperature of 80°C andoperating voltage of 0.6V.

Figure 4(a) shows the cemented tungsten carbide andpowder after 24 h of binder removal, which was sufficient toremove about 60% of the total binder phase. The remainingscraps are more or less spherical in shape, as shown inFig. 4(b). All 5 kg of scrap was processed by the 36 h mark,with the final WC mud product shown in Fig. 4(c). With

further leaching, washing, ball milling and drying, the WCpowder shown in Fig. 4(d) was obtained.

The shape and size of this final dried WC powder werefound to be dependent on not only a number of differentprocess variables, but also the degree of ball milling. Forexample, after 50 h of ball milling, the size of the recoveredWC powder was in the order of 0.26­3.75 µm; as confirmedby the SEM micrograph in Fig. 5(a) and the size distributionobtained through X-ray diffraction that is given in Fig. 5(b).This also shows that most of the recovered WC powder wasin fact at a submicron scale (<1.0 µm), resulting in a verynarrow size distribution. The TEM micrograph in Fig. 5(c)shows that most of the WC powder particles were quiteirregular shape, despite the fairly long ball milling time.These results demonstrate that a very fine (i.e., submicron)WC powder can be produced by recycling cemented tungstencarbide scraps using the CHEP process.

The issue of energy used in the recycling of WC wasaddressed by using an energy meter (SFERE, DDS1946,IEC62053-22-2003) to measure the energy consumption perkg of a WC powder produced by autoclaving. As shown inFig. 2, this revealed that the CHEP process has an averagepower consumption of 4 kwh/kg. However, this value isinfluenced by factors concerning the design of the autoclave,such as the use of a curved titanium plate as the cathode and

(a) (b) (c) (d)

Fig. 4 Binder phase removal sequence: (a) WC scraps remaining after initial binder phase removal, (b) WC mud after completion ofbinder phase removal, (c) ball milling and (d) dried WC powder.

Fig. 5 Size and shape of WC powder recovered after 50 h of ball milling: (a) SEM micrograph, (b) particle size distribution and (c) TEMmicrograph.

Development of Manufacturing Technology for Direct Recycling Cemented Carbide (WC-Co) Tool Scraps 73

its positioning to cover the cemented tungsten scraps(cathodes, anode and barrel), as well as the stability of thecurrent density and operating potential during electrochem-ical reaction. Moreover, it is also affected by the tumbling ofspecimens in contact with the anode, the external temper-ature, HCl concentration and pressure. The extraction ofcobalt binder therefore appears to be more effective at thegrain boundaries, with the resulting carbide “skeleton” easilycrushed to form the WC mud seen in Fig. 1 and Fig. 4(b).3.1.2 Effects of process variables

Three of the most important performance characteristics ofany recycling process are the speed at which can be achieved,the amount of material recovered from a given quantity ofscrap, and the quality (purity) of the recovered product. Ofthese, it is speed that determines the productivity of theprocess, and hence its commercial viability. However, it is theamount of material recovered (not how much is lost) thatultimately dictates the cost of the process, and therefore alsoinfluences its commercial viability. The purity can of coursealso be important, as this determines the customer acceptanceof the final product. Other factors such as cost effectivenessand environmental impact can certainly also be quiteimportant; but at this initial stage, only the recycling speed,purity, and recovery/loss of WC was examined.

With regards to the recycling speed, it was found that therate of binder phase removal is dependent on variablesassociated with all three characteristics of interest. The effectsof temperature under conditions of a 0.6V operating voltageand 7N HCl electrolyte are shown in Fig. 6, revealing that atroom temperature (30°C) binder phase removal progressesvery slowly. Indeed, even after 24 h, only about 40% of thebinder was removed. As the temperature is increased, so to isthe rate of binder removal, with complete removal achievedafter 36 h at 80°C.

Figure 7 shows the effect that the HCl concentration hason binder removal after 36 h at 80°C and 0.6V. We see from

this that although the percentage of binder phase removedincreases with HCl concentration, this effect levels off whenthe concentration reaches about 5­7N.

The effect of operating potential on the binder phaseremoval rate at various HCl concentrations is shown inFig. 8. Once again, an 80°C operating temperature and 36 hremoval time were used, revealing that binder phase removalincreases with operating potential up to about 0.6V, butdecreases thereafter. A similar trend was observed at allelectrolyte concentrations, and thus it is clear that 0.6Vrepresents the optimal operating potential in terms achievingthe highest rate of binder phase removal.

Regarding the percentage of WC recovered, it was foundthat this in fact decreases with increasing temperature(Fig. 9); that is, WC loss increases with temperature. Forexample, with a 1N electrolyte concentration and operatingpotential of 0.6V, the WC loss is almost 3% at 60°C, butincreases to almost 4% at 80°C.

Fig. 6 Effect of temperature on the binder removal rate (HCl electrolyteconcentration: 7N, operating potential: 0.6V).

Fig. 7 Effect of HCl concentration on the binder phase removal rate(temperature: 80°C, operating potential: 0.60V, time: 36 h).

Fig. 8 Effect of operating potential on the binder phase removal rate(temperature: 80°C, time: 36 h).

S. Wongsisa, P. Srichandr and N. Poolthong74

3.1.3 Product qualityThere are many dimensions of quality in the recovery of

WC, including its powder characteristics, particle size andsize distribution, physical structure and mechanical proper-ties. The purity of WC recovered is also an importantconcern, and was found in this study to be comparable to thatof virgin WC, as demonstrated in the X-ray diffractionpattern shown in Fig. 10(a) and the EDS analysis results inFig. 10(b). Although these show that there is virtually no Coleft in the WC powder recovered, the EDS results reveal thatsome titanium is present due to partial oxidation of the anode.This was confirmed by weighing the anode before and afteruse, and leaching the metal extracted. Subsequent XRFanalysis of the metal powder determined its composition tobe W = 99.68%, Ti = 0.21%, C = 0.01%, and O = 0.10%.

The re-sintering of new indexable insert tools to a standardsizing of SNM12G0408 is presented in Fig. 11(a). Theresulting grain structure is illustrated in Fig. 11(b), revealingfeatures very similar to the standard structure of WC-Co, butwith a hardness (1,520 HV30) that is slightly less than that ofhard metal produced from virginal WC powder. The grainsize is shown in Fig. 11(c) to be approximately 1.0­2.0 µm.As shown in Table 1, the results of the machine test depictedin Fig. 12 indicate that the flank wear of AISI 1045 bearingsteel is 0.50mm, and is therefore much more worn out thanvirginal hard metal at ³0.05mm.

Turning tests of 3000mm specimens to determine theirsurface roughness resulted in the re-sintered material beingworn down by approximately 0.08 Ra more than virginalhard metal. Nevertheless, the bearing capacity of the re-

Fig. 9 Effect of temperature on the recovery and loss of WC (HClconcentration: 1N, operating potential: 0.6V).

(a)

(b)

Fig. 10 (a) XRD and (b) EDS analysis of the WC powder recovered.

(a)

(b)

(c)

Fig. 11 New hard metal products: (a) indexable insert tools, (b) SEMmicrograph of WC-6 Co sintered at 1450°C for 60min and (c) Vickershardness indentation, HV30.

Table 1 Properties and machining test results of index able insert tools SNMG120408 (WC-6%Co).

WC powder sourceGreenDensity(g/cm3)

Density(g/cm3)

Vickerhardness(HV30)

Machining test

Flank wear(VB:mm)

Surface roughness(Ra)

Tools (verginal WC powder) 8.20 14.98 1550 0.45 2.20

Tools (recycling WC powder) 8.30 14.94 1530 0.50 2.28

Development of Manufacturing Technology for Direct Recycling Cemented Carbide (WC-Co) Tool Scraps 75

sintered hard metal exhibited similar standard properties andvalues to virginal hard metal. Furthermore, the recycled metalpowder was quite pure, and retained a high potential forreuse.

3.2 DiscussionThe results obtained in this study demonstrate that the

recycling of cemented WC scraps using the CHEP processcan achieve successful extraction and removal of the Cobinder phase.9) The purity of the WC recovered was also veryhigh compared to other studies,17,20) so much so in fact that itcould be used in the commercial fabrication of cutting toolsor other products as an alternative to virgin WC. Further-more, the very fine submicron particle size of the WC powdercreates significant potential for it to be used in a variety ofapplications.

Table 2 displays the CHEP recovery characteristics incomparison with other processes. If it is assumed that theoriginal cemented composition is 94WC%-6Co%), then thisconfirms that ³99% of the WC in a 5 kg sample can berecovered within 36 h. Since only 1% of the W is lost to theHCI, the environmental impact of the process is minimal. Theenergy consumption is also lower than other methods when

used at a similar economy of scale, presenting a promisingmeans of supporting and encouraging retail industries orsmall entrepreneurs, especially in developing countries wherethere is a vital need to balance societal, environmental andfinancial demands. It is believed that this small scale exampleprovides a suitable assessment of the environmental perform-ance of a larger manufacturing process,22,38) and hassignificant potential to help develop a widespread sustainablemanufacturing strategy.

The re-sintering of new hard metals with a hardness andgrain structure similar to that of conventionally cementedWC-Co work pieces was also achieved,37) demonstrating thesignificant potential of this process for the reuse of materials.Indeed, higher levels of WC purity were achieved by the useof this direct recycling process, as confirmed by XRD, XRF,and EDS analysis of the fundamental characteristics of theresulting powder.

It is worth noting here that CHEP-recycling is notnecessarily limited to WC, but could also be conceivablyapplied to the recycling of wastes with similar chemical,electrical and structural properties. By considering the grainboundaries of different metals, such wastes could includecermets scraps of titanium carbide (TiC)39­42) or tantalumcarbide (TaC).40,42) The process could also be used for theextraction and removal of the metal binder phases such ascobalt (Co), molybdenum (Mo), vanadium (V) and chromi-um (Cr).

4. Conclusion

This study was conducted to examine the viability of adirect recycling process (CHEP) for cement WC-Co scraps,and identify characteristics relevant to develop a sustainableindustry recycling approach. The following conclusions canbe drawn from the present study:(1) The combined hydrothermal and electrolysis process

can be used for recycling cemented tungsten carbidescraps effectively.

(2) The purity of recovered tungsten carbide was comparedto that of virgin material. The recovered WC was at avery fine, submicron size. The shape of the recoveredWC was mainly irregular.

(a)

(b)

(c)

Fig. 12 Metal removal through re-sintering of cemented carbides:(a) turning of re-sintered cemented WC, (b) a work piece after machiningand (c) surface roughness.

Table 2 Process for recycling WC powder from cemented carbide scraps.

Recycling processTungstencarbide

recovery (%)

Completeremoval ofcobalt(Hours)

HC1Loss(%)

WCLeached(%)

Energyconsumption(kwh/kg)

Economiesof scale(L-M-S)

Zinc process 98<36

Depended onscrap input

® <2 2­4 L

Electrolysis process(room temp.)

98 840 1.50 1.40 12 S,M

Electrochemicalprocess³1-2 bar 80°C

97.5 144 19.00 2.50 6­9 S,M

Electrochemicalprocess >5 bar 80°C

97.5 36 17.00 4.25 6­9 S,M,L

CHEP process 99 36 1.00 1.00 4 S

Note: Specimens indexable insert tools scraps WC-6%Co Economies of scale: L = production volume more than 300 kg. M = 50­299 kg. S = <50 kg.

S. Wongsisa, P. Srichandr and N. Poolthong76

(3) The recycling capability was better than other recyclingprocesses on a number of levels. However, thecharacteristics of this recycling process might changeat different or larger scales.

(4) The recycling methodology was appropriate for WCrecycling because of the low cost of the recyclingmachines, low energy consumption, and environmen-tally friendly results of the WC recovery.

Further research should be conducted investigating thisprocess in large scale industrial levels, particularly inindustries that generate a high volume of tungsten carbidetool scraps.

Acknowledgements

The authors are grateful to the National Research Councilof Thailand for their financial support as well as to theNational Metal and Materials Technology Center (MTEC),and Thailand Institute of Scientific and TechnologicalResearch (TISTR), for their operating support of equipmentand tools used for analysis and testing in this study.

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