effects of operational parameters of spiral in mica-feldspar

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Effects of operational parameters of spiralconcentrator on micafeldspar separation

O. Y. Gulsoy and M. Kademli

In the present study, effects of several operating parameters on the separation efficiency of mica

from feldspar by spiral concentrator were investigated. For this purpose, an albite ore containing

mica was treated in a full scale Reichert spiral (model HG7) under various test conditions. During

the study, particle size distribution, solid contents of the feed, feedrate and splitter position were

changed. It was observed that in a spiral concentrator mica could be separated from feldspar

owing to its laminar morphology. Accordingly, it was found that particle size and solid contents

had significant effect on the separation. Best results were obtained with feed solid content of 15%

by weight for the particle size fraction of 2212z74 mm. In line with this, Fe2O3content, which was

0.71% in the feed, decreased to 0.07% in concentrate.

Keywords:Feldspar, Mica, Spiral concentrator, Gravity separation

IntroductionMica is one of the main impurities in feldspar used in

ceramic and glass industries. It contains iron, which

causes colouring in ceramic and glass. Titanium is also a

colouring impurity in feldspar. The sources of titanium

in feldspar are rutile, sphene and ilmenite as well as

biotite, in some cases depending on displacement of

titanium with other metals in the crystal lattice.1

Flotation is usually applied to remove the colouring

impurities from feldspar ore. However, flotation may

cause some environmental problems because of the use

of some chemicals. Also, mica and oxide minerals

require different flotation steps and some additional

processes are required between the steps in order to

remove the reactant from the mineral surfaces and to

carry out reconditioning.26

The specific gravities of feldspar and mica minerals

are approximately 2.65 and 2.73.4 respectively. As

mentioned by Iverson, the difference between their

specific gravities is not enough to achieve efficient

separation of these minerals with gravity methods.7

Coarse mica grains are nearly equidimensional andspherical. However, in fine sizes the platy character of

the mica minerals is revealed. This physical character-

istic of the mineral has been responsible for its

separation by gravity from feldspar. This distinguishing

property of fine mica particles was first reported by

Iverson.7 In his study, Iverson managed to separate mica

from feldspar by tabling. Later, Adair et al.also showed

the possibility of concentration of mica in a Humphrey

spiral.8 Therefore, gravity methods are considered as an

alternative method to flotation.

The purpose of the present study was to investigate

the separation characteristics of mica in a Reichert spiral

and to determine the effects of operating parameters,

such as particle size distribution, feed solid contents,

feedrate and splitter position, on the separation effi-

ciency. Industrial scale equipment was used in the

present study, therefore the results can be applied to

the industry directly. A model HG7 Reichert spiral was

used because of its availability and because preliminaryexperiments showed potential for good separations.

Material and methodThe tests were carried out in an industrial scale Reichert

spiral (HG7). The equipment was operated in a closed

circuit, including a tank and a pump. There were two

splitters at the equipment discharge. The position of the

outer splitter was not suitable to control product

streams owing to the occurrence of a big gap largely

free of particles between the tailing and the concentrate

streams during the tests (Fig. 1). Therefore this splitter

was fixed for all conditions in the main series of tests.

The position of the inner splitter was adjusted to 1/4, 1/2and 3/4 of the maximum opening (16 mm, L). Sampleswere taken simultaneously of primary and secondary

concentrates and tailings during the tests (Fig. 1). Beforeeach test, the system was discharged, cleaned and then

operated in a manner appropriate to the new feed andsolid contents. Sampling time was measured by a digital

chronometer in each test. Samples were dried and

weighted. Therefore, flowrates of each stream could be

calculated.

Pulp flowrates studied were 1, 1.5 and 2 L s21, and

pulp solid contents for these flowrates were 15, 20 and

25 wt-%. The solid flowrates calculated according to

these test conditions are given in Table 2.Fe2O3 removal recovery was calculated from 12R,

where, R is Fe2O3 recovery in concentrate, which is

Hacettepe University, Department of Mining Engineering, BeytepeCampus, Ankara, Turkey

*Corresponding author, email [email protected]

2006 Institute of Materials, Minerals and Mining and The AusIMMPublished by Maney on behalf of the Institute and The AusIMMReceived 17 March 2005; accepted 19 July 2005

80 DOI 10.1179/174328506X99907Mineral Processing and ExtractiveMetallurgy (Trans. Inst. Min. Metall. C) 2006 VOL 11 5 NO 2


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calculated from equation (1)

R~Cc

Ff (1)

where C is the flowrate of concentrate (t h21), F isthe flowrate of feed (t h21), c is the Fe2O3 grade of

concentrate (%) and fis the Fe2O3 grade of feed (%).

Firing at 1200uC is a quick test method to control thequality of feldspar samples. Some impurities change the

colour of the firing buttons. Titanium gives pinkishcolours and iron is the source of the grey colours. The

density of the colours is directly related to the amount of

the impurities.

Because the main source of titanium in the ore was

generally rutile and sphene, a significant decrease in

titanium content might not be expected. However, thetitanium presented especially in the crystal lattices of the

biotite was removed by the separation of mica, and this

had the potential to result in a slight decrease in titanium

content.

ResultsIn the present study, the effects of operational para-

meters on the separation efficiency of mica in a spiral

concentrator were investigated for a wide range of

feedrate values, which were varied between 0.6 and2.1 t h21. This range stayed within normal industrial

operational limits of the equipment.

At the beginning of the tests, primary and secondaryconcentrates and tailing were obtained as shown in

Fig. 1, and Fe2O3 grades of the concentrates were

determined by chemical assaying. A comparison of

Fe2O3grades of primary and secondary concentrates for

all test conditions is given in Fig. 2. As can be seen fromFig. 2, there is no meaningful difference between the

primary and secondary concentrates, and a regression

analysis yields an intercept very close to zero and a slopeclose to 1. In addition a paired t test showed that there

was a negligible difference between the primary andsecondary concentrates at the 99.9% level of probability.

It was therefore apparent that dividing the concentrate

as primary and secondary was not necessary. Therefore,

only one set of concentrate data representing the average

characteristics of the two concentrates and one set oftailing data were used in the evaluation of the effect of

flow and percentage of solids, and there was no need to

take a middling stream using a second splitter in the

separation process. This enables the process to be used

and controlled easily at the plant level.

The major part of water in the feed accumulated at the

outside of the separation surface carrying most of the

platy mica with it. The feldspar particles moved

predominantly to the inner part of the surface forming

a natural gap between concentrate and tailing streams.

Because of this the outer splitter was not very effective in

controlling the concentrate quality. During the separa-

tion the outer splitter was roughly adjusted by visual

judgement of the best position. The effects of inner

splitter setting on the Fe2O3grade of the concentrate for

each test condition are given in Table 3. As can be seen

from Table 3, Fe2O3 grade of the concentrate increases

slightly by sliding the splitter to the outside position.

Table 2 Solid feedrates calculated for each testcondition

Pulp flowrate,

L s21Solid content,

wt-%

Solid flowrate,

t h21

1 15 0.596

20 0.82225 1.065

1.5 15 0.89420 1.23325 1.598

2 15 1.19220 1.64425 2.130

2 Comparison of Fe2O3 grades of primary and secondary

concentrates

1 View of spiral discharge

Table 1 Chemical compositions of spiral feed and slime (74 mm) fractions

Size fraction, mm Content, (sl ime, 74 mm), wt-% Fe2O3 content (slime, 74 mm), % Fe2O3content (feed), %

2850z74 4.20 0.03 0.742600z74 5.28 0.06 0.74

2425z74 7

.10 0

.07 0

.76

2300z74 8.54 0.08 0.772212z74 10.25 0.12 0.78

Gulsoy and Kademli Effects of operational parameters on micafeldspar separation

Mineral Processing and Extractive Metallurgy (Trans. Inst. Min. Metall. C) 2006 VOL 11 5 NO 2 81
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However, this did not affect the percentage of solids and

flowrate of concentrate significantly.

The minimum and maximum operating flowrates

were determined according to the specifications of the

Reichert spiral (HG7) used in the tests. Thus, three

different flowrates, 1, 1.5 and 2 L s2-1, were selected and

the tests were performed at these flowrates with three

different solid contents that were 15, 20 and 25 wt-%.

The effects of flowrate on Fe2O3grade of concentrate,

Fe2O3 removal and mass recovery were investigated for

each feed size. The relationships for 15, 20 and 25% solid

contents are shown in Figs. 35 respectively with

flowrate as the parameter and for each of the flowratesin Figs. 68 with the percentage of solids as the

parameter.

DiscussionIt can be seen from Figs. 38 that the particle size

distribution is the most effective parameter in the

separation. As explained above, the coarse mica grainsare nearly equidimensional, and the difference in specificgravity is not enough to make the separation of theseminerals possible. However, the platy character of thesmaller mica particles made the separation of mica fromfeldspar possible at fine particle sizes. This situation isnot related to the differences in the degree of liberation,because mica was in the form of liberated particles evenin the coarse fractions.

Fe2O3 grade of the concentrate, Fe2O3 removal andrecovery to feldspar were directly related to the changein maximum particle size. An increase in the particle size

increased Fe2O3grade of the concentrate and decreasedthe Fe2O3removal. The mass recovery decreased slightlywith finer particle size, because the amount of particlescarried by water to the tailings stream increased. Thisbehaviour was observed at all flowrates and feed solidcontents.

Figures 35 show that increasing the flowrate to thespiral generally caused an increase in the Fe2O3grade of

Table 3 Effect of inner splitter setting on Fe2O3 grades of concentrates at different test conditions

Feed topsize, mm

Splittersetting

Fe2O3grade, %

1 L s21 pulp flowrate 1.5 L s21 pulp flowrate 2 L s21 pulp flowrate

15%solids

20%solids

25%solids

15%solids

20%solids

25%solids

15%solids

20%solids

25%solids

212 1/4 L 0.065 0.101 0.157 0.070 0.102 0.169 0.078 0.110 0.2101/2 L 0.068 0.109 0.169 0.071 0.111 0.181 0.082 0.109 0.2173/4 L 0.068 0.118 0.179 0.079 0.110 0.179 0.090 0.130 0.241

300 1/4 L 0.095 0.188 0.238 0.138 0.209 0.251 0.154 0.199 0.2881/2 L 0.105 0.191 0.259 0.142 0.219 0.268 0.158 0.248 0.2993/4 L 0.118 0.202 0.270 0.152 0.228 0.279 0.169 0.259 0.311

425 1/4 L 0.293 0.398 0.478 0.319 0.413 0.498 0.379 0.449 0.5181/2 L 0.293 0.410 0.498 0.329 0.440 0.511 0.397 0.461 0.5323/4 L 0.298 0.423 0.509 0.338 0.458 0.527 0.411 0.479 0.547

600 1/4 L 0.610 0.759 0.839 0.699 0.788 0.830 0.757 0.800 0.8211/2 L 0.627 0.778 0.841 0.717 0.799 0.840 0.768 0.820 0.8213/4 L 0.659 0.791 0.841 0.738 0.817 0.831 0.778 0.817 0.837

850 1/4 L 0.844 0

.849 0

.852 0

.851 0

.852 0

.858 0

.839 0

.849 0

.849

1/2 L 0.848 0.849 0.852 0.838 0.851 0.848 0.842 0.842 0.8593/4 L 0.842 0.838 0.842 0.839 0.851 0.840 0.841 0.851 0.859

3 Variations in Fe2O3 grade of concentrate, Fe2O3

removal (dashes) and mass recovery (dot) as function

of feed top size for different flowrate at 15% solids





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the concentrate and a drop in the Fe2O3 removal.

However, the effect of the increase in the flowrate on

separation was small when compared with the effects of

other variables. There was virtually no flowrate effect

for a top particle size of 850 mm and very little for

200 mm. The negative effect of the flowrate on the

separation was progressively less evident with increasing

percentage of solids in the feed so that it was almost

negligible for 25% solids.

The effects of feed solid contents on Fe2O3 grade of

concentrates, Fe2O3 removal and mass recovery are

given in Figs. 68. These figures show that regardless of

feedrate, increasing percentage of solids in the feedincreased the Fe2O3grade of concentrate and decreased

percentage of Fe2O3removal except for the feed top size

of 850 mm. Also, reducing the separation efficiency

increases in the solid contents slightly reduced the

amount of concentrate. This occurred at all spiral

feedrates.

ConclusionsIn the present study, the effects of the process variables

such as particle size distribution, per cent solids in the

feed, splitter position and flowrate on mica separation

were examined. The results revealed that the maximum

particle size had an extreme effect on separation effici-

ency. Separation was not possible when the maximum

particle size was 850 or 600mm. The separation

efficiency of mica increased as the particle size distribu-

tion got finer, and the most suitable maximum size was

212 mm when Fe2O3 content of the concentrate was

reduced from 0.70 to 0.07% with 93% removal of Fe2O3

and mass recovery ofy70%. This iron content met thespecifications required by the glass industry. Firing

buttons with a pale pink colour confirmed this result. It

appeared that particle size needed to be reduced to

2212 mm, in order to ensure that the mica was in a platy

form which had the desired distinctive behaviour on the

spiral surface.

6 Variations in Fe2O3 grade of concentrate, Fe2O3removal (dashes) and mass recovery (dot) as function

of feed top size for solid content at flowrate of 1 L s21






of feed top size for solid content at flowrate of

1.5 L s21

8 Variations in Fe2O3 grade of concentrate, Fe2O3removal (dashes) and mass recovery (dot) as function

of feed top size for solid content at flowrate of 2 L s21


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Although the effect on separation efficiency offlowrate and percentage of solids in feed was lesspronounced than that of particle size, increasingflowrates or percentage of solids significantly reduced

the separation efficiency. Only concentrate obtainedwith the minimum flowrate (1 L s21) and minimum percent solids (15%) met the desired specification corre-sponding to a solid feedrate ofy0.6 t h21.

The position of the outer splitter was important in thisseparation. Serendipitously it was in the ideal positionand the small changes in the position of the splitter

available did not affect the separation efficiencysignificantly. A wide feldspar band on the inner surfaceof spiral and a mica flow close to the outer wall wereformed. Therefore, the separation between feldspar andmica minerals was sharp, and an absence of a middlingstream provided important advantages in control of theseparation.

To be effective separation with spirals requiredremoving material by screening which would tend toreport to the micaeous tailing stream and be lost toconcentrate. As mica was prone to accumulate in coarse

screen fractions, the mica and therefore iron contents ofthe fines were much lower than the coarse fractions. Theiron content of the 274 mm fraction was sufficiently lowfor it to be used directly in industry.

Because concentrate could be produced with ironcontent within the limits required by the glass industry,titanium minerals could be removed by flotation to

produce a final concentrate with suitable iron and

titanium contents as required by the ceramic industry.Therefore, one of two standard stages of flotation can beavoided by spiral separation.

Acknowledgement

The authors would like to thank A. S. C ine-Akmadenfor its contributions to supplying the samples used in the

present study.

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effects of operational parameters of spiral in mica-feldspar

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