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Dispersion of flotation concentrates before magnetic separation
Minerals Engineering, Vol. 7, No. 12, pp. 1505-1516, 1994 Copyright © Elsevier Science Ltd Printed in Great Britain. All rights reserved 0892-6875(94)00088-3 0892-6875/94 $7.00+0.00
Pergamon
DISPERSION OF FLOTATION CONCENTRATES BEFORE MAGNETIC SEPARATION
J.A. JIRESTIG and K.S.E. FORSSBERG Div. of Mineral Processing, Lule~I University of Technology S-952 87 Lulegt, Sweden (Received 20 June 1994; accepted 16 August 1994)
ABSTRACT Laboratmy HGMS and WHIMS tests on flotation concentrates proved that grade and recovery in magnetic separation is greatly affected by the particle dispersion of the head feed. ht this investigation, the recovery of a spodumene flotation concentrate, floated with a fatty acid collector, was improved by 10% when the pulp pH was reducedfi'om pH 7 to pH 2 in order to improve the particle dispersion. For a phosphine floated Pb product, carlyhlg sphalerite and chalcopyrite, grade and recovel y was opthnised in a window around pH 5. Recovely was improved by approximately 5%. ghe carly over capacity fi'om the non-magnetic to the magnetic product for agglomerates containing a small amount of magnetic particles can be estimated using the HGMS capture probability function and the magnetic susceptibility of the material. An estimate of the spodumene / amphibolite system indicates that as little as 3% amphibolite in an agglomerate may be sufficient for thefloc to be captured in the matrix. 777ecorresponding number for the galena / sphalerite system is about 20%. Keywords HGMS; WHIMS; flotation
INTRODUCTION Until recently the only uses of High Gradient Magnetic Separation (HGMS) and Wet High Intensity Magnetic Separation (WHIMS) were as primary separation methods for "weakly" magnetic iron ores such as hematite and taconites, and for the removal of iron containing minerals in kaolin clays, and these are still the most important uses. The high magnetic attraction force of the HGMS, however, also allows the treatment of a variety of paramagnetic minerals. In previous work [1 - 4] it has been proved that several sulphide minerals have sufficient magnetic susceptibility to be captured in the matrix. It has also been shown [5 - 6] that most ores, with few exceptions, contain large amounts of magnetic non-value minerals. In these cases, magnetic separation is unsuited as the main separation method. HGMS, however, has proved successful in the upgrading of pre-treated materials, such as flotation concentrates. A few interesting problems arise when minerals, coated with a surface active compound, are to be separated in a HGMS. Although the physics of magnetic separation deals with volume dependent parameters (volume or mass susceptibility counteracted by gravity and hydrodynamic drag force) rather than surface properties, a flotation collector may well have a significant effect on the separation efficiency. It is reasonable to assume that the majority of the various minerals reporting to the float product are covered with the collector and hence have a strong tendency to tbrm agglomerates due to 1505
1506
J.A. JIRESTIG and K. S. E. FORSSBERG
hydrophobic flocculation and shear forces. These particle groups will behave as individual bodies with a bulk-susceptibility that is dependent on the minerals enclosed. This makes proper dispersion vital for achieving good grade and recovery.
MATERIAL The effect of dispersion was tested on two flotation products, a spodumene and a galena flotation concentrate. The mineral surface of each of the two samples was covered with two different types of surface active compounds, one (spodumene) an oleate the other (galena) a phosphine based collector.
Spodumene concentrate production at the processing plant After comminution and sizing of the pegmatite ore, the lithium mineral is floated using a tall oil type fatty acid with 5 - 7 % rosin-acid content at neutral pH and a glycol type frother [8]. The conditioned pulp is floated at about 30% solids, cleaned and recleaned. The spodumene concentrate contains 10 - 11% dark minerals, identified as amphibolite and biotite. The iron content is not an exact evaluation of the amount of amphibolite, since several other minerals with low iron concentration are present. The spodumene itself carries approximately 0.75 - 0.80 % Fe. The iron content, however, does give a rough idea of the amount of non-lithium minerals. The iron containing amphibolite and biotite have sufficient magnetic susceptibility to be captured in a HGMS matrix while the spodumene susceptibility is too low. Chemical assay of the concentrate is presented in Table 1.
TABLE 1 Chemical assay of the spodumene flotation concentrate Chemical
Li20
Fe203
MgO
Assay
5.35%
2%
0.304%
Pb concentrate production at the processing plant After comminution and sizing, the copper and lead values are floated in two circuits at pH 8.2. The talc content is depressed using dextrin. The floated Cu-Pb product is separated into a copper concentrate and a lead product at pH 8.2. In this flotation step, Cyanamid's Aerophine 3418 is used as a collector. Finally the lead product is fed to a HGMS circuit. Aerophine 3418 is a relatively new collector based on phosphine chemistry. Chemical assay of the concentrate is presented in Table 2. TABLE 2 Chemical assay of the lead flotation concentrate
Chemical
Pb
Cu
Zn
Assay
67.5 %
0.36 %
5.60 %
I
I
I
During the Pb-flotation a significant amount of sphalerite reports to the float product. The rather high magnetic susceptibility of the sphalerite makes HGMS a suitable method for upgrading the product. Although HGMS technique has been used in the plant [5-6] since 1989 to reduce the zinc content in the lead product, no attempts have been made to optimise the separation by dispersing the pulp.
EXPERIMENT The two samples were tested using two different but similar magnetic separators. The Spodumene flotation concentrate was processed on an Eriez WHIMS (Wet High Intensity Magnetic Separator) L-4-20 Lab-
Dispersion of flotationconcentrates
1507
separator, while a SALA HGMS (High Gradient Magnetic Separator) 5 - 30 - 10 was used for the galena. Both separators are batch type, cyclic separators. The main difference between the two, is the generation of the magnetic field. The Eriez separator uses air cooled coils to magnetise two iron pole pieces. The matrix chamber is placed in the gap between the poles. In the SALA separator the matrix canister is placed in the bore of a water cooled solenoid. Another difference is the field / pulp flow geometry. In the Eriez separator, the magnetic field is perpendicular to the pulp flow, while the SALA magnet has a parallel configuration, see Figure 1. Near identical matrix media were used in both test series.
Fe;funnel /~gne t coil
•,
Matrixcanister
Matrix.
[1
II
II
l
Fig. 1 Eriez WHIMS (left) at NCSU Minerals Research Lab. Asheville, NC, USA, SALA HGMS (right) at Lulea University of Technology, Lulea, Sweden
Pulp dispersion It was felt that the flotation collector would be responsible for forming most of the expected flocs. If so, regeneration of the particle surface or deactivation of the collector would improve the particle dispersion. A well known method of removing fatty acid from particle surfaces is scrubbing at low pH. In this investigation only pH was used to change the surface properties of the particles. Pulp pH was changed by the addition of NaOH or H2SO4. Experiment design The material was scrubbed at varying pH to remove, or at least reduce, the agglomeration effects of the surface coating. After scrubbing, the pulp was fed to the WHIMS / HGMS matrix. The pH of the feed water and the wash water was kept the same as the feed slurry, in order to prevent agglomeration recurring (due to the surface active collector still in the pulp). The matrix was washed with low pressure, pH adjusted water to remove physically entrained non-magnetic particles after the feed cycle was completed. The magnetic field was then turned off and the magnetic product rinsed out. Both products were collected, dewatered, weighed and assayed by AAS. Schematic presentation of test design can be found in Figure 2. The magnetic field strength was set at 1.0 T (10 kGauss) in all test runs. It may well be that the addition of common dispersants to the pulp, such as sodium silicate or sodium hexametaphosphate would have been more efficient in breaking up the flocs than merely changing the pH. This investigation, however, was aimed at proving a general need for dispersion, rather than finding the optimum dispersant for each individual material.
1508
J.A. JIRESTIGand K. S. E. FORSSBERG
Test Design I HeadFeed Flotation conc. :
I
N~H
!
WHIMS / HGMS Sep~ation
I
J
I
[ Ma~aeti¢ I
Non-magnetlc[
Assay I AAS
Fig.2 Test design for the dispersion investigation
FLOCCULATION AND DISPERSION OF FLOTATION PRODUCTS It is thought that the flotation collector is responsible for the formation of floes at certain pH. It seems logical to assume that the strongly hydrophobic particles may connect and attach due to hydrophobicity. When the pH is decreased the flocs may be broken and the pulp dispersed. Unfortunately, available data for Cyanamid's Aerophine 3418 is insufficient to make a valid assessment of the dispersion mechanism. However, the oleate system is well investigated, therefore a plausible explanation for the mechanism may be found. Laskowski and Nyamekye [11] presented a domain diagram for sodium oleate, (Figure 3). It is shown that the solubility at low pH is greatly reduced and that oleic acid is the predominant phase.
'02 ~'fb,~.~',,"',~-'~'X'OLEIC ACIB~ . . . . . .
z"
"
~
) x -, ..,'!
' >'= - Y ' - ; < K "
<
cr
I--tlJ oz o
TRUE S O L U T I O N
10.6
]
~o7 ," ~ ~.,X,<: ,:_,r, ._..~£vj~_ _~-_~. ,.,
lo e 10-~
t
Solubility limit ~
1.
I
I
J
2
4
6
8
10
12
pH Fig.3 Domain diagram for sodium oleate, after Laskowski and Nyamekye [11] When the collector, adsorbed to the spodumene surface, loses its solubility during attrition scrubbing two things may happen. The crystal surface degrades and the collector is released and forms micro droplets
Dispersion o f flotation c o n c e n t r a t e s
1509
in the liquid. It may also form droplets on the mineral surface. Tests indicated that both phases are present. It is believed that when micro droplets are formed on the mineral surface the ordered structure is lost, (Figure 4). The carbon chain no longer dominates the surface and the hydrophobie properties of the particle disappear. This makes it possible to at least partially wet the surface.
O
Fig.4 At high pH the ordered structure of the adsorbed collector makes the surface hydrophobic. When droplets are formed hydrophobicity is lost Fuerstenau and Fuerstenau [12] determined the zeta-potential for spodumene in an oleate environment (Figure 5). The diagram shows the point of zero charge to be just above pH 2, at lower pH the zetapotential increase rapidly. This indicates that the disordered structure of the oleate collector together with positive zeta-potential is responsible for the dispersion. Hydrophobic flocculation is believed to be the reason why dispersion does not occur around pH 8.
20 0
E -20
v
,~, "~ ;':,~,'~ ,,,,t~\X,~ ~
Na-oleate • 0 • 10"
mo,/I
• 10-4 mol/l ' 1 0 -a m o l / I
"%,..-Lt~
=~ -40
mol/I
,
.J
C ¢1
g 76o
",:,'<,1,;--,-. \\ .// '%
-80
• •
!
~.,~. ,..,/
/
',,:.,,J-'4"
N
-100 -120
~" ii
x,
%
I
i
I
2
4
6
I
I
pH
8"
l o"
1'2
Fig.5 Zeta potential of spodumene versus pH as a function of oleate concentration, [12]
J. A. JIRESTIGand K. S. E. FORSSBERG
1510
TEST RESULTS Spodumene flotation concentrate
The agglomerates caused by the tall oil-type fatty acid collector on the spodumene surface seemed to be dispersed at reduced pH. Magnetic separation tests were done with pH varying from 7 to 2. By dropping the pH from 7 to 2 the Li20 grade in the non-magnetic product was improved by 0.15 % and Fe203 grade was decreased by 0.35 %. The loss of Li20 to the magnetic product (tailings) was reduced by 1.13 % (Figure 6, recovery in Figure 7, data in Table 3).
Li20 and Fe203 grades 1 7,00 6,00
/ ,,.......-J
%
f
~,
Li20 non-mag.
4,00
o
Fe203non-mag.
3,00
J"
Li20 mag.
=
Fe203mag.
5,00
f
/
t
---....._
2,00 1,00 0,00
]..
1 7
Y 6
5
4
3
2
pH Fig.6 Li20 and Fe203 grades in the magnetic and non-magnetic products at varying pulp pH
Li20 and Fe203 recovery 100,00 90,00 80,00 70,00 60,00 % 50,00 40,00 30,00 20,00 10,00 0,00
I
Li20 non-mag. -----o
Fe203non-mag.
.t
Li20 mag.
--
Fe203mag.
k---..-.
7
6
5
4
3
2
pH Fig.7 Li20 and F%O3 recovery in the mag. and non-mag, products at varying pH The recovery of lithia to the non-magnetic product greatly improved as the pH decreased. The pH reduction of the pulp from pH 7 to pH 2 caused a Li20 recovery improvement of more than 11%. Since
Dispersion of flotation concentrates
1511
the non-magnetic product is to be the final spodumene concentrate and the iron rich magnetic fraction is preferably to be disposed of as tailings, the improvement of lithia recovery is of great importance to the process economy. TABLE 3 Grades and recoveries in the magnetic and non-magnetic products
Grade
pHI
Recovery
Product
wt. %
Li20
FeqO3
Li20
Fe203
Head feed
100.00
5.38
1.63
100.00
100.00
7 7
Non-mag. Mag.
80.90 19.10
5.40 5.16
1.16 4.81
81.59 18.41
50.53 49.47
4 4
Non-mag. Mag.
85.17 14.83
5.40 4.90
1.04 6.22
86.36 13.64
48.99 51.01
Non-mag. Mag.
88.66 11.34
5.54 4.50
0.84 6.67
90.58 9.42
49.63 50.37
Non-mag. Mag.
90.86 9.14
5.55 4.03
0.81 6.97
93.19 6.81
50.59 49.41
It was suspected that the improved separation could be caused by selective leaching of iron from some of the minerals in the head feed. A series of tests with varying scrubbing time was performed to verify or contradict this theory. If selective leaching was the explanation, extended scrubbing time would yield a different product than a mere short conditioning. No detectable changes were noted as a result of the scrubbing time, indicating that iron is not leached by the acid in detectable amounts at the scrubbing times and pH used. Lead flotation concentrate
The flocculation caused by the tall phosphine type collector on the galena and sphalerite surface was only slightly affected by the pH. Tests were carried out with pH varying from 10 to 2. Pb grade in the magnetic product changed from 30 % to 20 % and then back to 40 % while passing through the pH range 2 to 10. The Zn grade was only marginally affected. The grade / pH diagram (Figure 8) indicates that there is a pH window around pH 6, where the separation performance is improved. The test results at the lowest pH (pH 2) is likely to be biased by the leaching of some of the sulphide minerals. While running tests at this pH, the smell of H2S was noted, indicating decomposition of sulphides. The recovery loss of galena (Figure 9) to the magnetic product is reduced in the pH window around pH 6. Compared to the recovery in the close proximity (pH 5 and 7) the loss is reduced by 3 - 4 % (from ca 10 - 7 %). Test results are summarised in Table 4. Process data from the plant and the laboratory investigation are compared in Table 4. First, it is clear that the cyclic laboratory separator is more precise in processing the flotation concentrate than the carousel HGMS used in Garpenberg. In spite of this, the comparison suggests that a better separation might be achieved if the pH is adjusted from 8 to 6.
1512
J.A. JIRESTIGand K. S. E. FORSSBERG
90 80 70
--...... ~...-~
..~, ~.-.._.__
a
Zn mag.
t > - - Zn non-mag. 30 ~ 20~
2
~ --
3
4
_.........~r--------~
?-.... j
5
6
7
8
f
9
.t
Pb mag.
"
Pb non-mag.
10
pH Fig.8 Pb and Zn grades in the magnetic and non-magnetic products at varying pulp pH
Zn and Pb recovery 10£ 9(3 8G 7(3
l
, ~..._..,...~ ~,......._
Zn mag. Zn non-mag.
4(1 30 20 10 0 2
3
4
5
6
7
8
9
~"
Pb ,nag.
"
Pb non-mag.
10
pH Fig.9 Pb and Zn recovery in the magnetic and non-magnetic products at varying pulp pH T A B L E 4 C o m p a r i s o n o f process d a t a f r o m G a r p e n b e r g a n d the l a b o r a t o r y i n v e s t i g a t i o n [6] Chem. assay
Product
Grade
Roe.
Garpenberg (pH 8)
Mag.
23.20
0.20
19.18
12.7
14.7
56.2
Garpenberg (pH 8)
nonmag.
60.84
0.45
5.70
87.3
85.3
43.8
Lab invest. (pH 8)
mag.
33.72
0.95
19.67
12.0
63.82
88.23
Lab invest. (pH 8)
nonmag.
82.30
0.18
0.87
88.0
36.17
11.77
Lab invest. (pH 6)
mag.
20.81
0.91
20.21
7.48
62.71
87.7
Lab invest. (pH 6)
nonmag.
79.98
0.17
0.88
92.52
37.29
12.30
Dispersion of flotation concentrates
1513
MAGNETIC SUSCEPTIBILITY OF PARTICLE AGGLOMERATES The physics of magnetic separation deals with volume dependent parameters (volume or mass susceptibility counteracted by gravity and hydrodynamic drag force) rather than surface properties. The attraction force, (Fmag) in the matrix follows
(1)
Fmag = 1/2 I.to V 1¢ H dHIdx
Where po is the permeability of flee space, V the particle volume, • the volume magnetic susceptibility, H and dH/dx are the magnetisation and field gradient respectively. In this equation, the volume magnetic susceptibility (g) is the bulk susceptibility of the particle or particle agglomerate. The magnetic susceptibility of any accumulation of particles is dependent on the intrinsic susceptibility of the individual minerals. The magnetic bulk susceptibility follows the graph in Figure 10 according to Derkach [9].
~S
~'
1.0O.10.01 -
.~
/
0.00!-
v.
/
[
/
A~_
~
~
t
V
1 + DK{
D
° o.ooo1I/ -6 ;>
I.,"
I
0.0001
I
I
I
I
I
I
t
0.001 0.01 0.1 1.0 10 100 1000 Intrinsic magnetic susceptibility, (~i)
Fig. 10 Bulk magnetic susceptibility as a function of the intrinsic magnetic susceptibility, for geometric demagnetisation factor D = 0.16 [9] The demagnetisation effect on the bulk susceptibility is considerable for minerals with high intrinsic susceptibility. The graph is based on the following equation x -
PKi
(2)
1 +(D+Di)P~:;
Where K is the bulk (volume) susceptibility, r,i is the intrinsic (volume) magnetic susceptibility, p is the packing density, D is the geometrical demagnetisation factor, and D i is the internal demagnetisation factor. The demagnetisation factor D is shape dependent and must be approximated with values calculated for simple geometrical bodies, such as spheres, ellipsoids or rods. Ki and D i can be determined by extensive measurements of the magnetisation of a mineral in a homogenous background field. This determination, however, is quite laborious. Fortunately, in dealing with HGMS or WHIMS, the attraction force in the matrix is strong enough to fully capture agglomerates already in the linear part of the graph. The demagnetisation effects on the bulk susceptibility can be disregarded. It has been proved [7] that the bulk susceptibility for para- and diamagnetic mixtures, and for small inclusions of ferro- and ferri-magnetic minerals in the agglomerates follows the equation 7:IZ-E
1514
J.A. JIRESTIOand K. S. E. FORSSBERG
r~b,,v, V,o, =
(3)
r.1 v t + r.2 v2 + . . . . . . . . .
Where Kbulk Vto t is the bulk (volume) susceptibility times the total material volume, and K1 V 1 + ~:22 V2 + ....... is the (volume) magnetic susceptibility times the volume of each individual constituent. This equation is less complex, but more important, the components are much more readily determined. Carry over capacity The maximum amount of non-magnetic material that may be carried over to the magnetic fraction as agglomerates can be estimated if the magnetic susceptibility of the minerals and the magnetic force distribution of the matrix is known. It is important to realise that when dealing with HGMS/WHIMS separation, much like screening, it is necessary to think in terms of probabilities, rather than absolute values. The ratio of non-magnetic minerals, carded over to the magnetic fraction as an agglomerate containing magnetic particles, at a given probability, follows Vl = V2
F0'~°b')
-__K2
x t IA I'toH d H / d c
(4)
r~t
Where V2 is the volume of carried over, non-magnetic minerals, Fprob. is the magnetic attraction force needed for the given probability of capture, V t and ~:1 are the volume and the (volume) magnetic susceptibility of the magnetic mineral respectively, K2 is the (volume) magnetic susceptibility of the nonmagnetic mineral, I.tois the permeability in vacuum and H and dH/dx are the magnetic field and the field gradient respectively. In a previous investigation [10] the capture probability in a HGMS matrix was determined. For a HGMS XRO (coarse expanded metal) matrix at 1.0 T, particles with a (mass) magnetic susceptibility of 15-20 x 10-9 m3/kg appear to have about 50% probability of being captured (Figure 11).
Capture probability in a XRO HGMS matrix I
ram mm
80 70
/
%
10 0 ~ -20,00
mm
_/ 0,00
20,00
40,00
60,00
80,00
100,00
120,00
140,00
Magnetic (mass) susceptibility. F i g . l l Work function for the HGMS XRO matrix at 1.0 T (10 kGauss). Susceptibility in SI units (10 -9 m3/kg) The amount of non-magnetic material, trapped in a floc with a few magnetic particles with a 50 % chance of being captured in the matrix, can be roughly estimated based on the data above and the volume magnetic susceptibilities of the minerals. Susceptibility data are shown in Table 5. Volume susceptibility = Mass susceptibility * Specific gravity
(5)
Dispersion of flotationconcentrates
1515
TABLE 5 Magnetic susceptibilities (mass) for the minerals used in the example (SI units)
Mineral
Sphalerite
Galena
Amphibolite
Spodumene
Mass suscept. (X) • 10-9
115 - 240
-5 10
350 - 430
5 - 15
Specific gravity (p)
4.1
7.4
2.7
3.1
Vol. suscept. (~:)
470 - 984
-40 - 74
945 - 1161
15 - 46
For the amphibolite/spodumene system an estimate suggest that little over 3 vol. % of the floc need to be amphibolite for a 50 % capture probability. For the sphalerite/galena mixture the corresponding figure is 20 vol. %. Naturally, the higher the susceptibility of the magnetic mineral, the less is needed for the capture.
CONCLUSION It is evident both from experiment and theoretical reasoning that proper dispersion of the pulp before HGMS/WHIMS separation is vital if optimal grade and recovery is to be achieved. In this investigation, only the pulp pH was used to change the level of agglomeration. In full scale separation, other means of dispersion may well be more efficient and cheaper, especially as very low pH may cause corrosion problems in valves and the matrix. Future tests involving sodium silicate, sodium hexametaphosphate, or others, may well prove these dispersants preferable. This investigation, however, has introduced the underlying principles as well as attempting to theoretically quantify the extension of the effect of flocculated particles in the pulp. It is important to remember that the theoretical figures above are merely rough estimates based on theory and an empirical determination of the HGMS capture profile. It is, however, beyond doubt that agglomeration may be detrimental to the separation precision and may be responsible for poor grade and recovery in both the magnetic and non-magnetic products.
ACKNOWLEDGEMENT We gratefully acknowledge the financial support from the Swedish Mineral research Foundation. Boliden Mineral and FMC Lithium Div. supplied the samples.
REFERENCES ,
2. 3.
.
.
6.
Jirestig, J.A. & Forssberg, K.S.E., Magnetic Characterisation of Sulphide Ores: Examples from Sweden. Magnetic and Electric Separation, 4, 31 (1993). Gaudin, A.M. & Spedden, H.R., Magnetic Separation of Sulphide Minerals. AIME Trans, No. 153, 563 (1943). Tawil, M.M. & Morales, M.M., Application of Wet High Intensity Magnetic Separation to Sulfide Mineral Beneficiation. Complex Sulfides, Processing of ores, concentrates and by products. (Proc. Cot~ ) San Diego California USA, 10-13 (Nov. 1985). Kim, Y.S., Fujita, T., Hashimoto, S. & Shimoiizaka, J., The Removal of Cu Sulphide Minerals from Pb Flotation Concentrate of Black Ore by High Gradient Magnetic Separation. Congr Int. Mineralurgie (CR) 15, 381 (1985). Jirestig, J.A. & Forssberg, K.S.E., Magnetic Separation of Sulphide Minerals. EI72netall,46, No. 1, 30 (1993). Jirestig, J.A. & Forssberg, K.S.E., Magnetic Separation in Sulphide Processing, Minerals & Metallurgical Processing Journal, 11, 176 (1993).
1516 .
8. 9. 10. 11.
12.
J.A. JIRESTIOand K. S. E. FORSSBERG Jirestig, J.A. & Forssberg, K.S.E., The Effect of Impurities on the Magnetic Susceptibility of Minerals. Scand. Journal of MetaUurgy, 21, No. 1, 189 (1992). Redeker, I.H., Concentration of Spodumene from North Carolina Pegmatite Ores. Mining Engineering, 31, No. 4, 395 (1979). Derkach, V.G., Special methods of the beneficiation of minerals. Nedra, Moscow, 1966, (quoted in Svoboda J. Magnetic methods for the treatment of minerals, Elsevier, (1987). Jirestig, J.A., Characterisation of a High Gradient Magnetic Separator Expanded Metal Matrix. (in Swedish). MinFo report No. 2905, (Jan. 1992). Laskowski, J.S. & Nyamekye, G.A., Colloid chemistry of weak electrolyte collectors: The effect of conditioning on flotation with fatty acids. SME Annual Meeting, Reno, Nevada, Feb. 15-18 1993, Pre-print No. 93-99, (1993). Fuerstenau, D.W. & Fuerstenau, M.C., The Flotation of Oxide and Silicate Minerals. King R. P (Ed) Principles of flotation. SAIMM, Monograph Series, No. 3, Johannesburg, (1982).
Pergamon
DISPERSION OF FLOTATION CONCENTRATES BEFORE MAGNETIC SEPARATION
J.A. JIRESTIG and K.S.E. FORSSBERG Div. of Mineral Processing, Lule~I University of Technology S-952 87 Lulegt, Sweden (Received 20 June 1994; accepted 16 August 1994)
ABSTRACT Laboratmy HGMS and WHIMS tests on flotation concentrates proved that grade and recovery in magnetic separation is greatly affected by the particle dispersion of the head feed. ht this investigation, the recovery of a spodumene flotation concentrate, floated with a fatty acid collector, was improved by 10% when the pulp pH was reducedfi'om pH 7 to pH 2 in order to improve the particle dispersion. For a phosphine floated Pb product, carlyhlg sphalerite and chalcopyrite, grade and recovel y was opthnised in a window around pH 5. Recovely was improved by approximately 5%. ghe carly over capacity fi'om the non-magnetic to the magnetic product for agglomerates containing a small amount of magnetic particles can be estimated using the HGMS capture probability function and the magnetic susceptibility of the material. An estimate of the spodumene / amphibolite system indicates that as little as 3% amphibolite in an agglomerate may be sufficient for thefloc to be captured in the matrix. 777ecorresponding number for the galena / sphalerite system is about 20%. Keywords HGMS; WHIMS; flotation
INTRODUCTION Until recently the only uses of High Gradient Magnetic Separation (HGMS) and Wet High Intensity Magnetic Separation (WHIMS) were as primary separation methods for "weakly" magnetic iron ores such as hematite and taconites, and for the removal of iron containing minerals in kaolin clays, and these are still the most important uses. The high magnetic attraction force of the HGMS, however, also allows the treatment of a variety of paramagnetic minerals. In previous work [1 - 4] it has been proved that several sulphide minerals have sufficient magnetic susceptibility to be captured in the matrix. It has also been shown [5 - 6] that most ores, with few exceptions, contain large amounts of magnetic non-value minerals. In these cases, magnetic separation is unsuited as the main separation method. HGMS, however, has proved successful in the upgrading of pre-treated materials, such as flotation concentrates. A few interesting problems arise when minerals, coated with a surface active compound, are to be separated in a HGMS. Although the physics of magnetic separation deals with volume dependent parameters (volume or mass susceptibility counteracted by gravity and hydrodynamic drag force) rather than surface properties, a flotation collector may well have a significant effect on the separation efficiency. It is reasonable to assume that the majority of the various minerals reporting to the float product are covered with the collector and hence have a strong tendency to tbrm agglomerates due to 1505
1506
J.A. JIRESTIG and K. S. E. FORSSBERG
hydrophobic flocculation and shear forces. These particle groups will behave as individual bodies with a bulk-susceptibility that is dependent on the minerals enclosed. This makes proper dispersion vital for achieving good grade and recovery.
MATERIAL The effect of dispersion was tested on two flotation products, a spodumene and a galena flotation concentrate. The mineral surface of each of the two samples was covered with two different types of surface active compounds, one (spodumene) an oleate the other (galena) a phosphine based collector.
Spodumene concentrate production at the processing plant After comminution and sizing of the pegmatite ore, the lithium mineral is floated using a tall oil type fatty acid with 5 - 7 % rosin-acid content at neutral pH and a glycol type frother [8]. The conditioned pulp is floated at about 30% solids, cleaned and recleaned. The spodumene concentrate contains 10 - 11% dark minerals, identified as amphibolite and biotite. The iron content is not an exact evaluation of the amount of amphibolite, since several other minerals with low iron concentration are present. The spodumene itself carries approximately 0.75 - 0.80 % Fe. The iron content, however, does give a rough idea of the amount of non-lithium minerals. The iron containing amphibolite and biotite have sufficient magnetic susceptibility to be captured in a HGMS matrix while the spodumene susceptibility is too low. Chemical assay of the concentrate is presented in Table 1.
TABLE 1 Chemical assay of the spodumene flotation concentrate Chemical
Li20
Fe203
MgO
Assay
5.35%
2%
0.304%
Pb concentrate production at the processing plant After comminution and sizing, the copper and lead values are floated in two circuits at pH 8.2. The talc content is depressed using dextrin. The floated Cu-Pb product is separated into a copper concentrate and a lead product at pH 8.2. In this flotation step, Cyanamid's Aerophine 3418 is used as a collector. Finally the lead product is fed to a HGMS circuit. Aerophine 3418 is a relatively new collector based on phosphine chemistry. Chemical assay of the concentrate is presented in Table 2. TABLE 2 Chemical assay of the lead flotation concentrate
Chemical
Pb
Cu
Zn
Assay
67.5 %
0.36 %
5.60 %
I
I
I
During the Pb-flotation a significant amount of sphalerite reports to the float product. The rather high magnetic susceptibility of the sphalerite makes HGMS a suitable method for upgrading the product. Although HGMS technique has been used in the plant [5-6] since 1989 to reduce the zinc content in the lead product, no attempts have been made to optimise the separation by dispersing the pulp.
EXPERIMENT The two samples were tested using two different but similar magnetic separators. The Spodumene flotation concentrate was processed on an Eriez WHIMS (Wet High Intensity Magnetic Separator) L-4-20 Lab-
Dispersion of flotationconcentrates
1507
separator, while a SALA HGMS (High Gradient Magnetic Separator) 5 - 30 - 10 was used for the galena. Both separators are batch type, cyclic separators. The main difference between the two, is the generation of the magnetic field. The Eriez separator uses air cooled coils to magnetise two iron pole pieces. The matrix chamber is placed in the gap between the poles. In the SALA separator the matrix canister is placed in the bore of a water cooled solenoid. Another difference is the field / pulp flow geometry. In the Eriez separator, the magnetic field is perpendicular to the pulp flow, while the SALA magnet has a parallel configuration, see Figure 1. Near identical matrix media were used in both test series.
Fe;funnel /~gne t coil
•,
Matrixcanister
Matrix.
[1
II
II
l
Fig. 1 Eriez WHIMS (left) at NCSU Minerals Research Lab. Asheville, NC, USA, SALA HGMS (right) at Lulea University of Technology, Lulea, Sweden
Pulp dispersion It was felt that the flotation collector would be responsible for forming most of the expected flocs. If so, regeneration of the particle surface or deactivation of the collector would improve the particle dispersion. A well known method of removing fatty acid from particle surfaces is scrubbing at low pH. In this investigation only pH was used to change the surface properties of the particles. Pulp pH was changed by the addition of NaOH or H2SO4. Experiment design The material was scrubbed at varying pH to remove, or at least reduce, the agglomeration effects of the surface coating. After scrubbing, the pulp was fed to the WHIMS / HGMS matrix. The pH of the feed water and the wash water was kept the same as the feed slurry, in order to prevent agglomeration recurring (due to the surface active collector still in the pulp). The matrix was washed with low pressure, pH adjusted water to remove physically entrained non-magnetic particles after the feed cycle was completed. The magnetic field was then turned off and the magnetic product rinsed out. Both products were collected, dewatered, weighed and assayed by AAS. Schematic presentation of test design can be found in Figure 2. The magnetic field strength was set at 1.0 T (10 kGauss) in all test runs. It may well be that the addition of common dispersants to the pulp, such as sodium silicate or sodium hexametaphosphate would have been more efficient in breaking up the flocs than merely changing the pH. This investigation, however, was aimed at proving a general need for dispersion, rather than finding the optimum dispersant for each individual material.
1508
J.A. JIRESTIGand K. S. E. FORSSBERG
Test Design I HeadFeed Flotation conc. :
I
N~H
!
WHIMS / HGMS Sep~ation
I
J
I
[ Ma~aeti¢ I
Non-magnetlc[
Assay I AAS
Fig.2 Test design for the dispersion investigation
FLOCCULATION AND DISPERSION OF FLOTATION PRODUCTS It is thought that the flotation collector is responsible for the formation of floes at certain pH. It seems logical to assume that the strongly hydrophobic particles may connect and attach due to hydrophobicity. When the pH is decreased the flocs may be broken and the pulp dispersed. Unfortunately, available data for Cyanamid's Aerophine 3418 is insufficient to make a valid assessment of the dispersion mechanism. However, the oleate system is well investigated, therefore a plausible explanation for the mechanism may be found. Laskowski and Nyamekye [11] presented a domain diagram for sodium oleate, (Figure 3). It is shown that the solubility at low pH is greatly reduced and that oleic acid is the predominant phase.
'02 ~'fb,~.~',,"',~-'~'X'OLEIC ACIB~ . . . . . .
z"
"
~
) x -, ..,'!
' >'= - Y ' - ; < K "
<
cr
I--tlJ oz o
TRUE S O L U T I O N
10.6
]
~o7 ," ~ ~.,X,<: ,:_,r, ._..~£vj~_ _~-_~. ,.,
lo e 10-~
t
Solubility limit ~
1.
I
I
J
2
4
6
8
10
12
pH Fig.3 Domain diagram for sodium oleate, after Laskowski and Nyamekye [11] When the collector, adsorbed to the spodumene surface, loses its solubility during attrition scrubbing two things may happen. The crystal surface degrades and the collector is released and forms micro droplets
Dispersion o f flotation c o n c e n t r a t e s
1509
in the liquid. It may also form droplets on the mineral surface. Tests indicated that both phases are present. It is believed that when micro droplets are formed on the mineral surface the ordered structure is lost, (Figure 4). The carbon chain no longer dominates the surface and the hydrophobie properties of the particle disappear. This makes it possible to at least partially wet the surface.
O
Fig.4 At high pH the ordered structure of the adsorbed collector makes the surface hydrophobic. When droplets are formed hydrophobicity is lost Fuerstenau and Fuerstenau [12] determined the zeta-potential for spodumene in an oleate environment (Figure 5). The diagram shows the point of zero charge to be just above pH 2, at lower pH the zetapotential increase rapidly. This indicates that the disordered structure of the oleate collector together with positive zeta-potential is responsible for the dispersion. Hydrophobic flocculation is believed to be the reason why dispersion does not occur around pH 8.
20 0
E -20
v
,~, "~ ;':,~,'~ ,,,,t~\X,~ ~
Na-oleate • 0 • 10"
mo,/I
• 10-4 mol/l ' 1 0 -a m o l / I
"%,..-Lt~
=~ -40
mol/I
,
.J
C ¢1
g 76o
",:,'<,1,;--,-. \\ .// '%
-80
• •
!
~.,~. ,..,/
/
',,:.,,J-'4"
N
-100 -120
~" ii
x,
%
I
i
I
2
4
6
I
I
pH
8"
l o"
1'2
Fig.5 Zeta potential of spodumene versus pH as a function of oleate concentration, [12]
J. A. JIRESTIGand K. S. E. FORSSBERG
1510
TEST RESULTS Spodumene flotation concentrate
The agglomerates caused by the tall oil-type fatty acid collector on the spodumene surface seemed to be dispersed at reduced pH. Magnetic separation tests were done with pH varying from 7 to 2. By dropping the pH from 7 to 2 the Li20 grade in the non-magnetic product was improved by 0.15 % and Fe203 grade was decreased by 0.35 %. The loss of Li20 to the magnetic product (tailings) was reduced by 1.13 % (Figure 6, recovery in Figure 7, data in Table 3).
Li20 and Fe203 grades 1 7,00 6,00
/ ,,.......-J
%
f
~,
Li20 non-mag.
4,00
o
Fe203non-mag.
3,00
J"
Li20 mag.
=
Fe203mag.
5,00
f
/
t
---....._
2,00 1,00 0,00
]..
1 7
Y 6
5
4
3
2
pH Fig.6 Li20 and Fe203 grades in the magnetic and non-magnetic products at varying pulp pH
Li20 and Fe203 recovery 100,00 90,00 80,00 70,00 60,00 % 50,00 40,00 30,00 20,00 10,00 0,00
I
Li20 non-mag. -----o
Fe203non-mag.
.t
Li20 mag.
--
Fe203mag.
k---..-.
7
6
5
4
3
2
pH Fig.7 Li20 and F%O3 recovery in the mag. and non-mag, products at varying pH The recovery of lithia to the non-magnetic product greatly improved as the pH decreased. The pH reduction of the pulp from pH 7 to pH 2 caused a Li20 recovery improvement of more than 11%. Since
Dispersion of flotation concentrates
1511
the non-magnetic product is to be the final spodumene concentrate and the iron rich magnetic fraction is preferably to be disposed of as tailings, the improvement of lithia recovery is of great importance to the process economy. TABLE 3 Grades and recoveries in the magnetic and non-magnetic products
Grade
pHI
Recovery
Product
wt. %
Li20
FeqO3
Li20
Fe203
Head feed
100.00
5.38
1.63
100.00
100.00
7 7
Non-mag. Mag.
80.90 19.10
5.40 5.16
1.16 4.81
81.59 18.41
50.53 49.47
4 4
Non-mag. Mag.
85.17 14.83
5.40 4.90
1.04 6.22
86.36 13.64
48.99 51.01
Non-mag. Mag.
88.66 11.34
5.54 4.50
0.84 6.67
90.58 9.42
49.63 50.37
Non-mag. Mag.
90.86 9.14
5.55 4.03
0.81 6.97
93.19 6.81
50.59 49.41
It was suspected that the improved separation could be caused by selective leaching of iron from some of the minerals in the head feed. A series of tests with varying scrubbing time was performed to verify or contradict this theory. If selective leaching was the explanation, extended scrubbing time would yield a different product than a mere short conditioning. No detectable changes were noted as a result of the scrubbing time, indicating that iron is not leached by the acid in detectable amounts at the scrubbing times and pH used. Lead flotation concentrate
The flocculation caused by the tall phosphine type collector on the galena and sphalerite surface was only slightly affected by the pH. Tests were carried out with pH varying from 10 to 2. Pb grade in the magnetic product changed from 30 % to 20 % and then back to 40 % while passing through the pH range 2 to 10. The Zn grade was only marginally affected. The grade / pH diagram (Figure 8) indicates that there is a pH window around pH 6, where the separation performance is improved. The test results at the lowest pH (pH 2) is likely to be biased by the leaching of some of the sulphide minerals. While running tests at this pH, the smell of H2S was noted, indicating decomposition of sulphides. The recovery loss of galena (Figure 9) to the magnetic product is reduced in the pH window around pH 6. Compared to the recovery in the close proximity (pH 5 and 7) the loss is reduced by 3 - 4 % (from ca 10 - 7 %). Test results are summarised in Table 4. Process data from the plant and the laboratory investigation are compared in Table 4. First, it is clear that the cyclic laboratory separator is more precise in processing the flotation concentrate than the carousel HGMS used in Garpenberg. In spite of this, the comparison suggests that a better separation might be achieved if the pH is adjusted from 8 to 6.
1512
J.A. JIRESTIGand K. S. E. FORSSBERG
90 80 70
--...... ~...-~
..~, ~.-.._.__
a
Zn mag.
t > - - Zn non-mag. 30 ~ 20~
2
~ --
3
4
_.........~r--------~
?-.... j
5
6
7
8
f
9
.t
Pb mag.
"
Pb non-mag.
10
pH Fig.8 Pb and Zn grades in the magnetic and non-magnetic products at varying pulp pH
Zn and Pb recovery 10£ 9(3 8G 7(3
l
, ~..._..,...~ ~,......._
Zn mag. Zn non-mag.
4(1 30 20 10 0 2
3
4
5
6
7
8
9
~"
Pb ,nag.
"
Pb non-mag.
10
pH Fig.9 Pb and Zn recovery in the magnetic and non-magnetic products at varying pulp pH T A B L E 4 C o m p a r i s o n o f process d a t a f r o m G a r p e n b e r g a n d the l a b o r a t o r y i n v e s t i g a t i o n [6] Chem. assay
Product
Grade
Roe.
Garpenberg (pH 8)
Mag.
23.20
0.20
19.18
12.7
14.7
56.2
Garpenberg (pH 8)
nonmag.
60.84
0.45
5.70
87.3
85.3
43.8
Lab invest. (pH 8)
mag.
33.72
0.95
19.67
12.0
63.82
88.23
Lab invest. (pH 8)
nonmag.
82.30
0.18
0.87
88.0
36.17
11.77
Lab invest. (pH 6)
mag.
20.81
0.91
20.21
7.48
62.71
87.7
Lab invest. (pH 6)
nonmag.
79.98
0.17
0.88
92.52
37.29
12.30
Dispersion of flotation concentrates
1513
MAGNETIC SUSCEPTIBILITY OF PARTICLE AGGLOMERATES The physics of magnetic separation deals with volume dependent parameters (volume or mass susceptibility counteracted by gravity and hydrodynamic drag force) rather than surface properties. The attraction force, (Fmag) in the matrix follows
(1)
Fmag = 1/2 I.to V 1¢ H dHIdx
Where po is the permeability of flee space, V the particle volume, • the volume magnetic susceptibility, H and dH/dx are the magnetisation and field gradient respectively. In this equation, the volume magnetic susceptibility (g) is the bulk susceptibility of the particle or particle agglomerate. The magnetic susceptibility of any accumulation of particles is dependent on the intrinsic susceptibility of the individual minerals. The magnetic bulk susceptibility follows the graph in Figure 10 according to Derkach [9].
~S
~'
1.0O.10.01 -
.~
/
0.00!-
v.
/
[
/
A~_
~
~
t
V
1 + DK{
D
° o.ooo1I/ -6 ;>
I.,"
I
0.0001
I
I
I
I
I
I
t
0.001 0.01 0.1 1.0 10 100 1000 Intrinsic magnetic susceptibility, (~i)
Fig. 10 Bulk magnetic susceptibility as a function of the intrinsic magnetic susceptibility, for geometric demagnetisation factor D = 0.16 [9] The demagnetisation effect on the bulk susceptibility is considerable for minerals with high intrinsic susceptibility. The graph is based on the following equation x -
PKi
(2)
1 +(D+Di)P~:;
Where K is the bulk (volume) susceptibility, r,i is the intrinsic (volume) magnetic susceptibility, p is the packing density, D is the geometrical demagnetisation factor, and D i is the internal demagnetisation factor. The demagnetisation factor D is shape dependent and must be approximated with values calculated for simple geometrical bodies, such as spheres, ellipsoids or rods. Ki and D i can be determined by extensive measurements of the magnetisation of a mineral in a homogenous background field. This determination, however, is quite laborious. Fortunately, in dealing with HGMS or WHIMS, the attraction force in the matrix is strong enough to fully capture agglomerates already in the linear part of the graph. The demagnetisation effects on the bulk susceptibility can be disregarded. It has been proved [7] that the bulk susceptibility for para- and diamagnetic mixtures, and for small inclusions of ferro- and ferri-magnetic minerals in the agglomerates follows the equation 7:IZ-E
1514
J.A. JIRESTIOand K. S. E. FORSSBERG
r~b,,v, V,o, =
(3)
r.1 v t + r.2 v2 + . . . . . . . . .
Where Kbulk Vto t is the bulk (volume) susceptibility times the total material volume, and K1 V 1 + ~:22 V2 + ....... is the (volume) magnetic susceptibility times the volume of each individual constituent. This equation is less complex, but more important, the components are much more readily determined. Carry over capacity The maximum amount of non-magnetic material that may be carried over to the magnetic fraction as agglomerates can be estimated if the magnetic susceptibility of the minerals and the magnetic force distribution of the matrix is known. It is important to realise that when dealing with HGMS/WHIMS separation, much like screening, it is necessary to think in terms of probabilities, rather than absolute values. The ratio of non-magnetic minerals, carded over to the magnetic fraction as an agglomerate containing magnetic particles, at a given probability, follows Vl = V2
F0'~°b')
-__K2
x t IA I'toH d H / d c
(4)
r~t
Where V2 is the volume of carried over, non-magnetic minerals, Fprob. is the magnetic attraction force needed for the given probability of capture, V t and ~:1 are the volume and the (volume) magnetic susceptibility of the magnetic mineral respectively, K2 is the (volume) magnetic susceptibility of the nonmagnetic mineral, I.tois the permeability in vacuum and H and dH/dx are the magnetic field and the field gradient respectively. In a previous investigation [10] the capture probability in a HGMS matrix was determined. For a HGMS XRO (coarse expanded metal) matrix at 1.0 T, particles with a (mass) magnetic susceptibility of 15-20 x 10-9 m3/kg appear to have about 50% probability of being captured (Figure 11).
Capture probability in a XRO HGMS matrix I
ram mm
80 70
/
%
10 0 ~ -20,00
mm
_/ 0,00
20,00
40,00
60,00
80,00
100,00
120,00
140,00
Magnetic (mass) susceptibility. F i g . l l Work function for the HGMS XRO matrix at 1.0 T (10 kGauss). Susceptibility in SI units (10 -9 m3/kg) The amount of non-magnetic material, trapped in a floc with a few magnetic particles with a 50 % chance of being captured in the matrix, can be roughly estimated based on the data above and the volume magnetic susceptibilities of the minerals. Susceptibility data are shown in Table 5. Volume susceptibility = Mass susceptibility * Specific gravity
(5)
Dispersion of flotationconcentrates
1515
TABLE 5 Magnetic susceptibilities (mass) for the minerals used in the example (SI units)
Mineral
Sphalerite
Galena
Amphibolite
Spodumene
Mass suscept. (X) • 10-9
115 - 240
-5 10
350 - 430
5 - 15
Specific gravity (p)
4.1
7.4
2.7
3.1
Vol. suscept. (~:)
470 - 984
-40 - 74
945 - 1161
15 - 46
For the amphibolite/spodumene system an estimate suggest that little over 3 vol. % of the floc need to be amphibolite for a 50 % capture probability. For the sphalerite/galena mixture the corresponding figure is 20 vol. %. Naturally, the higher the susceptibility of the magnetic mineral, the less is needed for the capture.
CONCLUSION It is evident both from experiment and theoretical reasoning that proper dispersion of the pulp before HGMS/WHIMS separation is vital if optimal grade and recovery is to be achieved. In this investigation, only the pulp pH was used to change the level of agglomeration. In full scale separation, other means of dispersion may well be more efficient and cheaper, especially as very low pH may cause corrosion problems in valves and the matrix. Future tests involving sodium silicate, sodium hexametaphosphate, or others, may well prove these dispersants preferable. This investigation, however, has introduced the underlying principles as well as attempting to theoretically quantify the extension of the effect of flocculated particles in the pulp. It is important to remember that the theoretical figures above are merely rough estimates based on theory and an empirical determination of the HGMS capture profile. It is, however, beyond doubt that agglomeration may be detrimental to the separation precision and may be responsible for poor grade and recovery in both the magnetic and non-magnetic products.
ACKNOWLEDGEMENT We gratefully acknowledge the financial support from the Swedish Mineral research Foundation. Boliden Mineral and FMC Lithium Div. supplied the samples.
REFERENCES ,
2. 3.
.
.
6.
Jirestig, J.A. & Forssberg, K.S.E., Magnetic Characterisation of Sulphide Ores: Examples from Sweden. Magnetic and Electric Separation, 4, 31 (1993). Gaudin, A.M. & Spedden, H.R., Magnetic Separation of Sulphide Minerals. AIME Trans, No. 153, 563 (1943). Tawil, M.M. & Morales, M.M., Application of Wet High Intensity Magnetic Separation to Sulfide Mineral Beneficiation. Complex Sulfides, Processing of ores, concentrates and by products. (Proc. Cot~ ) San Diego California USA, 10-13 (Nov. 1985). Kim, Y.S., Fujita, T., Hashimoto, S. & Shimoiizaka, J., The Removal of Cu Sulphide Minerals from Pb Flotation Concentrate of Black Ore by High Gradient Magnetic Separation. Congr Int. Mineralurgie (CR) 15, 381 (1985). Jirestig, J.A. & Forssberg, K.S.E., Magnetic Separation of Sulphide Minerals. EI72netall,46, No. 1, 30 (1993). Jirestig, J.A. & Forssberg, K.S.E., Magnetic Separation in Sulphide Processing, Minerals & Metallurgical Processing Journal, 11, 176 (1993).
1516 .
8. 9. 10. 11.
12.
J.A. JIRESTIOand K. S. E. FORSSBERG Jirestig, J.A. & Forssberg, K.S.E., The Effect of Impurities on the Magnetic Susceptibility of Minerals. Scand. Journal of MetaUurgy, 21, No. 1, 189 (1992). Redeker, I.H., Concentration of Spodumene from North Carolina Pegmatite Ores. Mining Engineering, 31, No. 4, 395 (1979). Derkach, V.G., Special methods of the beneficiation of minerals. Nedra, Moscow, 1966, (quoted in Svoboda J. Magnetic methods for the treatment of minerals, Elsevier, (1987). Jirestig, J.A., Characterisation of a High Gradient Magnetic Separator Expanded Metal Matrix. (in Swedish). MinFo report No. 2905, (Jan. 1992). Laskowski, J.S. & Nyamekye, G.A., Colloid chemistry of weak electrolyte collectors: The effect of conditioning on flotation with fatty acids. SME Annual Meeting, Reno, Nevada, Feb. 15-18 1993, Pre-print No. 93-99, (1993). Fuerstenau, D.W. & Fuerstenau, M.C., The Flotation of Oxide and Silicate Minerals. King R. P (Ed) Principles of flotation. SAIMM, Monograph Series, No. 3, Johannesburg, (1982).