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Studies on selective flocculation of complex sulphides using cellulose xanthate
IIII'UlIMIOMI. JOURIIIILOf
minERAL PRO(ESEInG ELSEVIER
~
Int. J. Miner. Process. 50 (1997) 177-186
°
Jtudles on selective flocculation of complex sulphides using cellulose xanthate N.R. Mandre *, D. Panigrahi Department of Fuel and Mineral Engineering, Indian School of Mines, Dhanbad, 826004, India
Received 25 June 1995; accepted 24 February 1997
Abstract In thi~; paper an attempt has been made to preconcentrate the sulphide minerals from complex sulphide ore by selective flocculation using a modified flocculant such as cellulose xanthate. The experiments carried out indicated that the metal grades were enhanced from 2 to 3.3% for lead and from 6 to 10.57% for zinc. The effectiveness of the process was assessed by a selectivity index which indicated that the process is effective and resulted in an index value of 0.3 for lead and 0.35 for zinc. © 1997 Elsevier Science B.V. Keywords; flocculation; agglomeration; fine particles; modified; polymers; bebeficiation
1. Introduction Depletion of high-grade complex sulphide ore reserves and increase in the degree of fineness of value minerals has necessitated the adoption of a pre-concentration technique. Moreover, the base metal sulphide deposits are now attaining a more complex nature a~ad in order to obtain a complete liberation of value minerals, the ore is generally subjected to extensive comminution operations resulting into the production of large quantities of fines. These fines, technically known as slimes, are often discarded as waste. From the literature (Attiya and Fuerstenau, 1978) it may be seen that discarding of such fines results into losses upto 30% of total valuable minerals. Also, from the literature it may be seen that the generation of fines and ultra-fines can be as high as 70% (Singh et al., 1992), depending upon the nature of the ore, mining and beneficiation techniques employed. Therefore, in order to process such fine particles, selective flocculation using
* Corre:;ponding author. 0301-7516/97/$17.00 © 1997 Elsevier Science B.V. All rights reserved. PI1 S0301-7516(97)00013-6
178
N.R. Mandre, .D. Panigrahi / lnt. J. Miner. Process. 50 (1997) 177-186
different polymers has been investigated in the past several years (Yarrar and Kitchener, 1970; Attiya and Kitchener, 1975; Drzymala and Fuerstenau, 1981; Marabini et al., 1988; Pradip and Moudgil, 1991). These studies show the use of starch, polyacrylic acids and modified polymer such as cellulose xanthate, starch xanthate as the selective flocculants (Pradip et al., 1980; Attiya, 1982; Acar and Somasundaran, 1985; Termes and Wilfong, 1985; Moudgil and Shah, 1987; Jawed Mohammed and Tare Vinod, 1991; Mariyani and Nelson, 1993; Ravishankar et al., 1995). A detailed literature survey reveals that only a small number of investigations were reported on selective flocculation of sulphides using a modified polymer. These studies show that the selective flocculation of sulphides can be achieved by incorporating the xanthate groups into cellulose at an alkaline pH (Rao, 1971; Attiya and Fuerstenau, 1978; Termes et al., 1983). Therefore, in this context an attempt has been made to investigate selective flocculation of sulphides from a complex sulphide ore using a modified flocculant such as cellulose xanthate.
2. Experimental The complex sulphide ore used in this study was collected from the Rajpura-Dariba mines, Udaipur, Rajasthan. The samples analysed contained 6.73% zinc, 2.1% lead and 5.5% iron. Initially the samples were subjected to crushing and grinding to produce 100% passing of 75-~m size fractions. The size analysis of the ground product is given in Table 1.
2.1. Synthesis of cellulose xanthate The cellulose xanthate was prepared according to the method described by Rao
Table 1 Size analysis of the sample Size (Ixm)
Under
Size (Izm)
In band
188 87.2 53.5 37.6 28.12 21.5 16.7 13.0 10.1 7.88 6.15 4.83 3.80 3.02 2.41 1.94
100 100 99.6 92.2 86.6 77.8 66.9 57.0 46.9 37.8 29.6 23.3 16.6 9.8 5.8 3.4
188-87.2 87.2-53.5 53.5-37.6 37.6-28.1 28.1-21.5 21.5-16.7 16.7-13.0 13.0-10.1 10.1-7.88 7.88-6.15 6.15-4.83 4.83-3.80 3.80-3.02 3.02-2.41 2.41-1.94
0.0 0.4 7.4 5.6 8.8 10.9 9.9 10.1 9.1 8.2 6.3 6.6 6.8 4.0 2.4
N.R. Mandre, .D. Panigrahi / lnt. J. Miner. Process. 50 (1997) 177-186
179
(1971) ~md Attiya and Kitchener (1975). For this purpose, 4 - 5 g of filter paper was soaked in 18% sodium hydroxide for 2 h to separate a-cellulose (insoluble form of cellulose. The excess alkali was filtered and the residue was squeezed out to remove all solution. Further, the residue was treated with 2 - 4 ml of carbon disulphide using a closed container. The resultant mass was agitated with 4% sodium hydroxide for 3 to 4 h and filtered to remove undissolved solid particles. The filtrate obtained was used for the flocculation studies. 2.2. Flocculation tests
The ground complex sulphide ore has been subjected to flocculation tests which were carried out in a 500-ml graduated cylinder. For this purpose a desired amount of ore was mixed in 450 ml water and the pH of the slurry was adjusted by using dilute HC1 and NaOH. Then the slurry was thoroughly mixed by inverting the cylinder 10-12 times. After a thorough mixing of the particles, the cylinder was allowed to stand undisturbed. Further~ the slimes were siphoned out after noting the mudline height (interface between settled pulp and clear water). The slimes and the settled solids were collected separately, filtered, dried and analysed for lead and zinc using an AAS PU9000 of Phillips.
3. Resvtlts and discussions Prior to the selective flocculation process, initially some experiments were carded out to study settling charactersfics as well as effect of pH on the settling rate of the ground
5
o 10 */, Solids by wl. 5%
,,
,,
,,
/ /
[] 2°/ . . . . . . .
/
/
4
23
0
I
i
I
I
I
8
9
lO
I!
12
pH
Fig. 1. Effect of pH on settling rate at various pulp densities.
180
N.R. Mandre, .D. Panigrahi / lnt. J. Miner. Process. 50 (1997) 177-186
ioo ~(+)
~
~.
so o
,
,,
o
50
~
;
3
l
c
~
9
,
II
pH
~
lO0
150
~ "~..
zOO
\
250 Fig. 2. Zeta-potential of particle as a function of pH.
sulphide ore. For this purpose, an experimental method described by Thalmage and Fitch (1955) was used and the results of the tests are given in Fig. 1. From the results it may be seen that increase in pH increases the settling rate and a maximum settling rate of 4.9 c m / m i n was obtained at pH 11. Therefore, in all flocculation tests, a constant pH of 11 was maintained. In order to support the above findings some experiments were carried out to study the zeta-potential of the ore mineral under different conditions. During these studies, the zeta-potential of the system was analysed as a function of pH and flocculant dosage. The results of the experiments are given in Figs. 2 and 3, respectively. From Fig. 2 it may be seen that the particles show a negative potential throughout the pH range and their negative potential increases from - 4 6 to - 1 8 5 mV with increase in pH. From the
75
50
pH = I1
t+] 25
~' o ~ ( _ ) 25 50
0.2
0.4
0.6
0.8
~-0
Ftocculant conc. (ml)
~
Ioo 125
Fig. 3. Zeta-potential as a function of addition o f l % solution o f cellulose xanthate.
N.R. Mandre, .D. Panigrahi / Int. J. Miner. Process. 50 (1997) 177-186
O
Assay
•
Recovery
pH:l~ 2 */o Solids
3.0
~00
8_ o
2.
95
2.1
~
o
,,o
I
2~o
~.o
Flocculent
41o
s:o 90
cont.(rot )
Fig. 4. Recovery and grade of lead as a function of concentration of cellulose xanthate (1% solution).
10./.
O
Assoy
I
Recovery
p H = 11
20/0 Solids lO.O
100
99 '~
9.6
.g
.
~9.2
o 98 ~
,
~" cl
cr
8.8
97
8.4
96
8.0
d 0
,
,
,
,
1
2
3
4
95
F l o c c u l e n t conc. ( mr )
Fig. 5. Recovery and grade of zinc as a function of concentration of cellose xanthate (1% solution).
181
182
N.R. Mandre, .D. Panigrahi / lnt. J. Miner. Process. 50 (1997) 177-186
Table 2 Effect of washing of flocs Washings
1 2 3 4
Assay value (%)
Recovery (%)
Separation index
Pb
Zn
Pb
Zn
Pb
Zn
3.15 3.26 3.33 3.11
10.16 10.53 10.78 10.31
98.95 98.42 98.00 92.71
99.49 99.20 98.99 95.90
0.33 0.36 0.37 0.30
0.36 0.37 0.39 0.36
Pulp density 2%, flocculant dosage 2 ml of 1% solution.
literature it may be seen that the point of zero charge for pure silica is around pH 3, for sphalerite 7.5 and galena does not show any point of zero charge (Huntee, 1981; Termes et al., 1983). Therefore, at higher pH, flocculation of silica is more difficult as a higher surface charge keeps the particles apart. However, only sedimentation of individual silica particles occurs in the suspensions. In a complex system having sphaleritegalena-quartz-calcite, it is very difficult to selectively flocculate only sulphide minerals as observed by Yarrar and Kitchener (1970) at natural pH. This is mainly because even at a pH of 8, calcite is slightly positively charged whereas silica, sphalerite and galena are negatively charged. Hence, mutual coagulation of silica and calcite occurs at pH 8. However, by increasing the pH to 10-11, the zeta-potential of calcite may come into a negative range eliminating mutual coagulation between quartz and other sulphide
Wt. %
5olids : 2
of sodium silicote
0 2 kg/t 4 kglt
,,
6 kg/t
.
.
,,
4.0
g 8 kg/t
.
.
.
.
.
....
"
#_ o 3.s
3.0
~
i
1
2
3
4
No, of woshings Fig. 6. Grade of lead as a function of number of washings at different dosages of sodium silicate with 2 ml of
1% cellulose xanthat¢ soludon.
N.R. Mandre, .D. Panigrahi / lnt. J. Miner. Process. 50 (1997) 177-186
183
minerals. Therefore, based on these observations selective flocculation experiments were carried out at pH 11. Further, zeta-potential measurements were made as a function of flocculant concentration at pH I I. The results of the studies are given in Fig. 2. From the figure it may be seen that the increase in the flocculant dosage decreases the zeta-potential giving rise to the adsorption of the polymer. From the literature (Attiya and Kitchener, 1975) it may be seen that sulphydryl compounds like xanthate, dithio-carbonates and dithio-phosphates are known to form insoluble compounds with minerals such as galena and chalcopyrite. Also, the adsorption of these reagents on mineral surfaces is mainly due to selective chemisorption of the reagents. Additionally, their studies have also shown a marked selectivity of cellulose xanthate towards base metal sulphides. 3.1. Selective flocculation tests:
After completion of the above studies, investigations were extended to study selective flocculation of sulphides using cellulose xanthate. For this purpose, the experiments were caJaied out using different concentrations of the flocculant and the results are given in Figs. 4 and 5 for lead and zinc, respectively. From these figures it may be seen that a maximum recovery of 95% lead and 98% zinc assaying 3 and 10% can be obtained
13.0 Wt-°/o S01ids:2 o2 kg/t
of sodium s i l i c a l e
&4 kg/t
,,
r3 6 k g / t
....
• 8 kg/t
....
"
" "
]2.0
o
y ,.o
I
I
NO. of woshings Fig. 7. Grade of zinc as a function of number of washings at different dosages of sodium silicate with 2 n'd of
1% cellulose xanthate.
184
N.R. Mandre, .D. Panigrahi / lnt. J. Miner. Process. 50 (1997) 177-186
using 2 ml of 1% cellulose xanthate. Further, these results were analysed to assess the effectiveness of the flocculation by calculating separation indices individually for lead and zinc using the equation proposed by Sresty and Somasundaran (1980): SI = [(percentage of value minerals recovered in the concentrate)+ (percentage of gangue rejected in the tailings) - 100]/100. From the results it was observed that the separation indices vary from 0.3 to 0.35 for lead and zinc, respectively. In order to enhance the grade and recoveries of the sulphides, washing of the flocs was carried out. During these studies a four-stage cleaning technique was employed and the results are given in Table 2. From the table it may be seen that a maximum recovery of 98% lead and zinc can be obtained with grades of 3.3 and 10%, respectively, after three stages of cleaning. The separation indices obtained show a maximum value of 0.4 for both lead and zinc. However, further increasing the cleaning resulted into decreased index values which may be attributed to the breaking of the flocs resulting in the loss of value metal in the slimes. Further studies were carried out to know the effect of dispersant on selective flocculation of sulphides, since the degree of dispersion dictates the extent of gangue rejection. To accomplish this, studies were carried out using sodium silicate as dispersant. All these studies were carried out using different dosages of sodium silicate in the presence of 2 ml of 1% cellulose xanthate with four stages of cleaning. The results of
0.5 Wt.% Solids_- 2 o 2 kg/t of sodium silicate Z, k g / t
-
,,
"
, ~
X g~ 0.3
\ 0.2
~
1
,
I
2
3
4
No. of wQshlngs Fig. 8. Effect of washing on separation index for galena.
N.R. Mandre, .D. Panigrahi / Int. J. Miner. Process. 50 (1997) 177-186
185
Wt.% Solids:2 O 2 Kg/t
No-Silicate
L~ 4 K g / t [] 6 Kg/t
"
• 8 Kg/t
"
0.5
•-~ 0.4
0.3
I
I
i
i
1
2
3
4
NO. of woshings
Fig. 9. Effect of washing on separation index for sphalerite.
the studies are given in Figs. 6 and 7 for lead and zinc, respectively. From these figures it may be seen that there is an increase in the grade of lead (3.8%) and zinc (12.16%) using 6 k g / t of dispersant after three stages of cleaning with a corresponding recovery of 95% for both. The analysis of separation indices (Figs. 8 and 9) shows maximum index values of 0.45 for lead and 0.48 for zinc. Therefore, it may be said that the use of dispersant increases the efficiency of the selective flocculation process.
4. Con,elusions Frora the above studies the following conclusions were drawn. (1) Studies carried out on settling rate of the particles show an increase in settling rate with increase in pH irrespective of the variation in solid content. (2) Experiments performed to know the effect of flocculant dosage indicated that best results can be obtained using 2 ml of 1% of flocculant for a pulp with 2% solid content. (3) The effect of cleaning of the floes as well as the addition of a dispersant improves the selective flocculation. A maximum improvement of 6.73 to 12.16% zinc and 2.1 to 3.8% lead with a recovery of 99% was achieved with the addition of 2 ml of 1% cellulo,;e xanthate and 6 k g / t of sodium silicate after three stages of cleaning.
186
N.R. Mandre, .D. Panigrahi / lnt. J. Miner. Process. 50 (1997) 177-186
Acknowledgements T h e f i n a n c i a l s u p p o r t g i v e n b y the C o u n c i l o f Scientific a n d I n d u s t r i a l R e s e a r c h o n ' S e l e c t i v e f l o c c u l a t i o n o f c o m p l e x s u l p h i d e s ' is a c k n o w l e d g e d .
References Acar, S., Somasundaran, P., 1985. Effect of dissolved mineral species on flocculation of sulphides. Miner. Metall. Process. 2 (2), 231-235. Attiya, Y.A., 1982. Fine particle separation by selective flocculation. Sep. Sci. Technol. 17 (3), 485-493. Attiya, Y.A., Fuerstenau, D.W., 1978. Principles of separation of ore minerals by selective flocculation. Recent Dev. Sep. Sci. 4 (5), 51-68. Attiya, Y.A. and Kitchener, J.A., 1975. Development of complexing polymers for selective flocculation of copper minerals. Proc. 1 lth Int. Mineral Processing Congress, pp. 1233-1248. Drzymala, J., Fuerstenau, D.W., 1981. Selective flocculation of hematite in hematitic-quartz-ferric ion polyacryl acid system, I. Activation and Deactivation of quartz. Int. J. Miner. Process., 8: 265-277. Huntee, T.K., 1981. The use of synthetic flocculants in mineral processing and hydrometallurgy. International Symposium on Beneficiation and Agglomeration, Bhubaneswar, pp. 6.41. 1-6.41.8. Jawed Mohammed, Tare Vinod, 1991. Application of starch xanthates for cadmium removal: a comparative evaluation. J. Appl. Polymer Sci., 42: 317-324. Marabini, A., Barbaro, M., Falbo, A., 1988. Possibility of starches using selective flocculation of a ruffle ore In: Y.A. Attiya, B.M. Moudgil, S. Chander (Editors), Interfacial Phenomena in Bio-Technology and Material Processing. Elsevier Amsterdam, pp. 345-361. Mariyani, R.D., Nelson, A.T., 1993. Silica fotation at the Tilden Mines. In: D. Malhotra (Editor), Flotation Plants, Are They Optimised? SME, Littleton, CO, pp. 119-122. Moudgil, B.M., Shah, B.D., 1987. Single and mixed mineral flocculation behaviour of apatite and dolomite. In: Y.A. Attiya (Editor), Flocculation in Biotechnology and Separation Systems. Elsevier, Amsterdam, pp. 729-739. Pradip, Moudgil, B.M., 1991. Selective flocculation of tribasic calcium phosphate from mixtures with quartz using polyacrylic acid flocculant. Int. J. Miner. Process., 32: 271-281. Pradip, Attiya, Y.A., Fuerstenau, D.W., 1980. Adsorption of polyacrytamide flocculants on apatites. Colloid Polymer Sci. 258, 1343-1353. Rao, S.R., 1971. Xanthate and Related Compounds. Marcel Dekker, New York, 464 pp. Ravishankar, S.A., Pradip, Khosla, N.K., 1995. Selective flocculation of iron oxides from its synthetic mixtures with clays: a comparison of polyacrylic acid and starch polymers. Int. J. Miner. Process., 43: 235-247. Singh, B.P., Das, B., Bhima Rao, R., 1992. Flocculation studies on redmud using polyacryl amide. Trans. I.I.M. 20 (90), 1-33. Sresty, G.C., Somasundaran, P., 1980. Selective flocculation of synthetic mineral mixtures using modified polymers. Int. J. Miner. Process. 6, 303-320. Termes, S.C., Wilfong, R.L., 1985. Flocculation of Metal Oxides and Hydroxide Minerals With Cross Linked Starches Containing Chelating Groups. U.S. Bureau of Mines, Pittsburgh, PA, R/8944. Termes, S.C., Wilfong, R.L., Richardson, P.E., 1983. Flocculation of Sulphide Mineral Fines by Insoluble Cross Linked Starch Xanthate. U.S. Bureau of Mines, Pittsburgh, PA, RI 8819. Thalmage, W.P., Fitch, E.B., 1955. Determining thickener unit areas. Ind. Eng. Chem., 47:38 pp. Yarrar, B., Kitchener, J.A., 1970. Selective flocculation of minerals. Trans. I.M.M., Sect. C, 79: 23-33.
minERAL PRO(ESEInG ELSEVIER
~
Int. J. Miner. Process. 50 (1997) 177-186
°
Jtudles on selective flocculation of complex sulphides using cellulose xanthate N.R. Mandre *, D. Panigrahi Department of Fuel and Mineral Engineering, Indian School of Mines, Dhanbad, 826004, India
Received 25 June 1995; accepted 24 February 1997
Abstract In thi~; paper an attempt has been made to preconcentrate the sulphide minerals from complex sulphide ore by selective flocculation using a modified flocculant such as cellulose xanthate. The experiments carried out indicated that the metal grades were enhanced from 2 to 3.3% for lead and from 6 to 10.57% for zinc. The effectiveness of the process was assessed by a selectivity index which indicated that the process is effective and resulted in an index value of 0.3 for lead and 0.35 for zinc. © 1997 Elsevier Science B.V. Keywords; flocculation; agglomeration; fine particles; modified; polymers; bebeficiation
1. Introduction Depletion of high-grade complex sulphide ore reserves and increase in the degree of fineness of value minerals has necessitated the adoption of a pre-concentration technique. Moreover, the base metal sulphide deposits are now attaining a more complex nature a~ad in order to obtain a complete liberation of value minerals, the ore is generally subjected to extensive comminution operations resulting into the production of large quantities of fines. These fines, technically known as slimes, are often discarded as waste. From the literature (Attiya and Fuerstenau, 1978) it may be seen that discarding of such fines results into losses upto 30% of total valuable minerals. Also, from the literature it may be seen that the generation of fines and ultra-fines can be as high as 70% (Singh et al., 1992), depending upon the nature of the ore, mining and beneficiation techniques employed. Therefore, in order to process such fine particles, selective flocculation using
* Corre:;ponding author. 0301-7516/97/$17.00 © 1997 Elsevier Science B.V. All rights reserved. PI1 S0301-7516(97)00013-6
178
N.R. Mandre, .D. Panigrahi / lnt. J. Miner. Process. 50 (1997) 177-186
different polymers has been investigated in the past several years (Yarrar and Kitchener, 1970; Attiya and Kitchener, 1975; Drzymala and Fuerstenau, 1981; Marabini et al., 1988; Pradip and Moudgil, 1991). These studies show the use of starch, polyacrylic acids and modified polymer such as cellulose xanthate, starch xanthate as the selective flocculants (Pradip et al., 1980; Attiya, 1982; Acar and Somasundaran, 1985; Termes and Wilfong, 1985; Moudgil and Shah, 1987; Jawed Mohammed and Tare Vinod, 1991; Mariyani and Nelson, 1993; Ravishankar et al., 1995). A detailed literature survey reveals that only a small number of investigations were reported on selective flocculation of sulphides using a modified polymer. These studies show that the selective flocculation of sulphides can be achieved by incorporating the xanthate groups into cellulose at an alkaline pH (Rao, 1971; Attiya and Fuerstenau, 1978; Termes et al., 1983). Therefore, in this context an attempt has been made to investigate selective flocculation of sulphides from a complex sulphide ore using a modified flocculant such as cellulose xanthate.
2. Experimental The complex sulphide ore used in this study was collected from the Rajpura-Dariba mines, Udaipur, Rajasthan. The samples analysed contained 6.73% zinc, 2.1% lead and 5.5% iron. Initially the samples were subjected to crushing and grinding to produce 100% passing of 75-~m size fractions. The size analysis of the ground product is given in Table 1.
2.1. Synthesis of cellulose xanthate The cellulose xanthate was prepared according to the method described by Rao
Table 1 Size analysis of the sample Size (Ixm)
Under
Size (Izm)
In band
188 87.2 53.5 37.6 28.12 21.5 16.7 13.0 10.1 7.88 6.15 4.83 3.80 3.02 2.41 1.94
100 100 99.6 92.2 86.6 77.8 66.9 57.0 46.9 37.8 29.6 23.3 16.6 9.8 5.8 3.4
188-87.2 87.2-53.5 53.5-37.6 37.6-28.1 28.1-21.5 21.5-16.7 16.7-13.0 13.0-10.1 10.1-7.88 7.88-6.15 6.15-4.83 4.83-3.80 3.80-3.02 3.02-2.41 2.41-1.94
0.0 0.4 7.4 5.6 8.8 10.9 9.9 10.1 9.1 8.2 6.3 6.6 6.8 4.0 2.4
N.R. Mandre, .D. Panigrahi / lnt. J. Miner. Process. 50 (1997) 177-186
179
(1971) ~md Attiya and Kitchener (1975). For this purpose, 4 - 5 g of filter paper was soaked in 18% sodium hydroxide for 2 h to separate a-cellulose (insoluble form of cellulose. The excess alkali was filtered and the residue was squeezed out to remove all solution. Further, the residue was treated with 2 - 4 ml of carbon disulphide using a closed container. The resultant mass was agitated with 4% sodium hydroxide for 3 to 4 h and filtered to remove undissolved solid particles. The filtrate obtained was used for the flocculation studies. 2.2. Flocculation tests
The ground complex sulphide ore has been subjected to flocculation tests which were carried out in a 500-ml graduated cylinder. For this purpose a desired amount of ore was mixed in 450 ml water and the pH of the slurry was adjusted by using dilute HC1 and NaOH. Then the slurry was thoroughly mixed by inverting the cylinder 10-12 times. After a thorough mixing of the particles, the cylinder was allowed to stand undisturbed. Further~ the slimes were siphoned out after noting the mudline height (interface between settled pulp and clear water). The slimes and the settled solids were collected separately, filtered, dried and analysed for lead and zinc using an AAS PU9000 of Phillips.
3. Resvtlts and discussions Prior to the selective flocculation process, initially some experiments were carded out to study settling charactersfics as well as effect of pH on the settling rate of the ground
5
o 10 */, Solids by wl. 5%
,,
,,
,,
/ /
[] 2°/ . . . . . . .
/
/
4
23
0
I
i
I
I
I
8
9
lO
I!
12
pH
Fig. 1. Effect of pH on settling rate at various pulp densities.
180
N.R. Mandre, .D. Panigrahi / lnt. J. Miner. Process. 50 (1997) 177-186
ioo ~(+)
~
~.
so o
,
,,
o
50
~
;
3
l
c
~
9
,
II
pH
~
lO0
150
~ "~..
zOO
\
250 Fig. 2. Zeta-potential of particle as a function of pH.
sulphide ore. For this purpose, an experimental method described by Thalmage and Fitch (1955) was used and the results of the tests are given in Fig. 1. From the results it may be seen that increase in pH increases the settling rate and a maximum settling rate of 4.9 c m / m i n was obtained at pH 11. Therefore, in all flocculation tests, a constant pH of 11 was maintained. In order to support the above findings some experiments were carried out to study the zeta-potential of the ore mineral under different conditions. During these studies, the zeta-potential of the system was analysed as a function of pH and flocculant dosage. The results of the experiments are given in Figs. 2 and 3, respectively. From Fig. 2 it may be seen that the particles show a negative potential throughout the pH range and their negative potential increases from - 4 6 to - 1 8 5 mV with increase in pH. From the
75
50
pH = I1
t+] 25
~' o ~ ( _ ) 25 50
0.2
0.4
0.6
0.8
~-0
Ftocculant conc. (ml)
~
Ioo 125
Fig. 3. Zeta-potential as a function of addition o f l % solution o f cellulose xanthate.
N.R. Mandre, .D. Panigrahi / Int. J. Miner. Process. 50 (1997) 177-186
O
Assay
•
Recovery
pH:l~ 2 */o Solids
3.0
~00
8_ o
2.
95
2.1
~
o
,,o
I
2~o
~.o
Flocculent
41o
s:o 90
cont.(rot )
Fig. 4. Recovery and grade of lead as a function of concentration of cellulose xanthate (1% solution).
10./.
O
Assoy
I
Recovery
p H = 11
20/0 Solids lO.O
100
99 '~
9.6
.g
.
~9.2
o 98 ~
,
~" cl
cr
8.8
97
8.4
96
8.0
d 0
,
,
,
,
1
2
3
4
95
F l o c c u l e n t conc. ( mr )
Fig. 5. Recovery and grade of zinc as a function of concentration of cellose xanthate (1% solution).
181
182
N.R. Mandre, .D. Panigrahi / lnt. J. Miner. Process. 50 (1997) 177-186
Table 2 Effect of washing of flocs Washings
1 2 3 4
Assay value (%)
Recovery (%)
Separation index
Pb
Zn
Pb
Zn
Pb
Zn
3.15 3.26 3.33 3.11
10.16 10.53 10.78 10.31
98.95 98.42 98.00 92.71
99.49 99.20 98.99 95.90
0.33 0.36 0.37 0.30
0.36 0.37 0.39 0.36
Pulp density 2%, flocculant dosage 2 ml of 1% solution.
literature it may be seen that the point of zero charge for pure silica is around pH 3, for sphalerite 7.5 and galena does not show any point of zero charge (Huntee, 1981; Termes et al., 1983). Therefore, at higher pH, flocculation of silica is more difficult as a higher surface charge keeps the particles apart. However, only sedimentation of individual silica particles occurs in the suspensions. In a complex system having sphaleritegalena-quartz-calcite, it is very difficult to selectively flocculate only sulphide minerals as observed by Yarrar and Kitchener (1970) at natural pH. This is mainly because even at a pH of 8, calcite is slightly positively charged whereas silica, sphalerite and galena are negatively charged. Hence, mutual coagulation of silica and calcite occurs at pH 8. However, by increasing the pH to 10-11, the zeta-potential of calcite may come into a negative range eliminating mutual coagulation between quartz and other sulphide
Wt. %
5olids : 2
of sodium silicote
0 2 kg/t 4 kglt
,,
6 kg/t
.
.
,,
4.0
g 8 kg/t
.
.
.
.
.
....
"
#_ o 3.s
3.0
~
i
1
2
3
4
No, of woshings Fig. 6. Grade of lead as a function of number of washings at different dosages of sodium silicate with 2 ml of
1% cellulose xanthat¢ soludon.
N.R. Mandre, .D. Panigrahi / lnt. J. Miner. Process. 50 (1997) 177-186
183
minerals. Therefore, based on these observations selective flocculation experiments were carried out at pH 11. Further, zeta-potential measurements were made as a function of flocculant concentration at pH I I. The results of the studies are given in Fig. 2. From the figure it may be seen that the increase in the flocculant dosage decreases the zeta-potential giving rise to the adsorption of the polymer. From the literature (Attiya and Kitchener, 1975) it may be seen that sulphydryl compounds like xanthate, dithio-carbonates and dithio-phosphates are known to form insoluble compounds with minerals such as galena and chalcopyrite. Also, the adsorption of these reagents on mineral surfaces is mainly due to selective chemisorption of the reagents. Additionally, their studies have also shown a marked selectivity of cellulose xanthate towards base metal sulphides. 3.1. Selective flocculation tests:
After completion of the above studies, investigations were extended to study selective flocculation of sulphides using cellulose xanthate. For this purpose, the experiments were caJaied out using different concentrations of the flocculant and the results are given in Figs. 4 and 5 for lead and zinc, respectively. From these figures it may be seen that a maximum recovery of 95% lead and 98% zinc assaying 3 and 10% can be obtained
13.0 Wt-°/o S01ids:2 o2 kg/t
of sodium s i l i c a l e
&4 kg/t
,,
r3 6 k g / t
....
• 8 kg/t
....
"
" "
]2.0
o
y ,.o
I
I
NO. of woshings Fig. 7. Grade of zinc as a function of number of washings at different dosages of sodium silicate with 2 n'd of
1% cellulose xanthate.
184
N.R. Mandre, .D. Panigrahi / lnt. J. Miner. Process. 50 (1997) 177-186
using 2 ml of 1% cellulose xanthate. Further, these results were analysed to assess the effectiveness of the flocculation by calculating separation indices individually for lead and zinc using the equation proposed by Sresty and Somasundaran (1980): SI = [(percentage of value minerals recovered in the concentrate)+ (percentage of gangue rejected in the tailings) - 100]/100. From the results it was observed that the separation indices vary from 0.3 to 0.35 for lead and zinc, respectively. In order to enhance the grade and recoveries of the sulphides, washing of the flocs was carried out. During these studies a four-stage cleaning technique was employed and the results are given in Table 2. From the table it may be seen that a maximum recovery of 98% lead and zinc can be obtained with grades of 3.3 and 10%, respectively, after three stages of cleaning. The separation indices obtained show a maximum value of 0.4 for both lead and zinc. However, further increasing the cleaning resulted into decreased index values which may be attributed to the breaking of the flocs resulting in the loss of value metal in the slimes. Further studies were carried out to know the effect of dispersant on selective flocculation of sulphides, since the degree of dispersion dictates the extent of gangue rejection. To accomplish this, studies were carried out using sodium silicate as dispersant. All these studies were carried out using different dosages of sodium silicate in the presence of 2 ml of 1% cellulose xanthate with four stages of cleaning. The results of
0.5 Wt.% Solids_- 2 o 2 kg/t of sodium silicate Z, k g / t
-
,,
"
, ~
X g~ 0.3
\ 0.2
~
1
,
I
2
3
4
No. of wQshlngs Fig. 8. Effect of washing on separation index for galena.
N.R. Mandre, .D. Panigrahi / Int. J. Miner. Process. 50 (1997) 177-186
185
Wt.% Solids:2 O 2 Kg/t
No-Silicate
L~ 4 K g / t [] 6 Kg/t
"
• 8 Kg/t
"
0.5
•-~ 0.4
0.3
I
I
i
i
1
2
3
4
NO. of woshings
Fig. 9. Effect of washing on separation index for sphalerite.
the studies are given in Figs. 6 and 7 for lead and zinc, respectively. From these figures it may be seen that there is an increase in the grade of lead (3.8%) and zinc (12.16%) using 6 k g / t of dispersant after three stages of cleaning with a corresponding recovery of 95% for both. The analysis of separation indices (Figs. 8 and 9) shows maximum index values of 0.45 for lead and 0.48 for zinc. Therefore, it may be said that the use of dispersant increases the efficiency of the selective flocculation process.
4. Con,elusions Frora the above studies the following conclusions were drawn. (1) Studies carried out on settling rate of the particles show an increase in settling rate with increase in pH irrespective of the variation in solid content. (2) Experiments performed to know the effect of flocculant dosage indicated that best results can be obtained using 2 ml of 1% of flocculant for a pulp with 2% solid content. (3) The effect of cleaning of the floes as well as the addition of a dispersant improves the selective flocculation. A maximum improvement of 6.73 to 12.16% zinc and 2.1 to 3.8% lead with a recovery of 99% was achieved with the addition of 2 ml of 1% cellulo,;e xanthate and 6 k g / t of sodium silicate after three stages of cleaning.
186
N.R. Mandre, .D. Panigrahi / lnt. J. Miner. Process. 50 (1997) 177-186
Acknowledgements T h e f i n a n c i a l s u p p o r t g i v e n b y the C o u n c i l o f Scientific a n d I n d u s t r i a l R e s e a r c h o n ' S e l e c t i v e f l o c c u l a t i o n o f c o m p l e x s u l p h i d e s ' is a c k n o w l e d g e d .
References Acar, S., Somasundaran, P., 1985. Effect of dissolved mineral species on flocculation of sulphides. Miner. Metall. Process. 2 (2), 231-235. Attiya, Y.A., 1982. Fine particle separation by selective flocculation. Sep. Sci. Technol. 17 (3), 485-493. Attiya, Y.A., Fuerstenau, D.W., 1978. Principles of separation of ore minerals by selective flocculation. Recent Dev. Sep. Sci. 4 (5), 51-68. Attiya, Y.A. and Kitchener, J.A., 1975. Development of complexing polymers for selective flocculation of copper minerals. Proc. 1 lth Int. Mineral Processing Congress, pp. 1233-1248. Drzymala, J., Fuerstenau, D.W., 1981. Selective flocculation of hematite in hematitic-quartz-ferric ion polyacryl acid system, I. Activation and Deactivation of quartz. Int. J. Miner. Process., 8: 265-277. Huntee, T.K., 1981. The use of synthetic flocculants in mineral processing and hydrometallurgy. International Symposium on Beneficiation and Agglomeration, Bhubaneswar, pp. 6.41. 1-6.41.8. Jawed Mohammed, Tare Vinod, 1991. Application of starch xanthates for cadmium removal: a comparative evaluation. J. Appl. Polymer Sci., 42: 317-324. Marabini, A., Barbaro, M., Falbo, A., 1988. Possibility of starches using selective flocculation of a ruffle ore In: Y.A. Attiya, B.M. Moudgil, S. Chander (Editors), Interfacial Phenomena in Bio-Technology and Material Processing. Elsevier Amsterdam, pp. 345-361. Mariyani, R.D., Nelson, A.T., 1993. Silica fotation at the Tilden Mines. In: D. Malhotra (Editor), Flotation Plants, Are They Optimised? SME, Littleton, CO, pp. 119-122. Moudgil, B.M., Shah, B.D., 1987. Single and mixed mineral flocculation behaviour of apatite and dolomite. In: Y.A. Attiya (Editor), Flocculation in Biotechnology and Separation Systems. Elsevier, Amsterdam, pp. 729-739. Pradip, Moudgil, B.M., 1991. Selective flocculation of tribasic calcium phosphate from mixtures with quartz using polyacrylic acid flocculant. Int. J. Miner. Process., 32: 271-281. Pradip, Attiya, Y.A., Fuerstenau, D.W., 1980. Adsorption of polyacrytamide flocculants on apatites. Colloid Polymer Sci. 258, 1343-1353. Rao, S.R., 1971. Xanthate and Related Compounds. Marcel Dekker, New York, 464 pp. Ravishankar, S.A., Pradip, Khosla, N.K., 1995. Selective flocculation of iron oxides from its synthetic mixtures with clays: a comparison of polyacrylic acid and starch polymers. Int. J. Miner. Process., 43: 235-247. Singh, B.P., Das, B., Bhima Rao, R., 1992. Flocculation studies on redmud using polyacryl amide. Trans. I.I.M. 20 (90), 1-33. Sresty, G.C., Somasundaran, P., 1980. Selective flocculation of synthetic mineral mixtures using modified polymers. Int. J. Miner. Process. 6, 303-320. Termes, S.C., Wilfong, R.L., 1985. Flocculation of Metal Oxides and Hydroxide Minerals With Cross Linked Starches Containing Chelating Groups. U.S. Bureau of Mines, Pittsburgh, PA, R/8944. Termes, S.C., Wilfong, R.L., Richardson, P.E., 1983. Flocculation of Sulphide Mineral Fines by Insoluble Cross Linked Starch Xanthate. U.S. Bureau of Mines, Pittsburgh, PA, RI 8819. Thalmage, W.P., Fitch, E.B., 1955. Determining thickener unit areas. Ind. Eng. Chem., 47:38 pp. Yarrar, B., Kitchener, J.A., 1970. Selective flocculation of minerals. Trans. I.M.M., Sect. C, 79: 23-33.