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Adsorption studies of gold on copper sulphide
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hydrometallurgy ELSEVIER
Hydrometallurgy 36 (1994) 385-391
Technical Note
Adsorption studies of gold on copper sulphide M. Sarwar, Sumra N a e e m Pakistan Council of Scientific and Industrial Research, FerozpurRoad, Lahore-54600, Pakistan Received 25 February 1993; revision accepted 28 January 1994
Abstract
In this investigation, an attempt has been made to study the adsorption of gold from dilute solutions on to copper sulphide. It was observed that gold is adsorbed on copper sulphide at low pH; 1 g of copper sulphide has the capacity to adsorb 400 mg of gold. This was then recovered by the zinc cementation method. The adsorption is also dependent on the concentration of gold in solution. Recovery of gold of 100% can be achieved from any solution. The method can be used for the extraction of gold from its minerals. Copper, iron, molybdenum, chromium are not adsorbed on copper sulphide at low pH while silver is adsorbed along with gold.
1. Introduction The adsorption-desorption technique is used for the separation of precious metals from minerals and also for the pre-concentration of certain metal ions on to certain adsorbent surfaces. The adsorption technique was studied by Harris, Byrn and Barry [ I ] for the recovery of gold from acidic solution using polyacrylate ester as adsorbent. The acidic solution was oxidised with H202 to Au 3+ before the extraction. Macheskey and co-workers [2 ] studied the adsorption of gold(Ill) chloride and gold (I) thiosulphate anions by goethite. This adsorption was pH dependent. In 0.01 M NaNo3 at pH 4, the adsorption isotherm of gold chloride showed a maximum adsorption density (210 #mol Au/g). However, in 0.01 and 0.1 M NaC1, adsorption increased from pH 4 to 7. The maximum adsorption density for Au ($203) 3at pH 4 in 0.01 MNaNo3 was only 35/zmol Au/g and decreased to 15/zmol/g in 0.1 M NaNO3. Adsorption decreased as pH was increased from 4 to 8. Other workers have also investigated the adsorption of gold and silver with 353E ion exchange resins (Peking Chemical Works) [ 3 ]. The adsorption of gold and silver 0304-386X/94/$07.00 © 1994 Elsevier Science B.V. All rights reserved SSD10304-386X (94) 00010-Z
386
M. Sarwar, S. Naeem / Hydrometallurgy 36 (1994) 385-391
cyanide reached a maximum value at pH 8.5-I 1 and no further adsorption was possible. Complete adsorption was achieved in 10 min contact time from solutions containing 50mg/1 Au or Ag. A thiourea/H2SO4 solution was used for the elution of gold and silver. The adsorption of gold cyanide complexes on activated carbon had also been studied by Thomas et al. [ 4 ]. This adsorption depended upon the initial complex concentration, temperature, carbon mesh size, amount of carbon, mixing speed and gases in contact with the solution. The equilibrium and the adsorption rate were affected by some of the chemical species present in solution. The kinetics of the gold loading from gold (III) chloride solution on to fresh activated coconut carbon has been studied [ 5 ] and gold was found to be deposited from gold (III) chloride solution as metallic gold on the surface of the carbon particles. The surface reaction for fresh GR22 carbon was rapid and the kinetics were first order. The adsorption of gold(I) cyanide on activated carbon was also studied using micro-analysis and X-ray photoelectron spectroscopy [ 6 ]. The effect of the presence of a clay laterite ore pulp (20-40 wt%) on the adsorption rate of gold on activated carbon was studied by Jones and Linge [ 7]. The reduction in the rate of adsorption appears to be caused by two effects: permanent carbon pore blocking by ore particles and temporary shielding of the carbon particles surface. The kinetics of adsorption of gold and zinc cyanide on to a strong base anion exchange resin using a mini-column technique has also been described [8 ]. Experimental breakthrough curves were successfully simulated using a model which included external film transfer and intraparticle surface diffusion. It was shown that, although gold was kinetically favoured and loaded more rapidly on to the resin, equilibrium considerations caused zinc to displace gold. Feasibility studies for the removal of heavy metals from waste water have been carried out using bentonite modified with clay tetramethyl ammonium ion [ 9 ]. This showed an increased adsorption capacity for the removal of lead and chromium. The linear partition coefficient for these two metal ions was increased by a factor of 18.4 and 1.4, respectively. The adsorption-desorption on goethite (FeO.OH) in aqueous suspension was investigated thermodynamically and kinetically [ 10 ]. The sulphate adsorption isotherm indicated that adsorption decreased with increased pH of the goethite suspension. It was found that the adsorption of sulphate on goethite occurred simultaneously with the protonation of neutral surface sites. The adsorption of cadmium in the presence of alkaline earth metals have been investigated with emphasis on the Cd-Ca binary system [ 11 ]. The adsorbent used in these studies was Fe203"H20 (amorphous). Adsorption of Cd increased with increasing calcium concentration at ionic strengths of 0.5 and 0.1 M, whereas there was no increase in Cd adsorption at ionic strenghts of 0.05 and 0.005 M. Finally, the adsorption of MoO4 ions has been studied on alumina [ 12 ]. Adsorption occurred at alkaline pH values. It was observed that, with the addition of various amounts of Na and Li in the alumina suspension, its sorption capacity increased. This might be due to the increase in the protonated hydroxyl ion on
M. Sarwar, S. Naeem / Hydrometallurgy 36 (1994) 385-391
387
the surface of adsorbent.The interaction between the adsorbed MoO4 also increased with the extent of adsorption. In this investigation gold in trace amounts was adsorbed on to CuS and separated by cementation with zinc metal. The technique is simple and is applicable to minerals containing gold.
2. Experimental
2.1. Reagents All reagents used in the experimental work were of analytical grade. The following reagents were employed: a 0.1 g/1 gold chloride stock solution was prepared from a 10% gold chloride solution (Merck). A 0.1% solution of O-toluidine was prepared in 10% hydrochloric acid solution. A 5% solution of sodium cyanide was used in the experiments. Buffer solutions from pH 1.0 to 7.0 were prepared using different molarities of hydrochloric acid, sodium chloride, potassium chloride, sodium acetate, potassium bicarbonate and ammonium oxalate. Wherever possible single salt buffers were preferred.
2.2. Experimental procedures Copper sulphide was prepared by dissolving copper sulphate in distilled water, acidifying it with hydrochloric acid and passing H2S gas into this solution until the precipitation was complete. The precipitate was left for 48 h for ageing. It was then filtered and washed with distilled water until no traces of metal were detected in the filtrate. The precipitate was then dried completely in an oven at 300°C for 4 h. This copper sulphide was used as adsorbent for the preconcentration of trace amounts of gold in the experiments. The copper sulphide precipitate was ground to 200 mesh before use. To 0.1 g of copper sulphide. 200 ml of 0.1 g/1 gold solution was added. The contents were stirred for 15 min. The solution was filtered through Whatman 41 paper and the precipitate was washed with distilled water. The filtrate was made up to the required volume and the concentration of gold at equilibrium in solution was determined. The amount of gold adsorbed was then determined spectrophotometrically.
3. Results and discussion The parameters pH, time, temperature and initial concentration of gold on adsorption were studied. It was observed that adsorption was highest at pH 1.0 and lowest at pH 7.0 (Table 1 ). It has been observed that stirring time has a clear effect on the adsorption of gold. The adsorption rate was faster in the first hour, then it slowed down gradually (Fig. 1 ). It was found that at higher temperature
M. Sarwar, S. Naeem / Hydrometallurgy 36 (1994) 385-391
388
Table 1 Effect ofpH on adsorption of Au on CuS at 23 °C
pH
Amount of Au taken (mg)
Amount of Au in solution at equilibrium (mg)
Amount of Au adsorbed on CuS (rag)
Adsorption (%)
1.0 2.25 4.20 5.70 7.00
20.0 20.0 20.0 20.0 20.0
7.20 11.75 16.68 19.12 20.00
12.80 8.25 3.32 0.88 0.00
64 41 17 4 0
Table 2 Effect of temperature on adsorption of Au on CuS at pH 1 Temperature Amount of Au taken Amount of Au in solution Amount of Au adsorbed Adsorption (°C) (rag) at equilibrium on CuS (%) (mg) (mg)
23 40 55
20,0 20.0 20.0
7.20 5.38 3.70
12.80 14.60 16.30
64 73 82
Table 3 Effect of initial concentration of gold on adsorption at pH 1 and 2 3 °C
Amount of adsorbent taken (mg)
Initialconc. of Au Conc. of Au at equilibrium Amount of Au Adsorption taken (mg) adsorbed (%) (mg) (mg)
100.00 100.00 100.00
40.00 50.00 60.00
8.70 8.75 9.34
31.30 41.25 50.66
78 82 85
the rate of adsorption increased (Table 2 ). The concentration of adsorbed gold increased with increasing concentration of this metal in solution (Table 3); it appears that it is a physical phenomenon. Adsorption isotherms were constructed at different temperatures keeping the working pH constant (Fig. 2 ). The Freundlich isotherm describes the adsorption according to the following relationship:
(Co - C ) / m = K C ~/n where Co = the initial concentration of gold ions in solution; C = the concentration of gold ions where the equilibrium was reached; m = the amount of copper sulphide used (g/100 ml); K and n = empirical constants. When log (Co- C)/m was plotted against log C a straight line was found, showing that the Freundlich equation is satisfied. There was little deviation from the rule so far as temperature dependence is concerned; there was a slight increase in adsorption with ris-
M. Sarwar, S. Naeem / Hydrometallurgy 36 (1994) 385-391
389
110
r-~ Eli CC)
I00
O--~--O
J
0 r'~
8(] n
lJ 0 roll
1,0
20
I
~
--J
-
-
TIME
IN
HOURS
Fig. 1. The effect of time on the adsorption of gold on copper sulphide (pH = 1.0, temperature = 23 °C ). Table 4 Recover of gold from copper sulphide at pH 1 and 23 °C
Amount of Au adsorbed on CuS (mg)
Amount of adsorbent (mg)
Amount of gold recovered (mg)
Recovery (%)
0.5 1.0 1.5 2.0 3.0
100.00 100.00 100.00 100.00 100.00
0.48 0.98 1.47 1.97 3.00
96 97 98 98.5 100
ing temperature. After a rise of 17 ° C the adsorption only increased by 9% (Table 2 ), which may be attributed to renewed surface area, due to a rise in temperature and agitation. Heterogenicity of the adsorbent system may also contribute to this sort of deviation. However, adsorption markedly increases with time and reaches a maximum value of over 95%. 3.1. Procedurefor recovery of goMfrom coppersulphide After the adsorption of gold, copper sulphide was dissolved in 5% sodium cyanide solution. This solution was treated with zinc dust and gold was then sepa-
390
M. Sarwar, S. Naeem / Hydrometallurgy 36 (1994) 385-391 0,000
1000
IE
100
*¢~
I0
0
1'0
100 log
c
1(300
b
Fig. 2. The Freundlich adsorption isotherm for the adsorption of gold on CuS.
rated as metal by reduction with zinc. The excess of zinc was dissolved in hydrochloric acid and gold as metal was separated. The metallic gold was then dissolved in aqua regia and determined spectrophotometrically. The results are given in Table 4.
3.2. Effect of other metal ions on the adsorption of gold It has been observed that copper, iron, molybdenum and chromium(VI) are not adsorbed on copper sulphide at the pH where gold is adsorbed. However, silver is adsorbed, which can be further separated from gold. Silver has been separated from gold by using 2 M NHO3.
References [ I ] Hams, G.B., Jeans, P. and Monette, S., Europ. Pat. Appl. EP-408 185 ( 1991 ) [2] Machesky, M.L., Audrade, O.W., Rose, O.A. and Arthur, W., Geochim. Cosmochim. Acta, 55 (1991): 769-776. [3] Thou, Yu.L. and Thou, Q., Youkuongue, 9 ( 1990): 55-59. [ 4 ] Zarrouki, M. and Thomas, G., J. Phys. Chim. Biol., 87 (1990): 1715-1762. [ 5 ] Hughes, H.C. and Linge, H.G., Hydrometallurgy, 22 (1989): 57-65.
M. Sarwar, S. Naeem / Hydrometallurgy 36 (1994) 385-391
391
[6] Cook, R., Crathorne, E.A., Monhemius, A.J. and Perry, D.L., Hydrometallurgy, 22 (1989): 171-182. [ 7 ] Jones, W.G. and Linge, H.G., Hydrometallurgy 22 (1989 ): 231-238. [ 8 ] Young, B.D., Bryson, A.W. and Glover, M.R.L., Hydrometallurgy, 22 ( 1991 ): 151-162. [9] Cadena, F., Rizvi, R. and Peters, R., Ind. Waste, 22 ( 1990): 77-94. [ 10] Zhang, P. and Spark, D., Soil Sci. Soc. Am. J., 54 ( 1990): 1266-1273. [ 11 ] Cowan, E.C., Zachara, M.R. and Rosch, C., Environ. Sci. Technol., 25 ( 1991 ): 437-446. [ 12] Vordonis, L., Kontsonkos, P.G. and Lycoughiotis, A., Coll. Surf., 50 ( 1990): 353-361. [ 13 ] Nicol, M.J., Schalch, E., Balestra, P.E.L. and Hegedus, H., J.S. Aft. Inst. Min. MetalI., 79 ( 1979 ): 191.
hydrometallurgy ELSEVIER
Hydrometallurgy 36 (1994) 385-391
Technical Note
Adsorption studies of gold on copper sulphide M. Sarwar, Sumra N a e e m Pakistan Council of Scientific and Industrial Research, FerozpurRoad, Lahore-54600, Pakistan Received 25 February 1993; revision accepted 28 January 1994
Abstract
In this investigation, an attempt has been made to study the adsorption of gold from dilute solutions on to copper sulphide. It was observed that gold is adsorbed on copper sulphide at low pH; 1 g of copper sulphide has the capacity to adsorb 400 mg of gold. This was then recovered by the zinc cementation method. The adsorption is also dependent on the concentration of gold in solution. Recovery of gold of 100% can be achieved from any solution. The method can be used for the extraction of gold from its minerals. Copper, iron, molybdenum, chromium are not adsorbed on copper sulphide at low pH while silver is adsorbed along with gold.
1. Introduction The adsorption-desorption technique is used for the separation of precious metals from minerals and also for the pre-concentration of certain metal ions on to certain adsorbent surfaces. The adsorption technique was studied by Harris, Byrn and Barry [ I ] for the recovery of gold from acidic solution using polyacrylate ester as adsorbent. The acidic solution was oxidised with H202 to Au 3+ before the extraction. Macheskey and co-workers [2 ] studied the adsorption of gold(Ill) chloride and gold (I) thiosulphate anions by goethite. This adsorption was pH dependent. In 0.01 M NaNo3 at pH 4, the adsorption isotherm of gold chloride showed a maximum adsorption density (210 #mol Au/g). However, in 0.01 and 0.1 M NaC1, adsorption increased from pH 4 to 7. The maximum adsorption density for Au ($203) 3at pH 4 in 0.01 MNaNo3 was only 35/zmol Au/g and decreased to 15/zmol/g in 0.1 M NaNO3. Adsorption decreased as pH was increased from 4 to 8. Other workers have also investigated the adsorption of gold and silver with 353E ion exchange resins (Peking Chemical Works) [ 3 ]. The adsorption of gold and silver 0304-386X/94/$07.00 © 1994 Elsevier Science B.V. All rights reserved SSD10304-386X (94) 00010-Z
386
M. Sarwar, S. Naeem / Hydrometallurgy 36 (1994) 385-391
cyanide reached a maximum value at pH 8.5-I 1 and no further adsorption was possible. Complete adsorption was achieved in 10 min contact time from solutions containing 50mg/1 Au or Ag. A thiourea/H2SO4 solution was used for the elution of gold and silver. The adsorption of gold cyanide complexes on activated carbon had also been studied by Thomas et al. [ 4 ]. This adsorption depended upon the initial complex concentration, temperature, carbon mesh size, amount of carbon, mixing speed and gases in contact with the solution. The equilibrium and the adsorption rate were affected by some of the chemical species present in solution. The kinetics of the gold loading from gold (III) chloride solution on to fresh activated coconut carbon has been studied [ 5 ] and gold was found to be deposited from gold (III) chloride solution as metallic gold on the surface of the carbon particles. The surface reaction for fresh GR22 carbon was rapid and the kinetics were first order. The adsorption of gold(I) cyanide on activated carbon was also studied using micro-analysis and X-ray photoelectron spectroscopy [ 6 ]. The effect of the presence of a clay laterite ore pulp (20-40 wt%) on the adsorption rate of gold on activated carbon was studied by Jones and Linge [ 7]. The reduction in the rate of adsorption appears to be caused by two effects: permanent carbon pore blocking by ore particles and temporary shielding of the carbon particles surface. The kinetics of adsorption of gold and zinc cyanide on to a strong base anion exchange resin using a mini-column technique has also been described [8 ]. Experimental breakthrough curves were successfully simulated using a model which included external film transfer and intraparticle surface diffusion. It was shown that, although gold was kinetically favoured and loaded more rapidly on to the resin, equilibrium considerations caused zinc to displace gold. Feasibility studies for the removal of heavy metals from waste water have been carried out using bentonite modified with clay tetramethyl ammonium ion [ 9 ]. This showed an increased adsorption capacity for the removal of lead and chromium. The linear partition coefficient for these two metal ions was increased by a factor of 18.4 and 1.4, respectively. The adsorption-desorption on goethite (FeO.OH) in aqueous suspension was investigated thermodynamically and kinetically [ 10 ]. The sulphate adsorption isotherm indicated that adsorption decreased with increased pH of the goethite suspension. It was found that the adsorption of sulphate on goethite occurred simultaneously with the protonation of neutral surface sites. The adsorption of cadmium in the presence of alkaline earth metals have been investigated with emphasis on the Cd-Ca binary system [ 11 ]. The adsorbent used in these studies was Fe203"H20 (amorphous). Adsorption of Cd increased with increasing calcium concentration at ionic strengths of 0.5 and 0.1 M, whereas there was no increase in Cd adsorption at ionic strenghts of 0.05 and 0.005 M. Finally, the adsorption of MoO4 ions has been studied on alumina [ 12 ]. Adsorption occurred at alkaline pH values. It was observed that, with the addition of various amounts of Na and Li in the alumina suspension, its sorption capacity increased. This might be due to the increase in the protonated hydroxyl ion on
M. Sarwar, S. Naeem / Hydrometallurgy 36 (1994) 385-391
387
the surface of adsorbent.The interaction between the adsorbed MoO4 also increased with the extent of adsorption. In this investigation gold in trace amounts was adsorbed on to CuS and separated by cementation with zinc metal. The technique is simple and is applicable to minerals containing gold.
2. Experimental
2.1. Reagents All reagents used in the experimental work were of analytical grade. The following reagents were employed: a 0.1 g/1 gold chloride stock solution was prepared from a 10% gold chloride solution (Merck). A 0.1% solution of O-toluidine was prepared in 10% hydrochloric acid solution. A 5% solution of sodium cyanide was used in the experiments. Buffer solutions from pH 1.0 to 7.0 were prepared using different molarities of hydrochloric acid, sodium chloride, potassium chloride, sodium acetate, potassium bicarbonate and ammonium oxalate. Wherever possible single salt buffers were preferred.
2.2. Experimental procedures Copper sulphide was prepared by dissolving copper sulphate in distilled water, acidifying it with hydrochloric acid and passing H2S gas into this solution until the precipitation was complete. The precipitate was left for 48 h for ageing. It was then filtered and washed with distilled water until no traces of metal were detected in the filtrate. The precipitate was then dried completely in an oven at 300°C for 4 h. This copper sulphide was used as adsorbent for the preconcentration of trace amounts of gold in the experiments. The copper sulphide precipitate was ground to 200 mesh before use. To 0.1 g of copper sulphide. 200 ml of 0.1 g/1 gold solution was added. The contents were stirred for 15 min. The solution was filtered through Whatman 41 paper and the precipitate was washed with distilled water. The filtrate was made up to the required volume and the concentration of gold at equilibrium in solution was determined. The amount of gold adsorbed was then determined spectrophotometrically.
3. Results and discussion The parameters pH, time, temperature and initial concentration of gold on adsorption were studied. It was observed that adsorption was highest at pH 1.0 and lowest at pH 7.0 (Table 1 ). It has been observed that stirring time has a clear effect on the adsorption of gold. The adsorption rate was faster in the first hour, then it slowed down gradually (Fig. 1 ). It was found that at higher temperature
M. Sarwar, S. Naeem / Hydrometallurgy 36 (1994) 385-391
388
Table 1 Effect ofpH on adsorption of Au on CuS at 23 °C
pH
Amount of Au taken (mg)
Amount of Au in solution at equilibrium (mg)
Amount of Au adsorbed on CuS (rag)
Adsorption (%)
1.0 2.25 4.20 5.70 7.00
20.0 20.0 20.0 20.0 20.0
7.20 11.75 16.68 19.12 20.00
12.80 8.25 3.32 0.88 0.00
64 41 17 4 0
Table 2 Effect of temperature on adsorption of Au on CuS at pH 1 Temperature Amount of Au taken Amount of Au in solution Amount of Au adsorbed Adsorption (°C) (rag) at equilibrium on CuS (%) (mg) (mg)
23 40 55
20,0 20.0 20.0
7.20 5.38 3.70
12.80 14.60 16.30
64 73 82
Table 3 Effect of initial concentration of gold on adsorption at pH 1 and 2 3 °C
Amount of adsorbent taken (mg)
Initialconc. of Au Conc. of Au at equilibrium Amount of Au Adsorption taken (mg) adsorbed (%) (mg) (mg)
100.00 100.00 100.00
40.00 50.00 60.00
8.70 8.75 9.34
31.30 41.25 50.66
78 82 85
the rate of adsorption increased (Table 2 ). The concentration of adsorbed gold increased with increasing concentration of this metal in solution (Table 3); it appears that it is a physical phenomenon. Adsorption isotherms were constructed at different temperatures keeping the working pH constant (Fig. 2 ). The Freundlich isotherm describes the adsorption according to the following relationship:
(Co - C ) / m = K C ~/n where Co = the initial concentration of gold ions in solution; C = the concentration of gold ions where the equilibrium was reached; m = the amount of copper sulphide used (g/100 ml); K and n = empirical constants. When log (Co- C)/m was plotted against log C a straight line was found, showing that the Freundlich equation is satisfied. There was little deviation from the rule so far as temperature dependence is concerned; there was a slight increase in adsorption with ris-
M. Sarwar, S. Naeem / Hydrometallurgy 36 (1994) 385-391
389
110
r-~ Eli CC)
I00
O--~--O
J
0 r'~
8(] n
lJ 0 roll
1,0
20
I
~
--J
-
-
TIME
IN
HOURS
Fig. 1. The effect of time on the adsorption of gold on copper sulphide (pH = 1.0, temperature = 23 °C ). Table 4 Recover of gold from copper sulphide at pH 1 and 23 °C
Amount of Au adsorbed on CuS (mg)
Amount of adsorbent (mg)
Amount of gold recovered (mg)
Recovery (%)
0.5 1.0 1.5 2.0 3.0
100.00 100.00 100.00 100.00 100.00
0.48 0.98 1.47 1.97 3.00
96 97 98 98.5 100
ing temperature. After a rise of 17 ° C the adsorption only increased by 9% (Table 2 ), which may be attributed to renewed surface area, due to a rise in temperature and agitation. Heterogenicity of the adsorbent system may also contribute to this sort of deviation. However, adsorption markedly increases with time and reaches a maximum value of over 95%. 3.1. Procedurefor recovery of goMfrom coppersulphide After the adsorption of gold, copper sulphide was dissolved in 5% sodium cyanide solution. This solution was treated with zinc dust and gold was then sepa-
390
M. Sarwar, S. Naeem / Hydrometallurgy 36 (1994) 385-391 0,000
1000
IE
100
*¢~
I0
0
1'0
100 log
c
1(300
b
Fig. 2. The Freundlich adsorption isotherm for the adsorption of gold on CuS.
rated as metal by reduction with zinc. The excess of zinc was dissolved in hydrochloric acid and gold as metal was separated. The metallic gold was then dissolved in aqua regia and determined spectrophotometrically. The results are given in Table 4.
3.2. Effect of other metal ions on the adsorption of gold It has been observed that copper, iron, molybdenum and chromium(VI) are not adsorbed on copper sulphide at the pH where gold is adsorbed. However, silver is adsorbed, which can be further separated from gold. Silver has been separated from gold by using 2 M NHO3.
References [ I ] Hams, G.B., Jeans, P. and Monette, S., Europ. Pat. Appl. EP-408 185 ( 1991 ) [2] Machesky, M.L., Audrade, O.W., Rose, O.A. and Arthur, W., Geochim. Cosmochim. Acta, 55 (1991): 769-776. [3] Thou, Yu.L. and Thou, Q., Youkuongue, 9 ( 1990): 55-59. [ 4 ] Zarrouki, M. and Thomas, G., J. Phys. Chim. Biol., 87 (1990): 1715-1762. [ 5 ] Hughes, H.C. and Linge, H.G., Hydrometallurgy, 22 (1989): 57-65.
M. Sarwar, S. Naeem / Hydrometallurgy 36 (1994) 385-391
391
[6] Cook, R., Crathorne, E.A., Monhemius, A.J. and Perry, D.L., Hydrometallurgy, 22 (1989): 171-182. [ 7 ] Jones, W.G. and Linge, H.G., Hydrometallurgy 22 (1989 ): 231-238. [ 8 ] Young, B.D., Bryson, A.W. and Glover, M.R.L., Hydrometallurgy, 22 ( 1991 ): 151-162. [9] Cadena, F., Rizvi, R. and Peters, R., Ind. Waste, 22 ( 1990): 77-94. [ 10] Zhang, P. and Spark, D., Soil Sci. Soc. Am. J., 54 ( 1990): 1266-1273. [ 11 ] Cowan, E.C., Zachara, M.R. and Rosch, C., Environ. Sci. Technol., 25 ( 1991 ): 437-446. [ 12] Vordonis, L., Kontsonkos, P.G. and Lycoughiotis, A., Coll. Surf., 50 ( 1990): 353-361. [ 13 ] Nicol, M.J., Schalch, E., Balestra, P.E.L. and Hegedus, H., J.S. Aft. Inst. Min. MetalI., 79 ( 1979 ): 191.