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Liquid-solid extraction of gold(III) from aqueous chloride solutions by macroporous resins impregnated with triisobutyl phosphine sulfide (Cyanex 471)
Reactive Polymers, 17 (1992) 69-73
69
Elsevier Science Publishers B.V., Amsterdam
LIQUID-SOLID EXTRACTION OF GOLD(III) FROM AQUEOUS CHLORIDE SOLUTIONS BY MACROPOROUS RESINS IMPREGNATED WITH TRIISOBUTYL PHOSPHINE SULFIDE (CYANEX 471) I. VILLAESCUSA a, V. SALVADO t~*, j . DE PABLO c, M. VALIENTE d and M. AGUILAR c
a Enginyeria Qubnica, Escola Universitaria Polit~cnica, Avda. Santal6 s/n, 17003 Girona (Spain) b Qufmica, Estudi General de Girona (U.A.B.), P~a. Hospital, 6, 17071 Girona (Spain) c Enginyeria Qufmica, E.T.S.E.LB. (U.P.C.), Avda. Diagonal, 647, 08028 Barcelona (Spain) d Qulmica Analltica, Universitat Aut6noma de Barcelona, 08193 Bellaterra, Barcelona (Spain) (Received December 5, 1990; accepted in revised form October 3, 1991)
The extraction of Au(III) from chloride solutions using the macroporous resins XAD-2 and XAD-7 impregnated with triisobutylphosphine sulfide (TIBPS) has been studied. Two different resins have been employed as solid support, i.e., polystyrene Amberlite XAD-2 and polyacrylate Amberlite XAD-7 which showed a similar capacity for the adsorption of TIBPS. Both impregnated XAD-2 and XAD-7 adsorbs Au(III) to a considerable extent (95%); the impregnation of XAD-7 does not increase the percentage of extraction (95%) obtained by the resin itself. The effect of chloride ion concentration on the metal adsorption process at the different resins has been studied. The results indicate that impregnated XAD-2 is independent on chloride ion concentration up to 1.0 mol d m - 3 while experiments with XAD-7 in the presence of different amounts of HCl (1-6 mol dm - 3) showed that Au(III) extraction increases up to 1.0 mol dm - 3 where a plateau region is reached. This behaviour is explained by two different extraction mechanisms. In the case of impregnated XAD-2, the formation of the species AuCI 3 • 2TIBPS may be the driving force, while in the case of XAD-7, the formation of the ion pair R-COOH ÷AuCI 4 is postulated and the extraction related to both the formation of the species AuCl 4 in the aqueous phase and to the existence of the positive counterion which is generated via a hydrolytic mechanism.
Keywords: gold extration, impregnated resins, Cyanex-471
INTRODUCTION
* To whom correspondence should be addressed.
The use of polymeric materials impregnated with extraction reagents offers many
0923-1137/92/$05.00 © 1992 - Elsevier Science Publishers B.V. All rights reserved
70 advantages over the use of liquid-liquid extraction, due to characteristics of the solid phase [1]. The impregnated solid support has the same chemical properties as the solvent extraction systems and an improved efficiency. In this context, recent studies [2,3] have shown a lot of similarities between both processes. So, XAD-2 impregnated with ethylene glycol dibutylether (a selective reagent for gold) has been employed in the separation of gold either from metal base or from precious metals [4]. On the other hand, Amberlite XAD-7 can adsorb Au(III) from dilute solutions of hydrochloric acid in the presence of small amounts of precious metals [5]. Recently, liquid-liquid extraction of gold from acidic chloride media by organic solutions containing triisobutylphosphine sulfide, TIBPS (Cyanex 471) has been studied [6]. The results have shown that the extent of gold extraction is very high and the extraction process seems to occur via a solvating mechanism, where AuCI 3 • 2TIBPS is postulated to be the predominant species. Hence, in the present study the extraction of gold with two different polymeric solid supports impregnated by organic solution of TIBPS has been undertaken. The object of the work was to study both the impregnation procedure and the extraction capacity under different experimental conditions. In order to understand the chemical behaviour of the different extraction systems, additional experimental information about the influence of the ionic medium has been collected.
EXPERIMENTAL Reagents and solutions of Au(III)
Stock solutions of Au(III) were prepared from solid H A u C I 4 (Merck A.R.). Solutions containing Au(III) (3-50 ppm) with total aqueous chloride of 0.1-1.0 mol dm -3 were employed. NaC1 and HC1 (Merck, A.R.) were
I. Villaescusa et al. / React. Polym. 17 (1992) 69-73
used to adjust the pH and the ionic strength of the gold solutions Cyanex 471, triisobutylphosphine sulfide (TIBPS), kindly supplied by American Cyanamide Co., was purified by recrystallization. Organic solution of Cyanex 471 in an ethanol-water (2: 1) mixture were used as impregnation solutions (100-1600 ppm). Solutions of KSCN, Na2S20 3 and thiourea (Merck, A.R.) (0.001 to 1.0 mol dm -3) were used in gold stripping procedures. The organic solvents ethanol and methanol (Merck, A.R.) were used without further purification. Amberlite XAD-2 and Amberlite XAD-7 were purified with a 4.0 mol dm-3 HCI solution and, after elimination of chlorides by washing with water, with a methanol-water (1 : 1) solution and washed with water again. Method of investigation Impregnation process The impregnations of the polymeric XAD2 and XAD-7 beads were carried out by using the "wet method" described elsewhere [7]. In this method, appropiated amounts of dry XAD-2 or XAD-7 were placed into Cyanex 471 (20 ml) organic solutions at different concentrations for 2 h, when equilibrium was reached. The impregnated resins were separated from the solution by filtration through a porous filter using a water pump, and washed several times with distillated water. The content of Cyanex 471 in the remaining organic solution was determined by gas chromatography. The results of the XAD-2 and XAD-7 impregnation by Cyanex 471 are respectively collected in Figs. 1 and 2. As seen, the highest values for both resins is about 16 mg Cyanex 471/g resin. Gold extraction processes In order to study the extraction of Au(III) by the impregnated supports, a weighed amount (0.1-0.3 g) of XAD-2 or XAD-7
I. Villaescusa et al./ React. Polym. 17 (1992) 69-73
71 17 []
0 0
a ,< X
O
El [] 0
16 [] 15
0 o
10" []
qr
o
i
[] []
[]
E
14 13
0 12
o
11
20"o0
1000
ppm G~a~x 471
4O0
[]
6c;o
8~o
lo'oo
I~'oo
~,'oo
ppm Cyanex 471
Fig. 1. Impregnation of XAD-2 resin with organic solutions of Cyanex 471 in ethanol-water. The highest value for this resin is about 16 mg Cyanex 471/g resin.
Fig. 2. Impregnation of XAD-7 resin with organic solutions of Cyanex 471 in ethanol-water. The highest value for this resin is about 16 mg Cyanex 471/g resin.
resin impregnated by Cyanex 471 was placed in contact with Au(III) solutions. The time for equilibrium was determined for each system under similar experimental conditions by periodical analysis of Au(III) adsorbed by the resin. The equilibrium was achieved in 30 min in all cases. The reproducibility of this process was verified. After equilibrium was attained, Au(III) was determined in the aqueous phase by AAS. In separate experiments, the adsorption of the metal by the XAD-2 and XAD-7 resins was studied. In
both cases, gold in the resin phase was determined after stripping with KSCN solutions. Figures 3 and 4 show the results of these experiments comparing the gold adsorption by Cyanex 4 7 1 / X A D - 2 or Cyanex 471/XAD-7 resins with respect to the solid supports without impregnation. In the first case (Fig. 3), the solvent-impregnated resin improved the extent of the extraction process. In contrast to these results, Cyanex 471/XAD-7 resin does not change the effi-
3-
X
<
E
0
0
O
[]
,'0
[]
[]
n
i"1
2'o
3'0
4'0
ppm A u (111)
Fig. 3. Adsorption of Au(III) by XAD-2 resin. Full points represent the gold adsorption by Cyanex 471/XAD-2 when the resin has 16 mg Cyanex 471/g XAD-2 compared to the gold adsorption by XAD-2 resin under identical conditions.
I. 1411aescusa et al. /React. Polym. 17 (1992) 69-73
72 60"
in 50-
g
0 0
O X
[]
? a < X
•
8
__~ 3o"
g
<
1.0.
0 • O
0.8.
0
Ell
0
0,8.
u
i
D
0,4'
E 10'
1;0
200
300
400
,'0
600
5;0
mg Cyanex-4711g XAD-2
ppm Au(lll)
Fig. 5. Effect of impregnated Cyanex 471 in XAD-2 at two different ionic strength on the adsorption of Au(III) (16.3 ppm): (U) I = 0 . 1 M; (m) •=0.5 M NaC1. (o) 1 M HC1.
Fig. 4. Adsorption of Au(III) by XAD-7 resin. Squares represent the gold adsorption by Cyanex 471/g XAD-7 when the resin has 16 nag Cyanex 471/g XAD-7 compared to the gold adsorption by XAD-7 resin under identical conditions.
Figure 5 shows that at ionic strengths of 0.1 and 1.0 M NaCI, the extent of the adsorption is similiar. However, when XAD-7 polymeric resin was used to adsorb the metal, the influence of hydrochloric acid concentration of the aqueous gold solutions on the adsorption process was tested from 0.1 to 6.0 M (Fig. 6). In this case, the extraction increases until 1 M HC1 where a plateau region is reached.
ciency of gold extraction obtained by the non-impregnated support (Fig. 4).
Effect of the ionic strength The ionic strength of gold solutions in NaC1 was varied in order to know how the adsorption of gold by the impregnated Cyanex 471/XAD-2 resins was influenced. 13-
[] 12 ¸
< x
0
[]
O
!
4o
D
O 11
o~
A
_=
[]
< E
8
o,o
~io
|
2,o
3,o
i
i
s,o
!
s,o
HCI c o n c e n t r a t i o n
Fig. 6. Effect of aqueous HCI concentration on the adsorption of Au(III) by XAD-7 polymeric resin. Solutions of Au(III) (63.4 ppm) were employed in these experiments. The adsorption of Au(III) by this resin from aqueous 3.0 M HNO3 and HCIO4 solutions were too low and they are out of the scale.
73
I. Villaescusa et al./React. Polym. 17 (1992) 69-73
DISCUSSION The results obtained in this work indicate that impregnation of both resins by the wet m e t h o d using Cyanex 471 is succesful and reaches a maximum level at 16 mg Cyanex 4 7 1 / g resin. In this process both type of solid supports behave similary. Concerning the gold extraction, reversibility of the adsorption process is assumed on the basis of the reproducibility of the experimental data u n d e r equal experimental conditions. The adsorption process can be reversed by adding complexing agents of Au(III), i.e., S C N - or thiourea [8], to the aqueous solutions and can be loaded afterwards to the same extent. The different behaviour of the two extraction systems has been attributed to the characteristics of the solid polymers. While the XAD-2 structure is based on polystyrene beads, the XAD-7 structure includes acrylic ester groups ( R - C O O ) . So, XAD-2 resin behaves as a non-active support and the extraction of gold seems to be governed by the strong interaction between the impregnation agent, Cyanex 471 (TIBPS), and AuC13 species as has been described in ref. 6. U n d e r these conditions, the addition of different amounts of C l - ions does not seem to contribute to the formation of new species which may increase the amount of gold in the resin or to produce a displacement in the main extraction reaction. The extraction of gold with Cyanex 4 7 1 / X A D - 7 may be attributed to the action of the polymer itself. In this sense, the literature [5] indicates that the resin which contains weak ester groups may form a hydrolytic product of the type R - C O O H + and is able to extract Au(III) in the form AuCI 4 via an ion-pair mechanism. The results of the experiments varying HC1 concentration (1.06.0 M ) agree with this explanation. Figure 6
shows that gold extraction is i n d e p e n d e n t of acid concentration w h e n HCI is 1.0 M where both the formation of the species AuCl 4 and the polymeric cation are assumed to be completely formed. Furthermore, information on the extraction of gold at [HNO 3] = 3.0 mol dm -3 and [HCIO 4] --3.0 mol dm -3 (Fig. 6) showed insignificant metal extraction indicating that the process is i n d e p e n d e n t of H + ion activity.
ACKNOWLEDGEMENTS This work has been supported by CICYT (Ministerio de Educaci6n y Ciencia, Spain). The assistence of Mr. Benet Garriga with the laboratory work is gratefully acknowledged.
REFERENCES 1 D.S. Flett, Resin impregnates: the current position, Chem. Ind. (London), (1977) 641. 2 I. Villaescusa, M. Aguilar, J. de Pablo, V. Salvad6 and M. Valiente, ISEC'90, 1991 (in press). 3 J.L. Cortina, N. Miralles, A. Sastre and M. Aguilar, ISEC'90, 1991 (in press). 4 A. Warshawsky, Polystyrene impregnated with ethers. A polymeric reagent selective for gold, Talanta, 21 (1974) 962. 5 R. Edwards, A.K. Haines and W.A.M. Te Triele, Separation of gold from acidic leach liquors with Amberlite XAD-7, in: M. Streat (Ed.), The Theory and Practice of Ion Exchange, Society of Chemical Industry, London, 1976, pp. 40.1-40.12. 6 V. Salvad6, M. Hidalgo, A. Masana, M. Mufioz, M. Valiente and M. Muhammed, Extraction of gold(III) from hydrochloric acid solutions by triisobutylphosphine sulfide in toluene. Solv. Extr. Ion Exch., 8 (1990) 491. 7 A. Warshawsky and A. Patchornik, Recent developments in metal extraction by solvent impregnated resins, in: M. Streat (Ed.), The Theory and Practice of Ion Exchange, Society of Chemical Industry, London, 1976, pp. 38.1-38.4. 8 Comprehensive Inorganic Chemistry, Vol. 3, Pergamon, Oxford, 1973.
69
Elsevier Science Publishers B.V., Amsterdam
LIQUID-SOLID EXTRACTION OF GOLD(III) FROM AQUEOUS CHLORIDE SOLUTIONS BY MACROPOROUS RESINS IMPREGNATED WITH TRIISOBUTYL PHOSPHINE SULFIDE (CYANEX 471) I. VILLAESCUSA a, V. SALVADO t~*, j . DE PABLO c, M. VALIENTE d and M. AGUILAR c
a Enginyeria Qubnica, Escola Universitaria Polit~cnica, Avda. Santal6 s/n, 17003 Girona (Spain) b Qufmica, Estudi General de Girona (U.A.B.), P~a. Hospital, 6, 17071 Girona (Spain) c Enginyeria Qufmica, E.T.S.E.LB. (U.P.C.), Avda. Diagonal, 647, 08028 Barcelona (Spain) d Qulmica Analltica, Universitat Aut6noma de Barcelona, 08193 Bellaterra, Barcelona (Spain) (Received December 5, 1990; accepted in revised form October 3, 1991)
The extraction of Au(III) from chloride solutions using the macroporous resins XAD-2 and XAD-7 impregnated with triisobutylphosphine sulfide (TIBPS) has been studied. Two different resins have been employed as solid support, i.e., polystyrene Amberlite XAD-2 and polyacrylate Amberlite XAD-7 which showed a similar capacity for the adsorption of TIBPS. Both impregnated XAD-2 and XAD-7 adsorbs Au(III) to a considerable extent (95%); the impregnation of XAD-7 does not increase the percentage of extraction (95%) obtained by the resin itself. The effect of chloride ion concentration on the metal adsorption process at the different resins has been studied. The results indicate that impregnated XAD-2 is independent on chloride ion concentration up to 1.0 mol d m - 3 while experiments with XAD-7 in the presence of different amounts of HCl (1-6 mol dm - 3) showed that Au(III) extraction increases up to 1.0 mol dm - 3 where a plateau region is reached. This behaviour is explained by two different extraction mechanisms. In the case of impregnated XAD-2, the formation of the species AuCI 3 • 2TIBPS may be the driving force, while in the case of XAD-7, the formation of the ion pair R-COOH ÷AuCI 4 is postulated and the extraction related to both the formation of the species AuCl 4 in the aqueous phase and to the existence of the positive counterion which is generated via a hydrolytic mechanism.
Keywords: gold extration, impregnated resins, Cyanex-471
INTRODUCTION
* To whom correspondence should be addressed.
The use of polymeric materials impregnated with extraction reagents offers many
0923-1137/92/$05.00 © 1992 - Elsevier Science Publishers B.V. All rights reserved
70 advantages over the use of liquid-liquid extraction, due to characteristics of the solid phase [1]. The impregnated solid support has the same chemical properties as the solvent extraction systems and an improved efficiency. In this context, recent studies [2,3] have shown a lot of similarities between both processes. So, XAD-2 impregnated with ethylene glycol dibutylether (a selective reagent for gold) has been employed in the separation of gold either from metal base or from precious metals [4]. On the other hand, Amberlite XAD-7 can adsorb Au(III) from dilute solutions of hydrochloric acid in the presence of small amounts of precious metals [5]. Recently, liquid-liquid extraction of gold from acidic chloride media by organic solutions containing triisobutylphosphine sulfide, TIBPS (Cyanex 471) has been studied [6]. The results have shown that the extent of gold extraction is very high and the extraction process seems to occur via a solvating mechanism, where AuCI 3 • 2TIBPS is postulated to be the predominant species. Hence, in the present study the extraction of gold with two different polymeric solid supports impregnated by organic solution of TIBPS has been undertaken. The object of the work was to study both the impregnation procedure and the extraction capacity under different experimental conditions. In order to understand the chemical behaviour of the different extraction systems, additional experimental information about the influence of the ionic medium has been collected.
EXPERIMENTAL Reagents and solutions of Au(III)
Stock solutions of Au(III) were prepared from solid H A u C I 4 (Merck A.R.). Solutions containing Au(III) (3-50 ppm) with total aqueous chloride of 0.1-1.0 mol dm -3 were employed. NaC1 and HC1 (Merck, A.R.) were
I. Villaescusa et al. / React. Polym. 17 (1992) 69-73
used to adjust the pH and the ionic strength of the gold solutions Cyanex 471, triisobutylphosphine sulfide (TIBPS), kindly supplied by American Cyanamide Co., was purified by recrystallization. Organic solution of Cyanex 471 in an ethanol-water (2: 1) mixture were used as impregnation solutions (100-1600 ppm). Solutions of KSCN, Na2S20 3 and thiourea (Merck, A.R.) (0.001 to 1.0 mol dm -3) were used in gold stripping procedures. The organic solvents ethanol and methanol (Merck, A.R.) were used without further purification. Amberlite XAD-2 and Amberlite XAD-7 were purified with a 4.0 mol dm-3 HCI solution and, after elimination of chlorides by washing with water, with a methanol-water (1 : 1) solution and washed with water again. Method of investigation Impregnation process The impregnations of the polymeric XAD2 and XAD-7 beads were carried out by using the "wet method" described elsewhere [7]. In this method, appropiated amounts of dry XAD-2 or XAD-7 were placed into Cyanex 471 (20 ml) organic solutions at different concentrations for 2 h, when equilibrium was reached. The impregnated resins were separated from the solution by filtration through a porous filter using a water pump, and washed several times with distillated water. The content of Cyanex 471 in the remaining organic solution was determined by gas chromatography. The results of the XAD-2 and XAD-7 impregnation by Cyanex 471 are respectively collected in Figs. 1 and 2. As seen, the highest values for both resins is about 16 mg Cyanex 471/g resin. Gold extraction processes In order to study the extraction of Au(III) by the impregnated supports, a weighed amount (0.1-0.3 g) of XAD-2 or XAD-7
I. Villaescusa et al./ React. Polym. 17 (1992) 69-73
71 17 []
0 0
a ,< X
O
El [] 0
16 [] 15
0 o
10" []
qr
o
i
[] []
[]
E
14 13
0 12
o
11
20"o0
1000
ppm G~a~x 471
4O0
[]
6c;o
8~o
lo'oo
I~'oo
~,'oo
ppm Cyanex 471
Fig. 1. Impregnation of XAD-2 resin with organic solutions of Cyanex 471 in ethanol-water. The highest value for this resin is about 16 mg Cyanex 471/g resin.
Fig. 2. Impregnation of XAD-7 resin with organic solutions of Cyanex 471 in ethanol-water. The highest value for this resin is about 16 mg Cyanex 471/g resin.
resin impregnated by Cyanex 471 was placed in contact with Au(III) solutions. The time for equilibrium was determined for each system under similar experimental conditions by periodical analysis of Au(III) adsorbed by the resin. The equilibrium was achieved in 30 min in all cases. The reproducibility of this process was verified. After equilibrium was attained, Au(III) was determined in the aqueous phase by AAS. In separate experiments, the adsorption of the metal by the XAD-2 and XAD-7 resins was studied. In
both cases, gold in the resin phase was determined after stripping with KSCN solutions. Figures 3 and 4 show the results of these experiments comparing the gold adsorption by Cyanex 4 7 1 / X A D - 2 or Cyanex 471/XAD-7 resins with respect to the solid supports without impregnation. In the first case (Fig. 3), the solvent-impregnated resin improved the extent of the extraction process. In contrast to these results, Cyanex 471/XAD-7 resin does not change the effi-
3-
X
<
E
0
0
O
[]
,'0
[]
[]
n
i"1
2'o
3'0
4'0
ppm A u (111)
Fig. 3. Adsorption of Au(III) by XAD-2 resin. Full points represent the gold adsorption by Cyanex 471/XAD-2 when the resin has 16 mg Cyanex 471/g XAD-2 compared to the gold adsorption by XAD-2 resin under identical conditions.
I. 1411aescusa et al. /React. Polym. 17 (1992) 69-73
72 60"
in 50-
g
0 0
O X
[]
? a < X
•
8
__~ 3o"
g
<
1.0.
0 • O
0.8.
0
Ell
0
0,8.
u
i
D
0,4'
E 10'
1;0
200
300
400
,'0
600
5;0
mg Cyanex-4711g XAD-2
ppm Au(lll)
Fig. 5. Effect of impregnated Cyanex 471 in XAD-2 at two different ionic strength on the adsorption of Au(III) (16.3 ppm): (U) I = 0 . 1 M; (m) •=0.5 M NaC1. (o) 1 M HC1.
Fig. 4. Adsorption of Au(III) by XAD-7 resin. Squares represent the gold adsorption by Cyanex 471/g XAD-7 when the resin has 16 nag Cyanex 471/g XAD-7 compared to the gold adsorption by XAD-7 resin under identical conditions.
Figure 5 shows that at ionic strengths of 0.1 and 1.0 M NaCI, the extent of the adsorption is similiar. However, when XAD-7 polymeric resin was used to adsorb the metal, the influence of hydrochloric acid concentration of the aqueous gold solutions on the adsorption process was tested from 0.1 to 6.0 M (Fig. 6). In this case, the extraction increases until 1 M HC1 where a plateau region is reached.
ciency of gold extraction obtained by the non-impregnated support (Fig. 4).
Effect of the ionic strength The ionic strength of gold solutions in NaC1 was varied in order to know how the adsorption of gold by the impregnated Cyanex 471/XAD-2 resins was influenced. 13-
[] 12 ¸
< x
0
[]
O
!
4o
D
O 11
o~
A
_=
[]
< E
8
o,o
~io
|
2,o
3,o
i
i
s,o
!
s,o
HCI c o n c e n t r a t i o n
Fig. 6. Effect of aqueous HCI concentration on the adsorption of Au(III) by XAD-7 polymeric resin. Solutions of Au(III) (63.4 ppm) were employed in these experiments. The adsorption of Au(III) by this resin from aqueous 3.0 M HNO3 and HCIO4 solutions were too low and they are out of the scale.
73
I. Villaescusa et al./React. Polym. 17 (1992) 69-73
DISCUSSION The results obtained in this work indicate that impregnation of both resins by the wet m e t h o d using Cyanex 471 is succesful and reaches a maximum level at 16 mg Cyanex 4 7 1 / g resin. In this process both type of solid supports behave similary. Concerning the gold extraction, reversibility of the adsorption process is assumed on the basis of the reproducibility of the experimental data u n d e r equal experimental conditions. The adsorption process can be reversed by adding complexing agents of Au(III), i.e., S C N - or thiourea [8], to the aqueous solutions and can be loaded afterwards to the same extent. The different behaviour of the two extraction systems has been attributed to the characteristics of the solid polymers. While the XAD-2 structure is based on polystyrene beads, the XAD-7 structure includes acrylic ester groups ( R - C O O ) . So, XAD-2 resin behaves as a non-active support and the extraction of gold seems to be governed by the strong interaction between the impregnation agent, Cyanex 471 (TIBPS), and AuC13 species as has been described in ref. 6. U n d e r these conditions, the addition of different amounts of C l - ions does not seem to contribute to the formation of new species which may increase the amount of gold in the resin or to produce a displacement in the main extraction reaction. The extraction of gold with Cyanex 4 7 1 / X A D - 7 may be attributed to the action of the polymer itself. In this sense, the literature [5] indicates that the resin which contains weak ester groups may form a hydrolytic product of the type R - C O O H + and is able to extract Au(III) in the form AuCI 4 via an ion-pair mechanism. The results of the experiments varying HC1 concentration (1.06.0 M ) agree with this explanation. Figure 6
shows that gold extraction is i n d e p e n d e n t of acid concentration w h e n HCI is 1.0 M where both the formation of the species AuCl 4 and the polymeric cation are assumed to be completely formed. Furthermore, information on the extraction of gold at [HNO 3] = 3.0 mol dm -3 and [HCIO 4] --3.0 mol dm -3 (Fig. 6) showed insignificant metal extraction indicating that the process is i n d e p e n d e n t of H + ion activity.
ACKNOWLEDGEMENTS This work has been supported by CICYT (Ministerio de Educaci6n y Ciencia, Spain). The assistence of Mr. Benet Garriga with the laboratory work is gratefully acknowledged.
REFERENCES 1 D.S. Flett, Resin impregnates: the current position, Chem. Ind. (London), (1977) 641. 2 I. Villaescusa, M. Aguilar, J. de Pablo, V. Salvad6 and M. Valiente, ISEC'90, 1991 (in press). 3 J.L. Cortina, N. Miralles, A. Sastre and M. Aguilar, ISEC'90, 1991 (in press). 4 A. Warshawsky, Polystyrene impregnated with ethers. A polymeric reagent selective for gold, Talanta, 21 (1974) 962. 5 R. Edwards, A.K. Haines and W.A.M. Te Triele, Separation of gold from acidic leach liquors with Amberlite XAD-7, in: M. Streat (Ed.), The Theory and Practice of Ion Exchange, Society of Chemical Industry, London, 1976, pp. 40.1-40.12. 6 V. Salvad6, M. Hidalgo, A. Masana, M. Mufioz, M. Valiente and M. Muhammed, Extraction of gold(III) from hydrochloric acid solutions by triisobutylphosphine sulfide in toluene. Solv. Extr. Ion Exch., 8 (1990) 491. 7 A. Warshawsky and A. Patchornik, Recent developments in metal extraction by solvent impregnated resins, in: M. Streat (Ed.), The Theory and Practice of Ion Exchange, Society of Chemical Industry, London, 1976, pp. 38.1-38.4. 8 Comprehensive Inorganic Chemistry, Vol. 3, Pergamon, Oxford, 1973.