LIQUID SOLID EXTRACTION OF GOLD(III) FROM AQUEOUS CHLORIDE SOLUTIONS BY MACROPOROUS RESINS IMPREGNATED WITH TRIISOBUTYL PHOSPHINE SULFIDE (CYANEX-471)

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 dm-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 AuCl3 . 2TIBPS may be the driving force, while in the case of XAD-7, the formation of the ion pair R-COOH+ -AuCl4- is postulated and the extraction related to both the formation of the species AuCl4- in the aqueous phase and to the existence of the positive counterion which is generated via a hydrolytic mechanism.