Abstract
The partition of gold from hydrochloric acid solutions by the phosphine oxide Cyanex 921 has been studied. The extraction system is exothermic (ΔH° = −44.6 kJ/mol), the extraction being influenced by several variables. Maximum gold extraction is obtained in the HCl concentration range 5–7 M. Experimental data were analyzed numerically using the program LETAGROPDISTR. The results showed that the extraction can be explained assuming the formation of the species HAUCl 4L (log K° = 1.99) and HAuCl 4L 2 (log K° = 6.68) in the organic phase, where L represents the organic extractant. From the experimental data the interaction coefficients for (AuCl 4 −1, H +) were estimated. Gold stripping is achieved effectively with water and the reaction is endothermic (ΔH°= 16.9 kJ/mol). Results on the extraction of HCl by Cyanex 921 are also presented.
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