GOLD EXTRACTION EQUILIBRIUM IN THE SYSTEM CYANEX 921 HCL-AU(III)

The partition of gold from hydrochloric acid solutions by the phosphin e oxide Cyanex 921 has been studied. The extraction system is exotherm ic (Delta H degrees = -44.6 kJ/mol), the extraction being influenced b y several variables. Maximum gold extraction is obtained in the HCl co ncentration range 5-7 M. Experimental data were analyzed numerically u sing the program LETAGROP-DISTR. The results showed that the extractio n can be explained assuming the formation of the species HAuCl4L (log K degrees = 1.99) and HAuCl4L2 (log K degrees = 6.68) in the organic p hase, where L represents the organic extractant. From the experimental data the interaction coefficients for (AuCl4-, H+) were estimated, Go ld stripping is achieved effectively with water and the reaction is en dothermic (Delta H degrees = 16.9 kJ/mol). Results on the extraction o f HCl by Cyanex 921 are also presented.