STUDY OF THE EXTRACTION OF GOLD(III) IN AQUEOUS HYDROCHLORIC-ACID MEDIA BY THE PHOSPHINE OXIDE CYANEX-925

The extraction of gold(III) from hydrochloric acid solutions by means of the phosphine oxide Cyanex 925 was studied as a function of differe nt variables: equilibration time, temperature, organic diluent, and co ncentration of gold, Cyanex 925, HCl, etc.; the system is selective wi th respect to the extraction of a number of metals. Gold(III) equilibr ium loading isotherms were also obtained at 20 degrees C. Experimental data were treated numerically showing that gold extraction can be exp lained assuming the formation of a complex with the general stoichiome try: HAuCl(4)L(2), where L represents the extractant. For the extracti on reaction log K-ext(o) = 8.1. The stripping of gold from loaded orga nic phases can be achieved with water. Data on the extraction of HCl b y Cyanex 925 are also presented.