The solvent extraction system Au(III) — HCl-Cyanex 471X

The effectiveness of Cyanex 471X as extractant of gold(III) from hydrochloric acid solutions is demonstrated. The extraction system is endothermic and experimental variables, such as extractant concentration, organic diluent and hydrochloric acid concentration, influence it. Maximum gold extraction is obtained in the range of 1–3 M HCl concentrations. Equilibrium loading isotherms showed that the [Cyanex 47lX]/[Au (III)] molar relationship in the organic phase is near l.5, which is the probable stoichiometry of the extracted species defined by HAUCl4L (log Kext° = 3.79) and HAUCI4L2 (log Kext° = 6.34), L representing the organic extractant. The system seems to be suitable for the selective extraction of gold. Stripping of the metal can only be accomplished using sodium thiosulphate solutions, the corresponding reaction also being endothermic.CSIC (Spain) is acknowledged for support of this work.Peer reviewe