Dissolution Rates of Au from Au-Zn Compounds Measured by Channel Flow Double Electrode Method

Anodic dissolution rates of Au and Zn from Au-Zn compounds (beta'-AuZn and gamma(2)-AuZn(3)) in 5 mol l(-1) hydrochloric acid were measured by channel flow double electrode method. Simultaneous dissolutions of Au and Zn were observed at potentials above 0.8 V from beta'-AuZn. The dissolution rate of Au from the compound at 1.0 V was about 10 times higher than that of pure Au. On the other hand, Zn dissolved preferentially from gamma(2)-AuZn(3) at all tested potentials between 0.1 and 1.2 V, and Au started to dissolve at around 0.9 V. Chronoamperometry at 1.0 V showed that dissolution of Au from gamma(2)-AuZn(3) was slower than that of pure Au at the earlier stage, but it accelerated gradually and eventually became faster than the dissolution of pure Au. An Au-enriched-layer consisting of beta'-AuZn and Au was generated with cracks at the compound surface during dissolution, and this morphological change explained the time variation of the dissolution rate. A more effective enhancement of Au dissolution was observed in beta'-AuZn than in gamma(2)-AuZn(3). The result demonstrated the effectiveness of a Zn vapor pretreatment for leaching of Au. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3494143] All rights reserved.