Abstract:Arsenopyrite was artificially added into the thiosulfate leaching solution to clarify the role of arsenopyrite on the thiosulfate leaching of gold. The effect of arsenopyrite on the thiosulfate leaching of gold was studied by the thermodynamic calculation, mineral dissolution test, leaching test and XPS analysis. The results show that the thiosulfate consumption slightly increases with increasing the concentration of arsenopyrite, but the gold dissolution is obviously hindered. This may mainly attribute to the catalytic effect of arsenopyrite on the thiosulfate decomposition and the formation of passivation layer on the gold foil surface. The passivation layer likely consists of Cu₂S or Cu(S₂O₃)₃^5-, element S, FeOOH and iron arsenate, which is deduced from the XPS analysis. However, the negative effect of arsenopyrite can be eliminated by adding additives. It is found that both additives of sodium carboxymethyl (CMC) and sodium phosphate (SHPP) can not only decrease the thiosulfate consumption but also improve the gold dissolution.

Key words: gold leaching; thiosulfate; arsenopyrite; passivation