Selective Leaching of Gold from Copper Anode Slime Using Concentrated Hydrochloric Acid and Hydrogen Peroxide

Leaching of copper anode slime using hydrochloric acid (HCl) and hydrogen peroxide (H2O2) is performed to recover Au. It is imperative to reduce the amount of the costly oxidizing agent, H2O2, used in this leaching. In conventional conditions, the Se contained in the slime is oxidized and dissolved by the leachant as well as Au. If Au alone can be selectively leached, it should reduce the use of H2O2. The calculation of equilibrium potentials showed that when the concentration of HCl is high, it is possible for Au to be selectively leached, while the dissolution of Se is suppressed. The selective leaching of Au was demonstrated by experiments using 8 mol L-1 and 12 mol L-1 HCl solutions with various amounts of added H2O2. In the selective leaching, the increase in the leaching rate of Au with increasing amounts of H2O2 diminished after the leaching rate reached 80%. This may be because Au remained inside the Se particles, and the contact between Au and the leachant was physically inhibited by the Se layer encompassing the Au atoms. However, a leaching rate of Au of greater than 95% was achieved, even when the leaching rate of Se was less than 30%. From these results, it was confirmed that the use of H2O2 can be reduced by the selective leaching of Au compared to the cases in which all Se in the slime is dissolved.