Pressure leaching of decopperized copper electrorefining anode slimes in strong acid solution

Anode slimes contain precious metals like silver, gold and platinum group metals (PGMs), base metals including copper, selenium, tellurium and nickel as well as other impurity elements. In order to recover valuable elements, it is important to be able to eliminate undesirable ones (e.g. Pb, Sb and Bi) at the initial stage. The aim of this study was to investigate the pressure leaching of pressure leached copper-free anode slimes in the laboratory-scale. Secondary autoclave leaching was performed in a strong acid medium with oxygen purging in order to dissolve residual copper, nickel and bismuth as well as other elements in a controlled way. Leaching tests showed that Cu, Ni, Bi, As, Te and Se were partially dissolved during the secondary autoclave leaching. The extraction of different metals showed the following variations: copper 65-100%, nickel 57-98%, bismuth 53-82%, arsenic 16-61%, tellurium =58% and selenium =57%. Furthermore, the effect of process conditions on the extraction of these elements was investigated using factor and regression analysis. The process variables investigated were: temperature (80-120 °C), partial pressure of oxygen (2-8 bar), sulfuric acid concentration (30-70 vol%) and solid concentration (200-400 g/dm3). Based on the regression analysis, a valid model for the dissolution of arsenic during secondary leaching could be built.