Pyrargyrite (Ag3SbS3): Silver and antimony dissolution by ozone oxidation in acid media

Silver and antimony leaching from pyrargyrite (Ag3SbS3) by ozone in acid media was experimentally studied in order to evaluate this method as an alternative to the conventional cyanidation. When 1 g pyrargyrite was leached in 800 mL of 0.18 M sulfuric and 0.079 g O3/L gas was bubbled, it was observed that after 80% of metals dissolution the silver and antimony dissolution rates decreased until completely stopping. These results suggest the presence of a solid product layer onto the unreacted pyrargyrite cores. The SEM-EDS and XRD analysis showed that antimony oxides were formed as a layer covering the surface of pyrargyrite particles, hindering reactants transferring/diffusion to the unreacted surface. The chemical composition of the layer was identified as a silver/antimony oxide AgxSb2Oy (x = 0.51 ± 0.04 and y = 6.08 ± 0.43). For low solid/liquid ratios the pyrargyrite dissolution reached about 98%, however, for high solid/liquid ratios a maximum value of antimony concentration was found to be around 0.0008 mol/L. An activation energy of 27.88 kJ/mol was calculated, which is a typical value for mixed-control systems. The kinetic study showed that the controlling step changed as the reaction proceeds. The oxidation pretreatment with ozone is a promising alternative for pyrargyrite dissolution, currently under development.