Catalytic effect of pyrite on the leaching of arsenopyrite in sulfuric acid and acid culture medium

In this study, the influence of pyrite on the leaching of arsenopyrite in sulfuric acid and iron-free 9K medium was investigated by leaching experiments and electrochemical analysis. During acid leaching, the addition of pyrite resulted in the further oxidation of arsenopyrite, for the reason that the galvanic interaction made the pH increase and redox potential decrease, and then the formation of arsenate precipitates with high crystallinity was depressed. While leaching in iron-free 9K medium, the buffer action keeping the pH stable promoted arsenopyrite dissolution as compared with acid leaching. And the addition of pyrite facilitated the arsenic extraction, but increasing the amount of pyrite added had no distinct impact on the further leaching of arsenopyrite. Electrochemical studies revealed that the presence of pyrite increased the conductivity of electrodes and electrolytes, verifying the catalytic effect of galvanic interaction on arsenopyrite leaching. Additionally, in the sulfuric acid electrolyte, the addition of pyrite also decreased the thickness of passivation layer on the arsenopyrite surface, confirming that the formation of ferric arsenate precipitates with high crystallinity was inhibited in the presence of pyrite. Therefore, the pyrite-promoted arsenopyrite oxidation in sulfuric acid was due to the galvanic effect and the control of pH and redox potential, whereas that in culture medium was only associated with the galvanic effect. Moreover, the electrochemical measurements also showed that the oxidation of elemental sulfur was the rate controlling step for arsenopyrite dissolution.