Bio-oxidation of pyrite during copper bioleaching in Zijinshan

During Zijinshan copper heap-leaching, lots of pyrite was leached and Fe³⁺ concentration was higher in solution with chalcocite and covellite leached. The oxidation behavior and mechanism of pyrite bioleaching, especially the chemical oxidation of Fe³⁺ and the influential factors of pyrite bioleaching were studied. The results showed that the pyrite leaching rate is 5%-8% when the pH value of solution was 1.6 and bacteria was in presence during composite leaching process at the initial stage. The redox potential of solution increases with the bioleaching time prolonging, After 15 d, when the redox potential was 500 mV, the pyrite leaching rate was over 25%. It was indicated that the higher redox potential was an important influential factor in pyrite bioleaching. The research on bioleaching mechanism showed that the indirect action of bacteria gave priority to the direct attack of microbial cells in pyrite bioleaching, and the attachment of bacteria to pyrite surface was synergetic effect to pyrite bioleaching.