BATCH BIOOXIDATION OF A GOLD-BEARING PYRITE ARSENOPYRITE CONCENTRATE

Batch biooxidation data were obtained for a gold-bearing arsenopyrite-pyrite concentrate at 12% solids, pH of 1.6 and temperature of 40-degrees-C. The specific rates of biooxidation of arsenopyrite and pyrite were found to be very similar at 0,15 d-1 or as mass rates, for arsenopyrite 2,1 kg m-3 d-1 and pyrite 6,5 kg m-3 d-1. However, it was found that the biooxidation of arsenopyrite preceded that of pyrite and was almost complete before the oxidation of pyrite commenced. Data were also obtained for four narrow size fractions prepared from the bulk concentrate. Sequential oxidation of arsenopyrite and pyrite was observed for all size fractions. The oxidation rate obtained from the linear portion of the curve was found to have a linear dependence on surface area concentration suggesting that area-based rates are more appropriate for characterizing biooxidation kinetics. The logistic equation was found to be a good fit to all the data obtained. It was found that gold liberation was linearly dependent upon the extent of arsenic oxidation. However, sulphide oxidation appeared to be preferential in the gold-rich regions, leading to a non-linear dependence of gold liberation on extent of sulphide oxidation.