Abstract:The effect of calcite and dolomite on the oxidation of pyrite was studied using batch-leaching experiments complemented with chemical modeling, solution analysis and solid characterization techniques. Leaching tests conducted at 80 °C and p(O₂)=1.013×10⁵ Pa and pH>13 showed that pyrite alkaline oxidation rate decreased in the presence of both calcite and dolomite, while more detrimental effect was observed in the case of calcite. FE-SEM/EDS analysis exhibited a surface layer containing Ca (in the case of calcite) and Mg (in the case of dolomite) on the pyrite surface, which justified the slowdown in pyrite leaching rate. This surface layer was formed due to partial dissolution of carbonate minerals, which was affected dominantly by the pH and temperature of the leaching solution based on the chemical modeling data. The surface layer was characterized as Ca or Mg hydroxide using XRD and FTIR analysis. It was also found that this layer was thin and continuous in the case of calcite while it was thick and discontinuous in the presence of dolomite.

Key words: pyrite; alkaline leaching; carbonate gangue; Carlin gold deposits