Copper extraction from chalcopyrite: Comparison of three non-sulfate oxidants, hypochlorous acid, sodium chlorate and potassium nitrate, with ferric sulfate

• Three reagents, hypochlorous acid, chlorate and nitrate, were assessed for their ability to oxidise chalcopyrite.
• All systems tested offered improved rates of copper extraction relative to systems utilising ferric sulfate as an oxidant.
• Hypochlorous acid was the most aggressive oxidant trialled, with copper extraction reaching a plateau after 1–5 h.
• Optimal conditions utilising chlorate as an oxidant measured final extractions of 66–72% after 168 h.
• Optimal conditions utilising nitrate enabled a final extraction of 92% in systems using milled ore.

Three oxidants, hypochlorous acid, chlorate and nitrate, were assessed for their ability to oxidise chalcopyrite (CuFeS2). Hypochlorous acid was the most aggressive oxidant trialled, with copper extraction reaching a plateau after 1–5 h. Extraction in this system was complete at room temperature when reagent concentrations of 0.3–0.4 M were supplied. Optimal conditions utilising chlorate as an oxidant measured final extractions of 66–72% after 168 h. Optimal conditions utilising nitrate enabled a final extraction of 92% in systems using milled ore. Gangue dissolution in the presence of each oxidant varied. The system utilising nitrate resulted in comparatively high levels of magnesium and aluminium extraction, 28% and 32%, respectively. The chlorate system, over an identical time period and similar solution pH, had magnesium and aluminium extractions of 7% and 6%. These data, together with those for silicon dissolution, are indicative of incongruent silicate dissolution. Iron extraction data indicated that ferric hydroxy-oxide precipitates formed during leaching in both nitrate and chlorate systems. All systems tested offered improved rates of copper extraction relative to systems utilising ferric sulfate as an oxidant.