Optimal conditions for ammonia leaching of copper/chalcocite-rimmed pyrite: Part 1

Oxidative ammoniacal leaching of copper/chalcocite-rimmed pyrite has been studied with the aim of searching for the optimal conditions for the separation of the pyrite that would preclude the formation of ammonium sulphate, the main drawback of the process. As the Redox Quotient (RQ) was varied, the resulting leached products were analyzed and the pH of the leached solution measured. At ambient temperature and a molar ratio of Cu:NH3 = 1:4, it was observed that the amount of oxidant (H2O2) supplied during the leaching process determines the maximum or minimum yield of copper. It has been found that the leaching process is most selective with respect to both copper and zinc when no external oxidant is supplied (RQ = 0). The optimum leaching of copper and zinc occurred at RQ = 2. It has been shown that at RQ = 8, no appreciable amounts of ammonium sulphate was formed and that the pH of the leached solutions, the yields of Cu and Zn, and the selectivity of the leaching process with respect to both Cu and Zn, are all periodic functions of the severity of the oxidation environment, as measured by RQ. It has also been demonstrated that even small deviations away from the maxima on the curves can significantly affect the process yield and selectivity negatively. This research showed that the more concentrated the leaching ammonia, the better the copper extraction and that it was more advantageous to do the extraction in multiple cycles in a single operation.