A model for the dissolution of metal sulphides under oxidative ammonia leaching conditions has been presented. The dissolution is assumed to follow surface reaction with shrinking core model. Ammonia molarity is chosen in a range where metal sulphide dissolution becomes independent of its concentration. The rate constant is calculated from absolute reaction rate theory. In case the oxidative dissolution of metal sulphide is enhanced due to the presence of any compound (a catalyst), an empirical factor can be introduced in the rate equation. The model was tested for oxidative ammonia leaching of pure zinc sulphide in presence of galena. Good agreement has been observed for experimentally observed extractions and the predicted values. The main limitation of the model is that: it does not provide any insight into the mechanism of dissolution reactions.
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