A MODEL FOR DISSOLUTION OF METAL SULFIDES UNDER OXIDATIVE AMMONIACAL CONDITIONS - ZNS-PBS-NH3-O-2 SYSTEM

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 i s chosen in a range where metal sulphide dissolution becomes independe nt of its concentration. The rate constant is calculated from absolute reaction rate theory. In case the oxidative dissolution of metal sulp hide 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 presen ce of galena. Good agreement has been observed for experimentally obse rved extractions and the predicted values. The main limitation of the model is that: it does not provide any insight into the mechanism of d issolution reactions.