| Summary: | A study has been made of the behaviour of pyrite and wolframite when leached in sodium hydroxide solutions. Oxygen was essential to both systems but the mechanisms of behaviour during leaching was different; with pyrite the reaction rate was controlled by the interaction of oxygen atoms at the mineral surface, and with wolframite, a small quantity of oxygen resulted in extensive mineral dissolution, the oxygen not being consumed by reaction between mineral and reactant ions. In the leaching of pyrite, determinations were made of the energy of activation and order of reaction with respect to reactant ions. The important aspect of both systems was the "in situ" deposition of the insoluble products of dissolution on the parent mineral. The nature and porosity of the product was critically affected by the leaching environment and their density and porosity controlled the rate of diffusion of reactants through the product and, therefore, the rate of mineral dissolution. Microscopic and X-ray studies have been made of the partially leached residues from which useful evidence regarding the reaction mechanisms and nature of the insoluble product has been obtained. Of particular importance is the structural relationship between pyrite and iron oxides of the cubic system and the apparent topotactic transformation from pyrite, through wustite and magnetite configuration to maghemite.
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