Abstract
The development of the kinetic expression for the dissolution of a nickeliferous sulfide by ferric sulfate and of pyrite by oxygen and ferric sulfate on the basis of its oxidation mechanism is discussed. The rate of dissolution of complex ores is determined not only by the kinetics of the heterogenous reactions (solid-liquid reactions) but also by the homogenous reactions taking place simultaneously in the leach liquor. The liquid phase in a leaching system contains a large number of species which are simultaneously reacting with one another such as in acid-base and complexation reactions at near equilibrium or at equilibrium. The heterogenous mineral solid-leaching solution reactions are limited by the kinetics of dissolution and often do not reach equilibrium. During the leaching process, the concentrations of chemical species in the liquid phase adjust rapidly to the changes in the liquid phase analytical concentrations. Chemical equilibrium is maintained in the homogenous phase although the mineral-leach solution reactions are far from equilibrium. If the reactions of the solid with the leach solution is considered to take place in very small increments, the pertubations to the analytical concentrations within the liquid phase can adjust quickly and thus remain at equilibrium as the leaching reaction proceeds. Following the changes in the liquid phase concentrations during the leaching step can be useful in optimizing the dissolution process and specifying the influent conditions to achieve optimum conditions. It may also be possible to specify the conditions under which selective leaching can be attained. The partial equilibrium model is capable of characterizing the minerals dissolution reactions and the associated changes in solution species concentrations. The modeling of the dissolution of chalcopyrite by ferric sulfate, ilmenite by hydrochloric acid, uranium dioxide-pyrite by ferric sulfate-sulfuric acid, and uraninite by ammonmium carbonate-hydrogen peroxide systems are discussed.
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