A general model for leaching of one or more solid reactants from porous ore particles
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INTRODUCTION
M A N Y coarse-ore leaching processes involve the dissolution of one or more solid reactants from an inert porous matrix. In recent years, the modeling of such phenomena has received much attention, especially as it applies to the large-scale leaching processes of copper sulfide ores. Braun e t al. tll derived a model for leaching of primary sulfide ores which assumed steady-state diffusion of dissolved oxygen as the rate-controlling factor, resulting in the formation of a narrow "reaction zone" which moves slowly toward the center of the ore fragments, similar to the familiar "shrinking core" model for gas-solid reactions, t2~ This model, which incorporates empirical rate enhancement parameters, was shown to fit experimental leaching data over a wide range of particle sizes and shape slt'3J and has subsequently been used as a basis for modeling large-scale in s i t u leaching processes.t4~ Models of copper sulfide leaching have not been limited to the shrinking core type. A more general model involving the unsteady-state continuity equation for dissolved oxygen in spherical coordinates was devised by Bartlett tSl to describe the leaching kinetics of low-grade chalcopyrite ores. In a low-grade ore, the rate of diffusion is often fast compared to the reaction rate, so that reaction occurs homogeneously throughout the particle. This model assumes a log-normal size distribution of spherical copper sulfide grains distributed evenly throughout the pore structure. A modified version of this model was later verified experimentally in autoclave leaching tests, t6] A similar model, which assumes the steady-state diffusion of ferric ion to be rate controlling, was derived by Madsen and Wadsworth tTj and included separate rate terms for a number of different copper sulfide minerals, as well as empirical rate enhancement parameters. While most of the attention has been focused on sulfides, several models have been developed to describe D.G. DIXON, Doctoral Candidate, Department of Chemical and Metallurgical Engineering, and J.L. HENDRIX, Dean of the Mackay School of Mines and Professor of Chemical and Metallurgical Engineering, are with the University of Nevada, Reno, NV 89557. Manuscript submitted March 27, 1992. METALLURGICAL TRANSACTIONS B
acid leaching of copper oxide ores. Roman e t al. taJ and Shafer e t a l . 191 w e r e able to simulate the results of column leaching tests of a copper oxide ore with the shrinking core model in unaltered form. More recently, Chae and Wadsworth t~~ have incorporated the reaction zone model of Braun e t al. t~l into an in s i t u copper oxide leaching simulation, accounting also for the consumption of acid by gangue minerals and the initial flushing of copper oxides from the external surfaces of ore fragments. Recently, Box and Prosser tl ~l have attempted to derive a general model for the leaching of several minerals with several reagents, which requires no prior laboratory test work. In this model, reactions which occur at similar rates are lumped into cohesive groups
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