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The mechanisms of the passivation of sulfide minerals in oxidative leaching processes

By D. Pugaev, M. Nicol and G. Senanayake


A number of sulfide minerals of copper, nickel and iron can only be effectively leached by methods that require elevated temperatures in acidic solutions. While suitable for concentrates, these processes are not applicable to tank or heap leaching of low grade ores. It is now generally accepted that many of these minerals are subject to so-called passivation under oxidising conditions. However, the mechanisms involved in this passivation are not well understood and this study will review some of these mechanisms and show that the passivation of several of these important minerals appears to follow similar trends. Electrochemical measurements using millerite, covellite and chalcopyrite electrodes were used to study the similarities of leaching and passivation processes taking place in oxidative acidic media. Thus, potentiostatic current-time transient experiments have demonstrated the resemblance with selective dissolution of metals from alloy systems. A model will be proposed which involves depletion of metal from outer layers of the minerals and the limiting step being diffusion of the metal ions through sulfur sub-lattice in these minerals. Potential step polarization experiments have enabled estimates to be made of the selfdiffusion coefficients of copper, nickel and iron which were in the range of published values extrapolated from higher temperatures. The well known parabolic leaching behaviour of these minerals is supported by solid state diffusion as the rate limiting step

Year: 2011
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