Iron control in medium temperature sulphide concentrate leaching

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TECK, through its subsidiary CESL, and Vale have commercial interests in the implementation of medium temperature copper and nickel sulphide concentrate leaching. "Medium temperature" is used to describe a variety of processes that operate above the melting point of sulphur (119C) but below the temperature where sulphur becomes highly viscous (159C). Both Vale and TECK operate their medium temperature leach processes at 150C. During leaching, and depending on various process parameters, iron may be precipitated as hematite, goethite, jarosite or other oxyhydroxide compounds, which may be more or less crystalline. These iron precipitates are eventually impounded as process residues. Hematite is the favored precipitate because it is the most environmentally (thermodynamically) stable and does not ad/absorb as much copper, nickel or other solution constituents during precipitation. This proposal describes an experimental plan to elucidate the conditions under which the precipitation of highly crystalline hematite occurs during medium temperature leaching of nickel and copper sulphide concentrates. It is proposed that two Ph.D. students study various process parameters at the lab scale and that they employ classical as well as newly developed methods to identify the optimal conditions for hematite precipitation.