Model for ferric sulfate leaching of copper ores containing a variety of sulfide minerals: Part II. Process modeling of
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I.
INTRODUCTION
A study was undertaken of the economic and technological feasibility of modified in situ recovery of copper from sulfide minerals in copper porphyry deposits at depths unattractive for surface mining. The method, flood drain leach cell (FDLC) mining, involves development of large 60 by 75 by 70 m cells of rubblized ore throughout the orebody. The cells are bulkheaded, flooded, drained, and artificially aerated to promote bacterial ferric sulfate leaching. The mining system has been explained in greater detail in another publication, i~ The leaching of copper sulfide minerals in porphyrytype deposits is catalyzed by bacteria. These bacteria live in acidic conditions, with a pH around 2, and obtain carbon and oxygen from the air and minerals from the rock. They oxidize ferrous ion to ferric ion, consuming oxygen and acid in the process. Ferric ion then diffuses into the rock fragments and oxidizes the copper sulfide minerals to soluble form. These leaching reactions generally are exothermic and release heat, and potentially toxic copper, into the surrounding enclosed bacterial environment. The FDLC mining method uses forced ventilation to BRADLEY C. PAUL, Assistant Professor of Mining Engineering, is with the Department of Mining Engineering, Southern Illinois University at Carbondale, Carbondale, IL 62901. H.Y. SOHN, Professor of Metallurgical Engineering, Department of Metallurgical Engineering, and M.K. McCARTER, Professor of Mining Engineering, Department of Mining Engineering, are with the University of Utah, Salt Lake City, UT 84112. Manuscript submitted July 1, 1991. METALLURGICAL TRANSACTIONS B
carry away the heat from the oxidation of sulfide minerals and to supply oxygen to the bacteria. The solubilized copper is carried away in solution when the leach cell is flooded. The acid required by the bacteria must be provided by sulfide oxidation reactions and iron precipitation. The rate at which sulfide oxidation will proceed depends on the reaction kinetics of the individual sulfide minerals, the size of the fragments into which ferric ion must diffuse, and the concentration of ferric ion. Ore fragmentation rounds, leach cell flood cycles, and ventilation systems must all be designed to maintain a conducive environment for the bacteria and to speed the recovery of copper. The amount and rate of copper recovery will determine whether the mine can be built and operated with an acceptable rate of return. The Lin-Sohn Leach simulation computer model (DLS) described in Part I t21 was developed to provide the required information on heat and oxygen requirements, in situ acid production, and copper solubilization.
II.
THE DLS COMPUTER MODEL
The DLS model uses an explicit numerical scheme to solve the steady state approximation to Fick's law of diffusion for spherical particles and ferric ion concentrations. It models individual reaction kinetics for six copper sulfides, two iron sulfides, and native copper. It keeps a strict mass balance on iron and outputs the amount of copper released, the amou
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