Model for ferric sulfate leaching of copper ores containing a variety of sulfide minerals: Part I. Modeling uniform size
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I.
INTRODUCTION
A study was undertaken to evaluate the technological and economic feasibility of recovering copper from copper sulfide porphyry type orebodies by a method referred to as flood drain leach cell (FDLC) mining. The process is briefly illustrated in Figure 1. Cells 60 by 75 m in plan view and 70 m in height are created throughout the ore body using modified vertical retreat mining with 25 pct removal of swell material. The swell material is leached in finger dumps on the surface, while the cells underground are bulkheaded, flooded, drained, and artificially aerated to promote bacterial ferric sulfate leaching. Solutions are cycled through several cells to reach a pregnant grade of 1 g of copper per liter of solution. These solutions are then pumped to an underground solvent extraction plant and then to a surface electrowinning tankhouse. A key to both the technical design and economic feasibility of this method is the prediction of leaching rates and the resulting heat and oxygen consumption loads on the ventilation system. A search was made for a model that could provide a simulation of the leaching process and output the needed information for design. A model prepared by Cathles and Schlitt t~ provides output on the temperature profile and oxygen concentration in waste dumps when air moves by convection. The air flow assumptions of the Cathles-Schlitt model do not fit forced ventilation of confined stopes, but more importantly, the model assumes that copper is extracted from a single narrow reaction zone (a shrinking core) in each of the fragments of the ore mass. As demonstrated later in Section V, many reaction zones may not be narrow and the 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
amount of oxygen used per unit of copper produced may not be a constant, as assumed in the Cathles-Schlitt model. Madsen and Wadsworth 121 developed a model that provides separate reaction kinetics for pyrite, chalcopyrite, chalcocite, and covellite, thus overcoming the single narrow reaction zone problem. Bornite, enargite, cubanite, native copper, and pyrrohtite are sometimes significant minerals in porphyry-like systems, but no model identified at the time deals with the bacterial leaching of these minerals. The implicit solution scheme used in the Madsen-Wadsworth model is subject to numerical problems associated with ill-conditioning and requires that kinetic equations be approximated as linear functions of ferric ion concentration. Bartlett pl has developed a model for pressure leaching that overcomes the numerical approximations of the Madsen-Wadsworth model using a rigorous explicit sch
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