A partial equilibrium model to characterize the precipitation of ferric ion during the leaching of chalcopyrite with fer
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NTRODUCTION
THE importance of the formation of iron-containing precipitates in copper sulfide dump leaching has long been recognized by the industry, l In the interior of a dump, precipitation contributes to a gradual reduction in permeability and a declining rate of copper recovery. Due to slowly decreasing throughputs of leach liquor, it often becomes uneconomic to continue leaching a particular dump well before complete copper recovery is achieved. A further important consideration is that the occurrence of precipitation in piping adds to maintenance costs; dump leaching is often economically possible only because of low operating and maintenance costs. A number of compounds have been reported to precipitate in leach dumps and laboratory column leaching apparatus. Unfortunately, however, these precipitates have been difficult to characterize thoroughly. A number of compounds appear to form simultaneously and often only the elemental composition of the precipitated material has been determined, leaving its precise identity uncertain. In column leaching experiments, Madsen and Groves reported the formation of gypsum, ferric sulfate, and a jarosite compound. 2 Ferric hydroxide and an iron sulfate were formed in the leach columns used by Bhappu e t al. 3 Hydronium jarosite (n3OFe3(SOa)2(OH)6) precipitated during the column leaching experiments performed on a chalcocite ore by Bruynesteyn and Cooper.4 Boorman and Watson 5 found iron hydroxides and oxides in an abandoned sulfide tailings dump; these precipitates proved to be amorphous when examined by X-ray diffraction. Streams receiving acid drainage from abandoned copper mines in Shasta County, California contain precipitates of amorphous ferric hydroxide, goethite, and potassium jarosite (KFe3(SOa)a(OH)6); they are supersaturated with respect KNONA C. LIDDELL, formerly Graduate Assistant, Ames Laboratory USDOE and Department of Chemical Engineering, Iowa State University, Ames, IA 50011, is now Assistant Professor, Department of Chemical Engineering, Washington State University, Pullman, WA 99164. RENATO G. BAUTISTA is Group Leader, Ames Laboratory USDOE and Professor, Department of Chemical Engineering, Iowa State University, Ames, IA 50011. Manuscript submitted November 9, 1981. METALLURGICALTRANSACTIONS B
to potassium jarosite. Closer to the source of the drainage, melanterite (FeSO4 9 7H20) was found; in dry areas on the surface of the ore itself, copiapite (FeZ+Fe3+(SO4)6(OH)2 9 20H20) and coquimbite (Fe2(SO4)3 9 9H20) occurred. 6 Based on these observations, it is likely that the ferric ion-containing precipitates forming in leach dumps include compounds of the jarosite family, ferric hydroxide, and material formed from the hydroxide by aging. These are the compounds whose precipitation in dumps has been modeled in the present investigation. Ferric or ferrous sulfates may form when a column or dump is allowed to dry out before samples are taken, but formation of these compounds seems less common under the conditions of interest in dump leaching and they have
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