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TRODUCTION

THEREhas been

growing concern about the adverse effects on the environment associated with high temperature processing of galena. Because of the difficulties encountered with conventional smelting, the use of hydrometallurgical techniques for lead processing has received considerable attention in the past few years. 1-8 With hydrometallurgical processing, sulfur dioxide is not produced and lead-bearing particles which always exist in high temperature processing are precluded. An early investigation of aqueous leaching of galena was conducted by Anderson et al. ~ who observed complete dissolution of 325 • 400 mesh particles in 1.2 hours when the reaction was carded out at 150 ~ and 5.7 atm of oxygen. Vizsolyi et al. 9 advanced an interesting technique for the leaching of galena which initially involves the oxidation of galena with oxygen to lead sulfate followed by dissolution with ethylenediamine. Seraphim and Samis 2 have shown that galena can be leached successfully with oxygen at neutral pH by forming acetate complexes and elemental sulfur at temperatures and oxygen pressures on the order of 120 ~ and 3 atm, respectively. Hayer et al. lOinvestigated recovering lead and sulfur from galena using ferric sulfate. The leach residue was treated with an ammonium carbonate solution to change the lead to an acid soluble form and to produce ammonium sulfate. Awakura et al. H presented a kinetic investigation of the dissolution of galena in a solution of hydrochloric acid and perchloric acid. Under the experimental conditions employed, dissolution rates were controlled by chemical reactions on the surface of galena. Various research w o r k e r s 3'6'7'12-14 have studied the leaching of galena in chloride solutions. Ferric chloride leaching of galena in the presence of hydrochloric acid and sodium chloride provides an excellent means of extracting lead M. C. FUERSTENAU, Professor and Head, and K. N. HAN, Professor, are with the Department of Metallurgical Engineering, South Dakota School of Mines and Technology, Rapid City, SD 57701. C.C. CHEN is Research Assistant, Department of Welding Engineering, The Ohio State University, Columbus, OH 43210. B.R. PALMER is Manager, Exploratory Research, Kerr-McGee Corporation, Oklahoma City, OK. Manuscript submitted June 3, 1985. METALLURGICALTRANSACTIONS B

hydrometallurgically because soluble lead-bearing species and elemental sulfur are formed. These important attributes have been noted by a number of investigators, and work concerning this leaching aspect has moved ahead at a considerable pace. More recently, Morin et al. 15studied the leaching kinetics in 4 M NaC1 at pH 2.4 and 75 ~ They postulated that the overall kinetics is controlled by a mixed model where ferric chlorocomplex diffusion through the sulfur layer and chemical reaction at the core interface are responsible for the overall rate of dissolution. Although the future of ferric chloride leaching of galena and other sulfide ores is certainly promising, little detailed information on the thermodynamics and ki