The dissolution behavior of metals from Ag/Cu and Ag/Au alloys in acidic and cyanide solutions
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INTRODUCTION
S C R A P from various sources represents an important component of the domestic supply of gold and silver as well as other metals. Hydrometallurgical methods of extracting precious metals have been introduced recently because such methods offer several advantages. Hydrometallurgical processes are, in general, believed to be beneficial due to their lower energy consumption, ability to produce higher purity metals, and their reduction of environmentally hazardous products. Systematic studies on the dissolution behavior of pure copper, silver, and gold in acidic, cyanide, or other lixiviant solutions have been conducted, and the results are well documented in the literature. [1'2'3] Chen et al.[4] carried out a study on the thiourea leaching of gold and silver in the presence of ferric sulfate using a rotating disc. The results showed that the system was not completely controlled by diffusion of ferric ions and may also be affected by intrinsic chemical reactions. Pesic and Seal [51 carried out a study on the silver dissolution with thiourea in the presence of ferric sulfate. The dissolution of silver was zero order with respect to the concentration of sulfuric acid, first order with respect to ferric sulfate, and second order with thiourea. Morrison 161 studied the dissolution of silver in ferric sulfate-sulfuric acid media using the rotating disc technique. The effect of ferric ion, ferrous ion, acid, trace chloride ion, total sulfate concentration, temperature, ionic strength, and the disc rotation speed on the silver dissolution rate was determined. The dissolution rate of silver was found to be controlled fully or partially by mass transport of ferric ions. The leaching studies on pure gold and silver in cyaY.U. CHOI, formerly with the South Dakota School of Mines and Technology, is Postdoctoral Fellow, Department of Metallurgy and Mining Engineering, University of Idaho, Moscow, ID. E.C. LEE, formerly Visiting Professor, South Dakota School of Mines and Technology, is Professor, Department of Metallurgical Engineering, Korea University, Seoul, Korea. K.N. HAN, Professor and Department Head, is with the Department of Metallurgical Engineering, South Dakota School of Mines and Technology, Rapid City, SD 57701. Manuscript submitted February 8, 1991. METALLURGICALTRANSACTIONSB
nide solutions have been documented in the literature. [7] The dissolution rates of pure silver and pure gold in cyanide solutions were known to be mass transfer controlled. The extraction of metals from scrap is, in general, much different from primary sources. There is an inherent major difference in the physical and chemical association of metals and their environment between scrap and primary sources. Metals occur in nature in elemental form, sulfides or oxides, while their occurrence in secondary sources is quite different, in that they are frequently associated with other metals to form alloys. There have been a few studies reported on the dissolution behavior of metals from alloys, t2m A hydrometallurgical process fo
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