Determination of the Optimum Conditions for Leaching of Zinc Cathode Melting Furnace Slag in Ammonium Chloride Media
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the nonferrous metals, zinc is one of the most commonly used metals, after aluminum and copper. Zinc is primarily found in various forms around the world (ZnCO3, ZnS, etc.).[1] Zinc is an important base metal required for various applications in metallurgical, chemical, and textile industries. It is mainly recovered from primary sulfide concentrates. A part of zinc is also recovered from different secondary resources such as zinc ash, zinc dross, flue dusts of electric arc furnace and brass smelting, automobile shredder scrap, rayon industry sludge, etc., which contain different level of impurities depending on their sources. In view of the above, there has been an increasing interest in developing processes for the recovery of zinc from secondaries/ wastes. Usually, pyrometallurgical and hydrometallurgical processes are employed for treating such secondaries. A major drawback of the pyrometallurgical method is high energy requirement and need of dust collecting/gas cleaning system. The hydrometallurgical
BAHRAM BEHNAJADY, Ph.D. Student, AMIN BABAEIDEHKORDI, M.Sc., and JAVAD MOGHADDAM, Assistant Professor, are with the Materials and Metallurgical Engineering Department, Advanced Material Research Centre, Sahand University of Technology, Tabriz, Islamic Republic of Iran. Contact e-mail: [email protected] and [email protected] Manuscript submitted January 20, 2013. METALLURGICAL AND MATERIALS TRANSACTIONS B
processes are more environmentally suitable and economical to treat even low zinc containing materials on small scale.[2] It is well known that sulfuric acid is often used as the leaching reactant in most of the hydrometallurgical processes. However, other reactants, such as ammonia with or without sulfate or carbonate, nitric acid, caustic soda, and chlorides, can be considered.[3] Nowadays, hydrometallurgy in ammonium chloride solution has been considered as a prospective medium for extracting nonferrous metals.[4] The reason probably lies in its advantages of both ammonia metallurgy and chloride metallurgy. First, many minerals such as ZnO, PbO, CuO, and Ag, can easily dissolve into the solution, because of the high complexation characteristics of both ammonia and chloride ions. Second, due to the relatively high pH (6 to 7) of the medium, impurities such as Fe2O3, SiO2, CaO, and MgO are not soluble in the resulting solution. Third, the purification of the leaching solution becomes very simple, since either metallic powder reduction or solvent extraction can be used.[5] Finally, treating the ore with high alkaline gangues in ammonium chloride solution will not cause excessive consumption of leaching reagent and so much trouble with filtration, as is the case in sulfuric acid media.[6,7] Metallic zinc cathode plates are produced by an electrowinning process. These plates are melted in furnaces and cast into ingots of various sizes. Zinc companies experienced problems with the formation of slag in the furnaces. A substantial amount of the molten zinc metal from the melt was lost to the zinc cathode
melting furnace
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