Tellurium distribution in copper anode slimes smelting
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I.
INTRODUCTION
DURING the electrolytic refining of copper, produced by fire-refining blister copper smelted from sulfide concentrates, a by-product known as ‘‘anode slimes’’ collects in the cells under the anodes. It originates from impurities in the copper and is a mixture of elements and compounds originally present in the copper or formed during or after anodic dissolution through reactions of the species with each other and the electrolyte. The mineralogy of anode slimes is complex, and almost 100 species have been identified.[1] Slimes are a valuable source of silver, gold, platinumgroup metals, selenium, and tellurium. The processing of slimes usually involves many steps; however, the main goal is to remove copper, selenium, tellurium, etc., and to leave behind silver, gold, and the platinum group metals as an alloy called ‘‘dore´.’’ Conventional processing involves pretreating the slimes to reduce the amounts of copper, selenium, tellurium, etc., then smelting the slimes in a small reverberatory furnace, or in more intense reactors such as a top-blown rotary converter[2] or bottom-blown oxygen converter,[3] to produce dore´ metal (an alloy containing 98 to 99 pct Ag). Anode slimes smelting is a batch process which involves melting of the slimes; additions of various proportions of fluxes such as sodium carbonate, borax, and silica; injection of air into the molten bath; numerous skimmings of the slag; fresh additions of fluxes and oxidizing agents (usually sodium nitrate); and recycling of slags to earlier stages of the process. The thermodynamics of the smelting of synthetic anode slimes consisting of AgSe0.5 and CuSe0.5 have recently been discussed in the literature.[4–7] A major factor in determining smelting behavior is the existence of a large miscibility gap in the Ag-Cu-Se system at 1100 7C,[8] as shown on Figure 1. During slimes smelting, selenide mattes form, whose D.R. SWINBOURNE, Discipline Leader, and G.G. BARBANTE, Research Fellow, are with the Department of Chemical and Metallurgical Engineering, Royal Melbourne Institute of Technology, Melbourne, 3001, Victoria, Australia. A. SHEERAN, Process Engineer, is with Group Technical Services, Pasminco Metals, Boolaroo, 2284, New South Wales, Australia. Manuscript submitted April 14, 1997. METALLURGICAL AND MATERIALS TRANSACTIONS B
composition corresponds to the upper boundary of the miscibility gap and which are in equilibrium with molten metal, whose composition corresponds to the lower boundary of the miscibility gap. The way in which the composition of each phase changes during smelting is difficult to predict. Experimental results for the laboratory-scale smelting of a silver-rich selenide matte[9] and of a copper-rich selenide matte[10] have been presented. It was shown that oxygen solubility in copper-rich selenide mattes is substantial, in contrast to that of silver-rich selenide mattes, and it strongly influences the course of smelting by effectively shifting the boundaries of the miscibility gap in the Ag-Cu-Se system. Finally, the therm
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