Evaluation of the behavior of selenium in silicate slag
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I.
INTRODUCTION
SELENIUM is both a valuable by-product in the smelting of copper concentrates and a deleterious contaminant of copper. Selenium is recovered as a by-product during processing of electrolytic copper refinery slimes for gold and silver. It is used in electronic and photocopier components, glass manufacturing, and in the production of chemicals and pigments. Yet small quantities of Se adversely affect the softening properties of copper, and is thought to be the worst impurity in that regard. For that reason the presence of Se in copper leads to higher energy costs for annealing, and, due to compound formation, it can result in failure of fine drawn wire. Selenium has a high affinity for copper. In the reverberatory-converter smelting process it is estimated that 60 pct of the selenium entering the converter leaves with the blister copper. Overall, approximately 25 pct of the selenium entering the reverberatory furnace in the concentrate remains with the blister copper. The concentration of Se in blister copper will be greater for single-step smelters where slag, matte, and molten copper coexist. Selenium can be removed from copper during electrolytic refining. In copper anodes Se forms Cu2Se and Ag2Se compounds which do not electrolytically dissolve in the electrolyte, but join the slime. The selenium that is found in the cathode copper has been physically trapped. A significant increase in the concentration of Se reporting to the anodes, such as occurs in a single-step smelter, will result in a significant increase in the amount of Se leaving with the cathode copper. Nagamori et al. 1,2 examined the behavior of Se and other minor elements in copper metallurgical slag. They found that Se exists in slag in both an elemental and combined form. They concluded that the combined form involved some form of an Fe-Se complex. In this investigation both the solubility of Se in slag, and the nature of the Fe-Se complex are examined. L. FANG is Process Engineer, Advanced Research and Development Laboratory, Fairchild Camera and Instrument Corporation, 4001 Miranda Avenue, Palo Alto, CA 94304. D.C. LYNCH is Associate Professor, Department of Materials Science and Engineering, University of Arizona, Tucson, AZ 85721. Manuscript submitted February 22, 1985. METALLURGICAL TRANSACTIONS B
II.
EXPERIMENTAL
Two techniques were used in an effort to examine the behavior of selenium in copper metallurgical slags. The isopiestic method that was used to evaluate the solubility and activity of selenium in slag proved unsuccessful. The solubility data obtained with that technique were not reproducible. Microscopic examination and energy dispersive analysis of X-rays of the quenched slag revealed extensive formation of a second phase rich in both Fe and Se. For those reasons the isopiestic method was abandoned in favor of a distribution technique. The distribution technique involved small specimens of slag and copper, the latter containing Se, which were equilibrated at 1458 and 1523 K. Approximately 0.6 g of both Cu-Se all
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