Vacuum distillation of copper matte to remove lead, arsenic, bismuth, and antimony
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INTRODUCTION
T H E R E exists a potential for increases in the impurity levels in cathode copper production worldwide. I~,2,3[Three factors can account for this: (1) impurity levels in copper concentrates are tending to increase as high-grade deposits are depleted; t4j (2) m o d e m trends toward high-grade, and if possible, single-step matte smelting decrease the extent of impurity elimination during the production of copper anodes; and (3) the electrolytic copper-refining process, whereby these impurities are presently kept at acceptable levels in the cathode copper by impurity rejection into the anode slimes or electrolyte, has a limited capacity to eliminate the bismuth, arsenic, and antimony in the refinery's anode copper feed. The severity of the problem of contamination of the anode copper varies from copper smelter to copper smelter but is particularly important in toll or custom smelters, for which the feed materials for smelting may contain high levels of bismuth, arsenic, and antimony. Impurity elements entering the smelting process can be eliminated only in the few outputs from conventional smelting: the anode copper, the offgas, the acid, and the discard slag.
A. ALLAIRE, formerly with McGill University, Montreal, PQ, is with Hatch and Associates, 630 Boul. Rene Levesque, Montreal, PQ H3A 2A7, Canada. R. HARRIS, Associate Professor, is with the Department of Mining and Metallurgical Engineering, McGill University, 3450 University Street, Montreal, PQ H3A 2A7, Canada. Manuscript submitted March 14, 1988. METALLURGICAL TRANSACTIONS B
The impurities of concern here are those which have proven to be difficult to eliminate to the slag and have a tendency to follow the copper. There are several methods to reduce the impurity contents of the copper matte, blister copper, or anode copper, from which cathode copper is produced: (1) control and homogenize the smelter inputs by blending, selection, and distribution of the feed and revert to the smelting unit, which gives the best possible elimination. This eliminates the peaks and valleys in the impurity contents so that, on average, fewer anodes exceed the tolerable limits; (2) schedule converter charges for m a x i m u m impurity volatilization and slagging; (3) operate smelting vessels for m a x i m u m volatilization, i.e., at as high a temperature as practical; (4) bleed dust from the electrostatic precipitators in order to create an additional outlet for impurities from the smelter; and (5) add an operation to the process in order to further increase the bleed of impurity from the process. Focusing on the last of these methods, recent research and industrial practice have found that arsenic and antimony may be eliminated by slagging with a soda slag, [SJ but that bismuth is not appreciably slagged. It has also been seen that it may be possible to eliminate volatile impurities from a smelter by using a dedicated volatilization process, namely, vacuum refining. This paper summarizes previous work on vacuum-refining metallurgical melts found in a copper s
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