Electrometallurgy of copper refinery anode slimes
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I.
INTRODUCTION
THE Kidd Creek Division of Falconbridge Limited operates a mine and smelter/refinery complex at Timmins, ON, Canada (for an overview of the operation, see Reference 1; for discussion of the smelter and refinery, see References 2 and 3). The ore body is remarkably high in selenium, the bulk of which is present in solid solution in the chalcopyrite t4] and, therefore, is impossible to remove by traditional mineral processing techniques, tS] Geological ore reserves t4] total 56.8 million tonnes, including a 10 pet dilution factor, grading 145 ppm Se, 66 ppm Ag, 3.21 pet Cu, 5.15 pet Zn, and 0.16 pet Pb. Formerly, this was mined as a zincrich high silver "C" ore (229 ppm Ag, 135 ppm Se) and a copper-rich low silver "A" ore (48 ppm Ag, 200 ppm Se); however, since April 1988, the two ore types have been combined and are now mined and processed as a single material. Copper concentrate produced by the concentrator for feed to the copper smelter presently averages 575 ppm selenium and 475 ppm silver. The smelter eliminates about 40 pet of this selenium by fuming it to the wet-gas cleaning system of the sulfuric acid plant; t~ an additional 7.5 pet is removed from the same gas stream via cottrell dust (which is sent to the zinc plant for zinc, copper, and indium recovery try) and some 2.5 pet is rejected in the discard slag. This means that almost exactly half of the selenium which enters the smelter appears in the copper anodes prepared for the copper refinery. ]7~ The "normal" level of selenium in the anodes is about 0.20 pet; however, during periods when material from the bornite zone t4~ is being processed in the concentrator, it can rise to 0.55 pet. Because of the X-ray identification of silver selenide and silver-copper selenide as major constituents of the anode slimes remaining after the electrolytic refining of copper, there is a long-standing myth in the literature that these are the forms in which selenium and silver occur in the anodes. Extensive research by the Kidd Creek Division and at CANMET, tS-lq has shown that this is not the case. Over 99 pet of the silver is dissolved in J.D. SCOT/', Senior Staff Scientist, is with the Kidd Creek Division, Falconbridge Limited, Timmins, ON, Canada P4N 7K1. Manuscript submitted July 28, 1989. METALLURGICAL TRANSACTIONS B
the copper, as the beta solid solution phase (0.13 to 0.26 pet Ag). The selenium, however, segregates on cooling of the coper during the casting operation and forms ring-shaped, tubular, and spherical copper selenide inclusions, usually rimming subspherical to tubular Cu20 or lead-arsenic-copper oxide inclusions. Microprobe analyses of the copper oxide inclusions show less than 0.05 pet Ag and an average of 0.44 pet Se; they are essentially stoichiometric Cu20. The lead-arsenic-copper oxide (with minor Sb and Bi) is generally a complex mixture of very fine-grained phases, although in one case, it could be approximated by the formula 6PbO.2As2Os.3CuO. In the Hazelett-cast anodes at Kidd Creek, the copper selenide contains an average of
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