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The fundamental study of impurity behavior in wet chlorination of decopperized anode slime Koga, Keitaro


The copper industry has been facing challenges associated with continuous declining ore grade and elevated levels of impurities in copper ores. Such challenges have already significantly impacted copper smelting and refining. The situation is compounded by increasingly complex feed materials processed by copper smelters. A major concern is the accumulation of impurity elements in copper anodes and the anode slimes generated in electrorefining. This, in turn, affects the downstream treatment of anode slimes for recovery of precious metals and platinum-group metals (PGMs) as valuable byproducts. Wet chlorination is hydrometallurgical process that involves the use of H₂O₂ and HCl for recovering these metals. The present study investigated the leaching behavior of not only gold and PGMs but also a range of impurity elements in the wet chlorination using both thermodynamic calculations and laboratory wet chlorination tests. The stable species of all elements present in the decopperized anode slime were identified in the Pourbaix diagram (Eh-pH diagrams) constructed. The results generally agreed with those reported in the literature, even though some species reported were not identifiable due to a lack of relevant thermodynamic data. The major findings of the laboratory wet chlorination tests were summarized as follows. Antimony played an important role in the behavior of impurity elements. The oxidation of antimony from Sb(III) to Sb(V) occurred in the ORP range of 600 - 700 mV, causing the precipitation of Sb(V) together with arsenic and bismuth as arsenato antimonates. The extractions of arsenic, antimony, bismuth, and tin were initially independent of but later affected by the rate of H₂O₂ addition due to the removal of antimony (V) from solution via precipitation of arsenato antimonates. The extraction of arsenic, antimony, bismuth, and tin increased with the leaching temperature. The extractions of arsenic, bismuth, and tin were affected by acidity but not by the total chloride concentration. However, the antimony extraction was affected by not only the proton concentration but also the chloride concentration. Simple alkaline leaching without H₂O₂ addition was shown to be possibly effective to remove some impurity elements, especially tellurium, arsenic, and tin, prior to the extraction of gold and PGMs.

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