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Chloride leaching for chalcopyrite Liddicoat, Jenni Anne

Abstract

Two new process flowsheets have been developed which combine chloride leaching for chalcopyrite with solvent extraction, to selectively transfer copper to a conventional sulfate electrowinning circuit. Both models were designed to address the common chloride hydromet problem of product impurity, and they differ with respect to iron deportment. Chloride leaching offers significant advantages for copper hydrometallurgy including increased solubility, increased rates of leaching and stabilization of Cu(I) through chloride complexation. A mass balance was completed for both models and enabled the determination of recycle leach liquor concentrations of copper and iron species for the countercurrent leach tests. To assist with solid-liquid (S-L) separation a bench size mini-thickener was designed and tested in the continuous countercurrent,leach experiments. One mini-thickener was used for leach stage 1 (LSI) S-L separation in a smooth, clean and semi-continuous manner. The leach tests were performed using a chalcopyrite concentrate, from Antamina in northern Peru, which contained a low to moderate amount of gangue material. The successful completion of mass balances for both circuits demonstrates potential for these two new chloride leach flowsheets particularly in addressing current purification difficulties and waste management issues. The goethite model leach experiments, in which oxygen was injected to leach stage 2 (LS2) to aid iron oxidation and precipitation, were unsuccessful in achieving >95% copper extraction in the atmospheric conditions tested. It is believed that further intensification of conditions could produce >95% copper extraction. The hematite model, in which no air is added to the leach, was successful in demonstrating the effect of varying particle size, leach time and temperature to achieve copper extractions >95%. Three hematite process variations achieved >95% copper extraction and these involved fine grinding of the concentrate, and either a 3h residence time at 95C (98% extraction), a 2h residence time at 95C (96% extraction) or a 3h residence time at 85C (96% extraction). One final experiment, based on the hematite model, was successfully conducted at optimum leach conditions employing Rosario concentrate from Chile, which contains chalcopyrite, chalcocite and a significant amount of pyrite. Copper extraction exceeded 99% for this experiment.

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