ACIDIC OXIDATIVE LEACHING OF CHALCOPYRITE AND ITS MECHANISM
Abstract
The soluble ions both iron and copper as well as the elemental sulfur are the products of the reaction of the chalcopyrite with the acidified ferric chloride solution during its acidic oxidative leaching. Originating elemental sulfur covers the leached particles and such way it hinders the transport of the reagents on / from leached interface. By this manner the leaching kinetics is significantly slower. However, a part of sulfur is oxidized into soluble sulphate form whereas the originated elemental sulfur amounts are between 62 and 96 %. These processes are not satisfactory explained and the opinions on the chalcopyrite acidic oxidative leaching mechanism published till now are rather contradictory in respect to the temperature effect, rate controlling step as well as the formation of the reaction products.
The proposed reaction mechanism is based on the fact that elemental sulfur precipitates from solution together with the formation of intermediate CuS. The chemical reaction of CuS dissolution is slowest - rate controlling step of chalcopyrite acid oxidative leaching. Proposed mechanism explains observed sulfur morphology better than the idea of sulfur surface migration. It is capable to explain the leaching process and the formation of relatively porous sulfur layer. Also, it is not necessary to consider the hypothetical solid state diffusion mechanism in
order to explain both the stoichiometric anomalies during starting stage of leaching and different rate of copper and iron dissolution. The precipitation of CuS explains the above phenomena adequately.
The results of this study are based on the chalcopyrite leaching experiments and the X-ray diffraction phase analyses as well as the scanning electron microscopy observations.
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