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Iodine-assisted heap leaching of chalcopyrite : laboratory and modelling studies Winarko, Ronny


Copper mine operations face increasing challenges of processing low-grade chalcopyrite ores with elevated concentrations of impurities. Heap leaching is considered to be an effective and economically viable technology for treating these low-grade, complex copper sulfide ores. The addition of iodide in ferric sulfate solution is found to significantly enhance the dissolution of chalcopyrite at ambient temperatures. The aim of this research was to better understand the key factors that control the reaction rate and the mechanisms by which iodine accelerates the leaching kinetics. This research aim was achieved by conducting experimental and modelling studies of the iodine-assisted leaching of chalcopyrite concentrate and ore. Specifically, a series of leaching tests of increasing scale, from 50-mL bottle to 1-L reactor to 1-m and 6-m column tests, were carried out under partially- or fully-controlled leaching conditions; these leaching tests data were used to develop a kinetic model that correlates the copper extraction with the leaching conditions; the solid surface properties were examined by XRD, MLA, and XPS to uncover the leaching mechanisms; the calibrated kinetic model was finally used to assess the effect of key design and operating parameters on the performance of chalcopyrite dissolution in heap leaching. The experimental results show that the redox potential is the primary factor controlling the chalcopyrite leaching by controlling the iodine speciation in solution. Either diiodine or triiodide is considered to be the active oxidant responsible for chalcopyrite dissolution depending on the solution potential. The solid surface examination shows that the elemental sulfur and iron precipitates formed during leaching did not hinder the dissolution of chalcopyrite and that pyrite was inert during leaching. The kinetic model developed could simulate the copper extraction as a function of solution potential, total iodide concentration, and temperature. The sensitivity tests with the calibrated kinetic model show that the performance of the iodine-assisted leaching process can be improved by increasing irrigation rate, ferric concentration, iodide concentration, and temperature. The experimental and modelling results obtained in the present study can guide the design and implementation of the iodine-assisted heap leaching of chalcopyrite at an industrial scale.

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