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Chalcopyrite (CuFeS2) is the most abundant of the copper sulfides and also one of the most refractory for leaching. Several processing routes have been proposed to overcome drawbacks associated with environmental problems related to copper extraction from this mineral. Atmospheric leaching in acidic ferric sulfate is regarded as being particularly attractive over other hydrometallurgical systems. However, the challenge has been to overcome the problem of slow extraction rates due to passivity encountered at high solution potentials in this system. This highlights the need to investigate better operating conditions to optimize copper extraction and prevent the problem of passivation, and to develop suitable modeling tools to assess and diagnose leaching performance. In this work, a dissolution rate expression for chalcopyrite leaching in acidic ferric sulfate media is proposed accounting for effects in the active and passive regions under potentials from 415 to 550 mV (Ag/AgCl). A model of chemical speciation in the bulk solution elucidates the idea of passivation caused by precipitation of ferric species and their consequent adsorption onto the chalcopyrite surface. Electrochemical studies on massive samples of chalcopyrite involving characterization and modeling of the anodic and cathodic half-cell reactions of chalcopyrite leaching together with mixed potential considerations lead to the development of the mathematical expression for dissolution rate. The mathematical model was calibrated with electrochemical parameters and results are in good agreement with real leaching data from batch tests for solution potential regions where passivity is not observed. On the other hand, the passive region was modeled by means of adjusting parameters related to adsorption energies of the passivating species. Results of the model for this region deviate from real data as potential becomes higher probably due to diffusion resistance through a layer composed of ferric complexes.

The abiotic leaching behavior of a chalcopyrite ore, from Asarco’s Ray-Mine, was conducted in shake flasks and miniature columns at elevated temperatures. The shake flask tests, with an ore particle size of 1.18mm-2.38mm, found the highest Cu extraction was obtained using 1M NaCl in a 9.8g/L sulphuric acid solution at 60°C, with 69% Cu extracted in 16 days. The next highest extraction, 59% Cu extracted in 16 days, was achieved by adding fine pyrite at a 4:1wt ratio with the chalcopyrite content, in a 9.8g/L sulphuric acid solution at 60°C. Flask tests using other lixiviants and additions found copper extractions in the range of 30-40% Cu after 16 days. In the mini-column tests, the rates of copper extraction were similar for all test conditions. The rate of Cu extraction, even with a small particle size of 1.18mm-2.38mm and an elevated temperature of 50°C, was slow for all test conditions with an average rate of ~0.15% Cu per day. The conceptual engineering of a hot, abiotic heap-leach for low-grade chalcopyrite ore, including hypothetical heat and mass balances was conducted. The leaching time for a commercial operation was estimated from published data on laboratory column leaching of chalcopyrite ores and extrapolated to a commercial heap-leach by analogy with known leaching times for chalcocite ores. In commercial abiotic heap-leaches of chalcopyrite ore, the partial oxidation reactions generate insignificant heat to maintain an elevated heap temperature therefore the heat required to maintain the elevated temperature must be provided externally. In commercial biotic chalcopyrite heap-leaches, the in-situ total oxidation reaction generates more heat than the abiotic reactions but is still insufficient to rapidly raise and maintain an elevated heap temperature. For a low-grade Chalcopyrite heap-leach the most practical method of providing this heat is by injecting steam into the base of the heap using current air injection pipes. An external oxidant is required and for an abiotic heap-leach external ferric generation will be required. / Thesis (Master, Mining Engineering) -- Queen's University, 2011-02-15 15:59:38.15

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