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Fundamental study of the controlled-potential leaching of chalcopyrite Lai, Jerry Cheng-Yen

Abstract

There is a well-established trend in copper hydrometallurgy to develop processes for the treatment of chalcopyrite ( CuFeS₂ ). Chalcopyrite receives considerable attention not only because of its relative abundance and widespread distribution in almost all sulfide deposits, but also because it is the most recalcitrant copper sulfide to leaching in most practical systems, particularly in sulfate media. The main practical difficulty encountered in the commercial acid ferric sulfate leaching of chalcopyrite (in heaps, dumps or concentrates) is its slow rate of reaction, which renders a long residence time and/or incomplete copper extractions. Chalcopyrite is generally agreed to be "passivated" in some fashion, exhibiting slow leaching kinetics and low copper extraction in sulfate media. This thesis work investigated the oxidation of chalcopyrite through the application of controlled-potential at different potentials (0.400-0.600 V[sub Ag/AgCl]) and temperatures (60-78°C). All experiments were carried out in a compact bench-scale 3-L glass jacketed bioreactor equipped with a servo motor and speed controller. Since the solution redox potential is dependent on the concentrations of ferric and ferrous ions in solution, a constant redox potential was maintained by controlled addition of potassium permanganate using an automatic titration unit. Chalcopyrite leaching in sulfuric acid is shown to be dependent on solution redox potential determined by the concentration ratio of ferric to ferrous ions and temperature. The most significant finding in this thesis work is the fact that the leaching; rate increases with increasing potentials but decreases above a critical potential under the reaction conditions studied. This critical potential is in the vicinity of 0.500 V[sub Ag/AgCl] and is within the mid-potential range of 0.45 to 0.55 V[sub Ag/AgCl] at which the leaching rate is maximal from 60 to 78°C. Leaching rates increase with increasing temperature. The leach residues contain sulfate (5- 33%), but primarily elemental sulfur (46-78%). XRD analysis confirmed the presence of sulfate sulfur, jarosite, and elemental sulfur in the leach residues. SEM analysis suggests that neither jarosite nor elemental sulfur is responsible for surface passivation or for preventing, the dissolution of chalcopyrite.

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