Influence of Fe3O4 on redox changes during Cu dissolution from CuFeS2 in acidified ferric sulfate
(1. Water Pollution Monitoring and Remediation Initiatives Research Group, School of Chemical and Minerals Engineering, Faculty of Engineering, North-West University, Potchefstroom, South Africa;
2. Department of Mining Engineering, College of Science Engineering and Technology, University of South Africa, Florida Science Campus, Johannesburg, South Africa;
3. Department of Metallurgy, Faculty of Engineering and Built Environment, University of Johannesburg, Doornfontein, Johannesburg, South Africa;
4. Department of Chemistry, School of Science and Technology, Cape Breton University, Canada;
5. School of Mining, Metallurgy and Chemical Engineering, Faculty of Engineering and the Built Environment, University of Johannesburg, Johannesburg, South Africa;
6. Institute for Nanotechnology and Water Sustainability, College of Science Engineering and Technology, University of South Africa, Florida Science Campus, Johannesburg, South Africa)
2. Department of Mining Engineering, College of Science Engineering and Technology, University of South Africa, Florida Science Campus, Johannesburg, South Africa;
3. Department of Metallurgy, Faculty of Engineering and Built Environment, University of Johannesburg, Doornfontein, Johannesburg, South Africa;
4. Department of Chemistry, School of Science and Technology, Cape Breton University, Canada;
5. School of Mining, Metallurgy and Chemical Engineering, Faculty of Engineering and the Built Environment, University of Johannesburg, Johannesburg, South Africa;
6. Institute for Nanotechnology and Water Sustainability, College of Science Engineering and Technology, University of South Africa, Florida Science Campus, Johannesburg, South Africa)
Abstract: Chalcopyrite (CuFeS2) leaching under oxidizing conditions is generally characterized by slow dissolution rates due to the formation of passivation layers. The aim of this study is to develop a method that will allow the minimization of the passivation effect on the leaching of chalcopyrite and enhance copper recovery. To achieve this goal, the effect of parameters such as magnetite (Fe3O4) addition to the lixiviant Fe2(SO4)3-H2SO4 during the leaching of CuFeS2 at various pH (1.0, 1.5 and 1.8) and temperatures (25 and 50 °C) on copper dissolution rate overtime, was investigated. The results revealed that the solution pH, potential and temperature played a vital role during the dissolution. The highest recovery rate (70%) of Cu was achieved at pH 1.8, 50 °C and 400 mV from the mixed Fe3O4- CuFeS2, whereas the recovery rate of Cu from CuFeS2 in the absence of Fe3O4 was relatively low (48%). It was found that the addition of Fe3O4 allowed to maintain higher redox potential values. The addition of Fe3O4 also decreased the activation energy from 79.04 to 53.69 kJ/mol, suggesting that CuFeS2 is easily oxidized in the presence of Fe3O4 through the formation of more soluble intermediates (bornite (Cu5FeS4) and chalcocite (Cu2S)). Both dissolution processes were chemically controlled on the surface of the mineral. Furthermore, the mineralogical analysis of leaching residues showed that jarosite which is a candidate for surface passivation appeared in higher concentration in the absence of Fe3O4. Therefore, the addition of Fe3O4 reduced the formation of a passivation layer and enhanced the recovery rate of Cu.
Key words: chalcopyrite; dissolution; magnetite; galvanic couple; passivation