Sulfate Leaching Of Chalcopyrite: The Use of Potassium Iodide to Enhance the Dissolution of Copper

"The high copper demand as well as the lack of new high-grade deposits, are pushing the copper industry to process low-grade and refractory ores containing chalcopyrite. However, for a quantitative dissolution of copper from the chalcopyrite, the leaching performances still need to be improved. In the present research, we studied and optimized the iodide-assisted leaching of chalcopyrite in H2SO4-Fe2(SO4)3 media. The evolution of surface species during leaching was determined by x-ray photoelectron spectroscopy (XPS) and mineral liberation analysis (MLA). Inductively-coupled plasma spectrometry (ICP-MS) was used to determine the dissolved copper. Significance of experimental results was assessed by statistical analysis while a kinetic analysis of the leaching process was performed by fitting the experimental data with the Shrinking-core model. Results showed the significant positive effect of iodide on copper extraction rate. In the presence of KI, the dissolution rate of copper was almost double than in the parallel experiments without KI. Whether using KI or not, elemental sulfur was generated on the surface of the leached chalcopyrite. Nevertheless, in the presence of KI, the passivation layer did not arrest the leaching. Analysis revealed that the leaching rate was limited by the chemical reaction control step.INTRODUCTION Due to the large demand of copper, processing low-grade ores containing copper sulfides such as chalcopyrite (CuFeS2) has become unavoidable (Watling, 2013). Since ores with CuFeS2 may also contain appreciable amounts of arsenic that cannot be smelted, and because low-grade ores are uneconomic to smelt, the hydrometallurgical technologies are crucial for recovering the copper (Dutrizac, 1978). Sulfate-based processes are attractive because of the lower operating costs and because the sulfate ion is more suitable in case copper would be recovered via electrowinning. In ferric sulfate solution, chalcopyrite undergoes oxidation due to the large amount of Fe(III) and dissolution due to the presence of the sulfate ion (Majima, et al., 1985). The leaching reaction in ferric sulfate medium can be represented as in (1):"