Electrochemical aspects of leaching copper from chalcopyrite in ferric and cupric salt solutions

Abstract

Electrochemical aspects of semiconductors are used to interpret well established observations on the kinetics of leaching of chalcopyrite. The oxidation of this n-type semiconductor is dominated by a surface film which is thermally unstable and breaks down in CS2, acetone or acidified water, or under dry nitrogen, over comparable time periods. The film is thought to be a semiconductor metal-deficient polysulfide which slows transport of Cu+ and Fe2+ products, slows electron transfer to oxidants such as Fe3+ and Cu2+, and dramatically slows supply of holes and thus electron transfer from reduced species such as Fe2+ on corroding chalcopyrite. Thus the Fe3+/Fe2+ couple (especially as sulfate) is much less reversible on corroding chalcopyrite than on pyrite or platinum. The couples Cu2+/Cu+,I3-/I- and Fe(CN)63-/Fe(CN)64- are more reversible than Fe3+ /Fe2+ but all couples are much less reversible on chalcopyrite than on pyrite. A layer of sulfur forms on corroding chalcopyrite, but this is not the species which slows transport of ions and transfer of electrons. A mixture of Fe3+/Cu2+ chlorides is one of the more effective oxidants for CuFeS2 because of relatively fast electron transfer from corroding chalcopyrite to Cu2+ and oxidation of Cu+ by Fe3+. Catalysis by iodine and by inclusion of Ag2S or FeS2 in natural chalcopyrite is explained by the electrochemical model.

Control of the redox potential by oxygen limitation improves bacterial leaching of chalcopyrite

“…It has been variously described as a metal-de®cient, chalcopyrite-like sul®de (Biegler and Home, 1985;Warren et al, 1982), a nonporous elemental sulfur layer (Dutrizac, 1989;Hirato et al, 1987), or a polysul®de (CuS x , where x > 2) (Majima et al, 1988;Parker et al, 1981).Whatever the nature of this layer, it has been observed consistently in this study that higher redox potentials and increased ferric ion concentrations promote rapid passivation of the chalcopyrite surface. The most likely explanation is that formation of the passivating layer is delayed at low redox potential, facilitating the continued dissolution of the mineral (Figs.…”

“…Chalcopyrite is known to be recalcitrant to hydrometallurgical processing due to``passivation``of the mineral surface, or formation of a physical surface layer that prevents further electron transfer between the ore and oxidizing medium (Dutrizac, 1981;Hirato et al, 1987;McMillan et al, 1982;Parker et al, 1981). Our results showed that bioleaching of chalcopyrite could be signi®cantly improved by limiting the supply of oxygen to the reaction, preventing accumulation of ferric ions.…”

Characterization and Flotation of Sulfur from Chalcopyrite Concentrate Leaching Residue

“…While sulfur coating, either porous or protective, on the surface of the sulfide minerals as the results of chloride leaching has been the subject of discussion [10][11][12][13], it is clear that the sulfur in this leaching residue is in a form of discrete crystals or crystal agglomerates. Mineralogical examinations on the leaching residue were conducted with scanning electron microscope and microprobe methods.…”

Effect of Mechanical Activation on the Kinetics of Copper Leaching from Copper Sulfide (CuS)

“…In addition, during reactions to extract copper from covellite in strongly acidic conditions, elemental sulfur may be formed on the particle surface. This layer is called 'passivation layer', and it acts as a blocking layer for copper leaching in solution [10][11][12][13][14][15][16].…”