Electrochemical oxidation of chalcopyrite (CuFeS_2) and the related metal-enriched derivatives Cu_4Fe_5S_8, Cu_9Fe_9S_(16), and Cu_9Fe_8S_(16)

摘要

The electrochemical oxidation of chalcopyrite (CuFeS2) and its metal-enriched derivatives, haycockite (Cu_4Fe_5S_8), mooihoekite (Cu_9Fe_9Si_6), and talnakhite (Cu_9Fe_8Si_6), have been investigated using electrochemical techniques and X-ray photoelectron spectroscopy. The results show that when chalcopyrite, haycockite, mooihoekite, and talnakhite are oxidized in 1 M HC104 in the electrode potential region of 0.2-0.6 V vs. S.C.E. at 298 K, the oxidation products are Cu_xS_zFe~(2+) and, at electrode potentials > 0.53 V vs. S.C.E., Fe ions; Cu_xS represents a metastable phase at the electrode surface. The relative rates of oxidation are in the order haycockite > mooihoekite > talnakhite > ehalcopyrite. After oxidation of Fe surface sites, the rate-determining step apparently involves transport of Fe has from the bulk to the solid-electrolyte interface. When ehalcopyrite, haycockite, mooihoekite, and talnakhite are oxidized in 0.1 M borax in the electrode potential range of -0.6-0.3 V vs. S.C.E. at 298 K, the primary oxidation products are Cu Sf and Fe_2O_3. The initial oxidation rates of haycockite, mooihoekite, and talnakhite are higher than chakopyrite, but this initially more facile oxidation of haycockite, mooihoekite, and talchalcopyrite results in metal oxide (mainly iron oxide) surface films, which retard further oxidation to a greater extent than on ehalcopyrite. When ehalcopyrite, haycockite, mooihoekite, and talnakhite are oxidized in 0.3 M NaCl + HO solution of pH 0.1, the oxidation rate remain essentially in the order haycockite > mooihoekite > talnakhite > chalcopyrite. However, probably because chloride ions form complexes with Cu+ ions and may act "￡ a bridge in electron transfer, the oxidation rate is significantly enhanced compared to that in 1 M perchloric acid and 0.1 M borax aqueous solutions.