<http://purl.org/dc/terms/description>
"Hydrometallurgy may be an alternative to the currently practiced smelting process for\ncopper extraction from chalcopyrite (CuFeS\u2082). However, the low temperature\nhydrometallurgical processes for chalcopyrite continue to face challenges, mostly relating to\ntheir slow dissolution rates or high sulfuric acid production. The slow dissolution rate of the\nmineral is strongly linked to the formation of the passive film on its surface. However,\ndespite 40 years of research on this topic, there is still not a complete agreement between\nresearchers about the composition and stability of chalcopyrite\u2019s passive film in sulfuric acid\nsolutions. In this work, the nature of chalcopyrite\u2019s passive film and its stability were studied\nby application of a variety of electrochemical techniques. Additionally, the electrochemical\nresults of the chalcopyrite study were compared to those obtained for a pyrrhotite electrode\n(Fe\u2081\u208BxS), as pyrrhotite electrochemistry represents a simplified case of the chalcopyrite\nsystem. X-ray photoelectron spectroscopy (XPS) was used to analyze the composition of the\nproduct layers formed on the surface.\nIt is shown that the chalcopyrite electrode is passive for potentials up to 0.90 VSHE.\nAbove this potential, transpassive dissolution occurs. Results of XPS studies have suggested\nthat a metal-deficient sulfide film (Cu\u2081\u208BxFe\u2081\u208ByS\u2082\u208Bz) is the most plausible copper and iron\ncontaining sulfide phase which passivates the surface of chalcopyrite. In addition, an outer\nlayer of iron oxyhydroxide (FeOOH) forms on the passive film. FeOOH forms via oxidation\nof the passive film\u2019s ferrous sulfide phases. The thickness of the sulfide passive film was\ncalculated to be approximately 6.7 nm. It is demonstrated that the transpassive dissolution of\nchalcopyrite is significantly linked to oxidation of sulfur (from sulfide in the passive film to\nelemental sulfur and maybe sulfur species with higher oxidation states, e.g. thiosulfate). No\nelemental sulfur or polysulfide species were detected on the surface for potentials below 0.90\nVSHE."@en
<https://open.library.ubc.ca/cIRcle/collections/ubctheses/24/items/1.0072933>