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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.