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Acid and Oxidizing Leaching of Chalcopyrite Concentrate by Ferric Sulphate and Fluorosilicic-Nitric Media

A hydrometallurgical treatment was applied to the Hajar Mine Copper Concentrate (HMCC), Morocco, containing ≈ 28.1% copper (the major copper mineral phase is chalcopyrite, CuFeS2), ≈ 26.1% iron, ≈ 5.8% zinc, ≈ 1.9% lead, ≈ 33.7% sulphur, and small amounts of silver (269 g/t) and nickel (219 g/t). Three acid media were used: ferric sulphate in sulfuric acid, ferric sulphate in hexafluorosilicic acid, and a hexafluorosilicic acid–nitric acid mixture. The results show that when a ferric sulphate reagent is used, in H2SO4, as well as in H2SiF6 media, dissolution of copper and iron do not exceed 30%, because of the formation of a passivation layer on chalcopyrite particles, whereas zinc is dissolved at about 90%. The final solid leachate residue represents 75% by weight of the initial solid and remains rich in copper (≈ 28%) and iron (≈ 25%). However, under strong acid and oxidizing conditions, in the hexafluorosilicic acid–nitric acid mixture, the dissolution of copper is more efficient, although it is nonselective, (92% Cu, 89% Fe, 98% Zn). The solid leachate residue represents only 40% by weight of the original sample, and assays 5.9% Cu, 7.3% Fe, 0.2% Zn, 4.1% Pb, and 56.4% Stotal. Mineralogical characterizations of the leachate solid residues show the formation of both elemental sulphur and a Cu1−xFe1−yS2−z layer on the surface of the nondissolved chalcopyrite.