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

Abstract

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% S_total.

Mineralogical characterizations of the leachate solid residues show the formation of both elemental sulphur and a Cu_1−xFe_1−yS_2−z layer on the surface of the nondissolved chalcopyrite.

Keywords:

• Copper
• Chalcopyrite
• Leaching
• Ferric sulphate
• Fluorosilicic acid
• Nitric acid

ACKNOWLEDGMENTS

Financial support of this study by the Reminex Society (Groupe Omnium Nord Africain, Morocco), is gratefully acknowledged.