Pressure oxidation of ferrous ions by oxygen and hematite precipitation from concentrated solution of calcium, copper and iron chlorides

This study was conducted as part of the development of a novel process for copper recovery from chalcopyrite by chloride leaching, simultaneous cuprous oxidation and cupric solvent extraction to transfer copper to a conventional sulfate electrowinning circuit, and hematite precipitation to reject iron. Ferrous pressure oxidation and hematite precipitation from concentrated solutions of calcium, copper and iron chlorides have been studied with respect to temperature, retention time, seeding, and the behavior of the impurities. As the temperature increased from 140 to 185 °C, the time for the complete oxidation of ferrous ions at an oxygen partial pressure of 310 kPa (45 psi) decreased from 17 to 9 min while the acid concentration increased from 0.02 to 0.1 M. At 140 °C, the iron precipitate consisted of akaganeite with a small amount of hematite. At 155 °C or higher, only hematite was precipitated. With increasing temperature, the iron content of the precipitate increased. The chloride contents of the precipitates were about 2.8% at 140 °C and 0.3% at 155 °C or higher. This is believed due to chloride becoming significantly incorporated into akaganeite, but not into hematite. At 155 °C or higher, the particle size increased with increasing temperature. Pb, Ni, and Hg were not incorporated into hematite while Zn, Co, Cd, Ag and Cr were slightly incorporated. As and Sb were co-precipitated with hematite. The iron precipitated was slightly more than that extracted in leaching. The pressure oxidation of ferrous ions and subsequent hematite precipitation are suitable for the rejection of the excess iron as a by-product for disposal or possibly for sale as pigments/coloring agents.