Recovery of Cu, Co, and Fe from Pyrite Cinder Based on Mineral Phase Reconstruction

Pyrite cinder (PyC) containing polymetallics is difficult to use due to the low grade of metals and complex mineral phase composition, the low reutilized rate of which causes the wastage of resources. In this paper, a novel approach based on mineral phase reconstruction was proposed to recover Cu, Co, and Fe from PyC. A feasible reduction roasting process was developed for mineral phase reconstruction, followed by leaching with sulfuric acid to recover Cu and Co; finally, the leaching residue was separated by a magnetic tube to recover Fe. The maximum copper and cobalt extract rates of 86.15 and 79.61% were achieved respectively under the optimized conditions of reduction roasting for 30 min at 550 °C and 30% CO/N₂ volume fraction, followed by leaching for 4 h at a liquid-solid ratio of 4:1 (mL/g), a mass concentration of 160 g/L sulfuric acid, and a temperature of 70 °C. The iron concentrate can be obtained with 63.08% Fe grade and 98.91% recovery rate by magnetic separation at a magnetic field strength of 28.26 kA/m. The mechanism analysis results of mineral phase reconstruction revealed that the primary copper sulfide in PyC was transformed into free copper oxide, combined copper oxide, and secondary copper sulfide without changing the valence state of copper by reduction roasting, resulting in a higher extraction rate of copper. Meanwhile, cobaltosic oxide and cobalt ferrite in PyC were transformed into cobalt sulfate and cobalt sulfide with the reduction of Co(III) to Co(II), improving the extraction rate of cobalt.