The Phase Transition and Element Distribution of Copper Smelting Slag in the Cooling—Sulfidation Process

Copper smelting slag is the largest solid waste produced in copper-making process, and slow cooling beneficiation technology is the most widely used method in recovering remaining treasures from the slag. The phase transition law and element distribution behaviors of the copper smelting slag in the cooling process have significant importance, and they have been experimentally investigated in the present study. CaS, which was produced from the reductive decomposition of gypsum residue, has been added for sulfidation purposes to improve the recovery. Fayalite, glassy slag, hercynite, magnetite, and matte were major phases in the final slag, and the adding amount of CaS had a small effect on the phase transition process. However, the cooling rate had a large effect on the slag phase composition. When decreasing the cooling rate, the mass fraction of glassy slag decreased dramatically. The distribution behavior of Fe, Cu, Zn, Pb, Se, Te, and Ag changed when increasing the CaS adding dosage, and that of Si, Ca, Al, and Mg changed slightly. The initial slag composition also influenced the element distribution behavior. When changing the CaS excess coefficient, the distribution behavior of As and Bi changed slightly in the slag with the initial Fe/SiO₂ mass ratio of 1.8. But when the smelting slag had the Fe/SiO₂ mass ratio of 1.0 and 1.3, more As entered the glassy slag when increasing the CaS adding dosage. Less Ca reported to the glassy slag when decreasing the cooling rate, and more Cu, Pb, Zn, Se, Te, and Ag entered the matte phase, but part of them were lost in the cooling process.