Mechanism and kinetics for chlorination roasting of copper smelting slag

Abstract

An efficient process based on chlorination roasting with CaCl2 was proposed to recover zinc from copper smelting slag. The reaction mechanism and the kinetics of the chlorination process were investigated by thermodynamic calculation, thermogravimetry and differential scanning calorimetry (TG−DSC) analysis and X-ray diffraction (XRD) methods. The results demonstrated that the temperatures of oxidative decomposition of CaCl2 and chlorination of all Zn-containing phases were above 774.3 and 825 °C, respectively. The chlorination roasting process was divided into four stages: precipitation of adsorbed water, extraction of crystallized water, oxidation of Fe-containing phases, and chlorination volatilization of zinc. The average apparent activation energies of the iron oxidation and zinc chlorination were 101.70 and 84.4 kJ/mol, respectively. The most probable mechanism function for the iron oxidation process was the Avrami−Erofeev model (n=2). Zinc chlorination followed the shrinking unreacted core model, and the chemical reaction was the rate-controlling step.