Study on Oxidation Kinetics and Mechanism of Copper Slag Under Non-isothermal Conditions

The oxidation behavior of copper smelting slag under non-isothermal conditions was studied by thermal analysis. The results indicate that the copper slag is mainly composed of fayalite (Fe2SiO4) and magnetite (Fe3O4). The oxidation behavior can be divided into two reaction stages with the increase in temperature; the first stage is the oxidation of fayalite to magnetite, and the second stage is the oxidation of magnetite to hematite. The two reaction stages cannot be strictly separated; that is, the reaction of fayalite is not complete, and magnetite has begun to transform into hematite. Based on the TG (thermogravimetric) curves, the ABS (Achar-Brindley-Sharp-Wendworth) differential and the Coats-Redfern integral methods were employed to investigate the oxidation kinetics of copper slag during the continuous heating process. The oxidation of fayalite into magnetite and amorphous silica phases occurs mainly in the temperature range of 673 to 1083 K. The activation energies calculated by the two methods are 193.69 and 195.52 kJ mol(-1), respectively. The reaction is consistent with Avrami-Erofeev equation, and the mechanism of oxidation is random nucleation and growth. The oxidation of magnetite to hematite occurs at 1083-1303 K. The activation energies are 308.79 and 328.77 kJ mol(-1), respectively. The mechanism conforms to the Jander equation and is controlled by the two-dimensional diffusion.