Phase Transformation of Fayalite from Copper Slag During Oxidation Roasting

The phase transformation of fayalite from copper slag during oxidation roasting was systematically studied in this work with an analysis using X-ray diffraction, X-ray photoelectron spectroscopy, vibrating sample magnetometer, scanning electronic microscope, and energy dispersive spectrometer. The results show that the oxidation of fayalite occurs at ≥300 ◦C. Fayalite is first oxidized into amorphous Fe3O4 and SiO2 during oxidation roasting. The former then converts into Fe2O3 while the latter converts into cristobalite solid solution with increasing temperature. Meanwhile, the specific saturation magnetization of roasted products increases from 9.43 emu/g at 300 ◦C to 20.66 emu/g at 700 ◦C, and then decreases to 7.31 emu/g at 1100 ◦C. The migration of iron in fayalite is prior to that of silicon during oxidation roasting. Therefore, the thickness of the iron oxide layer on the particle surface steadily increases with roasting temperature, from about 1.0 µm at 800 ◦C to about 5.0 µm at 1100 ◦C. This study has guiding significance for the iron grain growth in copper slag during the oxidation-reduction roasting process.