Effects of basicity, MgO and MnO on mineralogical phases of CaO–FeOx–SiO2–P2O5 slag

Abstract

The selective separation phosphorous rich phase from steel slag could be an effective way to utilise the steel slag. The mineralogical phase after cooling of steel slag is essential to selective separation of steel slag. In the present work, the mineralogical phases of CaO–FeOx–SiO2–P2O5 slag after controlled cooling were investigated by X-ray diffraction and scanning electronic microscopy and energy dispersed spectroscopy technique. It was found that the heat treatment at 1573 K would lead to the precipitation of Ca2SiO4–Ca3P2O8 (C2S-C3P) solid solution for all samples. The heat treatment at 1273 K would lead to the precipitation of C2S-C3P, CaSiO3 and Fe2O3. The increase of basicity would promote the crystallisation of CaO–FeOx–SiO2–P2O5 slag. The Effects of additions of MgO and MnO on phase formations of CaO–FeOx–SiO2–P2O5 slag were also studied. Fe2O3 gradually transformed into MgFe2O4 and MnFe2O4 in slag after crystallisation with addition of MgO and MnO, respectively. The sizes of MgFe2O4 and MnFe2O4 crystals increased with increases of MgO and MnO content. The increase of MgO and MnO content would promote the precipitation of MgFe2O4 phase and MnFe2O4, respectively. The precipitation of crystals from slag during cooling was interpreted by the kinetic and thermodynamic factors. It was proposed that addition of MgO and MnO in slag would be beneficial to magnetic separation of steel slag.