Effects of basicity, MgO and MnO on mineralogical phases of CaO-FeO_x-SiO_2-P2O_5 slag

摘要

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-FeO_x-SiO_2-P_2O_5 slag after controlled cooling were investigated by X-ray diffraction and scanning electronic microscopy and energy dispersed spectroscopy technigue. It was found that the heat treatment at 1573 K would lead to the precipitation of Ca_2SiO_4-Ca_3P_2O_8 (C2S-C3P) solid solution for all samples. The heat treatment at 1273 K would lead to the precipitation of C2S-C3P, CaSiO_3 and Fe_2O_3. The increase of basicity would promote the crystallisation of CaO-FeO_x-SiO_2-P_2O_5 slag. The Effects of additions of MgO and MnO on phase formations of CaO-FeO_x-SiO_2-P_2O_5 slag were also studied. Fe_2O_3 gradually transformed into MgFe_2O_4 and MnFe_2O_4 in slag after crystallisation with addition of MgO and MnO, respectively. The sizes of MgFe_2O_4 and MnFe_2O_4 crystals increased with increases of MgO and MnO content. The increase of MgO and MnO content would promote the precipitation of MgFe_2O_4 phase and MnFe_2O_4 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.