Effects of basicity,MgO and MnO on mineralogical phases of CaO–FeO x –SiO 2 –P 2 O 5 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–FeO _x –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–FeO _x –SiO₂–P₂O₅ slag. The Effects of additions of MgO and MnO on phase formations of CaO–FeO _x –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 MnFe₂O_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.