Dissolution behaviour of valuable elements from the CaO–SiO 2 –Fe 2 O 3 glassy phase modified with Na 2 O and Al 2 O 3 in an acidic solution

Abstract

Dephosphorisation slag generally consists of a 2CaO·SiO₂–3CaO·P₂O₅ (C₂S–C₃P) solid solution, CaO–SiO₂–FeO_x glassy phase, and RO phase (FeO_x, MgO and MnO). Its components, such as CaO, FeO_x, MnO, and MgO, can be used as a soil conditioner in agriculture to improve acidic soil and supply nutrient elements. To promote its dissolution, CaO–SiO₂–Fe₂O₃ glassy phases with different Al₂O₃ and Na₂O contents were synthesised, and their dissolution behaviour and mechanism were investigated. The addition of Al₂O₃ significantly inhibited the dissolution of the glassy phase because it increased the degree of polymerisation of the silicate network, and the glassy phase structure became more stable as the Al₂O₃ content increased. When 3% Na₂O was added, the dissolution ratios of elements from the glassy phase were the highest, with the dissolution ratio of Si reaching 21.0% and the dissolution ratios of Ca and Fe reaching 21.6% and 17.7% at pH 5. The substitution of CaO with Na₂O significantly reduced the dissolution ratios of all elements. As the Na₂O content increased, Na₂O had a bigger influence on the silicate structure. Na₂O addition enhanced the proportion of $Q_{\mathrm{Si}}^2$ units and formed additional bonds by interacting with non-bridging oxygens in the silicate tetrahedra, strengthening the stability of the glass network. Lowering pH increased the dissolution ratios of elements.