Dissolution of dolomite and doloma in silicate slag

Abstract

Dissolution mechanisms of dolomite CaMg(CO₃)₂, and doloma CaO.MgO, in a model basic oxygen furnace (BOF) slag based on the CaO–MgO–SiO₂–FeO–MnO system have been characterised with regard to the reaction product phases at the dolomite/slag and doloma/slag interfaces by post-mortem microstructural analysis. It was found that after 1 h immersion at 1350°C in a stagnant molten slag, the CaO and MgO in doloma react with SiO₂ and FeO in the slag forming dicalcium silicate (2CaO . SiO₂ or C₂S), MgO-rich magnesiowüstite ((Fe,Mg)O), and dicalcium ferrite (2CaO.Fe₂O₃ or C₂F). The formation of (Fe,Mg)O and C₂F breaks up the C₂S layer, leaving it discontinuous. Similar reactions take place in dolomite, but at a later stage of dissolution since they are retarded by the intermediate decomposition of dolomite in which rapid CO₂gas evolution quenches the resulting C₂S layer and forms a gap between the resulting doloma and slag. A more complete and continuous dicalcium silicate layer was observed in dolomite compared with doloma.