Distribution Behavior of Titanium Between Ferrosilicon Melt and CaO-SiO2-Al2O3 Slag: Thermochemical and Structural Assessments

The titanium distribution ratio (\({L}_{Ti}\)) between ferrosilicon (FeSi) melt and the CaO-SiO₂-Al₂O₃ slag was measured at 1773 K (1500 °C). FeSi-slag equilibration was carried out using various slag compositions. The \({L}_{Ti}\) was presented against the Vee ratio (pct CaO/pct SiO₂ = C/S) between 0.3 and 1.2, and Al₂O₃ content from 5 to 20 mass pct. The \({L}_{Ti}\) exhibited minima at about C/S=0.7(±0.1) at a fixed Al₂O₃ content. In a C/S < 0.7 regime, i.e., relatively acidic melts, Ti⁴⁺ ions were considered as network forming [TiO₄]-tetrahedron unit in the aluminosilicate framework. However, in a C/S > 0.7 regime, i.e., relatively basic melts, Ti⁴⁺ ions were considered to form the [TiO₅]-pyramid structure unit compensated by Ca²⁺. When adding Al₂O₃ into the basic melts over 10 mass pct, [AlO₄]-tetrahedrons take Ca²⁺ ions for charge compensation, resulting in a decrease of stability of [TiO₅] unit because of Ca²⁺ depletion. At a greater than 10 mass pct Al₂O₃ content in the basic melts, Ti⁴⁺ replaced Al³⁺ to form the [TiO₄]-tetrahedron unit, decreasing the activity coefficient of TiO₂ in the slag.