Effect of Al₂O₃ on the Viscosity and Structure of CaO-SiO₂-MgO-Al₂O₃-Fe_tO Slags

The present paper provided a fundamental investigation on the effect of Al₂O₃ on the viscosity and structure of CaO-SiO₂-MgO-Al₂O₃-Fe_tO slags for the purpose of efficiently recycling the valuable elements from the steelmaking slags. The results show that the viscosity of CaO-SiO₂-Al₂O₃-MgO-Fe_tO slags slightly increases with increasing Al₂O₃ content. The degree of the polymerization (DOP) of quenched slags, determined from Raman spectra and magic angle spinning–nuclear magnetic resonance, is also found to increase with increasing Al₂O₃ content. It can be deduced that the increasing DOP can promote the formation of gehlenite phase (Ca₂Al₂SiO₇), thus facilitating the formation of higher phosphorous (or vanadium) contained solid solution (n′Ca₂SiO₄·Ca₃((P or V)O₄)₂). As Al₂O₃ content increases up to a specific value, the charge compensating ions which present near [AlO₄]-tetrahedra and [FeO₄]-tetrahedra are not fully supplied due to the scarcity of Ca²⁺. In this case, the existing Fe³⁺ in the melt cannot completely form [FeO₄]-tetrahedra and part of Fe³⁺ would form [FeO₆]-octahedra to substitute Ca²⁺ to modify the slags.