China Nonferrous Metallurgy

Viscosity is a crucial physicochemical parameter that regulates mass and heat transfer kinetics at the slag-metal interface in pyrometallurgical reactors. In this study, a quaternary CaO-MgO-Al₂O₃-SiO₂ reference slag system was examined within the framework of the Ion-Molecule Coexistence Theory. Using MATLAB based algorithms, the equilibrium activities of all likely structural entities were carefully calculated; then, an Arrhenius-type regression was applied to develop a semi-empirical viscosity model. Experimental validation over different compositional ranges showed that the predicted viscosities closely matched the measured data, with deviations in activation energy for viscous flow limited to 0.08, 0.61, 0.10, and 0.28 kJ·mol^-1, respectively. Spectroscopic and phase-equilibrium analyses confirm that the melt consists of simple ionic species (Ca²⁺, Mg²⁺, O^2-) coexisting with [Si_xO_y]^z- and [AlO_m]^n- polymeric units. Increasing concentrations of Ca²⁺ and Mg²⁺ ions have a network-modifying effect, depolymerizing the aluminosilicate structure and causing a structural shift from molecular to ionic dominance. During controlled cooling, the primary solid phases identified were 2CaO·SiO₂, MgO·Al₂O₃, CaO·Al₂O₃·SiO₂, and CaO·MgO·SiO₂. This model provides the metallurgical community with a fast, composition-dependent viscosity predictor for CaO-MgO-Al₂O₃-SiO₂ slags and explains the direct link between melt speciation and overall transport properties.