Effect of Al₂O₃/SiO₂ mass ratio and CaO content on viscosity and structure of slag for pyrometallurgical processing of spent automotive catalysts

The effect of Al₂O₃/SiO₂ mass ratio and CaO content on the viscosity and structure of the CaO–Al₂O₃–SiO₂–6MgO–1.5ZrO₂–1.5CeO₂ slag was investigated. The results show that with the increase in Al₂O₃/SiO₂ mass ratio, the viscous flow units within the slag gradually change from Si–O–Si to Al–O–Al and Al–O–Si. Furthermore, the substitution of Al₂O₃ for SiO₂ leads to the transformation of Si–O bonds towards weaker Al–O bonds, which weaken the bond strength of the aluminosilicate networks, thus leading to a decrease in the viscosity of slag. The increase in CaO content effectively promotes the depolymerization of the aluminosilicate networks, resulting in a significant decrease in the viscosity of the slag. The slag with Al₂O₃/SiO₂ of 0.7–1.5 and CaO of 30 wt.% shows promise as the reference slag system for the Fe-collection smelting of spent automotive catalysts due to its good comprehensive performance.