Experimental Determination of Liquidus Temperature and Phase Equilibria of the CaO–Al2O3–SiO2–Na2O Slag System Relevant to E-Waste Smelting

The recovery of valuable and critical metals from electronic wastes (e-waste) via the pyrometallurgical route has some challenges including high processing temperatures. Designing appropriate slag systems based on the major elemental components in e-waste could bring operational advantages by lowering the liquidus temperature. In this study, the quaternary slag system CaO–Al2O3–SiO2–Na2O was investigated to determine the liquidus temperature and phase equilibria of slags relevant to e-waste smelting. The slags were thermally equilibrated at different temperatures inside a vertical tube furnace followed by rapid quenching. The quenched slags were examined by SEM to observe the phase formed and the equilibrium compositions were determined using energy dispersive (ED) spectrometry. The liquidus temperature of the slags in the anorthite (CaO·Al2O3·2SiO2) phase field was significantly decreased with increasing levels of Na2O. The slag composition moved towards the pseudo wollastonite (CaO·SiO2) region upon the addition of Na2O.