Copper Stabilization in Glass-Ceramics: Effect of CaO and SiO2 on CuAlxFe2-xO4 Formation

Industrial activities discharge heavy metal-laden wastes; and copper is one of these metals that can be stabilized after ceramic sintering by Al- or Fe-containing precursors. Besides traditional precursors, Al- and Fe-containing solid wastes (e.g., sewage sludge incineration ash, coal fly ash) were found equally capable of copper stabilization when they were adopted in the reaction matrices. However, the effect of CaO and SiO2, the predominant components in most of the inorganic solid wastes, on metal transformation and stabilization has not been addressed. Therefore, a CaO-SiO2-CuO-Al2O3-Fe2O3 reaction matrix was proposed in this study, focusing on the effect of CaO and SiO2 on copper transformation and immobilization. Results showed that a single-phase CuAlxFe2-xO4 spinel solution was developed in the system without CaO and SiO2, whereas the addition of CaO led to the generation of two separate spinel phases: CuAl2O4 and CuFe2O4. Compared with CaO, the existence of SiO2 showed less impact on the phase transformation. The effect of sintering temperature and additive dosage was also illustrated in this study and the results provided useful guidance for the optimization of reaction systems to achieve beneficial utilization of solid wastes for heavy metal stabilization.