Preparation of enstatite-spinel based glass-ceramics by co-utilization of ferronickel slag and coal fly ash

Abstract In this study, a new approach was proposed to prepare high-quality enstatite-spinel based glass-ceramics from the mixture of ferronickel slag (FNS) and coal fly ash (CFA) by examining the effect of CFA content on the preparation process based on both thermodynamic and experimental analyses. The thermodynamic exploration indicated that choosing enstatite as the main crystal phase in the target glass-ceramics along with spinel was suitable for co-utilization of both wastes. The experimental analysis showed that the crystallization temperature of parent glass, an intermediate product prepared from the mixture, increased from 864 °C to 907 °C as the content of CFA increased from 20 wt % to 35 wt %. Conversely, the depolymerization degree of the glass presented a decreasing trend, implying the denser glass structure which could promote chemical stability of the product. After crystallization of the parent glass, the main phase in the resulting glass-ceramic sample was transformed from enstatite (MgSiO3) to aluminum enstatite (Mg0.96Al0.027SiO3). There were simultaneous microstructural transitions from a spherical structure through a blocky structure to a plate-like prismatic structure, lowering bending strength of the product. By controlling crystallization of the melted mixture of 75 wt % FNS and 25 wt % CFA at 867 °C for 2 h, the resulting enstatite-spinel based glass-ceramic obtained excellent properties, namely density of 3.11 g/cm3, bending strength of 116 MPa, acid resistance of 99.97%, and alkali resistance of 99.70%. With a much higher utilization percentage of FNS, the product had properties comparable to those derived from similar wastes reported in literature. This study provides an efficient method for co-utilization of FNS and CFA.