Mechanism of carbide slag substitution for conventional flux on sintering mineralization

With the advancement of green and low-carbon transformation in the steel industry, the demand for comprehensive utilization of solid wastes in the metallurgical sector continues to grow. Carbide slag, a high-calcium solid waste generated by the chemical industry, not only occupies land resources but also poses environmental risks due to its large-scale accumulation. As a high-calcium solid waste, carbide slag holds significant potential for replacing conventional calcium-based fluxes in iron ore sintering. This study aimed to systematically investigate the feasibility of using carbide slag as a substitute for conventional fluxes in iron ore sintering and its impact mechanism on the sintering and mineralization processes. Mineralogical analyses of carbide slag, limestone, and quicklime were conducted using XRF, XRD, laser particle size analyzer and thermogravimetric analyzer. The results indicate that compared to conventional fluxes, carbide slag exhibits higher CaO content, finer particle size, lower thermal decomposition temperature and higher thermal stability, demonstrating its suitability as a sintering flux. Through fundamental sintering characteristic tests and micro-sintering experiments, combined with the mineralogical properties of carbide slag, the effects of its substitution for conventional fluxes on sintering characteristics and the mineral phase structure of sinter were systematically analyzed. The results show that as the substitution ratio of carbide slag increases from 0 to 60%, the assimilation temperature decreases, while the fluidity of the liquid phase, the strength of the binding phase and the formation capacity of calcium ferrite improve, promoting the development of an interwoven-corroded structure. However, when the substitution ratio exceeds 60%, although the assimilation temperature continues to decrease, the fluidity of the liquid phase and the formation capacity of calcium ferrite decline, accompanied by an increase in silicate minerals and porosity, leading to a deterioration in the mineral phase structure of the sinter. At a substitution ratio of 60%, the sinter exhibits a uniform mineral phase structure, the highest content of calcium ferrite, predominantly in acicular and columnar forms. The findings of this study provide new insights into the resource utilization of carbide slag and the cost reduction and efficiency improvement in sinter production.