Effect of Spinel Growth and Texture on Chromium Immobilization During EAF Slag Cooling

The slag from electric arc furnace (EAF) steelmaking has potential for various applications, but its safe use requires the assessment of heavy metals, such as chromium leaching, to meet environmental standards. This study investigates the microstructure of EAF slag cooled in a slag pot and its effect on Cr immobilization. Slag samples were collected at full scale using a representative sampling method, dividing the slag pot into six zones (internal and external, top to bottom). Microstructural analysis was performed using scanning electron microscopy coupled with energy dispersive spectroscopy and X-ray diffraction, followed by leaching tests on the milled samples. Thermodynamic calculations were performed using FactSage 8.4 to evaluate phase stability and composition. The results indicate that cooling conditions inferred from slag-pot location, spinel size, and spinel zoning are correlated with variations in Cr leaching under neutral conditions. Slower cooling is associated with the formation of large, reverse-zoned spinel phases that may contribute to Cr stabilization, whereas rapid cooling is associated with smaller, homogeneous spinel phases that may increase leaching risk. These findings provide insights for the environmentally safe utilization of EAF slags and inform strategies to minimize Cr release during slag valorization.