Crystallization Behaviors of Spinel During Cooling Process of Modified EAF Slag

EAF slag constitutes a major waste in the steel industry, which necessitates the development of processes to recover its valuable compounds and thermal energy values. A promising method involves the modification of the composition of EAF slag melts to utilize its waste heat and recover more valuable elements by controlled crystallization of spinel under a cooling process. In this study, crystallization behaviors of modified EAF slag melts with a basicity of 1.2 were investigated, with the aim of precipitating more magnetic spinel phases, and leaving a matrix with the amorphous phase, which favors subsequent utilization in the cement industry. Samples were prepared at different cooling temperatures, for different holding times, or quenched by air or water. Results show that two kinds of spinel phases were found during the cooling process of the melts. One was bulky spinel (BS) in granular form with size > 40 μm, and the other was dendritic spinel (DS) with arms < 20 μm. Three stages existed in the crystallization process of the melts. It is crucial to keep the slag melts in stage one for less than 30 minutes and then rapidly cool it to stage three. More and larger BS was obtained when this method was applied.