Selective metal cation concentration during the solidification of stainless steel EAF dust and slag mixtures from high temperatures for increased Cr recovery

The selective concentration of valuable metal cations in FetO-Cr2O3-NiO-MnO-containing stainless steel dust has been studied. The hazardous metal cations Fe, Cr, Ni and Mn could be locally concentrated during the solidification of a molten stainless steel slag and dust mixture from high temperatures by controlling the primary crystalline spinel phase. The nucleation and growth of the primary spinel phase could be controlled by varying the slag to dust mixing ratio and the cooling temperature. Significant redistribution between the primary spinel and amorphous phases could be observed, where the contents of Cr and Mn in the crystalline phase could be increased up to 40% and 10%, respectively, from their initial contents of 5% and 4% in the melt. Using the specified controlled cooling conditions, a primary spinel phase concentrated with Fe-Cr-Ni-Mn could be formed, which could be clearly distinguished and eventually separated from the amorphous matrix. The mixed stainless steel slag and dust samples were quenched at various cooling temperatures and with varying amounts of dust to identify and optimize the crystalline phases formed using SEM-EDS (scanning electron microscopy-energy dispersive spectroscopy) and XRD (X-ray diffraction) analyses.