Selective Extraction of Chromium from EAF Stainless Steel Slag by Pressurized Oxidation in a NaOH Solution

Chromium was selectively extracted from electric arc furnace (EAF) slag by pressurized oxidation in a NaOH solution. The effect of the temperature (T), NaOH concentration, oxygen pressure and reaction time on the extraction ratio of the chromium was investigated. It was found that the chromium extraction rate was significantly impacted by the temperature. At the optimum conditions of T = 170 degrees C, NaOH concentration of 40 wt.%, oxygen pressure of 1.6 MPa and reaction time of 4 h, a maximum chromium extraction rate of 60.04% was obtained. It was observed by scanning electron microscopy (SEM) with energy dispersive spectrometry (EDS) that the residual particles were enclosed by a "secondary precipitation layer" mainly composed of Fe and O, which prevented further extraction of the chromium from the core residues. The leaching process of chromium was controlled by the diffusion of the solid phase product layer, and the activation energy of the extraction reaction was 56.67 kJ/mol.