A Comparison Study on Formation and Stabilities of Chromium Bearing Spinels

Chromium, broadly present in metallurgical systems such as stainless steel slags and vanadium-bearing slags, tends to be in a trivalent form bound in spinel phases due to their ultrahigh stability. To explore the stability of chromium bearing spinels with different divalent cations, herein ACr 2 O 4 (A=Mg, Zn, Mn) spinels were synthesized and stability-tested under both alkaline and acidic environments. X-ray diffraction (XRD) and refinement results reveal that MnCr 2 O 4 exhibited the largest lattice parameters. X-ray photoelectron spectroscopy (XPS) results show that MnCr 2 O 4 had the highest oxygen vacancy concentration, potentially triggering structural instability, consistent with the Fourier-transform infrared (FTIR) and Raman analyses. To further investigate the stability of ACr 2 O 4 spinels in alkaline and acidic environments, we introduced CaO and SiO 2 , respectively, for high temperature calcinations. XRD analyses reveal that ACr 2 O 4 spinels exhibited a high instability under an alkaline condition, with an increasing degree of instability for MgCr 2 O 4 , ZnCr 2 O 4 , and MnCr 2 O 4 successively. We further quantified the relationship between the oxygen vacancy concentrations and the divalent cations containing in spinels as well as the spinel stabilities under an alkaline environment. Under an acidic condition, all ACr 2 O 4 spinels demonstrated a relatively strong structural stability. The understanding of formation and stability of chromium bearing spinels under different conditions could contribute to potential modifications and applications of spinels especially with regard to resource recycling in metallurgy.