Understanding the atomic-scaled evolution mechanism of V and Cr in V slag with high Cr content during magnesiation roasting toward tailing toxicity minimization

V slag with high Cr content (VS-HCC) serves as the primary raw material for extracting V, and the evolution mechanism of V and Cr in VS-HCC decides the eco-friendliness of V extraction process. To minimize the Cr(VI) and residual V(V) content in tailings produced after V extraction, this work introduces the "atomic atmosphere" method to investigate the evolution mechanism of V and Cr in VS-HCC during magnesiation roasting at the atomic scale. In the early stage of roasting at 900℃, the FeV 2 O 4 and FeCr 2 O 4 spinel disappear and are converted into Fe 2 O 3 •V 2 O 3 and (Fe 0.6 Cr 0.4 ) 2 O 3 , with the chemical states of V and Cr unchanged; Fe 2 TiO 4 spinels are oxidized to generate FeTi 2 O 5 . After roasting for 10 min, Fe 2 SiO 4 structure is completely destroyed. Both the conversion of spinels and the complete decomposition of Fe 2 SiO 4 have created favorable conditions for the oxidation of V-bearing phases. After roasting for 50–90 min, V atoms transitioned from the mixed valence states (V 4 + /V 5+ ) to V 5+ . This transformation involved the combination of Mg 2+ , O 2- V 5+ and Mn 2+ ions, resulting in the formation of Mg 2 V 2 O 7 and Mn 2 V 2 O 7 crystals. Meanwhile, Cr atoms still exist as nontoxic Cr 3+ in the form of (Fe 0.6 Cr 0.4 ) 2 O 3 , ensuring the eco-friendliness of the magnesiation roasting of VS-HCC.