Competitive extraction behaviors of vanadium and chromium in the sodium roasting - Water leaching process

The separation of vanadium and chromium from vanadium-chromium slag constitutes the greatest bottleneck in the exploitation and utilization of high-chromium vanadium-titanium magnetite, which mainly results from the insufficient understanding of the behavior of similar elements vanadium and chromium during the extraction process. In this research, a series of spinels FeVxCr2-xO4 (0 <= x <= 2) were synthesized via the high-temperature solid-state method, and their sodium roasting and leaching behavior were comprehensively analyzed. The transformation rules of sodium vanadate and chromate were investigated by XRD, SEM-EDS, FTIR, and thermodynamic calculation. The results indicate that in the FeVxCr2-xO4 (0 <= x <= 2)- Na2CO3 system, at 300 degrees C, a portion of chromium spinel phase is preferentially and slowly oxidized to Cr2O3, while the vanadium spinel rapidly oxidizes to form NaVO3 at 400 degrees C. Above 500 degrees C, NaVO3 further reacts with Na2CO3 to form Na4V2O7, and Na2CrO4 also begins to form concurrently. As the proportion of Cr in FeVxCr2-xO4 increases, both the leaching efficiencies of vanadium and chromium from the sodium-roasted samples decrease, with the leaching efficiency of chromium decreasing more significantly. Significant competitive and synergistic effects between vanadium and chromium are observed in the roasting of FeVxCr2-xO4 with Na2CO3. This study is expected to provide theoretical support for the development of efficient vanadium-chromium extraction processes.