Green redox separation and efficient extraction of vanadium and chromium from leaching solution of chrome-vanadium slag

Green separation and efficient extraction of vanadium and chromium from vanadium-chromium leaching solution are serious challenges for the utilization of chrome-vanadium slag. A green sucrose reduction-H2O2 selective oxidation route is proposed for deep separation of vanadium and chromium from vanadium-chromium leaching solution based on different redox properties. Eh-pH diagram of V-Cr-H2O system and existence forms of vanadium and chromium ions are calculated. Obvious difference of redox properties between V(V) and Cr(VI) exists in acidic environment. The dependences of selective separation on pH for reduction, temperature, m(sucrose)/m(Cr(VI)) and n(H2O2)/n(V(V)) are studied. The concentration ratio of vanadium to chromium in solution after selective separation of chromium decreases from 1.6 to 0.06. The extraction ratios of Cr2O3 and V2O5 are 96.3% and 93.8%, respectively. The redox behavior of V(V) and Cr(VI) is revealed. Cr(VI) and V(V) are reduced to Cr(Ⅲ) and V(IV) by 5-hydroxymethylfurfural, a hydrolysate of sucrose, and then V(IV) is selectively oxidized to V(V) by H2O2. Cr2O3·n(H2O) and ammonium polyvanadate obtained by hydrolysis and ammonium precipitation are calcined to Cr2O3 and V2O5, respectively. Cr2O3 with the purity of 99.4% can be used as high-quality pigment. The purity of V2O5 meets the requirements of YB/T 5304–2011 for 98 V2O5.