Investigation on separation principle of vanadium and chromium among Fe2VO4-CaO-FeCr2O4 system: Simplify and simulate calcification roasting process of vanadium-chromium slag

Abstract

The competitive reaction of vanadium and chromium with calcium additives, along with the formation mechanism of calcium vanadate and calcium chromate are the central issue to the efficient separation and extraction of vanadium and chromium from vanadium-chromium slag (V-Cr slag) by calcification roasting. In this study, Fe2VO4 and FeCr2O4 were synthesized to simulate the vanadium chromium spinel in V-Cr slag; then, the reaction mechanism of Fe2VO4-CaO-FeCr2O4 powder system was studied by XRD, SEM and leaching experiments. Results showed that calcium vanadate and calcium chromate are generated after roasting Fe2VO4-CaO system and FeCr2O4-CaO system individually. In Fe2VO4-CaO-FeCr2O4 system, as n(CaO)/n(V2O3) is 2, vanadium exists in the form of Ca2V2O7 while almost all Cr2O3 from the decomposition of FeCr2O4 reacts with Fe2O3 to continuously form solid solution with more FeCr2O4 adding. After leaching, the addition of FeCr2O4 has no obvious effect on the leaching ratio of vanadium, and the leaching ratio of chromium decrease with FeCr2O4 adding. Consequently, 94.03% of vanadium and 0.15% of chromium are leached with n(CaO)/n(V2O3)/n(Cr2O3) of 2/1/1.03 at 900 °C. When n(CaO)/n(V2O3) is 4, Fe2VO4 is oxidized and calcified gradually to form Ca2V2O7 and Ca3V2O8 with increasing roasting temperature. A small amount of CaCrO4 is generated owing to the calcification of chromium, and most chromium still exists in the form of solid solution. The reaction result of Cr2O3 and Fe2O3 is the superposition of solid solution reactions with different degrees. Increasing the roasting temperature can significantly reduce the chromium leaching ratio. All above would provide a theoretical support for the calcification roasting process from V-Cr slag.