Clean and efficient extraction of vanadium from vanadium slag: Effect of manganese on the phase composition and vanadium extraction process

Manganese in vanadium slag plays an important role in the clean and efficient extraction of vanadium, attributed to the effect of manganese content on the phase of vanadium slag and the synergistic effects between manganese and roasting additives during the roasting process. In this study, remelting and crystallization method were used to prepare vanadium slag with different MnO mass fractions. The aforementioned effects were examined using XRD, SEM, and roasting-leaching experiments. The results show that manganese in vanadium slag always occupies the lattice of iron and forms (Mn, Fe)(V, Cr)2O4 and (Fe, Mn)2SiO4. With the increasing MnO content, the diffraction peaks of both spinel and olivine shift to a small angle due to the lattice distortion. Moreover, the MnO content has a greater influence on olivine than on spinel. Mn2V2O7 and Ca2V2O7 are the main vanadates of blank roasting and calcification roasting using n(CaO)/n(V2O3) of 2, respectively. During calcification roasting with n (CaO)/n(V2O3) less than 2, calcium vanadate and manganese vanadate coexist in the roasted samples. During leaching, the vanadium leaching rate shows a completely opposite trend after blank roasting and calcification roasting using n(CaO)/n(V2O3) of 2 as the MnO content increases. By reducing the amount of the added calcium salt, the vanadium leaching rate increases slightly compared with that in the case of n(CaO)/n(V2O3) is 2.0, which fluctuates between 83% and 86%. Furthermore, around 30% of manganese in vanadium slag transforms the vanadium-bearing phase and is further transferred to the leaching solution when reducing the amount of calcium salt properly.