Effective removal of impurities from Bayer crystallized vanadium slag for the separation of high-purity V₂O₅

Bayer vanadium slag, obtained through evaporation and crystallization of Bayer liquor in alumina industry, is a potential vanadium-bearing resource. At present, vanadium is hardly extracted from Bayer vanadium slag due to high impurity contents, especially As and P. Herein, a controllable route is proposed to separate high-purity V₂O₅ from Bayer vanadium slag after deep impurity removal by Mg²⁺-NH₄⁺ system. It is found that As and P contents are up to 1.39％ and 1.29％ in Bayer vanadium slag used in this study. After water leaching at a liquid/solid ratio of 4 and 80°C, the concentrations of As and P in the leaching solution reach 3.54 g/L and 2.73 g/L, respectively. By theoretical calculation of chemical equilibrium and solubility, Mg²⁺-NH₄⁺ system brought about lower arsenic equilibrium concentration and higher arsenic removal rate. It is inferred that the impurity removal effect of Mg²⁺-NH₄⁺ system is better than that of single Mg²⁺ or Ca²⁺. The optimum conditions for As removal from leaching solution, such as Mg/(As + P) and NH₄⁺/(As + P) molar ratio, pH, temperature, and reaction time, are studied. The maximum As removal efficiency is 94.8%. P and Al removal efficiency are 99.3% and 99.7%, respectively. Total vanadium loss rate is only 8.3%. 98.4% of vanadium can be separated from leaching solution after impurity removal. The purity of V₂O₅ products is 99.61% and the total recovery rate of vanadium in whole process reaches 90.23%. This work achieves the separation of high-purity V₂O₅ from Bayer vanadium slag by hydrometallurgy strategy and broadens the source of vanadium-bearing resource.