Cleaner and cost-efficient extraction of vanadium from Bayer vanadium sludge based on BaCO3, NaOH, and ammonium circulation

Abstract

Bayer vanadium sludge, as a by-product generated from the Bayer process, is a potential secondary resource for vanadium recovery. To alleviate the problems of reagent consumption and effluent treatment presented in vanadium extraction processes, a novel and sustainable process featuring phosphate removal by CaCO3, vanadium precipitation by BaCO3, and NH4HCO3 leaching is carried out to separate and recover vanadium from Bayer vanadium sludge efficiently based on thermodynamic analysis. A maximum phosphate removal efficiency of 99.88% is achieved with a Ca/P molar ratio of 5 at 90 °C for 3 h, whereas the loss of vanadium is only 0.25%. Moreover, 98.57% of vanadium along with only 1.15% arsenate and 0.12% fluoride are co-precipitated from phosphate-free liquors containing 60 g/L NaOH with a Ba/V molar ratio of 1.6 at 90 °C for 4 h. After vanadium precipitation, the remaining large amounts of NaOH in supernatant can be recycled after the removal of arsenate and fluoride by evaporation crystallization. The NH4HCO3 leaching results illustrate that the vanadium leaching efficiency reaches 95.99% under 100 g/L NH4HCO3 at 70 °C for 30 min with a liquid-to-solid ratio of 20. The NH4VO3 in the leaching liquor can be readily crystallized by cooling, and then V2O5 product with a purity of 99.81% is prepared after calcination. The leaching residues and the spent liquor after crystallization can be circulated as vanadium precipitant and leaching medium, respectively. Herein, three circulation routes realize the closed-circuit circulation of BaCO3, NaOH, and ammonium, saving production costs and avoiding effluent pollution.