Thermodynamic simulation of stepwise precipitation of NH4VO3 and NaHCO3 from carbonating Na3VO4 solution

Abstract

Thermodynamic simulation was conducted to design a new process of stepwise precipitating NH₄VO₃ and NaHCO₃ from regulating the CO₂ carbonation of Na₃VO₄ solution. Firstly, a new V(V) speciation model for the aqueous solution containing vanadate and carbonate is established by using the Bromley−Zemaitis activity coefficient model. Subsequently, thermodynamic equilibrium calculations are conducted to clarify the behavior of vanadium, carbon, sodium, and impurity species in atmospheric or high-pressure carbonation. To ensure the purity and recovery of vanadium products, Na₃VO₄ solution is initially carbonated to the pH of 9.3−9.4, followed by precipitating NH₄VO₃ by adding (NH₄)₂CO₃. After vanadium precipitation, the solution is deeply carbonated to the final pH of 7.3−7.5 to precipitate NaHCO₃, and the remaining solution is recycled to dissolve Na₃VO₄ crystals. Finally, verification experiments demonstrate that 99.1% of vanadium and 91.4% of sodium in the solution are recovered in the form of NH₄VO₃ and NaHCO₃, respectively.