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

Thermodynamic simulation was conducted to design a new process of stepwise precipitating NH 4 VO 3 and NaHCO 3 from regulating the CO 2 carbonation of Na 3 VO 4 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, Na 3 VO 4 solution is initially carbonated to the pH of 9.3−9.4, followed by precipitating NH 4 VO 3 by adding (NH 4 ) 2 CO 3 . After vanadium precipitation, the solution is deeply carbonated to the final pH of 7.3−7.5 to precipitate NaHCO 3 , and the remaining solution is recycled to dissolve Na 3 VO 4 crystals. Finally, verification experiments demonstrate that 99.1% of vanadium and 91.4% of sodium in the solution are recovered in the form of NH 4 VO 3 and NaHCO 3 , respectively.