Determination and Analysis of Solubility of Na3VO4 in Aqueous NaOH Solutions Containing Na2CO3, NaAlO2, or Na2SiO3 at 298.15–353.15 K

In a new vanadium extracting process, the effective separation of Na3VO4 from the aqueous NaOH solution containing impurities of Na2CO3, NaAlO2, or Na2SiO3 plays a significant role. The solubility data of NaOH-Na3VO4-H2O system and NaOH-Na2CO3-Na3VO4-H2O system at 298.15, 313.15, and 353.15 K were measured. The Na3VO4 solubility in NaOH solutions containing 30.4 g.L-1 NaAlO2 or Na2SiO3 at 313.15 and 353.15 K were also studied for comparison. Na2CO3 has a strong salting-out effect on Na3VO4 with NaOH molality <7 mol.kg(-1). Moreover, NaAlO2 and Na2SiO3 have a little inhibitory effect on the Na3VO4 solubility, and the effect of NaAlO2 is more significant. The equilibrium solid phases of sodium orthovanadate in the above systems were identified, which mainly presented Na3VO4 center dot 12H(2)O at NaOH molality <10 mol.kg(-1) and Na3VO4 at NaOH molality >10 mol.kg(-1). The determined solubility data and equilibrium solid phases are essential in optimizing the operating parameters for Na3VO4 crystallization from actual NaOH solutions. To balance the crystal purity and vanadium recovery, a strategy has been proposed for the effective separation of Na3VO4 by evaporation/cooling crystallization after decreasing the Na2CO3 concentration.