Modeling for tungstic precipitation and extraction based on Pitzer equation.

This work presented the results of tungstic precipitation from NaWO-NaSO-HO system at 293.15 K, with which the Pitzer parameters of $$\beta _{N{a_2}W{O_4}}^{\left( 0 \right)}$$ and $$\beta _{N{a_2}W{O_4}}^{\left( 1 \right)}$$ were determined from Pitzer equation by regression. Thus the mean ionic activity coefficients of sodium tungstate were calculated. The obtained $$\beta _{N{a_2}W{O_4}}^{\left( 0 \right)}$$ and $$\beta _{N{a_2}W{O_4}}^{\left( 1 \right)}$$ were substituted as fixed values in extraction modeling from NaWO-HSO-HO system by primary amine (N1923) in toluene as diluent. Meanwhile the activity coefficient expressions in organic phase were varied based on Pitzer theory that the interaction term for the solvent should not be included. The Pitzer parameters for organic phase were re-regressed in order to make the model more accurate. The average absolute relative deviation (AARD) for calculated and experimental molality of WO in aqueous phase was 5.24%. The results showed that the model can not only correlate but also predict the liquid-liquid equilibrium (LLE) data. [ABSTRACT FROM AUTHOR]