Determination and modeling for the solubility of Na2WO4·2H2O and Na2MoO4·2H2O in the (Na+ + MoO42− + WO42− + SO42− + H2O) system

• The solubility of Na2MoO4·2H2O and Na2WO4·2H2O in Na2MoO4–Na2WO4–Na2SO4–H2O were performed.
• The solubility of sodium tungstate dihydrate in Na2WO4–Na2SO4–H2O was determined.
• The new model was established via regressing the published and the determined data.
• The Pitzer parameter and the solubility product constant of the salt in solution were calculated.
• The model was used to estimate the solubility of the sodium molybdate and sodium tungstate.

The solubility of sodium tungstate dihydrate and sodium molybdate dihydrate in the (Na2MoO4 + Na2WO4 + Na2SO4 + H2O) system was studied using experimental and calculated methods. The osmotic coefficient of sodium tungstate was fitted to calculate the thermodynamics parameters of (Na2WO4 + H2O) system. The solubility of sodium tungstate dihydrate was determined using the dynamic method in Na2WO4–Na2SO4–H2O to establish the new model which can provide an estimate the solubility of sodium tungstate dihydrate in various conditions, combined with the data published, the solubility of sodium tungstate dihydrate and the sodium molybdate dihydrate in quaternary system of (Na2MoO4 + Na2WO4 + Na2SO4 + H2O) was estimated using the parameters of the two ternary systems of (Na2WO4 + Na2SO4 + H2O) and (Na2MoO4 + Na2SO4 + H2O). The results show that the AARD is always small and the calculated value is basically consistent with the experimental values for the system studied.