Thermodynamic analysis of solute-solvent interactions in the solubility-temperature relations of alkaline-earth metal tungstates and sodium tungstate

This paper presents a study of thermodynamic analysis of the solubility-temperature phase diagrams for solutions of calcium, strontium and barium tungstate in sodium tungstate melts in the temperature range 660 to 1200 0C. At temperatures 1000 0C and above, the solutions were ideal but below 1000 0C the solutions became non-ideal and the non-ideality increased with decreasing temperature. At any mole fraction concentration of the solute the excess free energies of mixing and the activity coefficients increased in the order CaWO4 > SrWO4 > BaWO4, whereas the excess chemical potentials decreased in the order CaWO4 < SrWO4 < BaWO4. (author)