The crystallisation of alkaline-earth metal tungstates from metal chloride melts: solubility - temperature phase diagram studies

The solubility vs temperature phase diagrams, for magnesium, calcium, strontium and barium tungstate solutions in lithium, sodium, potassium chloride melts and in the alkaline-earth metal chloride melts, have been analysed. The solutions in the alkali metal chloride melts are pseudo-binary reciprocal ternary mixtures; the more soluble barium tungstate systems show small deviations from ideality, while the less soluble magnesium tungstate systems show marked deviations from ideality, especially in sodium and potassium chloride melts. These deviations are related to electrostatic effects in solution, that depend on some function of reciprocal solute and solvent cation radii. The solutions in the alkaline-earth metal chlorids melts are binary mixtures with no solvate formation; these systems show some deviations from ideality at low mole fractions (x = 0.1 to 0.25) but they are practically ideal at mole fractions from 0.25 to 0.6. (author)