THERMODYNAMICS OF MIXING OF LIQUIDS IN THE SYSTEM CA3(PO4)2CACL2CAF2CA(OH)2

Abstract

Molten calcium halide and hydroxide salts may be used as flux and reactants in determining apatite exchange equilibria and solid solution behavior. New experimental data and published phase equilibria are used to determine a thermodynamic model of melts and solids along the binary joins of the anhydrous apatite system Ca3(PO4)2-CaCl2-CaF2-Ca(OH)2. In this model, melt components are expressed as Ca0.5X, where X is hydroxide or a halogen, or as Ca1.5PO4. The derived binary interaction parameters (WG's) are sufficient to describe deviations from Raoultian behavior for the data. Standard state data are derived for molten Ca(OH)2 and Ca3(PO4)2, and for the intermediate compounds CaClF, CaClOH, and Ca2PO4Cl.