Thermodynamics Research Center / ThermoML | Fluid Phase Equilibria

ABSTRACT

The concentered region of the CaCO3_P2O5_H2O ternary system was investigated at 25,35 and 70 deg.C using Schreinemaker's method and synthetic method based on conductivity measurement. The characterization of stable solid phase was realized by X-ray diffraction and complexometric titration, which shows the presence of three solids stable region Ca(H2PO4)2.H2O_Ca(H2PO4)2_CaHPO4 in the three isotherms. H3PO4.12H2O presents stable equilibria with liquid and Ca(H2PO4)2 at 25 deg.C, these equilibria do not occur at 35 and 70 deg.C. Equilibrium zone between H3PO4 and Ca(H2PO4)2 was determined at 25 and 35 deg.C but disappeared at 70 deg.C. The limits between different regions were determined by the titration of the phosphoric acid (H3PO4) and calcium cation (Ca2+) concentrations in the liquid phase.