Thermodynamics Research Center / ThermoML | Journal of Chemical Thermodynamics

ABSTRACT

Fluoride is highly related to human health. Thermodynamic equilibrium models can used as be powerful predictive and interpretive tools to evaluate its potential hazards. A few works have ever been conducted to deal with fluoride involved aqueous solutions. However, bicarbonate and sulfate, which have a positive relationship with the concentration of fluoride in aqueous solutions, have not been evaluated. In this work, the solubilities in the NaF-Na2CO3-H2O system and the NaF-Na2CO3-NaHCO3-H2O system were determined with the isothermal dissolution method at (308.15 and 323.15) K and atmosphere pressure. Using this set of experimental data and those from the literature, a thermodynamic equilibrium model in the mixed system Na-F-CO3-HCO3-H2O was developed based on the Pitzer specific interaction model. The model gave very good agreement with the experimental solubility data. For the Na-F-SO4-H2O system, the solubility products of the double salt NaF*Na2SO4 and ternary Pitzer parameters were determined from experimental data available in the literature. Combining the parameters evaluated in this work and those from previous literature, a solid-liquid equilibrium model was developed for the Na-F-Cl-SO4-CO3-HCO3-H2O system at temperatures up to 363.15 K. The model was validated by comparing solubility predictions with experimental data given in literature, and those were not used in the parameterization process.