Isopiestic Studies On Thermodynamic Properties Of The System LiCl-Li₂B₄O₇-H₂O Containing Lithium And Boron At Different Temperatures

The isopiestic molalities and water activities have been determined for the systems LiCl-H₂O,Li₂B₄O₇-H₂O and LiCl- Li₂B₄O₇-H₂O at 273.15K by the isopiestic method established for low temperatures using an improved equipment in the ion strength ranges of 0.2046-2.5055 mol · kg^-1, 0.1295-0.4431 mol · kg^-1 and 0.1032-2.5113 mol· kg^-1 and at 298.15K in the ion strength ranges of 0.1578-4.0594 mol· kg^-1, 0.1770—0.4176 mol · kg^-1 and 0.1618-4.0710 mol · kg^-1 . The osmotic coefficients and saturated vapor pressures have been calculated at the different temperatures .The experimental values of the osmotic coefficients for the LiCl-H₂O system were consistent with the values in the references. The results reveal the rules of the changing in osmotic coefficients and saturated vapor pressures with ion strengths and the molality fractions of Li₂B₄O₇ at different temperatures. The change rules of those were compared at different temperatures. The isopiestic equilibrium molalities were correlated by using modified and the extended Zdanovskii rules for non-ideal mixtures, and obey well the Zdanovskii rules. The ion interaction parameters of Pitzer model have been determined by using the two methods for LiCl- Li₂B₄O₇-H₂O system. One series of parameters of Pitzer model were evaluated from the measured data in this work and the data in the references by using multiple regression analysis, according to the stoichiometric concentrations of Li₂B₄O₇ in the solutions. The standard deviations between the calculated and the experimental osmotic coefficients were reported, which indicated that the Pitzer ion -interaction model can describe the thermodynamic properties for the systems under the experimental conditions. Another series of parameters of Pitzer model have been evaluated by using multiple regression and iterative methods, according to the differentboron species existing in the solutions, and discussed. The mean activity coefficients of LiCl and Li₂B₄O₇ for LiCl- Li₂B₄O₇-H₂O system were calculated using Pitzer model at different temperatures and the results reveal the rules of the mean activity coefficients of LiCl and Li₂B₄O₇ in the mixing solutions changing with the ion strengths and the molality fractions. This work has offered the lacking basic thermodynamic data for LiCl-Li₂B₄O₇-H₂O system at 273.15K and 298.15K. This work is useful to improve the thermodynamic model for salt lake brine systems containing Lithium and borates and to make utilization of the resources in salt lake.