Isopiestic measurements at high temperature: II. The ternary system LiCl-MgCl₂-H₂O at 155°C

Abstract

The ternary system LiCl−MgCl₂−H₂O has been investigated at eight different solution compositions and at 155 5°C. Isopiestic measurements have been made for total equilibrium molalities ranging up to 16.6 mol-kg⁻¹, using MgCl₂(aq) as the reference electrolyte. A description of the osmotic coefficients by the ion interaction model of Pitzer gave an overall standard error of 0.006 for the whole data set. The binary Pitzer parameters for MgCl₂(aq) were taken from Valyashko and co-workers, whereas the parameters for LiCl(aq) have been determined by the authors in a previous work. It was necessary to use both mixing parameters θ_MgLi and ψ_MgLiCl for the fit. The regression gave values of 0.075626 for θ_MgLi and −7.1392×10⁻³ for θ_MgLiCl. The modified B.E.T. equation according to Stokes and Robinson was applied succesfully for water activities lower than 0.4. Using only a linear relationship between the LiCl salt mole fraction and the B.E.T. parameters r and ΔE it was possible to describe the water activities to within 0.36%.