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

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 θMgLi and ψMgLiCl for the fit. The regression gave values of 0.075626 for θMgLi and −7.1392×10−3 for θMgLiCl. 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%.