SOLVENT-EXTRACTION STUDY OF ND3-F- AND TM3+-F- INTERACTION IN MIXED SYSTEM OF METHANOL AND WATER()

The stability constants of the monofluoride complex of Nd(III) and Tm( III) have been determined in mixed solvents of methanol and water at 0 .1 mol dm(-3) ionic strength, using a solvent extraction technique. Th e values for both lanthanides increase as the mole fraction of methano l in the mixed solvent system increases. The variation of the stabilit y constants was accounted for by the Gibbs' free energy of transfer of F- between water and the mixed solvents. Furthermore, a small effect of cation solvation on the variation of ln beta(1) was also interprete d as due to both (1) a low preferential solvation of methanol and (2) a difference between the electrostatic solvation energies of Nd3+ and NdF2+, and Tm3+ and TmF2+, in water and the mixed solvent solutions.