AM3-F- INTERACTION IN MIXED SYSTEM OF METHANOL AND WATER()

The stability constants of americium monofluoride complex, beta(1), ha ve been determined in mixed solvents of methanol and water at 0.1 mol dm(-3) ionic strength using a solvent extraction technique. The values of ln beta(1) increase as the mole fraction of methanol in the mixed solvent system (X-s) increases. The Variation of ln beta(1) with an in crease of X-s could be explained by the effect of the solvent on the s olvation of Am3+, F- and AmF2+. The variation of the cation solvation effect for ln beta(1) as a function of X-s can be represented by two s traight lines, which have an inflection point in the neighborhood of X -s = 0.10. The change of the cation solvation effect at the inflection point could be interpreted by a variation of the solvation number in the primary solvation sphere of Am3+. The solvation number is 9 for th e region of X-s < 0.10 and a mixture of 9 and 8 for the region of 0.10 < X-s < 0.29.