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

The stability constant (beta(1)) of AmF2+ in the mixed solvent system of dimethyl sulfoxide and water with 0.1 mol dm(-3) ionic strength was determined using a solvent extraction technique to compare with Nd(II I) bearing similar chemical properties to Am(III). The value of ln bet a(1) was nearly constant when the mole fraction of DMSO in the bulk so lution (X-s) was less than 0.04 and it increased with an increase in X -s in the range of 0.04 < X-s < 0.25. The variation of ln beta(1) with X-s is obviously different from the result of Nd(III). The difference between the variations of ln beta(1) of Am(III) and Nd(III) with X-s could be associated with (1) the cation solvation effect (containing t he variation effect of the solvation number in the primary solvation s phere of tripositive cation) and (2) the variation effect of interioni c distance between tripositive cation and fluoride ion. The variation of In beta(1) of Am(III) in 0.04 < X-s < 0.25 of the DMSO-H2O system i s considerably influenced by both effects due to the variation of solv ation number in the primary solvation sphere and the variation of inte rionic distance, but that of Nd(III) in X-s < 0.28 hardly contains tho se effects.