NEPTUNIUM(V) COMPLEXATION BY ACETATE, OXALATE AND CITRATE IN NACLO4 MEDIA AT 25-DEGREES-C

Complexes of neptunyl, NpO2+, with acetate, oxalate, and citrate have been investigated by the solvent extraction method with HDEHP in 0.1-9 .0 m NaClO4. The stability constants of the 1:1 complexes with acetate and oxalate increase with ionic strength up to 9 m NaClO4 whereas tho se with citrate show a maximum at 7 m NaClO4. A thermodynamic model wa s constructed to predict the apparent stability constants at different ionic strengths by applying the Fitter equation using the interaction parameters beta((0)), beta((1)), and C-phi which were obtained by fit to the data. Thermodynamic stability constants of NpO2Ac0, NpO(2)Ox(- ), and NpO(2)Cit(2-) complexes were calculated to be log beta(101)(0) = 1.35 +/- 0.08, 3.84 +/- 0.07, and 3.74 +/- 0.03, respectively, as ob tained by extrapolation to zero ionic strength using Pitzer model.