COMPLEXATION OF NP(V) WITH FULVIC-ACID

A spectroscopic study is presented for the complexation of the pentava lent neptunyl ion with fulvic acid, extracted from the Gorleben aquife r system, at pH 6 to 8 in 0.1 M NaClO4. The speciation is made by UV-V IS spectroscopy in the wavelength range of 950-1020 nm. The complexati on reaction is described according to the metal ion charge neutralisat ion model by introducing the loading capacity (LC) of given fulvic aci d for the NpO2+ ion at each pH under consideration. Only 1:1 humate co mplex is found as prevalent without formation of higher order complexe s. The complexation constant is found to be log beta = 3.53 +/- 0.04, which appears independent of the metal ion concentration and pH, and c omparable to the value found for its complexation with humic acid. Dis cussion is extended to different methods of calculation for the free f ulvic acid concentration and their importance to the evaluated constan ts.