Further investigations of the humate complexation of very low concentrations of neptunium(V)

Further investigations were made by continuous electrophoretic ion focusing on the humate complexation of Np(V) in very low concentrations - about 10-13 M - at ionic strength 0.01 M, pH 5 and various humic acid concentrations. In addition an anion exchange chromatographic technique with DEAE-Sephadex A25 was applied to separate Np-humate from free Np(V). With both separation techniques the ratio Npbound/Npfree was determined and from this an estimate of the interaction constant ss for humate complexation of Np(V) was made. A logss of 5.18 ± 0.08 was obtained by ion focusing and 5.26 ± 0.05 by anion exchange chromatography under the assumption of a humic acid loading capacity of 5%. Experiments of humate complexation of neptunium in presence of calcium have shown that calcium acts as a competing ion and diminishes the complexation of trace amounts of neptunium. (orig.)