INFLUENCE OF SOME SEAWATER COMPONENTS ON THE SORPTION BEHAVIOR OF NEPTUNIUM(V)

The fate of neptunium in the aquatic environment is dependent upon, am ongst other processes, the extent of uptake by particulate material. I n oxic natural waters it exists predominantly in the V-valent state. A number of laboratory experiments have been carried out, using Np-239 tracer, particulate material prepared from Irish Sea sediment and vari ous synthetic solutions, to determine the influence of chemical parame ters on the sorption behaviour of Np(V) in marine waters. The data sug gest that uptake is highly dependent upon solution pH both as a result of changes in charge on particle surfaces and, at high pH values (>9. 0), from the formation of hydrolysis species. Np(V) uptake by marine p articulate material was essentially independent of ionic strength with in the pH range of natural seawater. The presence of Mg2+, Ca2+ and HC O3- ions was found to inhibit Np(V) sorption; removal of Np(V) was, ho wever, increased from solutions which were supersaturated with respect to CaCO3. The data indicate that, although Np(V) sorption in seawater is controlled by interactions between Mg2+, Ca2+ and HCO3- ions, the effect of the combined presence of all three constituents is more comp lex than might be expected from the action of individual components.