Evaluation of a large-volume water sampling technique for determining the chemical speciation of radionuclides in groundwater

A laboratory evaluation of a large volume water sampling technique was conducted to determine the effects of various environmental parameters on the retention behavior of radionuclides processed through the sampler. The effects of cation resin type (H+ or Na+), pH, and additions of humic acid and EDTA on the chemical species of radionuclides in simulated groundwater were evaluated. It was shown that the use of H+ vs. Na+ cation resin greatly affected the uptake behavior of 237Pu(IV), and 237Pu(VI), 54Mn, 59Fe, 60Co and 155Eu tracers on the cation and anion resin beds. It is believed that pH reductions in the water passing through the H+ cation resin section disturbs the chemical equilibria of the species of radionuclides present in the water causing changes from anionic to cationic forms. By adding as little as 5 ppm of humic acid or EDTA, it was possible to simulate the anionic forms of 54Mn, 60Co, 63Ni, 55Fe, 155Eu and Pu observed in field sampling operations. The role of organic complexation of these radionuclides to form mobile anionic species is strongly implicated. Thus, the alternative use of Na+ and H+ cation resins, in combination with anion resin and aluminum oxide, appears to provide a technique for studying chemical speciation of radionuclides in groundwaters. (author)