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 Battelle Large Volume Water Sampler (BLVWS) consists of an inline membrane prefilter assembly connected to a housing containing multiple beds of cation resin, anion resin and activated aluminum oxide. This sampler quantitatively extracts radionuclides from large volumes (up to 4000 liters) and partitions the radionuclides according to their chemical forms. The effects of cation resin type (H/sup +/ or Na/sup +/), 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/sup +/ vs. Na/sup +/ cation resin greatly affected the uptake behavior of /sup 237/Pu(IV), and /sup 237/Pu(VI), /sup 54/Mn, /sup 59/Fe, /sup 60/Co and /sup 155/Eu tracers on the cation and anion resin beds. It is believed that pH reductions in the water passing through the H/sup +/ 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 acidmore » or EDTA, it was possible to simulate the anionic forms of /sup 54/Mn, /sup 60/Co, /sup 63/Ni, /sup 55/Fe, /sup 155/Eu 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/sup +/ and H/sup +/ cation resins, in combination with anion resin and aluminum oxide, appears to provide a technique for studying chemical speciation of radionuclides in groundwaters. 19 refs., 5 tabs.« less