Groundwater radionuclide species

Generally, a significantly increased distribution coefficient is obtained after a contact time of 6 months in comparison with 1 week (by a factor of less than five), especially for the tri-and tetravalent elements (and Ra) on granite. Evidently the diffusion of hydrolyzed products into the grains is a slow process. Radionuclide Species in Groundwater... 

Proposed radionuclide species in non-oxidizing granitic groundwater... 

Chemical Retention in the Ground. Due to chemical interac-tions with the rock and with species in the groundwater the radionuclides will be retarded. This would be the final barrier preventing a release into the biosphere. 

Of the elements considered in this study (see Table II), nickel, palladium, antimony, and lead are particularly sensitive to the presence of reduced sulfur species (S2, HS") in the groundwater. For each of these radionuclides, if sulfur speciates under thermodynamic equilibrium conditions, solid sulfide phases will control their solubility at low Eh values. The implication of this fact is illustrated in Figure 1 by a bold, dashed line that corresponds to the solubility of nickel in the reference groundwater and a patterned zone representing the total range... 

It is clear from previous comments that radionuclide speciation studies must consider not only oxidation states and specific inorganic forms but also complex species arising through association with natural organic matter and the possibility of different physical states. The relative importance of these various physicochemical forms will, in practice, be dictated by a combination of the basic elemental characteristics of the radionuclide and the type of environment into which it is placed. Thus in seawater, colloidal organic complex species are likely to be far less dominant than for the same radionuclide in a very low ionic strength freshwater. In the case of soil and sediment interstitial waters or groundwaters,... 

When a contaminant species of interest is already present in the soil or groundwater, it is highly recommended that the water and soil be sampled and analyzed for the contaminant to determine an in situ value. This is, after all, the we are interested in. Its value often differs substantially from a measured in the laboratory. For example, Fruchter et al. (1985) report respective laboratory AT/s of 3560,400, and 19 ml/g for Co, Ru, and Sb. Respective in situ K s for these radionuclides equaled 9,6, and 4, indicating that, in fact, they were relatively mobile in the groundwater. The authors point out that the laboratory K/s were measured in noncomplexing electrolyte solutions, whereas in the field the radionuclides were complexed, probably by organic substances, making them less likely to be adsorbed. 

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