Geochemical Factors Affecting the Behavior of Antimony, Cobalt, Europium, Technetium, and Uranium in Vadose Zone Sediments

Abstract

In developing the Field Investigation Report for the Waste Management Area S-SX at the Hanford Site, 137 Cs was the only gamma emitting radionuclide of concern (Knepp 2002). a However, in WMA B-BX-BY, the spectral gamma logging data identify seven gamma emitting radionuclides, 137 Cs, 125 Sb, 152 Eu, 154 Eu, 60 Co, 235 U, and 238 U (DOE-GJPO 1998). b The geochemical behaviors of several of these radionuclides, 125 Sb and the two europium isotopes, have not been extensively investigated at the Hanford Site. This task was initiated to assure that our understanding of the geochemical properties affecting the environmental behavior of these radionuclides reflects the current state of knowledge. A literature review was conducted to assess the important oxidation/reduction, aqueous speciation, solubility, and adsorption processes affecting the environmental behavior of antimony, cobalt, europium, technetium, and uranium in vadose zone sediments with low-organic matter content in semi-arid environments such as those at the Hanford Site. Technetium-99 was included in this task because of its importance in the long-term risk calculations. This report presents the results of this literature review.

Antimony in the environment: knowns and unknowns

“…Various examples of such diagrams can be found in the literature. [18][19][20][21][22][23][24] All of these diagrams suffer in part either from the fact that inaccurate thermochemical parameters were available at the time of their construction or that data were selected arbitrarily from one of several sources. In addition, metastable phases, notably Sb 2 O 5 (s), were sometimes modelled or species such as Sb(OH) 3 (s), which are not known to occur naturally, were included in the calculations.…”

Tc-99 Ion Exchange Resin Testing

“…In oxic environments, technetium is present as Tc(VII). Technetium(VII) is not adsorptive and has high mobility, which results in K d values of approximately 0 mL/g (Krupka and Serne 2002).…”

“…Because 99 Tc is highly mobile and generally non-adsorptive, 99 Tc that is released from the resin because of degradation is assumed to be leachable with deionized water (Krupka and Serne 2002). To evaluate whether the 99 Tc has desorbed from the spent resin, a series of leaching tests was conducted using deionized water extractions.…”

Chemical Differences Between Sludge Solids at the F and H Area Tank Farms

“…Technetium can exist in five different oxidation states, 27 but the states most prevalent for environmental conditions are Tc(IV) and Tc(VII). 28 In SRS Tank Farm waste, it is assumed that the vast majority of technetium existing in sludge solids is present as Tc(IV) and relatively insoluble, in the form of hydrated technetium dioxide (TcO 2 xH 2 O) 29 and/or co-precipitated with iron(II) sorbed onto iron(III) oxide and/or oxyhydroxide particles. 30,31 In contrast, the majority of technetium existing in salt waste is assumed to be present as Tc(VII) and relatively soluble, in the form of sodium pertechnetate (NaTcO 4 ).…”