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Effect of Organic Co-Contaminants on Technetium and Rhenium Speciation and Solubility under Reducing Conditions

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journal contribution
posted on 01.09.2006, 00:00 by Estela Reinoso Maset, Stephanie H. Sidhu, Andrew Fisher, Andrew Heydon, Paul J. Worsfold, Andrew J. Cartwright, Miranda J. Keith-Roach
The chemical and biogeochemical reduction of pertechnetate (TcO4-) and perrhenate (ReO4-) have been compared alongside complexation of the reduced species by three anthropogenic ligands relevant to nuclear waste (ethylenediaminetetraacetic acid (EDTA), nitrilotriacetic acid (NTA), and isosaccharinic acid (ISA)). An HPLC size-exclusion column coupled to ICP-MS was used to separate the species and quantify Tc and Re. During method development, ReO4- showed recalcitrance to direct chemical reduction by Sn(II) under conditions that readily reduced TcO4- and resulted in Tc(IV)−organic complexes. In microcosm experiments of a silty loam soil containing TcO4-, ReO4-, and ISA (3.0 mM), EDTA (0.17 mM), or NTA (2.4 mM), anoxia developed to iron-reducing conditions during the 42 day experimental period. The majority of the TcO4- was reduced to particle-reactive Tc(IV) and removed from solution during nitrate reduction, but there was no chromatographic evidence of Tc(IV)−organic complexes in the porewater. Overall, the excess organic complexants added did not cause a measurable difference in the solubility of Tc(IV) over the control experiments in this organic-rich (12% organic carbon) soil. ReO4- did not undergo reduction, as shown by the constant porewater concentration and the chromatographic data, and thus Re does not function as an analogue for Tc under environmental nitrate- and iron-reducing conditions.