Assessment of natural attenuation and targeted in-situ remediation of radioactively contaminated land

UoM administered thesis: Phd

  • Authors:
  • Adrian Cleary

Abstract

Radioactive contaminants, including uranium, strontium-90 and technetium-99 are present at elevated concentrations within groundwaters at several nuclear facilities around the world such as Sellafield (UK), Hanford (USA), Oak Ridge (USA) and Mayak (Russia). In-situ remediation technologies are therefore currently receiving attention as a favourable means of treating the subsurface as opposed to “dig and dump” or traditional engineered barrier systems. It is important that treatment of these co- contaminants using in situ remediation approaches considers the biogeochemical behaviour of each radionuclide and long term stability of the treatment products. The mobile forms of uranium (U(VI)O22+) and technetium (Tc(VII)O4-) may precipitate as insoluble U(IV) and Tc(IV) minerals following microbial reduction, stimulated by the addition of an organic electron donor. In contrast, the mobility of strontium in the environment is predominantly limited by sorption to clay minerals and Fe oxides. Sorbed strontium is susceptible to mobilisation by other divalent cations, e.g. Mg 2+ and Ca 2+ . However both Sr and U(VI) may be incorporated into biominerals including phosphate phases. In this study, the potential of glycerol phosphate to co-treat strontium, technetium and uranium was investigated in pure culture, sediment microcosms and flow-through sediment column systems. Anoxic pure cultures of an isolate of Serratia stimulated with glycerol phosphate showed both microbial growth and removal of Sr from solution via co-precipitation within amorphous calcium phosphate biominerals. Amending sediment microcosms with glycerol phosphate resulted in the enhanced removal of both Sr and Tc from solution by stimulating both phosphate biomineralisation and reductive precipitation. Finally, in flowthrough sediment column experiments, stimulation with glycerol phosphate resulted in restricted migration of both U and Sr compared to an untreated sediment column. These results indicate that the in-situ bioremediation, with a glycerol phosphate amendment, may be suitable for the immobilisation of a number of radionuclides with different biogeochemical characteristics through stimulating both anaerobic microbial reduction and phosphate biomineralisation.

Details

Original languageEnglish
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Award date1 Aug 2019