T88 Uranium in Groundwater: Biogeochemical Controls on Mobility and Persistence

Monday, 10 October 2011
8:00 AM - 12:00 PM
Room 211AB

HARNESSING MICROBIAL PROCESSES FOR THE BIOREMEDIATION OF URANIUM AND OTHER RADIONUCLIDES

Paper number: T88-2
Program: Technical Sessions
Time: 8:05 AM – 8:25 AM

Authors

Abstract

Microbial metabolism can have a controlling influence on the solubility of actinides and fission products in natural and engineered environments. Mechanisms of uranium removal that can be important include a broad range of biomineralization processes linked to the production of surface localized or secreted ligands. Most interest, however, has focused on the microbial redox cycling of uranium, with anoxic reduction of relatively soluble and mobile U(VI) facilitated by specialist metal-reducing bacteria, resulting in the formation of essentially insoluble U(IV) (e.g. uraninite). There has been a significant body of research addressing such transformations in "far field" aquifer type systems, following "biostimulation" of the extant microbial communities with simple electron donors. These studies have ranged from the mechanisms of bioreduction, including identification of the genes, proteins and other redox active biomolecules involved in electron transfer, to the post-reduction fate of the actinide. These studies have also addressed U(IV) re-oxidation and remobilization, which can be appreciable, under a range of environmental conditions. The importance of redox cycling to estimating the persistence of U plumes is now being considered, with the oxidation of U(IV) recognized as a potential source of soluble U(VI).

Complementary studies have also addressed the fate of other redox active radionuclides (including Np, Pu and Tc) under similar redox cycling scenarios. They show a surprising variation in behaviour under reducing and oxidizing conditions, and suggest that the impact of biostimulation of anaerobic uranium-reducing bacteria should be accompanied by a deeper understanding of the impact of such processes on a broad-range of toxic and radioactive elements, where they are present. There is also an increasing interest in the microbial redox cycling or uranium and other radionuclides in a broad range of engineered environments and wasteforms under biogeochemically more extreme conditions. Recent studies in these areas, and their implications, will also be discussed.