Aqueous Complexation Reactions

Aqueous Complexation Reactions Governing the Rate and Extent of Biogeochemical U(VI)ReductionDissimilatory metal reducingbacteria (DMRB) can reduce oxidized uranium (U(VI)) leading to the precipitation of U(IV)O2. Despite the promise of bioreduction asa remediation strategy, the factors that enhance or inhibit the rate and extent of biogeochemical U(VI) reduction underrepresentative environmental conditions are not well defined. Before effective bioimmobilization can be realized, the factorsgoverning contaminant reactivity in multicomponent systems must be better understood. Only recently has the quantification of a fewkey interactions been established. For example, we recently reported the inhibition of bacterial U(VI) reduction by DMRB in thepresence of environmentally realistic concentrations of soluble calcium (Ca) (Brooks et al., 2003). This finding has significantimplications for field applications of bioreduction because Ca2+ is a dominant soluble and cation-exchangeable species in soils andaquifers. We propose to identify and quantify the important biogeochemical reactions that may inhibit or enhance U(VI) reduction.Using a combination of cation exchange resins, pure minerals and natural mineral assemblages we will establish the distribution ofCa-U-carbonate species and other potentially important competing cations (e.g., Mg2+, Sr2+). Concurrent with the measurement of thecompeting equilibria among soluble and cation exchangeable phases, the reduction of the major cation-U-carbonate species will bestudied using both abiotic and microbial agents. Our state-of-the-art measurement techniques (XAS, XRFS, EDX, TEM, radioisotopes,ICPMS, and KPA) will be applied to quantify these soluble complexes and precipitated phases. By understanding these important keyequilibiria, more predictable and effective approaches can be established for in situ bioremediation of U under realistic fieldconditions.Carryover oper funds $1K in B&R code KP1301010.