Microbial mineral transformations at the Fe(II)/Fe(III) redox boundary for solid phase capture of strontium and other metal/radionuclide contaminants. Annual progress report, September 15, 1996--June 15, 1997

'The objectives of the project remain the same as those stated in the original proposal. Specifically, to determine microbiological and geochemical controls on carbonate mineral precipitation reactions that are caused by bacterial reduction of Fe(III)-oxides, and identify contributions of these processes to solid phase capture of strontium and other metal/radionuclide contaminants. The project on microbial mineral transformations at the Fe(II)/Fe(III) redox boundary for the solid phase capture of strontium is progressing well. Thus far, the authors have been able to demonstrate that: pH and DIC concentrations increase during microbial reduction of HFO in batch culture experiments with G. metallireducens lasting 30 days with high concentrations of strontium (1.0 \265m) and calcium (10 \265m) do not inhibit microbial HFO reduction, the extent of change in pH and DIC concentrations brings about supersaturation with respect to carbonate minerals including siderite (FeCO{sub 3}), strontianite (SrCO{sub 3}), and calcite/aragonite (CaCO{sub 3}); in addition, precipitation of siderite has been documented in cultures of HFO reducing bacteria significant amounts of strontium and calcium (40 to 50% of the total initial concentration) sorb to particulate solids (i.e., HFO and bacteria cells)-in batch culture experiments l sorption of strontium to HFO conforms with Langmuir single site sorption models derived from corresponding mass action and mass balance relationships anticipated from thermodynamic equilibrium considerations the sorption behavior of strontium with S. alga is more complex and seems to involve two sets of reactive surface sites on the bacterial cells; a high affinity site of low total sorption capacity, and a low affinity site with high sorption capacity the total strontium sorption capacities of S. alga and HFO are comparable the observed solid phase partioning of strontium in the culture experiments is in excellent agreement with sorption characteristics measured with HFO and S. alga.