Sorption of Strontium by Bacteria, Fe(III) Oxide, and Bacteria-Fe(III) Oxide Composites

This study provides the first quantitative comparison of the sorptive capacities of a bacteria-Fe oxide composite to its individual components. These results have enormous significance for understanding the fate and transport of inorganic contaminants in natural aqueous environments where heterogeneous bacteria-oxide composite solids are commonly found. We quantify Sr 2+ sorption to the bacteria Shewanella alga, Shewanella putrefaciens, amorphous hydrous ferric oxide (HFO), and S. alga coated with HFO over a range of total Sr 2+ concentrations (0.005-10 mM) and pH (2.5-11 at 0.5 pH increments), under well controlled laboratory conditions. Significant Sr 2+ sorption occurred at significantly lower pH values to the bacteria and S. alga-HFO composite (5.5-5.9) compared to HFO (7.6). Geochemical modeling using a generalized Langmuir equation showed that the bacteria sorb significantly greater quantities of Sr 2+ (maximum sorptive capacity: BSr max ) 0.079 and 0.075 mmol‚g -1 for S. alga and S. putrefaciens, respectively) than the HFO (0.001 mmol‚g -1 ). The observed BSr max for the S. alga-HFO composite (0.034 mmol‚g -1 ) was less than the combined sorptive properties of its components (BSr max ) 0.041 mmol‚g -1 ), likely reflecting HFO masking of bacterial surface binding sites