| Identifying and quantifying the controls on metal mobilities in weathering environments is critical in order to understand processes such as global element cycling, mass transport in near-surface water-rock systems, and sedimentary diagenesis. Bacteria are ubiquitous in low temperature geologic systems, and numerous laboratory and field studies demonstrate that bacteria can facilitate the, formation and dissolution of minerals, and enhance or inhibit metal transport through adsorption reactions. However, despite the growing evidence that bacteria play a key role in many geologic processes in low temperature systems, our understanding of the rates and mechanisms of bacterial effects remains rudimentary.;The reversibility of metal-bacteria adsorption reactions were studied utilizing batch desorption and pH-stat experiments. The observed extent of desorption in the experimental systems is in excellent agreement with the amount estimated from a surface complexation model based on independently conducted adsorption experiments. Competitive cation adsorption experiments were conducted in experimental systems containing one or two bacterial species. In all cases studied, the estimated adsorption behavior is in excellent agreement with the observations, with only slight differences that were within the uncertainties of the estimation and experimental procedures. The adsorption of the uranyl ion to Bacillus subtilis was studied as function of time, pH, and solid:solute ratio. The U adsorption data require two separate adsorption reactions, with the uranyl ion forming surface complexes with the neutral phosphate functional groups and the deprotonated carboxyl functional groups of the bacterial cell wall.;A systematic study of the effects of bacteria cell walls on the extent of mineral precipitation is also described. The results indicate that bacterial cell walls can not induce precipitation at under-saturated mineral conditions. These experiments unequivocally constrain the effects non-metabolizing bacteria have on mineral precipitation, and are in disagreement with previous unconstrained experiments.;The results presented within this dissertation demonstrate that bacteria are likely to have a profound effect on the mobility of metal cations in many near-surface geological systems, and that these interactions can be constrained through the use of equilibrium thermodynamics. |
