Quantifying Bacteria-Metal-Mineral Adsorption: Wet Chemistry and Advanced Photon Source Approaches

拟议的研究将使用体积吸附和EXAFS实验来校准表面络合方法，以量化地下水系统中含水金属的细菌吸附。为了修复地下水中溶解性重金属污染，必须了解污染物迁移的化学控制。细菌在低温水岩中无处不在，根据条件的不同，它们可以通过吸附反应增强或阻碍污染物的迁移。以我们目前的知识，不可能预测细菌吸附效应是否会在给定的一组条件下发生，也不可能预测这种效应的大小。我们将通过提出的研究回答的主要问题如下：(1)金属-细菌吸附反应是否存在可逆平衡状态，或者动力学，无机金属沉淀或细胞代谢过程是否阻止达到平衡？(2)我们从体吸附实验中获得的反应化学计量学是否与我们将在阿贡国家实验室的先进光子源上使用XAFS研究对金属-细菌表面复合物的直接观察相一致？(3)能否扩展表面络合平衡热力学方法来描述细菌-矿物吸附反应？开展主体吸附解吸实验，考察分离金属-细菌体系和细菌-矿物体系，严格检验金属-细菌-矿物吸附反应的可逆性。此外，我们将量化吸附/解吸动力学、表面沉淀和细胞对金属吸收的代谢的重要性。结合先进光子源对表面复合物的直接观察和实验室吸附/脱附实验是一种强大的技术，可以明确地确定重要的吸附/脱附反应的化学计量学和平衡常数。该提案是响应环境地球化学和生物地球化学招标NSF 99-9而提交的，由化学部、地球科学部、海洋科学部和MPS多学科活动办公室联合资助。

Fein9905704The proposed research will use bulk adsorption and EXAFS experiments to calibrate a surface complexation approach to quantifying bacterial adsorption of aqueous metals in groundwater systems. In order to remediate dissolved heavy metal contamination in groundwater, we must understand the chemical controls on contaminant mobilities. Bacteria are ubiquitous in low-temperature water-rock, and depending on conditions, they can either enhance or retard contaminant transport through adsorption reactions. With our current knowledge, it is impossible to predict if bacterial adsorption effects occur given a set of conditions, or to predict the magnitude of such effects. The primary questions we will answer with the proposed research are as follows: (1) Does a reversible equilibrium state exist for metal-bacteria adsorption reactions, or do kinetics, inorganic metal precipitation, or cell metabolic processes prevent equilibrium from being attained?; (2) Do the reaction stoichiometries that we obtain from bulk adsorption experiments agree with direct observations of the metal-bacteria surface complexes that we will make using XAFS studies on the Advanced Photon Source at Argonne National Laboratory?; and, (3) Can we expand the surface complexation equilibrium thermodynamic approach to describe bacteria-mineral adsorption reactions? We will conduct bulk adsorption and desorption experiments, examining both isolated metal-bacteria and bacteria-mineral systems, to rigorously test the reversibility of the metal-bacteria-mineral adsorption reactions. Furthermore, we will quantify the importance of adsorption/desorption kinetics, surface precipitation, and metabolism on metal uptake by the cell. Coupling the direct observations of the surface complex that are possible with the Advanced Photon Source with the laboratory adsorption/desorption experiments is a powerful technique to unequivocally determine both the reaction stoichiometry and the equilibrium constants for the important adsorption/desorption reactions.This proposal was submitted in response to the Environmental Geochemistry and Biogeochemistry solicitation NSF 99-9, and is being funded jointly by the Divisions of Chemistry, Earth Sciences, Ocean Sciences, and MPS Office of Multidisciplinary Activities.