The Role of Biogenic Solids in Thereductive Stabilization of Metal Contaminats: Influences Onmicrobial Versus Chemical Pathways and Reaction Products

[摘要] In situ stabilization of toxic metals and radionuclides such as chromium and uranium is an attractive approach for remediating many contaminated DOE sites. To enhance in situ remediation, microbiological reductive stabilization of contaminant metals has been, and continues to be, actively explored. It is likely that surface and subsurface microbial activity can alter the redox state of toxic metals and radionuclides so they are rendered immobile. The reaction products and their stability will depend on the specific mechanism by which reduction takes place--the focus of this work. Uranium and Cr exist in more than one oxidation state in the surface- and near-surface environment; different oxidation states of these elements have markedly different properties. The fully oxidized species of Cr and U, both hexavalent forms, have a high solubility in soils and groundwaters, and consequently they tend to be mobile in the environment. Chromate is also subject to biological uptake, a factor that contributes to its toxicity. In contrast, the reduced form of chromium, Cr(III), has a limited hydroxide solubility and forms strong complexes with soil minerals, it is therefore less mobile and has a lower bioavailability than Cr(VI). Similarly, the oxidized forms of U have a greater solubility and hence exhibit greater mobility in soils and subsurface environments than either U(VI) or U(V). They may conclude that oxidized forms of these radionuclides and metals are subject to enhanced migration through surface and subsurface environments. Reductive stabilization is therefore a desirable pathway for these elements.

[发布日期] 2002-08-31 [发布机构] Stanford University

[关键词] Uranium;Hydroxides;Stabilization;Chromates;Radioisotopes