Abstract
The possible role of biogeochemical processes in the transport of colloidal and pseudo-colloidal U, Np, and Pu during bioremediation of radionuclide- and nitrate-contaminated groundwater was investigated. In two laboratory experiments with water samples taken from contaminated aquifers before and post bioremediation, we found that microbial processes could cause clayed, ferruginous, and actinide colloids to coagulate. The main mechanisms are biogenic insoluble ferrous iron species formations (goethite, pyrrhotite, siderite, troilite, and ferrihydrite), the aggregation of clay particles by microbial metabolites, and the immobilization of actinides in the bacterial cells, large polymers, and iron and clayed sediments. This process decreases the risk of colloidal and pseudo-colloidal transport of actinides.
Highlights
The possible role of biogeochemical processes in the transport of colloidal and pseudo-colloidal U, Np, and Pu during bioremediation of radionuclide- and nitrate-contaminated groundwater was investigated
Subsurface uranium leaching, radiation accidents, underground nuclear explosions and improper handling of surface waste storages of radiochemical production plants and ore processing sites may cause the ingress of actinides into groundwater
Biogenic processes stimulated by nitrate reduction, for example, might have stabilized pseudo-colloidal actinide particles due to production of exopolysaccharide m etabolites[28,29] or biogenic nano colloidal u raninite[30]
Summary
The possible role of biogeochemical processes in the transport of colloidal and pseudo-colloidal U, Np, and Pu during bioremediation of radionuclide- and nitrate-contaminated groundwater was investigated. The main mechanisms are biogenic insoluble ferrous iron species formations (goethite, pyrrhotite, siderite, troilite, and ferrihydrite), the aggregation of clay particles by microbial metabolites, and the immobilization of actinides in the bacterial cells, large polymers, and iron and clayed sediments This process decreases the risk of colloidal and pseudo-colloidal transport of actinides. Decreased uranium content was observed in samples taken after the bioremediation Such results have shown promising possibilities for developing a biogeochemical barrier for radionuclides under the conditions of the aquifer in consideration. These possibilities assume the continuous stimulation of the microbial community and formation of local areas with reducing conditions so that elements are immobilized in poorly soluble form
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