Experimental Study Of Uranium Sorption Onto Biological Substrates
Experimental study of uranium sorption onto biological substrates
B. Kornilovich, P. Gvozdyak, G. Pshinko, L. Spasenova, I. Kovalchuk
A.V. Dumansky Institute of Colloid Chemistry and Chemistry of Water, Ukrainian National Academy of Sciences,
Vernadsky avenue 42, 03680, Kyiv-142, Ukraine
As a result of anthropogenous impact, the water quality in Ukraine gets worse sharply. The problem of water pollution by the radionuclides of natural origin causes the greatest apprehensions, especially in the regions where the mining-dressing plants of the uranium-producing industry are located. These radionuclides are as follows: uranium, radium-226, thorium, polonium-210, and lead-210. The effective and highly evolved in an economic angle purification system not only mine and ore waters but also surface ones is necessary to solve the problem of the pure potable water in these regions and other ones. Therefore, in each particular case, a choice in the purification method will be determined not only by the qualitative indices as for the purification level of these or other waters but also the economic aspect of these problems will be accounted for.
We have demonstrated a possibility to apply the biological method of water purification from uranium (VI) and assessed the prospects in its practical application.
The biological method is based on the capability of certain strains of microorganisms to sorb selectively the radionuclides and the toxic metal ions due to the specific adsorptive reactions occurring among their functional groups and the ions of metals. We studied the adsorption processes of uranium on Active sludge and Xantomonas сampestris bacteria. These processes might be characterized as absorptive complex formation onto the surface of bacteria. To study the accumulation of uranium ions on the Active sludge biosorbent, the experimental trials have been performed in both the flowing mode of operation and the circulating one. The bacteria were placed on the support (a "viya" type) and laid down into the bioreactor designed specially for this
purpose. It consisted of five chambers, which provided water motion at a rate of 2 l/h. The sorption of uranium by the Active sludge and Xantomonas сampestris bacteria has been also studied under the static conditions.
The functional complexing groups are known to be characteristic for the surface of bacteria. These groups are capable to the deprotonation reactions. This is explained by the fact that the negatively charged surface of bacteria at the deprotonation reaction (when pH rises) is capable to bind the uranium in its cationic form, i.e., in the form of UO22+ cation. Formation of the neutral form of uranium at pH 8.0, and the complexing character of metal binding by the surface of bacteria are confirmed by the fact that uranium (VI) sorption at a given pH falls to zero. An analogous surface complex formation is also characteristic for Хantomonas саmpestris, the total amount of the acidic functional groups of which is equal to » 2,0 mg-eq/g.
The optimum conditions in extraction of uranium (VI) from waters differing in their salt content have been determined. A suitability to apply the biosorbents has been demonstrated.
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