Biogeochemical In Situ Barriers in the Aquifers near Uranium Sludge Storages

Abstract

The long-term operation of uranium sludge storages causes serious problems: it contaminates the neighboring aquifers with dangerous substances (uranium, nitrate, ammonium, and sulfate). To purify the aquifers can be costly and time-consuming; therefore, it is important to use the potential of in situ conditions, e.g., the aboriginal microflora and its ability to biologically remediate water reservoirs. In this work, we study the geological, geochemical, and microbiological characteristics of groundwater contaminated by uranium sludge storages resulting from the production cycles of four Russian chemical plants. All of the sites under consideration were extremely contaminated with nitrate (up to 15 g/L); in each case, we used denitrifying bacteria as a dominant group of microorganisms for purification. Our laboratory studies showed that microbial stimulation of water samples by milk whey promotes O2 and nitrate removal; this, in turn, started the cycle of anaerobic processes of authigenic precipitation caused by the reduction of iron and sulfate in the system. Thus, a mineral geochemical barrier preventing uranium immobilization formed. As a result, the uranium of the liquid phase decreased about 92–98% after 3–6 months (decomposition time depends on the nitrate concentration in the groundwater probe). The resulting amorphous biogenic phases contain sulfur, iron, phosphorus, and uranium.

Authigenic Mineral Formation in Aquifers near the Uranium Sludge Storage Facility of Chepetsky Mechanical Plant during the Formation of a Biogeochemical Barrier in a Laboratory and Field Experiment

“…Since the middle of the 20th century, uranium-bearing sludge has been stored in the presence of a high levels of carbonate, nitrate, sulfate calcium and ferruginous mineral phases [1,2]. One of the important problems remaining after the conservation of such repositories is the complex contamination of underground aquifers of water-soluble waste components (nitrates, ammonium, sulphates, carbonates, uranium and heavy metals, such as iron) [5][6][7][8] due to violation of the integrity of engineering safety barriers. This leads to the uncontrolled migration of pollutants and creates risks of polluting different water supply sources.…”