Deep anoxic aquifers could act as sinks for uranium through microbial-assisted mineral trapping


Deep anoxic aquifers could act as sinks for uranium through microbial-assisted mineral trapping

Pidchenko, I. N.; Christensen, J. N.; Kutzschbach, M.; Ignatyev, K.; Puigdomenech, I.; Tullborg, E.-L.; Roberts, N. M. W.; Troy Rasbury, E.; Northrup, P.; Tappero, R.; Kvashnina, K.; Schäfer, T.; Suzuki, Y.; Drake, H.

Uptake of uranium (U) by secondary minerals, such as carbonates and iron (Fe)-sulfides, that
occur ubiquitously on Earth, may be substantial in deep anoxic environments compared to
surficial settings due to different environment-specific conditions. Yet, knowledge of U
reductive removal pathways and related fractionation between 238 U and 235 U isotopes in
deep anoxic groundwater systems remain elusive. Here we show bacteria-driven degradation
of organic constituents that influences formation of sulfidic species facilitating reduction of
geochemically mobile U(VI) with subsequent trapping of U(IV) by calcite and Fe-sulfides.
The isotopic signatures recorded for U and Ca in fracture water and calcite samples provide
additional insights on U(VI) reduction behaviour and calcite growth rate. The removal effi-
ciency of U from groundwater reaching 75% in borehole sections in fractured granite, and
selective U accumulation in secondary minerals in exceedingly U-deficient groundwater
shows the potential of these widespread mineralogical sinks for U in deep anoxic
environments.

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Permalink: https://www.hzdr.de/publications/Publ-36865
Publ.-Id: 36865