Biomineralization of uranium-phosphates fueled by microbial degradation of isosaccharinic acid (ISA)

Kuippers, Gina and Morris, Katherine and Townsend, Luke T. and Bots, Pieter and Kvashnina, Kristina and Bryan, Nicholas D. and Lloyd, Jonathan R. (2021) Biomineralization of uranium-phosphates fueled by microbial degradation of isosaccharinic acid (ISA). Environmental Science and Technology, 55 (8). pp. 4597-4606. ISSN 0013-936X (

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Geological disposal is the globally preferred long-term solution for higher activity radioactive wastes (HAW) including Intermediate Level Waste (ILW). In a cementitious disposal system, cellulosic waste items present in ILW may undergo alkaline hydrolysis, producing significant quantities of isosaccharinic acid (ISA), a chelating agent for radionuclides. Although microbial degradation of ISA has been demonstrated, its impact upon the fate of radionuclides in a geological disposal facility (GDF) is a topic of ongoing research. This study investigates the fate of U(VI) in pH-neutral, anoxic, microbial enrichment cultures, approaching conditions similar to the far field of a GDF, containing ISA as the sole carbon source, and elevated phosphate concentrations, incubated both (i) under fermentation and (ii) Fe(III)- reducing conditions. In the ISA-fermentation experiment, U(VI) was precipitated as insoluble U(VI)-phosphates, whereas under Fe(III)-reducing conditions, the majority of the uranium was precipitated as reduced U(IV)-phosphates, presumably formed via enzymatic reduction mediated by metal-reducing bacteria, including Geobacter species. Overall, this suggests the establishment of a microbially-mediated "bio-barrier" extending into the far field geosphere surrounding a GDF is possible and this bio-barrier has the potential to evolve in response to GDF evolution and can have a controlling impact on the fate of radionuclides.


Kuippers, Gina, Morris, Katherine, Townsend, Luke T., Bots, Pieter ORCID logoORCID:, Kvashnina, Kristina, Bryan, Nicholas D. and Lloyd, Jonathan R.;