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<p>In radioactive waste repositories, cement is used for construction, backfill, and waste encapsulation. Over time, cracks may form, creating potential pathways for contaminant migration. A self-sealing mechanism is through calcium carbonate (CaCO<sub>3</sub>) precipitation, which can be driven by microbial oxidation of organic compounds. We explored microbially induced calcite precipitation facilitated by metabolism of citrate, a complexant in low- and intermediate- level radioactive waste (L/ILW). Nitrate-reducing microcosms containing cement pellets, citrate, nitrate, alkaline sediment inoculum, and synthetic groundwater (pH 11.2) were incubated in the dark (20 °C, 40 days). Aqueous geochemical data revealed complete citrate removal, denitrification, pH decrease to pH 9, and removal of Ca<sup>2+</sup><sub>(aq)</sub>. Furthermore, 16S rRNA gene sequencing showed enrichment of citrate-oxidising/nitrate-reducing bacteria. Solid phase analysis (XRD, SEM-EDS, µXCT) confirmed new calcite precipitates reduced cement porosity and sealed cracks at the surface. Overall, microbial oxidation of organic ligands under alkaline conditions may reduce contaminant mobility in L/ILW repositories through calcite precipitation and crack sealing.</p>

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Microbial degradation of citrate mediates sealing of cement cracks under anaerobic conditions relevant to radioactive waste disposal

  • 期刊论文

  • 出版模式：

    开放获取

  • 发表日期：

    2025年11月20日

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  • Natalie Byrd,
  • Ananya Singh,
  • Naji M. Bassil,
  • Joe S. Small,
  • Frank Taylor,
  • Christopher Boothman,
  • Dirk L. Engelberg,
  • Sultan Mahmood,
  • Tristan Lowe,
  • Jonathan R. Lloyd,
  • Katherine Morris

摘要

In radioactive waste repositories, cement is used for construction, backfill, and waste encapsulation. Over time, cracks may form, creating potential pathways for contaminant migration. A self-sealing mechanism is through calcium carbonate (CaCO3) precipitation, which can be driven by microbial oxidation of organic compounds. We explored microbially induced calcite precipitation facilitated by metabolism of citrate, a complexant in low- and intermediate- level radioactive waste (L/ILW). Nitrate-reducing microcosms containing cement pellets, citrate, nitrate, alkaline sediment inoculum, and synthetic groundwater (pH 11.2) were incubated in the dark (20 °C, 40 days). Aqueous geochemical data revealed complete citrate removal, denitrification, pH decrease to pH 9, and removal of Ca2+(aq). Furthermore, 16S rRNA gene sequencing showed enrichment of citrate-oxidising/nitrate-reducing bacteria. Solid phase analysis (XRD, SEM-EDS, µXCT) confirmed new calcite precipitates reduced cement porosity and sealed cracks at the surface. Overall, microbial oxidation of organic ligands under alkaline conditions may reduce contaminant mobility in L/ILW repositories through calcite precipitation and crack sealing.