The Biogeochemical Fate of Se(VI) in Bentonite Systems Relevant to the Disposal of High-Level Radioactive Waste

Authors

• Max Rose, University of Manchester
• Samuel Shaw, University of Manchester
• Katherine Morris, University of Manchester
• Christopher Boothman, University of Manchester
• Matthew Bailey, School of Geography, Earth and Environmental Sciences
• Dirk Engelberg, University of Manchester
• Jonathan R. Lloyd, University of Manchester

ORCID

• Matthew Bailey: 0000-0002-1029-225X

Document Type

Article

Abstract

Selenium-79, a radionuclide present in higher-activity radioactive wastes destined for deep geological disposal, is mobile under oxic conditions, where Se(IV) and Se(VI) dominate. Anoxic batch microcosm incubations were constructed containing Wyoming MX80 bentonite (a candidate buffer material in geological disposal) and artificial groundwater with or without steel coupons to represent canister materials. Se(VI)_(aq) bioreduced and was removed by 7 days when lactate was added as an electron donor, after which sulfate reduction occurred. With H₂ gas as the electron donor, Se(VI) bioreduction slowed, with complete removal at 14 days and minimal sulfate reduction thereafter. 16S rRNA gene sequencing highlighted the dominance of Anaerobacillus spp. (44% at 28 days) during Se(VI)-reduction, and in the lactate-amended systems, there was a subsequent enrichment in sulfate-reducing bacteria affiliated with Desulfosporosinus spp. (60% relative abundance at 84 days). Extended X-ray absorption fine structure (EXAFS) analyses identified monoclinic Se(0) as the bioreduction product after 28 days, but by 84 days this evolved to trigonal Se(0) in the absence of steel coupons or was further reduced to FeSe₂ with steel present. The reduction of Se(VI)_(aq) to poorly soluble Se(0)/FeSe₂ mediated by indigenous bentonite microbial communities highlights their potential importance in promoting Se-79 retention during deep geological disposal.

DOI Link

10.1021/acs.est.5c09387

Publication Date

2026-02-10

Publication Title

Environmental Science and Technology

Volume

60

Issue

5

ISSN

0013-936X

Acceptance Date

2026-01-14

Deposit Date

2026-09-28

Embargo Period

2027-01-26

Additional Links

https://www.scopus.com/pages/publications/105029875335

Keywords

Bentonite, Bioreduction, Geological Disposal Facility, Selenium-79, Steel corrosion

First Page

4124

Last Page

4133

Recommended Citation

Rose, M., Shaw, S., Morris, K., Boothman, C., Bailey, M., Engelberg, D., & Lloyd, J. (2026) 'The Biogeochemical Fate of Se(VI) in Bentonite Systems Relevant to the Disposal of High-Level Radioactive Waste', Environmental Science and Technology, 60(5), pp. 4124-4133. Available at: 10.1021/acs.est.5c09387