Issue 10, 2023

In situ (bio)remediation treatment options for U and Sr contaminated land: a comparison of radionuclide retention and remobilisation

Abstract

The past 60+ years of global nuclear activity has resulted in a significant legacy of radioactive contaminated lands which have high economic costs associated with their remediation. Developing clean-up technologies that are environmentally friendly, economically viable and effective in the long-term is key, with in situ remediation techniques as an important option. However, questions remain regarding the most favorable methods of remediation, and the long-term stability of any immobilised radionuclide(s). Here, we used sediment microcosms to assess the long-term (300 day) stability of immobilised U and Sr formed during anoxic microbial and chemical treatments, and assessed their stability during re-oxidation scenarios (with oxygen or nitrate additions, 100 days). We used six contrasting treatment approaches which resulted in 89 to >99%, and 65–95% removal efficiencies for U and Sr, respectively. These included two Zero Valent Iron (ZVI) based products (NANOFER 25S and Carbo-Iron); a slow-release electron donor (Metals Remediation Compound, MRC) to stimulate U(VI) bioreduction alongside a readily bioavailable electron donor control (lactate/acetate mix); electron donor (lactate/acetate) with elevated sulfate to stimulate metal and sulfate reduction; glycerol phosphate to promote both bioreduction of U(VI) and biomineralization of inorganic U/Sr phosphates; and finally a natural attenuation (no remediation agent added) control. X-ray Absorption Spectroscopy (XAS) revealed that whilst aqueous U was removed from solution via multiple mechanisms including sorption, reduction and incorporation, aqueous Sr was mostly removed via outer sphere complexation mechanisms. Re-oxidation with air led to increased U remobilisation (≤89%) compared to nitrate oxidation (≤73%), but neither oxygen or nitrate re-oxidation led to significant Sr remobilisation (≤38%), suggesting Sr speciation may be stable over extended timescales post remediation. Treatments amended with ZVI or glycerol phosphate not only removed the most U and Sr from solution (>99%) but they also retained the most U and Sr following re-oxidation (retaining ≥75% of the originally added U and Sr). XAS analyses suggests that enhanced immobilisation, as seen in the treatments amended with ZVI or glycerol phosphate, may be due to the U/Sr incorporation into mineral phases (i.e., iron oxyhydroxide and phosphate phases). This suggests that optimal (bio)remediation strategies should target both reduction and biomineralisation mechanisms to facilitate radionuclide-mineral incorporation, promoting longer-term stability.

Graphical abstract: In situ (bio)remediation treatment options for U and Sr contaminated land: a comparison of radionuclide retention and remobilisation

Supplementary files

Article information

Article type
Paper
Submitted
27 4月 2023
Accepted
08 8月 2023
First published
14 8月 2023
This article is Open Access
Creative Commons BY-NC license

Environ. Sci.: Adv., 2023,2, 1423-1435

In situ (bio)remediation treatment options for U and Sr contaminated land: a comparison of radionuclide retention and remobilisation

G. F. Vettese, K. Morris, M. White-Pettigrew, L. T. Townsend, S. Shaw, C. Boothman and J. R. Lloyd, Environ. Sci.: Adv., 2023, 2, 1423 DOI: 10.1039/D3VA00104K

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