Kinetics of 99Tc speciation in aerobic soils

Izquierdo, Maria; Bailey, Elizabeth H.; Crout, Neil M.J.; Sanders, Heather K.; Young, Scott D.; Shaw, George G.

Abstract

© 2019 The Authors Technetium-99 is a significant and long-lived component of spent nuclear fuel relevant to long-term assessments of radioactive waste disposal. Whilst 99Tc behaviour in poorly aerated environments is well known, the long-term bioavailability in aerobic soils following direct deposition or transport to the surface is less well understood. This work addresses two questions: (i) to what extent do soil properties control 99Tc kinetics in aerobic soils and (ii) over what experimental timescales must 99Tc kinetics be measured to make reliable long-term predictions of impact in the terrestrial environment? Soil microcosms spiked with 99TcO4− were incubated for 2.5 years and 99Tc transformations were periodically monitored by a sequential extraction, which enabled quantification of the reaction kinetics. Reduction in soluble 99Tc was slow and followed a double exponential kinetic model including a fast component enhanced by low pH, a slow component controlled by pH and organic matter, and a persistently soluble 99Tc fraction. Complexation with soil humus was key to the progressive immobilisation of 99Tc. Evidence for slow transfer to an unidentified ‘sink’ was found, with estimated decadal timeframes. Our data suggest that short-term experiments may not reliably predict long-term 99Tc solubility in soils with low to moderate organic matter contents.

Citation

Izquierdo, M., Bailey, E. H., Crout, N. M., Sanders, H. K., Young, S. D., & Shaw, G. G. (2020). Kinetics of 99Tc speciation in aerobic soils. Journal of Hazardous Materials, 388, Article 121762. https://doi.org/10.1016/j.jhazmat.2019.121762

• Journal Article Type: Article
• Acceptance Date: Nov 25, 2019
• Online Publication Date: Nov 26, 2019
• Publication Date: Apr 15, 2020
• Deposit Date: Dec 6, 2019
• Publicly Available Date: Mar 20, 2020
• Journal: Journal of Hazardous Materials
• Print ISSN: 0304-3894
• Electronic ISSN: 1873-3336
• Publisher: Elsevier
• Peer Reviewed: Peer Reviewed
• Volume: 388
• Article Number: 121762
• DOI: https://doi.org/10.1016/j.jhazmat.2019.121762
• Keywords: Environmental Engineering; Waste Management and Disposal; Pollution; Health, Toxicology and Mutagenesis; Environmental Chemistry
• Public URL: https://nottingham-repository.worktribe.com/output/3498067
• Publisher URL: https://www.sciencedirect.com/science/article/pii/S0304389419317169?via%3Dihub