Paper No. 13-3
Presentation Time: 8:40 AM
A HOLISTIC APPROACH TO MULTICOMPONENT EXAFS: SR COMPLEXATION IN CLAYEY SOIL (Invited Presentation)
BOTS (THEY/HE), Pieter1, COMARMOND, M. Josick2, PAYNE, Timothy E.2, LUNN, Rebecca J.1, SCHELLENGER, Alexandra3 and RENSHAW, Joanna C.1, (1)Department of Civil and Environmental Engineering, University of Strathclyde, James Weir Building, 75 Montrose Street, Glasgow, G1 XJ, United Kingdom, (2)Australian Science and Technology ORganisation, New Illawarra Road, Lucas Heights, NSW 2234, Australia, (3)Water Science Institute, School of Water, Energy & Environment, Cranfield University, College Road, Cranfield, MK43 0AL, United Kingdom; Department of Civil and Environmental Engineering, University of Strathclyde, James Weir Building, 75 Montrose Street, Glasgow, G1 XJ, United Kingdom
Strontium is a fission product of concern at many nuclear legacy sites, which require assessment and possibly engineered long-term management to minimize the risk of radionuclides to the environment and the public. One such site is the Little Forest Legacy Site (LFLS) in New South Wales, Australia. In the 60s low-level radioactive wastes were disposed at LFLS in unlined trenches. The location of LFLS was selected based on the clayey nature of the soils and rocks present (~50 % kaolinite and illite-smectite), limiting water movement and migration of radioactive contaminants [1,2]. Despite the clay-rich environment, radioactive contaminants (including fission products and actinides) have been detected in sediments, groundwater, surface runoff and vegetation at the Little Forest Legacy Site [2,3]. Understanding the geochemical speciation of radionuclides in the soils and groundwater at LFLS is essential to develop evidence-based engineered management strategies.
In this study we investigated the geochemical speciation of Sr in clayey soils by performing a comprehensive set of adsorption experiments (on single minerals and a clayey soil) and subsequent X-ray absorption spectroscopy analyses. Furthermore, in order to fully benefit from such experimental and analytical methodologies, we developed and utilized a comprehensive dual/holistic approach to fitting multicomponent EXAFS. First, a shell-by-shell fitting strategy enabled us to determine Sr complexation with anatase and illite-smectite through bidentate edge sharing complexes and with kaolinite at the silicon vacancy sites on the basal surface [4]. Subsequently, we utilized a holistic approach to determine predominance of each of these complexes within a composite clayey soil to inform that Sr complexation with kaolinite (25-30%) and illite-smectite (72-76%) governs Sr speciation in clayey soils [4]. The presented surface complexation and dual/holistic approach to fitting EXAFS spectra will strengthen predictive modelling on the behaviour of elements of interest.
References
[1] Payne. Background Report on the Little Forest Burial Ground Legacy Waste Site. (ANSTO, 2012).
[2] Cendón et al. Aust. J. Earth. Sci. 62, 123-141, (2015).
[3] Payne et al. Environ. Sci. Technol. 47, 13284-13293, (2013).
[4] Bots et al. Environ. Sci.: Process. Impacts (2021).
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