A holistic approach to multicomponent EXAFS: Sr complexation in clayey soil

Bots, P; Comarmond, MJ; Payne, TE; Lunn, RJ; Schellenger, AEP; Renshaw, JC

A holistic approach to multicomponent EXAFS: Sr complexation in clayey soil

Date

2021-10-10

Authors

Publisher

Geological Society of America

Abstract

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. © Copyright 2021 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes.

Description

A recorded presentation is available at the following URL: https://gsa.confex.com/gsa/2021AM/videogateway.cgi/id/3591?recordingid=3591

Keywords

Radioactive waste disposal, Contamination, Soils, Adsorption, Kaolinite, Illite, Clays, Strontium

Citation

Bots, P., Comarmond, M. J., Payne, T. E., Lunn, R. J., Schellenger, A., & Renshar, J. C. (2021). A holistic approach to multicomponent EXAFS: Sr complexation in clayey soil. Paper presented to the GSA Connect 2021!, 10-13 October 2021, Portland, Oregon and online. doi:10.1130/abs/2021am-365989