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EXAFS study of Sr sorption to illite, goethite, chlorite and mixed sediment under hyper-alkaline conditions

DOI: 10.1021/acs.langmuir.5b04633 DOI Help

Authors: Adam Fuller (University of Leeds) , Sam Shaw (University of Leeds) , Caroline Peacock (University of Leeds) , Divyesh Trivedi (National Nuclear Laboratory Ltd, U.K.) , Ian T. Burke (University of Leeds)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Langmuir , VOL 32 (12) , PAGES 2937–2946

State: Published (Approved)
Published: March 2016
Diamond Proposal Number(s): 8667

Abstract: Strontium is an important contaminant radionuclide at many former nuclear sites. This paper investigates the effect of changing pH and ionic strength on the sorption Sr to a range of common soil minerals. Specifically it focuses on the sorption of Sr onto illite, chlorite, goethite and a mixed sediment. The interplay between ionic strength and pH was determined by varying the background ionic strength of the system using both NaCl (for a constant pH) and NaOH (to also vary pH). Under conditions of moderate pH Sr sorption decreased with increasing ionic strength, due to competition between the Na and Sr atoms for the outer-sphere complexes. However, where increasing ionic strength was accompanied by increasing pH Sr sorption remained high. This suggested that Sr was sorbed to the minerals without competition from background Na ions. Extended X-ray Absorption Fine Structure (EXAFS) spectra confirmed that at highly alkaline pH (>12.5) Sr was forming inner-sphere complexes on the surfaces of all minerals. This specific adsorption of the Sr (as SrOH+) explains why it was still adsorbed to the minerals under very high ionic strength conditions and was not out-competed by Na.

Subject Areas: Earth Science

Instruments: B18-Core EXAFS , I20-Scanning-X-ray spectroscopy (XAS/XES)

Other Facilities: European Synchrotron Radiation Facility