Uranium retention by weathered schists - the role of iron minerals
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Date
1994-12
Journal Title
Journal ISSN
Volume Title
Publisher
De Gruyter
Abstract
Uranium sorption experiments were carried out on weathered schist samples which had been treated with citrate/dithionite/bicarbonate (CDB) reagent to remove iron oxides, and the results were compared to those of similar experiments with untreated samples. Uranium sorption was greatly decreased by the CDB extraction, which reduced the surface area of the samples by about 30-40%. Chemical analysis and XRD confirmed that iron oxides were the major mineral phase extracted by the CDB reagent. To further elucidate the role of iron minerals in the natural environment, we carried out transformation (aging) experiments with synthetic ferrihydrite which contained adsorbed natural uranium (predominantly 238U). In these experiments, the ferrihydrite was partially converted to crystalline forms such as hematite and goethite. The uptake of an artificial uranium isotope (236U) and the leaching of 238U form the samples were then studied in adsorption/desorption experiments. The results showed that the transformation of ferrihydrite to crystalline minerals substantially reduced the ability of the samples to adsorb 236U from solution. The desorption data for 238U showed that some of the 238U which was adsorbed to the samples prior to the transformation step was irreversibly incorporated within the mineral structure during the transformation process. These experiments highlight the potential importance of iron minerals both in the initial sorption of radionuclides and in isolating them from interactions with the aqueous phase. Transformation of iron minerals from amorphous to crystalline forms provides a possible mechanism for uranium immobilisation. In considering the overall effect on U migration, this must be balanced against the reduced ability of the transformed iron oxide to adsorb U from solution. © 2013 Oldenbourg Wissenschaftsverlag GmbH.
Description
Physical copy held by ANSTO Library at DDC: 577.277/45.
Keywords
Adsorption, Actinide nuclei, Alpha decay radioisotopes, Desorption, Experimental data, Inclusions, Iron compounds, Qualitative chemical analysis, Radionuclide migration, Uranium 236, Uranium 238, Weathering, X-ray diffraction, Uranium isotopes, Years living radioisotopes
Citation
Payne, T. E., Davis, J. A., & Waite, T. D. (1994). Uranium retention by weathered schists - the role of iron minerals. Paper presented to Chemistry and migration behaviour of actinides and fission products in the geosphere : fourth International Conference in Charleston, SC (USA), 12-17 December 1993. In Radiochimica Acta, Vol. 66-67, Supplement, 1994, 297-304. doi:10.1524/ract.1994.6667.special-issue.297