Rare Earth element (REE) incorporation in natural calcite: Upper limits for actinide uptake in a secondary phase
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S. L. S. Stipp
Secondary minerals have the potential to sequester escaped actinides in the event of a radioactive waste repository failure, but currently, data to define their maximum uptake capacity are generally lacking. To estimate a maximum limit for solid solution in calcite, we took advantage of the behavioural similarities of the 4f-orbital lanthanides with some of the 5f-orbital actinides and used rare Earth element (REE) concentration as an analogue. A suite of 65 calcite samples, mostly pure single crystals, was assembled from a range of geological settings, ages and locations and analysed by isotope dilution MC-ICP-MS (multiple-collector inductively-coupled plasma mass spectroscopy). All samples were shown to contain significant lanthanide concentrations. The highest were in calcite formed from hydrothermal solutions and from carbonatite magma. Maximum total mole fraction of REE was 4.72×10-4, which represents one substituted atom for about 2000 Ca sites. In comparison, synthetic calcite, precipitated at growth rates slow enough to insure solid solution formation, incorporated 7.5×10-4 mole fraction Eu(III). For performance assessment, we propose that 7.5 mmole substitution/kg calcite should be considered the upper limit for actinide incorporation in secondary calcite. The largest source of uncertainty in this estimate results from extrapolating lanthanide data to actinides. However, the data offer confidence that for waters in the hydrothermal temperature range, such as in the near-field, or at groundwater temperatures, such as in the far-field, if calcite formation is favoured and actinides are present, those with behaviour like the trivalent lanthanides, especially Am3+ and Cm3+, will be incorporated. REE are abundant and widely distributed, and they have remained in calcite for millions of years. Thus, one can be certain that incorporated actinides will also remain immobilised in calcite formed in fractures and pore spaces, as long as solution conditions do not favour complete dissolution. Partial dissolution only results in resequestration to calcite again.
© Oldenbourg Wissenschaftsverlag
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Articles in the same Issue
- Preface Migration 2005
- Solubility measurement of zirconium(IV) hydrous oxide
- Solubility of ThO2·xH2O(am) and the formation of ternary Th(IV) hydroxide-carbonate complexes in NaHCO3-Na2CO3 solutions containing 0−4 M NaCl
- Ion interaction (SIT) coefficients for the Th4+ ion and trace activity coefficients in NaClO4, NaNO3 and NaCl solution determined by solvent extraction with TBP
- Leaching of neptunium from garnet- and murataite-based ceramics
- Coprecipitation of thorium and lanthanum with UO2+x(s) as host phase
- Rare Earth element (REE) incorporation in natural calcite: Upper limits for actinide uptake in a secondary phase
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- Complexing properties of α-isosaccharinate: thorium
- Determination of the thermodynamic quantities of complexation between Eu(III) and carboxylic acids by microcalorimetry
- Potentiometric investigations on the interaction of humic acid with Cu(II) and Eu(III) ions
- Investigation of complexation of thorium by humic acid using chemically immobilized humic acid on silica gel
- Correlation between X-ray chemical shift and partial charge in Tc(IV) complexes: Determination of Tc partial charge in TcnOy(4n-2y)+
- Oxidation and dissolution rates of UO2(s) in carbonate-rich solutions under external alpha irradiation and initially reducing conditions
- On the stability of Pu(III) at different pH under non-inert conditions
- Reduction behavior of uranium in the presence of citric acid
- Leaching of zirconolite ceramics under H+ and He2+ irradiation
- Reduction of plutonium(VI) in brine under subsurface conditions
- Theoretical first step towards an understanding of the uranyl ion sorption on the rutile TiO2(110) face: A DFT periodic and cluster study
- Cm(III) sorption onto γ-Al2O3: New insight into sorption mechanisms by time-resolved laser fluorescence spectroscopy and extended X-ray absorption fine structure
- Modelling sorption data for the actinides Am(III), Np(V) and Pa(V) on montmorillonite
- Sorption of Cs, Ni, Pb, Eu(III), Am(III), Cm, Ac(III), Tc(IV), Th, Zr, and U(IV) on MX 80 bentonite: An experimental approach to assess model uncertainty
- The uptake of radium by calcium silicate hydrates and hardened cement paste
- Np(V)O2+ sorption on hydroxyapatite-effect of calcium and phosphate anions
- Uranium(VI) interaction with pyrite (FeS2): Chemical and spectroscopic studies
- Interaction of U(VI) with pyrite, galena and their mixtures: a theoretical and multitechnique approach
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- Comparative study of cesium sorption on crushed and intact sedimentary rock
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- Biotransformation of plutonium complexed with citric acid
- Iodination of humic acid samples from different origins
- The fate of the epsilon phase (Mo-Ru-Pd-Tc-Rh) in the UO2 of the Oklo natural fission reactors
- Rhenium migration at the Maqarin natural analogue site (Jordan)
- Classic adsorption isotherms incorporated in modern surface complexation models: Implications for sorption of actinides
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