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@INPROCEEDINGS{Klinkenberg:909871,
      author       = {Klinkenberg, Martina and Marques Fernandes, M. and Baeyens,
                      B. and Bosbach, D. and Brandt, F.},
      title        = {{R}etention of 226{R}a by montmorillonite},
      reportid     = {FZJ-2022-03480},
      year         = {2022},
      abstract     = {Although 226Ra is a critical radionuclide in the safety
                      analysis for deep geological disposal of spent nuclear fuel,
                      adsorption data for 226Ra onto clay minerals are sparse in
                      the open literature. So far, the adsorption and diffusion of
                      226Ra in clay minerals is assumed similar to that for Sr and
                      Ba, based on chemical analogy. In this study, we present new
                      experimental data that improves the quantitative
                      understanding of the retention of 226Ra in 2:1 clay minerals
                      relevant for radioactive waste disposal. Montmorillonite as
                      a major constituent of bentonite (up to 90 $wt.-\%)$ is an
                      important sink for potentially released radionuclides. To
                      study the 226Ra adsorption behaviour on bentonites,
                      adsorption experiments were carried out onto the homo-ionic
                      Na form of Wyoming montmorillonite (SWy-2) in diluted
                      systems and compared to the adsorption of Ba under the same
                      conditions. 226Ra and Ba adsorption edges in the pH range 5
                      to 10 at different ionic strengths (0.01 - 0.3 M NaCl) and
                      an isotherm (pH 7, 10-9 M < [Ra,Ba] > 10-2 M) were carried
                      out on Na-SWy. Our results c The 2-site Protolysis Non
                      Electrostatic Surface Complexation and Cation Exchange
                      adsorption model reproduces the experimental data for both
                      elements quite well. The Kc values for Ba2+-Na+ and
                      226Ra2+-Na+ exchange equilibria are in good agreement at low
                      ionic strength (log Kc = 0.70 - 0.84), whereas at high ionic
                      strength, the Kc (Ba-Na) is slightly higher (log Kc of 0.90
                      (0.3 M) vs 0.70 (≤ 0.02 M)). In contrast, the Kc (Ra-Na)
                      exhibits a clear dependency on ionic strength, with log Kc
                      values of 0.7, 1.14 and 1.34 at NaCl background
                      concentrations of 0.01/0.02 M, 0.14 M and 0.3 M,
                      respectively. The results presented here indicate that Ba
                      can be used as a good analogue for 226Ra regarding the
                      adsorption on montmorillonite at ionic strengths < 0.1 M and
                      pH < 8, but deviates in its behaviour at higher ionic
                      strength. This evident higher selectivity of Ra on Na-SWy
                      may be due to the larger ionic radius of Ra compared to Ba.
                      The contribution of surface complexation to the overall
                      adsorption is the same for Ba and Ra and is independent of
                      ionic strength.},
      month         = {Jun},
      date          = {2022-06-13},
      organization  = {8th International Conference on Clays
                       in Natural and Engineered Barriers for
                       Radioactive Waste Confinement, Nancy
                       (France), 13 Jun 2022 - 16 Jun 2022},
      subtyp        = {Other},
      cin          = {IEK-6},
      cid          = {I:(DE-Juel1)IEK-6-20101013},
      pnm          = {1411 - Nuclear Waste Disposal (POF4-141) / EURAD - European
                      Joint Programme on Radioactive Waste Management (847593)},
      pid          = {G:(DE-HGF)POF4-1411 / G:(EU-Grant)847593},
      typ          = {PUB:(DE-HGF)24},
      url          = {https://juser.fz-juelich.de/record/909871},
}