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@INPROCEEDINGS{Brandt:1016755,
      author       = {Brandt, Felix and Klinkenberg, Martina and Baeyens, Bart
                      and Marquez Fernandes, Maria and Barthel, Juri and Bosbach,
                      Dirk},
      title        = {{R}etention {M}echanisms for 226{R}a: solid-solution
                      formation and adsorption},
      reportid     = {FZJ-2023-03741},
      year         = {2023},
      abstract     = {The fate of Ra, a decay product of 232Th, 235U, and 238U,
                      in the environment is relevant because Ra is an important
                      source of radioactivity in technically enhanced naturally
                      occurring radioactive materials (TENORM). Ra-containing
                      TENORM essentially originates from mining (e.g., uranium,
                      phosphate) and milling operations, from coal ash, and raw
                      material production processes e.g., oil extraction,
                      geothermal energy production. 226Ra is a critical
                      radionuclide in nuclear waste management, originating from
                      e.g., nuclear industry in spent nuclear fuel or other wastes
                      from processing uranium ore, past legacies from industry and
                      medicine. 226Ra, is safety relevant for the deep geological
                      disposal of spent nuclear fuel (SNF) because it is a
                      long-lived alpha emitter (t1/2 = 1600 yrs) which dominates
                      the radioactive dose in some scenarios regarding the late
                      stages of SNF disposal. The prediction of 226Ra migration
                      requires a quantitative process-understanding of the
                      relevant retention mechanisms, i.e. adsorption, and uptake
                      of 226Ra into a solid phase. Here we present results of
                      experimental and theoretical studies on the structural
                      uptake of 226Ra into the ternary solid solution of
                      (Ba,Sr,Ra)SO4 due to the recrystallization of sulfates. This
                      mechanism is relevant due to the fact that the
                      solid-solutions are thermodynamically more stable than the
                      pure phase RaSO4 and their formation leads to a lower
                      solubility of 226Ra compared to the pure phase. The results
                      show that already at time scales observable in the
                      laboratory, pure sulfates are able to take up 226Ra and that
                      their uptake can be described with thermodynamic
                      solid-solution models. In addition, we present results
                      regarding the adsorption of 226Ra on two important clay
                      minerals, illite and montmorillonite. Our results show
                      distinct differences between the selectivity of 226Ra
                      adsorption to the two clay minerals, with a higher
                      selectivity observed on illite. Parallel experiments with Ba
                      indicate that 226Ra behaves similar in many geochemical
                      conditions but is adsorbed stronger than Ba.},
      month         = {Oct},
      date          = {2023-10-04},
      organization  = {21st Jena Remediation Symposium, Jena
                       (Germany), 4 Oct 2023 - 6 Oct 2023},
      subtyp        = {Invited},
      cin          = {IEK-6 / ER-C-2},
      cid          = {I:(DE-Juel1)IEK-6-20101013 / I:(DE-Juel1)ER-C-2-20170209},
      pnm          = {1411 - Nuclear Waste Disposal (POF4-141)},
      pid          = {G:(DE-HGF)POF4-1411},
      typ          = {PUB:(DE-HGF)31},
      url          = {https://juser.fz-juelich.de/record/1016755},
}