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@INPROCEEDINGS{Brandt:852442,
      author       = {Brandt, Felix and Klinkenberg, Martina and Poonoosamy,
                      Jenna and Barthel, Juri and Weber, Juliane and Bosbach,
                      Dirk},
      title        = {{R}a {U}ptake by the {S}r-{R}ich {S}olid {S}olution of
                      ({S}r, {B}a){SO}4},
      reportid     = {FZJ-2018-05388},
      year         = {2018},
      abstract     = {Solid solution formation is an important mechanism of
                      radionuclide uptake by mineral phases which is favored in
                      natural systems due to a lowered configurational entropy.
                      Recent studies have shown that the formationof a (Ba,Ra)SO4
                      solid solution significantly reduces the solubility of 226Ra
                      in aqueous systems. This result is very relevant for the
                      direct disposal of spent nuclear fuel in a deep geological
                      formation, where 226Ra would dominate the dose after 100,000
                      years [1]. In natural systems SrSO4 often occurs along with
                      BaSO4 implying that Ra-uptake should be assessed within the
                      system of (Sr,Ba,Ra)SO4 + H2O. A recent thermodynamic
                      modelling study [2] predicted a significant uptake of Ra
                      into the ternary (Sr,Ba,Ra)SO4 solid-solution. Here we
                      present results of long-term batch-recristallisation
                      experiments on Ra-uptake in a Sr-rich part of the ternary
                      system. A mechanical mixture of celestite with a small
                      amount of barite and a (Sr,Ba)SO4 solid solution of
                      equivalent comoposition were put into a contact with
                      226Ra,aq. We observed a significant uptake of 226Ra in both
                      cases proceeding via the formation of the minor ternary Sr-,
                      Ba- and Ra-rich phase within the major Sr-rich phase. In
                      longer experiments the ternary phase disappeared leading to
                      the formation of a mixture of Sr- and Ba-rich phases, within
                      which Ra could not be detected by scanning transmission
                      electron microscopy-energy-dispersive X-ray spetroscopy
                      (STEM-EDX). The final 226Ra concentrations in both
                      experiments were similar and close to predicted levels. The
                      formation of the intermediate phase is interpreted based on
                      structural and kinetic considerations. [1] Norrby, S. et al.
                      (1997). “SKI SITE-94 Saekerhetsanalys foer Djupfoervar
                      iett Kristallint berg”.Stockholm, Sweden. [2] Vinograd et
                      al. (2018). Applied Geochemistry, in press.},
      month         = {Aug},
      date          = {2018-08-12},
      organization  = {Goldschmidt, Boston (USA), 12 Aug 2018
                       - 17 Aug 2018},
      subtyp        = {Other},
      cin          = {IEK-6 / ER-C-2},
      cid          = {I:(DE-Juel1)IEK-6-20101013 / I:(DE-Juel1)ER-C-2-20170209},
      pnm          = {161 - Nuclear Waste Management (POF3-161)},
      pid          = {G:(DE-HGF)POF3-161},
      typ          = {PUB:(DE-HGF)6},
      url          = {https://juser.fz-juelich.de/record/852442},
}