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@ARTICLE{MarquesFernandes:1017537,
      author       = {Marques Fernandes, Maria and Klinkenberg, Martina and
                      Baeyens, Bart and Bosbach, Dirk and Brandt, Felix},
      title        = {{A}dsorption of {B}a and 226{R}a on illite: {A} comparative
                      experimental and modelling study},
      journal      = {Applied geochemistry},
      volume       = {159},
      issn         = {0883-2927},
      address      = {Amsterdam [u.a.]},
      publisher    = {Elsevier Science},
      reportid     = {FZJ-2023-04186},
      pages        = {105815 -},
      year         = {2023},
      abstract     = {Illite, smectite and illite/smectite mixed layers are major
                      phases in various argillaceous rock formations foreseen as
                      potential host rocks for the deep geological disposal of
                      high-level radioactive waste and are important sorbents for
                      cationic radionuclides potentially released in the
                      repository. 226Ra is a critical radionuclide in the safety
                      analysis and an important source of radioactivity in
                      technically enhanced naturally occurring radioactive
                      materials. A comprehensive study was carried out on the
                      adsorption of Ba and Ra on purified homoionic Na-illite
                      (Illite du Puy) over a wide range of experimental conditions
                      (pH, concentration, ionic strength) allowing for the
                      development of a quasi-mechanistic Ba/Ra adsorption model
                      for illite. Ba adsorption isotherms obtained at fixed ionic
                      strength and pH exhibit a non-linear behaviour in the Ba
                      equilibrium concentration range between ∼10−7 and
                      ∼10−2 M. The pH dependent adsorption of trace 226Ra and
                      Ba was investigated at different ionic strengths and
                      evidenced a more pronounced adsorption of 226Ra than Ba on
                      illite. Finally, a competition experiment of trace 226Ra in
                      the presence of increasing Ba concentrations showed an
                      unexpected 226Ra adsorption behaviour which was not observed
                      for montmorillonite in earlier studies. This large set of
                      experimental data could be successfully modelled by Ba/226Ra
                      exchange reactions against Na, together with selectivity
                      coefficients, on two different site types, namely planar
                      sites and high affinity sites. The modelling of the pH
                      dependent adsorption of Ba and 226Ra at high ionic strength
                      and high pH required an additional surface complexation
                      reaction. Two additional exchange sites had to be introduced
                      to quantitatively describe the 226Ra uptake on illite in the
                      226Ra/Ba competition experiment. The nature of these sites,
                      however, remains unclear. The implementation of the 226Ra
                      adsorption model into predictive transport modelling codes
                      is of key importance for the safety analysis of deep
                      geological disposal of radioactive waste.},
      cin          = {IEK-6},
      ddc          = {550},
      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)16},
      UT           = {WOS:001102594700001},
      doi          = {10.1016/j.apgeochem.2023.105815},
      url          = {https://juser.fz-juelich.de/record/1017537},
}