Kansallisen ydinjätehuollon tutkimusohjelma (KYT 2010) Kolmenarvoisten aktinidien kiinnittyminen savi- ja (hydr)oksidimineraalien pinnoille Sorption of trivalent actinides onto clay- and (hydr)oxide minerals Nina Huittinen Radiokemian laboratorio, Helsingin Yliopisto

1 - General background  Deep geological formations are considered for the long-term disposal of radioactive waste  Knowledge of geochemical processes essential for a thorough nuclear waste disposal safety assessment – e.g. solid-water interface reactions and redox- and complexation reactions in solution  For a thorough safety assessment over long time-scales, understanding of atomic- and molecular scale interactions of radionuclides with the solid-water environment is imperative

2 – Project motivations  Trivalent actinides  Am and Cm are together with Pu responsible for the long-term radiotoxcicity of spent fuel.  Trivalent oxidation state soluble – radionuclide dissolution and migration  Minerals  Gibbsite α -Al(OH) 3 – used e.g. as a model mineral for aluminosilicates and iron oxides/hydroxides found in vast quantities in natural systems  Kaolinite Al 2 Si 2 O 5 (OH) 4 – one of the main mineral components of clay-rich host formations  Silica SiO 2 – presence of silica ubiquitous in most natural materials and groundwaters, colloids Pu(III) Am(III) Cm(III)

3 – Aim of project  Characterization of present reactive OH-groups on the mineral surface  Determination of surface sites involved in An(III)/Ln(III) sorption  Characterization of sorption mechanisms and surface complexes Possible interactions of radionuclides with present mineral phases

4 - Methods  Mineral synthesis – clean minerals  FTIR - identification of OH groups and knowledge of specific bonding to the surface  Solid state NMR- identification of OH groups and knowledge of specific bonding and coordination to the surface  TRLFS – knowledge of An(III) hydration sphere and surface complexes  SEM  XRD  N 2 -BET  Micro electrophoresis  ICP-MS Mineral characterization

5 – Objectives for 2008  Mineral synthesis  Mineral characterization  Basic sorption studies and mass balance studies (master’s thesis)  IR experiments  NMR experiments  International collaboration with INE, Karlsruhe, Germany - Inclusion of 5- sulphosalicylic acid (model compound for humic acids) to study ternary surface complex formation

6 – Results 2008  Kaolinite synthesis and characterization - Université de Poitiers, France  Gibbsite synthesis and characterization, Department of Chemistry, University of Helsinki  Silica purchase EVONIK industries

6 – Results 2008  Sorption studies and mass balance studies with all chosen minerals Modeling → mass balance of Eu 3+, H +, Al 3+ /Si 2+, anions in solid and liquid phase respectively  ξ-potential measurements → net charge of mineral surface  Batch experiments Ln(III) sorption as a function of pH → K d values and titration curves  Isotherm experiments – concentration of adsorbed Ln(III) as a function of Ln(III) concentration in solution→ types of OH groups

6 – Results 2008  IR-studies, FTIR- NesteOil Oy Finland, ATR-FTIR - Department of Chemistry, University of Helsinki Gibbsite – 6 structural OH groups 1- Intralayer OH groups oriented parallel to the (001) face (OH1, OH2 and OH4) 2- Interlayer OH groups oriented nearly perpendicular to the (001) face (OH3, OH5 and OH6)

7 – Outlook  October 2008 – Spring 2009: Collaboration with the Instute for nuclear waste management (INE), Forschungszentrum Karlsruhe, Germany  TRLFS investigations using synthetic kaolinite and Cm(III)  Addition of model ligand to mineral/metal ion system  Possibly investigations using well characterized humic acid and natural montmorillonite 5-sulfosalicylic acid

7 - Outlook   NMR-studies, National Institute of Chemical Physics and Biophysics, Tallinn, Estonia  IR studies using alumina and silica, possibly kaolinite  Surface complexation modeling  4-5 publications  Ph.D dissertation