TY  - CONF
AU  - Klinkenberg, Martina
AU  - Brandt, Felix
AU  - Barthel, Juri
AU  - Bosbach, Dirk
TI  - Solid-solution formation of (Ba,Sr,Ra)SO4: Microscopic approaches
M1  - FZJ-2023-03739
PY  - 2023
AB  - The minerals of the isostructural barite ((Ba,Sr)SO4) group are frequently occurring and characterized by their low solubility. These sulfates are associated with the formation of technically enhanced naturally occurring radioactive material (TENORM). The radioactivity of TENORM is often a result of solid solution formation with 226Ra because of the higher thermodynamic stability compared to the pure endmember RaSO4. The (Ra,Ba,Sr)SO4 is also relevant for the safety assessment of deep geological repositories for spent nuclear fuel. In this contribution, the application of microscopic approaches on the solid-solution formation of (Ba,Sr,Ra)SO4 to understand macroscopic observations will be discussed.A combination of scanning electron microscopy (SEM), energy dispersive x-ray spectrometry (EDX), focused ion beam (FIB), transmission electron microscopy (TEM) as well as time of flight secondary ion mass spectroscopy (ToF-SIMS) and atom probe tomography (APT) was applied to unravel the up-take of 226Ra into (Ba,Sr,Ra)SO4 on a molecular scale. SEM-EDX was used to follow the morphological and chemical evolution of the sulfate particles during the Ra-uptake. The Ra-uptake into the solid was observed by a 3D analysis of complete grains via ToF-SIMS. The FIB, producing very small samples and extremely thin samples for TEM and atom probe tomography (APT), enables the detailed investigation of even highly radioactive materials due to the low radioactivity of the FIB sections. TEM and APT were applied to unravel the details of this recrystallization process from the solid materials perspective, indicating an important role of fluid inclusions and internal porosity typical for these sulfates. Our studies not only show that 226Ra is taken up structurally during recrystallisation of (Ba,Sr)SO4, but also that kinetically controlled initial stages eventually are followed by thermodynamically controlled Ra-uptake which can be described via solid-solution aqueous-solution modeling.
T2  - 21st Jena Remediation Symposium
CY  - 4 Oct 2023 - 6 Oct 2023, Jena (Germany)
Y2  - 4 Oct 2023 - 6 Oct 2023
M2  - Jena, Germany
LB  - PUB:(DE-HGF)24
UR  - https://juser.fz-juelich.de/record/1016753
ER  -