%0 Conference Paper
%A Brandt, Felix
%A Klinkenberg, Martina
%A Poonoosamy, Jenna
%A Barthel, Juri
%A Weber, Juliane
%A Bosbach, Dirk
%T Ra Uptake by the Sr-Rich Solid Solution of (Sr, Ba)SO4
%M FZJ-2018-05388
%D 2018
%X 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.
%B Goldschmidt
%C 12 Aug 2018 - 17 Aug 2018, Boston (USA)
Y2 12 Aug 2018 - 17 Aug 2018
M2 Boston, USA
%F PUB:(DE-HGF)6
%9 Conference Presentation
%U https://juser.fz-juelich.de/record/852442