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Title: Desorption of plutonium from montmorillonite: An experimental and modeling study

Desorption of plutonium (Pu) will likely control the extent to which it is transported by mineral colloids. In this article, we evaluated the adsorption/desorption behavior of Pu on SWy-1 montmorillonite colloids at pH 4, pH 6, and pH 8 using batch adsorption and flow cell desorption experiments. After 21 days adsorption, Pu(IV) affinity for montmorillonite displayed a pH dependency, with K d values highest at pH 4 and lowest at pH 8. The pH 8 experiment was further allowed to equilibrate for 6 months and showed an increase in K d, indicating that true sorption equilibrium was not achieved within the first 21 days. For the desorption experiments, aliquots of the sorption suspensions were placed in a flow cell, and Pu-free solutions were then pumped through the cell for a period of 12 days. Changes in influent solution flow rate were used to investigate the kinetics of Pu desorption and demonstrated that it was rate-limited over the experimental timescales. At the end of the 12-day flow cell experiments, the extent of desorption was again pH dependent, with pH 8 > pH 6 > pH 4. Further, at pH 8, less Pu was desorbed after an adsorption contact time of 6more » months than after a contact time of 21 days, consistent with an aging of Pu on the clay surface. In addition, a conceptual model for Pu adsorption/desorption that incorporated known surface-mediated Pu redox reactions was used to fit the experimental data. The resulting rate constants indicated processes occurring on timescales of months and even years which may, in part, explain observations of clay colloid-facilitated Pu transport on decadal timescales. Importantly, however, our results also imply that migration of Pu adsorbed to montmorillonite colloids at long (50–100 year) timescales under oxic conditions may not be possible without considering additional phenomena, such as co-precipitation.« less
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  1. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States). Glenn T. Seaborg Institute, Physical & Life Sciences
Publication Date:
Report Number(s):
Journal ID: ISSN 0016-7037
Grant/Contract Number:
Accepted Manuscript
Journal Name:
Geochimica et Cosmochimica Acta
Additional Journal Information:
Journal Volume: 197; Journal ID: ISSN 0016-7037
The Geochemical Society; The Meteoritical Society
Research Org:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org:
USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23); USDOE Office of Nuclear Energy (NE)
Country of Publication:
United States
54 ENVIRONMENTAL SCIENCES; 58 GEOSCIENCES; Plutonium; Sorption; Desorption; Montmorillonite
OSTI Identifier:
Alternate Identifier(s):
OSTI ID: 1410717