Quantification of Cation Sorption to Engineered Barrier Materials Under Extreme Conditions

Technical Report · Tue Feb 02 00:00:00 EST 2016

DOI:https://doi.org/10.2172/1253947· OSTI ID:1253947

Powell, Brian ^[1]; Schlautman, Mark ^[1]; Rao, Linfeng ^[2]; Nitsche, Heino ^[3]; Gregorich, Kenneth ^[3]

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1. Clemson Univ., SC (United States)
2. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
3. Univ. of California, Berkeley, CA (United States)

The objective of this research is to examine mechanisms and thermodynamics of actinide sorption to engineered barrier materials (iron (oxyhydr)oxides and bentonite clay) for nuclear waste repositories under high temperature and high ionic strength conditions using a suite of macroscopic and microscopic techniques which will be coupled with interfacial reaction models. Gaining a mechanistic understanding of interfacial processes governing the sorption/sequestration of actinides at mineral-water interfaces is fundamental for the accurate prediction of actinide behavior in waste repositories. Although macroscale sorption data and various spectroscopic techniques have provided valuable information regarding speciation of actinides at solid-water interfaces, significant knowledge gaps still exist with respect to sorption mechanisms and the ability to quantify sorption, particularly at high temperatures and ionic strengths. This objective is addressed through three major tasks: (1) influence of oxidation state on actinide sorption to iron oxides and clay minerals at elevated temperatures and ionic strengths; (2) calorimetric titrations of actinide-mineral suspensions; (3) evaluation of bentonite performance under repository conditions. The results of the work will include a qualitative conceptual model and a quantitative thermodynamic speciation model describing actinide partitioning to minerals and sediments, which is based upon a mechanistic understanding of specific sorption processes as determined from both micro-scale and macroscale experimental techniques. The speciation model will be a thermodynamic aqueous and surface complexation model of actinide interactions with mineral surfaces that is self-consistent with macroscopic batch sorption data, calorimetric and potentiometric titrations, X-ray absorption Spectroscopy (XAS, mainly Extended X-ray Absorption Fine Structure (EXAFS)), and electron microscopy analyses. The novelty of the proposed work lies largely in the unique system conditions which will be examined (i.e. elevated temperature and ionic strength) and the manner in which the surface complexation model will be developed in terms of specific surface species identified using XAS. These experiments will thus provide a fundamental understanding of the chemical and physical processes occurring at the solid-solution interface under expected repository conditions. Additionally, the focus on thermodynamic treatment of actinide ion interactions with minerals as proposed will provide information on the driving forces involved and contribute to the overall understanding of the high affinity many actinide ions have for oxide surfaces. The utility of this model will be demonstrated in this work through a series of advective and diffusive flow experiments.

• Research Organization: Clemson Univ., SC (United States)
• Sponsoring Organization: USDOE Office of Nuclear Energy (NE)
• DOE Contract Number: AC07-05ID14517
• OSTI ID: 1253947
• Report Number(s): DOE/NEUP-11-3180; 11-3180; TRN: US1601398
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES
BENTONITE
ABSORPTION
RADIOACTIVE WASTES
CATIONS
IRON OXIDES
REACTION KINETICS
ABSORPTION SPECTROSCOPY
X-RAY SPECTROSCOPY
TEMPERATURE RANGE 0273-0400 K
ACTINIDES
SURFACES
WATER
INTERFACES
ELECTRON MICROSCOPY
CALORIMETRY
SUSPENSIONS
AFFINITY
FORECASTING
PARTITION
PERFORMANCE
SEDIMENTS
SOLIDS
THERMODYNAMICS
VALENCE
RADIOACTIVE WASTE DISPOSAL