Technetium and neptunium reactions in basalt/groundwater systems
Sorption isotherms and apparent concentration limits for Tc(VII) and Np(V) for a variety of groundwater/basalt systems were determined using Grande Ronde basalt samples representative of the Hanford Site candidate high-level waste repository. Under oxic redox conditions (air present), little or no sorption of technetium was observed; neptunium exhibited low to moderate sorption ratios. Under anoxic redox conditions (oxygen-free), low to moderate sorption of technetium was often observed, but the extent of sorption was highly dependent upon the groundwater composition and the method of pretreatment (if any) of the basalt. Sorption isotherms for technetium under reducing redox conditions (hydrazine added) indicate an apparent concentration limit of approximately 10/sup -6/ mol/l Tc. No apparent concentration limit was found for neptunium for concentrations in groundwater up to 10/sup -6/ mol/l and 8 x 10/sup -7/ mol/l under oxic and reducing (hydrazine added) redox conditions, respectively. Valence control and valence analysis experiments suggest that the sorption or precipitation of Tc and Np from groundwater in the presence of basalt may result from a heterogeneous reaction occurring on the surface of the basalt. One of the critical factors of this reduction reaction appears to be the accessibility of the reactive ferrous iron component of the basalt. The laboratory simulation of groundwater redox conditions representative of the repository environment through the use of solution phase redox reagents is of questionable validity, and information obtained by such experimental methods may not be defensible for site performance assessment calculations. Anoxic experiments conducted in an argon-filled glove box appear better suited for the laboratory simulation of in situ redox conditions. 15 references, 6 figures.
- Research Organization:
- Oak Ridge National Lab., TN
- DOE Contract Number:
- AC05-84OR21400
- OSTI ID:
- 7185085
- Journal Information:
- Mater. Res. Soc. Symp. Proc.; (United States), Journal Name: Mater. Res. Soc. Symp. Proc.; (United States) Vol. 44; ISSN MRSPD
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES
ACTINIDES
ADSORPTION ISOTHERMS
BASALT
BENCH-SCALE EXPERIMENTS
CHEMICAL REACTIONS
ELEMENTS
GROUND WATER
HANFORD RESERVATION
HIGH-LEVEL RADIOACTIVE WASTES
HYDROGEN COMPOUNDS
IGNEOUS ROCKS
ISOTHERMS
MANAGEMENT
MATERIALS
METALS
NATIONAL ORGANIZATIONS
NEPTUNIUM
OXYGEN COMPOUNDS
QUANTITY RATIO
RADIOACTIVE MATERIALS
RADIOACTIVE WASTE STORAGE
RADIOACTIVE WASTES
REDOX REACTIONS
ROCKS
SORPTION
SORPTIVE PROPERTIES
STORAGE
SURFACE PROPERTIES
TECHNETIUM
TRANSITION ELEMENTS
TRANSURANIUM ELEMENTS
US DOE
US ERDA
US ORGANIZATIONS
VOLCANIC ROCKS
WASTE MANAGEMENT
WASTE STORAGE
WASTES
WATER