Diffusion of ion-exchanging electrolytes in montmorillonite gels

Thesis/Dissertation · Thu Jan 01 04:00:00 EST 1987

OSTI ID:7079699

Jahnke, F M

The primary contributions of this work are: (1) Development of a unique radially perfused diffusion cell suitable for measuring transient diffusion rates in compacted, highly adsorbing and swelling porous media such as montmorillonite clay gels; (2) examination of the effective diffusion coefficient (D{sub 6}) of electrolytes in montmorillonite clay gels; and (3) Measurement of the transient diffusion rates of cesium, chloride and tritium in 15 w/o montmorillonite clay gels at pH 9 and sodium chloride backgrounds of 10{sup {minus}1} to 10{sup {minus}3} kmol/m{sup 3}. Results are interpreted by using the dilute limit of the multicomponent transport equations derived for species migration in a single clay pore after macroscopic averaging. The tortuosity of the clay gel is found by tritium diffusion. Transient chloride diffusion rates are found to be at molecular rates. Negative adsorption of anions from the clay gel, required for an a priori prediction of chloride profiles, are calculated from site-binding theory. Surface diffusion is the primary mode of cesium transport in montmorillonite clay gels. Migration of cesium is primarily along the inner Helmholtz plane of clay particles. The primary implication for the montmorillonite clay-based packing as a nuclear waste migration barrier is that surface diffusion must be included to describe properly diffusion rates of either anions or cations. Currently surface diffusion is neglected and cesium penetration into the packing is drastically underestimated. Penetration depths of anions is grossly overestimated. In either case, the appropriate diffusion coefficient of ions in compacted packing will be in considerable error relative to current design recommendations.

• Research Organization: California Univ., Berkeley, CA (USA)
• OSTI ID: 7079699
• Country of Publication: United States
• Language: English

Related Subjects

052002* -- Nuclear Fuels-- Waste Disposal & Storage
12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES
ALKALI METALS
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
CESIUM
CHLORIDES
CHLORINE COMPOUNDS
CLAYS
COLLOIDS
CRYSTAL STRUCTURE
DIFFUSION
DISPERSIONS
ELECTROLYTES
ELEMENTS
ENVIRONMENTAL TRANSPORT
GELS
HALIDES
HALOGEN COMPOUNDS
HYDROGEN ISOTOPES
INORGANIC ION EXCHANGERS
ION EXCHANGE
ION EXCHANGE MATERIALS
ISOTOPES
LIGHT NUCLEI
MASS TRANSFER
MATERIALS
MEASURING INSTRUMENTS
METALS
MICROSTRUCTURE
MONTMORILLONITE
NUCLEAR FACILITIES
NUCLEI
ODD-EVEN NUCLEI
PERMEABILITY
PH VALUE
POROSITY
POROUS MATERIALS
RADIOACTIVE MATERIALS
RADIOACTIVE WASTE FACILITIES
RADIOACTIVE WASTES
RADIOISOTOPES
RADIONUCLIDE MIGRATION
SORPTION
TRITIUM
WASTES
YEARS LIVING RADIOISOTOPES