Effect of cation exchange of major cation chemistry in the large scale redox experiment at Aspo. Revision 1

Conference · Sat Jun 01 04:00:00 EDT 1996

OSTI ID:266648

Viani, B E; Bruton, C J

Geochemical modeling was used to test the hypothesis that cation exchange with fracture-lining clays during fluid mixing in the Aespoe Hard Rock Laboratory can significantly affect major element chemistry. Conservative mixing models do not adequately account for changes in Na, Ca and Mg concentrations during mixing. Mixing between relatively dilute shallow waters and more concentrated waters at depth along fracture zones was modeled using the EQ3/6 geochemical modeling package. A cation exchange model was added to the code to describe simultaneously aqueous speciation, mineral precipitation/dissolution, and equilibration between a fluid and a cation exchanger. Fluid chemistries predicted to result from mixing were compared with those monitored from boreholes intersecting the fracture zone. Modeling results suggest that less than 0.1 equivalent of a smectite exchanger per liter of groundwater is necessary to account for discrepancies between predictions from a conservative mixing model and measured Na and Ca concentrations. This quantity of exchanger equates to an effective fracture coating thickness of 20 {micro}m or less given a fracture aperture width of 1,000 {micro}m or less. Trends in cation ratios in the fluid cannot be used to predict trends in cation ratios on the exchanger because of the influence of ionic strength on heterovalent exchange equilibrium. It is expected that Na for Ca exchange will dominate when shallow waters such as HBHO2 are mixed with deeper waters. In contrast, Na for Mg exchange will dominate mixing between deeper waters.

• Research Organization: Lawrence Livermore National Lab., CA (United States)
• Sponsoring Organization: USDOE, Washington, DC (United States)
• DOE Contract Number: W-7405-ENG-48
• OSTI ID: 266648
• Report Number(s): UCRL-JC--118592-Rev.1; CONF-9406401--1-Rev.1; ON: DE96012512; BR: ?
• Country of Publication: United States
• Language: English

Related Subjects

05 NUCLEAR FUELS
CALCIUM
CLAYS
COMPUTERIZED SIMULATION
CONTAINMENT SYSTEMS
EXCAVATION
GEOCHEMISTRY
GEOLOGIC FRACTURES
GEOLOGIC MODELS
GROUND WATER
ION EXCHANGE
MAGNESIUM
MIXING
RADIOACTIVE WASTE DISPOSAL
RADIOACTIVE WASTE FACILITIES
SITE CHARACTERIZATION
SODIUM
SWEDEN
UNDERGROUND DISPOSAL
WATER CHEMISTRY