High-field 1Q MAS and MQMAS Solid-State NMR Studies of the Dissolution of Montmorillonite Clays Under Alkaline Conditions
EMSL Project ID
3317
Abstract
We studied the incongruent weathering of montmorillonite clay samples in our laboratory with conditions representative of the vadose zone beneath waste storage tanks at the Hanford reservation (2.0 M Na+, 1 M NO3-, 1 M and 1 M OH- in the presence of varied amounts of cesium and strontium). We performed batch mode experiments from 0 to 369 days using stable, non-radioactive isotopes of cesium and strontium. We observed at 300 MHz, via 27Al single-resonance NMR, that four-coordinate aluminum phases (possibly zeolitic in nature) form as a function of time. Previously we showed that the rates of formation of these new phases in both clays are inversely related to the initial concentrations of cesium and strontium in kaolinite systems, and this trend was expected and observed in montmorillonite systems. Single-pulse experiments performed at 300 MHz on montmorillonite, after a 190-day reaction period, suggests the presence of different 4-coordinate aluminum environments. However, the new tetrahedral resonances are poorly resolved. In previous studies of kaolinite clay at 300, 400, and 500 MHz, unresolvable tetrahedral resonances were also observed. Better resolution of the kaolinite resonances was achieved only when using the 750 MHz instrument made available at PNNL. (Please see report.) Thus, based on previous studies with kaolinite and current preliminary studies of montmotillonite, the complete resolution, identification, and quantification of all aluminum environments in montmorillonite systems can only be achieved utilizing the highest field strengths available for 27Al NMR.
Project Details
Project type
Capability Research
Start Date
2003-04-12
End Date
2004-04-09
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members