High-resolution 27Al MAS NMR of Weathered Clays and Hanford Sediments
EMSL Project ID
17693
Abstract
In prior research at PNNL, kaolinite and montmorillonite minerals weathered under near-field exposure to simulated Hanford tank waste were examined with 10 kHz 27Al MAS NMR on the 17.61 T spectrometer. In the case of kaolinite, the isotropic quadrupolar shift and line narrowing due to the high field strength permitted the resolution of multiple overlapping resonances corresponding to multiple weathering products. The rates of kaolinite dissolution and product formation were determined by monitoring the 27Al peak integrals for each species as a function of weathering time. However, similar kinetic analyses could not be completed in the case of weathered montmorillonite samples: the presence of a strong aluminum background signal and lack of sensitivity (only low sample volumes available) in the short exposure time samples produced un-interpretable spectra. By increasing the field strength to 21.14 T and using a 20 kHz spin rate, we will increase the sensitivity of 27Al and the resolution, which should permit a full kinetic analysis of montmorillonite weathering. In addition, samples of vadose zone sediments (Hanford coarse, Hanford fine, and Ringold silt) weathered with identical simulated tank waste are now available for analysis. Each of these parent sediments consists of a number of mineral phases before exposure to simulated tank waste leachate and subsequent weathering. The number of unique mineral phases in these samples severely complicates our ability to resolve each parent and daughter phase; therefore, analysis at the highest possible field strength is warranted for the sediment studies to provide resolvability while maintaining quantitative accuracy. In this proposal, we intend to apply 20 kHz 27Al MAS NMR on the 21.14 T spectrometer to study montmorillonite, Ringold silt, Hanford coarse, and Hanford fine sediments weathered under simulated tank waste chemistry. We hope to (i) resolve and quantify each of the parent minerals and neoformed phases as a function of weathering time as well as (ii) use the NMR results to calculate the kinetics of dissolution and precipitation for each of these samples.
Project Details
Project type
Capability Research
Start Date
2006-04-20
End Date
2007-05-21
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members
Related Publications
Bowers GM, MC Davis, R Ravella, S Komarneni, KT Mueller. 2007. "NMR studies of heat induced transitions in structure and cation binding environments of a strontium-saturated swelling mica." Applied Magnetic Resonance, in press.
Geoffrey M. Bowers, Michael C. Davis, Ramesh Ravella, Sridhar Komarneni, and Karl T. Mueller. NMR Studies of Heat Induced Transitions in Structure and Cation Binding Environments in a Strontium Saturated Swelling Mica. Applied Magnetic Resonance, 32 (2007) 595-612.