High-field Solid-State NMR Studies of Weathered Specimen Kaolinite Clays
EMSL Project ID
2578
Abstract
The dissolution or weathering of specimen kaolinite clay samples has been studied in our laboratory under geochemical conditions characteristic of those found in the vadose zone beneath leaking nuclear waste storage tanks (2.0 M Na+, 1 M NO3-, 1 M OH- in the presence of varied amounts of cesium and strontium). Weathering experiments were conducted in batch mode over the course of 0 to 369 days, using stable Cs and Sr isotopes as surrogates for radioactive isotopes. It was observed via 27Al single-resonance NMR that four-coordinate aluminum phases (possibly zeolitic in nature) form as a function of time. Furthermore, the rates of formation of these new phases appear to be inversely related to the initial concentrations of cesium and strontium in the systems, whereas the recalcitrance of these new phases (as evaluated by treatments with acidic oxalate solutions) exhibit linear concentration dependences. Single-resonance 27Al NMR performed at multiple fields indicate the presence of multiple aluminum environments in these weathered systems. However, at the magnetic field strengths utilized (7.04 T, 9.4 T and 11.7 T), the new tetrahedral resonances are poorly resolved. Consequently, the highest magnetic field strengths obtainable for 27Al NMR are needed to resolve, identify, and quantify the various aluminum environments in these weathered systems.
Project Details
Project type
Capability Research
Start Date
2002-10-01
End Date
2002-12-18
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members