Structural Investigations of Strontium in Inorganic Crystals, Organic Crystals, and Phyllosilicate Minerals with Strontium-87 NMR

Open Access
Author:
Bowers, Geoffrey M
Graduate Program:
Chemistry
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
June 08, 2006
Committee Members:
  • Karl Todd Mueller, Committee Chair
  • Thomas E Mallouk, Committee Member
  • Alan James Benesi, Committee Member
  • Brian Dempsey, Committee Member
Keywords:
  • strontium
  • NMR
  • phyllosilicate
  • DOE
Abstract:
At numerous United States Department of Energy (US DOE) facilities such as Hanford near Richland, Washington, an enormous volume of high-level liquid nuclear waste has been released from leaking storage tanks. The immobilization and remediation of strontium from the environment and the remaining stored waste are issues of great importance to the US DOE and populations surrounding the storage facilities: a portion of any strontium-90 ingested from contaminated food or drinking water will be incorporated into bone mass, leading to bone defects in minors and cancer in adults. In order to design appropriate waste remediation strategies and predict the mobility of strontium in the environment, it is necessary to understand the interactions of strontium with soil minerals and remediation materials on the molecular level. This dissertation seeks to enhance our grasp of strontium-mineral interactions through solid-state strontium-87 nuclear magnetic resonance (NMR). The first series of studies examines the effectiveness of magic angle spinning (MAS) at improving the sensitivity and resolution of strontium-87 NMR spectra. While this technique is effective for materials with a negligible electric field gradient, both experimental and theoretical results show that MAS is not effective at improving sensitivity or the interpretability of strontium-87 resonances with quadrupolar couplings larger than 10 MHz. The remaining studies probe the effectiveness of more complex pulse sequences at enhancing sensitivity and characterizing the strontium binding structure. The quadrupolar Carr-Purcell-Meiboom-Gill (QCPMG) pulse sequence combined with a double frequency sweep (DFS) preparatory pulse at a 21.14 T static field is shown to provide significant sensitivity enhancement, enabling strontium detection in complex materials. The QCPMG and DFS-QCPMG sequences are used at 21.14 T to characterize the strontium binding structure in a number of inorganic and organic crystalline systems where the structure is known, establishing the relationship between the local strontium binding structure and strontium quadrupolar parameters. These relationships are used along with fluorine-19 MAS NMR and x-ray diffraction to analyze the strontium binding site in a number of synthetic and natural strontium-sorbing phyllosilicate minerals and other environmentally relevant materials in the remainder of the dissertation.