The Implications of Secondary Mineral Formation on the Fate of Cesium in Aluminosilicate Minerals: A Solid-State Nuclear Magnetic Resonance StudyEPA Grant Number: U916124
Title: The Implications of Secondary Mineral Formation on the Fate of Cesium in Aluminosilicate Minerals: A Solid-State Nuclear Magnetic Resonance Study
Investigators: Crosson, Garry S.
Institution: Pennsylvania State University
EPA Project Officer: Lee, Sonja
Project Period: January 1, 2003 through January 1, 2006
Project Amount: $150,163
RFA: STAR Graduate Fellowships (2003) Recipients Lists
Research Category: Academic Fellowships , Engineering and Environmental Chemistry , Fellowship - Chemistry and Materials Science
Aqueous radioactive metals leaking from the waste storage tanks have contaminated the soils at Department of Energy Facilities. The interactions with natural soil particles govern the mobility of radionuclides (such as 137Cs and 90Sr) in the saturated and unsaturated zones of contaminated sites (e.g., Hanford Site, Savannah River Site). High surface area aluminosilicate clay minerals, a soil component at these sites, are recognized as important radionuclide sorbents. The extreme characteristics of the contaminant medium (high pH, high Al, and high ionic strength) make clay minerals prone to weathering-induced transformations during exposure, which could affect the fate and mobility of harmful nuclei in the subsurface environment. The overall objective of this research project is to gain a better understanding of fundamental processes taking place in the vadose and saturated soil environments using specimen clay samples in environments that mimic those present at the Hanford site in Richland, WA. Various solid-state nuclear magnetic resonance (SSNMR) spectroscopic methods will be employed. The specific objectives of this research project are to: (1) develop a microscopic framework for the interactions of 133Cs with weathered specimen clays; (2) observe and identify neophases formed in weathered clay systems, such as kaolinite, as a function of contact time with a synthetic tank waste leachate solution and as a function of 133Cs and 88Sr initial concentrations in the synthetic leachate; and (3) resolve, characterize, and quantify the aluminum environments in select weathered samples.
SSNMR spectroscopy has been shown to be a very powerful analytical tool capable of studying amorphous and crystalline aluminosilicate mineral phases (in contrast to x-ray diffraction, which requires crystalline phases). Using NMR, the local environment around a variety of nuclei can be studied. Some NMR active nuclei relevant to mineral phases studied thus far include 29Si, 27Al, 23Na, and 133Cs. This research project will utilize the following SSNMR techniques in an attempt to accomplish the overall objective. Single-resonance 133Cs NMR studies will be used to follow changes in the chemical environment of cesium over time within reacted clays and will provide information on the nature of adsorption sites and the relative mobility of cesium within this weathered environment. Low field (400 MHz for 1H) single-resonance 27Al and 29Si NMR will be used to evaluate changes in the chemical environment of aluminum and silicon, which would indicate the formation of secondary mineral phases. Additionally, high-field (750 and 800 MHz for 1H) single-resonance and Multiple-Quantum Magic Angle Spinning 27Al NMR techniques, in conjunction with NMR simulations, will be utilized to calculate the quadrupolar interaction and the asymmetry parameters for all aluminum environments, along with the isotropic chemical shifts of the varied environments, which will aid in the identification of newly formed phases. Finally, more advanced double-resonance techniques such as 1H/29Si Cross-Polarization with Magic Angle Spinning, Transfer of Populations at Double Resonance, Rotational Echo Adiabatic-Passage Double Resonance, and Rotational Echo Double Resonance NMR will be used in an attempt to identify the location of cesium in the weathered system (i.e., investigate whether it interacts more favorably with neophases, or whether there is a preference for the clay phase).