High Resolution Multinuclear NMR of Waste-Weathered Hanford Sediments
EMSL Project ID
47534
Abstract
Our research team is part of a multi-laboratory/university project funded by the Department of Energy that is investigating the fate of uranium and strontium in waste-weathered sediments such as those found near to the U-8 and U-12 crib sites at the Hanford reservation (Washington State). This project seeks to predict reactive contaminant migration in Hanford sediments that have received acidic uranium and strontium bearing waste streams from these cribs. We will employ bench-scale experimentation with unimpacted Hanford sediments in order to simulate acidic U and Sr waste stream introductions. Batch and column experiments will simulate sediment dissolution, nucleation, crystal growth, and ripening processes that likely occurred in situ, in the presence of the acidic waste. Based on an analysis of available documentation, we have developed a range of aqueous geochemical conditions that we propose represents the acidic wastes historically introduced into Hanford sediments, and we have used this parameter space in our bench study experimental design. Samples from batch and column studies will be subjected to a suite of complementary analytical methods over an experimental time series to obtain kinetic data across a range of spatial scales. Key analytical methods that will be brought to bear on these impacted sediment samples include high-field, high-resolution solid-state NMR studies of the multi-component solid phases both before and after acidic impact. In this proposal we request resources on the high-field (17.6 T) nuclear magnetic resonance spectrometer that will be relocated to the new EMSL Radiochemical Annex, where we will perform solid-state NMR experiments on a range of impacted (weathered) samples, many of which will contain radioactive U. Since these experiments must involve magic-angle spinning NMR, there is a finite (although small) probability that samples could become dispersed in the atmosphere as the result of a catastrophic MAS rotor crash, and such risk must be mitigated by performing the experiments in a safe location with equipment designed specifically to spin and contain radioactive samples. Experiments on non-radioactive samples could begin before the scheduled move (fall 2012 or later), and non-radioactive samples will also be studied on the 21.1 T NMR system. Additional studies at 17.6 T would take place once the move has occurred. Experiments to be performed on a suite of approximately 12 -15 samples will include:(a) 29Si, 27Al, and 31P magic-angle spinning (MAS) NMR studies of unweathered and weathered samples to determine bulk compositional changes as a function of acidic weathering.
(b) 1H/27Al, 1H/29Si, and 1H/31P cross-polarization MAS NMR studies of unweathered and weathered samples to determine compositional changes related to hydroxylated/hydrated neophases.
(c) Additional double- and triple-resonance heteronuclear MAS measurements (including 27Al/31P TRAPDOR, etc.) for discerning more subtle structural changes or adsorption of specific species to sediment surfaces.
(d) 27Al multiple-quantum (MQ)MAS measurements on unweathered and weathered samples for defining local aluminum quadrupolar and shift parameters for comparison to computational chemistry results.
Project Details
Project type
Large-Scale EMSL Research
Start Date
2012-10-01
End Date
2015-09-30
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members