The Chemistry of Hanford Sediments Reacted with Simulated Tank Waste Leachates: High-Resolution 27Al MAS and MQMAS NMR Studies
EMSL Project ID
40064
Abstract
At sites such as Hanford, a former US Department of Energy (DOE) plutonium production facility, caustic nuclear waste (containing Cs-137 and Sr-90) has leaked from underground waste storage tanks into the soil, and is believed to cause subsequent mineral transformation reactions that form zeolite-like precipitated phases. To address concerns regarding the ultimate fate of radionuclides released into the environment, our research is focused on characterization of Hanford sediments reacted with synthetic tank waste leachate (STWL) containing contaminant Cs and Sr (in non-radioactive forms) in both batch weathering (contamination) experiments and flow-through column experiments where a simulated Hanford background pore water (BPW) is allowed to interact with the contaminated sediments. We are using nuclear magnetic resonance (NMR) to elucidate mineral transformations during weathering, and coupling those results with XRD and wet chemical analyses to determine modes of cation sequestration in sediments reacted as a function of time. We have established that nitrate-bearing feldspathoid and zeolite phases form with time as a result of sediment reaction with caustic STWL. These secondary phases are capable of taking up both Cs and Sr from solution as they form. Characterization of reaction products by Al-27 MAS NMR experiments conducted across a range of field strengths at PSU and EMSL have proven useful in determining the time-dependent formation and the relative mass fractions of neophases in model clay systems, but characterization of waste-impacted sediments has proven difficult using MAS methods alone. We propose a number of Al-27 MAS and multiple-quantum MAS (MQMAS) studies to resolve and quantify each of the parent minerals in the sediments, as well as to identify and quantify neoformed phases as a function of weathering time and post-reaction flushing with circumneutral BPW. Also informed by collaborative XRD analyses and Al-27 NMR of homogeneously precipitated samples, our team will use the quantitative NMR results to calculate the kinetics of parent-phase dissolution and neophase precipitation/dissolution for each of 23 samples. We will use these data to inform new reactive transport studies of contaminated Hanford sediments. While these computational studies will not take place at EMSL, the data acquired in this research will be essential for future modeling, thus satisfying the spirit of the EMSL mission to combine cutting-edge experiments with excellence in computational analysis. The EMSL facility is a unique resource for these studies due to the availability of high field (>17 T) solid-state NMR systems and high spinning speed MAS NMR probes that are essential for these quantitative analyses.
Project Details
Project type
Large-Scale EMSL Research
Start Date
2010-10-01
End Date
2012-09-30
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members