Caustic Waste-Soil Weathering Reactions and Their Impacts on Trace Contaminant Migration & Separation - Final Report

Studies of the reactivity of radionuclides (Cs, Sr, I) in STWL with model clays and natural sediments were conducted by coupling macroscopic sorption-desorption experiments with spectroscopic and microscopic investigations over a wide range of reaction times. Three experimental systems were studied: (1) model clay minerals, (2) products of homogeneous precipitation from STWL, and (3) representative Hanford sediments, with (1) and (3) reacted with STWL from 1 h to 369 d. The clay minerals included illite, vermiculite, smectite and kaolinite, which constitute a sequence of micaceous weathering products with variable reactivity toward Cs+, Sr2+ and I-. Coarse and fine sediments collected from the Hanford formation (HC and HF, respectively) and Ringold Silt (RS) were studied in batch experiments and Warden silt loam was used in batch and column experiments. Solutions were analyzed by inductively coupled plasma-mass spectrometry (ICP-MS). Solid products (referred to here as ''secondary phases'' relative to the initial reactant minerals) were analyzed for time-dependent changes in mineralogy and modes of contaminant bonding by a variety of methods, including X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM and TEM) with energy dispersive spectrometry (EDS), thermogravimetric analysis (TGA), nuclear magnetic resonance (NMR), X-ray absorption spectroscopy (XAS), including extended X-ray absorption fine structure (EXAFS) and X-ray absorption near-edge structure (XANES) analysis, and Fourier-transform infrared spectroscopy (FTIR)