As one of the most abundant natural ore of aluminum, boehmite is also found in the radioactive waste storage tanks at Department of Energy (DOE) Hanford site in Eastern Washington State, U.S.A, as large quantities of liquid wastes from the dissolution of aluminum casings of the fuel rods were disposed of in the tanks more than half a century ago. Over time, the liquid wastes evaporate and aluminum precipitated out in various forms of aluminum (oxyhydroxides) oxides, with boehmite being the major component. Dissolution tests have showed that the surface area-normalized dissolution rate of boehmite in the tank waste sludge is at least an order of magnitude lower than that predicted from pure boehmite under simulated solution conditions. It has been hypothesized that other metal contaminants in the wastes might inhibit boehmite dissolution in the caustic environment. Cr(III), an abundant species in the tank waste has been shown to be one of the metal ions inhibiting boehmite dissolution by adhering to the boehmite surface, either as nano/micron size precipitates or as adsorbed complexes. In this work, we synthesized boehmite nanoplates via hydrothermal treatment of amorphous Al(OH)3 gels and used for the adsorption of Cr(III) in caustic solutions. The adsorption isotherm and kinetics were determined by bench top adsorption measurement in which the Cr(III) remaining in the supernatant after centrifugation was determined using inductively coupled plasma - optical emission spectrometry (ICP-OES). X-ray diffraction (XRD) was used to identify the phase of boehmite and Cr(III)-adsorbed boehmite in the solid, and extended X-ray absorption fine structure (EXAFS), X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectroscopy (FT-IR), and Raman spectroscopy were used to explore the adsorption mechanism. Furthermore, the dissolution rate of pure boehmite and Cr(III)-adsorbed boehmite were investigated to understand the effect of Cr(III) adsorption on the boehmite corrosion. Finally, we synthesized the micro-sized boehmite plates and investigated the surface dynamics of boehmite and Cr (III) adsorbed boehmite in the caustic solutions using the in situ liquid cell Atomic Force Microscope (AFM).

Adsorption mechanism of Cr(III) on boehmite nanoparticles and the effect of Cr(III) on the dissolution of boehmite in caustic solution

256th National Meeting (2018)

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