Aluminum Removal From Hanford Waste by Lithium Hydrotalcite Precipitation - Laboratory Scale Validation on Waste Simulants Test Report

Sams, T.L.; Hagerty, K.J.

doi:10.2172/1010336

Cited by 1 publication

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“…LiAl-LDH is an important precursor of lithium aluminate (LiAlO 2 ), which is widely used in energy applications including tritium production, , fuel cells, and lithium batteries . LiAl-LDH precipitation in caustic solutions has also been proposed as a strategy to control Al 3+ concentrations in Al 3+ -rich radioactive high-level nuclear wastes (HLW) for processing into more stable glass wasteforms. , Large quantities of this waste are located at Department of Energy (DOE) sites such as Hanford, Washington, USA, where the predominant Al 3+ phase is gibbsite (α-Al(OH) 3 ) coexisting with high concentrations of soluble aluminate ions (Al(OH) 4 – ) . At such sites, the efficiency of HLW stabilization through vitrification can be greatly improved by reducing the concentration of Al 3+ in the waste stream, enabling increased waste loading in the glass. , Li + addition is motivated by two factors: Al 3+ solubility in Li + -rich caustic electrolytes is low compared to NaOH solutions (e.g., ca.…”

Section: Introductionmentioning

confidence: 99%

Unraveling Gibbsite Transformation Pathways into LiAl-LDH in Concentrated Lithium Hydroxide

Graham

Zhang

et al. 2019

Inorg. Chem.

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Gibbsite (α-Al(OH) 3 ) transformation into layered double hydroxides, such as lithium aluminum hydroxide dihydrate (LiAl-LDH), is generally thought to occur by solidstate intercalation of Li + , in part because of the intrinsic structural similarities in the quasi-2D octahedral Al 3+ frameworks of these two materials. However, in caustic environments where gibbsite solubility is high relative to LiAl-LDH, a dissolutionreprecipitation pathway is conceptually enabled, proceeding via precipitation of tetrahedral (T d ) aluminate anions (Al(OH) 4 − ) at concentrations held below 150 mM by rapid LiAl-LDH nucleation and growth. In this case, the relative importance of solid-state versus solution pathways is unknown because it requires in situ techniques that can distinguish Al 3+ in solution and in the solid phase (gibbsite and LiAl-LDH), simultaneously. Here, we examine this transformation in partially deuterated LiOH solutions, using multinuclear, magic angle spinning, and high field nuclear magnetic resonance spectroscopy ( 27 Al and 6 Li MAS NMR), with supporting X-ray diffraction and scanning electron microscopy. In situ 27 Al MAS NMR captured the emergence and decline of metastable aluminate ions, consistent with dissolution of gibbsite and formation of LiAl-LDH by precipitation. High field, ex situ 6 Li NMR of the the progressively reacted solids resolved an O h Li + resonance that narrowed during the transformation. This is likely due to increasing local order in LiAl-LDH, correlating well with observations in high field, ex situ 27 Al MAS NMR spectra, where a comparatively narrow LiAl-LDH O h 27 Al resonance emerges upfield of gibbsite resonances. No intermediate pentahedral Al 3+ is resolvable. Quantification of aluminate ion concentrations suggests a prominent role for the solution pathway in this system, a finding that could help improve strategies for manipulating Al 3+ concentrations in complex caustic waste streams, such as those being proposed to treat the high-level nuclear waste stored at the U.S. Department of Energy's Hanford Nuclear Reservation in Washington State, USA.

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