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

Trent R Graham; Jian Zhi Hu; Xin Zhang; Mateusz Dembowski; Nicholas R Jaegers; Chuan Wan; Mark Bowden; Andrew S Lipton; Andrew R Felmy; Sue B Clark; Kevin M Rosso; Carolyn I Pearce

doi:10.1021/acs.inorgchem.9b02000

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

Inorg Chem. 2019 Sep 16;58(18):12385-12394. doi: 10.1021/acs.inorgchem.9b02000. Epub 2019 Sep 5.

Authors

Trent R Graham^{1

2}, Jian Zhi Hu^{1

3

4}, Xin Zhang¹, Mateusz Dembowski¹, Nicholas R Jaegers^{1

3

4}, Chuan Wan³, Mark Bowden^{1

5}, Andrew S Lipton⁵, Andrew R Felmy¹, Sue B Clark^{6

7

8}, Kevin M Rosso¹, Carolyn I Pearce⁸

Affiliations

¹ Physical and Computational Sciences Directorate , Pacific Northwest National Laboratory , Richland , Washington 99354 , United States.
² The Voiland School of Chemical and Biological Engineering , Washington State University , Pullman , Washington 99164 , United States.
³ Institute for Integrated Catalysis , Pacific Northwest National Laboratory , Richland , Washington 99354 , United States.
⁴ Biological Science Directorate , Pacific Northwest National Laboratory , Richland , Washington 99354 , United States.
⁵ Environmental Molecular Sciences Laboratory , Pacific Northwest National Laboratory , Richland , Washington 99354 , United States.
⁶ Department of Chemistry , Washington State University , Pullman , Washington 99164 , United States.
⁷ Materials Science and Engineering Program , Washington State University , Pullman , Washington 99164 , United States.
⁸ Energy and Environment Directorate , Pacific Northwest National Laboratory , Richland , Washington 99354 , United States.

PMID: 31486636
DOI: 10.1021/acs.inorgchem.9b02000

Abstract

Gibbsite (α-Al(OH)₃) transformation into layered double hydroxides, such as lithium aluminum hydroxide dihydrate (LiAl-LDH), is generally thought to occur by solid-state intercalation of Li⁺, in part because of the intrinsic structural similarities in the quasi-2D octahedral Al³⁺ frameworks of these two materials. However, in caustic environments where gibbsite solubility is high relative to LiAl-LDH, a dissolution-reprecipitation 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 Al³⁺ 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 (²⁷Al and ⁶Li MAS NMR), with supporting X-ray diffraction and scanning electron microscopy. In situ ²⁷Al 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 ⁶Li 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 ²⁷Al MAS NMR spectra, where a comparatively narrow LiAl-LDH O_h ²⁷Al resonance emerges upfield of gibbsite resonances. No intermediate pentahedral Al³⁺ 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 Al³⁺ 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.