An amorphous sodium aluminate hydrate phase mediates aluminum coordination changes in highly alkaline sodium hydroxide solutions
[1];
[1];
[1];
[3];
[1]
- Pacific Northwest National Laboratory, Richland, WA 99354, USA
- Pacific Northwest National Laboratory, Richland, WA 99354, USA, The Gene and Linda Voiland School of Chemical Engineering and Bioengineering, Washington State University, Pullman, WA 99164, USA
- Pacific Northwest National Laboratory, Richland, WA 99354, USA, Department of Crop & Soil Sciences, Washington State University, Pullman, WA 99164, USA
Aluminum (Al) transformations between solid and liquid states in the Na2O : Al2O3 : H2O system often involve changes in coordination and polymerization, with the intermediate molecular states challenging to resolve. To detect Al transformations in situ, a solid-state mixture of sodium hydroxide monohydrate (NaOH·H2O) and boehmite (AlOOH) was heated above the melting point of NaOH·H2O to dissolve AlOOH and prepare nonasodium bis(hexahydroxyaluminate) trihydroxide hexahydrate (NSA). In situ27Al magic angle spinning, nuclear magnetic resonance (MAS NMR) spectroscopy was used to monitor Al speciation and coordination during AlOOH dissolution into a homogenous melt, and the crystallization of NSA during cooling to room temperature, supported with ex situ X-ray diffraction, Raman spectroscopy, and 27Al multiple-quantum, 3QMAS NMR spectroscopy. Novel metastable aluminate species were identified during the transformation. Dissolution of AlOOH in molten NaOH·H2O entails a transition from octahedral Al in AlOOH to tetrahedral Al in the aluminate anion [Al(OH)4]– and mu-oxo aluminate dimer [Al2O(OH)6]2– present in solution. These tetrahedral solution-state species then precipitate to form an intermediate, amorphous, tetrahedrally coordinated, sodium aluminate hydrate phase which is stable at 70 °C, and subsequentially crystallizes during cooling to form monomeric octahedral Al in the NSA structure. These transformations and associated intermediates provide insight into the molecular scale mechanisms of Al coordination changes, which in this case appear to be mediated by an amorphous precursor containing oligomerized, tetrahedral Al.
- Research Organization:
- Pacific Northwest National Laboratory (PNNL), Richland, WA (United States)
- Sponsoring Organization:
- USDOE; USDOE Office of Science (SC), Basic Energy Sciences (BES). Chemical Sciences, Geosciences & Biosciences Division (CSGB)
- Grant/Contract Number:
- AC05-76RL01830
- OSTI ID:
- 1885473
- Alternate ID(s):
- OSTI ID: 1987536
- Report Number(s):
- PNNL-SA-169590; ICFNAW
- Journal Information:
- Inorganic Chemistry Frontiers (Online), Journal Name: Inorganic Chemistry Frontiers (Online) Vol. 9 Journal Issue: 24; ISSN 2052-1553
- Publisher:
- Royal Society of Chemistry (RSC)Copyright Statement
- Country of Publication:
- United Kingdom
- Language:
- English
Similar Records
Solid-State Recrystallization Pathways of Sodium Aluminate Hydroxy Hydrates
Intermediate Species in the Crystallization of Sodium Aluminate Hydroxy Hydrates