Zur Kenntnis der kristallinen Phasen in den Systemen MOAl2O3H2O (MI = K, Na)

Geßner, W.; Weinberger, Martin; Müller, D.; Ni, Leonid P.; Chaljapina, Olga B.

doi:10.1002/zaac.19875470404

Cited by 18 publications

(14 citation statements)

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“…Such observations indicate that the Al 3+ coordination change occurs either on the NSA crystal surface or during a solid-state amorphous-to-crystalline transition but not in solution. Given that the isolation of Na 2 Al 2 O(OH) 6 has eluded many others exploring the Na 2 O/Al 2 O 3 /H 2 O phase space, − it is reasonable to infer from the instability of Na 2 Al 2 O(OH) 6 that it may exist as a reactive intermediate during solid-state crystallization, linking the soluble tetrahedral aluminates under highly alkaline conditions to the monomeric octahedra in NSA. Further isolation of crystallization pathways, including the prospect of solid-state transformation, is underway to better understand Al 3+ coordination change mechanisms in caustic environments relevant to myriad process applications.…”

Section: Discussionmentioning

confidence: 99%

“…One potentially important species is the μ-oxo aluminate dimer (Al 2 O(OH) 6 2– ), which can form by oxolation in solution and, in concentrated potassium and rubidium hydroxide, leads directly to crystallization of M 2 Al 2 O(OH) 6 salts (M = K + or Rb + ), principally comprised of this dimer motif. ,,− However, crucially, in the sodium system, no comparable sodium aluminate dimer crystal structure has been found despite thorough exploration of the Na 2 O/Al 2 O 3 /H 2 O phase diagram. − Analysis of the formation, reactivity, and dynamics of Al 2 O(OH) 6 2– in solution is challenging because of rapid exchange of Al 3+ ion speciation through hydrolysis and condensation during nuclear magnetic resonance (NMR) spectroscopy, ,,,, degenerate Raman-active vibrational modes, nonmonotonic trends in pre-edge features in X-ray absorption spectroscopy, and multimodal relaxation processes in both dielectric spectroscopy and quasielastic neutron scattering . Among such techniques, the most diagnostic is Raman spectroscopy, which clearly shows that vibrational modes of sodium aluminate solutions contain a component similar to that of K 2 Al 2 O(OH) 6 . ,, …”

Section: Introductionmentioning

confidence: 99%

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Intermediate Species in the Crystallization of Sodium Aluminate Hydroxy Hydrates

Graham

Dembowski

et al. 2020

J. Phys. Chem. C

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In highly alkaline "water-in-salt" Na 2 O/Al 2 O 3 /H 2 O solutions where the monomeric Al(OH) 4− anion dominates, isolation of transitional species that seed crystallization of sodium aluminate salt hydrates has been challenging. For example, discrimination of dimeric [for example, Al 2 O(OH) 62− ] species via 27 Al nuclear magnetic resonance (NMR) spectroscopy is limited via fast interconversion through hydrolysis and condensation reactions. Despite this, using magicangle spinning NMR ( 27 Al MAS NMR) at high magnetic field strengths (14.1 and 20.0 T) on crystals of nonasodium bis(hexahydroxyaluminate) trihydroxide hexahydrate [NSA, Na 9 [Al(OH) 6 ] 2 •3(OH)•6(H 2 O)], we observed a 27 Al resonance consistent with Na 2 Al 2 O(OH) 6 . This tetrahedral dimeric species was also identified in the mother liquor by Raman spectroscopy while remaining expectedly unresolved by high-field liquid-state 27 Al NMR. Its substantial abundance in the mother liquor and as either an interstitial or an adsorbate on precipitated solids suggest that it plays a crucial role in NSA crystallization. Our detailed characterization, which includes single-pulse 27 Al MAS NMR, nutation 27 Al MAS NMR, and multiple quantum 27 Al MAS NMR, provides new molecular insights into how aluminate transitions from tetrahedral in solution to octahedral in solid. This understanding could ultimately lead to better predictions of aluminum phase change behavior in caustic sodium hydroxide with wide-ranging technological and environmental implications.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Intermediate Species in the Crystallization of Sodium Aluminate Hydroxy Hydrates

Graham

Dembowski

et al. 2020

J. Phys. Chem. C

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“…At low total [NaOH], gibbsite, its structural polymorph bayerite, and boehmite are the solubility-controlling phases, and these minerals have octahedrally coordinated Al in a hydroxy- or oxy-bridged network. However, when total Na + /Al(OH) 4 – ratios are greater than 1 and total [NaOH] is above ∼10 m (molality), gibbsite (or bayerite or boehmite) gives way to solubility-controlling phases of (1) monosodium aluminate hydrate (Na 2 [Al 2 O 3 (OH) 2 ]·1.5H 2 O) composed of chains of tetrahedral aluminates each coordinated to three bridging oxygens and one terminal hydroxy group and/or (2) nonasodium bis(hexahydroxy aluminate) trihydroxide hexahydrate (Na 9 [Al(OH) 6 ] 2 (OH) 3 ·6H 2 O), in which aluminum speciates as monomeric aluminate octahedra coordinated to six hydroxides. − It is noteworthy that none of the crystalline solids in the sodium case have any significant topological resemblance to the monomeric Al(OH) 4 – and μ-oxo-bridged dimeric Al 2 O(OH) 6 2– speciation in solution …”

Section: Introductionmentioning

confidence: 99%

Theory-Guided Inelastic Neutron Scattering of Crystalline Alkaline Aluminate Salts Bearing Principal Motifs of Solution-State Species

et al. 2021

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Aluminate salts precipitated from caustic alkaline solutions exhibit a correlation between the anionic speciation and the identity of the alkali cation in the precipitate, with the aluminate ions occurring either in monomeric (Al(OH) 4 − ) or dimeric (Al 2 O(OH) 6 2− ) forms. The origin of this correlation is poorly understood as are the roles that oligomeric aluminate species play in determining the solution structure, prenucleation clusters, and precipitation pathways. Characterization of aluminate solution speciation with vibrational spectroscopy results in spectra that are difficult to interpret because the ions access a diverse and dynamic configurational space. To investigate the Al(OH) 4 − and Al 2 O(OH) 6 2− anions within a well-defined crystal lattice, inelastic neutron scattering (INS) and Raman spectroscopic data were collected and simulated by density functional theory for K 2 [Al 2 O(OH) 6 ], Rb 2 [Al 2 O(OH) 6 ], and Cs[Al(OH) 4 ]•2H 2 O. These structures capture archetypal solution aluminate species: the first two salts contain dimeric Al 2 O(OH) 62− anions, while the third contains the monomeric Al(OH) 4 − anion. Comparisons were made to the INS and Raman spectra of sodium aluminate solutions frozen in a glassy state. In contrast to solution systems, the crystal lattice of the salts results in well-defined vibrations and associated resolved bands in the INS spectra. The use of a theory-guided analysis of the INS of this solid alkaline aluminate series revealed that differences were related to the nature of the hydrogen-bonding network and showed that INS is a sensitive probe of the degree of completeness and strength of the bond network in hydrogen-bonded materials. Results suggest that the ionic size may explain cation-specific differences in crystallization pathways in alkaline aluminate salts.

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“…Fricke et al determined the solid phase of potassium aluminate hydrate as KAlO 2 ·2H 2 O by using Schreinemaker’s method. Gessner et al reported that potassium aluminate crystals, K 2 O·Al 2 O 3 ·3H 2 O, K 2 O·Al 2 O 3 ·2H 2 O, K 2 O·Al 2 O 3 ·H 2 O, and K 2 O·Al 2 O 3 could be respectively obtained at high temperatures of 403.15, 423.15, 643.15, and 773.15 K, and also investigated the crystal lattice parameters. Only Du measured the phase equilibria for the ternary system K 2 O–Al 2 O 3 –H 2 O at 313.15 K by the isothermal method, and showed that the equilibrium solid-phase K 2 O·Al 2 O 3 ·3H 2 O was found besides KOH·H 2 O in the concentrated alkali region of the phase diagram.…”

Section: Introductionmentioning

confidence: 99%

“…Fricke et al3 determined the solid phase of potassium aluminate hydrate as KAlO 2 •2H 2 O by using Schreinemaker's method. Gessner et al17 reported that potassium aluminate crystals, K 2…”

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confidence: 99%

Phase Equilibrium in the Ternary System K₂O–Al₂O₃–H₂O at 323.15, 333.15, 343.15, and 353.15 K

Luo

Xue

et al. 2020

J. Chem. Eng. Data

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Phase equilibrium of ternary system K2O–Al2O3–H2O is the key in realizing seeded precipitation process of aluminum hydroxide product from alkaline leaching solution in the alunite tailings metallurgical industry. However, little work has been carried out about the solubility of the K2O–Al2O3–H2O system, especially for the concentrated alkali solution region. The corresponding phase equilibria at 323.15, 333.15, 343.15, and 353.15 K were researched by using the isothermal dissolution method and the Pitzer ion-interaction model. The calculated Al2O3·3H2O solubilities corresponding to the crystallization region of Al2O3·3H2O in the ternary system at each temperature basically agree with experimental values when K2O concentration is below 30 wt %. Furthermore, the ternary system at each temperature contains two invariant points, three univariant isothermal dissolution curves, and five crystallization fields corresponding to Al2O3·3H2O (gibbsite), K2O·Al2O3·3H2O, KOH·H2O, Al2O3·3H2O + K2O·Al2O3·3H2O, and K2O·Al2O3·3H2O + KOH·H2O. According to the phase diagrams of the ternary system, it can be indicated that the low alkali concentration and temperature are in favor of the crystallization of Al2O3·3H2O, while the high alkali concentration and low temperature are beneficial to the crystallization of K2O·Al2O3·3H2O.

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Zur Kenntnis der kristallinen Phasen in den Systemen MOAl₂O₃H₂O (M^I = K, Na)

Cited by 18 publications

References 10 publications

Intermediate Species in the Crystallization of Sodium Aluminate Hydroxy Hydrates

Intermediate Species in the Crystallization of Sodium Aluminate Hydroxy Hydrates

Theory-Guided Inelastic Neutron Scattering of Crystalline Alkaline Aluminate Salts Bearing Principal Motifs of Solution-State Species

Phase Equilibrium in the Ternary System K₂O–Al₂O₃–H₂O at 323.15, 333.15, 343.15, and 353.15 K

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Zur Kenntnis der kristallinen Phasen in den Systemen MOAl2O3H2O (MI = K, Na)

Cited by 18 publications

References 10 publications

Intermediate Species in the Crystallization of Sodium Aluminate Hydroxy Hydrates

Intermediate Species in the Crystallization of Sodium Aluminate Hydroxy Hydrates

Theory-Guided Inelastic Neutron Scattering of Crystalline Alkaline Aluminate Salts Bearing Principal Motifs of Solution-State Species

Phase Equilibrium in the Ternary System K2O–Al2O3–H2O at 323.15, 333.15, 343.15, and 353.15 K

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Zur Kenntnis der kristallinen Phasen in den Systemen MOAl₂O₃H₂O (M^I = K, Na)

Phase Equilibrium in the Ternary System K₂O–Al₂O₃–H₂O at 323.15, 333.15, 343.15, and 353.15 K