Structure of Aqueous Sodium Aluminate Solutions:  A Solution X-ray Diffraction Study

Abstract

A structural analysis of six alkaline sodium aluminate aqueous solutions by the X-ray diffraction method is reported. On average, each Al atom is surrounded by four oxygens, indicative of the predominance of Al(OH) 4 -(aq) in these solutions. Detailed least-squares fitting indicates that a significant contraction of the Al-O distances occurs with increasing aluminate concentration, from 1.80 Å at 2 M to 1.74 Å at 6 M Al-(OH) 3 in 8 M NaOH. The local structure has been described by models that have separate hydrated ions in the most dilute aluminate solution but contact sodium aluminate ion pairs in the most concentrated solution. The hydration number of the sodium ion decreases with increasing concentration, but the overall coordination number appears to be unchanged by the ion pair formation. An extensive rearrangement in the hydrogenbonded network of bulk water also occurs as the aluminum concentration rises, with the appearance of new diffraction distances at 3.3 and 3.9 Å. A gradual appearance and disappearance of shorter hydrogen bonds between first neighboring O atoms is observed. The data are consistent with the occurrence of oligomeric aluminate species but are not conclusive within the limits of the experimental error.

The structure of hyperalkaline aqueous solutions containing high concentrations of gallium – a solution X-ray diffraction and computational study

“…In aluminates with similar concentrations, the dimeric species (OH) 3 Al-O-Al(OH) 3 2-is present in significant and experimentally detectable concentrations. [42][43][44] For analogous Ga-containing solutions, the experimental observations and the findings from quantum chemical calculations are consistent with the absence of the dimeric gallate species, (OH) 3 Ga−O−Ga(OH) 3 2-. This finding is particularly surprising, as solid crystalline compounds with this dimeric unit as the building block have been possible to be prepared from concentrated NaOH/Ga(OH) 3 solutions.…”

“…[42][43][44] The analysis has been performed along a similar way to the gallate solutions, mostly because we wanted to study the eventual similarities or find the differences between the two systems. The main results of the aluminate structural analysis are: (i) The monomeric aluminate form with tetrahedral structure is confirmed.…”

“…The main results of the aluminate structural analysis are: (i) The monomeric aluminate form with tetrahedral structure is confirmed. 8 (ii) Beyond that, a more extended structure with two tetrahedron (that is: dimeric aluminate species) is possible, both from experimental 8,[42][43][44][45] and from computational 46 means further structural units are also possible, even if they were not fully confirmed. Moreover, spectroscopic and other studies reported the extended network of numerous structural forms in aluminate solutions, however, they are scarcely confirmed.…”

Attapulgite‐supported aluminum oxide hydroxide catalyst for synthesis of poly(ethylene terephthalate)

“…According to the results mentioned above, we can infer the formation process of AlO(OH). It is generally believed that Al(OH) 4 − is the main existence form in sodium aluminate solution,19, 20 so the following reactions will be carried out during the preparation of aluminum oxide hydroxide/AT. During the drying process of aluminum oxide hydroxide/AT, the balance in eq.…”

Synthesis of Al(OH) 3 Nanostructures from Al(OH) 3 Microagglomerates via Dissolution‐Precipitation Route

“…The synthesis of Al(OH) 3 nanostructures has been paid much attention in recent years owing to their unique properties and wide applications in plastics, rubbers, papers, glasses and medicines, and so forth [1][2][3][4]. Al(OH) 3 microparticles were usually produced in the aluminum metallurgical factories via the Bayer route, which included the leaching of the bauxite ores at alkaline hydrothermal condition (150-250 ∘ C), the removing of impurities as Si and Fe at elevated temperatures, and the precipitation of the Al(OH) 3 microparticles in the presence of Al(OH) 3 seed by gradually cooling of the sodium aluminate solution from 90-100 ∘ C to 50-60 ∘ C which usually lasted 48-72 h [5][6][7][8]. Many wet chemical methods have been developed to synthesize the Al(OH) 3 nanostructures.…”