Influence of soluble oligomeric aluminum on precipitation in the Al–KOH–H₂O system

Abstract

Combination of solution state Raman and 27Al NMR spectroscopic measurements paired with elemental analysis reveal a strong correlation between the quantity of soluble Al in caustic solutions and the extent of oligomerization.

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

“…Ice Ih forms a regular hexagonal lattice, but the positions of the H atoms are disordered. 50 Hda ice has a denser structure produced at high pressure 51 and exhibits a lower onset of the librational region than ice Ih (∼411 vs ∼508 cm −1 ). 53 This difference is attributed to a weakening of the In the INS spectra, increasing the aluminate concentration shifts spectral weight from the low-energy region to higher frequencies, while the Raman analysis (summarized in Table S2 and Figure S3) indicates that the ratio of aluminate dimers to monomers increases.…”

“…Based on estimates from the nominal concentrations (Table ), water librational motions are responsible for more than 60% of the intensity of the spectra for the Na-aluminate solutions, even at the high salt concentrations studied here (Figure ). Ice Ih forms a regular hexagonal lattice, but the positions of the H atoms are disordered . Hda ice has a denser structure produced at high pressure and exhibits a lower onset of the librational region than ice Ih (∼411 vs ∼508 cm –1 ) .…”

“…INS spectra of the dilute (black) and concentrated (yellow) Na-aluminate solutions and the Rb-aluminate (red) and Cs-aluminate (blue) salts as collected using VISION. INS spectra of hda ice (light blue) and ice Ih replotted from refs –. Vertical black lines indicate the location of strong Raman transitions associated with monomeric (dashed line) and dimeric (solid lines) aluminate ions in solution.…”

Solution and Interface Structure and Dynamics in Geochemistry: Gateway to Link Elementary Processes to Mineral Nucleation and Growth

“…− , the excess OH − concentration, water activity, and the nature of the cation (e.g., Sipos et al, 57 Wang et al, 58 Dembowski et al 59 and references therein). If one would keep the same concentration of the constituted elements (m M , total and m Al,total ) except the identity of cations in these solutions, the influence of cation chemistry has a major impact on the extent of aluminate oligomerization and imposes control over which of the M + -aluminate coordination compounds are present in the precipitating crystalline solid.…”

“…These reactions determine the extents of the aggregated ion–water networks, change the nucleation mechanisms, and influence the structure of the precipitated phase(s). It is generally known that the degrees of aluminate polymerization and reaction dynamics largely depend on the ratio of M + /Al­(OH) 4 – , the excess OH – concentration, water activity, and the nature of the cation (e.g., Sipos et al, Wang et al, Dembowski et al and references therein). If one would keep the same concentration of the constituted elements ( m M , total and m Al,total ) except the identity of cations in these solutions, the influence of cation chemistry has a major impact on the extent of aluminate oligomerization and imposes control over which of the M + -aluminate coordination compounds are present in the precipitating crystalline solid.…”