Quantitative determination of an aluminate dimer in concentrated alkaline aluminate solutions by Raman spectroscopy

P. Sipos, Peter M. May, Glenn Hefter

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Abstract

Raman spectra of concentrated alkaline aluminate solutions in various M′OH media (M′+ = Na+, K+, Cs + and (CH3)4N+) have been investigated systematically as a function of concentration and water activity, aw. All spectra at [Al(iii)]T ≤ 1 M and at 0.1 ≤ [M′OH]T/M ≤ 5 (where the square brackets denote concentrations and the subscript T totals) exhibit one significant Raman mode in the low frequency region, at ca. 620 cm-1, due to the symmetric Al(OH)4- stretch. At higher [Al(iii)]T and [M′OH]T new modes appear at 530-550 and 700-720 cm -1. The intensities of these new bands depend on [Al(iii)] T and aw but are independent of [OH-] T and are only slightly cation-dependent. All three bands shift towards higher wavenumbers at [M′OH]T > 10 M, probably due to ion-pairing. Spectra at [M′OH]T <10 M have been interpreted quantitatively by assuming that the integrated peak area of the 620 cm-1 mode is linearly proportional to [Al(OH)4 -] at constant aw and that the only significant equilibrium in these systems is the formation of a dimer that can be represented as (Al(OH)4)22-(aq), although it may exist in an oxo-bridged form such as [(HO)3Al-O-Al(OH)3] 2. The (aquated) species Na+, OH-, Al(OH) 4-, the dimer, and their ion-pairs, were sufficient to interpret all the Raman observations. No evidence was found for various other species that have been claimed to exist in concentrated alkaline aluminate solutions.

Original languageEnglish
Pages (from-to)368-375
Number of pages8
JournalDalton Transactions
Issue number2
DOIs
Publication statusPublished - 2006

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Dimers
Raman spectroscopy
Ions
Cations
Raman scattering
Water
hydroxide ion

ASJC Scopus subject areas

  • Chemistry(all)

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Quantitative determination of an aluminate dimer in concentrated alkaline aluminate solutions by Raman spectroscopy. / Sipos, P.; May, Peter M.; Hefter, Glenn.

In: Dalton Transactions, No. 2, 2006, p. 368-375.

Research output: Contribution to journalArticle

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