A Hydrogen Electrode Study of Concentrated Alkaline Aluminate Solutions

Abstract

A detailed study of highly concentrated aqueous alkaline aluminate solutions has been made by hydrogen electrode potentiometry in cells with liquid junction at 25°C in 8 M Na(ClO4) media. Measurements were performed over the total concentration ranges 0·1 M < [NaOH]T < 4·0 M and 0·02 M < [AlIII]T < 3·2 M, and at total concentration ratios of 6·92 ≥ [OH-]T/[AlIII]T ≥ 4·3. Nernstian electrode behaviour was observed at [NaOH]T ≤ c. 2 M in pure NaOH/NaClO4 mixtures. At low [AlIII]T the data were consistent with the formation of only the well known Al(OH)4-(aq) species but there is clear evidence of a systematic release of hydroxide as [AlIII]T and [NaOH]T increase. The data are consistent with the formation of polymeric aluminate complexes having a stoichiometry of Alq(OH)3q - rr+ (q = 4–7, q + r = 1 or 2). However, unequivocal identification of these species is difficult on account of strong correlations in the data and the possible effects of ion-pairing.