Hydroxide speciation in highly alkaline aluminate solutions

A detailed investigation of the behaviour of concentrated MOH/MAl(OH)4 solutions in 4 M MCI media, where M+ = Na+, K+ or Cs+, has been made by high precision hydrogen electrode potentiometric titrations. The performance of the electrodes in each of the I = 4 M (M(Cl)) media was established up to high hydroxide concentrations (up to 2 M) by strong acid-strong base titrations. The data confirm previous observations in NaC104 media that there is a release of OH- with increasing [OH-] and [Ai(OH)4-]. More significantly this release appears to be independent of the cation in the medium. These effects are consistent with competitive ion pairing interactions or the possibility of the formation of an aluminium-containing dimer. Raman spectra of MOH solutions were not fully consistent with literature results but do indicate the presence of significant ion pairing, although no ion pairing constants could be derived