Hydrogen bonded associates in concentrated aluminate lyes (in the Bayer process): the mechanism of gibbsite nucleation.

The low water activity and the strong competition for water molecules are c harasteristic of highly alkaline aluminate lyes, produced in the Bayer proc ess. The consequence of these effects is that two (or more) negatively char ged species can interact and anionic type hydrogen bonded complexes can be formed. Depending on temperature, total concentration and aluminate to hydr oxide ratio, aluminate - hydroxide as well as aluminate - aluminate associa tes can be stabilized. Among the oligomeric aluminates, the cyclic hexamer seems to be the most important species, because it contains octahedrally co ordinated aluminiums and is able to form nuclei in further polymerization f or the precipitation of Al(OH)(3). The interactions have been experimentall y investigated using specially developed methods and computational analysis .