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

Abstract

The highly alkaline aluminate lye, which is produced in the first step of Bayer process, is characterized by low water activity and strong competition for water molecules. The consequence of these effects is that two (or more) negatively charged species can be brought together and stabilized in the form of anionic hydrogen bonded complexes. Depending on temperature, total concentration and aluminate to hydroxide ratio, aluminate–hydroxide as well as aluminate–aluminate associates can be formed. Among the oligomerized aluminates, the cyclic hexamer seems to play a key role, as it contains octahedrally coordinated aluminate ions and is able to form nuclei in further polymerization for the partial precipitation of Al(OH)₃ . The interactions have been experimentally investigated using specially developed methods and a detailed computational analysis.

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