The effects of model organic compounds on gibbsite crystallization from alkaline aluminate solutions: Polyols

The crystallization of gibbsite from synthetic Bayer liquors is known to be inhibited by compounds containing adjacent hydroxyl groups such as the polyhydric alcohols or polyols. Complementary studies examining the inhibition of gibbsite crystallization by polyols, and the interaction of the same compounds with aluminate ions in solution (by C-13 NMR and Raman spectroscopy) have shown that the strongest inhibitors also complex aluminate under Bayer liquor conditions. By examining the most likely conformations of metal-ligand complexes in solution, we are able to make suggestions for the mechanism by which these compounds adsorb onto gibbsite seed and hence cause inhibition of crystallization. Specifically, it has been found that the strongest polyol inhibitors are able to form solution complexes with a single aluminium atom through a particular conformation of three oxo bonds. It is proposed that the inhibiting strength of polyols is related to the ease with which similar connections are formed with aluminium sites on the surface of the gibbsite seed.