THE INFLUENCE OF CRYSTAL GROWTH MODIFYING REAGENTS ON SECONDARY NUCLEATION OF BAYER ALUMINIUM HYDROXIDE

Counter, J.A., Malito, J.T., Addai-Mensah, J. and Li, J.

The kinetics of isothermal crystallisation of gibbsite from synthetic Bayer liquors was studied in the presence of a growth modifying chemical reagent at various temperatures, spanning the range found in typical crystallisation circuits. The de-supersaturation kinetic data were fitted with empirical power law models, wherein the secondary nucleation rate constant and activation energy were computed.

The studies presented here, in the absence of any chemical additive were consistent with those reported in the literature for synthetic aluminate liquors. It was found that in the presence of the chemical additive the crystallisation process could be markedly influenced. Compared to the undosed control liquors, the treated liquors yielded a marked reduction in the number of new fine particles produced, yet with an increase in total surface area. This finding was supported by the treated liquors exhibiting an increased rate constant, increased secondary nucleation rate as well as an increase in activation energy. SEM evidence indicated a more porous particle, with large amounts of secondary nuclei remaining on the surface for the treated samples.