Gibbsite crystallization inhibition - 1. Effects of sodium gluconate on nucleation, agglomeration and growth

Conditions that facilitate the study of gibbsite secondary nucleation; agglomeration and growth as separate crystallization processes have been described. The effects of sodium gluconate, one of the strongest inhibitors of gibbsite crystallization from alkaline aluminate solutions, have been studied under the selected conditions. Sodium gluconate was found to promote secondary nucleation, relative to a control, when present at very low concentrations (1-3 mmol L-1); at slightly higher concentrations (4-6 mmol L-1) it suppressed the release of secondary nuclei. Gluconate caused an increase in the induction period, delayed but did not prevent agglomeration, and reduced ordered growth rates significantly. The observed small changes in crystal morpholog ies, induced by 4-6 mmol L-1 gluconate in solution, should assist in understanding the mechanisms of gibbsite crystallization inhibition because they reflect different deposition rates on specific crystal faces. (C) 2000 Elsevier Science B.V, All rights reserved.