GENERAL CONCEPTS OF HYDRARGILLITE AL(OH)3 AGGLOMERATION

Agglomeration is an important stage of the Bayer process aiming at inc reasing the initial size of Al(OH)3 particles. In the present work, we investigate the effects of supersaturation, seed charge and stirring rate on the agglomeration of hydrargillite crystallites, the size of w hich ranges from about 2 to 10 mum. The experiments are carried out in a batch crystallizer at constant temperature and caustic concentratio n. It is shown that the agglomeration rate increases with increasing s eed charge, but rapidly reaches a plateau before decreasing when the s eed charge is too high. On the other hand, agglomeration continuously decreases with increasing stirring rate, while it is favoured by incre asing supersaturation. In the latter case, growth of the crystallites contributes to coarsening the agglomerates. We propose the general out lines of an agglomeration model taking collision and disagglomeration probabilities into account.