AGGLOMERATION DURING PRECIPITATION - AGGLOMERATION MECHANISM IDENTIFICATION FOR AL(OH)(3) CRYSTALS IN STIRRED CAUSTIC ALUMINATE SOLUTIONS

Reported here are the results of a study on the mechanism for Al(OH)(3 ) agglomeration during precipitation in caustic aluminate solutions. T wo independent techniques are used to identify the agglomeration mecha nism. Both identification techniques show that Al(OH)(3) agglomeration may be described by a size-independent agglomeration mechanism. The r esiduals between the experimental data and estimates from the proposed model are normally distributed, with a mean of zero and a standard de viation of 1. The size-independent model conflicts with the current vi ew that there exists an upper limit, imposed by the hydrodynamics, to the aggregate size. Tracer crystal experiments, using Zn-doped Al(OH)( 3) crystals, as well as the observed evolution of the experimental siz e distribution with time both demonstrate that crystals (or crystal ag gregates) were agglomerating at sizes larger than the expected maximum aggregate size. This supports the size-independent model for the rang e of conditions studied. The analysis of the experimental Al(OH)(3) pr ecipitation data also confirms that the growth rate is size independen t and that there is no growth dispersion.