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Abstract: The crystal agglomeration of Ni/Co/Mn hydroxide (NCM hydroxide) in a continuous Couette–Taylor (CT) crystallizer was experimentally studied. The NCM hydroxide crystals produced by the reaction crystallization were simultaneously coagulated to form agglomerate particles via the consecutive steps of physical adhesion of the crystals and molecular growth. Thus, the hydrodynamic conditions and supersaturation profile in the CT crystallizer were the most critical influencing parameters determining the agglomerate particle size and shape. The particle size was reduced when increasing the rotation speed of the inner cylinder in the CT crystallizer, as enhancing the intensity of the Taylor vortex broke and re-dispersed the physically adhered crystals. In addition, a high Taylor vortex changed the irregularly shaped agglomerate particles into spherical ones. The supersaturation profile in the CT crystallizer was prolonged when increasing the mean residence time and decreasing the feed concentration, thereby enlarging the particle size. Similarly, a chelating reaction also prolonged the supersaturation profile in the CT crystallizer, resulting in a larger particle size. In the agglomeration, the individual crystals created a hexagonal system stacked on the (001) face, meaning that the particles were mostly covered by the (101) face. In general, under the tested operating conditions, the CT crystallizer was able to produce agglomerate particles that were narrowly distributed and smaller than 5μm in size within 10min of the mean residence time. [Copyright &y& Elsevier]

Abstract: Sonication and turbulent agitation were used to investigate the mechanism of crystal aggregation and agglomeration during the reaction crystallization of cerium carbonate. Aggregation and agglomeration occurred simultaneously during the crystallization, thus the product suspension included both crystal aggregates and agglomerates. As crystal aggregation involves the physical adhesion of crystals, the particle size changed sensitively according to the sonication energy and agitation speed during the crystallization. In contrast, since crystal agglomeration is based on molecular growth following crystal aggregation, the agglomerates were strong enough to resist the acoustic impact of the sonication and turbulent shear of the agitation during the crystallization. Thus, the crystal aggregates in the product suspension were completely re-dispersed by an acoustic after-treatment of 30W for 20min. Acoustic after-treatment was also used to determine the agglomerate size and estimate the degree of aggregation of the product suspension. As a result, sonication above 60W was found to be adequate to prevent any aggregation or agglomeration during the crystallization, regardless of the agitation conditions. [ABSTRACT FROM AUTHOR]