Agglomeration of nickel/cobalt/manganese hydroxide crystals in Couette–Taylor crystallizer

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 (0 0 1) face, meaning that the particles were mostly covered by the (1 0 1) face. In general, under the tested operating conditions, the CT crystallizer was able to produce agglomerate particles that were narrowly distributed and smaller than 5 μm in size within 10 min of the mean residence time.