Spherical agglomeration of nickel-manganese-cobalt hydroxide in turbulent Batchelor vortex flow

Abstract In this study, turbulent Batchelor vortex flow, due to its periodic fluid motion, was used to produce highly dense and spherical Ni-Mn-Co (NMC) hydroxide agglomerates (microparticles) in a rotation disk crystallizer. A high shear stress (1500 rpm) in the turbulent Batchelor vortex regime, and the presence of ammonia at a pH of 12, help form spherical shaped agglomerates with a high tap density (2.1 g/m3) from irregular shaped agglomerates. The coefficient of variation (0.38) of the agglomerates also narrowed while using this approach. When sufficient ammonia was supplied to form a complex ([M(NH3)n]2+) with all M2+, the reaction rate with OH– slowed and the agglomeration process was affected by the high shear stress in a sufficient amount of time. On the contrary, when ammonia is not present in the reaction solution, free M2+ ions rapidly react with OH– ion, resulting in irregular shaped agglomerates. The pH was related to the OH– concentration and all of the [M(NH3)n]2+ complex was consumed during the agglomeration process when the OH– concentration reached a mol ratio of 1:2 ([M(NH3)n]2+:OH–). When the ammonia feeding rate was higher than 1.2 mL/min, highly dense agglomerate was obtained. However, the [M(NH3)n]2+ complex could not be generated when the pH exceeded a value of 12, according to the mass and equilibrium calculations. In addition, the residence time was significantly shorter (30 min) in the turbulent Batchelor vortex flow regime compared to previous studies (~12 to 50 h). This study suggests that the high shear stress in the turbulent Batchelor vortex flow regime can be effectively used for making highly dense and spherical NMC hydroxide, with high tap density, in a short amount of time.