Agglomeration of Ni-rich hydroxide crystals in Taylor vortex flow

Highlight
• Taylor vortex was highly effective to the agglomeration of Ni-rich hydroxide crystal.
• Spherical and uniform agglomerates were formed in Taylor vortex flow.
• Powder of high tap-density (2.13 g/cm3) was produced at short mean residence time.

The agglomeration of Ni-rich hydroxide crystals (Ni0.9Co0.05Mn0.05)(OH)2 was studied in a continuous Couette-Taylor (CT) crystallizer. Due to the excellent mixing and periodic fluid motion of the Taylor vortex flow in the CT crystallizer, the formation of spherical and uniform agglomerate particles of Ni-rich crystals was promoted as the rotation speed and the mean residence time increased. Thus, for a rotation speed of 1500 rpm and mean residence time of 60 min, with a high feed concentration of 3.0 mol/L produced a high tap-density of agglomerate particles of 2.13 g/cm3, which is higher than any previously reported values. These results were due to the excellent micromixing effects of Taylor vortex in the CT crystallizer. In addition, the long mean residence time contributed to the formation of spherical particles due to the extended exposure of the agglomerates to the fluid shear. Furthermore, the formation of spherical particles was optimized at a pH of 12.0 and required a high concentration of ammonia due to the high composition of Ni ions in the Ni-rich hydroxide crystals and the short mean residence time in the continuous CT crystallizer. Moreover, when comparing the crystallization in a continuous MSMPR crystallizer, which required a long mean residence time of 12 h for a high tap-density of above 2.0 g/cm3, the continuous CT crystallizer was clearly much more effective for the formation of uniform spherical particles due to the more efficient hydrodynamic fluid motion of the Taylor vortex in the CT crystallizer in contrast to the random turbulent eddy motion in the MSMPR crystallizer.

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