Analysis of the microstructure and morphology of disordered kaolinite based on the particle size distribution

The defected kaolinite is common in sedimentary kaolin, but its structure and disorder mechanism remains unclear. In this paper, three different size distributions of kaolinite particles: 0–300 nm, 200–1000 nm, and 500–2000 nm, were separated and classified from high-defect sedimentary kaolin, collected from Quaternary sedimentary kaolin in Guangxi Zhuang Autonomous Region of China. The three particle sizes of kaolinite have been monitored by particle size analyzer, high-resolution magic-angle spinning NMR (MAS NMR), small and wide-angle X-ray scattering (SAXS and WAXS), X-ray diffraction (XRD), BET surface analyzer, nitrogen gas-adsorption, scanning electron microscopy (SEM), and high-resolution transmission electron microscopy (HRTEM). The results revealed that the smallest particle size of kaolinite exhibited high degrees of broken Al-O-Al and Si-O-Si bonds, more disordered structure, and elevated specific surface area. The degree of the structural disorder of kaolinite increases as the particle size decreases, which can be attributed to the more aluminum substituted for silicon in tetrahedron sheet in the finer kaolinite crystal, compared to the coarser kaolinite crystals.