FANG Yan1,2,3, TAO Qi1, 2*, CHEN Ai-qing1,2,3, HE Hong-ping1,2
(1. CAS Key Laboratory of Mineralogy and Metallogeny, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, 511 Kehua Street, Guangzhou 510640, China;
2. Key Lab of Guangdong Province for Mineral Physics and Materials, 511 Kehua Street, Guangzhou 510640, China;
3. University of Chinese Academy of Sciences, 19 Yuquan Road, Beijing 100049, China)
Abstract: Effects of mechanical grinding on the physicochemical properties of Maoming kaolinite, including particle size distribution, morphology, microstructure etc.were investigated. Furthermore, 29Si and 27Al MAS NMR spectroscopy were adopted to investigate the dehydroxylation process, the Si and Al coordination environments, the new sites formed during grinding treatment etc. The characterization results show that the hexagonal layer of kaolinite was crushed quickly in the first grinding stage, companied with the decrease of particle sizes and the increase of specific surface area until reached the maximum value (43.8 m2/g) in 1 h. Further grinding produced spheroidal aggregation of fine particles, and caused the decrease of the specific surface area. Grinding led to extensive dehydroxylationand the adsorption water content increase. New signals at ‒100.5 ppm and 14.8 ppm 29Si NMR and27Al NMR spectra, respectively, were attributed to a Q3 Si‒OH+‒Al structure formed via protonation of the top oxygen interconnected between tetrahedral Si and octahedral Al. Grinding led to a dehydroxylation of kaolinite, whose AlⅥ (5.8 ppm) gradually transform to AlⅣ (56.5 ppm) via a AlⅤ (31.2 ppm) transition structure.
Keywords: kaolinite; mechanical grinding; tetrahedral sheet; octahedral sheet; solid state NMR
ACTA MINERALOGICA SINICA Vol. 37, No. 6, 2017, Page 677-683