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Open AccessArticle

Dehydroxylation and Structural Distortion of Kaolinite as a High-Temperature Sorbent in the Furnace

Jiangsu Provincial Key Laboratory of Materials Cycling and Pollution Control, School of Energy and Mechanical Engineering, Nanjing Normal University, Nanjing 210023, China
Key Laboratory of Energy Thermal Conversion and Control of Ministry of Education, School of Energy and Environment, Southeast University, Nanjing 210096, China
Zhenjiang Institute for Innovation and Development, Nanjing Normal University, Zhenjiang 212050, China
Authors to whom correspondence should be addressed.
Minerals 2019, 9(10), 587;
Received: 8 August 2019 / Revised: 21 September 2019 / Accepted: 26 September 2019 / Published: 27 September 2019
(This article belongs to the Special Issue Mineral Sorbents)
As a high-temperature sorbent, kaolinite undergoes the flash calcination process in the furnace resulting in the dehydroxylation and structural distortion, which are closely related to its heavy metal/alkali metal adsorption characteristics. We investigated the flash calcination of kaolinite by the experiments using a drop tube furnace and by the characterization of flash-calcined products using thermogravimetric-differential scanning calorimeter (TG-DSC), X-ray diffraction (XRD), Fourier Transform Infrared Spectrometer (FTIR)and nuclear magnetic resonance (NMR). There were three kinds of hydroxyl groups in kaolinite during flash calcination at 800–1300 °C, E-type (~50%, easy), D-type (~40%, difficult) and U-type (~10%, unable) according to the removal difficulty. The hydroxyl groups activation was believed to be the first step of the removal of E-type and D-type hydroxyl groups. The kinetics model of dehydroxylation groups at 900–1200 °C was established following Arrhenius equation with the activation energy of 140 kJ/mol and the pre-exponential factor of 1.32 × 106 s−1. At 800 °C, the removal of E-type hydroxyl groups resulted in the conversion of a part of VI-coordinated Al in kaolinite to V-coordinated Al and the production of meta-kaolinite. When the temperature rose up to 1200 °C, mullite was produced and a part of V-coordinated Al converted to IV-coordinated Al and VI-coordinated Al. Finally, the adsorption characteristics of kaolinite was discussed according to the results of dehydroxylation and structural distortion. View Full-Text
Keywords: kaolinite; sorbent; flash calcination; dehydroxylation; structure distortion kaolinite; sorbent; flash calcination; dehydroxylation; structure distortion
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Cheng, Y.; Xing, J.; Bu, C.; Zhang, J.; Piao, G.; Huang, Y.; Xie, H.; Wang, X. Dehydroxylation and Structural Distortion of Kaolinite as a High-Temperature Sorbent in the Furnace. Minerals 2019, 9, 587.

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