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Open AccessArticle

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

1
Jiangsu Provincial Key Laboratory of Materials Cycling and Pollution Control, School of Energy and Mechanical Engineering, Nanjing Normal University, Nanjing 210023, China
2
Key Laboratory of Energy Thermal Conversion and Control of Ministry of Education, School of Energy and Environment, Southeast University, Nanjing 210096, China
3
Zhenjiang Institute for Innovation and Development, Nanjing Normal University, Zhenjiang 212050, China
*
Authors to whom correspondence should be addressed.
Minerals 2019, 9(10), 587; https://doi.org/10.3390/min9100587
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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