Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
5468572 | Applied Clay Science | 2017 | 7 Pages |
Abstract
Thermal decomposition, phase transformation and microstructure change for the mixture of kaolinite and sodium carbonate (Na2CO3) calcined at different temperatures were studied through experimental investigation and theoretical analysis. Thermo-gravimetric and differential scanning calorimetric coupled with mass spectrometer (TG-DSC/MS) were utilized to determine the reaction temperature of kaolinite and Na2CO3. The calcinated products at different temperatures were characterized by X-ray diffraction (XRD), magic angle spinning nuclear magnetic resonance (MAS-NMR) and Fourier transform infrared (FT-IR). The results showed that the solid-state reaction between kaolinite and Na2CO3 mainly occurred within the temperature of 300-850 °C. During the calcining process, kaolinite was decomposed and transformed into meta-kaolin (MK), low-temperature carnegieite (L-phase), nepheline and zeolite in turn, which can be interpreted in terms of the combination change of different oxygen coordination. With the increase of temperature, the [AlO6] octahedron in kaolinite gradually transformed into the [AlO4] tetrahedron in MK by dehydroxylation, and the bridging oxygen between [AlO4] and [SiO4] layers together with the bridging oxygen in [AlO4] layer and [SiO4] layer were broken with the participation of Na2CO3. Subsequently, the obtained individual [AlO4] and [SiO4] tetrahedrons alternately recombined and formed an anion frame-like structure by sharing the oxygen atom owing to the limitation of Pauling's electrostatic valence rule. In order to further maintain the charge neutrality and structural stability, Na+ ions were filled in the anion frame-like structure of L-phase, nepheline and zeolite. This research is of some theoretical significance for the Na2CO3-assisted thermal activation of kaolinite and kaolinite-based solid wastes.
Related Topics
Physical Sciences and Engineering
Earth and Planetary Sciences
Geochemistry and Petrology
Authors
Kezhou Yan, Yanxia Guo, Li Fang, Li Cui, Fangqin Cheng, Tongyang Li,