Study on the Overall Reaction Pathways and Structural Transformations during Decomposition of Coal Fly Ash in the Process of Alkali-Calcination
Abstract
:1. Introduction
2. Experimental
2.1. Sample Materials and Their Characterization
2.2. Experimental Procedure and Apparatus
2.3. Characterization Techniques
3. Results and Discussion
3.1. Analysis for Activated CFA by NaOH Calcination
3.2. FTIR Characterization
3.3. Deconvolution Methods
3.4. SEM and EDS Analysis
4. Conclusions
- The main aim of this research was to investigate in-depth the vibrations of the functional groups of CFA during NaOH calcination. The chemical structure of the CFA was found to consist of silicate chains. XRD and FTIR analyses were combined to reveal the decomposition pathways of CFA at the molecular level during the alkali calcination process using NaOH.
- The aluminosilicate network in the raw CFA gradually disaggregated into clusters with different degrees of reaction during the NaOH calcination process. The number of small clusters increased with temperature, which facilitated structural rearrangements.
- The results of the FTIR and XRD undoubtedly demonstrated the existence of Si-O-Si linkages in the glass phases of CFA. Pronounced Si-O-Al linkages were present in the structure on account of substitution reactions with a certain portion of the Al in the aluminosilicate. Based on the deconvolution of the main region of interest (800–1300 cm−1), several special peaks were identified. The information on the thermal history of the CFA and the chemical and molecular structural changes during the NaOH calcination were clearly identified. The calcination temperature and time were both positively correlated with the reduction of functional groups.
- In the future, combining current methods with those in other fields, such as alkali calcination followed by hydro-chemical process to synthesize zeolite and alkali calcination followed by recovery of other valuable materials, will contribute to multipurpose use of CFA.
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Acknowledgments
Conflicts of Interest
References
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Component | SiO2 | Al2O3 | TFe2O3 | MgO | CaO | K2O | LOI a |
---|---|---|---|---|---|---|---|
Content (wt.%) | 46.23 | 39.71 | 3.32 | 0.18 | 1.37 | 0.71 | 3.41 |
Samples Label | Calcination Conditions | Sample Label after Water Leaching | ||
---|---|---|---|---|
Mass Ratio CFA:NaOH | Calcination Temperature (°C) | Calcination Time (h) | ||
C4-1 | 1:4 | 400 | 0.5 | S4-1 |
C4-2 | 1:4 | 400 | 1 | S4-2 |
C4-3 | 1:4 | 400 | 1.5 | S4-3 |
C4-4 | 1:4 | 400 | 2 | S4-4 |
C6-1 | 1:4 | 600 | 0.5 | S6-1 |
C6-2 | 1:4 | 600 | 1 | S6-1 |
C6-3 | 1:4 | 600 | 1.5 | S6-1 |
C6-4 | 1:4 | 600 | 2 | S6-1 |
Component | SiO2 | Al2O3 | TFe2O3 | Na2O | CaO | K2O | MgO |
---|---|---|---|---|---|---|---|
Content (wt.%) | 37.61 | 29.85 | 3.64 | 22.37 | 3.65 | 1.56 | 1.32 |
Position/cm−1 | Assignment | Position/cm−1 | Assignment |
---|---|---|---|
1120–1190 | Asymmetric stretching of Si-O-Si [Q4] | 900–920 | Symmetric stretching of Si-O-Si [Q1] |
1139–1161 | a Asymmetric stretching of (Si,Al)-O-Si | ~850 | Symmetric stretching of Si-O-Si [Q0] |
1050–1100 | Symmetric stretching of Si-O-Si [Q3] | 795–814 | Symmetric stretching of Si-O-Si and stretching of Al-O |
1085–1092 | b Asymmetric stretching of (Si,Al)-O-Si [Q3] | 692–730 | Symmetric stretching of Al-O in Si (Al)-O- Al linkages |
997–1011 | c Asymmetric stretching of (Si,Al)-O-Si | 612–618 | Bending of O-Al-O |
1000–950 | Symmetric stretching of Si-O-Si [Q2] | 543–554 | Symmetric stretching of Al-O-Si |
900–915 | Stretching of Si-O-(M d,Me e,Fe) | <461–465 | Bending of Si-O-Si and O-Si-O |
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Yang, J.; Sun, H.; Peng, T.; Zeng, L.; Chao, L. Study on the Overall Reaction Pathways and Structural Transformations during Decomposition of Coal Fly Ash in the Process of Alkali-Calcination. Materials 2021, 14, 1163. https://doi.org/10.3390/ma14051163
Yang J, Sun H, Peng T, Zeng L, Chao L. Study on the Overall Reaction Pathways and Structural Transformations during Decomposition of Coal Fly Ash in the Process of Alkali-Calcination. Materials. 2021; 14(5):1163. https://doi.org/10.3390/ma14051163
Chicago/Turabian StyleYang, Jingjie, Hongjuan Sun, Tongjiang Peng, Li Zeng, and Li Chao. 2021. "Study on the Overall Reaction Pathways and Structural Transformations during Decomposition of Coal Fly Ash in the Process of Alkali-Calcination" Materials 14, no. 5: 1163. https://doi.org/10.3390/ma14051163