Removal of AAEMs from high alkali coal under supercritical CO₂ fluid-citric acid extraction system

ABSTRACT

In this paper, a method for dealkalization and upgrading of high alkali coal by supercritical CO₂ fluid-citric acid extraction system is proposed. The leaching mechanism was explored by microstructural changes of elements and functional groups in coal samples, and single-factor optimization experiment was conducted. The result shows that supercritical CO₂ fluid-citric acid extraction can effectively remove alkali and alkaline earth metals. The extraction mechanism is the reaction of H⁺ with inorganic minerals and the ion exchange of H⁺ with the form of phenolic hydroxyl and carboxyl groups. Under the optimum conditions, the removal rates of Ca and Mg are 44.95% and 65.75% respectively. The ash content of coal is 2.42%, and the content of Na₂O (calculated by ash) is 1.13%, which meet the standards of power coal in China. Supercritical CO₂ fluid-citric acid extraction is an effective and promising method for the cleaning of high alkali coal.

KEYWORDS:

• Supercritical CO₂ fluid
• citric acid
• extraction
• mechanism
• high alkali coal

Acknowledgements

This work was supported by the National Key R&D Program of China (2022YFC2905900), the National Nature Science Foundation of China (U2003126, 52004282), the Fundamental Research Funds for Central Universities (2021GJZPY01, 2021YCPY0108), the Graduate Innovation Program of China University of Mining and Technology （2023WLKXJ070）and the Postgraduate Research & Practice Innovation Program of Jiangsu Province.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Authorship contribution

Junwei Guo: Conceptualization, Methodology, Investigation, Data curation, Visualization, Writing – original draft. Mingrui Zhang: Formal analysis, Data curation. Guanghui Yan: Methodology, Formal analysis. Zhenxing Zhang: Formal analysis, Data curation. Pengfei Zhao: Software, Formal analysis. Mengyao Guo: Formal analysis. Bo Zhang: Supervision, Funding acquistion, Writing – review & editing.

Additional information

Funding

The work was supported by the National Key R&D Program of China [2022YFC2905900]; National Nature Science Foundation of China [U2003126, 52004282]; Fundamental Research Funds for Central Universities [2021GJZPY01, 2021YCPY0108]; Graduate Innovation Program of China University of Mining and Technology [2023WLKXJ070]; Postgraduate Research & Practice Innovation Program of Jiangsu Province.