Title: Iron Extraction from Coal Fly Ash: A Comprehensive Review of Methods, Kinetics, and Thermodynamics
Authors: Mutalibkhonov S.S., Kholikulov D.B., Khudoymuratov Sh.J., Khushbakov D.T., Abdukarimov O.U.
Volume: 9
Issue: 12
Pages: 23-31
Publication Date: 2025/12/28
Abstract:
Coal fly ash (CFA), a major industrial byproduct from pulverized coal combustion, contains significant iron oxide content (10-15 wt%) that represents both an environmental challenge and a valuable resource. This review comprehensively analyzes iron extraction methods indexed in Scopus-based journals, focusing on physical separation, hydrometallurgical leaching, and pyrometallurgical reduction approaches. Comparative analysis of ten extraction techniques reveals that ionic liquid extraction achieves maximum efficiency (95%) at moderate operating temperatures (60°C), while carbochlorination reaches 92.85% recovery at 1000°C. Kinetic investigations demonstrate that hydrochloric acid leaching of magnetite follows mixed-control mechanisms with activation energies of 33.25 kJ/mol, significantly lower than sulfuric acid leaching (50.68 kJ/mol). Thermodynamic calculations utilizing Ellingham diagrams confirm that iron oxide reduction becomes thermodynamically favorable at temperatures above 1100-1300°C depending on the specific iron oxide phase and reductant. Mineral phase analysis via X-ray diffraction reveals magnetite constitutes approximately 80% of iron oxides in typical fly ash samples, with hematite comprising the remaining 20%. Scanning electron microscopy coupled with energy dispersive spectroscopy indicates iron-bearing particles exist as both discrete microspheres and phases within aluminosilicate grains. This review synthesizes recent advances in iron recovery technologies and provides recommendations for sustainable valorization of coal fly ash resources.