Alumina Extraction from Coal Fly Ash
Summary
Coal fly ash, a by-product of thermal power generation, contains significant quantities of alumina bound within aluminosilicate phases such as mullite and glass. Extraction methods seek to liberate Al₂O₃ by transforming these recalcitrant phases into soluble forms. Common approaches include acid leaching with hydrochloric or sulfuric acid, alkali treatment to dissolve silica and raise the Al/Si ratio, and salt-assisted calcination techniques that convert alumina into readily leachable salts. Pre-desilication and activation pretreatments improve acid accessibility by removing silica or disrupting dense crystal lattices. Low-temperature calcination with potassium bisulfate has demonstrated high alumina recovery at reduced energy inputs. Advances in process integration are focused on maximising yield and purity, minimising energy consumption and secondary waste, and enabling circular-economy valorisation of fly ash as an alternative to bauxite for smelter-grade alumina production.
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Alumina Extraction from Coal Fly Ash publication trend
The graph below shows the total number of articles in alumina extraction from coal fly ash across all publications each year (not limited to Nature Index journals).
Technical terms
Coal fly ash: Finely divided residue from coal combustion rich in aluminosilicates and trace metals.
Acid leaching: Use of mineral acids to dissolve and mobilise metal oxides from solid matrices.
Desilication: Selective removal of silica to enhance the aluminium-to-silicon ratio prior to extraction.
Mullite: A stable aluminium silicate phase in fly ash that resists direct acid attack.
Potassium bisulfate calcination: Low-temperature thermal treatment with KHSO₄ converting alumina into soluble sulphate salts.
References
- A mini review on the separation of Al, Fe and Ti elements from coal fly ash leachate. International Journal of Coal Science & Technology (2024).
- An Efficient Approach for Lithium and Aluminum Recovery from Coal Fly Ash by Pre-Desilication and Intensified Acid Leaching Processes. Metals (2017).
- Activation Pretreatment and Leaching Process of High-Alumina Coal Fly Ash to Extract Lithium and Aluminum. Metals (2020).
- Complete Extraction of Amorphous Aluminosilicate from Coal Fly Ash by Alkali Leaching under Atmospheric Pressure. Metals (2020).
- Alumina Extraction from Coal Fly Ash via Low-Temperature Potassium Bisulfate Calcination. Minerals (2019).
- The Recycling of Coal Fly Ash: A Review on Sustainable Developments and Economic Considerations. Sustainability (2022).
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