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The Recycling of Coal Fly Ash: A Review on Sustainable Developments and Economic Considerations

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  • Amanda Qinisile Vilakazi

    (School of Chemical and Metallurgical Engineering, University of the Witwatersrand, Johannesburg 2050, South Africa
    DSI/NRF SARChI: Hydrometallurgy and Sustainable Development, University of the Witwatersrand, Johannesburg 2050, South Africa)

  • Sehliselo Ndlovu

    (School of Chemical and Metallurgical Engineering, University of the Witwatersrand, Johannesburg 2050, South Africa
    DSI/NRF SARChI: Hydrometallurgy and Sustainable Development, University of the Witwatersrand, Johannesburg 2050, South Africa)

  • Liberty Chipise

    (School of Chemical and Metallurgical Engineering, University of the Witwatersrand, Johannesburg 2050, South Africa
    DSI/NRF SARChI: Hydrometallurgy and Sustainable Development, University of the Witwatersrand, Johannesburg 2050, South Africa
    Department of Metallurgical Engineering, Manicaland State University of Applied Sciences, Mutare 00263, Zimbabwe)

  • Alan Shemi

    (School of Chemical and Metallurgical Engineering, University of the Witwatersrand, Johannesburg 2050, South Africa
    DSI/NRF SARChI: Hydrometallurgy and Sustainable Development, University of the Witwatersrand, Johannesburg 2050, South Africa)

Abstract

The recycling and utilization opportunities for coal fly ash (CFA) have increased in the past two decades. However, limited commercialization of the material is still reported, while disposal and management remain major concerns. CFA utilization is currently commercially feasible in the building and construction industry. Other alternative uses that are being explored involve the extraction of valuable metals and the purification of wastewater. The CFA-produced adsorbent material utilized in wastewater purification processes should be able to generate water that meets the legal quality requirements for reutilization in alternative applications. On the other hand, in the recovery of metallic components such as smelter-grade alumina, high recovery and high purity products are only achievable through the processing of CFA using expensive and energy—intensive processes. Furthermore, most of the current CFA recycling processes tend to generate secondary solid residues (SSR), which can cause environmental pollution, thus requiring further downstream processing. In this context, this paper reviews and discusses current research on CFA recycling methods, challenges and opportunities associated with resource recovery from CFA, and the acceptability of the value-added products, and it therefore proposes sustainable processes for CFA utilization. This review further suggests that to successfully compete with bauxite for production of smelter-grade alumina, other saleable value-added products such as Ti, Fe and the REEs should be recovered by engineering an integrated process design. The generated SSR in each process must also be characterized, recycled and re-used to reduce waste production and advance the circular economy concept. The review concludes that for CFA to become considered as a more attractive commercial resource, there is need for its complete and holistic utilization in high volumes and in different applications to offset its low value.

Suggested Citation

  • Amanda Qinisile Vilakazi & Sehliselo Ndlovu & Liberty Chipise & Alan Shemi, 2022. "The Recycling of Coal Fly Ash: A Review on Sustainable Developments and Economic Considerations," Sustainability, MDPI, vol. 14(4), pages 1-32, February.
    • Handle: RePEc:gam:jsusta:v:14:y:2022:i:4:p:1958-:d:745262
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    References listed on IDEAS

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    1. Hassan Ali & Han Phoumin & Steven R. Weller & Beni Suryadi, 2021. "Cost–Benefit Analysis of HELE and Subcritical Coal-Fired Electricity Generation Technologies in Southeast Asia," Sustainability, MDPI, vol. 13(3), pages 1-16, February.
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    2. Aziman, Eli Syafiqah & Ismail, Aznan Fazli & Rahmat, Muhammad Abdullah, 2023. "Balancing economic growth and environmental protection: A sustainable approach to Malaysia's rare-earth industry," Resources Policy, Elsevier, vol. 83(C).
    3. Yixuan Du & Minxuan Chen & Kaibao Wang & Tianyu Wang & Legeng Wang, 2025. "Integrating Fly Ash into High-Temperature Ceramic Glazes: Achieving Sustainability, Cost-Effectiveness, and Aesthetic Appeal," Sustainability, MDPI, vol. 17(17), pages 1-12, September.
    4. Isaac Akinwumi & Manuela Onyeiwu & Promise Epelle & Victor Ajayi, 2023. "Soil Improvement Using Blends of Coal Ash and Plantain Peel Ash as Road Pavement Layer Materials," Resources, MDPI, vol. 12(3), pages 1-16, March.
    5. Ewa Strzałkowska, 2023. "Ashes Qualified as a Source of Selected Critical Elements (REY, Co, Ga, V)," Energies, MDPI, vol. 16(8), pages 1-19, April.
    6. Jabir Dubaish Raib & Fujian Zhou & Tianbo Liang & Anas A. Ahmed & Shuai Yuan, 2025. "Synergy of Fly Ash and Surfactant on Stabilizing CO 2 /N 2 Foam for CCUS in Energy Applications," Energies, MDPI, vol. 18(15), pages 1-18, August.
    7. Ratidzo Yvonne Nyakudya Ncube & Michael Ayomoh, 2025. "Optimisation Strategies and Technological Advancements for Sustainable Direct Reduction Iron Production—A Systematic Review," Sustainability, MDPI, vol. 17(5), pages 1-23, March.
    8. Shuliu Wang & Wenhui Huang & Weihua Ao, 2025. "The Distribution of Rare Earth Elements in Coal Fly Ash Determined by LA-ICP-MS and Implications for Its Economic Significance," Sustainability, MDPI, vol. 17(1), pages 1-17, January.
    9. Ahmad Mukhtar & Asad Ullah Qazi & Qasim Shaukat Khan & Muhammad Junaid Munir & Syed Minhaj Saleem Kazmi & Asif Hameed, 2022. "Feasibility of Using Coal Ash for the Production of Sustainable Bricks," Sustainability, MDPI, vol. 14(11), pages 1-15, May.

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