Sustainable remediation of acid mine drainage using coal fly ash: A comprehensive review and bibliometric analysis

Acid mine drainage (AMD) remains one of the most persistent environmental challenges linked with mining activities, characterized by low pH and high concentrations of sulfate and dissolved metals. In recent years, Coal Fly Ash (CFA), a significant industrial by-product of burning coal, has become a viable, affordable, and sustainable material for treating AMD. This review critically analyses current developments in the use of CFA for AMD remediation, emphasizing its physicochemical characteristics, pollutant removal methods, and performance-enhancing changes. Key findings from experimental and pilot-scale studies show that CFA can effectively neutralize acidic pH, remove up to 99% of heavy metals, and precipitate sulphates through adsorption and co-precipitation processes. Modified CFA materials, including those treated with acids, bases, or nanomaterials, further enhance removal efficiencies and broaden application potential. Challenges related to CFA variability, long-term stability of treated effluents, and potential secondary pollution are critically discussed. The integration of CFA into sustainable AMD management frameworks is also explored, along with emerging innovations such as CFA-based composites and combined treatment systems. A bibliometric analysis highlighted important authors and nations that contribute to this topic and identified key trends in research production. These insights highlight the growing global interest and collaboration in developing sustainable, circular solutions for mine water remediation using industrial by-products.