Critical Elements Potential in Coal and Coal By‐Products for Resource Sustainability

The escalating demand for critical elements (CEs), particularly rare earth elements and yttrium (REY), driven by their indispensability in modern green technologies, electronics, and defence, emphasises the urgency for identifying secure and sustainable alternative sources. This review broadly evaluates the viability of coal and its by‐products, fly ash, bottom ash, and slag, as promising reservoirs for these strategic elements. Key findings reveal that REYs are significantly enriched in coal combustion residues, with fly ash demonstrating higher concentrations than bottom ash, while certain volatile elements partition into the flue gas. The occurrence and enrichment of CEs are governed by coal rank and maceral composition, with elements like gallium associated with collodetrinite and cobalt with inertinite. Critically, REYs are primarily hosted within amorphous aluminosilicate glass and specific mineral phases, such as haematite in fly ash, whose disordered atomic structures facilitate element incorporation. The distribution patterns of REY in power plants consistently show a hierarchy, lowest in raw coal, medium in slag, and highest in fly ash. While acknowledging the technological and economic challenges in extraction, this review synthesises and proposes an integrated recovery flowchart that synergises physical separation, acid/alkali leaching, and purification techniques to enhance efficiency. The recovery of critical elements from coal and its combustion by products holds significant strategic implications for India's long term resource security. As global supply chains for rare earths and other strategic metals remain highly concentrated, domestic extraction from coal based sources could help reduce import dependence and enhance supply resilience. Leveraging India's vast coal reserves for secondary recovery of elements such as REEs, Ga, Ge, and U align with the objectives of the National Critical Minerals Mission, supporting both industrial diversification and clean energy transitions. This approach also offers a dual benefit addressing environmental concerns related to coal waste management while advancing self‐reliance in critical mineral supply.