Rare Earth Elements in Turkish Coal Fly Ashes: Enrichment Patterns and Secondary Resource Perspective

In thermal power plants, fly ash produced from coal combustion is a solid waste that requires large storage areas and poses environmental risks. In addition, coal ash can contain significant amounts of critical elements, including rare earth elements and yttrium (REY). Despite high supply risks, demand for REY is increasing in parallel with technological developments. Therefore, the recovery of REY from coal ash is becoming increasingly important for both solid waste disposal and as a raw material source. This study presents an integrated geochemical assessment of REY in fly ashes from coal-fired thermal power plants in Türkiye, based on systematically compiled and harmonised datasets. The REY concentration of fly ash varies between 134.00 and 429.48, with an average of 230.06 ppm. Light REY are predominant in all samples. The proportion of critical REY averages 34.75, with the highest value calculated at 42% in fly ash from the Yatağan thermal power plant. While most fly ashes show L-type enrichment, there are also samples showing M-type and H-type enrichment. According to initial national-scale estimates, coal fly ashes in Türkiye may contain approximately 3.7–5 kt of rare earth oxides per year. Despite their low REY content, Turkish fly ashes can be considered a potential source for REY recovery when considering the large waste volume, in conjunction with an integrated evaluation strategy. This study establishes a geochemical basis for future process-oriented and recovery-focused investigations.