Coal fly ash as a sustainable alternative source for rare earth elements and metal-based nanoparticles: Advances, challenges, and perspectives

Abstract

The growing global reliance on coal for energy production has led to the accumulation of large volumes of coal fly ash (CFA), a by-product traditionally regarded as hazardous waste. However, CFA is increasingly recognised as a promising secondary source of rare earth elements (REEs) and metal-based nanoparticles, both of which are critical for advanced technologies and are seeing rapidly increasing demand amid supply risks stemming from the depletion of primary ore deposits. This structured narrative review evaluates conventional and emerging techniques for the recovery of REEs and metal-based materials from CFA, with emphasis on recovery efficiency, key factors influencing recovery and the associated advantages and limitations of each method. It further addresses the gap between laboratory-scale advancements and large-scale industrial implementation by examining techno-economic feasibility. Case studies indicate that single-element recovery is economically unviable, highlighting the need for integrated multi-element recovery strategies to enhance both sustainability and profitability. Other key challenges, including environmental and optimisation concerns, are discussed alongside forward-looking solutions, such as integrating artificial intelligence for process optimisation. This work positions CFA as a strategic resource and provides insights into advancing sustainable, economically viable recovery pathways.