Advancing the circular economy: green recovery of rare earth elements (REEs) from coal combustion fly ash using biohydrometallurgical techniques with mixotrophic bacteria

Coal remains a crucial energy source, with European countries reactivating coal-fired stations to prevent winter blackouts, highlighting its energy security importance. This research investigates coal fly ash (CFA) from a power plant in Indonesia, which is rich in rare earth elements (REEs) that are vital for contemporary technologies. The analysis reveals that the CFA is primarily composed of Si, Fe, Al and Ca, and is notably concentrated in REEs such as Ce, Y, La, Nd, Sc and Pr. Employing biohydrometallurgical techniques involving mixotrophic bacteria, this study aims to sustainably extract these REEs. The findings indicate effective recovery, especially of heavy REEs like terbium, achieving a maximum extraction rate of 70%. Six bacterial strains demonstrated enhanced efficacy in extracting heavy rather than light REEs. The research emphasises the potential of CFA as a significant secondary source of critical metals, promoting eco-friendly extraction methods as feasible and sustainable alternatives.