A sequential integration approach using Aspergillus Niger to intensify coal fly ash as a rare metal pool

•Hydrothermal alkali treatment was proved to be an effective approach for releasing rare metals from coal fly ash.•A sequential integration approach was developed for bioleaching rare metals.•The rare metal pool of coal fly ash was strengthened. As the primary solid waste product from coal-fired power plants, a large amount of coal fly ash (CFA) has caused serious environmental pollution to cultivated land, groundwater, and regional air. Meanwhile, CFA contains certain amounts of rare metals, making it a potential rare metal pool (RMP). Reducing CFA stock can alleviate its pollution to environment through an effective recycling approach. However, the extraction of rare metals from CFA, a pool of rare metals, has not received enough attention until now. Here, we present a sequential integration approach (SIA) of hydrothermal alkali treatment (HAT) and bioleaching to enhance recovery rate of rare metals from CFA. The results showed that the leaching rates of Ti, Ga, Sr, Zr, and Ba were significantly increased using one-step extraction method, reaching 89.20%, 32.00%, 54.30%, 74.50%, and 35.40%, respectively. The results demonstrated that HAT combined with bioleaching can improve the recovery rate of some rare metals from CFA. This study sheds new light on the valuable development of CFA as RMP with potential to mitigate the environment pollution.