An integrated approach combines hydrothermal chemical and biological treatment to enhance recycle of rare metals from coal fly ash

Abstract Coal fly ash rich in rare metals accounts for a large amount of solid waste released from coal-fired power plants. However, rare metals, the components of coal fly ash with the highest economic value, are not fully recycled due to the lack of an effective, low-cost approach. Therefore, it is urgent to develop a new approach, aiming at increasing the recycling efficient, decreasing the cost and strengthening the high economic value of fly ash. Here, we developed an integrated approach combines hydrothermal chemical treatment process (HTCP) and biological leaching process (BLP) to improve recycle of rare metals from coal fly ash. The results showed that the one-step bioleaching method could obtain more kinds of rare metals and dramatically improve bioleaching rate after hydrothermal-alkali treatment (HAKT) using Acidithiobacillus thiooxidans. After HAKT, the leaching rates of metals V, Sr, Y, La, and Ce were higher than those of the untreated pure fly ash (UPFA) with the maximum values of 51%, 70.52%, 37.48%, 64.77%, and 76.37%, respectively; after hydrothermal-acid treatment (HTAT), the bioleaching rates of rare metals Ni, Sr, and Y, were higher than those of the UPFA with the maximum values of 70.24%, 20.26%, and 34.54% respectively. The results also showed that, for most rare metals, the recovery rate following HAKT was higher than that following HTAT. This result can be demonstrated via analyzing adsorption quantity, adsorption kinetics and diffusion model of fly ashes for A.thiooxidans. Our study provides an important pathway for recycling rare metals from coal fly ash.