Study on Rare Earth Elements Leaching from Magnetic Coal Fly Ash by Citric Acid

The production of fly ash as a solid waste of coal combustion increases with electricity demand growth in Indonesia. Fly ash is usually discarded in landfills due to its lack of utilization. Poor handling of the material can cause pollution and harm to human health. One potential of fly ash that can be further explored is as an alternative source of rare earth elements. The use of citric acid in the recovery process will be more environmentally friendly. The magnetic phase of fly ash is used as it is more favorable for the leaching process due to the smaller amount of acid-resistant components. This research aims to study the leaching mechanisms, evaluate the effect of temperature and acid concentration, and determine the appropriate kinetics model. Magnetic fly ash of less than 38 µm was leached using 300 mL of citric acid with an S/L ratio of 1:10 at a 400 rpm stirring rate. The leaching experiments were carried out for 4 h and samples were taken at the designated time. Acid concentration of 0.5 M, 1 M, 1.5 M, and 2 M was used, while the temperature was varied from 25 ºC, 45 ºC, 65 ºC, and 75 ºC to 90 ºC. The results show that acid concentration does not affect La, Ce, and Y recovery. Meanwhile, the temperature has a significant impact where the recovery increases as temperature elevates. Leaching at lower temperatures (25 ºC and 45 ºC) fits the Z–L–T kinetics model, while at higher temperatures (65 ºC, 75 ºC, and 90 ºC) it follows the Kröger-Ziegler model. Graphical Abstract: Figure not available: see fulltext.. © 2021, The Minerals, Metals & Materials Society.