Recovery of rare-earth elements from coal fly ash via enhanced leaching

Coal fly ash is regarded as a potential alternative source of rare-earth elements and has gained much attention over the past few years. However, the majority of rare-earth elements in coal fly ash are entrapped in the glassy phase, which makes the recovery of rare-earth elements from coal fly ash extremely challenging. In this paper, two pre-treatments (mechanical grinding and alkali solution treatment) were conducted to enhance the leaching recovery of rare-earth elements from coal fly ash. The best recovery of rare-earth elements by acid leaching after grinding is 79.19% at the optimal conditions. That is due to the increase of surface area, resulting in more rare-earth elements exposed from the glass phase and increase the rate of leaching. The highest rare-earth element recovery gained by acid leaching after alkali pre-treatment is 95.50% in the paper. Alkali solution destroyed the glassy aluminosilicate spheres (such as metal oxide, amorphous silicon in amorphous silica-aluminosilicate) of coal fly ash more efficiently, making it more solvable in hydrochloric acid. This research has focussed on grinding and alkali pre-treatment to provide a theoretical foundation and technology support to the extraction of rare-earth elements from coal fly ash.