Effects of acid concentration on the recovery of rare earth elements from coal fly ash

A rise in global energy demand has led to an increase in coal consumption. Consequently, global coal fly ash production has increased creating a pressing need for recycling and utilisation of coal fly ash. Since coal fly ash is enriched with rare earth elements one application is to extract rare earth elements from this waste material. There has been a rise in demand for rare earth elements over the past decades due to their use in optics, automotive, electronics, energy, defence industries etc. In this study, a two-stage hydrometallurgical process (alkali fusion-acid leaching) was used to recover rare earth elements from coal fly ash from a South African Power Station (Tutuka Power Station). The coal fly ash was firstly roasted at high temperature with sodium hydroxide, followed by acid leaching with hydrochloric acid. The effect of acid concentration on the recovery of rare earth elements from coal fly ash was investigated. Results indicated that acid concentration had a significant effect on rare earth element recovery. Rare earth element recovery increased as HCl concentration increased from 1 mol/L (0%) to 2 mol/L (33%) and decreased as acid concentration increased to 3 mol/L (29%). Thus, the acid concentration of 2 mol/L was the optimal concentration for rare earth element recovery. In addition, the study showed that the alkali fusion-acid leaching method favoured the recovery of heavy rare earth elements (47.78%) and medium rare earth elements (46.78%) over light rare earth elements (33.93%) due to their mineral associations.