Sequential particle-size and magnetic separation for enrichment of rare-earth elements and yttrium in Indonesia coal fly ash

Abstract

Coal fly ash is known to contain rare-earth elements and yttrium (REY). In this research, three Indonesian coal fly ashes were characterized and subjected to sequential physical separation processes. The characterization results showed that the ashes had a critical REY content exceeding 38 % and outlook coefficient (Coutlook) of 1.1 - 1.2; however, enrichment is required prior to REY recovery. Coal fly ash from the Indramayu power plant also contained high concentrations of Fe2O3 and CaO, which occurred as magnetite, hematite, spinel, and srebrodolskite. Sequential physical separation consisting of sieving and magnetic separation was conducted to enrich the REY content of this ash. The sieving results showed that the REY content increased with a decrease of particle size. The highest REY recovery (58.69 %) and enrichment factor (1.1) were obtained in ashes with a size fraction of < 38 μm. Magnetic separation results showed that the nonmagnetic fraction contained more REY than the magnetic fraction. The enrichment factor and REY recovery in the magnetic separation step were 1.12 and 91.64 %, respectively. Overall REY recovery for the sequential separation process was 71.21 %, with an overall enrichment factor of 1.23. Sieving followed by magnetic separation effectively decreased the Fe2O3 and CaO contents of this fly ash.