Precipitation of Rare Earth Element from Indonesian Coal Fly Ash Using Sodium Sulfate
I D Tajayani1, Sarto1, W Astuti2, Sutijan1,*

1 Department of Chemical Engineering, Universitas Gadjah Mada, Jl. Grafika 2, 55281 Yogyakarta, Indonesia
2 Research Unit for Mineral Technology, National Research and Innovation Agency (BRIN), Jl. Ir. Sutami Km. 15, Tanjung Bintang, Lampung Selatan, Lampung 35361, Indonesia
*Corresponding author: sutijan[at]ugm.ac.id

Abstract

Coal ash is a waste product of power plant combustion. Previous research revealed that coal ash contained levels of rare earth elements. This research uses coal fly ash from the Paiton power plant. The objectives of this study were to determine the effect of the Na2SO4 concentration, stirring rate, and temperature on the recovery of REE concentrate. The experiment was conducted in four steps (1) alkaline leaching, the process was carried out for 2 hours at 90 C with a fly ash solids to 8 M NaOH solution ratio of 1:4 to break the aluminosilicate bonds. (2) Acid leaching of residue for 4 hours at 90 C in 3 M HCl. (3) Precipitation of residue to remove the impurities such as Fe using 1 M NaOH at pH 5. (4) Precipitation of filtrate from process (3) using Na2SO4 to produce REE concentrate precipitates. The best conditions for obtaining REE residue recovery at the concentration of 20% Na2SO4, a stirring rate of 500 rpm, and a temperature of 50 C with the recovery is 88.72%.

Keywords: Coal fly ash, rare earth element, leaching, precipitation, sodium sulfate

Topic: Environmental Chemistry and Engineering