Microwave-assisted extraction of rare earth elements from phosphogypsum—Effect of hydrogen peroxide addition

Abstract

Phosphogypsum (PG) is a by-product of phosphate fertilizer manufacturing which is produced in significant amount. It is one of the promising secondary sources of rare earth elements (REEs). The study investigated microwave-assisted extraction (MAE) of yttrium (Y), lanthanum (La), and neodymium (Nd) from the PG, obtained from a fertilizer company in Gresik, Indonesia, using hydrochloric acid (HCl). Extraction efficiency increased as acid concentration increased from 0.25 N to 1.0 N, and increased slightly as reaction temperature increased from 100 °C to 150 °C. When using 1.0 N HCl, solid concentration of 20 g/L, 100 °C, and reaction time of 5 min, complete leaching of REEs was achieved, while 87.0 % of P was leached out. The total energy consumption was 3.74×105 kJ/kg, implying the MAE process was very energy-efficient. The addition of 1 or 2 wt% H2O2, however, decreased leaching efficiency of REEs. It was because the MW/H2O2 system produced hydroxyl radical (•OH), which induced the formation of the passivation layer of zirconium dioxide (ZrO2) on PG surfaces, and hindered REEs leaching. Simulation results revealed that recovery of P via selective precipitation was not feasible due to the interference of calcium (Ca) in the extractant.