Selective Recovery of Y-Eu and Tb-La-Ce Oxides from Fluorescent Lamp Waste Using a Two-Step Conventional and Microwave-Assisted Hydrometallurgical Process

Abstract

The growing demand for rare-earth elements (REEs) has spurred interest in their recovery from waste materials, offering environmental and economic benefits. This study investigated the selective leaching of Y, Eu, and other rare-earth elements from phosphor-rich powder derived from fluorescent lamp waste, resulting in the recovery of Y-Eu mixed oxides and mixed oxides of Tb, La, and Ce. Conventional leaching examined the effects of temperature (25-80 degrees C), time (30-360 min), acid type (HCl, HNO3, H2SO4), concentration (0.5-6 M), and solid-to-liquid ratio (1:100-5:100) on Y, Eu, and Ca leaching. Using 3.25 M HNO3 at 80 degrees C for 90 min with a 3:100 S/L ratio, leaching efficiencies were 67.12% (La), 46.14% (Ce), 95.82% (Gd), and 40.04% (Tb). Incomplete dissolution of La, Ce, and Tb occurred due to stable phosphates and aluminates in blue and green phosphors. Conventional leaching residues were further processed via microwave-assisted leaching, optimizing temperature (80-160 degrees C), acid type (HCl, HNO3), concentration (0.5-6 M), S/L ratio (1:100-5:100), and time (5-90 min). Optimal conditions (3.25 M HCl, 3:100 S/L ratio, 120 degrees C, and 47.5 min) achieved recovery efficiencies of 96.81% La, 98.45% Ce, 97.16% Gd, and 97.83% Tb. Finally, Y-Eu oxides and Tb-La-Ce mixed oxides were obtained through calcination and oxalic acid precipitation from conventional and microwave-assisted leaching solutions, respectively.