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

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 °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 °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 °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 °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.