Innovative sulfation strategy for efficient recovery of rare earth elements from spent fluorescent lamp powder

The recovery of rare earth elements (REEs) from spent fluorescent lamp phosphors is essential for resource sustainability and circular hydrometallurgy. While yttrium (Y) and europium (Eu) can be recovered through simple acid leaching, extracting cerium (Ce), lanthanum (La), and terbium (Tb) from green phosphors is challenging due to their resistance to dissolution. This study presents a novel sulfation-based process at relatively low temperatures to selectively recover REEs, particularly Tb, while minimizing energy consumption and environmental impact by preventing sulfuric acid and mercury evaporation. Initially, sulfuric acid leaching selectively recovered most of Y and Eu, leaving other REEs in the solid residue. These elements were then precipitated as a nearly pure REE oxalate mixture (>99 % purity). The effects of sulfation time, temperature, and acid-to-powder weight ratio were optimized using Response Surface Methodology (RSM). Sulfation at 150 °C for 5 h enabled the recovery of nearly 100 % Ce and Gd, 98.01 % La, and 98.15 % Tb through water leaching. The mixed oxalate precipitate, enriched in La, Ce, and Tb, exhibited >98 % purity. SEM analysis revealed the formation of flower-like mixed REE oxides after calcination. This process achieved high recovery efficiencies of 99.98 % Y, 100 % Eu, 99.92 % Ce, 97.22 % La, 97.68 % Tb, and 99.97 % Gd. By using only sulfuric and oxalic acid, it aligns with sustainable hydrometallurgy, reducing chemical diversity and enabling acid regeneration. This study provides an efficient, environmentally friendly approach for REE recovery from phosphor waste.