A novel method for leaching rare earth element from fluorescent lamp waste via acid fusion

Spent fluorescent lamps are alternatives to primary sources of rare earth elements. For recycling, the most common hydrometallurgical processes involve leaching with mineral acids, combined or not with alkaline fusion, which must be followed by another acidic leaching step for terbium, cerium, and lanthanum recovery. This study proposes a novel method employing acid fusion with potassium pyrosulfate (K₂S₂O₇) and leaching with water at 25 °C. A full factorial design (2³) was employed to study the following variables for the fusion process: temperature (450–550 °C), flux/sample mass ratio (2.2–3.0), and time (30–120 min). Under the optimal experimental conditions, the maximum recovery for La was 56.0 %. Recoveries were close to or greater than 70 % for Y, Ce, Eu, and Tb, at lower temperatures compared to those used in alkaline fusion, without the need for additional reagents and heating in the REE leaching step after fusion.