Evaluation of alkali processing for the recycling of rare earth values from spent fluorescent lamps.

Phosphor samples collected after crushing and sieving of discarded fluorescent lamps comprise approximately 31 % rare earth elements in the form of Y1.90Eu0.10O3, Al11Ce0.67MgO19Tb0.33, and Al10.09Ba0.96Mg0.91O17: Eu2+ phase. Direct leaching and mechanical activation assisted leaching are incapable of recovering Ce, Tb values from the Al11Ce0.67MgO19Tb0.33 phase. Heat treatment with NaOH was found successful for dissociation of Ce, Tb phase via substitution of rare-earth ion by Na+ ion to form rare earth oxide and water-soluble NaAlO2. Y, Eu, Ce, and Tb values were recovered from heattreated mass in a two-step leaching process followed by recovery from the leach solution by oxalic acid precipitation. Over 95 % extraction rate was attained after heat treatment at 400 °C with 150 wt-% NaOH for 1 h. It was found that Y, Eu containing phase does not take part in the heat treatment process whereas the Ce, Tb phase undergoes a solid-state chemical reaction with NaOH via product layer diffusion model with 41.5 kJ/mol activation energy. Approximately 15 g mixed oxide (purity >95 %) of Y (79 %), Eu (7 %), Ce (5 %), and Tb (4 %) could be recovered from 100 units of discarded FLs. Microwave treatment of phosphor and NaOH (50 wt-%) yielded approximately 42 % Y, 100 % Eu, 65 % Ce, and 70 % Tb recovery in just 5 min. Approximately 9 g of REO and 5 g of cerium enriched leach residue were recovered from the microwave route within 5 min and depicted high microwave potential application in the recovery of Ce and Tb values from waste phosphor sample. [ABSTRACT FROM AUTHOR]