Recovery of Rare Earth Oxide from Phosphor Powder of Spent Fluorescent Lamp

Abstract

Phosphor powder contained inside fluorescent tubes is a rich source of rare earths. Phosphor used in fluorescent lamps is of tricolour type that emits visible light of three different colours, i.e., red, green and blue. Among three phosphors, europium-doped Y2O3 is a typical red phosphor that is used predominantly in triband phosphor for displays and fluorescent lamps. In view of above, the present work was focussed on optimising conditions to recover yttrium and europium selectively and synthesizing highly pure Y2O3:Eu3+ (red phosphor) from the liquor arising from leaching of a phosphor powder of spent fluorescent lamps in chloride medium and using oxalic acid as precipitant. The typical composition of the leach liquor obtained at optimum leaching conditions was (g/L): 26.9 Y, 1.6 Eu, with slight impurities of Al and Ca. Process parameters, including acidity, concentration of oxalic acid and temperature, were optimized to produce yttrium oxalate. Under the optimum conditions, the recovery of yttrium and europium as oxalates was quantitative. The synthesised yttrium-europium oxalate was calcined at 600°C to convert it into Y2O3:Eu3+. The yttrium-europium oxalate/oxide powder so formed was characterized by thermogravimetric differential thermal analysis, X-ray diffraction, scanning electron microscopy and chemical analysis, all of which confirmed the presence of pure Y-oxalate and oxide. The microscopy image of the synthesised Y2O3:Eu3+ exhibited flaky particles of 5 μm size; the purity of synthesized red phosphor was >99%, as determined by chemical analysis and energydispersive spectroscopy.