Valorization of phosphor powder of waste fluorescent tubes with an emphasis on the recovery of terbium oxide (Tb4O7)

Abstract

Waste fluorescent tubes containing yttrium, europium, lanthanum, cerium, and terbium are considered important resources of rare earths. Due to the scarcity of terbium in natural deposits, phosphor powder from waste fluorescent tubes could be a potential source of terbium. The presence of terbium with stable aluminates matrix in the phosphor powder makes the terbium recovery challenging. The present paper aims to develop a process to recover high pure terbium oxide (Tb4O7) from phosphor powder of waste fluorescent tubes. In the developed process, leach residue obtained after selective leaching of yttrium and europium was treated for the recovery of terbium. The leach residue was treated by alkali roasting-water leaching to break the aluminates and phosphates matrix. Further, La, Ce, and Tb were recovered by HCl leaching. Terbium from lanthanum and cerium was separated by solvent extraction using D2EHPA as an extractant. Various parameters such as extractant concentration, phase ratio, etc. were optimized for the selective extraction of terbium in the organic phase. The counter-current process was simulated for terbium extraction. High pure terbium oxide (99.8%) was produced from the loaded organic by precipitation stripping followed by calcination. The solid residues and final products were characterized by chemical analysis, XRD and SEM-EDS.