Leaching and Separation of Rare Earth Elements from Waste Fluorescent Powder

Fluorescent powder contains rare earth elements in the form of phosphates of La3+, Ce3+ and Tb3+ and oxides of Y3+ and Eu3+. The phosphates are sparsely soluble, and are generally dissolved by treatment with concentrated sulfuric acid or sodium hydroxide at high temperature. In this study, a more environmentally friendly process was developed for leaching and effective separation of rare earth elements from waste fluorescent powder. Leaching of fluorescent powder with sulfuric acid at 50 degrees C dissolved more than 90% of Y3+ and Eu3+. Mechanochemical treatment with NaOH of the leaching residue of the previous step removed more than 90% of the phosphates of La3+, Ce3+ and Tb3+. Each rare earth element was then extracted from the leaching solutions by solvent extraction and precipitation. Y3+ and Tb3+ were extracted in the organic phase comprising PC-88A and recovered as Y-2(C2O4)(3) and Tb-2(C2O4)(3) by crystallization-stripping using oxalic acid. Oxalic acid precipitation was used to recover Eu3+ in the raflinate, while hydroxide and oxalic acid precipitation respectively were applied for Ce3+ and La3+. Ce3+ was oxidized to Ce4+ by adding H2O2, and Ce4+ was precipitated as Ce(OH)(4). La3+ was recovered as La-2(C2O4)(3).