Leaching and separation of rare earth elements from waste fluorescent powder

Abstract

Fluorescent powder contains rare earth elements in the form of phosphates of La3+, Ce3+ and Tb3+ and oxides of Y3+ and Eu3+. Te 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°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 Y2(C2O4)3 and Tb2(C2O4)3 by crystallization-stripping using oxalic acid. Oxalic acid precipitation was used to recover Eu3+ in the reunite, 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 La2(C2O4)3. © 2013 The Society of Chemical Engineers, Japan.