Study on the Recovery of Lutetium from Lutetium Yttrium Silicate Scrap by Molten NaOH

Lutetium yttrium silicate (LYSO) scintillation crystals are the key materials for PET, which is the most advanced medical imaging diagnostic device today. However, only about 40% of the crystal blanks can be converted into qualified crystal devices. And the rest of the crystal blanks were converted into scraps. In this study, the phase transformation in the decomposition of LYSO by molten NaOH was studied. The main phase of the decomposition products were proven to be NaLuSiO4, LuO(OH), Lu(OH)3, Na3LuSi2O7, and Na2SiO3. And Lu3+ in LYSO was replaced by Na+ ions during decomposition with molten NaOH. When the mass ratio of alkali to LYSO scrap exceeded 2:3, the leaching ratio of rare earth elements (REEs) reached its maximum at 95 wt%. After water leaching, the silicon content of the slag decreased with the increasing amount of alkali. After leaching with hydrochloric acid (HCl), only SiO2 and adsorbed LuCl3 were detected in the slag, indicating that NaLuSiO4 and Na3LuSi2O7 in decomposition products could be dissolved by HCl. The LYSO crystal was almost destroyed at high alkali dosage. This work provides an alternative method for the efficient recycling of REEs from LYSO scrap.