Extraction of yttrium and europium from waste cathode-ray tube (CRT) phosphor by subcritical water

The current study investigated leaching of yttrium (Y) and europium (Eu) from waste cathode ray tube (CRT) phosphor by subcritical water extraction (SWE). The leaching efficiency of Y and Eu were 28.15% and 35.92%, respectively, when using 0.5 M sulfuric acid (H2SO4) at 65 °C within 12 h of conventional extraction, and shrinking core model could describe its kinetics. Experimental results from SWE showed it very effective and efficient. The leaching efficiency of Y and Eu was the best when using H2SO4 and that of Zn and Pb was the lowest compared with hydrochloric acid (HCl) and nitric acid (HNO3). The leaching efficiency increased five folds as H2SO4 concentration increased from 0.1 M to 0.75 M. It is noted that leaching of Y and Eu increased significantly with temperature and reached 97.51% at 125 °C using 0.75 M of H2SO4. In addition, sequential extraction was conducted to assess speciation of Zn and Pb in waste CRT phosphor residue after SWE. Fractionation results revealed that SWE process transformed heavy metals to a more stable state.