Green Recovery of Rare Earths from Waste Cathode Ray Tube Phosphors: Oxidative Leaching and Kinetic Aspects

In this work, we developed a green and efficient process for the recovery of rare earths from waste cathode ray tube phosphors. The mixture of hydrochloric acid and hydrogen peroxide was identified as the most suitable leaching agent due to the synergistic effect. The effects of various parameters on leaching process were explored, and the optimal conditions with stirring speed 600 rpm, temperature 313 K, 1 M of H2O2 4 M of HCl, and leaching time of 90 min were determined. Furthermore, a possible reaction mechanism was proposed, and the kinetics for the leaching process was investigated in detail. The leaching process was found to follow a shirking-core model, with the chemical reaction as the rate-controlling step. The apparent activation energy of the reaction was calculated as 52.3 kJ/mol, and the reaction orders for H2O2 and HCl were established as 0.82 and 2.13, respectively. The kinetic equation was established. Moreover, the optimal leaching conditions were applied to the waste phosphors, and the oxalate precipitation process was employed, achieving the recovery rate of rare earths >99.5%. After calcining, a well crystallized (Y0.95Eu0.05)(2)O-3 product with a purity of 99% was obtained with an average diameter of 5 mu m.