Leaching of rare earth elements from waste lamp phosphor mixtures by reduced alkali fusion followed by acid leaching

• A novel process to recover rare earth from lamp phosphors mixtures is proposed.
• A reductive process using iron and alkali fusion was tested.
• The reductive iron added in the process has great improvement on leaching efficiency of rare earth.
• Under the optimum conditions, the leaching efficiencies of Ce and Tb can reach to 98.12% and 99.37%, respectively.

Because of the complex crystal structures of the blue powder and green powder in waste rare earth phosphor powder and the relative high content of Ce and Tb, efficient extraction of rare earth elements (REEs) is difficult. The highest leaching efficiency of REEs is only about 90% with present processes, and utilization of the REEs is low. To improve the leaching efficiency of waste rare earth phosphor, a novel process of reduced alkali fusion followed by acid leaching to recover REEs from waste phosphor powder is proposed. Under the conditions of mass ratio of reductive iron powder to waste rare earth phosphor of 1:200, alkali to phosphor mass ratio of 2:1, alkali fusion temperature of 700 °C, alkali fusion time of 3 h, hydrochloric acid concentration of 3 mol L− 1, liquid to solid ratio (v/w) of 7.5:1, acid leaching temperature of 70 °C, and acid leaching time of 1 h, the total leaching efficiency of REEs is as high as 99.35%, and the leaching efficiencies of Ce, Eu, Tb, and Y are 98.12%, 99.93%, 99.37%, and 99.60%, respectively. The results indicate that the REEs in waste phosphor powder can be efficiently recovered by the proposed process.