Recovery of rare earth elements from waste phosphors via alkali fusion roasting and controlled potential reduction leaching

[Display omitted] •The waste phosphors were alkali roasted using NaOH.•The aluminum-magnesium spinel structure in the waste phosphors was destroyed.•The washed residue was leached via controlled potential with FeCl2 as the reductant.•The cerium and terbium were reduced from a valence of +4 to a valence of +3.•The leaching efficiencies of Ce and Tb were up to 98.6 % and 98.8 %, respectively. Waste phosphors, which contain the quantity of rare earth and toxic metals, need to be recycled for both environmental protection and the sustainable development of rare earth resources. Due to the magnesium-aluminum spinel structure, it is difficult to extract cerium and terbium from waste phosphors. In this study, a facile process for recovering rare earth elements from waste phosphors was developed. First, the waste phosphors were alkali roasted to destroy the aluminum-magnesium spinel structure in the blue and green powders. NaOH was found to be a more suitable additive than Na2CO3, NaHCO3, and K2CO3 for alkali roasting. Then, the roasted slag was washed with water to remove the aluminum and controlled potential reduction leaching was conducted. FeCl2 was used as the reductant (dosage of 0.04) in the 3 mol·L−1 HCl solution at a leaching temperature of 50 °C for 60 min. The leaching efficiencies of Y, Eu, Ce, and Tb were up to 99.1 %, 99.4 %, 98.6 %, and 98.8 %, respectively. The reduction leaching process obeys the shrinking core model and depends on the diffusion. This process can effectively improve the leaching efficiency of rare earth elements from waste phosphors and provides theoretical and technical support for the recycling of waste phosphors.