Synergistic recovery of mercury and rare earth elements from waste phosphors by microwave alkali fusion-carbothermal reduction followed by acid leaching.

Waste phosphors (WP) containing mercury from discarded fluorescent lamps is not only a dangerous solid waste but also a secondary resource for recycling of rare earth elements (REEs) and mercury. This study aimed to investigate synergistic recovery of REEs and mercury from WP by microwave alkali fusion-carbothermal reduction followed by acid leaching. Phosphors and mercury compounds were decomposed by NaOH and carbon to rare earth oxides with low-valence and elemental mercury. When WP was roasted with alkali and carbon powder at 900 °C for 30 min, mercury removal efficiency reached 99.9 %; the leaching efficiency of REEs reached 93.67 % after HCl leaching without reducing agent. The addition of carbon enhanced alkali fusion according to thermodynamic and kinetic analysis. When carbon addition amount was 30 % during microwave alkali fusion, the dissociation activation energy of Ce and Tb decreased by 4.33 and 15.8 kJ·mol respectively, the activation energy of mercury removal decreased by 15.05 kJ·mol. Mixed rare earth oxides with purity of 91.2 % were obtained from the acid leaching solution by oxalic acid precipitation followed by roasting. This work provided a new idea for synergistic recovery of REEs and mercury from real WP by microwave roasting with additives.