Alkali Fusion Deconstruction and Rare-Earth Recovery from Hazardous Spent Fluorescent Lamp Phosphors: Experimental and Theoretical Calculations

Large amounts of hazardous spent fluorescent lamp phosphors (HSFLPs) are generated globally every year. The highly stable structures of BaMgAl10O17:Eu2+ (BAM) and MgAl11O19:Ce3+, Tb3+ (CAT) components as well as potential environmental risks impede the recycling of HSFLPs. In this study, nearly 100% of Eu, Ce, and Tb can be extracted from the HSFLPs based on the Na2O2 roasting method. The experimental results demonstrated that evidence of Eu2+ ions in BAM as well as Ce3+ and Tb3+ in CAT can be completely released and converted into acid-soluble rare-earth substances. First-principles calculations further revealed that O– in Na2O2 can both transfer electrons to and accept electrons from the surface of BAM and CAT, leading to their structural instability; this electron transfer enhances the electrostatic interaction with Ba, Mg, and rare-earth elements in BAM and CAT, facilitating their detachment from the crystal lattice. The binding energy (Eb (BAM001-Eu): −1302.5 kJ/mol; Eb (CAT001-Tb): −1417.5 kJ/mol; Eb (CAT001-Ce): −1125.0 kJ/mol) and smaller reaction barriers indicate a preference for forming rare-earth oxides like Eu2O3, CeO2, and TbO2. Furthermore, as-formed CeO2 and TbO2 can be further converted into Na2CeO3 and Na2TbO3, which is beneficial for the subsequent leaching of Ce and Tb. This research offers a theoretical basis for the efficient recycling of rare-earth elements from HSFLPs.