Free oxoanion theory for BaMgAl10O17:Eu2+ structure decomposition during alkaline fusion process

Abstract

The alkaline fusion process is a useful pretreatment for rare earth elements (REEs) recycling from blue phosphor (BaMgAl₁₀O₁₇:Eu²⁺, BAM), but the lack of basic theory affects the further development of the alkaline fusion process. Different substances (KOH, NaOH, Ca(OH)₂, NaCl, Na₂CO₃, and Na₂O₂) were chosen to react with BAM to explain the alkaline fusion process; only KOH, NaOH, Na₂CO₃, and Na₂O₂ can damage the BAM structure. The BAM alkaline fusion reactions share similar processes. Europium and magnesium ions were bonded with free oxoanion (OH⁻, CO₃²⁻, O₂²⁻) preferentially to escape from the BAM structure. The remaining structure of barium aluminate eventually decomposed into aluminate and BaCO₃ in air. Cations (Na⁺, K⁺) were introduced to bond with the aluminate ions to maintain the charge balance of the reaction system. Free Oxoanion Theory (FOAT) was summarized to elucidate the structure decomposition process of BAM. The variation principle of determined lattice energy was in agreement with the FOAT analysis results. FOAT is very beneficial for the REEs recycling mechanism and alkaline fusion technology theory.