Recovering rare earths and aluminum from waste BaMgAl10O17:Eu2+ and CeMgAl11O19:Tb3+ phosphors using NaOH sub-molten salt method

In this study, a novel process was developed for recovering rare earth elements and Al from the waste BaMgAl10O17:Eu2+ and CeMgAl11O19:Tb3+ phosphors using NaOH sub-molten salt method. By sub-molten salt method, the spinel structures of blue and green phosphors can be decomposed, Al can be extracted into the solution, and after leaching by HCl solution, the rare earth elements present in the sub-molten salt residues can also be efficiently extracted into the leach solution. Influence of reaction temperature, reaction time, alkali-to-residues mass ratios and the NaOH concentration in the sub-molten salt process affecting on leaching rate of rare earths and Al were investigated to obtain an optimum condition. Maximum leaching rate of Al (99.39%) Ce (96.47%), Tb (92.23%) and Eu (82.43%) was obtained at the condition: NaOH initial concentration 70% (ω), 280 °C temperature and 4 h of reaction time and 4:1 alkali-to-residues mass ratios. After removing impurities and roasting, the Al2O3 products (79.67%) and the RE oxides (94.12%) were obtained eventually.