Comparative leaching of spent fluorescent lamp for extracting yttrium and europium: kinetics and optimization studies

Abstract

ABSTRACT Electronic (e-)waste viz. the spent fluorescent lamps can be a rich source of rare earth elements (REEs) for the secondary supply of them. This article reports a comparative study on mineral acid leaching and, then, compared an alkali diffusion-acid leaching process for higher efficiency of yttrium and europium. Using a direct acid leach process, 2 M HNO3 yielded a better dissolution efficiency of REEs at the moderate temperature of 60°C and in the presence of H2O2in comparison to 91% and 87% leaching efficiency with 2.0 M H2SO4. On the other hand, the alkali-fused phosphor mass leached in 2.0 M H2SO4 without H2O2 addition showed remarkable progress in dissolution efficiency, yielding >99% and >98% of yttrium and europium in the leach liquor. Furthermore, the leaching kinetics of the alkali-diffused phosphor showed the best fit with the logarithmic rate law. The apparent activation energy was calculated to be 43.3 kJ/mol and 35.1 kJ/mol for yttrium and europium, indicating two different mechanisms during the leaching process by following the chemical- and diffusion-controlled reactions, respectively.