Recycling of rare earths from fluorescent lamp waste by the integration of solid-state chlorination, leaching and solvent extraction processes

Abstract

Rare earths (RE) are currently considered some of the most critical elements, being crucial in future sustainable applications. Their high demand, price fluctuations, supply risk and geopolitical factors increase the interest in recovering RE from secondary sources such as pre-consumer scrap, industrial residues and end-of-life products. RE recovery from fluorescent lamp wastes and their subsequent selective separation was successful along a three-step process: (i) solid-state chlorination (SSC), (ii) leaching at pH 3 and (iii) solvent extraction. SSC is the key-step to separate RE from residual material. Optimal SSC parameters were set by using an experimental statistical design which allows for evaluating the cross effects between temperature, residence time and NH4Cl:waste ratio. The digestion step was optimized as well reaching a liquid:solid ratio (L:S) of 40 which accounted for a reduction of 20% in the use of water. Yttrium and Europium have been recovered separately from the pregnant solution by a four-stage cross-flow solvent extraction process combining Cyanex 923 and Cyanex 572 reaching initial purities ≥ 94%. This approach is an integrated process for RE recycling from fluorescent lamp wastes, which contributes to reducing chemicals consumption at better process economy.