Rare earth elements recovery from secondary wastes by solid-state chlorination and selective organic leaching

Abstract

Processing of end-of-life products (EoL) containing rare earth elements (REE) has gained increasing importance in recent years with the aim of avoiding supply risks. In addition, circular economy renders complete recirculation of technology metals mandatory. Fluorescent lamp wastes are an important source for REE recovery since they contain significant amounts, up to 55 wt%, of Y and Eu in red phosphors. For these purposes, solid-state chlorination (SSC) is an economically attractive alternative to wet acid leaching treatment, which profits from a considerable reduction of chemicals consumption and process costs. Chlorination takes place with dry HCl_(g) produced from thermal decomposition of NH₄Cl_(s), not only converting the REE content of the Hg-free phosphor waste into water soluble REE metal chlorides, but also avoiding the implications of aqueous complex chemistry of REE. To establish an industrial process viable on a commercial scale, the SSC process has been optimized by (i) using a design of experiment (DOE) varying temperature, residence time, and g_NH4Cl/g_solid ratio and (ii) improved leaching of the chlorinated metals with an organic mixture selective for REE. As a result, 95.7% of the Y and 92.2% of the Eu were selectively recovered at 295.9 °C, 67 min and a ratio of 1.27 g_NH4Cl/g_solid, followed by quantitative selective leaching of the REE. Owed to its low chemicals consumption and operation costs, the current process allows for valorizing lamp waste even when raw material prices are low.

Keywords: Chlorination; Electronic waste; Fluorescent powder; Rare earths recovery; Recycling.