Novel closed-loop recovery of light rare earth elements, as their oxides, from end-of-life mobile phone speakers using [Hbet][Tf2N]

The use of rare earth elements (REEs) in many applications has proliferated in recent years. Growing demand for these elements, driven by global economic growth, a shift towards green technologies and the monopoly of their production by China, has led to their instability and shortage. The drive to source REEs from alternative secondary sources is imperative. Here, End-of-Life Mobile Phones (EoL-MPs), which represent a resource-rich stream for critical metals in general, and, specifically REEs, are used as feedstock. Exploiting the thermomorphic properties of the IL system, [Hbet][Tf2N]:H2O, the effects of time, water content and temperature for optimal leaching are determined in binary (Nd2O3-Pr2O3) and ternary (Nd2O3-Pr2O3-Fe2O3) systems, with the IL showing strong selectivity for oxides of light REEs. A complete hydrometallurgical process for the recovery of REEs, as oxides, from as-received EoL-MP speakers is developed involving pre-treatment, leaching, precipitation, and calcination, using the IL, [Hbet][Tf2N], as leaching agent. Each step was optimised to convert embedded REEs into their oxides to permit their full recovery. This novel closed-loop recycling process offers high selectivity for light REEs, utilising mild conditions, permitting the reuse of the IL up to five cycles, generating little waste and recovering the light REEs (Nd and Pr) with ≥ 90% efficiency and purity of product of ≥ 98%. Moreover, other highly valuable heavy REEs (Dy and Tb) are retained in the residue offering potential for their recovery. The proposed process provides a sustainable and efficient approach to close the gap between their supply and demand for these critical materials.