Ever increasing demand for new technologies mandates exponential growth in production of electronics. This technological growth is accompanied by continuous accumulation of electronic waste containing significant amounts of rare earth elements (REEs) that may be extracted and reused. Current chemical methods of recycling electronic waste suffer from low selectivity and efficiency and produce over 800 million tons of CO₂ annually which is predicted to continue increasing. Separation of REEs in electronic waste through electrochemical approaches has been found to be sustainable and energy-efficient, but it currently lacks elemental selectivity due to the similar electrochemical properties of REEs (e.g., reduction potential). In this work, we demonstrate how ionic liquids may be used to modulate the solvation dynamics of REE ions and co-ions in aqueous based electrolyte to achieve an expanded electrochemical stability window and aid selective enrichment of common REEs (La³⁺, Eu³⁺, and Gd³⁺) found in electronic waste at the electrified interface. We employed 1-ethyl-3-methylimidazolium chloride (EMIMCl) as a co-solvent ionic liquid (CSIL) in the aqueous chloride-based electrolyte containing known amounts of LaCl₃, EuCl₃, and GdCl₃. We investigate the physical and chemical properties as well as interfacial changes in the solvation shell of REEs and CSIL ions at electrified interface as a function of the molar ratio of CSIL/water/REE and applied potential using a combination of experimental (i.e., dynamic light scattering, streaming potential, electrochemical impedance, dielectric constant, Raman and infrared spectroscopies) and computational (i.e., density functional theory, molecular dynamics) approaches. We establish correlations between the electron transfer properties and charge state of selected REEs towards formation of a selective solvation shell with CSIL and how it promotes the underpotential selective enrichment and electrodeposition of REEs at electrochemical interfaces. Our CSIL based selective ion enrichment represents a novel approach for the separation of REEs during electronic waste recycling.

Yang Huang

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