Gallium and Indium Selective Sulfidation and Vapor Phase Transport from e-Waste Feedstocks

Abstract

Gallium (Ga) and indium (In) share similarities in their chemical behavior, their dilute presence in waste electronics (e-waste), and recycling rates close to 0% from such streams. Designing processes to extract gallium from LED chips and indium from LCD screens simultaneously reveals the potential and necessary distinctions for a flexible process based on elemental sulfur reactivity, which can be applied to both feedstocks. Whereas Ga- and In-compounds found in e-waste (gallium nitride, GaN; indium tin oxide, ‘ITO’) are recalcitrant to dissolution in aqueous feedstocks, the reaction with sulfur gas to form volatile sulfides may support their selective extraction from prepared e-waste. Process conditions for selective sulfidation are herein informed from thermodynamics and demonstrated experimentally. Vapor phase transport of the volatile sulfides is a powerful means to collect and enrich gallium and indium. Practical implementation likely calls for physical separation approaches to disassemble e-waste, remove excess material (epoxy, glass, metallic leads, and housing) from LED chips, and expose the ITO layer within LCD screens.