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There is urgent, unprecedented demand for critical, by- and coproduct metallic elements for the infrastructure (magnets, batteries, catalysts, electronics) needed to power society with renewable electricity1–3. However, extraction of these d- and f- block metals from mineral and recycled streams is thermodynamically difficult, typically requiring complete dissolution of the materials, followed by liquid-liquid separation using metal ion complexing or chelating behavior4,5. The similar electronic structure of these metals results in poor separation factors, necessitating immense energy, water and chemicals consumption6–8. Here, a processing approach based on selective anion exchange is proposed. Several simple process levers (gas partial pressure, gas flowrate, carbon addition) were demonstrated to selectively sulfidize a target metal from a mixed metal oxide feed. The physical and chemical differences between the sulfide and oxide compounds (e.g. density, magnetic susceptibility, surface chemistry) can then be exploited for vastly improved separation over liquid–liquid methods9. The process conditions of sulfidation are provided for 56 elements and demonstrated for 15 of them. The assessment of the environmental and economic impacts suggests a path toward 60–90% reductions in greenhouse gas emissions while offering significant capital cost savings compared to liquid–liquid hydrometallurgy.

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