Highlights
- Researchers demonstrate hydrophobic ionic liquids and deep eutectic solvents as environmentally friendly alternatives for extracting strategic metals.
- New solvent systems could transform critical metal recycling, potentially disrupting current geopolitically concentrated supply chains.
- An innovative approach offers the potential to close the loop on lithium-ion battery recycling, rare-earth element recovery, and precious-metal recovery, with reduced environmental impact.
A new review by Xiaohui Lu and colleagues from Yunnan University, published in Separation and Purification Technology (Vol. 380, Part 3, February 2026), highlights a quiet revolution underway in the field of critical-metal recovery. The paper, “Separation and recovery of strategic metals by solvent extraction based on hydrophobic ionic liquids and deep eutectic solvents”, synthesizes years of work on hydrophobic ionic liquids (HILs) and hydrophobic deep eutectic solvents (HDESs)—two classes of green, designable solvent systems that could transform how the world extracts lithium, cobalt, nickel, rare earth elements, and precious metals.
Findings
Lu’s team demonstrates that HILs and HDESs offer powerful, environmentally friendly alternatives to traditional hydrometallurgical solvents such as kerosene or toluene, which are highly toxic and generate persistent pollution. The authors detail how tailored cation–anion combinations in ionic liquids and hydrogen-bond donor–acceptor synergies in HDESs allow scientists to fine-tune solvation, hydrophobicity, and metal-ion selectivity.
These green solvents show strong promise for closed-loop recycling of lithium-ion batteries, rare earth separation from brines and slag, and precious-metal recovery from e-waste. Laboratory systems have achieved high extraction selectivity with low volatility and reusability, positioning them as key enablers for sustainable “urban mining.”
Implications
If scalable, HILs/HDESs could disrupt the economics of critical-metal supply chains, reducing dependence on geopolitically concentrated reserves—such as lithium in South America or rare earths in China—and enabling cleaner, decentralized recycling hubs.
For investors and policy makers, this signals a maturing frontier where chemistry meets circular-economy imperatives. As the EU, U.S., and Japan impose stringent recovery targets (e.g., the EU’s 95 % cobalt-recycling rule), these solvent systems could become foundational to next-generation metallurgical infrastructure—potentially lowering lifecycle emissions and enhancing resource security.
Limitations
The review also notes formidable barriers. Most studies remain bench-scale, with limited real-world validation of solvent stability, regeneration cost, and compatibility with industrial throughput. Viscosity control, phase-separation kinetics, and recyclability of complex solvent mixtures pose unresolved engineering challenges. Moreover, while “green,” some ionic liquids carry high synthesis costs and uncertain biodegradability profiles.
The authors urge future research on process intensification, mechanistic modeling, and cost-effective solvent design to bridge lab innovation and commercial viability.
Conclusion
Lu et al.’s review is both timely and visionary: it reframes solvent extraction not as a relic of 20th-century hydrometallurgy but as a cornerstone of sustainable materials recovery. For the rare-earth sector and broader critical-minerals landscape, it underscores that chemical innovation—rather than new mining alone—may ultimately secure the green-tech future.
Citation: Lu X., Wang C., Deng R., Wang J., Zhang Q. (2026). Separation and recovery of strategic metals by solvent extraction based on hydrophobic ionic liquids and deep eutectic solvents. Separation and Purification Technology, 380 (3): 135433. https://doi.org/10.1016/j.seppur.2025.135433 (opens in a new tab)
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