Highlights

• Researchers at Yunnan University unveil innovative hydrophobic ionic liquids and deep eutectic solvents for extracting critical metals with minimal environmental impact.
• New solvent technologies promise more efficient and sustainable metal recovery from batteries, electronic waste, and complex ores.
• Emerging green chemistry approach could revolutionize strategic metal supply chains by enabling cleaner, more decentralized extraction processes.

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A landmark review led by Dr. Xiaohui Lu and colleagues Chaowu Wang, Rongrong Deng, Jie Wang, and Qibo Zhang from Yunnan University, China, published October 2, 2025, in Separation and Purification Technology (Elsevier), maps out a rapidly evolving frontier in sustainable metallurgy: the use of hydrophobic ionic liquids (HILs) and hydrophobic deep eutectic solvents (HDESs) for extracting and recycling strategic metals such as lithium, cobalt, nickel, rare earth elements (REEs), and precious metals.

The Breakthrough: Cleaner Chemistry for Critical Metals

As the clean-energy economy accelerates, demand for rare and strategic metals is outpacing supply, exposing the fragility of global supply chains. Traditional hydrometallurgical processes—while mature—remain pollution-heavy and energy-intensive. Lu’s team identifies HILs and HDESs as promising green alternatives capable of selective, low-temperature metal extraction with minimal waste and volatility.

These designer solvents can be fine-tuned by adjusting cation–anion or hydrogen bond donor–acceptor structures, allowing researchers to control solubility, viscosity, and metal selectivity. The review highlights successful use cases:

• Lithium extraction from salt lake brines;
• Cobalt and nickel recovery from spent lithium-ion batteries;
• Rare earth separation from complex ores; and
• Precious metal reclamation from electronic waste.

Importantly, these methods achieve high separation efficiency while aligning with green chemistry principles—reducing dependency on toxic organic solvents like kerosene and chloroform.

Why It Matters: From Lab Innovation to Industrial Revolution

The implications stretch far beyond laboratory walls. If commercialized, HILs/HDESs-based processes could decarbonize and decentralize key metal supply chains, making secondary resource recycling—so-called “urban mining”—economically and environmentally viable. With the EU’s 2023 Batteries Regulation mandating closed-loop recovery of cobalt and lithium, solvent systems like these could enable compliance while lowering environmental footprints.

For rare earth processing, where solvent extraction dominates but generates significant organic waste, HDESs could help establish non-aqueous, recyclable, and modular refining flowsheets, offering cleaner pathways for separation of neodymium, dysprosium, and other magnet-critical elements.

Caveats and Constraints

Despite their promise, HILs and HDESs are not ready for full industrial deployment. The review highlights persistent challenges in terms of cost, viscosity, and recyclability, as well as unclear degradation pathways that complicate lifecycle management. The scalability of solvent synthesis and regeneration remains a bottleneck. Moreover, while these systems show selectivity advantages in the lab, performance consistency in multi-metal, real-world matrices has yet to be demonstrated.

Conclusion: Toward the Age of Smart Solvents

Lu et al. position HILs and HDESs as catalysts for a new era of green solvent engineering, merging chemistry and sustainability. As rare earth and battery-metal supply chains come under geopolitical pressure, these technologies may help forge a future where strategic metal recovery is not only efficient but environmentally restorative—closing loops rather than widening them.

Citation: Lu, X., Wang, C., Deng, R., Wang, J., Zhang, Q. (2025). Separation and recovery of strategic metals by solvent extraction based on hydrophobic ionic liquids and deep eutectic solvents. Separation and Purification Technology. https://doi.org/10.1016/j.seppur.2025.135433 (opens in a new tab)

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