Biomimetic Membrane Enables Efficient Lithium Extraction from Complex Brines

markrenngont

A research team has developed a cutting-edge membrane that imitates the function of biological ion channels to selectively isolate lithium ions from complex brine mixtures. The study, published in Nature Communications, was led by Professor Gao Jun from the Qingdao Institute of Bioenergy and Bioprocess Technology (QIBEBT) of the Chinese Academy of Sciences, in collaboration with Qingdao University.

Lithium, a vital component in batteries and clean energy systems, is typically found in low concentrations and mixed with high levels of other ions such as sodium, potassium, magnesium, and calcium. Existing extraction methods often struggle with efficiency, cost, and environmental concerns.

Drawing inspiration from nature, the researchers created a sulfonic acid-functionalized covalent organic framework (COF) known as r-TpPa-SO3H. The membrane features a randomly oriented nanocrystalline design that forms ultra-narrow, maze-like channels capable of distinguishing ions by their size and hydration energy.

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This novel structure operates via a reverse-sieving mechanism, where sodium, potassium, and even divalent ions like magnesium and calcium are allowed to pass through under an electric field, while hydrated lithium ions are effectively blocked.

“Instead of pulling lithium through the membrane, we remove competing ions and retain lithium in solution,” said Bao Shiwen, co-first author from QIBEBT. “This allows for efficient, one-step purification.”

Lab experiments showed that the membrane achieved impressive selectivity between sodium/lithium and potassium/lithium ions, matching the precision of biological ion channels. It also maintained its performance in real-world conditions, including salt-lake brines. During electrodialysis, the membrane consistently removed interfering ions, leaving behind a lithium-enriched solution ready for further processing.

“Achieving high selectivity while maintaining usable ion flux is notoriously difficult, but this membrane delivers on both fronts,” said co-corresponding author Professor Gao. “Its integration with electrodialysis systems makes it a promising solution for sustainable lithium extraction.”

To explore the underlying mechanism, the team used computational modeling. Simulations showed that the sulfonic acid groups within the COF structure attract partially dehydrated sodium and potassium ions, aiding their passage. Meanwhile, lithium ions, which cling to their hydration shells, face steric and energetic barriers that prevent them from crossing the membrane.

This design eliminates the need for complex multi-stage separation processes, offering a streamlined method for recovering lithium from increasingly important low-grade or magnesium-rich brine sources.

The researchers also highlighted the membrane's adaptability. Though initially fabricated on anodic aluminum oxide, it can be transferred onto ceramic substrates for scalable industrial use—making it a practical candidate for large-scale deployment in the global lithium supply chain.