Sieving Lithium Out of Salty Waters Get a Boost From a Nature-inspired Membrane

From Anthropocene: Lithium is key to our electric, low-carbon future. The best known rechargeable batteries for electric vehicles and renewable energy storage rely on the silvery metal. But the supply of lithium is uncertain.

An efficient, sustainable new lithium extraction technology could help combat the lithium shortage. Researchers have designed a membrane that can quickly separate lithium from salt-lake brines. The membrane, reported in the journal Science Advances, draws inspiration from the tiny channels that separate ions in biological tissue.

Conventional lithium mining involves letting lithium salt-laced brines evaporate in giant ponds until the salts can be filtered out. The process takes over a year and produces piles of waste. It will not be sustainable for meeting lithium demand. In 2021, the world used about 100,000 tons of lithium, but that demand will likely go up more than tenfold to over 1.3 million tons by 2030, according to the International Energy Agency.

Many companies are now turning to other more direct ways to get lithium from brines. The technology, called direct lithium extraction, involves chemically or physically filtering out lithium and injecting the salty water back underground. The technologies could be used in low-concentration brines found in many places around the world.

One challenge with DLE technologies is that brines also contain salts of magnesium and that are very similar to lithium salts. Drawing only lithium out is crucial.

And this is what the new membrane does well. The team at the Chinese Academy of Sciences took inspiration from biological channels that are adept at only letting certain ions go through. They made a membrane out of the semiconductor carbon nitride.

The membrane contains a combination of rigid, crystalline forms of carbon nitride as well as soft, non-crystalline forms. This gives the membrane a combination of uniformity and narrow pores. It lets small, smoother lithium ions go through while excluding larger hydrated magnesium ions. The researchers report that the new membrane efficiently extracts lithium ions from a lithium-magnesium mix with a selectivity ratio of 1,708:1. It can operate continuously for 10 days.

Source: Yuanyuan Zhang et al, Congener-welded crystalline carbon nitride membrane for robust and highly selective Li/Mg separation, Science Advances, 2024.

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