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Harvesting lithium from seawater electrochemically

By Gerald Ondrey |

Although the oceans contain about 5,000 times more lithium than what is found on land, the low concentrations (about 0.2 parts per million (ppm)), as well as the predominance of other larger ions (sodium, magnesium and potassium) makes Li extraction difficult. Now, researchers from King Abdullah University of Science and Technology (KAUST; Thuwal, Saudi Arabia; www.kaust.edu.sa) have developed an economically viable system that can extract high-purity lithium from seawater.

As described in a recent issue of Energy & Environmental Science, the KAUST team developed an electrochemical cell featuring a solid-state electrolyte membrane — a ceramic membrane made from lithium lanthanum titanium oxide (LLTO). This membrane’s crystal structure has holes just wide enough to let Li+ ions pass through, while blocking larger metal ions. The electrochemical cell contains three compartments. Seawater flows into a central feed chamber, where Li+ ions pass through the LLTO membrane into a side compartment that contains a buffer solution and a copper cathode coated with platinum and ruthenium. Meanwhile, negative ions exit the feed chamber through a standard anion-exchange membrane, passing into a third compartment containing a NaCl solution and a Pt-Ru anode.

The system has been shown to enrich lithium from seawater from the Red Sea by 43,000 times — boosting the concentration from 0.2 ppm to more than 9,000 ppm, with a Li/Mg selectivity of over 45 million. Li3PO4 with a purity of 99.94% — sufficient for battery manufacturing — is formed by precipitation. The value of gases produced by the cell (H2 at the cathode, Cl2 at the anode) would more than offset the cost of electricity, which is estimated at $5 per 1 kg of Li extracted.

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