New “cheap and easy” approach to extracting lithium from seawater

Researchers at King Abdullah University of Science and Technology have developed what they believe is a cost-effective way to extract high-purity lithium from seawater.

Previous efforts to extract lithium from the mixture the metal makes along with sodium, magnesium and potassium in seawater have produced very little. Although the liquid contains 5,000 times more lithium than can be found on land, it is present at extremely low concentrations of about 0.2 parts per million (ppm).

To address this problem, the team led by Zhiping Lai tried a method that had never before been used to extract lithium ions. They employed an electrochemical cell containing a ceramic membrane made of lithium lanthanum titanium oxide (LLTO).

In a paper published in the journal Energy & Environmental Science, the researchers explain that the membrane’s crystal structure contains holes large enough to let lithium ions through while blocking larger metal ions.

The cell itself, on the other hand, contains three compartments. Seawater flows into a central feed chamber, where positive lithium ions pass through the LLTO membrane into a side compartment that contains a buffer solution and a copper cathode coated with platinum and ruthenium.

At the same time, negative ions exit the feed chamber through a standard anion-exchange membrane, passing into a third compartment containing a sodium chloride solution and a platinum-ruthenium anode.

Lai and his group tested the system using seawater from the Red Sea. At a voltage of 3.25V, the cell generates hydrogen gas at the cathode and chlorine gas at the anode. This drives lithium transport across the LLTO membrane, where it accumulates in the side chamber.

This lithium-enriched water then becomes the raw material for four more processing cycles, eventually reaching a concentration of more than 9,000 ppm.

To make the final product pure enough to meet the requirements of battery manufacturers, the scientists then adjusted the pH of the solution to provide solid lithium phosphate that contains only trace amounts of other metal ions.

According to the researchers, the cell will likely need $5 of electricity to extract 1 kilogram of lithium from seawater.

This means that the value of the hydrogen and chlorine produced by the cell would eventually offset the cost of energy, and the residual seawater could also be used in desalination plants to provide fresh water.