It's Official. We Can Now Harvest Usable Lithium From Seawater
Without lithium, the all-electric vehicles of today wouldn't be feasible, and with an increasing demand for EVs expected to exhaust reserves on land by 2080, this might become inevitable. But there is another way to extract the vital element, or rather another place.
The oceans contain roughly 5,000 times more lithium than land, but at unconscionably small concentrations of roughly 0.2 parts per million (ppm). And a team of researchers has developed a new system capable of extracting concentrated lithium from seawater, according to a recent study published in the journal Energy & Environmental Science.
Enriching the lithium content in seawater via an electrochemical cell
The research team from KAUST developed an electrochemical cell containing a ceramic membrane composed of lithium lanthanum titanium oxide (LLTO), whose crystal structure possesses holes wide enough to allow lithium ions to move through, while also blocking the larger metal ions. "LLTO membranes have never been used to extract and concentrate lithium ions before," said Zhen Li, a postdoc researcher who developed the cell. The cell is comprised of three compartments: First, seawater flows into the central feed chamber, and then positive lithium ions move through the LLTO membrane, and into an adjacent compartment equipped with a buffer solution, in addition to a copper cathode coated in ruthenium and platinum.
While this is happening, negative ions leave the feed chamber via a standard anion exchange membrane, and pass through a third section containing a sodium chloride solution, and a platinum-ruthenium anode. The new lithium-extracting system was tested with seawater sucked up from the Red Sea, and with a voltage of 3.25 V, the cell can generate chlorine gas at the anode, and hydrogen gas at the cathode. This directs the lithium through the LLTO membrane, where it aggregates in the side-chamber from above. The result is lithium-enriched water that is then fed back into the cell through four more cycles of processing, enriching the element's concentration until it reaches 9,000ppm.
Five dollars of electricity is needed per kilogram
The researchers then alter the pH of the solution, creating a solid lithium phosphate that only contains traces of other metal ions. In other words, the final product is pure enough to fall within all-electric vehicle battery manufacturers' standards to build. This process would require only five dollars of electricity to extract 2.2 lbs (1 kg) of lithium from seawater. Five dollars!
And, the value of chlorine and hydrogen produced from the cell would more than pay for the cost, leaving residual seawater to be used in desalination plants to offer freshwater. "We will continue optimizing the membrane structure and cell design to improve the process efficiency," said Zhiping Lai, who leads KAUST. His team also aims to enter a collaboration with the glass industry, to develop the LLTO membrane at greater scales with affordable cost.
Needless to say, this is an extremely promising system. Auto manufacturers like Ford are increasingly following Tesla's lead in pivoting to all-electric, to eventually move away from fossil fuels, which are linked to high carbon emissions and global climate. But if we run out of lithium, these plans are only stop-gaps for the transportation and auto industries. This is why, most crucial to the KAUST team's electrochemical cell is not the ability to simply procure concentrated lithium ions, but the capability to do it at low cost, with sustainable outputs.
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