Discovery could unlock oceans of lithium
New process efficiently harvests battery metal from seawater Metal Tech News – June 9, 2021
Last updated 6/8/2021 at 3:12pm
Driven largely by the increased production of electric vehicles, the demand for lithium has more than doubled since 2015 and is forecast to expand by another seven times to around 2.8 million metric tons per year by 2030.
Predicting this soaring demand will exhaust land-based lithium reserves by 2080, researchers at the King Abdullah University of Science & Technology in Saudi Arabia have developed a system that has the potential to economically extract high-purity lithium from seawater.
KAUST says there is roughly 5,000 times more lithium in the water that makes up Earth's oceans than there is on land. The problem is the lithium concentration in this salty brine is only about 0.2 parts per million and is mixed in with much larger concentrations of sodium, magnesium, and potassium. This combination of low concentrations and competitive minerals has rendered traditional separation technologies such as membrane filtration, ion exchange, and reverse osmosis largely ineffective and inefficient.
To cost-effectively filter lithium out of seawater without the other minerals clogging the system, the KAUST team has developed an electrochemical cell containing a ceramic membrane made from lithium lanthanum titanium oxide. The crystal structure of this LLTO membrane has holes just large enough for lithium ions to pass through but small enough to block the much larger sodium, magnesium, and potassium ions.
"LLTO membranes have never been used to extract and concentrate lithium ions before," says Zhen Li, a KAUST postdoctoral scholar who developed a lithium extractions cell using this membrane.
The cell contains three compartments. Seawater flows into a central feed chamber, where positive lithium ions pass through the LLTO membrane into a side compartment that holds 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 sodium chloride solution and a platinum-ruthenium anode.
The researchers tested the system using seawater from the Red Sea.
With only 3.25 volts of electricity, the cell generates hydrogen gas at the cathode and chlorine gas at the anode. KAUST says this drives the transport of lithium through the LLTO membrane, where it accumulates in the side-chamber. This lithium-enriched water then becomes the feedstock for four more cycles of processing, eventually reaching a concentration of more than 9,000 ppm. Adjusting the pH of this solution delivers solid lithium phosphate that is pure enough to meet battery manufacturers' requirements.
The researchers estimate that the cell would need only consume US$5 of electricity to extract one kilogram of lithium from seawater, and the value of hydrogen and chlorine produced would more than offset this cost.
The seawater could also be used in desalination plants to provide fresh water.
"We will continue optimizing the membrane structure and cell design to improve the process efficiency," says Zhiping Lai, who is leading the KAUST team carrying out the lithium extraction research.
Lai's team also has plans to collaborate with the glass industry to produce the LLTO membrane at larger scale and affordable cost.