Novel lithium extraction technique harnesses solar energy, offering an efficient alternative amid rising demand for lithium. — SCMP
Chinese scientists say they have discovered a promising and sustainable method for extracting lithium from seawater, offering an efficient alternative amid increasing demand for lithium in renewable energy technologies while minimising the environmental impact.
The surge in production of new energy vehicles and energy storage devices has led to a robust demand for lithium. But currently, lithium is primarily sourced from hard rock ores, such as spodumene, or from natural brines, both of which involve energy-intensive and environmentally costly processes.
A groundbreaking study published on Friday in the peer-reviewed journal Science presents a novel seawater lithium extraction technique that harnesses solar energy as the driving force.
Led by Zhu Jia, of Nanjing University, and Mi Baoxia, from the University of California, Berkeley, the research team proposed a solar transpiration-powered lithium extraction and storage (STLES) device that extracts and stores lithium from brine using sunlight.
The STLES device consists of a solar transpirational evaporator, a lithium storage layer and a nanofiltration membrane. It uses solar energy to generate high capillary pressure within the evaporator, which drives lithium through the membrane and into the storage layer.
Lithium extraction from seawater has been a technology that appeared attractive but had many challenges. All the seawater on Earth contains around 230 billion tonnes of lithium – a resource amounting to 16,000 times the world’s currently exploitable lithium reserves.
The presence of abundant magnesium, calcium, sodium, potassium and lithium in seawater complicates the separation process.
According to a report from the Shanghai-based news outlet The Paper in 2023, industry insiders noted that the low concentration of lithium in seawater typically required desalination before extraction, making the overall cost of this method more than 10 times higher than other techniques.
Due to these costs and technical challenges, seawater lithium extraction has not yet become a mainstream source of lithium. However, recent research may change that.
Zhu’s team designed an aluminum oxide membrane modified with aluminium nanoparticles. As water vaporises under solar transpiration and moves through the channels in the membrane, lithium ions (Li+) are extracted and separated from divalent ions such as magnesium (Mg2+) and calcium (Ca2+).
According to the paper, a porous silica frit, or porous ceramic material, above the membrane captures the separated lithium salts. Lithium recovery from the silica frit is achieved with a simple water rinse, which can be performed at night when salt production is lower.
“Long-term experiments, various membrane tests and different size assessments demonstrate the stability, compatibility and scalability of the STLES,” Zhu stated in the paper.
The STLES device operates passively – without the need for additional energy input – making it cost-effective and environmentally friendly. It can also be integrated with existing evaporation ponds, helping to cut installation costs, and has the potential to treat hypersaline brines with high osmotic pressures.
In the same issue of Science, another study conducted by Chinese researchers at King Abdullah University of Science and Technology (KAUST) in Saudi Arabia reported success in extracting lithium from Dead Sea brine using electrochemical cells.
In pilot tests involving simulated brine with less than 0.1% lithium chloride, the researchers achieved lithium recovery rates exceeding 80%, marking a significant step towards real-world feasibility.
Although these technologies have shown promise in the laboratory and at the preliminary pilot scale, the economics and environmental impact in commercial-scale applications require further evaluation.
“A key challenge that remains is optimising extraction efficiency while minimising environmental impacts, particularly in terms of water usage and land disruption,” Seth B. Darling from the University of Chicago noted in a perspective article in the same issue.
“The economic viability of these new methods is still uncertain. The materials used in these processes, such as aluminium nanoparticles and anodic aluminum oxide membranes, are generally costly and may need to be replaced with more affordable alternatives that maintain comparable performance,” he said. – South China Morning Post
