Lithium is the mineral on everyone’s mind. Also termed as the ‘white oil’ of the renewable revolution, the material is a central component of batteries for electric vehicles (EV’s) and energy storage solutions and economies across the globe are vying to monopolise on the blossoming market. Currently, the world’s largest lithium producers are Australia and the ‘Lithium Triangle’ producers; Chile, Bolivia and Argentina. While Australia predominantly extracts the mineral from the ground using open-cut mining methods, the latter countries have their lithium abundance in its salt pans which is sourced using solar evaporation – a time and cost consuming method. Finding economic and effective ways of extracting lithium from water has thus far proven a challenge, and has limited the amount of material that can be reaped from the aqueous sources.
Now, a team of engineers from the University of Texas at Austin and University of California, Santa Barbara have announced the development of a novel means to extract lithium from contaminated water using new membrane technology. While this solution remains in its nascent stages, it could prove a huge development for the lithium industry in the provision of a cost effective way to extract the mineral from aqueous brines. We took a closer look at the research, and what it could mean for the rare earths sector.
The new technology
The latest research was published last week in Proceedings of the National Academies of Sciences and demonstrates how the team introduced a new class of ‘polymeric membranes’ to separate lithium from water, leaving behind other ions such as sodium (a common contaminant in water). While polymeric membranes are already an established means of water filtration, traditional forms do not have high levels of ion selectivity and so yield low grades of lithium – something that the researchers’ solution seeks to remedy.
“Extraction of lithium salts from brines is currently based on solar evaporation, which is inherently time consuming and laborious,” the team said in an email. “Brines also contain high concentrations of other contaminant salts (e.g., sodium and magnesium salts), which cause inefficient extraction of lithium salts.”
“We incorporated ion specific chemical sites (ligands) into synthetic membranes to develop a material that permeates lithium salts faster than sodium salts and observed the highest LiCl/NaCl selectivity in polymer membranes reported to date,” they added. “Using a combination of polymer synthesis, materials characterisation, and computer modeling, we discovered the origins of this remarkable behavior: sodium interacts strongly with these specific chemical sites, slowing it considerably, while lithium does not interact, leading it to pass through the membrane more freely.”
That is, while in typical membranes sodium passes through more rapidly than lithium, the new model swaps this around to make lithium travel faster as the sodium binds to the crown ethers and delays their movement. Such a discovery could prove significant for lithium extraction, as it would allow for higher quantities of the mineral to be captured in the filtration process.
While synthetic membranes are already a popular method of water purification – particularly in seawater desalination – the team says existing models are not capable of separating certain contaminants.
“Today’s membranes were not designed to treat highly contaminated water and lack sufficient solute specific selectivity to access these treatment opportunities,” they say. “Developing membrane materials to achieve higher specificity using easily processable chemistries will be crucial to advancing this frontier.”
The future of membrane technology
According to the team, their tech also has the potential to extract lithium from water generated in oil and gas production for batteries. Indeed, wastewater from the oil and gas industry often contains high concentrations of lithium yet it has thus far remained unexplored. The research team found that a week’s worth of water from hydraulic fracturing in Texas’ Eagle Ford Shale could produce enough lithium for 300 EV batteries, if only it was tapped into. As such, progressing the tech to commercialisation is the next step for the team.
“As the project evolves, we seek to further enhance membrane selectivity for targeted molecules, like lithium, by varying polymer structure/chemistry and uncovering the mechanisms underpinning selectivity in such systems,” they said in an email. “This will guide design rules for new synthetic membranes that rival the specificity of biological membranes. Progress towards commercialization relies on this and the ability to mass produce optimal polymer chemistries as thin, defect free membranes.”
If scaled up to commercial levels, the tech could certainly open the door to larger supplies and lower costs for lithium. As the world is currently only able to tap into a small portion of its lithium supplies, there is seemingly scope for technologies to enter the fray and expand our supply, and the American universities are not the only ones looking into ways of streamlining water-based lithium extraction.
In June this year, Researchers at King Abdullah University of Science and Technology (KAUST) in Saudi Arabia announced they had developed a means of extracting lithium from seawater in what they say is a more cost-effective way than existing methods. The team deployed a ‘solid-state electrolyte membrane’ and designed a continuous electrically-driven membrane process to enrich the lithium found in seawater samples by 43,000 times. While the structure has holes large enough to allow lithium to pass through, other minerals and ions are trapped. Any residual seawater could also be used in desalination plants to provide freshwater.
Solutions such as these are certainly needed as global demand for battery materials is set to increase as we turn to cleaner storage and transportation alternatives. A 2020 piece from the New Statesman said global demand for lithium is expected to more than double by 2024 as EV production increases from 3.4 million vehicles to a projected 12.7 million in 2024. With demand on the rise, developing low cost and efficient methods of tapping into currently inaccessible sources would change the face of the industry, and bring us closer to a battery-powered future.
