A solar-powered lithium extractor uses sunlight to drive evaporation that concentrates seawater and helps a lithium-selective material capture Li+ ions, while producing freshwater as a byproduct. In the recent Zhejiang University “solar-powered seesaw” design, photothermal heating boosts lithium adsorption and the device alternates wetting and drying to limit mineral scaling from competing ions. The goal is to co-extract lithium from seawater and desalinate water in a single, low-energy setup.
What is a solar-powered lithium extractor?
A solar-powered lithium extractor is a compact system that couples solar-driven evaporation with lithium-selective capture. It targets lithium in seawater or brines and integrates a photothermal surface, fluid channels, and an adsorbent that prefers Li+ over more abundant ions like sodium and magnesium. The Zhejiang University prototype, reported in the media and academic literature, is described as a “seesaw” because the module’s geometry or operation cycles between wet and dry states to improve capture efficiency and reduce fouling from salts.
How does a solar-powered lithium extractor work?
Although specific designs vary, the core steps are similar:
- Photothermal evaporation: A dark, solar-absorbing layer converts sunlight to heat, raising the surface temperature and evaporating water. This concentrates dissolved salts at the interface.
- Lithium-selective adsorption: A nearby sorbent, often a lithium-ion sieve or related material, captures Li+ ions preferentially. Materials are engineered for size and charge selectivity so Li+ is favored over Na+, Mg2+, Ca2+, and K+.
- Anti-scaling operation: The “seesaw” cycling alternates wetting and drying or tilts flow paths so that salt crystals do not accumulate on critical surfaces, which preserves evaporation and adsorption rates under real seawater conditions.
- Freshwater collection and lithium recovery: Water vapor condenses as low-salinity product. Periodically, the sorbent is rinsed or eluted to recover lithium into a smaller volume stream that can be refined to battery-grade chemicals.
This coupling is attractive because solar heat is free at the point of use, and combining desalination with metal capture can improve the overall value of each liter processed.
How much lithium is in seawater?
Seawater contains roughly 0.17 milligrams of lithium per liter, orders of magnitude less than sodium and magnesium, which dominate ocean salinity.
At about 0.17 mg/L, recovering 1 kilogram of lithium would require processing on the order of 6 million liters of seawater, even with highly selective materials. This dilution is the central challenge. Conventional lithium supply relies on higher-grade resources such as continental brines and hard-rock spodumene, which contain lithium at levels thousands of times higher than seawater. Agencies such as the U.S. Geological Survey and the International Energy Agency note that current markets are primarily supplied by these terrestrial sources.
Why pair lithium capture with desalination?
Producing lithium from seawater alone is energetically and economically difficult because of low concentrations. Pairing with desalination leverages an existing flow of seawater and infrastructure for intake, pretreatment, and brine handling. Solar photothermal modules can reduce electricity use relative to electrically driven processes, and any lithium recovered is an added value stream. Even if lithium revenues are modest, the combined process can offset some desalination costs, especially in remote or off-grid settings.
Global desalination plants discharge concentrated brine that is typically 1.5 to 2.5 times as saline as seawater, raising local environmental concerns if not properly managed (UNU-INWEH).
Integrating metal recovery can be part of a broader brine management strategy that includes dilution, dispersion engineering, and resource recovery.
What are the limitations and open questions?
- Selectivity and capacity: Lithium-selective adsorbents must discriminate against much higher concentrations of Na+, Mg2+, and Ca2+. Ion sieves such as lithium manganese oxides can lose capacity over cycles and may require chemical elution.
- Scaling and fouling: Carbonates and sulfates precipitate during evaporation. Designs like the “seesaw” aim to minimize this, but long-term performance in real seawater needs validation.
- Throughput and footprint: Because lithium is so dilute, very large water volumes must be processed. Practical systems will likely target co-location with existing desalination or saltworks to achieve scale.
- Energy and cost: Solar heat reduces electrical demand, yet materials manufacturing, pumping, and lithium refining still carry costs. Today, seawater lithium extraction remains at lab or pilot scale and is not competitive with conventional resources according to industry assessments by IEA and USGS.
- Environmental outcomes: Any system must manage concentrated brine responsibly. Best practices include diffuser design, blending with other streams, and monitoring to protect marine ecosystems, as highlighted by UNU-INWEH.
What does this mean for batteries and water supply?
If prototypes like the Zhejiang University “seesaw” extractor scale successfully, they could create new pathways to supplement lithium supply, particularly for coastal regions with desalination infrastructure. The approach would not replace mining and high-grade brine projects, but it could diversify sources, reduce sensitivity to supply disruptions, and add value to desalination by turning a waste challenge into a resource stream. As materials and module designs improve, pilot demonstrations at desalination plants or solar saltworks are the logical next step.
In the near term, the most realistic role for seawater extraction is as a complementary source that co-produces freshwater and a lithium-rich concentrate, not as a standalone replacement for existing lithium supply.