Scientists find a smarter way to make drinking water from seawater — and the leftover salt could help supply lithium for future electric car batteries

Scientists at the University of Rochester have found a way to make seawater produce more than just drinking water. Their solar-powered desalination system turns seawater into fresh water while pushing much of the leftover salt into a solid form that could be collected and reused.

The process may also help recover valuable minerals such as lithium, a key ingredient in electric vehicle batteries and other rechargeable devices.

That could give the technology an advantage over conventional desalination plants, which are often left with large volumes of concentrated liquid brine after removing fresh water.


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His team published its findings in Light: Science & Applications.

A related study exploring lithium recovery was published in the Journal of Materials Chemistry A.

Why traditional desalination creates a difficult waste problem

Fresh water is becoming harder to secure in places where rainfall cannot keep up with demand.

From the Middle East to California, desalination plants are turning seawater into drinking water and supplies for industry. But producing fresh water from the ocean comes with a stubborn problem: what to do with all the salt left behind.

The most widely used method is reverse osmosis, which forces seawater through specialised membranes that trap salt and other impurities. Another option, thermal distillation, relies on heat to separate water from dissolved minerals.

Both approaches can consume large amounts of energy and may require chemical treatment, depending on the quality of the seawater.

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And then there is the waste.

Desalination does not destroy salt. Instead, it leaves behind a smaller amount of liquid packed with much higher concentrations of dissolved minerals. This salty by-product, known as brine, can be difficult and expensive to manage.

When discharged into the ocean, it may increase local salinity and reduce oxygen levels, creating stressful conditions for marine organisms.

The University of Rochester’s system takes a different approach.

Rather than leaving the salt trapped in a concentrated liquid stream, it directs dissolved minerals toward a separate area where they can gradually form a solid deposit. That material could then be collected instead of being released as brine.

The idea could turn a major desalination headache into a potential resource—allowing the same process to produce fresh water while capturing minerals that may have commercial value.

Black metal panels use sunlight to evaporate seawater

The system relies on black metal surfaces treated with extremely short laser pulses.

The researchers used femtosecond lasers, which release bursts of light lasting only a quadrillionth of a second. These pulses create microscopic patterns on the metal, changing the way its surface interacts with sunlight and water.

The treatment gives the material two important properties.

First, it makes the surface highly effective at absorbing solar energy. Second, it gives the metal what scientists call superwicking behaviour. Instead of forming droplets, water spreads quickly across the surface in a thin layer.

When sunlight strikes the dark metal, the surface heats the water and causes it to evaporate. The water vapour can then be collected as fresh water, while the salts and minerals remain behind.

The challenge is preventing those salts from covering the part of the panel responsible for evaporation.

If salt crystals form a thick layer over the active surface, they can interrupt water movement, reduce sunlight absorption and eventually stop the process. Salt buildup is a major obstacle for many solar desalination designs.

Guo’s team addressed the problem by separating the panel into active and passive regions.

The active region is where sunlight heats the seawater. The passive region, positioned toward the sides, is where salts and minerals are directed as the water evaporates.

A microscopic design keeps salt away from the working surface

The researchers created tiny grooves in the laser-treated metal to guide dissolved minerals away from the evaporation zone.

The design also uses a process known as the coffee ring effect. When a drop of coffee dries, particles often move toward the edge and leave a dark ring behind. The same basic movement can occur as water evaporates from a surface containing dissolved material.

In the Rochester system, the researchers use this effect to move salts toward the passive region rather than allowing them to form a hard layer over the active section.

This is particularly important when working with real seawater.

Artificial seawater used in laboratory tests often contains mainly sodium chloride. As it dries, the salt can form a relatively porous, grainy structure that still allows water to move through it.

Natural seawater contains many other substances, including magnesium and calcium. These compounds can form dense mineral deposits similar to the scale found inside a kettle, shower head or water pipe.

Such deposits are harder to remove and can quickly damage desalination performance.

To test whether their design could handle this complexity, the researchers used seawater collected from the Pacific, Atlantic and Indian oceans.

The system directed the remaining minerals toward the passive areas, where they could be collected. According to the researchers, the buildup did not significantly reduce the panel’s desalination efficiency during the experiments.

The salt waste could become a source of lithium

The system’s possible benefits extend beyond fresh water.

Because the dissolved minerals are collected as solids instead of being discharged as liquid brine, they may be easier to process.

Some of the recovered material could potentially be used as salt or as a source of other commercially valuable elements.

Lithium is widely used in rechargeable batteries found in electric vehicles, smartphones, laptops and energy-storage systems. Demand for lithium has increased as countries expand electric transport and renewable energy storage.

Traditional lithium extraction can involve mining, large quantities of water or energy-intensive processing. Recovering lithium from salty water could offer another route, although it comes with its own technical and economic challenges.

In a related experiment, Guo’s team modified the solar panels by adding nanoparticles made from hydrogen titanate inside the microscopic grooves.

These particles were designed to selectively capture lithium from the mixture of salts left after desalination.

Using samples from the Great Salt Lake, the researchers recovered approximately 50% of the lithium contained in the remaining salts.

FAQs

1. How does the system work?

Laser-treated black metal absorbs sunlight and spreads seawater into a thin layer. The heat evaporates the water, while grooves guide the remaining salts toward separate collection areas.

2. Does the system produce liquid brine?

The design is intended to avoid concentrated liquid brine by directing nearly all of the leftover salts into solid deposits that can be collected.

3. Can the technology recover lithium?

In a related experiment, modified panels recovered about 50% of the lithium from samples taken from the Great Salt Lake. The process has not yet been demonstrated at commercial scale.

4. Is the invention ready for use in desalination plants?

Not yet.