Materials

New desalination membrane produces both drinking water and lithium

A scanning electron microscope image of metal-organic frameworks, crystals that can separate lithium from seawater
A scanning electron microscope image of metal-organic frameworks, crystals that can separate lithium from seawater
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A scanning electron microscope image of metal-organic frameworks, crystals that can separate lithium from seawater
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A scanning electron microscope image of metal-organic frameworks, crystals that can separate lithium from seawater

Seawater is a complex cocktail of useful minerals, but it's hard to separate out the specific ones we need. Now, a team of scientists from Australia and the US has developed a new water desalination technique that can not only make seawater fresh enough to drink, but recover lithium ions for use in batteries.

The key to the process is metal-organic frameworks (MOFs), which boast the largest internal surface area of any known material. Unfolded, a single gram of the material could theoretically cover a football field, and it's this intricate internal structure that makes MOFs perfect for capturing, storing and releasing molecules. Recent research into the material could see MOFs put to work as carbon emission sponges, high-precision chemical sensors, and urban water filters.

Currently, reverse osmosis membranes are the most commonly-used technology for water filtration, and they work on a fairly simple principle. The membrane's pores are large enough for water molecules to pass through, but too small for most contaminants. The problem is that to work, these systems require water to be pumped through at relatively high pressure.

MOF membranes, on the other hand, can be more selective and efficient. Researchers at Monash University, the CSIRO and the University of Texas at Austin have now developed just such a membrane. The design was inspired by the "ion selectivity" of biological cell membranes, allowing the MOF material to dehydrate specific ions as they pass through. Better yet, these filters don't require water to be forced through, saving on energy use as well.

"We can use our findings to address the challenges of water desalination," says Huanting Wang, an author of the new study. "Instead of relying on the current costly and energy intensive processes, this research opens up the potential for removing salt ions from water in a far more energy efficient and environmentally sustainable way."

But clean drinking water isn't the only end product of the MOF membrane. Lithium is in high demand, thanks to the lithium-ion batteries that power everything from smartphones to electric cars. Those ions are left behind in the spongey structure, ready for the taking.

"Lithium ions are abundant in seawater, so this has implications for the mining industry who currently use inefficient chemical treatments to extract lithium from rocks and brines," says Wang. "Global demand for lithium required for electronics and batteries is very high. These membranes offer the potential for a very effective way to extract lithium ions from seawater, a plentiful and easily accessible resource."

The technique could also be put to work filtering waste water from industrial processes like fracking.

"Produced water from shale gas fields in Texas is rich in lithium," says Benny Freeman, co-author of the study. "Advanced separation materials concepts such as ours could potentially turn this waste stream into a resource recovery opportunity."

The researchers say they plan to continue studying how to make MOFs even better at selecting for lithium ions.

The study was published in the journal Science Advances.

Sources: CSIRO, UT Austin, Monash University via Science Daily

12 comments
S Michael
What about gold particles.
MartinVoelker
This is obviously early stages but I wonder how these membranes could help reduce the volume of salt brine left behind after desalination. Typically around 20 % of the volume of the seawater is brine which is toxic or at least disruptive to ecosystems in such high concentration. Unless there's a solution on this front desalination remains a method of last resort.
JimFox
MartinVoelker--- good point- are there many large salt caverns & old underground salt mines that could be filled to dispose of this stuff, after natural evaporation in hot climates?
Snerdguy
This is the kind of technology that governments should be watching and investing resources into, albeit carefully. We have to recognize that clean water supplies are being strained and that an electrically powered society is going to need more lithium than current methods of mining will be able to supply. This is far more critical than space exploration and the fantasies of people landing on other planets.
Douglas Bennett Rogers
The main use of lithium in about 100 years may be as fusion fuel.
DCDaly
Hi! Question: It would be helpful if the reporters and writers would mention what corporations, if any, were financially supporting this powerful research. Normally, they would have some ownership of the results of this project. This could create a huge, lucrative patent and have a great impact in states threatened with drought. dcd
DaveWesely
MartinVoelker, JimFox -- Of course high concentrations of brine are toxic. But remember, tons of seawater is evaporated off the surface of the ocean every day - leaving behind a higher concentration of brine. The solution is simple. Don't dump all the brine into a shallow bay area. Pipe what you don't use out to an area with significant currents and volume to distribute the salts back into the ocean.
DavidRogerBrown
MartinVoelker- Certainly know little on the subject but couldn't the salt brine be used as additional products or safely returned to the ocean? Snerdguy- Totally agree. Smart research funding solving human induced massive problems facing us here on our blue planet should be greatly increased. Funding could be transferred from "pie in the sky" human space travel illusions that machines like Hubble do far better & cheaper. But how does one convince the large numbers that have their heads in the sand and deny overwhelming evidence of a near future sixth extinction? While China and other countries are pulling ahead of the U.S. in science research & problem solving. The powerful carbon industry will fight tooth & nail to slow down anything that affects their bottom line.
ljaques
Cleanup of any part of the fracking fields is a good thing. They waste millions of gallons of fresh water on each hole drilled.
DaleBarclay
We should be taking the salt from the ocean and lakes and use it to melt the snow and ice on roads instead of removing it from the ground and adding it to the oceans and lakes increasing their salt content.