Researchers discover efficient and sustainable way to filter salt and metal ions from water

February 9, 2018, Monash University
Credit: CC0 Public Domain

With two billion people worldwide lacking access to clean and safe drinking water, joint research by Monash University, CSIRO and the University of Texas at Austin published today in Sciences Advances may offer a breakthrough new solution.

It all comes down to metal-organic frameworks (MOFs), an amazing next generation material that have the largest internal surface area of any known substance. The sponge like crystals can be used to capture, store and release chemical compounds. In this case, the salt and ions in sea water.

Dr Huacheng Zhang, Professor Huanting Wang and Associate Professor Zhe Liu and their team in the Faculty of Engineering at Monash University in Melbourne, Australia, in collaboration with Dr Anita Hill of CSIRO and Professor Benny Freeman of the McKetta Department of Chemical Engineering at The University of Texas at Austin, have recently discovered that MOF membranes can mimic the filtering function, or 'ion selectivity', of organic cell membranes.

With further development, these membranes have significant potential to perform the dual functions of removing salts from seawater and separating metal ions in a highly efficient and cost effective manner, offering a revolutionary new technological approach for the water and mining industries.

Currently, reverse osmosis membranes are responsible for more than half of the world's desalination capacity, and the last stage of most water treatment processes, yet these membranes have room for improvement by a factor of 2 to 3 in energy consumption. They do not operate on the principles of dehydration of ions, or selective ion transport in biological channels, the subject of the 2003 Nobel Prize in Chemistry awarded to Roderick MacKinnon and Peter Agre, and therefore have significant limitations.

In the mining industry, processes are being developed to reduce water pollution, as well as for recovering valuable metals. For example, batteries are now the most popular power source for mobile electronic devices, however at current rates of consumption, there is rising demand likely to require production from non-traditional sources, such as recovery from salt water and waste process streams. If economically and technologically feasible, direct extraction and purification of lithium from such a complex liquid system would have profound economic impacts.

These innovations are now possible thanks to this new research. Monash University's Professor Huanting Wang said, "We can use our findings to address the challenges of water desalination. 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."

"Also, this is just the start of the potential for this phenomenon. We'll continue researching how the lithium ion selectivity of these membranes can be further applied. Lithium ions are abundant in seawater, so this has implications for the mining industry who current use inefficient chemical treatments to extract lithium from rocks and brines. 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."

Building on the growing scientific understanding of MOFs, CSIRO's Dr Anita Hill said the research offers another potential real-world use for the next-generation material. "The prospect of using MOFs for sustainable water filtration is incredibly exciting from a public good perspective, while delivering a better way of extracting lithium ions to meet global demand could create new industries for Australia," Dr Hill said.

The University of Texas in Austin Professor Benny Freeman says, "Produced from shale gas fields in Texas is rich in lithium. Advanced separation materials concepts, such as this, could potentially turn this waste stream into a resource recovery opportunity. I am very grateful to have had the opportunity to work with these distinguished colleagues from Monash and CSIRO via the Australian-American Fulbright Commission for the U.S. Fulbright Distinguished Chair in Science, Technology and Innovation sponsored by the Commonwealth Scientific and Industrial Research Organization (CSIRO)."

Explore further: Lithium ion extraction

More information: "Ultrafast selective transport of alkali metal ions in metal organic frameworks with subnanometer pores" advances.sciencemag.org/content/4/2/eaaq0066

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11 comments

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gkam
1 / 5 (1) Feb 10, 2018
How do you get the salts out of the media?
Turgent
1 / 5 (1) Feb 11, 2018
reverse osmosis membranes, precipitation of some salts, and vaporization
Osiris1
5 / 5 (3) Feb 11, 2018
We simply can not get this tech into the hands of de-salination plant engineers and designers fast enough, especially here in California! We have thousands of miles of sea coast and a terrific drought that is only going to get worse with global warming. And we have an ignorant fool for a president that is too mentally old and set in his ways to the point of being a danger to himself and others. No 25th Amendment or impeachment is going to come from a billionaire bribed majority party that put this danger to the public good or his toadies into office on the backs of: 1) crooked blood money from super rich foreigners and Russian agents; 2) gutter politics; 3) internally conflicted ignorant democratic opposition that is yet stuck on 'superdelegates' and anti-second Amendment freaks= impotent. So we here are on our own! Solutions must come from us! This tech or osmosis are our only choices and we got to pay for it ourselves. THANK YOU GOD!
gkam
1 / 5 (1) Feb 11, 2018
Turge, I meant out of the media which traps the minerals. You are not going to vaporize calcium and Magnesium and Iron. How will they get it out of the molecular traps to re-use them? Or do they just throw them "away"?
gculpex
not rated yet Feb 11, 2018
Turge, I meant out of the media which traps the minerals. You are not going to vaporize calcium and Magnesium and Iron. How will they get it out of the molecular traps to re-use them? Or do they just throw them "away"?

More likely they are either recycled or thrown away.
Turgent
not rated yet Feb 11, 2018
Turge, I meant out of the media which traps the minerals. You are not going to vaporize calcium and Magnesium and Iron. How will they get it out of the molecular traps to re-use them? Or do they just throw them "away"?


As regard Ca,Na, Mg, etc., I meant boil off the water, then distill. For molecular filtering reverse flow and flush.
Turgent
not rated yet Feb 11, 2018
gkam

What I don't know is how they keep F, Cl, and Br ions from getting through as their ionic radius are so small.
savvys84
not rated yet Feb 12, 2018
this has great potential
crlMidi
not rated yet Feb 12, 2018
The article is not clear regarding the projected energy consumption with respect to the thermodynamic limit for any reversible desalination process. See http://urila.trip...tion.htm which was the first hit I got from a simple web search. All the article does is imply vaguely that reverse osmosis exceeds that limit by a factor of 2 or 3. Please could we have some precise scientific information?
Turgent
not rated yet Feb 12, 2018
I did read:
http://urila.trip...tion.htm
https://arstechni...it-gets/
And the paper http://advances.s...eaaq0066

This paper speaks to subnanometer filtration. One nanometer equals 1000 picometers. A Cl anion would have a diameter of less than 160 nanometers and a Na ion less than 380, depending on which, calculated or empirical radii used.
This method of ion extraction looks to be very different than simply filtering Na and Cl ions. The top of the illustration on page 3 illustrates what this paper defines as a hydrated ion. This is different than simple hydration. The number of weakly (my guess) bound H2O atom is huge per anion and cation, making the hydrated ion relatively huge. The ionic attraction of H2O is due to the fact that H2O is diamagnetic or the charge on water is polar.

cont.
Turgent
not rated yet Feb 12, 2018
Note the orientation of the water molecules. This makes the hydrated diameter relatively huge. In the top illustration on page 4 lower right quarter illustration is the sieve which uses a dehydration/hydration process. This appears to be a novel approach.

This is a non-expert interpretation of the paper.

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