Become a fan of Slashdot on Facebook

 



Forgot your password?
typodupeerror
×
Earth Science Technology

Scientists Discover a Game-Changing Way To Remove Salt From Water 176

An anonymous reader quotes a report from CNET: [T]he ability to quickly and easily desalinate water has long been a goal of scientists around the world. And now, a group of researchers from Columbia University believe they've found a way to do it. The process is called Temperature Swing Solvent Extraction (TSSE) and it's designed to purify hypersaline brines (water that contains a high concentration of salts, making it up to seven times as salty as seawater). This kind of waste water is produced by industrial processes and during oil and gas production and it poses a major pollution risk to groundwater.

The research team, led by Columbia Engineering's assistant professor of earth and environmental engineering Ngai Yin Yip, mixed a solvent (dyed red) in with a sample of hypersaline brine (dyed blue). The liquids appear to stay separated in the jar, but after heating them, and then decanting the red solvent into another jar to be heated separately, the team was left with a layer of clear water. While the science is complicated, the above video shows the process in a pretty simple way (no chemistry PhD required). What's most exciting about the process is its implications. The team was able to remove up to 98.4% of the salt, which is comparable to the current "gold standard" process, reverse osmosis. But unlike reverse osmosis or other methods of desalination, this process doesn't require high temperatures or high pressures -- just a low-grade heat of less than 70C (158F).
The study has been published in the journal Environmental Science & Technology Letters.
This discussion has been archived. No new comments can be posted.

Scientists Discover a Game-Changing Way To Remove Salt From Water

Comments Filter:
  • I found a way to remove water from salt.

    • Watching the video, this appears to be what they're actually doing.

      The solvent strips the water from the brine, and then you recover the pure water from the solvent. So the salt is left behind and the water is removed.

  • Hypersaline brines are also produced by conventional desalination plants, so could this provide perpetual recycling... :)
  • Solvents (Score:5, Informative)

    by Meneth ( 872868 ) on Wednesday May 08, 2019 @08:35AM (#58557018)
    TFA doesn't mention the name of the solvents, but the abstract [acs.org] does:

    This study demonstrates TSSE desalination of high-salinity brines simulated by NaCl solutions with three amine solvents: diisopropylamine (DIPA), N-ethylcyclohexylamine (ECHA), and N,N-dimethylcyclohexylamine (DMCHA). We show that TSSE can desalinate brines with salinities as high as 234000 ppm total dissolved solids (i.e., 4.0 M NaCl) and achieve salt removals up to 98.4%.

    • And for those of us without a chemistry degree, how bad/toxic/rare/expensive are those solvents?

      • Re: Solvents (Score:4, Informative)

        by Anonymous Coward on Wednesday May 08, 2019 @08:57AM (#58557186)

        Amines smell like rotting fish. Those particular solvents are fairly expensive. $4.50/oz and up.

        Anything treated this way is going to need secondary treatment with Fenton's reagent (H2O2 and iron (III) sulfate) to destroy the residual amines or you'll have one hell of a pissed off customer base. Fortunately, this is standard wastewater treatment stuff.

        • Re: Solvents (Score:5, Interesting)

          by Anonymous Coward on Wednesday May 08, 2019 @11:04AM (#58558214)

          Right, unless you used that desalinated water for agriculture, in which case it would be fresh water with trace amounts of fertilizer.

          • by TWX ( 665546 )

            If that can cost-effectively reduce California's dependence on the Colorado River then it may well be worth it. The Salton Sink at the southern end of inland California is below sea level and isn't all that far from the Mexican Gulf of California. A system that can desalinate seawater en-masse and then deliver it into the Imperial and Coachella valleys, predominately gravity-fed to keep costs down, could supplement California's, Baja California's, Sonora's, and Arizona's agricultural needs for water where

      • Re: (Score:2, Interesting)

        by Anonymous Coward

        DMCHA is £27 per 100ml in "synthetic grade" purity
        ECHA is £16 per 25ml at 98% purity
        DIPA is £31 per 250ml at 99% purity

        All are considered corrosive and poisonous in high concentrations, but none are classed as environment hazards, so that's good! They're pretty common reagents, not least of which because you can buy them from a catalogue.

        At industrial scale, you would use less pure and cheaper by volume amounts of the stuff, or manufacture it yourself from cheaper reagents on the fly. That

    • by Anonymous Coward

      Now the question is: how do we remove the salt from the solvents so that they can both be re-used? Otherwise we have just another waste stream to deal with.

    • This study demonstrates TSSE desalination of high-salinity brines simulated by NaCl solutions with three amine solvents...

      Unfortunately seawater isn't a pure NaCl brine. After sodium, other ions include magnesium, sulfur, calcium, potassium, and bromine. There's darn little bromine in it, but the magnesium might be a problem. The chlorine is ~2% by mass, the sodium is ~1% by mass, and the magnesium is ~0.1% by mass.

  • by Anonymous Coward

    TSSE utilizes a low-polarity solvent with temperature-dependent water solubility for the selective extraction of water over salt from saline feeds. Because it is membrane-less and not based on evaporation of water, it can sidestep the technical constraints that limit the more traditional methods. Importantly, TSSE is powered by low-grade heat (50%) for the hypersaline brines, also comparable to current seawater desalination operations. But, unlike TSSE, reverse osmosis cannot handle hypersaline brines.

    Kind of like how water in a gasoline tank sinks to the bottom. This solvent absorbs some water at around room temperature, and holds less water at a higher temperature... it "floats higher" on the water (there's less water in it). Vid might be a bit confusing since the solvent is initially added as red. At the end of the video [youtu.be] the clear stuff is the solvent, the red stuff is the water. I guess the dye is an impurity not purified by the solvent.

  • by PPH ( 736903 )

    ... where does the salt go? And where do you dump it?

    It might be fine for desalinization. Where the brine can be dumped back into the sea and diluted. But if the point is to process high salinity industrial waste, you still have the same quantity of salt to dispose of. And how efficient is the solvent recovery?

    • Re:But ... (Score:4, Informative)

      by Zocalo ( 252965 ) on Wednesday May 08, 2019 @09:11AM (#58557288) Homepage

      It might be fine for desalinization. Where the brine can be dumped back into the sea and diluted.

      No, it can't, at least not without consequences. It severely upsets the salinity [sciencenews.org] around the point you pump the brine into the sea and is wreaking havoc [pacinst.org] on the marine ecosystems around larger desalination plants. Desalination sounds great on paper, but unless we can extract the solvents and salt from the resulting brine reusing the solvents and using the salt in bulk for things like energy storage, it's not quite the panacea it's cracked up to be.

      We're going to keep running the plants for the fresh water regardless of the ecological consequences, of course.

    • The various salts that sea water contains are useful. If I were to use this process of desalination in my company I would also look for ways to separate the various salts from the process and sell them to industries interested in them (your table salt for example usually come from sea water evaporation).
      • by PPH ( 736903 )

        your table salt for example usually come from sea water evaporation

        From TFS:

        This kind of waste water is produced by industrial processes and during oil and gas production

        I think I'm going to pass on that fracking brand table salt. Desalinization of sea water is one thing. Sell the salt or dump the brine in that nearby salty body of water. Taking careful steps to dilute it properly. It's the stuff that, as the summary states "poses a major pollution risk to groundwater". That sounds like stuff that you just can't dump nearby. Or at all.

    • I would think of it more as a brine concentration tool. The standard zero liquid discharge approach is to go for evaporation ponds, and crystalize the salt. You essentially keep the brine at saturation concentrations, so you can reduce the liquid needed to be evaporated by 30-50%.

  • by n2hightech ( 1170183 ) on Wednesday May 08, 2019 @09:05AM (#58557236)
    Ok the solvent takes some of the water out of the brine leaving it at an even higher salt level. Can the solvent be reused over and over? Is the solvent recovery cost higher or lower than other methods. It looked like it only recovered a small amount of water from the brine. The question is the energy cost + capital for equipment + cost of solvents per gallon of water recovered lower than current methods. And how toxic is the solvent and how many ppm are left in the water.
    • by Anonymous Coward

      they work with the temp differential of 50 degrees (20-70), the salinity of the solvent doesnt matter, at 20 degrees it holds only so much water+salt, at 70degrees it hold less water and more salt, so it's recovering the water from the temp change, if you let it cool down without removing the water at the end, i would assume the water would be reabsorbed into the solvent

    • by Shotgun ( 30919 )

      The sense I get of the chemistry is that the solvent works like a sponge. It suck up lots of water and only a little salt when it is cold, then it dumps the water when it is warmer, but holds onto the salt even more. Heating it "squeezes" the sponge.

      So the process would dump the solvent into the brine, mix it, then let it settle while it is cooled. That would happen is an sealed tank. At the opposite end, the saturated solvent is pulled over to a tank where it is heated. The "fresh" water is pulled out

  • I found the video to be hard to follow. But if I understand what I saw (I may not), I have a couple of questions:

    1. It looks to me like the amount of purified water produced was rather small.

    2. Where did the salt go? They haven't shoved it through a wormhole into another dimension or anything. My guess is that it is dissolved in the amine solution. That's fine, but what do you do with a large amount of fluid that looks to be even more saline than the hypersaline solution you started with, and also co

    • The salt apparently concentrated in the solvent. From what I gather these solvents can draw in both water and salt, but are more likely to kick out just the water when the solubility changes due to the heat.
  • Hmm (Score:3, Interesting)

    by Smidge204 ( 605297 ) on Wednesday May 08, 2019 @09:11AM (#58557290) Journal

    Something seems fishy here.

    First thing I noticed was that the camera pans up as the person pours the blue-colored water into the red-colored solvent, obscuring the bottom of the jar. it then pans back down to show a very clean separation between the two colors. That's a very unusual - and suspicious - camera movement to make. They could easily be hiding a video edit there.

    The second thing I thought about is, if the two fluids are dyed, how did they prevent the dyes themselves from mixing? Not only would the water and solvent need to be immiscible, the dyes would have to be as well while also being compatible with the liquids they're coloring.

    Neither of these prove anything of course, but I think they are valid questions at least.
    =Smidge=

  • by Anonymous Coward

    so in effect they created a chemical pump, to pump out the water, with the pumping step being (scoop) collect water at room temp 20, then heat it up to (dump) 70 degrees to dump the water back out, then cool the solvent and do it all over again, neat.!

  • "Game changing", that is. Is they have a prototype running that can do this for a long time with limited maintenance, we can start to call it that, but not before. What is it with the stupid reporting?

  • The camera just happens to pan up when the actual "reaction" happens, missing the whole thing.

    Its like movies that cut after every punch in a fight scene to hide sloppy choreography.

  • Here in Indianapolis we ADD salt to our water...

Hold on to the root.

Working...