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Graphene-Based Sieve Turns Seawater Into Drinking Water (bbc.com)
An anonymous reader quotes a report from BBC: A UK-based team of researchers has created a graphene-based sieve capable of removing salt from seawater. The sought-after development could aid the millions of people without ready access to clean drinking water. The promising graphene oxide sieve could be highly efficient at filtering salts, and will now be tested against existing desalination membranes. It has previously been difficult to manufacture graphene-based barriers on an industrial scale. Reporting their results in the journal Nature Nanotechnology, scientists from the University of Manchester, led by Dr Rahul Nair, shows how they solved some of the challenges by using a chemical derivative called graphene oxide. Isolated and characterized by a University of Manchester-led team in 2004, graphene comprises a single layer of carbon atoms arranged in a hexagonal lattice. Its unusual properties, such as extraordinary tensile strength and electrical conductivity, have earmarked it as one of the most promising materials for future applications. But it has been difficult to produce large quantities of single-layer graphene using existing methods, such as chemical vapor deposition (CVD). Current production routes are also quite costly. On the other hand, said Dr Nair, "graphene oxide can be produced by simple oxidation in the lab." Graphene oxide membranes have already proven their worth in sieving out small nanoparticles, organic molecules and even large salts. But until now, they couldn't be used to filter out common salts, which require even smaller sieves. Previous work had shown that graphene oxide membranes became slightly swollen when immersed in water, allowing smaller salts to flow through the pores along with water molecules. Now, Dr Nair and colleagues demonstrated that placing walls made of epoxy resin (a substance used in coatings and glues) on either side of the graphene oxide membrane was sufficient to stop the expansion.
We could use it as salt, or we could fill in the salt mines we've been digging, or we could drop it into the oceans to counteract all the freshwater melt coming off the polar ice caps from the global warming.
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1. What throughput / flowrate can you achieve, per unit of area?
2. How do you clear clogging?
I'm no chemistry expert, but isn't graphene oxide simply CO2?
Only the same way graphene is diamond.
Allotropes.
How is the Riemann zeta function like Trump rallies? Both have an endless number of trivial zeros.
No. But it's not graphene either. Graphene oxide has been around since the 1850s. Graphene (isolated planes of graphite). The first single-layers of graphene were grown in small amounts in the 1970s, but it wasn't really until the 2000s that sizeable amounts produced by macroscopic means were achieved.
This article is playing on graphene hype to try to play up graphene oxide, which is a more mundane substance. Don't get me wrong, it's neat and has uses (due to how planar its membranes are), but it doesn't have the properties of graphene itself. And it's been used in this particular application (desalination membranes) since the 1960s. Lockheed has had them on the market since 2013.
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Desalination of seawater by reverse osmosis is an old hat. The main challenge from an energy POV is the high pressure differential (and the flow, of course) needed. This won't change much with a new membrane.
Of course, a new membrane might have other desirable properties (cost, robustness, whatever), so every new option is a Good Thing, but the abstract suggests that graphene is something new here. It isn't. Just one more tool in an old chest.
unless you spread it very, very thinly over a wide area, you'll end up with pockets of highly concentrated saline ocean which is very harmful to sea life.
An obvious solution would be to dilute it with fresh water before dumping it into the ocean.
Scientist: Do you know what this means?
Nick: There'd be an *awful* lot of salt.
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Yes.
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"The biggest problem isn't removing the salt, it is what to do with all the excess salt that remains. If you dump it back into the ocean, it wipes out all sea life in a large radius. It is pretty devastating."
This is classic enviro bullshit.
And your response is typical reaction to an uninfomed person, making their statement magically said by all people concerned about the environment
You just claimed that if we suck in some seawater, separate the water from the minerals, and then return the minerals to the ocean again, that they magically turn toxic against the same species that have been spending their lives in it? Human desalination cannot change the amount of water or salt in the environment. "Excess salt" does not exist.
Okay lads, let's sit down and talk like adults, because you are both wrong.
One of the first things we have to look at is the amount of salt that might be returned to the ocean. So we have a desalinization plant. Until the plant is taking a significant amount of water out, extracting the salt, and returning the salt to the ocean, it is hardly going to be a blip in the percentage of salt. So that environut you're railing at is generally wrong. Because there is one hellava lot of water in the ocean.
note: because of local conditions, you would want to have a distributed return of the salt. You do not want to just dump it on the shoreline.
But before you go patting yourself on the back, it is possible to get so much salt that it affects what if anything can live in the water. Mono Lake is one example. It has become so salty that no fish live in it. Brine shrimp and algae are it. The salinity level has varied - topping out at alomst 100 framps per liter in the early 80s. We've stopped diverting so much water, and the salinity level is lowering now, the target is 70 grams per liter. The reason we'r eallowing the lake to replenish is that it is an important migratory pathway for a lot of birds. The Great Salt Lake in Utah, which is the remnant of Lake Bonneville is another hypersaline body of water, and ecologically similar to Lake Mono. The Dead Sea is another hypersaline area, and it's named dead sea for a reason. Not much can live there. A few types of bacteria. So you are completely wrong - It is highly possible to have excess salt.
So by spreading the return of the salt to the ocean over an area that avoids local hypersalinization, we'll not have much effect on the salinity of the oceans.
The shepherds did so well protecting the flock that the sheep no longer believed that wolves existed.
Los Angeles consumed about 17,957,000,000 in August of 2013
A gallon of sear water contains 4.5 oz of salt
So if LA used exclusively desalinized water, they would have 10,100,812,500 lbs of salt on their hands (17,957,000,000*4.5/8)
This is about 126,260,156 cubic feet.
Your average Panamax cargo ship has about 3.6 million cubic feet of space.
This is about 35 ships worth of salt.
There are about 16,900 bulk carrier ships operating in the world.
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This entire thread has been idiotic, because everybody's missing the most important factor:
The desalinized water doesn't leave the system; it gets used and returned.
People drink the water, piss it back out, and flush it down the drain. The drain goes to the sewer. The sewer goes to the wastewater treatment plant. So re-salinize the wastewater after treating it and you can dump it back into the ocean at the same salinity you started with! (Give or take losses from outdoor watering and gains from precipitation falling into combined sewers, anyway. The net difference could be significant, but we shouldn't dismiss the idea out-of-hand by assuming so.) So just build the two treatment plants next to each other and pipe the salt across from the desalinizer to the resalinizer.
Or better yet, just build one plant capable of treating any water (seawater or wastewater) to a drinkable standard, and make the damn thing a closed loop!
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