Question: is it possible to desalinite a small salt lake (turn to freshwater)? Could it be done with the Caspian?

Can you basically remove all the salt from a salt lake let's say the size of Liechtenstein and turn it into a freshwater lake? And could that be done with the Aral (which is now salt basically) and even the caspian sea?
 
Desalination is very expensive from a power and equipment standpoint. I served on one of the largest ships in the US Navy and our nameplate capacity for turning sea water into fresh with steam distillation was 100,000 gallons per day. Might sound like a lot, but it's a drop in the bucket (literally) for something the size of the Caspian Sea. Newer technology (reverse osmosis) might be marginally more efficient but I can't believe the difference is substantial.
 
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Can you basically remove all the salt from a salt lake let's say the size of Liechtenstein and turn it into a freshwater lake? And could that be done with the Aral (which is now salt basically) and even the caspian sea?

A "salt lake" is the end point of a water system with no outlet so the salts build up. You end up with a place that's literally 'plated' in salt to a very deep level so you still have the problem of all the inputs having some level of salt AND the place where it all ends up being a deep salt pan. Doesn't really matter what you do to desalinate the water the very ground it rests on is deeply salty so you'd have to remove all that as well.

Randy
 
Desalination is very expensive from a power and equipment standpoint. I served on one of the largest ships in the US Navy and our nameplate capacity for turning sea water into fresh with steam distillation was 100,000 gallons per day. Might sound like a lot, but it's a drop in the bucket (literally) for something the side of the Caspian Sea. Newer technology (reverse osmosis) might be marginally more efficient but I can't believe the difference is substantial.

Mother nature (as always) has us humans beat all to heck already, it's called evaporation :)

Most of the water ends up evaporating (we're doing that currently at a greater rate than replacement with all the issues that causes) and with diverting all the input water the levels are dropping like a rock. As I noted the main issue isn't the salt WATER but all the salt flats and beds being thick with salt.

Randy
 
Let's see: Clear Lake in California is about the same surface area as Lichtenstein and holds about 10^12 liters of water. If it were full of seawater with molarity 0.6, it would contain 6x10^11 mol of salt. The enthalpy of solution for salt is 4kJ/mol, so at an absolute minimum it would take 2.4×10^15 J to undissolve it all, about 667 gigawatt-hours at a cost of $33 million (and realistically, many times that because this will be nowhere near 100% efficient). Very expensive but physically possible.

Caspian Sea: much bigger at 8x10^16 liters but the water is less salty, maybe molarity 0.2, for a total 1.6x10^16 mol of salt that requires 6.4x10^19 J to desalinate, about 2 terawatt years at a cost of several trillion dollars. Funding may be a problem.
 
One of the things to remember it that something has to be done with the salt removed by desalination (whether very salty brine or solid). Sea salt is a saleable commodity so it has some potential value, but the Caspian would generate an awful lot to be disposed of.
 
One of the things to remember it that something has to be done with the salt removed by desalination (whether very salty brine or solid). Sea salt is a saleable commodity so it has some potential value, but the Caspian would generate an awful lot to be disposed of.

Yeah, if I calculated right, 10^15 kg or an 8 km high pile. Cover it in clay and gravel and call it Mount Nacl ?
 
Desalination plants on coasts take seawater, move salt from part of it to the other (larger) part, resulting in a stream of fresh water that's kept and a larger stream of salty brine that's returned to the ocean.
This is doable with reverse osmosis.

Extracting ALL the salt is much harder.

Plus you then have to ship all thatvsalt somewhere. Tonnes and tonnes of the stuff.
One of the things to remember it that something has to be done with the salt removed by desalination (whether very salty brine or solid). Sea salt is a saleable commodity so it has some potential value, but the Caspian would generate an awful lot to be disposed of.
 
Desalination plants on coasts take seawater, move salt from part of it to the other (larger) part, resulting in a stream of fresh water that's kept and a larger stream of salty brine that's returned to the ocean.
This is doable with reverse osmosis.

Extracting ALL the salt is much harder.

Plus you then have to ship all thatvsalt somewhere. Tonnes and tonnes of the stuff.
If you've got so much extra energy that you're desalinating entire lakes, you could further electrolyze the salt to make sodium metal for batteries. Sodium metal and sodium-ion batteries are a developing technology that might offer an alternative to lithium-based battery chemistries in the future. Sodium can be used in nuclear reactors, too.

Of course, you then have a whole lot of chlorine. The best use I can think of for that would be to turn the new freshwater lake into the Unintended Consequences National Swimming Pool... because a future where we have enough energy to get fresh water by desalinating inland seas is just too bright to be plausible, and we'd have to do something where we seriously mess with whatever ecological balance the planet has left.

(Bonus: if the National Swimming Pool is in California, then Los Angeles — if there still is a Los Angeles — gets the Olympics even more than it already has.)
 
Desalination plants on coasts take seawater, move salt from part of it to the other (larger) part, resulting in a stream of fresh water that's kept and a larger stream of salty brine that's returned to the ocean.
This is doable with reverse osmosis.

Extracting ALL the salt is much harder.

Plus you then have to ship all thatvsalt somewhere. Tonnes and tonnes of the stuff.
Yep. Shipboard steam distilling plants reject brine overboard, after first recovering as much heat from it as practical. There's a goodly amount of it (brine, that is).

If the Caspian was above sea level one could cut a channel to the ocean and let nature take its course over time. But that's not practical for most salt lakes, although it might work with the Great Salt Lake which is 4200' above sea level. But it would take an engineering or tunneling project of unprecedented scope to cut a channel out of the Great Basin into either the Atlantic or Pacific watersheds.
 
If you've got so much extra energy that you're desalinating entire lakes, you could further electrolyze the salt to make sodium metal for batteries. Sodium metal and sodium-ion batteries are a developing technology that might offer an alternative to lithium-based battery chemistries in the future. Sodium can be used in nuclear reactors, too.

Heat of formation of NaCl is -410kJ/mol, so it would take 200 terawatt years to electrolyze Mount Nacl into Mount Sodium (the world's biggest and most violent science-fair volcano, as soon as it rained)
 
Actually I wonder if a channel or pipeline wouldn’t work just as fast and cheeper. A big pump station to pump out the water let it run clean for a while. Dredge the bottom/shore to eliminate the salt then allow to refill with fresh water, A huge project but probably easier the any other method
 
Actually I wonder if a channel or pipeline wouldn’t work just as fast and cheeper. A big pump station to pump out the water let it run clean for a while. Dredge the bottom/shore to eliminate the salt then allow to refill with fresh water, A huge project but probably easier the any other method

The Caspian is below sea level though. Pumping the water up to sea-level would require about 10^20J, as much energy as desalinating it.
 
I would raise the question, "What is your actual objective here?" What would you be trying to accomplish with this hypothetical project, because there's almost certainly a better, faster, and cheaper way to achieve it. Do you need additional fresh water for agriculture, industry, or settlers? Go to the nearest source of ocean-quality salt water and build a big honkin' nuclear-powered distilling plant (or solar, if you swing that way and there's adequate available land area and insolation) and pipe it to your point of use. You'll avoid losses from evaporation and groundwater seepage and you won't be fighting centuries or millennia of salt buildup around your lake bed. If on the other hand there is an adequate fresh water inflow but your objective is a fresh water reservoir for recreation, aquaculture, or similar then simply construct an artificial freshwater lake uphill of the salt lake and let the former outflow into the latter.

Or you could combine the two. If you're into blue-sky mega-engineering, I have an idea for boring a sea-level tunnel from the Gulf Coast to the Pacific Ocean sized for marine traffic and dotted (on the surface) with nuclear desalination plants. Yes, there would need to be a separate smaller tunnel for brine return and exhaust ventilation, but imagine the possibilities....
 
Basically no and no.
However, that's presupposing current technology; there is some interesting work that may be fruitful in the near-future that uses biotech to desalinate water. In theory this might manage what you're looking for.
 
It is not simply a mater of energy. It is a mater of practicality. Huge pumps and giant earth movers are a known technology that humans have perfected. And can easily build and maintain. Desalinization on this scale is something that does not exist. You would probably need more desalinization then we have built in all of human history.
Don‘t get me my method is extremly difficult and probably would be the largest project in human history. But it is not high tech and requires nothing that we can’t built tomorrow If the money is available.

As for the energy…. frankly I think you may be wrong on that. You will need not just the energy to desalinate the water but you also have to get rid of the salt somewhere. Current tech does NOT 100% clean the water. It cleans SOME water and the rest (as well as everything that is removed from the clean portion) is discharged back into the source. This method will not do anything to clean to original source. So either you need to pump that now saltier water discharge somewhere or you need to invent a mass scale method of 100% desalinization. And I suspect that this 100% method will use a huge amount of energy.

But 10,000 giant earth movers just need a lot of fuel. And a huge power plant running tones of giant pumps is pretty easy to build. You will need one set to lift the water coming in from various locations that feed the body of water and another set that empties the body of water itself. The scale would be ridiculous but it is nothing we can’t currently do.
 
Or you could combine the two. If you're into blue-sky mega-engineering, I have an idea for boring a sea-level tunnel from the Gulf Coast to the Pacific Ocean sized for marine traffic and dotted (on the surface) with nuclear desalination plants. Yes, there would need to be a separate smaller tunnel for brine return and exhaust ventilation, but imagine the possibilities....

I would as you not to give the nutter-butter's any MORE grand and impractical ideas please. I'm already dealing with far to many people who think a pipeline to the Pacific ocean "isn't all that difficult" to achieve :)

Randy
 
You could just aerosolize the salt and let the wind carry it away to poison everything east of you, for minimal energy cost but yeah, probably throw in another terawatt year to haul the salt away.
 
I would as you not to give the nutter-butter's any MORE grand and impractical ideas please. I'm already dealing with far to many people who think a pipeline to the Pacific ocean "isn't all that difficult" to achieve :)

Randy
Oh, then I shouldn't mention the seven-mile-long (6 x 1 mile spans + approaches) stainless steel rail+transit+highway suspension bridge over San Francisco Bay between Point Richmond and the Embarcadero? Of course, back when I came up with this notion, there was still the stub of the Embarcadero Freeway to connect to as well as the rail spur to the wharves. But, then...oh, wait. Whoops...!
 
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