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Q & A: desalting via freezing

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Most recent answer: 02/04/2013
Q:
can you separate salt from water by freezing?
- Emil Menzies
Miami, Florida, USA
A:
Yes, because when ice and liquid water are in equilibrium, the concentration of salt in the liquid is much higher than in the ice. From what we hear, it sounds like you need to be careful to freeze the ice very slowly to let the salt get out into the liquid, rather than getting trapped in little pockets in the ice, if you want to do a good de-salting job this way.

Mike W.

(published on 10/22/2007)

Follow-Up #1: Desalinating water through freezing

Q:
Can you separate salt from water by freezing?
- Asher,Curtis (age 13)
Chico,California,USA
A:

Yes, it is possible to separate salt from water, but only if you are careful. As you might already know, a salt water solution lowers the freezing point of water because the salt ions get in the way of the water molecules as they try to freeze by sticking together. However, if you lower the temperature enough, you will get some water to freeze, expelling the salt that would be in that water to the rest of the solution. This will make the rest of the water saltier. Now the water does not form perfect ice crystals, so there could be a bit of salt in some of the spaces in the ice. However, if you let the water freeze slowly, this will give the salt more time to get expelled from the ice. If you want to make sure that all the salt is out of the ice, you should remove the ice, let it melt in another container and repeat again. I you want to read more, look .

Erik


(published on 02/04/2013)

Follow-up on this answer.