dodecahedron
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Recrystallization of water?
I'm an amateur in the extreme, and I don't have any formal chemistry education. But I got to wondering: could water be purified by recrystallization?
Obviously it'd have to be something like a low-freezing alcohol or similar. Or is my entire line of thinking flawed?
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Sigmatropic
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Perhaps it can, but to what end? Demineralization with ion exhgange resins gives water which is suitable for almost all purposes and is hard to beat
efficiency wise.
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Texium
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Thread Moved
12-11-2019 at 15:28 |
Sulaiman
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Water as ice crystalised from water is purer than the starting water.
If you have free cooling (e.g. winter in the northern hemisphere)
you could slowly freeze water, and collect the (e.g. first 1/4 volume of water converted to) ice,
then recover the water when the ice melts.
This would remove some of the dissolved gasses,
and much of the dissolved salts.
I have not tried this myself, but I may give it a try this winter.
I may also try heating the melted ice water to remove dissolved gasses,
not free, but a lot cheaper than distillation.
https://www.google.com/search?q=purification+of+water+by+fre...
CAUTION : Hobby Chemist, not Professional or even Amateur
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Pumukli
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Ice wine is made in a similar process: slow freezing of regular (12% alcohol) wine and filtering off the ice (water) crystals from the slush yields a
very strong wine. (Alcohol content can be raised well over the original 12%) this way. 
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dodecahedron
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Quote: Originally posted by Sigmatropic  | | Perhaps it can, but to what end? Demineralization with ion exhgange resins gives water which is suitable for almost all purposes and is hard to beat
efficiency wise. |
I should've mentioned this in my initial post--I don't have any particular application in mind. I know distillation/deionization is a much more
practical way to achieve the same thing. I'm just trying to get a better grasp on the mechanism of recrystallization.
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dodecahedron
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Huh. There's a thought: recrystallizing water from...water. I know ice tends to be purer than the parent water. That's interesting.
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MrHomeScientist
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Not everybody has ion exchange resins at home.
It should work the same as any other recrystallization, by concentrating impurities in the leftover liquid. It's an interesting idea to explore, and
could make a good science fair project (if you're in that age range). You could buy a TDS or conductivity meter and test the water pre- and
post-purification, and compare that against other methods like filtration (using, say, your fridge water filter) and distillation. Sure it may not be
as effective or fast as other methods, but I think it's worth at least trying a few experiments.
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j_sum1
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It is common knowledge that ice floes are lower salinity than the sea they float on. They have been used for drinking water: particularly old ice
where there has been some freeze-thaw action on the surface.
This is different from regular recrystallisation in that it is the solvent that is being purified and not the solute.
The method is used for concentrating acetic acid (glacial acetic acid). Also hydrogen peroxide. It has implications for casting metals. And you should
look up "zone refining" of metals if you are interested in that kind of thing. If I was going to purify my scrap lead, that is what I would do.
To fully understand the process and why it works, a phase diagram is your friend.
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