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Q & A: drinking water from frozen sea water

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Most recent answer: 01/03/2013
Q:
is it possible to obtain drinking water from sea water by freezing?
- nadia (age 35)
pakistan
A:
 In principle this is possible. The reason it could work is that the salt ions don't fit well in the ice crystals, so they're left behind in the liquid. When it gets very cold, so that nearly all the water joins the ice, the salt just forms separate salt crystals rather than squeezing into the ice crystals.

If you freeze the water too quickly, however, a lot of the salt can get trapped in little pockets and channels in the ice. Freezing more slowly gives it time to get away from the ice.

Thinking about this as a practical question, in Pakistan I think that the regions with a lot of cold weather and those near the sea aren't so close. So if you have to use a refrigerator or other power-consuming heat pump. there are more efficient ways to do this de-salting. You would use the hot end of the heat pump to evaporate water and the cold end to condense it in a still. The evaporation process does an excellent job of leaving the salt behind, so freezing is unnecessary. This is why snow is salt-free, since it comes from water vapor in the atmosphere.

Mike W.

(published on 01/03/2013)

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