I’m sure its harder than mining, but how and why?
In: Technology
It take _a lot_ of energy to boil water. One BTU is the amount of heat energy required to raise one pound of water by 1ºF. Water weighs 8.33 pounds per gallon so we can calculate that one gallon of water requires 8.33 BTU to raise the temperature 1ºF. So, to raise water at “room temperature” of 70ºF to boiling it takes 1,182 BTUs of energy.
Seawater is about 3.5 percent salt by weight, which means a gallon of water (eight pounds) should yield about 4.5 ounces of salt. So, excluding the costs of gathering, filtering and collecting the salt, it would take ~260 BTU to get one ounce of salt.
Now, that isn’t that much – about 1/3 of a cent per ounce (based on using natural gas at about $15 per 1M BTU) – but that is still much more energy than it required to just mine salt in salt deposits – which are plentiful.
**Edit**: While 1/3 of a cent doesn’t seem like much, it is a lot when you factor in how cheap salt is. A 40lb (640 oz) bag of salt costs about $5, which works out to a little less than 4/5 of a cent per oz. The cost of energy to boil seawater would be almost half the cost of the salt alone if we extracted from sea water
This is the same reason that desalination plants aren’t used to get drinking water in areas near the ocean – while it _can be_ (and sometimes is) done, it is usually much cheaper to just pipe water in from other places than expend the energy required.
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