Why is salt mined when there’s a bunch of it available in the ocean?

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I’m sure its harder than mining, but how and why?

In: Technology

6 Answers

Anonymous 0 Comments

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.

Anonymous 0 Comments

Sea salt takes a lot of space and time to produce.
You have to be able to flood huge fields and then you have to wait for evaporation to remove the water and leave the salt behind.

So basically you need a hot, dry country, a coastal area that can be turned into salt fields and quite a lot of time and effort.

Mining is a lot quicker, takes up less space, and can be done in countries with colder, damper climates.

Obviously there are pro’s and cons to both which is why we see so many different kinds of salt production.

Anonymous 0 Comments

Water loves salt. Getting water to give up salt is hard, so if you can find a place where past sunlight drove the water off to leave salt that saves process energy.

Anonymous 0 Comments

Taking the salt out of the water requires an Evaporation process or “train”. The reason it is harder is because of the energetic demands vs the amount of salt obtained.

Anonymous 0 Comments

1) Not everyone lives near the ocean or a sea.

2) It takes either a lot of energy or a lot of time to evaporate enough sea water to collect sea-salt. Mining deposits of salt already evaporated is often less energy/time intensive.

Anonymous 0 Comments

In Western Australia they use salt pans to evaporate water out of seawater leaving salt behind. They’ve made large shallow inlet ponds that they open for the seawater to come in, then let it sit in the baking hot air to gradually become salt. Due to the high ambient temperature this process is pretty cheap, but you need the right environmental conditions for it to be reliable. Iirc it takes about 2-3 months and obviously it can only be done during the dry season.