Having watched Ganhdi, the Indian's of India showed civil disobedience to the British by making their own salt. They did this by continually evaporating sea water.
Sea water cannot help but have all types of ionic salts in it. Probably has dirt and insoluble elements too.
But for instance, aluminum chloride is a "salt" and is ionic, so it dissolves in water. Since all the sewage and chemicals flushed down the toilet in almost any country eventually end up in rivers which invariably end up in the ocean, then all that "stuff" is in the sea water.
So yes, sea salt is probably cleaned by filtering out insoluble elements, it could also be "washed" by using some cold solvent in which the salt is not soluble. This is a well-known technique in chemistry to purify a compound or molecule(s).
Anyway, sea salt with have trace ionic "salt" elements in it. The amounts differ according to the area from which the sea water is taken, and probably the technique used to create the sea salt for sale. For sure, it will have some potassium chloride (KCl) in it, just to name one salt that isn't particularly sodium chloride (NaCl), along with the Aluminum Chloride, and just so you know, salts don't necessarily have to have a "chloride" in them. Aluminum sulphate is also a salt. So is dexamethasone sodium phosphate. The list is endless as are the pollutants in the ocean.
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