[Seasalter]

Hello chemistry people, I need your help and knowledge (I hope this is the appropriate forum to post this query in) please forgive any chemistry ignorance i reveal throughout this post as I have a physics background and my chemistry knowledge is very limited to stuff that explodes. I have been researching methods and processes for making edible sea salt crystals from sea water for my own use. I want it be safe and clean, so that in the case that I do give any to friends or family, i know there isn't anything a bit ropey in there.
 So far, I have researched several commercial producers and their methods. However as you would expect they are kind of vague with exactly how they do it. One person who produces in America basically collected sea water, poured it through a 50 micron filter- reasons that algae add to the taste, although algae is generally larger than that? and then, puts it in settling tanks before pouring it in to large trays to dry in the american sun. He did not state if he did anything else with the solids produced, so i assume that is his finished product, as i'm not sure what he could do after that point to separate the solids formed from the salt.

Cornish sea salt, collect sea water which is ~3.5% salt and reduces the solution to a 25% salinity (which i believe is the max limit for water) then slowly heat it, allowing the salt crystals to form and sink to the bottom, which are collected before other salts such as magnesium and potassium form because they add a bitter taste. Then the salt is dried. They also say the salt contains 60  minerals. It is stated however, they filter the water 3 times but no more information is given at which stages or what filter sizes are used.

The last methods i found was literally just boiling sea water on a stove until all the water is evaporated after putting it through a rough sieve. This i imagine to be the least desirable but (logically safest due to boiling?) methods. Reasons cited against this is potential to 'scorch' the salt and previously mentioned other salts forming to subjectively ruin the taste, as well as not removing any unwanted finer solids

I'm planning to use North sea water near where i live, which is rated at excellent water quality. Collecting away from any outlets

This is my current rough method so far which is basically a combination of the 2 commercial methods:

1. Gather sea water
2. Pour through 50 micron filter
3. Let it settle
4. Heat solution until 25% salinity
5. Transfer into another larger surface area container to heat slowly - remove salt crystals that fall to the bottom of the solution
6. Dry salt under grill or oven bake. (i live in the UK, so am unable to dry outside)

As far as i know salt is anti bacterial due to osmosis, but i am concerned with other undesirables that might be lurking in the sea water such as viruses or suspended particles. Is a 50 micron filter really sufficient? from my research sea salt is 0.35-0.5 microns. 50 microns seems like it might be letting through some undesirable stuff, however i can't seem to find the composition of North sea sea water. Would there be anything gained (or lost) filtering the water again with a finer filter after making it more concentrate after step 4. Would the salt ions have started to form precipitate by that point and i may be filtering them out? I'd like to retain the latent heat from step 4 to 5 to make the process more efficient and eco friendly - any suggestions which could improve the process in that respect are also welcome. Any input your have about filters size, potential process/method, the nature and behaviour of salt ions during the process (like when do the 'unwanted salts' start to form into crystals) or just general things i should be aware of would be greatly appreciated.

Thanks a lot, Aaron

[AWK]

https://www.salinedellalaguna.it/en/

the only problem is good sun and sufficiently clean sea water.

[billnotgatez]

Can we question the purity of sea water with the advent of industrial pollution and garbage / trash dumping.

[Borek]

Can we question the purity of sea water with the advent of industrial pollution and garbage / trash dumping.

We do it all the time. We have methods of determining whether sea water in a particular place is pure enough for a given application. We can also relatively easy check level of contamination of the final product.