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Goals

There are a few things that I'm looking to do:

  1. Separate salt from seawater via some evaporation technique.
  2. Separate the each of the major salts from the resulting sea water to get each into their purest possible form.
  3. In particular--and if possible--I want to try and separate any iodine-containing salts from the salt water.

General Information

As I've found, salt water is composed of much more than just $\ce{NaCl}$. According to Britannica, 99% of all sea salts are composed of the following ions by weight: $\ce{Ca^2+, Mg^2+, K+}$, and $\ce{Na+}$ cations, as well as $\ce{Cl-}$ and $\ce{SO4^2-}$ anions (they have a table showing concentrations of all of these ions). There are many more molecules and ions to find to find in the ocean, but these are the major ones in terms of weight. With respect to iodine (you'll see why this is relevant later), I've found other sources that say that iodine is one of the more abundant micronutrients in seawater.

These dissolved ions, without the presence of water, can combine with themselves and other substances found within seawater to create salts including calcium carbonate, gypsum (hydrate of calcium carbonate), sodium chloride (halite), potassium chloride and magnesium chloride (source). Note the way that the salts are separated by solubility here.


My Plan (WIP)

First, I'm going to get a boat out into the middle of the ocean and get a few liters of sea water--ideally, as much as I can take.

Then, I'll reduce the solution until only particulate matter is left, either by evaporating the sea water outside with the sun and/or boiling the seawater in batches over a stove. Once the particulate matter is isolated, I could dry it further in an oven. I'm not sure about any of the advantages or disadvantages with these methods aside from power consumption, so I'll make more than one batch and subject each of them to different procedures so as to see what kinds of yields I get for each batch.

Finally, I'll have to separate the salts somehow, and this is where I'm lost. I have a couple of ideas for doing this:

  1. Using a microscope, I could separate crystals with visually different shapes from others. I would like to avoid this, since it seems both inefficient, imprecise, and time-consuming. Plus, I don't own a microscope.
  2. In one of the sources above, they say to separate the salts by solubility. I have never separated soluble solids before by differing degrees of solubility, so this would be new for me, since I wouldn't be able to just dissolve a completely insoluble solution in water and filter the concentrated particulate from the water. However, this seems like the most reliable method I could find for separating sea salts, so I think this would be the best method for doing this.

Tl;dr, I plan to make my own sea salt by getting salt water from the ocean and evaporating the water out (either via boiling or leaving it out in the sun) until only salt is left. Although, instead of using the sea salt as is, I want to see if I can separate it to see what particular kinds of salts are left behind. In particular--and if possible--I'm looking for iodine salt, to see if I can make my own iodized salt from just seawater. However, I don't really know how to separate water-soluble solid substances from each other, and I don't know if I'll even be able to obtain any salt with iodine in it, so I'm looking for any tips, guides or procedures for doing this.

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    $\begingroup$ Not all sea water is the same. If you want iodine salts, you might need to start with some that is high in iodine. OR, perhaps better, start your experiments by acquiring some sea salt (ie flakes produced by evaporating sea water which saves a step in your experiment). $\endgroup$
    – matt_black
    Feb 20, 2023 at 21:47

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Sounds like you're on the right track -- but rather than separating crystals by hand, use the difference in solubility of salts to make the work easier.

In commercial salt evaporation ponds, with a concentration gradient, the least soluble salts will precipitate first. This is perhaps the least work-intensive way to separate the various salts. So you might try letting the brine slowly trickle down an incline in the sun, and see what precipitates out at various places. This Wikipedia solubility table might give you an idea of what will precipitate, knowing the concentrations of species in sea water, for example. BTW, this may be used to recover the now-valuable lithium from brines.

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