[WARIV]

I want to order a test that list the percentages of dissolved solids in a water sample. Is there an official name for this kind of test?

I am not looking for TDS, but rather the individual components.

[Borek]

No such test as far as I am aware. This is quite complex analysis, not something that can be done by simple means.

[WARIV]

Thanks for the feedback.

Would it be too much trouble to ask a few more questions in regards to my root problem? Perhaps I am going about things the wrong way? I am not a Chemist, but i do believe what I am trying to ascertain is within my grasp.

My root issue has to do with the solubility and precipitation of solids from a water source. Wasn't sure which forum to post in. Inorganic/General if I had to render a guess?

[John623]

Is this not something that can be done using a mass spectrometer?

[Arkcon]

Water testing is a diverse topic, but there are plenty of organizations that will offer you an answer.  But you have to ask what you want to know, and what your application is.  Companies will gladly test your well, as an example, to determine the levels of toxic minerals or common pesticides, if that's what you want to know.

Is this not something that can be done using a mass spectrometer?

This is exactly the problem we're facing -- what are you assaying for?  What answer will you hope to get with your method?

[WARIV]

Ok, Here is the deal. I make Sea Salt. I want to make better Sea Salt.

The problem is probably pretty simple for someone with the correct experience.

Sea water is composed of several components beyond Water and Sodium Chloride. Some of the other major players are Calcium, Potassium, Magnesium, and Sulfate. These other substances make the salt taste bitter. It's not a huge deal, but to a salt connoisseur it is noticeable.

How to extract pure NaCl?

Well, I boil down the seawater. Eventually it will reach a saturation point that Calcium Sulfate CaSO4 precipitates out. I can see this change physically as the water will turn "murky".

I then filter the Solid CaSO4 out of the water and continue to boil. NaCl is next solid to precipitate out.

[Here is where I need help]

When to stop precipitating NaCl and harvest? Needs to occur before Magnesium and Potassium based solids start precipitating. I cannot visually determine this point while producing the salt.

Now, I will repeat, I am not a chemist. I am standing on the shoulders of others before me. I've done much research into the topic and the averages are as follow.

1.) CaSO4 will begin precipitating out when sea water is reduced to 27-28% of its volume. (This is visible)
2.) NaCl will precipitate as the solution is reduced down to 10-12%
3.) Harvest Product
4.) Discard remaining liquid.


Will I need to know the exact individual percentages of magnesium, calcium, potassium in order to calculate when to stop producing NaCl?

I am just the type of person who likes to be a little more exact. I want to learn the math behind this process. Here is a great document that is almost exactly what I do:

http://nzic.org.nz/ChemProcesses/production/1H.pdf

[Borek]

You will never get pure salt this way, that's why it is later further processed in vacuum evaporators.

Most important thing you will need to learn about is the solubility product. However, brine is so concentrated, calculations are extremely difficult because of the high ionic strength of the solution.

Yes, knowing exact composition of the starting solution will help to some extent, but the sea water from different places is quite similar (to the point there is a well known recipe for "standard sea water").

[Arkcon]

What you are doing is called fractional crystallization, its a pretty well known concept.  Basically, you will stop making sodium chloride, when you're done.  That sounds like sloppy English, but it is true.  You won't get every last bit of NaCl, leaving behind all other salts, like you did when you precipitated calcium sulfate.  You'll simply get most of it, and rinse the rest of the waste free.  If this process is meant to be food grade, taste a bit of your calcium sulfate on the tip of your tongue, you'll see that some of you NaCl has traveled with it.  Likewise, the best, NaCl you produce will have some other salts in it.

[WARIV]

All, Thank you for the replies.

I realize I will never create a chemically pure NaCl. That was my fault with how I worded my scenario. In fact, a small amount of other substances is what gives various salts their unique flavors. I was just a on a quest to extract as much of the product as possible while mitigating the inclusion of other substances. I'll try my hand at the math using the "general" makeup of seawater.

I'm happy to know the name of the process though! I'll definitely do some more research on Fractional crystallization.

[Intanjir]

You should just do the analysis yourself.
You could add additional calcium in some form to precipitate out remaining sulfate. What forms do you think might work?
Since calcium and magnesium are chemically fairly distinct from sodium and potassium(different column from them in the periodic table) you can suspect that many compounds formed from them will have very different solubilities.
Keeping everything simple and ionic this just amounts to finding an anion which when combined with magnesium or calcium will precipitate out but when combined with sodium or potassium would be soluble (or the other way around).

Distinguishing sodium from potassium is a little harder since they are in the same column. But then again Calcium and Magnesium were in the same column... and they were easily distinguished. Now given that the solubility of potassium chloride is very close to that for sodium chloride one might well question how much potassium you are removing in your process. Indeed if all you had was a solution of sodium and potassium chloride and you tried to fractionally crystallize you would have little success at separating them. However this is not all that you have...

Anyways keep in mind that whatever methods you come up with don't have to be perfectly precise if all you really need is a tool that lets you optimize your process.

[WARIV]

There is another substance that can be added to the water to act as a catalyst for precipitation. However, the name is slipping my mind at this moment. The big salt companies use it.

I can't travel down that road though. We are trying to keep the process as natural as possible. I understand that it will eventually come out of the water, buy my clients might not.

What makes this work is that my two major resources are more or less free. Sunlight and Seawater Keeps my margins high.

[Arkcon]

Actually, the common ion effect is used to make the purest salt from a concentrated brine solution. Hydrogen chloride gas is bubbled into a saturated solution.  As the HCl dissolves, making dilute hydrochloric acid, the sodium chloride has to precipitate.  I'm left assuming the HCl is evaporated off the precipitated crystals, and so doesn't contaminate final product.  But I really don't think you want to go that route.

[Intanjir]

Carbonate is the anion that can be used to precipitate magnesium and calcium.
The companies use sodium carbonate which I guess isn't natural enough for you.
In principle carbonate could be obtained 'naturally'. It's just the carbon dioxide in the air.
However it won't work on its own. You can't precipitate out Magnesium Carbonate by adding Carbonic Acid to Magnesium Sulfate.

Limestone is fairly natural. It can be dissolved by Carbonic acid to form Calcium Bicarbonate.
Calcium Bicarbonate is more soluble than Calcium Sulfate, so if you add enough Limestone and Carbon Dioxide you can remove a great deal of the sulfate.
Drying everything should convert the soluble bicarbonates to insoluble carbonates.
Adding water again should then yield a solution of Sodium/Potassium Chloride with only small amounts of Magnesium Chloride and Sulfates.

That's my hypothesis anyway.
If limestone isn't natural enough for you then seashells would work.

I doubt its at all economically practical, but marketing it as sea salt purified with sunlight, air, water and sea shells might work.... and if you are real cynical you can throw in that it sequesters carbon dioxide.

[Arkcon]

. and if you are real cynical you can throw in that it sequesters carbon dioxide.

I gotta love that angle.