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Author: Subject: Sodium chloride and sodium nitrate seperation.
danieldavies
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[*] posted on 12-10-2021 at 00:24
Sodium chloride and sodium nitrate seperation.


How would I go about separating a solution of sodium chloride and sodium nitrate? I want to reuse the sodium nitrate for making nitric acid.

I dissolved silver in nitric acid to form silver nitrate. I then added sodium chloride to precipitate silver chloride. I decanted the solution from the silver chloride. This solution is sodium nitrate contaminated with sodium chloride?
I am looking to get a pretty pure product back?
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j_sum1
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[*] posted on 12-10-2021 at 00:58


Why bother? Use it as is.
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danieldavies
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[*] posted on 12-10-2021 at 01:13


I do believe, when making nitric acid the bisulphate method, salt contamination can form hydrogen chloride which will get into the nitric acid.
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B(a)P
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[*] posted on 12-10-2021 at 01:28


Boil it down until you get the first crystals then chill it and filter out fairly pure sodium nitrate.
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j_sum1
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[*] posted on 12-10-2021 at 01:58


Quote: Originally posted by B(a)P  
Boil it down until you get the first crystals then chill it and filter out fairly pure sodium nitrate.
NaCl has a fairly flat solubility curve. It might not be easy to get all of it.
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danieldavies
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[*] posted on 12-10-2021 at 02:38


Is there a way to remove HCl contamination from HNO3 instead? I am just trying to recycle my chemicals.
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B(a)P
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[*] posted on 12-10-2021 at 02:55


Quote: Originally posted by j_sum1  
Quote: Originally posted by B(a)P  
Boil it down until you get the first crystals then chill it and filter out fairly pure sodium nitrate.
NaCl has a fairly flat solubility curve. It might not be easy to get all of it.


Sorry, what I meant was to make use of that flat solubility curve. I also made the assumption that the OP had mostly sodium nitrate in solution. If the solution is boiled down until crystals first form then cooled the vast majority of the precipitate should be sodium nitrate, which can be filtered out
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Bedlasky
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[*] posted on 12-10-2021 at 04:28


HNO3 reacts with HCl to form nitrosyl chloride and chlorine.



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danieldavies
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[*] posted on 12-10-2021 at 05:29


Are you saying any HCl contamination will gas off as nitrosyl chloride and chlorine?
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Tsjerk
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[*] posted on 12-10-2021 at 14:01


Quote: Originally posted by danieldavies  
Are you saying any HCl contamination will gas off as nitrosyl chloride and chlorine?


Chloride and nitrate can't be easily separated in an highly acid environment like this. The nitrosyl makes that impossible. You can't gas of nitrosyl chloride easily, unless you boil down extensively.

Edit: when boiling down nitrosyl chloride, part of it will decompose to a chloride, leaving the chloride behind in solution. Unless you use a big excess of nitrate.

[Edited on 12-10-2021 by Tsjerk]
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danieldavies
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[*] posted on 12-10-2021 at 23:49


All i want, is to keep chloride contamination out of my nitric acid.
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B(a)P
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[*] posted on 12-10-2021 at 23:53


Quote: Originally posted by danieldavies  
All i want, is to keep chloride contamination out of my nitric acid.


Then use the flat solubility curve of sodium chloride to precipitate your sodium nitrate.
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danieldavies
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[*] posted on 13-10-2021 at 00:38


Can you explain a bit more please?
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B(a)P
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[*] posted on 13-10-2021 at 02:49


Presumably you know how much sodium chloride you have? The solubility of sodium chloride is largely uneffected by temp. Boil your solution down until you have just a little more than would dissolve your quantity of sodium chloride. Then chill the solution down to around 0C and sodium nitrate will precipitate out. You can do a recrystallisation to improve purity
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danieldavies
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[*] posted on 13-10-2021 at 04:39


I don't have a clue on how much sodium chloride is in the solution.
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B(a)P
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[*] posted on 13-10-2021 at 04:48


Did you weigh any of your reagents? Do you have a feel for how much excess sodium chloride was added? If so go from there, if not boil untill you see your first crystals then chill and filter off your sodium nitrate. Using the latter method you may have significant chloride contamination so a recrystallisation is definitely needed.
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danieldavies
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[*] posted on 13-10-2021 at 05:25


Ratio is around 10/1. So 10% sodium contamination at the most. Would a 3rd recrystallisation be of any benefit?
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macckone
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[*] posted on 13-10-2021 at 07:20


Quote: Originally posted by danieldavies  
Ratio is around 10/1. So 10% sodium contamination at the most. Would a 3rd recrystallisation be of any benefit?


Separating sodium chloride and nitrate using water is going to be difficult. Lets look at a solubility graph to understand why.
Keeping in mind common ion effects make this even more complicated.

if you dissolve it in minimum boiling water then allow to cool you should get almost pure sodium nitrate with 50% recovery.
Depending on the purity to you need, it may take a couple of rounds. The second crystallization should be pure enough for most purposes, certainly making nitric acid.


Sodium potassium salts solubility graph.png - 291kB
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[*] posted on 13-10-2021 at 08:16


You can try to distill the mixture of HNO3 and HCl with Pb(NO3)2. I suppose it will precipitate chloride ions as PbCl2. My assumption is based on the fact that distilling HNO3 with AgNO3 is the method of getting chloride-free HNO3. Pb is just much cheaper. But for complete removal, you can try the second run with AgNO3.

Edit.

Of course, as the first step you should add Pb(NO3)2 to your mixture of NaNO3 and NaCl and filter, but a small percent of chloride will stay in the solution (PbCl2 is slightly soluble). Filter it after cooling, it will allow precipitate more chloride.

Update.

PbCl2 you can convert to Pb(OH)2 with NaOH and then use HNO3 to regenerate Pb(NO3)2.

In a case when you have too much NaCl in the starting mixture (which makes no sense of the above procedure) you can try to melt the salt mix. I suppose NaCl will go to the separate layer because its melting temperature is MUCH higher.


[Edited on 13-10-2021 by teodor]
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Fulmen
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[*] posted on 13-10-2021 at 11:15


Wouldn't the common ion effect work to our advantage here? The highly soluble nitrate ion should depress the solubility of the chloride further. So boiling it down should precipitate NaCl first fairly exclusively.



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Tsjerk
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[*] posted on 13-10-2021 at 11:28


Quote: Originally posted by Fulmen  
Wouldn't the common ion effect work to our advantage here? The highly soluble nitrate ion should depress the solubility of the chloride further. So boiling it down should precipitate NaCl first fairly exclusively.


Probably
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macckone
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[*] posted on 13-10-2021 at 12:03


Fulmen,

With only 10% NaCl, he would get nitrate precipitating first.
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[*] posted on 13-10-2021 at 13:05


Quote: Originally posted by danieldavies  
Ratio is around 10/1. So 10% sodium contamination at the most. Would a 3rd recrystallisation be of any benefit?


Maybe you should clarify here: 10 NaNO3 or 10 NaCl?
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papaya
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[*] posted on 13-10-2021 at 15:03


I have a similar problem, since once in the past I've had bought a NaNO3 reagent that turned out to be adulterated with significant amount of chloride (why ???). I've researched a little bit into this problem, read some literature, and it turns out that this particular System is indeed difficult to separate but NOT IMPOSSIBLE. It is described that if a saturated hot solution (by both salts) is cooled down sodium nitrate is precipitaed mostly, while some amount of chloride even can be dissolved back during the process, i.e. chloride forces out nitrate! Also it is known that NaCL solubility is nearly temperature independent! Combining these two facts there is a route for seperation : FIRST we boil down the mixed solution untill significant amounts of precipitate forms (NACL !!!) in still BOILING solution, which is quickly hot filtered and thrown away. SECOND: the filtrate is cooled down to precipitate the NaNO3 this time! Now nitrate is collected and the filtrate sent back to step one (repeated). I've done this myself once for a test and it really worked, but due to much labour I've not continued it to the whole batch. Please report back if you try this yourself. EDIT: This should work well for depleted mixes, rather than something like 90+% nitrate, in that case you will probably loose some nitrate alongside with chloride in the step one. however once your solution gets "depleted"(saturated by both salts?) then you can continue with this method.

[Edited on 13-10-2021 by papaya]
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Fulmen
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[*] posted on 14-10-2021 at 08:39


@macckone: I think papaya is right.

First boil it down until most of the chloride is precipitated. The high solubility of the nitrate should depress the chloride solubility at this point.
Then cool to precipitate the nitrate. As this decreases the sodium concentration the solubility of NaCl should increase (or at least drop less than it normally would), increasing separation.




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