dann2
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Seperating Nitric from Phosphoric acid
Hello,
I have obtained a cleaning product that contains Nitric acid + Phosphoric acid.
Can I simply distill out the Nitric acid. I do not want the Phosphoric acid.
(I once tried to make Lead Nitrate with the product + Lead Metal and obtained a large amount gray ppt. I thought at the time the product contained
Nitric + Sulphamic acid but I have subsequently been informed that it is Nitric + Phosphoric)
Cheers,
Dann2
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bilcksneatff
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Nitric acid boils at 83 C, phosphoric boils at 158 C. You might be able to seperate them by fractional distillation.
Salt (NaCl) reacts with phosphoric acid to form HCl and NaH2PO4. I'm not sure if the NaCl will react with the nitric. If it doesn't, then you can then
seperate the nitric by placing the mixture in an all glass retort.
I think it would be easier to combine sulfuric acid and NaNO3 to get HNO3 and NaHSO4. You also would place this into an all glass retort to seperate
the nitric.
[Edited on 19-11-2007 by bilcksneatff]
[Edited on 19-11-2007 by bilcksneatff]
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The_Davster
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Is there water in there as well? What are the concentrations of each?
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not_important
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The_Davster asks some important questions.
Assuming the likely condition that this is a fairly dilute solution of the acids, you won't be distilling 100% nitric acid boiling at 83 C, but rather
the azeotrope boiling at 120,5 C This means that you'll boil off water until the nitric acid concentration gets high enough that the azeotrope begins
to distill. If you don't have some degree of fractionation in your distillation setup you'll see a slow rise from around 100 C to the 120,5 of the
azeotrope, with dilute nitric acid distilling over at the intermediary temperatures.
If the concentration of nitric acid is very low, it's probably not cost effective to buy that product. Better to find a source of a nitrate and
sulfuric acid.
Another questions is "what else is in there?" Much organics could spell trouble, but a just dye to colour it isn't likely to be a problem.
Don't heat too hot while distilling, hot phosphoric acid will attack glass and etch it.
Adding chlorides to that product gives a mixture that acts like aqua regia. You'll lose nitric acid, and have to deal with the Cl2 and NOCl boiling
off the hot acids. Even if they didn't react, the constant boiling mix of HCl and water boils at 108,6 C, close enough to that CB nitric to
complicate separation. Phosphoric acid doesn't boil, but ratherr starts to lose water, you can run it up to red heat without much but water coming
off.
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S.C. Wack
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bilcksneatff, you're going to have to do better than just quote from wikipedia...
dann2, have you looked at say an MSDS to see what else might be in there? I get the feeling that there may be little of either acid in the product, or
at least the HNO3, and that the HNO3 won't be coming over at 83C.
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dann2
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Hello Folks,
Thanks for replys.
Firstly the unmentioned third ingredient....water
The product has quite high conc. of Nitric acid AFAIK, about 30-40%. Don't know about the Phosphoric acid content.
I do not want/need fuming or high conc. Nitric, I would be more than happy with dilute Nitric so long as other crap (only Phosphoric acid AFAIK) stays
behind.
The product has to be diluted when used, you do not use straignt from the can. It is used for washing milking machines once in a while. I'm no
microbiologist (spelling?) but I guess it burns the ass off any linguring bacteria.
The product, in the past, was a simple solution of Nitric acid + water (40% Nitric).
Will try distilling.
Dann2
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BromicAcid
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As Not_Important pointed out, organics can be trouble. Superficially because they will oxidize/nitrate/etc and generally make a mess of your
distillation pot. However from experience one of the most frustrating organic components are surfactants, especially when distilling or driving off
water. I once purchased some phosphoric acid cleaner, 40-50% Phosphoric Acid with the balance water and 0.01% surfactants or something similar to
that. When heated the mess it created was unreal, lots of foaming over, solidifying bubbles, sputtering, unpredictable. Watch out especially in the
beginning of the distillation but I don't see any problem distilling out your HNO<sub>3</sub> from the phosphoric acid otherwise.
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The_Davster
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As Not_Important has stated, fractionating will allow you to obtain the azeotrope, around 69-70% nitric. So called 'concentrated' nitric acid.
But as you do not want or need conc nitric acid, just distill that mix at 120C for a while, making sure not to get too hot to boil the phosphoric or
etch your glass. You should end up with relatively pure dilute nitric acid, somewhere greater than 30-40 as the phosphoric has been removed.
Or if you have lots of something like calcium nitrate you could precipitate out calcium phosphate leaving a nitric acid solution. Check Ksp s first
of course.
[Edited on 19-11-2007 by The_Davster]
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12AX7
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I doubt it, phosphoric acid isn't nearly as acidic as HNO3. It would be almost entirely protonated, so the best you could do is calcium
dihydrogenphosphate (Ca(H2PO4)2), which isn't all that insoluble.
If you wanted to go give it the whole aqueous treatment, sure, you could neutralize, precipitate phosphate (tribasic) and get nitrate in solution, but
that's a lot more hassle. Distillation, assuming the glass doesn't get etched badly, is the way to go.
Tim
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not_important
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Tim's correct on getting calcium dihydrogenphosphate and its solubility. You could add enough Ca(NO3)2 to get to CaHPO4, and just distill, picking up
2/3 of the phosphoric acid as nitric. The non-volatility of H3PO4 (and its salts) lets you drive the reaction to the distillable HNO3.
Heating to 120 to 130 C shouldn't cause etching, SFAIK.
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dann2
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Hello,
Forgot to mention product.
It is Acid-O-Phy (used to be called Acidophy).
The MSDS says it is >30% HNO3, and less than 5% Phosphates.
(does not actually mention Phosphoric acid).
Dann2
[Edited on 25-11-2007 by dann2]
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dann2
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Hello,
I started to distill this product. It starts to come over at 100C. (Thermometer in still head) The temperature rises fairly steady as the product
comes over. When all the product is coming to an end in the boiling flask the temperature at the still head is 120C.
There is nothing staying behind in the flask (if I boil all off, the still head reads 120C).
The product is described in the materials safety data sheet as 30% Nitric acid and less than 5% phosphates. (It does not say Phosphoric acid).
There is no etching of the boiling flask.
I am leaving behind about 30ml in the 250ml flask. (The Phosphates??)
Is there any quick way I can check for phosphates in the distillate.
MSDS attached.
Cheers,
Dann2
[Edited on 23-1-2008 by dann2]
Attachment: Acid-O-Phy.pdf (11kB)
This file has been downloaded 646 times
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garage chemist
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Phosphates and Phosphoric acid will not distill over. They will dehydrate to polyphosphates and polyphosphoric acid.
I have done this myself to get metaphosphoric acid as a dehydrating agent.
The 158°C "boiling point" (probably from a worthless MSDS) of phosphoric acid is most likely the temperature at which it will start to split off
water!
You can be completely sure that your distillate is free of phosphates.
And the 120°C boiling point indicates that 69% azeotropic HNO3 is coming over at the time the thermometer shows that temperature.
A precipitate from lead and your HNO3 could be either actual lead nitrate crystallizing because of saturation (it can easily appear as a fine powder
that way, I have seen this myself with pure HNO3) or hydrous SnO2 from strong contamination of your lead with tin.
[Edited on 23-1-2008 by garage chemist]
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DerAlte
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I find myself totally in agreement with garage chemist only. The best information I have is CRC that states that orthophosphoric acid boils at 407C
(no pressure stated). However, I believe this to be incorrect at least at 760mm Hg.
Other sources state that it is converted to metaphosphoric acid at around 260C, by expelling part of the H2O
H3PO4 --> HPO3 + H2O
Further heating converts this to pyrophosporic acid
HPO3 --> H4P2O7 (somehow!) +H20
Pauling (General Chemistry) states, however that metaphosphoric acids are obtained by heating either ortho or the pyro acid and are "condensed" acids
of general formula n(HPO3), and the heating of ortho acid produces the pyro 2H3PO4 <--> H4P2O7 +H2O
Whatever ( I like Pauling's reasoning on aestetic grounds and after all he was a Nobel Laureate). The point is that none of the phosphoric
acids is volatile. Eventually, very strong heating will produce P2O5.
Which tells us that heating phosphic and ntric acis will cause the azetrope HNO3/H2O to distill over at 120C after the concentration in the liquid
gets to that level.
This is moot because Dann2 says the substance he has contains phosphates not the acid. In that case, barring other contaminants being reactive with
HNO3, he should get fairly pure nitric acid at 68% for the 120C fraction.
Orthophosphoric acid is a most useful substance because of this property. It can release every volatile acid from its salts. In days long ago I had a
retort (how many of you have ever seen one, or touched one, let alone possessed one - a thing of real (chemical) beauty!). I tried reacting Na2SO4
with phosphoric acid. Sure enough, H2SO4 distilled over (BP about 340C IIRC) after water was expelled.
Der Alte
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woelen
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Phosphates can be detected with molybdates, especially the ammonium salt. Dissolve a molybdate salt in a solution of ammonium chloride or ammonium
sulfate. Even better to use ammonium molybdate. Add this to the acidic solution with the phosphate.
Molybdate salts can be obtained easily. Dissolve potteries MoO3 (cheap stuff) in some dilute NaOH and you have your molybdate.
If there is no phosphate, then the solution will remain colorless. If there is phosphate, then the solution turns yellow and at sufficiently high
concentration, a fine crystalline precipitate of a yellow ammonium molybdophosphate complex is formed.
At very low concentrations of phosphoric acid, the yellow color may become too faint, but then still you can detect phosphate. In the presence of
phosphate, molybdate(VI) is easily reduced to a deep blue compound with a mild reductor like sulfite, without phosphate, this blue compound only is
formed when somewhat more vigorous reductors are used.
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chloric1
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Phosphates can also be detected via magnesium+ammonium ions. You get magnesium ammonium phosphate which is then ignited to anhydrous pyrophosphate
and weighed. The is also from Linus Pauling.
Fellow molecular manipulator
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microcosmicus
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| Quote: |
Is there any quick way I can check for phosphates in the distillate.
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For a quick check, try a cation which makes an insoluble phosphate
but a soluble nitrate. A readily available example is Ca++ --- add some
of your product to a solution of some calcium salt (e.g. CaCl2) and look for
a precipitate. The solubilities of calcium phosphates in g/l are as follows:
Ca(H2P04)2.......18
CaHPO4...............0.043
Ca3(PO4)2.........0.02
By contrast, 1290 g CaNO3 dissolve in a liter.
Of course, this test isn't specific to phosphates but that may not matter
for your purposes --- your goal is to purify nitric acid, so anything which
precipitates out but whose nitrate is soluble means some impurity.
If you get no precipitate, pat yourself on the back; otherwise, you might
need to do one of the more specific tests mentioned above. GIven
that industrial phosphoric acid is made by running H2SO4 over phosphate
rock, all sorts of junk could be present.
[Edited on 23-1-2008 by microcosmicus]
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