Sciencemadness Discussion Board - Nitric acid from ammonium nitrate and sodium bisulfate

Nitric acid from ammonium nitrate and sodium bisulfate

Chemgineer - 5-2-2024 at 04:09

I normally produce nitric acid by dry distilling magnesium nitrate with sodium bisulfate and it works quite well to produce around 50% concentration.

I was experimenting with using some ammonium nitrate as I happen to have some of it, this time I used a 200g of it in 200ml of water and then added 300g of sodium bisulfate.

This worked but it foamed constantly and was a pain, even blocking the neck of the flask towards the end.

Would it be better to dry distil in the same way as I have done above?

andyloris - 5-2-2024 at 08:31

Don't forget that ammonium nitrate decomposes explosively at high temperatures !
I don't think a dry distillation would be a good idea.

Chemgineer - 6-2-2024 at 15:29

I can't make my mind up on whether this would be safe not and have a respect for ammonium nitrate so for the time being have put this on hold.

Sir_Gawain - 6-2-2024 at 19:11

Even with the low temperature method (AN&sulfuric acid) the ammonium nitrate decomposes to some extent, diluting the acid. I've only been able to achieve 85% nitric acid with ammonium nitrate, while the same sulfuric acid with sodium nitrate produced 99%.

chloric1 - 26-8-2025 at 11:22

Quote: Originally posted by Chemgineer

I normally produce nitric acid by dry distilling magnesium nitrate with sodium bisulfate and it works quite well to produce around 50% concentration.

I was experimenting with using some ammonium nitrate as I happen to have some of it, this time I used a 200g of it in 200ml of water and then added 300g of sodium bisulfate.

This worked but it foamed constantly and was a pain, even blocking the neck of the flask towards the end.

Would it be better to dry distil in the same way as I have done above?

You have posted a couple of places on this forum regarding dry distillation of magnesium nitrate with sodium bisulfate to obtain a 50% nitric acid. Question I have for you is that do you use 2 moles of bisulfate per one mole of magnesium nitrate? Or do you find you need a stoichiometric excess of bisulfate to complete the reaction. Magnesium is CHEAP for me but I have not purchased yet!

teodor - 28-8-2025 at 00:19

Molten ammonium nitrate should be stable at some ranges of temperatures, but if the temperature increases the the nitric acid part of it starts to oxidise tha ammonia, and at some temperature the reaction will be very violent, like jet from a rocket, but it is not the same as explosion. You can look how it happens on videos or try experiment with a little of ammonium nitrate on the bottom of a test tube. Make sure the salt is pure. For this start with a tiny amount. It is not bad to check how it behaves in mixtures if you really start with a very little amount first. (I think the worst case is the presence of nitrite, nitrite + NH3 = explosion).

Violent decomposition could be converted to explosion if you put the salt in a closed space, like some metal capsules.

The standard test to check wether salt is heat-sensitive is to make a metal piece red-hot and then drom some crystalls on that. This termal shock should reveal what can happen on heating in the worst case.

Generally, in the molten state ammonium nitrate properties are the same as solution of nitric acid: NH4NO3 = NH3 + HNO3, this is not a salt anymore but a solution of 100% nitric acid in liquid ammonia. That's why the behaviour is different from e.g. NaNO3 in which you don't have nitric acid but only the nitric anion. Also, this is water-free nitric acid, so you can think about that as WFNA solution in non-aqueous solvent.

The proposed method NH4NO3 + bisulfate is not the best because
1) (water-free) nitric acid at high temperature is decomposing
2) ammonium sulfate is also decomposing at similar temperature to ammonia, water and SO3, so you (probably) unable to distill HNO3 from there.

Also for the yield it is always better to distill HNO3/water mixture, it is more stable than the pure acid.

I would buy another nitrate, they sell it as fertilizers or food additives, and I would keep NH4NO3 for other experiments where other nitrates doen't work (all kind of reactions in water-free nitric acid in presence ammonia as a solvent). But if you absolutely need you can convert NH4NO3 to some other nitrate:

NH4NO3 + MeOH --(water solution, heat)--> NH3 + H2O + MeNO3

(for example Me = Na) and than use it for making nitric acid.

Also I think there is a far better method of utilization your NH4NO3 by reaction of heating the salt mixture:

3 K2HPO4 + 3 NH4NO3 = (KPO3)3 + 3 KNO3 + 3 H2O + 3 NH3

You will get 2 very useful salts - potassium trimetaphosphate and potassium nitrate. They could be separated by crystallization. Or you can heat it further, at higher temperature another reaction will proceed:

4 (KPO3)3 + 12 KNO3 = 6 K4P2O7 + 12 NO2 + 3 O2

You will get quite pure stream of NO2. Both (KPO3)3 and K2P2O7 are powerful dehydrating agents which could be used as an alternative to P2O5 in the big range of reactions.

Also, as you see that 4 to 1 proportion of NO2 and O2 is ideal for

4 NO2 + O2 + 2H2O = 2 HNO3

So, you can make HNO3 from NH4NO3 by quite different way

[Edited on 28-8-2025 by teodor]

chloric1 - 28-8-2025 at 01:52

Yes I can confirm! I make my own ammonium nitrate via calcium nitrate and ammonium sulfate double displacement. The clear filtrate dissolves some of the calcium sulfate precipitate so you will get gram quantities of gypsum crystals as you concentrate the ammonium nitrate solution. Sometimes, I boil off most of the water and I have a clear liquid I think is a saturated ammonium nitrate solution only to find it forms a solid brick on cooling! It can be melted and handled safely if you keep it under 200 °C and don’t let combustibles near it. Other nitrates are better for nitric acid production

Chemgineer - 28-8-2025 at 04:56

Quote: Originally posted by chloric1

Quote: Originally posted by Chemgineer

I normally use 200g of magnesium nitrate (bearing in mind this also contains water) and 330g sodium bisulfate which I think is a slight excess of sodium bisulfate.

[Edited on 28-8-2025 by Chemgineer]

chloric1 - 28-8-2025 at 11:44

The bisulfate ion is regarded as strongly acidic but just barely so I figured an excess could only help. Thanks for your reply. I’m already producing nitric acid for like $8 a liter this will make it even cheaper! Also, this would free up sulfuric acid for just concentrating the acid as opposed to being consumed as a bisulfate salt. In fact using 93 % drain cleaner sulfuric acid to concentrate nitric acid also destroys the additives in the drain cleaner so you can boil down to crystal clear 93 or 98% sulfuric acid since the NO2 and nitric acid are such vigorous oxidizers.

Chemgineer - 29-8-2025 at 05:59

Quote: Originally posted by chloric1

The bisulfate ion is regarded as strongly acidic but just barely so I figured an excess could only help. Thanks for your reply. I’m already producing nitric acid for like $8 a liter this will make it even cheaper! Also, this would free up sulfuric acid for just concentrating the acid as opposed to being consumed as a bisulfate salt. In fact using 93 % drain cleaner sulfuric acid to concentrate nitric acid also destroys the additives in the drain cleaner so you can boil down to crystal clear 93 or 98% sulfuric acid since the NO2 and nitric acid are such vigorous oxidizers.

How are you concentrating nitric acid with sulfuric? Are you just mixing them and distilling and the sulfuric will hold onto water?

teodor - 29-8-2025 at 06:39

[Edit] Oh, I was wrong
vvvvvvvvvvvvvvvvvvvv

As I remember going up to 98-99% HNO3 requires the residual concentration of H2SO4 close to 82-85%, so you can calculate how much you need based on the initial concentration of H2SO4.

^^^^^^^^^^^^^^

I checked the literature and if the residue H2SO4 is more than 70% concentration a nitrosyl compound is forming in the source flask which could never be distilled, so you get not the full yield.

According to scientific journals to get max concentration H2SO4 must be added draduatelly during distillation to achieve both yield and concentration. But I believe you don't ask about water-free acid, also you can probably search the forum.

And, of course, more diluted HNO3 need to be concentrated to azeotrope first.

Of course, this method is good if you can easily get concentrated H2SO4 (92-96% is recommended). It's not always the case, so there could be other methods for that case.

Also it is good to remove chloride ions because I think they are partially the reason of decomposition on highest concentrations.

Also,

there was question about nitrate/bisulfate ration. The best yield when the solid residue has 28-35% calculated as pure H2SO4. This is according to experiments published in different scientific journals in the beginning of 20 centure.

The mechanism of action H2SO4 on alkali nitrate is not so simple. The actual component which cause nitrate decomposition, let say, NaNO3 at 155C is NaH3(SO4)2, so mixture of bisulfate and free sulfuric acid can do job better than bisulfate or sulfuric acid alone.

[Edited on 29-8-2025 by teodor]

teodor - 30-8-2025 at 05:52

Some missing references to what I had written yesterday to follow SM rules:

https://doi.org/10.1021/ja02124a037
https://doi.org/10.1021/ja02033a013
https://doi.org/10.1021/ja02017a003

Those publication covers such thing as difference between distilling HNO3 from mixtures of nitrate and sulfuric acid vs nitrate, sulfuric acid and bisulfate. It happens than even when free sulfuric acid is used the forming of the stable compound MeH3(SO4)2 stops distillation of the half of the acid untill quite hot temperature which was carefully investigated for the case Me = Na. So, for the case of NaNO3 usage of bisulfate alone would be probably the waste of chemicals.

I can guess that for some other nitrates like magnesium you can use bisulfate, but I can explain it only that in this case magnesium sulfate is more stable than sodium bisulfate. But you never can use it as a general rule to make possible to produce nitric acid with any nitrate by bisulfate.

[Edited on 30-8-2025 by teodor]