Making Sodium Nitrate from Ammonium Nitrate

[ANFO]

So today I was looking at alternative nitrate salts, because here in South Africa potassium nitrate isn't available in large enough quantities to do anything pyrotechnic with. So I found a way to make Sodium Nitrate from Ammonium nitrate and Sodium Hydroxide(aka caustic soda, lye).

Place 80 grams of ammonium nitrate in a tall container and pour 40 grams of sodium hydroxide on top. Then carefully pour 30mL of water and stand back. It will quickly react to generate ammonia gas and sodium nitrate. Stir the mixture to make sure it's completely reacted and then add another 50mL of water and stir until dissolved. Filter it out and let the clear solution evaporate

This is great and all, but naturally ammonium nitrate isn't available at my local shops either. However, there is an awful lot of limestone ammonium nitrate (LAN) for sale, which is very cheap. This doesn't really help in its current form, as there is limestone in it.

That got me thinking, is there a way to separate the limestone and the AN? The "limestone" in the LAN is calcium carbonate (or agricultural lime). Calcium carbonate reacts with many things, such as CO2 saturated water (soda water), however it always forms a soluble salt which doesn't help in the extraction process.

 

Any thoughts on how to do this? Or would the caustic soda reaction still produce sodium nitrate even if there is still limestone in the mixture? All input much appreciated

EDIT: It seems after some further research that ammonium nitrate is much more soluble than calcium carbonate. Calcium carbonate: 0.15 g/100 mL (25°C) Ammonium nitrate: 150 g/100 ml (20 °C) and 118 g/100 ml (0 °C) .

 

I think if I dissolve the LAN in very cold water, the calcium carbonate will precipitate. I'll extrapolate a graph to try and find the exact temperature at which calcium carbonate is barely soluble at all

EDIT 2: It seems that according to the physics, lime is actually MORE soluble at low temperatures, counter intuitive though it may be. This is a very good thing, because AN becomes more soluble with an increase in temperature, and calcium carbonate becomes less soluble with a increase in temperature. So if I warm some water up to almost boiling and add the LAN, most of the calcium carbonate should precipitate and the AN will remain in solution.

Edited August 15, 2012 by ANFO

[Swede]

I am not familiar with this sort of conversion, so as to whether it works well or not, I can't say. But substituting KOH rather than NaOH as the solid caustic may yield KNO3.

 

Calcium carbonate is just chalk, and indeed it is barely soluble at all, at whatever temp water you use. Traces of calcium carbonate probably aren't going to hurt whatever oxidizer you seek.

 

Be sure you get the molar ratios correct if you do this sort of reaction. The MW of AN is 80.052 g/m, and NaOH is 40, so the ratio described is correct. If you use KOH, use 56.1 grams.

 

You don't need to "add it all at once." This procedure sounds like a recipe for a hot reaction that could turn violent. I'd dissolve the AN in just enough water to dissolve completely, then do the same for the hydroxide, and slowly add the caustic over time, avoiding overheating and vast amounts of ammonia gas. In the end, though, you're going to have a solution heavy in ammonia. Boiling should drive off the aqueous NH3.

 

It's sad that you'd have to jump through such hoops for a benign oxidizer like KNO3, but you gotta do what you gotta do. Don't they have KNO3-based "stump removers" and the like in SA?

Edited August 15, 2012 by Swede

[ANFO]

Theres a video of the guy doing it, including a method using baking soda instead of sodium hydroxide, which definitely looks less dangerous.

http://www.youtube.com/watch?v=hQJhf_24-QM&feature=player_embedded

The nitrate content of LAN is about 28%, so there's a fair amount of lime in there and probably some other micro nutrients like magnesium so I definitely want to try precipitate that out.

 

Sad is definitely the correct word :| But honestly I enjoy the challenge I've been actively looking for stump removers, but I haven't found any KNO3 based ones-yet. I'm actually missioning up to a big nursery on the weekend to see what they have.

Edited August 15, 2012 by ANFO

[taiwanluthiers]

So they don't have potassium nitrate based oxidizers, what about chemical shops?

 

If worst comes to worst you can do it like how they did it back in the Middle Ages, collect them from stale urine/manure...

 

And here I am complaining about the price of perchlorates in Taiwan...

Edited August 15, 2012 by taiwanluthiers

[ANFO]

I've even considered middle ages stuff, but nitrate bearing earth is not hard to come by, that's just most organic fertilizer so no need for urine.. but the quantities produced aren't great and the quality is dubious.

There are chemical 'shops', but they are more laboratory suppliers and they don't sell large quantities really. And getting stuff shipped here is a bit of a problem. But I haven't really looked into the online ordering angle that much, not until I've exhausted the local options. But if there's any online chemical shops that can ship world wide somehow, let me know..

Edited August 15, 2012 by ANFO

[taiwanluthiers]

Try pyro garage, the Polish supplier... but if they are unfamiliar with your country they may not ship to you.

 

You can also try bangkok pyro, but there is a 10kg minimum and their prices are a little on the high side.

[ANFO]

Thanks for the advice, I'll check them out