Sciencemadness Discussion Board

Fertilizer impurities nowadays

Oxirane - 14-10-2014 at 22:07

Because major regulations are being forced all around leading to severe dilution of most useful fertilizers as nitrates source, I think it is a good idea to discuss about different methods how we can still extract the useful nitrogen from that mess. Farming grade contains mostly only calcium carbonate, which is quite easy to separate, but commercial stuff is fortified with all kind of stuff that is more or less nasty.

The problems arise with solubilities and reactivity of the contents. One may not expect to just filter and evaporate to get pure product. Second to that, one may not get what he expects by just reading out the NPK(S) content: when you expect it to be ammonium nitrate, it may actually contain urea and ammonium sulfate. These mixtures may go metathesis when dissolved in water or mixed with any aggregate, deteriorating the purifying process.

So I hope more discussion about how to identify the true contents of different fertilizers. This varies by manufacturer and brand of course, but there would be some common factors, and there is always the question, what does the chemist want from it?

I have, for example, a fertilizer that has NPKS of about 12-0-10-12. The manufacturer just broadly states that it contains 0-100% of ammonium nitrate, but from the NPKS content it is evident that it contains a lot more than that. Mixing it with hot water stirring it forms thick slurry, which is extremely difficult and slow to filter, but sand filter clears it. At least 50% is not dissolved. When concentrating this solution, crystals begin to form, and they are not ammonium nitrate or urea, because their solubility rises beyond their melting point, meaning they will stay liquid at all times. This crystal batch is filtered and concentrating is continued, and another batch is filtered out. Ammonia-smelling fumes are released, indicating presence of urea which pyrohydrolyses into ammonia at over 114C, and finally the liquid gets hotter and thicker, and heating is stopped at around 140C. This mass is cooled and it seems to be somewhat pure ammonium nitrate. No further tests were performed. Yield is about 25-30% at max.

Bert - 14-10-2014 at 23:01

You might want to look at this-

Oxirane - 14-10-2014 at 23:22

That sounds a little bit of what I faced. That stinky gunk got a whole day to filter through. I added some ethanol to the initial water mixture in attempt to ease the viscous liquid, and difficult to say if it worked or not.

Anyway, the point is that as long as there is nitrate in the mixture, it is possible to extract it from there. I have had several options on my mind, including extraction of pure AN, converting it to another form of nitrate in order to consume some unwanted side products off, and converting it directly to nitric acid with either sulfuric or hydrochloric acid, latter being more preferable due to near-free availability as long as there is PVC in the world.

Bert - 14-10-2014 at 23:48
Quote:

I added some ethanol to the initial water mixture in attempt to ease the viscous liquid, and difficult to say if it worked or not.


Adding ethanol to nitrate solutions in water can drastically DECREASE solubility of the nitrate, it is a method used to precipitate dissolved Potassium nitrate in some pyrotechnic manufacturing manipulations.

It is NOT an accident that it takes a lot more than a simple dissolve/filter/recrystalize technique to clean up your fertilizer... Admixtures that screw up your filter media were chosen for that very reason.

Search, lots of others have been trying for work arounds.

feacetech - 16-10-2014 at 19:20

If you can get CAN

120 grams CAN plus 120 grams water (boiling) stirred for about 1 min until all dissolved. Allowed to settle and yielded 200 grams of clear solution.

The solution was boiled down (10 min) until the temp was 160°C and allowed to cool and crystallize.

Yield 85 grams of Crystalline AN

in my country comerical AN is almost impossible to get as a fertiliser and if you can get AN it might be the yara one with propertity anti explosive additive

CAN is readily avaliable however

careysub - 16-10-2014 at 20:36

Quote: Originally posted by feacetech  
If you can get CAN

120 grams CAN plus 120 grams water (boiling) stirred for about 1 min until all dissolved. Allowed to settle and yielded 200 grams of clear solution.

The solution was boiled down (10 min) until the temp was 160°C and allowed to cool and crystallize.

Yield 85 grams of Crystalline AN


You can also do a metathesis reaction with ammonium sulfate and CAN and convert all the nitrate to ammonium nitrate.

Bert - 17-10-2014 at 15:07
Quote:

You can also do a metathesis reaction with ammonium sulfate and CAN and convert all the nitrate to ammonium nitrate.


Or just skip buying ANY ammonium nitrate fertilizer or mixture-

Start with Calcium nitrate, which has wide availability due or it's common agricultural use and low potential for diversion to high explosive, and ammonium sulfate, also a common agricultural chemical.

I actually keep both of these chemicals on hand for use on my fruit trees (Calcium nitrate) and my plantings of blueberries and evergreens (ammonium sulfate), which need an acidifying fertilizer.

I have never had an issue with buying either chemical, although I understand a sophisticated amateur COULD make water gel explosives with Calcium nitrate, and industrious meth cooks ARE using ammonium sulfate to generate ammonia gas to dry and cryogenically condense when they can't access anhydrous ammonia tanks.

[Edited on 17-10-2014 by Bert]