Sciencemadness Discussion Board

Potassium nitrate from 15-15-15 fertilizer

Random - 7-8-2013 at 22:34

From what I read on the fertilizer it contains the following:
Quote:

15% Nitrogen: around 6.4% nitrate nitrogen
around 8.6% ammoniacal nitrogen

Now I highly estaminate that fertilizer doesn't contain any nitrogen from urea.

15% SO3
15% K2O



To the fertilizer solution I could add calcium hydroxide which would precipitate phosphate ions as calcium phosphate and get hydroxide ions into solution.

Then I would have in solution:
very small amount of Ca2+ ions
K+ ions
NH4+ ions
NO3- ions
OH- ions

Then I would bubble CO2 through the solution to make it slightly acidic.

Ca would precipitate as CaCO3 and OH would be neutralized leaving

K+
NH4+
NO3-
CO3(2-)

Then I would leave it outside to evaporate and add boiling water to dissolve everything in minimal amount.

Then I would cool the solution down in ice bath to get crystals of KNO3.

Does this method sound reliable? Any better method?


Oscilllator - 7-8-2013 at 23:43

Well just FYI wikipedia says ammonium carbonate decomposes in hot water, presumably to release CO2, which would leave ammonia behind and something else (?)
It can also decomposes spontaneously as per (NH4)2CO3 → NH4HCO3 + NH3.
Either way, it releases ammonia which will introduce more hydroxide ions into your water (NH3 + H2O <-> NH4OH)

Actually, Im not sure why you want to get rid of the hydroxide anyway. At 0 degrees, potassium nitrate is the least soluble of all the possible combinations of ions there (KOH, KNO3, K2CO3, NH4NO3, NH4CO3, NH4OH) and so it should crystallise out first.

3rd thing, I'm not sure calcium phosphate is less soluble that calcium hydroxide given calcium hydroxide has a solubility of 0.189g/100ml at 0C. I'll leave that one to you...

Mercedesbenzene - 8-8-2013 at 07:14

You should try to confirm that the fertilizer does actually have nitrates in it. From what I have found this 15-15-15 fertilizer is based off diammonium phosphate and urea
http://www.proapfertilizer.com/uploads/MSDS%20M01-020.pdf
and this one is based off potassium sulfate
http://www.yara.us/images/TDS_Mila15-15-15_tcm362-56389.pdf

So it might be wise to check if it actually contains any nitrate before trying any larger scale extractions.

Marvin - 8-8-2013 at 09:19

It's difficult enough to make pure potassium nitrate do anything useful. The fertiliser grade may benefit from a recrystalisation anyway. Among the issues are that ammonium compounds tend to make calcium compounds soluble.

Buy the real stuff and don't use aluminium pans.

ElectroWin - 8-8-2013 at 09:37

if there's a question of nitrate yield, you could apply a semi-quantitative test for nitrate, as i understand test strips are not so expensive.
http://www.galladechem.com/catalog/emd_teststrips/nitrate-te...

[Edited on 2013-8-08 by ElectroWin]

hyfalcon - 8-8-2013 at 15:10

Go to the same place you got the 15-15-15 and ask from greenhouse grade potassium nitrate. It's water soluble and over 98% pure. One filtration and recrystallization and you're good to go.

Random - 11-8-2013 at 05:19

Quote: Originally posted by Oscilllator  
Well just FYI wikipedia says ammonium carbonate decomposes in hot water, presumably to release CO2, which would leave ammonia behind and something else (?)
It can also decomposes spontaneously as per (NH4)2CO3 → NH4HCO3 + NH3.
Either way, it releases ammonia which will introduce more hydroxide ions into your water (NH3 + H2O <-> NH4OH)

Actually, Im not sure why you want to get rid of the hydroxide anyway. At 0 degrees, potassium nitrate is the least soluble of all the possible combinations of ions there (KOH, KNO3, K2CO3, NH4NO3, NH4CO3, NH4OH) and so it should crystallise out first.

3rd thing, I'm not sure calcium phosphate is less soluble that calcium hydroxide given calcium hydroxide has a solubility of 0.189g/100ml at 0C. I'll leave that one to you...



Actually that might be true. Ca(OH)2 could actually not be used for precipitation of phosphate because it is not soluble enough. I did one experiment though.

Mixed Calcium acetate solution with fertilizer solution and got a white precipitate of phosphate I guess. But that again introduces acetate ions.

Now I am not even sure what would be the best way to do this?


I wonder if there is application where I can put all the ions in the solution and check the most favorable way of extracting the compound out of that.

[Edited on 11-8-2013 by Random]