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Author: Subject: I want to recover potassium ion from NPK fertilizer
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[*] posted on 17-11-2012 at 15:32
I want to recover potassium ion from NPK fertilizer


In need of some potassium ions..

I have this NPK fertilizer that probably contains ammonium ions, urea, phosphates and of course potassium.

So I am thinking about the way to isolate the stuff from it.

What would be the best way? I have thought about it and I think it would be the best idea to mix it with calcium hydroxide and let it react and evaporate to get rid of urea and ammonia and then crystalize KNO3 from ca(NO3)2 and KNO3 mixture.

Or maybe even better would be saturating KNO3 and Ca(NO3)2 mixture with sodium carbonate to get rid of calcium ions.

[Edited on 17-11-2012 by Random]
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violet sin
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[*] posted on 18-11-2012 at 04:01


well... do you know what is in it? or the NPK values? because if it is a random x/y/z( i.e 3-4-3) number product it sounds like you just wanna do it the hard way for fun?! :)

if all you really want is K+ ions for a rxn then obviously it would be good to get a 0-0-?. preferably a large K value. cheap as dirt, well cheaper than potting soil, potassium sulfate. or sulfated potash. mine was ~1.50-2.00$US/lb. no sodium salt is about 8$US/lb in almost any grocery store. but maybe that's not the point...

so if you are just dead set on getting it out of the stuff you have and it is only urea, ammonium(?phosphate?), and with something K in there... you could (1) drop in some anhydrous MeOH (HEET) to the dry(ed) product to get out the urea, checking completion by evaporation of washes for crystals or haze in dish. drying leached product of MeOH. (maybe a conflict of mutual solubility in MeOH??) (2)add calcium hydroxide to an aq. sol. to drop the phosphate(Ca++) and leaving ammonium hydroxide and a K+ salt, hopefully KOH by this point. (3) after filtering out phosphate, (4) heat sol. to drive off the ammonia, and (5) neutralize with HCl to crystallized KCl to purity???

or maybe (*3*) just filter out Ca phosphate and (*4*) neutralize all hydroxides with HCl and (*5*)heat to drive off NH4Cl, leaving KCl? just my guess and what I would try on a small scale. more than likely there is flaw(or fifty) here and more reading would ensue. I'm not too skilled at this type of thing so don't back lash too hard if I got something OBVIOUSLY wrong here. like I said just a guess

still would be nice to look up a MSDS or other product info for definite composition for proper process. good luck.
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[*] posted on 18-11-2012 at 10:47


tartaric acid. assuming the mixture is just straight NPK of course. trace elements will likely bind to tartrate as well but they are trace elements. seems a bit of a silly place to look for potassium when you can get potassium salts more cheaply in other ways. tartaric acid makes potassium insoluble hence its being a waste product of wine making, and potassium tartrate is a common cake-making ingredient.

if you are looking for potassium hydroxide, the simplest form of potassium available, it is not that hard to find, look around for soap making supplies and biodiesel supplies. both sell it for their respective industries.

[Edited on 18-11-2012 by l0k1]
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[*] posted on 19-11-2012 at 08:29


I have been looking in supermarkets and there is no cream of tartar available I'm 100% sure
other thing is that potassium in any quantity isnt available to me except in potassium metabisulfite which I dont want to use because of SO2


I will try violet sin's method, sounds good
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[*] posted on 19-11-2012 at 09:32


your original scheme sounds like a good starting point. ammonium is easy to remove. calcium phosphates are only slightly soluble. precipitate the remaining calcium ions with as little sodium carbonate as possible. potassium salts are not as soluble as their sodium analogs and will crystallize out first. if you don't care about the nitrate ions you can just calcine the stuff and recover potassium carbonate.
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[*] posted on 19-11-2012 at 17:15


What about skipping all this and calcinating the whole thing? The remainder Ca and K can be easily separetad.
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[*] posted on 20-11-2012 at 16:54


1. I agree with the guy above. Burn it. You will end up with K2CO3.
2. You can probably buy KCl at supermarkets known as NoSalt or Morton's Salt.
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[*] posted on 25-11-2012 at 12:53


I am scared to calcine the stuff, urea and nh4no3..I don't wanna be making explosive mixtures.
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violet sin
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[*] posted on 25-11-2012 at 14:09


honestly I just figured you wanted to take the scenic route, ie. long way for fun. are you not able to get KCl as a salt alternative at your location? or is the chloride not what you wanted? it seems quite messy to be mucking around with so many unwanted species in there if you can avoid it for a few bucks. litteraly 2-3$ of the right fertilizer would leave you just with what you want... I am having a hard time here figuring out what your limitations are?

I mean if you got K2SO4 from a garden shop and added a sol. of CaCl2 it seems that you could filter off the gypsum and evaporate the solution to KCl quite easily, though filtering might take a while. and the potassium sulfate/ sulfate of potash is really really affordable as is the CaCl2

or if you have a supply of K2S2O5 and some outdoors place or a fume hood, wiki says you can fire it to a really easy temp:
Potassium metabisulfite... which decomposes at 190 °C, yielding potassium oxide and sulfur dioxide. K2S2O5(s) → K2O(s) + 2SO2(g)

not hard to manage that, but again I have a hard time reading what would be hard/undesirable to you.
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