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Author: Subject: Drying out aqueous ammonium nitrate
ampakine
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[*] posted on 1-5-2011 at 06:47


Boil off the water then try recrystallising from water or another suitable solvent.
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IndependentBoffin
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[*] posted on 1-5-2011 at 15:32


Alright guys here's what I did today:

I got 1 mole of impure (NH<sub>4</sub>;)<sub>2</sub>SO<sub>4</sub> as Sinclair Sulphate of Ammonia fertiliser of mas 132.1g. As you can see from the picture it is extremely dirty when it should be white crystals.

ammonium_sulphate.jpg - 132kB

I then added roughly 200ml of water so that the crystals should dissolve completely. 200ml should dissolve 148.8g at 20C.

200ml_water_added.jpg - 106kB

The dissolved stuff is shown below. Note the insoluble sediment stuck to the walls of the flask and near opaque brown colour.

dissolved_ammonium_sulphate.jpg - 164kB

The filtered stuff is shown next:

filtered_ammonium_sulphate.jpg - 76kB

And what gunk we find in the filter paper! Clarification: no activated carbon was used yet and the black stuff in the filter paper was what was in the fertiliser, and not added by me.

filter.jpg - 155kB

I will boil off as much water as possible and then try to recrystallise. 25kg of dirty sulphate of ammonia fertiliser cost about £50 incl. shipping. Not worth the trouble, in terms of time, hassle and electricity.

Does anyone know a supplier who will sell a 25kg sack of purer (NH<sub>4</sub>;)<sub>2</sub>SO<sub>4</sub> fertiliser in the UK?

BTW the boiling point of the (NH<sub>4</sub>;)<sub>2</sub>SO<sub>4</sub> solution is about 106 Celcius. I'm not going to risk leaving the electric hotplate on overnight even on low to dry the sample so I'll call it a day and continue tomorrow.

[Edited on 1-5-2011 by IndependentBoffin]




I can sell the following:
1) Various high purity non-ferrous metals - Ni, Co, Ta, Zr, Mo, Ti, Nb.
2) Alkex para-aramid Korean Kevlar analogue fabric (about 50% Du Pont's prices)
3) NdFeB magnets
4) High purity technical ceramics
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ldanielrosa
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[*] posted on 1-5-2011 at 23:36


You can dissolve more ammonium sulfate in boiling water, then let it cool to room temperature and some crystals will precipitate out. Remove crystals, reheat and repeat until the crystals come out dirty.

As for overnight, a crock pot filled with sand is a wonderful thing.
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IndependentBoffin
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[*] posted on 2-5-2011 at 04:56


Well folks after boiling down the solution to about half volume late at night and letting it cool down + recrystallise overnight, I filtered out the remaining aqueous solution and scooped out the crystals.

With heating, more brown insoluble sediment has appeared in the solution, which started off clear brown. The insoluble sediment is caught in the filter paper as seen below.

filtered_recrystallised_solution.jpg - 140kB

The filtered solution is a lighter brown than in previous pictures.

filtered_recrystallised_solution2.jpg - 92kB

But the recrystallised ammonium sulphate crystals are still filthy:

recrystallised_ammonium_sulphate.jpg - 87kB

So it seems that the impurity in the (NH<sub>4</sub>;)<sub>2</sub>SO<sub>4</sub> is something which decomposes or undergoes a chemical change at about 106 Celcius (the BP of the saturated (NH<sub>4</sub>;)<sub>2</sub>SO<sub>4</sub> solution) to produce impurities with a dark brown colour and insoluble brown-black precipitates.




I can sell the following:
1) Various high purity non-ferrous metals - Ni, Co, Ta, Zr, Mo, Ti, Nb.
2) Alkex para-aramid Korean Kevlar analogue fabric (about 50% Du Pont's prices)
3) NdFeB magnets
4) High purity technical ceramics
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a_bab
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[*] posted on 2-5-2011 at 05:39


I'd dare to say your ammonium sulphate is adulterated with some sulphate, that would somehow react and turn to the insoluble, disgusting-looking iron hydroxide when boiled.
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IndependentBoffin
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[*] posted on 2-5-2011 at 06:36


I don't have the chemicals to do a thiocyanate test (which might be too sensitive anyway) and carbonate test (would sodium bicarbonate do?) but AIUI Fe<sup>3+</sup> catalyses the decomposition of H<sub>2</sub>O<sub>2</sub>.

I added some 35% H<sub>2</sub>O<sub>2</sub> to the brown recrystallised (NH<sub>4</sub>;)<sub>2</sub>SO<sub>4</sub> and got no effervescence. I'm waiting to see if any bleaching of the brown colour occurs.

Good suggestion though, Fe<sup>3+</sup> is brown and soluble with the right anion.

There can't be many brown soluble salts that go even more brown and produce a brown/black precipitate when heated at 106 Celcius. Has to be organic to have such a low decomposition temperature, but if so why can't activated carbon get rid of it? The organic molecule has to be simple or with lots of polar groups to be so soluble in water.

[Edited on 2-5-2011 by IndependentBoffin]




I can sell the following:
1) Various high purity non-ferrous metals - Ni, Co, Ta, Zr, Mo, Ti, Nb.
2) Alkex para-aramid Korean Kevlar analogue fabric (about 50% Du Pont's prices)
3) NdFeB magnets
4) High purity technical ceramics
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pjig
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[*] posted on 2-5-2011 at 06:56


Maybe it would be worth ditching that batch of A-sulfate and purchasing from a diff source. It is a cheap material, and not worth the time your spending in trying to clean it up.
Id try to get the hydro-grade crystal A-sulfate. It has way less impurities and dissolves very well.
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IndependentBoffin
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[*] posted on 2-5-2011 at 08:03


Yeah I had already decided to do that. I just find it really annoying that I don't know what the impurity is and my methods to separate it out are failing.

You know that feeling when you have a puzzle you can't solve in front of you? I'm just trying to purify it now for the science.

P.S. I have about 25 kg of impure ammonium sulphate fertiliser for sale. Any takers? :P




I can sell the following:
1) Various high purity non-ferrous metals - Ni, Co, Ta, Zr, Mo, Ti, Nb.
2) Alkex para-aramid Korean Kevlar analogue fabric (about 50% Du Pont's prices)
3) NdFeB magnets
4) High purity technical ceramics
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watson.fawkes
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[*] posted on 2-5-2011 at 19:09


Quote: Originally posted by IndependentBoffin  
So it seems that the impurity in the (NH<sub>4</sub>;)<sub>2</sub>SO<sub>4</sub> is something which decomposes or undergoes a chemical change at about 106 Celcius (the BP of the saturated (NH<sub>4</sub>;)<sub>2</sub>SO<sub>4</sub> solution) to produce impurities with a dark brown colour and insoluble brown-black precipitates.
106 &deg;C is the boiling point at atmospheric pressure. Seems like vacuum stripping of the water would be something to try.
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pjig
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[*] posted on 7-5-2011 at 14:12


Quote: Originally posted by IndependentBoffin  


You know that feeling when you have a puzzle you can't solve in front of you? I'm just trying to purify it now for the science.



I know exactly what you mean.. I too was loosing sleep over trying to extract CCB's from my CAN for quite some time... Very frustrating for sure.
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