pesco
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Monoammonium phosphate (MAP) from fire extiguishers
Hi,
I have several (and many more if needed) expired ABC fire extinguishers. The active component is monoammonium phosphate
(NH4)(H2PO4).
Very useful to me chemical. Not just in the lab, but also in my cultures of phytoplankton, spirulina and on veggie patch 
I've opened one and retrieved the MAP powder. When tried to dissolve some in water it turned out it is HIGHLY hydrophobic. Upon sitting on top of the
water in closed jar for several weeks I can't see any changes in amount on top of the water. I was hoping that in closed jar it will eventually "get
wet" and dissolve. Nothing like that happened.
Done some googling and couldn't find anything relevant.
I guess the MAP is mixed/deposited on/coated with some silicates, what would make sense giving the fire suppression purpose of this particular MAP.
Silicates/silica gels are used in some fire extinguishers.
As it is the MAP is pretty much unusable.
There are few ways I can think of:
1) heat the powder to above 200°C, drive off and capture the NH4 and melted H3PO4 should be easy to dissolve after
it is cooled.
2) treat with hot NaOH, replace NH4 with Na and potentially dissolve alleged silicates. Problem is I am not sure if the silicates are
responsible. Don't have straight use for Na salt and wont have any KOH before March/April. Would need to convert into K/NH4 salt or to
phosphoric acid.
Have anyone encountered such behaviour of MAP and do you have any suggestions?
I wont be able to do any small scale test until well after Christmas. Till end of January I will be working 7 or even 8 days a week
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clearly_not_atara
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I would suggest trying to grind it in a mortar with a little water and see if you form a paste. If it is coated with silica (likely) the coating will
be destroyed by grinding.
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Fulmen
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I tried the same once and had the same problem as you. The powder is too hydrophobic to dissolve in water and a mess to handle. Never put much effort
into a solution at the time so I can't really come with any tested solution. But I wonder if some water miscible solvent could wet the powder.
We're not banging rocks together here. We know how to put a man back together.
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Hexabromobenzene
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I got about 6 kg of MAP from fire extinguishers. You do not need any solvents
You will need a 5 -liter bottle. Pour the powder with a volume of half a bottle and the other half of the hot water of 60 degrees. Close the bottle
and mix with your hands for a few minutes
After that, you need to filter the mixture. I use reusable polypropylene packages. Put on gloves and squeeze a bag with powder and liquid with your
hands. You can rinse the powder 2 times until complete extraction
Next, evaporate the solution until the first crystals appear and slowly cool in the refrigerator. You will have many crystals of ammonium phosphate.
The remaining solution will contain ammonium sulfate with some phosphate. You can repeat the process evaporation to extract all ammonium phosphate
[Edited on 16-12-2024 by Hexabromobenzene]
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pesco
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Great!
Now I know irs not just me being unlucky!
I'll do the bottle trick next week. Thanks for the tip.
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Rainwater
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Its the abc rating. It is designed for flammable liquids, which always float on water, so it too must float.
You can buy that stuff in 50lb buckets for about 45usd. It sold as a refill kits for restaurant steam hoods fire supression system.
90% according to the label
"You can't do that" - challenge accepted
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Hexabromobenzene
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After extraction with water, the powder may appear dry, but this is an illusion. It absorbs a lot of solution and must be squeezed out.
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