RogueRose
International Hazard
Posts: 1585
Registered: 16-6-2014
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Cross contamination with used activated carbon - how much can be expected?
I've read that AC can be cleaned to some degree by boiling (possibly even in a pressure cooker would be better..?) and rinsing there-after. Some say
that rinsing alone is sufficient for some applications. I'm wondering what the holding ability is for the carbon to retain a compound vs it dissolving
into a solution of water (or even another solvent).
I filtered 100g of ammonium sulfate (100g in 250ml water) solution with about 50cc's of AC (2-4mm diam pieces), then rinsed the AC with 250ml of hot
(145F degree water) 4 times then ran 1L of hot water through the AC filter afterwards then set it aside to dry and use later (for the same compound).
98g of sulfate was recovered - so some was lost between the filtration & evaporation process - IDK how much is retained in the AC.
I had a K2CO3 solution that needed filtered and I passed it through this AC (label had fallen off and I thought it had been only used for filtering
snow water). When adding the filtrate to a hot K2CO3 solution, the smell of ammonia was immediate and the solution turned cloudy.
Upon heating the solution started burping at a relatively low temp - 150-170 I would say. I assume that some ammonium carbonate/bicarbonate was
created along with some potassium sulfate. At this temp, the carbonate was probably decomposing to CO2 and ammonia and IDK if the ammonia would react
quickly with the carbonate or not - IDK what the reaction would be here.
I'm wondering how much ammonium sulfate could have been passed on to this solution and how contaminated my K2CO3 solution may be. Obviously there
can't be more than 2g of ammonium sulfate in the solution (as stated above) but I'd like to figure out how much contamination I can expect in this
solution.
Anyone have any experience with AC passing on compounds it had removed from previous filtration? This is exactly why I keep my used AC separated and
labelled so this thing doesn't happen.
This experience does show that AC may be used to pass on some compounds or hold a catalyst while a liquid can pass over/through it. IDK how or if it
retains the catalyst without it falling off into the liquid - that is curious.
[Edited on 4-6-2017 by RogueRose]
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AvBaeyer
National Hazard
Posts: 644
Registered: 25-2-2014
Location: CA
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I have never heard of any attempt to recycle activated carbon. It is truly a one use material and is generally very cheap.
Activated carbon (AC) has been used I recall in some forms of elution chromatography which implies that certain substances have more or less affinity
for AC. Unfortunately I cannot cite a reference for this right now. This implies that there may be routes to recycling but at what cost in time and
purification materials? How would you be able to know if the AC is clean?
But as I stated above, in typical lab operations AC is used once and then disposed of. There is just too much risk of cross contamination as you
apparently have experienced.
AvB
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alking
Hazard to Others
Posts: 252
Registered: 11-3-2016
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Unless it's contaminated with metals or something you could easily purify it in a calcining oven probably. Not very feasible for the home chemist
however.
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