aga
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Iodine Recovery
Testing carbon for it's 'activation' required an iodine solution containing 12.7g of elemental iodine, also a quantity of KI.
This used up all of my supply of iodine, and i would like to get it back to re-use it.
More is on order, but i got carbon to test !
Roughly 1 litre of a solution of water, iodine, potassium iodide, sodium thiosulphate and starch waste were kept from the titrations, all mixed in the
same bottle.
So far i have passed a lot of chlorine through the solution which eventually caused the iodine to appear as purple streaks, then as a completely
brown/black solution.
The theory being that the chlorine will replace the iodine, leaving it as elemental iodine which is poorly soluble in water (0.29g should dissolve in
1L).
No iodine appears to be precipitating out.
I tried filtering some of this solution and it passes straight through the filter paper, leaving a brown ring.
The assumption was that the I2 would appear as crystals at the bottom of the vessel.
Do i need to chlorinate it more, wait longer, or is there something key that i'm missing here ?
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gdflp
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My guess is you haven't fully chlorinated yet. If the iodine coloration is clearly present, you have almost certainly rid the solution of
thiosulfate, but you likely haven't fully reacted the KI. This will have a particularly drastic effect on the yield because, in addition to having
iodine atoms bound up in iodide, elemental iodine is quite soluble in iodide solutions due to the formation of the triiodide ion, KI +
I<sub>2</sub> --> KI<sub>3</sub>.
Also, I would be wary of ICl(or other interhalogen) contamination in your final product. Shouldn't be terribly significant since they typically
hydrolyze quickly, but might show up in later reactions if said reaction is sensitive to chlorine.
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unionised
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Until you convert all the iodide to iodine most of the iodine will dissolve as tri-iodide.
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aga
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So more chlorine gas.
When to stop ?
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AvBaeyer
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Aga,
I recover iodine from similar mixtures by adding oxone to the mixture and ensuring that it remains acidic. This gives a fine precipitate of elemental
iodine which can be filtered, dried, and then further purified by sublimation. Recoveries are excellent. Sounds more difficult than it actually is.
AvB
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j_sum1
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Chemplayer used ammonium peroxydisulfate. The K salt works as well. Available as pool oxidisers and they work without acid.
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Sulaiman
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So far, whenever I bubble gas into liquid, most of it escapes,
so for bubbling gas into liquids I have been considering at these aquarium CO2 diffusers,
ceramic diffuser in glass,
http://www.ebay.co.uk/itm/For-Plant-Fish-Tank-Aquarium-Hot-H...
http://www.ebay.co.uk/itm/Aquarium-Spiral-CO2-Diffuser-Glass...
You could test them for me ? 
CAUTION : Hobby Chemist, not Professional or even Amateur
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aga
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Thanks for the suggestions.
Not surpringly, i have no peroxysulphates and the pool stuff here is either Na-DCCA tablets/granules, or a 25L container of 30% sodium hypochlorite
I'll check what's in the flocculants and algicides.
Edit:
Adding more chlorine overnight seems to have worked !
Next: extract, wash, dry and sublime ...
[Edited on 6-11-2016 by aga]
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aga
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Those glass things look hard to use - they're too big.
These might work, as they can be put inside something glass.
http://www.ebay.co.uk/itm/Aquarium-Bubble-Air-Stone-Aerator-...
3 are now on order, so i'll test them when they arrive and let you know.
Here's the rig i used for the chlorination :
The dead space in the RBF fills with gas, so it remains in contact with the liquid for as long as possible before heading for the scrubber.
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Sulaiman
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I like the chlorine generator reaction vessel.
I doubt that you will be able to (safely) use an airstone without using a pressurised equalising funnel,
turn the tap to allow liquid flow, and chlorine comes up - and out !
(without having the funnel full, having to pour probably contaminated excess back into storage)
with a p-e funnel you can generate several inches of water pressure,
to overcome the 'back pressure' of the airstone, for depth of bubbling. or to use the excess chlorine for a 'side' experiment etc.
and I would use a keck clip on all joints
(how chlorine gets out of a well fitting greased joint to attack the clips is still a mystery
pressurised chlorine gas ... one of my favourites ....
I know that you know all of this, just a reminder to take care.
P.S. I guess that the white plastic inserts of the airstones may be unsuitable for chlorine, but in overall cost, expendable.
[Edited on 6-11-2016 by Sulaiman]
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aga
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Normally the P-E funnel is used with the gas take-off at the top.
Mr P-E was in the dishwasher.
We'll see what these airstones can stand up to when they arrive.
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aga
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I tried subliming the recovered iodine and got some very nice purple smoke.
The iodine was put in a 250ml beaker on a hotplate with a 250ml RBF full of cold water on top.
Not much of it recondensed on the RBF, around a gramme 
About 0.5g recondensed on the sides of the beaker.
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Daffodile
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At least you got something dude
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aga
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Yep.
I got to find out for myself how Iodine behaves, which is priceless.
Also got a replacement 250g on it's way, so no loss really.
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unionised
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Just a thought: How much faith do you have in the "scrubber"?
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aga
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Works pretty well.
The fume hood fan is crap, hence a scrubber.
I still get a whiff of gas when i open the 'hood, but not enough to be a problem.
Once a crap cork was used. It disintegrated very fast, releasing a Lot of Cl2.
I got a lot of gas that time, hence, know the difference.
With or without the gas mask, the shed is in the middle of nowhere, has a double-sliding door (wide) so simply running away is always an option.
Edit:
If i lived near other people, like in a city, there is no way i would have done some of the stuff i have done.
Chlorine gas is harzardous m'kay.
[Edited on 6-11-2016 by aga]
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unionised
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And, for my next question- if the scrubber design is that good, why don't you use it for the primary gas absorbtion/ reaction?
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aga
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Good ? It's just an inverted funnel in some NaOH to try to catch escaping Cl2.
Much smaller diameter than the 1L RBF.
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Bezaleel
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Hi Aga,
lease let know if you obtain more success on the sublimation part in future experiments. I tried purifying iodine this way myself and my problem is
that the iodine obtained is wet. Water also condenses on the RBF, and I end up with what I started with: wet iodine. And with me too, a lot of the
iodine crystallized on the walls of the uncooled beaker instead of on the cooled RBF.
I ultimately made this a very long running experiment by adding CaCl2 to the wet iodine. I put the mix in a closed glass vial and just let it stand
against a concrete wall in my house. After a year, the CaCl2 was left at the bottom and the iodine had formed crystals which stuck to the wall of the
vial (virtually all of it was on the side of the vial which touched the concrete wall of my house). The setup stands in a place which becomes warm in
the evening, when the CV in my house is switched on.
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aga
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Atmospheric moisture condensed on my RBF, so even if the I2 had been 100% dry, it'd have ended up wet anyway.
I'm guessing that the sublimation/recondensation thing only works with very dry iodine and/or under a vacuum.
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Sulaiman
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I have recrystalised iodine by sublimation,
first try I did not want to loose any precious iodine vapour so I used ice water, and got wet crystals.
If you heat iodine GENTLY it melts, all of the water should evaporate,
then use an rbf with warm water, increse heat slowly, ... choke a little, and you get shiny crystals.
Irrelevant:
If you have some napthalene, try re-sublimation,
no special danger, (don't breathe/burn/look etc)
just a very interesting crystal formation - like super thin mica snowflakes.
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macckone
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Better method on a mix like this. Neutralize with base to get all the iodine as sodium or potassium iodide. Boil it down to crystalize the salt.
Then redissolve in minimal water and add hydrochloric acid and hydrogen peroxide. Crystals form rapidly. Resublime to seperate any chlorine.
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Sulaiman
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I just came across this image
https://encrypted-tbn3.gstatic.com/images?q=tbn:ANd9GcSLZrUc...
if you are still looking for a lab-scale iodine purification techique,
I thought that maybe an electrically heated crucible of 'impure' iodine inside a flask may be a way of subliming/refining the iodine with minimal
losses ?
CAUTION : Hobby Chemist, not Professional or even Amateur
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