j_sum1 - 13-3-2018 at 18:19
I have just spent some time in the lab processing mixed iodine waste including wet elemental iodine, an aborted previous recovery
effort that contained excess persulfate and had corroded through the container it was in, various solutions, floor sweepings from a KI spill, and
various reaction products.
I ended up using acidified hypochlorite to oxidise since that was the cheapest I had on hand. I was expecting iodine to be its usual messy self but I
feel like I have been battling with it. The scale I am working at is about 200g of I2 but I have had significant losses. So I'd love to know how
others deal with it.
The precipitated I2 is very fine and holds onto its water. Really difficult to wash and dry. I was trying to avoid using vacuum
filtration since I only have a small bushner at present and last time the I2 did damage to the Al parts of my vacuum pump.
The liquor remaining after precipitating iodine still contained a lot of dissolved I2. A second recovery meant I was dealing with a much greater
volume than I would have liked.
This stuff is volatile and gets everywhere. Quite a lot of losses. I put some in the fridge overnight and spent a lot of time the next day
spraying everything with thiosulfate and wiping them down.
I have some insolubles in with the iodine - perhaps 20%. Purification via sublimation is fine but (a) it seems to be a pretty small-scale
process. (b) vapours still get everywhere. (c) I had problems with water condensing as well and ending up in the product.
How do others store I2? I found half way through the process that I don't have much in the way of suitable containers. I ended up ampouling
some (although much of that still contains water.) I dissolved most of it in ethanol which will let most of my impurities settle and allow me to
recover the iodine at a later date.
Any suggestions?
CobaltChloride - 14-3-2018 at 01:59
I can only advise you on storage, as all the iodine I have is in prill form. I put it in a glass vial whose cap was completely covered in teflon tape.
I also found out that iodine vapors can penetrate PP plastic, but not PE, so if you have a good resealable PE bag, you could use that to contain the
vial as well.
[Edited on 14-3-2018 by CobaltChloride]
UC235 - 14-3-2018 at 02:59
It stores well in a FEP or PFA bottle in a freezer. I even have bromine that way for the last several years. Considering it's sold in glass with
teflon liner, that should be okay. I recommend secondary bagging and putting it in a -20C freezer for the latter.
Point 2: Are you sure you've used up all the iodide? Remainder creates soluble triiodide ion. You're better off having a slight excess of oxidant.
Point 4: Maybe melt it under sulfuric acid to make a solid non-porous (dry) chunk beforehand.
Melgar - 15-3-2018 at 21:26
I've tried this myself, and had more success with some parts than others.
First step is to convert to iodide, then evaporate organic solvents. That alone is pretty annoying.
Next step is to mix with dilute hydrochloric acid, then add chlorine bleach dropwise until everything falls out and the liquid has a green tint. Wash
a few times. I don't know why everyone recommends H2O2 for this. I- decomposes H2O2, and all the bubbles tend to make it so that you NEVER get a
good precipitate.
Next step may be stupid on my part it does work. Make sure it's in a glass vessel that can withstand a bit of pressure. Heat it until the I2 visibly
melts. I2 melts at 113˚C, and the stuff you have won't be super pure (will probably contain ICl among other things) and should melt a bit lower than
that. Then just pour off the water and sublimate it or something.
edit: Maybe if you start with phosphoric acid or sulfuric acid when adding bleach, the boiling point will be raised enough that there will be no
pressure to speak of? Would be worth a shot.
[Edited on 3/16/18 by Melgar]