From: Liam Lawless (lawless@ic24.net)
Date: 05/03/00-12:47:28 PM Z
>>it's (I imagine) almost as easy to treat
>the stuff as it is to throw it away, so I'll do it in future.
>
>Gosh, that's GREAT Liam! Thanks so much for setting an example!
Hopefully,
>other will follow suit.
Unfortunately, it didn't quite turn out that way. I did the test and here's
what happened.
Began with 500 ml of my reversal bleach, unused and at working strength
(therefore containing 2.5 g of pot. dichromate and 2.5 ml sulphuric acid),
and added 100 ml fresh working strength fixer to it (about 24 g crystalline
hypo, 2 g sulphite & a little acetic acid). As reported earlier, the
solution turned green-blue but nothing had settled out after 3 hours, so
sod. hydroxide was added (about 50 ml of 30% NaOH).
The solution clarifies from the top down (as we might expect!) - it takes a
long time for anything to happen, but after 15 hours it had formed three
strata of roughly equal thickness: at the top, pale green perfectly clear
liquid; under that darker in colour and containing a small amount of a
flocculent suspension; at the bottom, an almost black gelatinous gunge. As
time goes by, more of it clears and the layer of black stuff gets thicker
(adding more NaOH does not seem to speed things up). There's also a small
amount of white precipitate on the bottom.
Left for 48 hours in total, it has almost but not quite fully cleared; the
three strata are still visible, but there is still a little of the
suspension hanging about between the black stuff at the bottom and the clear
liquid at the top - my guess is that it would require another couple of days
to settle out completely. However, at this point I decided to try and
filter it off.
With care, most of the clear liquid can be poured off the sediment without
disturbing it (sediment not being quite the right word - more of a liquid
jelly in a 1.5 inch thick layer at the bottom of a 600 ml beaker), but I put
all of it through a coffee filter paper, and the whole lot passed right back
through it!
The difficulty, then, seems to be separating the "solid" from the liquid.
Evaporation might be an option (more than a pint of liquid!) but not for me
as I don't have the equipment and am no longer allowed to do such things in
the kitchen (following previous disasters). I therefore concede defeat,
and, since we now know that my chrome (VI) has become relatively benign
chrome (III), I flushed it down the toilet. But I tried.
Liam
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