>Having about an ounce of 26% ammounium dichromate to dispose of
>in an environmentally responsible manner, & having read contributions to
>this list about adding strong alkali & filtering....... ???????
>
>I added an equal quantity of household ammonia, which made no impression,
>except for the perfume. (I know household is only 4 or 5% but I was trying to
>get rid of it because it made prints smell like low-grade bordello.)
>
Changing pH doesn't make much difference. Dichromate turns into chromate.
>Next I added maybe a tablespoon of sodium carbonate. This foamed up, like
>orange sherbert, and was still bright orange, which I took to mean it still
>possessed hexavalency. I couldn't find litmus paper, but it was about pH 6
>on Hydrion paper.
>
>So I added about 2 teaspoons sodium hydroxide -- all, remember, for an
>ounce of original solution. At this point the test color didn't match
>any of the squares on the chart. The difference on the chart from 6.5 to 8
>was pretty indistinguishable anyway (maybe it faded?).
chromates/dichromates are strong oxidizing agents, therefore will react
with most of pH indicators. Not to mention colour, which will mask most of
changes of the indicator.
Hexavalent chromium is cancerogenic! How to dispose? Well, as I mentioned,
dichromate, especially in acidic environment is a strong oxidizer. If you
mix it with something that can be oxidized, like spend fixer, bingo. There
is plenty cheap chemicals that could be used to reduce chromium 6 to 3 or 2.
Once reduced, rise pH to precipitate hydroxide (oxide).
But, ammonium dichromate as a dry compound has very interesting property. It
will decompose quite nicelly. If you prepare a model of a volcano (plaster
of Paris will do) with a crater and a hole (shaft ~10 cm) and put some
ammonium dichromate crystals down and lower red hot nail into that hole,
then you'll get working model of a volano. It will send greenish chromium
oxide plus some gases and bit of flame. Collect that greenish stuff, it is
great as a polishing agent. But be careful with an acidic solution of
dichromates. Chromic acid is very strong oxidizer and will eat most of
metals, like your plumbing.
OK, Judy, some more mail is waiting. If you need more, just say a word.
Roman
>
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Roman Kielich (Lane Cove, NSW, Australia)
e-mail: romek@ozemail.com.au (or roman_kielich@sydpcug.org.au)
Fidonet 3:712/505 phone: 61-2-418 6971