Chromium (Smith's fixative etc) disposal
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From: | "J. A. Kiernan" <jkiernan@julian.uwo.ca> (by way of histonet) |
To: | histonet <histonet@magicnet.net> |
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On Thu, 10 Dec 1998, Gayle Callis wrote:
> The EPA frowns on potassium dichromate being drain dumped.
> We collect and give it to our chemical safety facility
> for disposal.
As what?
Do these regulations apply to all the oxidation states of
chromium? It is easy to reduce dichromate to chromic ions
(as present in chrome alum), and in this lower oxidation
state (3 rather than 6) chromium is present in all sorts
of places, perhaps most notably in chrome-tanned leather,
which is used for the softer and more colourful products
of cow-hide, like gloves.
The product of alkaline reduction of potassium dichromate
is a polymeric green "chromium hydroxide," which is quite
difficult to redissolve. Safety officers in the 1970s & '80s
told us it was OK to send it down the drain. This was mostly
the end-product of spent and neutralized "chromic acid" used
for cleaning glass pipettes. In the late '90s it's the
fumes from incinerated plastic pipettes that they worry
about.
It costs very little to reduce a dichromate-containing
solution. Add some formalin. Wait a few days. Add some
strong ammonia. Wait a few days to let the unreacted
ammonia evaporate. Wait several weeks until most of
the water has evaporated (hood not needed because no
fumes). Put the residual sludge in a plastic jar, for
disposal as wet, insoluble mineral waste.
At least some of the chromium toxicity scare comes
from the electroplating industry, where large volumes
of cyanide-containing solutions are used. This is a
different kind of danger, well known since the turn
of the century. Mists of chromium (? as) trioxide in
refineries are another well known industrial hazard,
hopefully now in the past.
John A. Kiernan,
Department of Anatomy & Cell Biology,
The University of Western Ontario,
LONDON, Canada N6A 5C1
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