kasim@juno.com
Date: 04/27/00-07:58:13 PM Z
Years ago there was a very good reply (below) to this in the Usenet
darkroom group. I suspect that disposal of old stock solution is much
more relevant that wash water. Anyway, a little old fixer makes it much
less hazardous - - read on.
My editor in Juno is simple - - sorry about the word wrap.
Alex Sim
*********************************
Newsgroups: rec.photo.darkroom
From: carson@HQ.Ileaf.COM (Carson Graves x4692 3NE)
Subject: (more) Safe Disposal of Dichromates
Nntp-Posting-Host: zama
Reply-To: carson@HQ.Ileaf.COM (Carson Graves x4692 3NE)
Organization: Interleaf, Inc.
Date: Mon, 7 Nov 1994 15:23:35 GMT
I got the following email in response to my last post on safe
disposal of dichromates. As the author doesn't have the ability to
post to newsgroups he gave permission to post it. I thought it was
a useful update as it adds information about the current OSHA
regulations in addition to clarifying some of my confusion.
Carson Graves
carson@ileaf.com
------------------------cut here---------------------------------
From: dbailey@titan.iwu.edu (Dave Bailey)
Subject: Dichromate disposal
To: carson@HQ.Ileaf.COM
Sorry about the e-mail, my site will not let me post to newsgroups.
I am a professional chemist (Ph.D.) and serve as the chemical hygiene
officer for my university. As such, I need to know a good deal about
disposal
of chemicals and hazards of chemicals.
Unfortunately, the 1973 book by Kodak was published before the current
set of regulations and, especially, before the concern about release of
carcinogenic chemicals into the environment. Chromium (VI) has now been
classed as
a carcinogen and OSHA prohibits its release into public sewer systems
(and probably also into private septic systems). Chromium (III), its
reduction product, has also been under suspicion for carcinogenicity, but
I do
not believe it has yet made the OSHA list of banned chemicals.
Nevertheless, it is a Rheavy metalS and may be banned, at least in
quantities over a
certain amount, in your sewer system.
The method of converting hexavalent chromium into trivalent chromium in
the Kodak book is a good one and should work well. Simply dump into
the chromium solution spent (or good, for that matter) thiosulfate fixer
and wait.
You can monitor what is going on rather easily as the yellow-orange
dichromate color will slowly change to a green color characteristic of
chromium (III) -- although the green color may vary depending upon what
else may be in the fixer. Since you should not dump that chromium (III)
away because it, too, may be bad, I would recommend precipitating it as
chromium hydroxide and filtering the precipitate. This should be easily
done by
adding almost anything basic to the solution. Some things that might be
used
are baking soda (it may take quite a bit if the solution is very acidic,
however), washing soda, or lye (if you can get it). Do not use ammonia
because
it may complex the chromium and prevent it from precipitating. If you
use
some of the stronger bases such as washing soda or lye, get the solution
just
on the basic side of neutrality, i.e., do not make it strongly basic.
This
may be checked with litmus paper. Added just enough of the base to turn
litmus blue.
You can then filter the solution to remove the solid metal hydroxides.
Yes, a coffee filter will probably do the job very nicely. I would not
advise
using the equipment to do the filtering for later making coffee, however.
You will then be left with a problem of getting rid of the solids.
They should probably be given to a hazardous waste disposal company.
They
should NOT be put out with the domestic trash.
Addition of chloride will, indeed, precipitate silver ion as wellunless
there
is much thiosulfate (or ammonia) present. Table salt will work well as
a source of chloride.
Good luck. If you think that this is useful enough, please do not
hesitate to post it to the newsgroup for me.
David Bailey
*************************
From: monson@mycroft.ECE.ORST.EDU (Ty Monson)
Newsgroups: rec.photo.darkroom
Subject: Re: Disposal of Dichromates
Date: 7 Nov 1994 19:39:51 GMT
Organization: Electrical and Computer Engineering
NNTP-Posting-Host: mycroft.ece.orst.edu
In article <<CyuuB1.IB0@hq.ileaf.com>,
Carson Graves x4692 3NE <<carson@HQ.Ileaf.COM> wrote:
>it says about disposing dichromates:
(deletions)
>ions leave the processing laboratory. Dichromate ion in
>bleach solutions contains hexavalent chromium (that is having a
>valence of six), and can be converted into trivalent chromium
>(and thus precipitated) by the addition of any of several
>chemical reducing agents such as thiosulfate or sulfite. Any
>alkaline material (including waste developer) can be added to
>neutralize the acidity and cause the chromium to precipitate as
>the hydroxide.
>The mixture can be filtered so that the solid waste can be
>disposed of without discharging soluble dichromate or chromate
>ions into the sewer. Note that any silver bearing dichromate
>bleach can be desilvered by adding sodium chloride after treatment
>with hydroxide [??? I assume this refers to using something like
>sodium hydroxide to neutralize acidity]. The silver chloride
>can be filtered off along with the chromium hydroxide and sent
>out for refining."
(thanks for the useful info., Carson)
I think the Kodak writer presumed that a lab would add a base, such as
sodium hydroxide, to effect the shift to a basic solution. (Note that
Rodinal developer uses KOH to achieve a basic pH.) What the text above
implies is that you can remove Cr and Ag from solution by mixing
in some lye and common table salt. It appears that this is an
alternative
to simply mixing some sodium thiosulfate or sodium sulfite into
the dichromate solution to precipitate Cr, as Cr2O3?
On Thu, 27 Apr 2000 17:07:08 -0500 (CDT) Linda Phillips
<linda__phillips@hotmail.com> writes:
>My excitement at having recently discovered the Gum Bichromate process
>is being threatened by the hazards of working with Potassium Dichromate.
>This stuff is NASTY, being both caustic AND carcinogenic.
>My question: how do other dichromate users, gum printers, carbon
>printers, etc., dispose of the used dichromate water? Obviously, there
are
>local ordinances about putting this stuff into the environment. I've
been
>collecting this stuff is gallon jugs and I'm at a loss as to what to
>do with it! Is there some kind of chemical means of rendering it
harmless?
>________________________________________________________________________
>Get Your Private, Free E-mail from MSN Hotmail at
>http://www.hotmail.com
>
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