[Alt-photo] Dichromates and Septic System?

David Robertson david at robertson.yt
Thu Feb 15 17:12:00 UTC 2018

Adding sulphite to a dichromate solution causes the colour to change from orange/yellow to green. Since sulphite is cheap (I actually sell sodium sulphite on eBay so I have rather a lot of it) I just toss in an arbitrary amount, probably way more than is necessary. Not very scientific! Once it’s been reduced to Cr(III) I just rinse it down the drain with plenty of water - though I don’t have a septic tank.


> On 15 Feb 2018, at 14:10, Diana Bloomfield <dlhbloomfield at gmail.com> wrote:
> Thank you so much, David.  And I hate to be a pain here, but can you detail exactly what you do (ie, steps, amount, etc).  You can just email me if you'd rather.  Thanks again.
> Diana
> On Feb 15, 2018 8:55 AM, "David Robertson" <david at robertson.yt <mailto:david at robertson.yt>> wrote:
> Adding a reducing agent like sodium sulphite (or bisulphite) would reduce the chromium to the 3+ oxidation state. Chromium (III) is much less toxic than chromium (VI). I always do this before disposing of any hexavalent chromium compounds.
> David
> > On 15 Feb 2018, at 13:46, Diana Bloomfield via Alt-photo-process-list <alt-photo-process-list at lists.altphotolist.org <mailto:alt-photo-process-list at lists.altphotolist.org>> wrote:
> >
> > I'm sure this question has been asked and answered before, but I can't
> > locate it.  A friend who wants to learn gum printing asked about what to do
> > if you have well water?  Does anyone know the answer?  I thought there was
> > something you could add to a septic system that neutralizes the dichromate
> > somehow??  Thanks!
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