Re: Gum Dichromate print washing

Peter Marshall (petermarshall@cix.compulink.co.uk)
Thu, 6 Apr 95 19:53 BST-1

In-Reply-To: <199504061544.LAA03677@mcmail.CIS.McMaster.CA>
> From a hazardous chemicals disposal guide - for both sodium and
> potassium dichromate:
>
> In a solution of 5g dichromate per 100ml. of water add about 40 to 60
> ml. of 3M sulphuric acid. (rest deleted)

This post by John Hudak I think shows one of the problems. In
photographic processes we are not dealing with 5% solutions of waste
dichromates, but typically solutions that are several orders of magnitude
less concentrated. There may be a case - in some areas - for altering
our procedures, for example to give an initial wash in a minimum quantity
of water to remove the bulk of the dichromate. This could then be treated
to precipitate chromium as hydroxide (a good use for waste developer).

Further washes are probably going to be too dilute for such methods to be
really practiable. Possibly ion-exchange methods could be used?

I suspect in many areas the amounts and levels from small-scale
operations would be acceptable.

Peter Marshall
petermarshall@cix.compulink.co.uk