----- Original Message -----
From: "P. J. Alling"
Subject: Re: Developing Chemical Disposal
a septic system as it will have that effect on the flora that breaks
down waste. There's a lot of silver in the fixer when it's exhausted,
something like 90% of the amount originally present, you can recover
that.or you can build your own which considering the price of silver
might be worth while. You might want to look into one of these.
http://www.porters.com/catalogsearch/result/?q=Silver+Magnet
I believe that the dissolved silver in fixer is part of a sulpher compund
(silver sulphite).
I could be wrong though.
Did the OP ever say if he was using a septic field or just a tank that
was pumped out periodically?
William Robb
I haven't looked at the chemestry in a long time. A little silver nitrate
can kill a lot of bacteria though. Recovering the silver before
discarding the solutions just strikes me as good economics, if you're
processing enough film. It's up to you to decide what's enough. I'll bet
the break even point on silver recovery is sooner than the break even
point on installing solar power panels, and I know people who have done
that recently.
We did electrolitic recovery at a few of the labs I worked at, but
eventually gave them up as not being cost effective.
It just took too much electricity to crack out the silver.
All the labs I worked in since ~1990 used recovery tanks that were, in
essence, iron wool with channels for the chemistry to flow through and a
catalyst to make the ionic exchange process happen.
This is a very cheap recovery process, as it is using a sacrificial metal
process to capture the silver.
It is really hard on sewer systems, since the iron bearing effluent has
really good pipe clogging properties.
I just did a quick look at Wikipedia, and it bears out what I remember,
which is that the dissolved silver is tied to sulper as silver thiosulphate.
Although silver nitrate is a precursor to the silver used in photographic
materials, it is generally treated with either sodium or potassium to form
the light sensitive silver halide that becomes part of the film stock, and
as there is no nitric acid used in any of the common processes, I don't
think there is any way for silver nitrate to form in the used chemistry.
Whether it is worthwhile to recycle it, dump it or recover the silver
depends to a great extent on the amount of product that is used. The old
school way of thinking was that the average home darkroom user who was only
processing a few films a month was presenting no harm to the environment by
flushing used chemistry down the sewer.
This doesn't address a septic system that is incorporating either a small
septic pond or field. I expect the biology of those is easily enough knocked
out of whack that some care wants to be taken.
If, OTOH, he is using a septic tank that is pumped out from time to time,
there would be much less to worry about WRT the toxicity of the chemistry,
especialy if all that is being done is low volume B&W.
William Robb
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