Ferric chloride solution is somewhat acidic. If you add some baking
soda, you will precipitate out almost all the iron. If you first use
the solution till it doesn't etch well any longer, there's not a whole
lot of ferric left in it; it's mostly ferrous, which isn't
particularly corrosive. You can toss in a couple old steel nails to
finish the conversion from ferric if you wish. Considering the amount
of rust in junkyards, I wouldn't be concerned about the small amount
of ferrous you're adding. HOWEVER, I would be more concerned with the
copper ions, which, I believe, are considerably more toxic than iron
to most life on earth, including things that digest sewage. If it's
tiny hobby amounts, it may not be a significant increment, because of
all the copper plumbing in homes, but to be safe you can lock it up in
Portland cement as Ian says.

Another etchant to consider is cupric chloride. You can make a
self-regenerating etchant; etching boards makes more etchant.
Instructions at http://users.rcn.com/rexa/Projects/CuCl_ech.html.

Cheers,
Tom


Dick wrote in message ...
Thanks to the group for all the past advice given on PCB
drafting software & UV exposure boxes, it's all being put to good use.

In the past I've used ferric chloride professionally as my
etchant (and left disposal of the etching solution to the work's
chemist) but now I'm doing things for myself safe disposal is going to
be my problem, searching on the web for an answer ammonium and sodium
persulphate come up as a suitable alternatives but not ones I've used.
Does anyone have experience of using persulphates as a D-I-Y PCB etchant
? Are they as good as ferric chloride, are there any problems with using
them & how easy is it to dispose of the spent solution ?