DJ Delorie wrote:
>
> IIRC you add a base (sodium hydroxide (drain cleaner) if you have it,
> else baking soda) until the copper precipitates. That tells you the
> pH has just passed neutral. Let the water evaporate, leaving a copper
> salt "brick" at the bottom. Bring that to a hazmat place.
>
Not really like that. I don't really know what chemistry things happens
for sure but i can say that (since dumbly i try it once with a bit of
used etchant) if you add NaOH until the thing starts to warm and get hot
(or warm it by other means), after it cool and settle down you will end
with a black fine powder mud at bottom that should be the complex
Cu(FeO(OH)2)2 thing, above it a block of crystal NaCl in about the same
amount of added NaOH, and all the remaining up top is clean transparent
water. But it end even worst for disposal (etchant plus NaOH). SO DONT
DO IT!!
There is no away i know to precipitate the copper on Cl based etchants.
But i guess in my ignorance that FeCl3 etchants should be possible to
expensively recover copper like CuCl with those DuPont ion membrane,
large platinum anodes and ~1000A psu like some big pcb shops seem to do,
ending with HCl and copper bars IIRC.
Anyway nobody should use Ferric Chloride etchant this days, is a mess,
non recoverable, not simple to disposal (pollutant if you dump it),
expensive, and in 2010 you have plenty alternatives available like
Cupric Chloride.