--- In
Homebrew_PCBs@yahoogroups.com, "Stefan Trethan"
<stefan_trethan@...> wrote:
>
> On Mon, 15 Jan 2007 23:54:43 +0100, William Carr <Jkirk3279@...>
> wrote:
>
> >
> > I bring this up because I wondered if the process could be used to
> > recharge etchant. If you put a copper rod in as the sacrificial
> > scrap metal, you'd force copper into the solution.
> > William Carr
>
>
> Actually, you use a graphite rod as one electrode, or both, since
you want
> to get copper out of it not into it.
I've tried something similar to regenerate Ferric Chloride, using
an Iron electrode. I did get Copper deposited out in the form of
Copper crystals. And, some of the Iron was dissolved into the
solution. However, I'm not sure if it formed Ferric Chloride or
Ferrous Chloride (or something else entirely). I dont' remember
evolving any Chlorine gas, although I kept the current density
pretty low.
> I've tried it, but it doesn't work very well.
I don't remember if I ever tried the "regenerated" solution
(Like so many of my projects, I became distracted, and started
working on something else.).
> Chlorine gas is produced at the electrode (of course! you plate
> the Cu away from CuCl).
Or reacted with the electrode material to form some nonvolatile
compound.
> This chlorine gas would need dissolving in the etchant, otherwise
> you just pollute the air.
And poison yourself and others. Chlorine gas is NOT something to
play around with. It will kill you in a most unplesant way.
> One suggestion to do this was a rotating electrode. i am not
> impressed by that idea. I think one should try to make a downstream
> gas dissolver like used by aquarium people to dissolve CO2.
It might be a good idea to check the solubility of Chlorine in
water first. And, even if it dissolves, I'm not sure that's any
improvement, since it could later (when you least expect it) come
out of solution. In my opinion, it'd be better to react it to
a nonvolatile form.
> Basically a vertical tube filled with obstructions like marbles,
> gas introduced at the bottom, and a pump circulating water (in our
> case etchant) from the top to the bottom, so there is a downflow.
> This slows down the gas dramatically, giving time for dissolution
> (it could be closed up on top so any chlorine reaching the top
> would accumulate for later dissolving instead of escaping).
Perhaps. But, I'd want to work out all of the chemical equations
before even setting up a prototype operation.
> Who knows it may even be suffucient to catch the chlorine gas in an
> upside-down container and keep it there presented to the etchant
> for slow dissolving without any pumps. I never tried.
Perhaps. But, from what little I've done with Chlorine gas, and
from what I know about it, I'd just as soon stay as far away from it
as I can. That sounds too much like an accident trying to happen.
> A simple addition may be a magnetic stirrer to stir up the static
> gas/water for faster reaction.
Magnetic stirrers might help. Also, maintaining the correct pH
of the solution may help. Even irridation of the Cl2 might help
it to ionize and react with something (what?).
> The way this copper recovery is done industrially is by using a
> membrane between the electrodes that allows only ions through or
> something like that, i don't fully understand the process. But it
> works for them.
Such membranes usually aren't cheap, nor are they usually
inexpensive. But, they're probably the safer way to do things.
> It seems lotsa effort for little gain to me.
Probably. The only reason I was looking into this was that Ferric
Chloride is a bit of a pain to obtain locally (inexpensively),
so regenerating the spent solution sounded like an interesting
option. However, the Copper Chloride etchant sounds like an even
better idea (Note that you don't have to use the Hydrogen Peroxide
(H2O2) if you can areate the solution.).
> With the small number of boards i do excess CuCl has never been a
> problem.
And, even if it was, there are probably better ways of handling
that.
> ST
Dave