Homebrew PCBs

"perri.anthony" <perri.anthony@...> writes:
> So I mixed a solution of Muriatic Acid (1/2 cup) & Hydrogen Peroxide (1
> Cup) to etch a board. It worked very well but now I am trying to figure
> our how much baking soda it would take to neutralize that solution so it
> can be safely disposed of.

A couple of things...

First, don't!  Keep the solution around and use it for other boards.
Eventually it will turn a dark green and become copper chloride
etchant, which doesn't "expire".  Note that this works if you're going
to do it soon, else the peroxide breaks down and etching takes a lot
longer.  If you leave it as-is for a while and want to re-use it, just
add a little more acid and peroxide to "charge" it again.  Once
there's enough copper in solution, you can recharge (regenerate) it
with an air bubbler, then it's good pretty much forever.

Alternatively, add a bunch of copper to it now just to convert it.  I
think I figured a half pound of copper per liter of HCl - you want the
specific gravity (density) of the solution up to at least 1.2 for CuCl
etchant (for details, see Adam's page at:
http://members.optusnet.com.au/~eseychell/PCB/etching_CuCl/)

Second, the copper in solution acts as a pH guide.  It's green/brown
in solution, but once the pH rises above 7 it precipitates out as a
white milky fog.  This assumes you have enough in solution to see the
change, though.