I've looked a little more into the question of recycling ferric chloride
etchant by electroplating the copper out and revitalizing the reduced iron
to the oxidized form.

The standard potential for the cell

        Fe | FeCl3 | CuCl2 | Cu

is -0.78 V, with the driving EMF cathode at the Fe electrode and the anode
connected to the Cu electrode.

Unfortunately, it takes a lot of current to plate out the copper. A
double-sided, 12-sq.in. board at 1 oz/sq.ft./side contains 4.7 g Cu.
Therefore it takes 2.4 amp-hrs of current to plate it out!

Using iron nails as electrodes, you can drive about 0.1 A, so the process
would take about 24 hrs for each circuit board. For totally spent etchant
(i.e., 200 sq. in. per pint) the process could be up to 15x longer!

Obviously a larger surface electrode is needed to allow more current flow.

But now there's the problem of an efficient, high current, low voltage
power supply.

Anyone got any ideas on how to efficiently generate 1 A @ 1 V?

By the way, a double-sided 3" x 4" pcb will use about $.20 of etchant, if
you buy in large containers (e.g., 1/2 gal.), so this is more an
intellectual exercise than a major cost-saving issue.



================================================================
Robert A. LaBudde, PhD, PAS, Dpl. ACAFS  e-mail: ral@lcfltd.com
Least Cost Formulations, Ltd.                   URL: http://lcfltd.com/
824 Timberlake Drive                            Tel: 757-467-0954
Virginia Beach, VA 23464-3239                   Fax: 757-467-2947

"Vere scire est per causae scire"
================================================================