Homebrew PCBs

Dave wrote:
> 
> 
> Over the years, I've wondered about regenerating Ferric Chloride, 
> too.  One approach I've tied is reverse electroplating the Copper 
> (from the Copper Chloride) out of the solution, replacing it with
> Iron.  It seems to work, in that I definitely produced Copper on
> on the cathode, while the Iron anode was dissolved (Actually, my
> current density was a bit high, so I produced crystals of metallic
> Copper on the cathode).  Of course, one concern is that you don't
> produce Chlorine gas (and, if you do, you want to make VERY sure
> you don't breathe it!).  
> 
> I don't remember how the resulting solution worked (It's been quite
> a number of years ago.), although my main idea at the time was 
> removing the Copper from the spent solution (since dissolved Copper
> compounds are lethal to most biological life forms).
> 
> Anyway, I don't know that I'd recommend this to anyone, but it may
> be something to think about (especially if there are any 
> electrochemists in the group).
> 
> Dave
> 


You have to use inert anodes, so the chlorine can react with the ion(II) 
and convert it back to iron(III), ferric. If you use metallic iron 
anodes then that'll just be replacing the copper(II) with iron(II) ions. 
To get iron(III), you somehow have to 'harness' the chlorine gas. 
Graphite is a common anode for this purpose. Rods available from 
industrial welding suppliers. You may need to spin the anode(s) to 
minimize gas bubbles, and get the gas to dissolve fast as possible. 
Spinning also greatly extends anode life. You also have to avoid freshly 
generated iron(III) chloride from contacting the copper cathode or 
you'll be etching fast than plating out and so cell efficiency drops to 
zero. Wrapping the cathode in layers of polyester/polypropylene cloth to 
avoid solution flow is one method.
Another problem is knowing the termination point. Continuing 
electrolysis after most of the iron(II) has oxidized to iron(III) will 
causes chlorine to have no where else to go except in the room.

I've never tried the above, but who knows, there may exist a simple and 
safe way to regenerate spent FeCl3.

Adam.