Homebrew PCBs

Adam,
Thanks for the info on slaked lime.
But go with the iron: aluminum may be better at getting the copper out, 
but when I asked a company that deals with powdered metals about the 
toxic waste thing, they said that aluminum was considered more hazardous 
then copper.  They said there were no restriction on copper for them, 
but there were aluminum restrictions.
But if you do use aluminum, treat it right.  Small aluminum 
powder/crystals are not a fire hazard directly, like phosphorus or 
plutonium (phosphogenic?), but they are a combustion hazard.  My father 
told me that in Viet Nam, they used aluminum powder with a small starter 
charge to blow up buildings,  The small charge mixed the aluminum powder 
with the air, and started it burning.  Aluminum burns fairly slowly 
(compared to explosives), so it's not a sharp explosion, just a big old 
push that lifts the roof up and knocks the walls down.  I expect that is 
the case with most metallic powders.  I don't know the powder volume 
requirements to do damage, so be careful with it, or store it outside. 
 But even plate aluminum burns - that is, sustains a fire with no help 
once started (USS Stark and M113s, for instance), while iron plate does 
not.  I guess Aluminum burning releases more KWatts per unit mass, and 
has a lower ignition temperature then steel or iron.
Richard

>If you want to remove copper then easiest approach is throw in some scrap 
>iron and/or aluminum while the etchant is still slightly acidic. The copper 
>precipitates as copper metal and aluminium/iron goes into solution.
>After about 1 week the solution will be crystal clear with brown copper 
>sludge on the bottom. Syphon out most of the liquid being careful not to 
>disturb the sediment, neutralize the remaining sludge and leave few days to 
>dry to a dark crust. Works well with spent ammonium persulfate etchant and 
>CuCl. But I havn't tried treating FeCl3 etchant this way.
>
>Adam
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