Homebrew PCBs

On 6/27/07, Gordon Couger <gordon.couger@...> wrote:
> The old saw, "Dilution is the solution to pollution", sure applies to
> Ferric chloride. It is used in fertilizer in dilute amounts.
> Neutralizing the acid and diluting it in 10 or 20 volumes of water makes
> it pretty safe. I can assure you Radio Shack doesn't sell anything that
> exposes them to much liability it's not good for the bottom line.  Here
> they use it in Compost http://www.greenmeadowfarms.com/manuretreatment.htm
>
> The dose makes the poison. Things that are deadly toxins in large
> amounts such a iron, zinc and copper are necessary to sustain all life
> in small amounts.

I don't think the etchant itself is any problem with most etchants,
acids are quickly neutralised (otherwise the hydrochloric acid in the
stomachs of our dead ancestors would have killed the planet long ago
;-).
Just pour HCL on limestone if you don't believe it.

The only problem might be copper, and remember radio shack does not
sell etchant with copper in it, you add it. So no "clean" FeCl MSDS or
disposal guideline does apply.

Sea water also contains copper (horseshoe crabs even have a
copper-based blue blood which is useful for medicine, and for the
horseshoe crabs of course.)

Deer (and probably most animals but i only know for sure with deer)
need some copper for their development, and if they are kept on ground
with not enough copper supplements must be given. I believe copper
sulphate is used which is also "very poisonous" just not in very tiny
amounts...

It's all a matter of quantity and while i don't intentionally dispose
of etchant via the sewer i don't hesitate washing PCBs and equipment
in the sink which by necessity flushes down some copper chloride. I've
also washed it on the grass and it didn't die. Tiny amounts......

Now a PCB manufacturing company is another matter, they must have
cascading washes and purify their waste, but they don't have tiny
amounts.

ST