Archive of the former Yahoo!Groups mailing list: Homebrew PCBs

--- In Homebrew_PCBs@yahoogroups.com, "dl5012" <dl5012@...> wrote:
(snip)
> What is the proper way to dispose of used ferric chloride?
(snip)

Go to the grocery store and but a box of washing soda (sodium
carbonate) for a dollar or two. When you have exausted the ferric
chloride, or just wish to dispose of some, just slowly neutralize it
(in an oversized container) with washing soda. I say, "slowly",
because the reaction will produce a lot of foam. When there is no
more visible reaction, the ferric chloride will have almost totally
been converted to insoluble iron and copper carbonate, that will
settle to the bottom as a mud. After that happens, you can pour the
liquid (salt water) down the drain, and put the mud in the garbage.
In effect, you have recreated some iron and copper ore.

Other carbonate based chemicals can also be used (sodium bicarbonate,
calcium carbonate or lime, even portland cement). But sodium
carbonate is very cheap; the liquid residue is just salt and any extra
washing soda, and sodium carbonate also serves as a developer for many
kinds of positive resist, so it is handy to have some around.