I know that iron salts are safe to dump (in reasonable concentrations), but
that news about aluminum in the environment is good to know. So scrap iron
it is. Small pieces are faster because increased surface area, but metal
powder is definitely not required, steel food cans out of the trash bin do
a perfectly fine job. Over the years I have dumped many liters of this
neutralized precipitated etchant solution on my garden, with zero effect.
Steve,
I should try write up a web page someday on treating etchants with scrap
iron, but I would only doing this after getting more scientific results and
doing a few experiments. I suspect the copper concentration in the solution
after 1 week is under 100 ppm (%0.01 or 0.1 g/liter). I can test this by
adding excess ammonium hydroxide and so any copper dissolved in there will
form deep blue copper complex. Normally, in clear solutions a extreamily
faint blue tint is visible at Cu concentrations around 10ppm. But the
dissolved iron(II) ions forms cloudy yellow/brown iron(II) hydroxide with
the ammonium hydroxide and makes it difficult see the blue shade. The
ammonium hydroxide is only needed as a test to confirm the process is working.
Adam
Richard Mustakos wrote:
> 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.
> ....