When etching circuit boards, a somewhat commonly used substitute for (expensive and messy) ferric chloride is a mixture of an acid, a source of chloride ions, and hydrogen peroxide. If I understand the chemistry correctly, the acidic environment allows the copper to react with the chlorine ions to make $\ce{CuCl2}$, which will more slowly react with the copper again to make $\ce{2 CuCl}$. Adding oxygen to the solution (from the peroxide or just by aerating it) makes $\ce{CuO}$ and $\ce{CuCl2}$ again, allowing the process to repeat.
I meant to mix $\ce{H2O2}$, acetic acid and table salt, but accidentally used citric acid instead of acetic acid. After realizing my mistake, I added scraps of aluminum foil to the mixture to displace the copper, and render the mixture safer to dispose of. I went to filter out the copper and dispose of the rest, when I found that there was a layer of some kind of gelatinous substance coating the exposed surfaces in my container. Does anyone have any idea of what it could be, and how I might safely dispose it?
