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Registered Member #1497
Joined: Thu May 22 2008, 05:24AM
Location: Toronto, Ontario, Canada
Posts: 801
So after having etched a ton of boards, I've produced something like 2L of etchant, mostly low concentration due to unavailability of 30% hydrogen peroxide. Chris helped me figure out a procedure to recover the copper so that copper is not introduced into the water table. If you can get ahold of NaOH pellets (or other hydroxides), this is a easy (albeit time consuming) way to clean up the copper before disposing of etchant, and the CuO can be used for other reactions.
Note: this procedure may also work with sodium bicarbonate (baking soda), although you will produce the slightly soluble CuCO3, and you will need to heat it strongly to get the oxide, however baking soda is more readily available.
Procedure: - Take aqueous solution, add NaOH pellets slowly with stirring (this step is exothermic, do not let the temperature rise to the point where the solution bumps/boils and splatters all over). A water bath to help cool the beaker can be used.
- Add NaOH pellets until turquoise or blue-green precipitate begins to form without redissolving, let the solution settle for 10 minutes, add another portion of NaOH pellets slowly.
- When mixture begins to thicken, continue stirring, do not add more NaOH, let sit for at least 10-20 minutes until solution darkens (Cu(OH)2 has formed, but Cu(OH)2 -> CuO is a slower reaction).
- pH should be approximately 10-13 when reaction is complete, there should be no visible blue-green precipitate.
- Filter suspension by gravity, use coarse filter paper (coffee filters acceptable substitute), then wash continually with water until wash water tests pH ~7 (it is advisable to use multiple funnels and set up several smaller filtrations as the CuO is fine enough to slow filtration).
- Once pH is neutral, let the filter drain as much as possible, transfer CuO paste to a heat-resistant container (preferably glass, metals may react and is untested) and set in oven at approx 300degF until dry and crumbly.
- Break chunks of CuO to check for moist pockets, once completely dry, CuO can be ground to powder if desired.
So now I'm wondering, what uses are there for CuO.... the only one so far that I know of is dissolving in sulfuric acid to form CuSO4, and copper plating.
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Cleanup of HCl + CuCl2 etchant (or HCl + H2O2, however you want to look at it)
