Precipitating Excess Copper in a Peroxide-Sulfuric Etchant

Procedure:

1. Use the sulfuric acid analysis procedure to determine the sulfuric acid content.
2. If necessary, add enough acid to bring the total concentration up to a minimum of 10% (by volume). The level of acid will bring bring the pH of the bath down to a point where the excess copper will spontaneously precipitate out as the bath cools.

3. One half of the etchant should now be drained into the carboy supplied with the system (marked ETCHANT) and allowed to sit in a cool place until it's temperature drops below 20 degrees C. At that point the copper will precipitate out as copper sulfate pentahydrate, a bright blue crystal that will settle to the bottom of the carboy. Precipitation will commence as soon as the etchant has cooled, but the carboys should be allowed to sit for at least a couple of days to ensure that adequate separation occurs. Note: precipitation can be accelerated by using a lower temperature, the lower the better, as long as the electrolyte does not freeze.

4. Once precipitation is complete, the etchant should be pumped back into the etcher with care being exercised to avoid picking up any of the sediment. After the etcher is refilled, it should be re-analyzed for both hydrogen peroxide and acid content.
5. Decant the copper sulfate pentahydrate crystals into a holding container (plastic) and allow it to air dry. These crystals can be used to make a concentrated solution of copper sulfate which, after carbon treating, can be added to the acid copper plating bath to reduce erosion of the anode material.

Chemical Analysis