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Abstract

In addition to catalyzing the reoxidization of spent alkaline etching age the suspension of activated carbon powder in the etching solution also increases the speed of etching when the etching solution is recirculated in the etching of printed circuit boards. The ammonium sulfate etching solution is set to a pH of about 9 by the addition of ammonia gas. In the recirculation of the etching solution, a part of the solution can be freed by filtration from suspended carbon particles and passed through the cathode and anode chambers of an electrolysis cell for the recovery of the etched metal by deposition on the cathode. The activated carbon powder for this purpose is calcined before use, at a temperature of between 900.degree. and 1200.degree. C. in vacuum or in an atmosphere that is inert, reducing, or only slightly oxidizing as in the case of an atmosphere containing carbon dioxide, water vapor or both, in a concentration that does not appreciably oxidize the carbon particles.

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First Claim