Method and apparatus for regenerating an ammoniacal etching solution

Abstract

Ammoniacal etching solution containing metal ions as the result of etching is withdrawn from an etching bath and while part of it goes to an electrolysis cell for removal of metal ion, the remainder goes back to the etching bath through a liquid jet pump in which it serves as the working liquid, while the pump sucks in from the electrolysis cell the anodically evolved oxygen. The thorough mixing of the oxygen into the etching solution performed by the pump results in oxidation so rapid that in many cases it becomes unnecessary to suspend catalyst particles in the electrolyte to accelerate the oxidative regeneration of the etching solution. Where use of such particles is still desired, the solution drawn from the etching bath goes through a cylindrical filter unit from which a filtrate is drawn off laterally for the electrolysis cell, while the remainder of the input goes to the jet pump. Controls are provided for using the electrolysis cell only when the metal ion concentration is above a predetermined value, for adding ammonia to the oxygen line in order to maintain a particular value of pH and for controlling the temperature of the electrolyte in the electrolysis cell in order that a desired quantity of water can be condensed from the oxygen line for use in rinsing the work pieces after they are taken out of the etching bath.