Regeneration of plastic etchants

Claim 1

In a plastic etching process wherein plastic workpieces are subjected to etching by a chromic acid-sulfuric acid etchant solution in an etch zone and then rinsed with water in a rinse zone, and wherein during the course of the process the etchant solution and the rinse water become spent, the spent etchant being depleted in hexavalent chromium, enriched in trivalent chromium and contaminated with plastic organic breakdown products, the spent rinse water being enriched with such spent etchant, the method of at least partially removing such organic breakdown products from the spent etchant, while regenerating etchant for reuse within the plastic etching process, which method comprises: withdrawing spent etchant from the etch zone and spent rinse water from the rinse zone; diluting spent etchant with spent rinse water; heating the diluted spent etchant to at least about 60° C.; passing said heated diluted etchant solution into the anode chamber of an electrolytic cell, which contains a permselective ion exchange membrane which divides the cell into said anode chamber and a cathode chamber; maintaining an aqueous sulfuric acid solution in the cathode chamber; electrically energizing the solutions in the anode and cathode chambers by cooperating anode and cathode means; oxidizing plastic organic breakdown products in said anode chamber at a temperature of at least 60° C. while preventing transfer of anions to the cathode chamber; withdrawing a chromic acid-sulfuric acid solution, which is depleted in organic content and enriched in hexavalent chromium, from the anode chamber into an evaporation zone; increasing the temperature of said chromic acid-sulfur acid solution in the evaporation zone to remove additional quantities of organic breakdown products, to evaporate water from said solution and to recover a reconcentrated regenerated chromic acid-sulfuric acid solution, and passing said concentrated solution to the etch zone.