Regeneration of Waste Chromic Acid Etching Solutions in an Industrial-scale Research Unit.
George-LC; Soboroff-DM; Cochran-AA
Proc 3D EPA/aes Conf on Advanced Pollution Control for the Metal Finishing Industry Kiss Florida :4 pages
Substantial amounts of chromium are lost in various surface- finishing operations and pollution problems are created when spent solutions containing hexavalent chromium and sulfuric acid are discarded. Laboratory research has shown that these spent etching solutions can be regenerated in a diaphragm cell. When the spent solution is placed in the anode chamber, most of the cr3+, produced during etching operations, is oxidized to cr6+. Impurity metals dissolved during the etching operation are transferred to the catholyte. When waste brass etchants are treated, about one-third of the copper and zinc is removed. The energy consumption is less than 9 kwhr/kg of sodium dichromate regenerated. Similar results are obtained with spent printed-circuit-board etchants and rinse waters from plastic etching operations. An industrial-scale research unit capable of oxidizing up to 0.5 Kg/hr of trivalent chromium has been operated to demonstrate the viability of the recycling techniques. Regenerated brass etchants evaluated by two companies equaled or exceeded the performance of fresh etchants.
Proc. 3D EPA/aes Conf. on Advanced Pollution Control for the Metal Finishing Industry, Kiss. Fl