A method for removing cyanides from cyanide-containing aqueous alkaline electrolyte by electrolytic oxidation of the cyanide

摘要

1,226,684. Electrolytically decomposing cyanide; degreasing. NORDNERO A.G. June 18, 1969 [June 19, 1968], No.30843/69. Heading C7B. In a multi-bath process for the surface treatment of metal articles which uses an aqueous cyanide solution, e.g. for Zn, Cu or Ag plating, the cyanide-containing liquid resulting from the rinsing of the articles after treatment is returned for oxidative electrolytic decomposition (to form carbonate and ammonia) to one or more electrolytic pre-treatment baths, e.g. alkaline anodic and cathodic degreasing baths, respectively containing a steel cathode and graphite anode, and both containing NaOH, Na 2 CO 3 and Na 2 SiO 3 ; the anodic degreasing bath may further contain a gluconate. Liquid from the post-treatment rinsing baths may be circulated through one or more ionexchange units, e.g. anion and cation exchange filters, to remove any remaining CN ions or metal CN complexes. An example of a Zn-plating bath contains 35 g/1 Zn, 30 g/1 NaOH and 110 g/1 NaCN, operating at a C.D. of 3-6 amp/sq dm. After plating, the articles may be HNO 3 pickled, then chromated in a bath containing alkali metal bichromate and F and SO 4 ions.