GB1388204A - Process for the treatment of exhausted chromium-plating solutions - Google Patents

Abstract

1388204 Treating chromium plating solution FUJI KUROMU SHA KK 4 April 1972 [5 April 1971 14 Aug 1971 (2)] 15428/72 Heading C1A [Also in Division C7] Exhausted aqueous chromium plating solution is treated with chromium trihydroxide or an alcohol of formula ROH wherein R is an alkyl group having 1 to 3 carbon atoms (e.g. ethyl alcohol), to convert all chromium values contained in the exhausted solution to a chromium chromate complex compound containing Cr<SP>6+</SP> and Cr<SP>3+</SP> ions and to convert iron values contained in the exhausted solution to ferric hydroxide and the resulting mixture is filtered to separate the aqueous chromium chromate complex compound solution from the ferric hydroxide. The chromium trihydroxide may be employed in a stoichiometrically equivalent amount to the chromic anhydride content of the exhausted solution and the alcohol may be employed in an amount of 400 ml. per 1 kg. of chromic anhydride in the exhausted solution. The ferric hydroxide residue may be burnt to convert it to ferric oxide and the aqueous chromium chromate complex solution obtained may be recycled to the chromium plating solution or can be used as an anode electrolyte in diaphragm electrolysis employing potassium dichromate, sodium dichromate, ammonium dichromate, potassium chromate, sodium chromate or ammonium chromate alone or in admixture as the cathode electrolyte to produce regenerated chromium plating solution.