Electrochemical process for the production of chromic acid

US5068015A · kind A · utility

Assignee

• BAYER HEALTHCARE LLC · DE

Inventors

• Hans-Dieter Block · Cologne, DE
• Norbert Lonhoff · Leverkusen, DE
• Bernd Makowka · Bensberg, DE
• Helmut Klotz · Friedrichshafen, DE
• Rainer Weber · Leverkusen, DE
• Bernhard Spreckelmeyer · Johannesburg, ZA

Key dates

• Filing date: Aug 15, 1989
• Grant date: Nov 26, 1991
• Expiry date: Aug 15, 2009

Classification

• Technology area (CPC C): Chemistry; Metallurgy
• CPC primary: C25B1/22
• WIPO field: Surface technology, coating
• WIPO sector: Chemistry

Abstract

A process for the production of chromic acid by the multistage electrolysis of dichromate and/or monochromate solutions in two-compartment electrolysis cells, of which the anode and cathode compartments are separated by cation exchanger membranes, at temperatures in the range from 50.degree. to 90.degree. C., the dichromate and/or monochromate solutions being obtained by the digestion of chrome ores and leaching, the improvement wherein, optionally after the removal of aluminum, vanadium and other impurities, the monochromate solution obtained after leaching is adjusted at 20.degree. to 110.degree. C. to a pH value of from 8 to 12 by the addition and/or in situ formation of carbonate in a quantity of from 0.01 to 0.18 mol/l (for 300 to 500 g/l Na.sub.2 CrO.sub.4, converted with CO.sub.2 under pressure into a dichromate-containing solution, the dichromate-containing solution is introduced into the anode compartment of the electrolysis cell, a solution containing chromic acid, in which the molar ratio of Na ions to chromic acid is from 0.45:0.55 to 0.30:0.70, is electrolytically produced and the chromic acid is worked up by crystallization, washing and drying.