Process for the preparation of chromic acid

US5096548A · kind A · utility

Assignee

• BAYER HEALTHCARE LLC · DE

Inventors

• Norbert Lonhoff · Leverkusen, DE
• Ludwig Schmidt · Krefeld, DE
• Hans-Dieter Block · Cologne, DE
• Rainer Weber · Leverkusen, DE

Key dates

• Filing date: Dec 11, 1990
• Grant date: Mar 17, 1992
• Expiry date: Dec 11, 2010

Classification

• Technology area (CPC C): Chemistry; Metallurgy
• CPC primary: C25C1/10
• WIPO field: Surface technology, coating
• WIPO sector: Chemistry

Abstract

A process for the production of chromic acid, comprising PA1 (a) dissolving ferrochrome in sulphuric acid and mother liquor from the subsequent crystallization of ammonium chrome alum, optionally with the addition of at least one of catholyte and anolyte overflow from the subsequent electrolysis, PA1 (b) removing undissolved constituents by filtration, PA1 (c) removing dissolved iron by the addition of at least one of ammonia and ammonium sulphate to the filtrate obtained, crystallizing iron ammonium sulphate and filtering, PA1 (d) crystallizing and filtering ammonium chrome alum from the remaining solution and returning the filtrate for dissolving ferrochrome in step (a), PA1 (e) dissolving the ammonium chrome alum in water, PA1 (f) precipitating and separating chromium-(III) hydroxide from the resulting solution by adding a base, optionally under reducing conditions, PA1 (g) dissolving the separated chromium hydroxide in chromic acid and optionally sulphuric acid so that either a single solution in chromic acid is obtained or two solutions are obtained, one in chromic acid and another in sulphuric acid, PA1 (h) separating the solution(s) from undissolved constituents, and PA1 (i)…