Process for the preparation of chromic acid

US5181994A · 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: Jan 26, 1993
• Expiry date: Dec 11, 2010

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, comprising PA0 a) dissolving ferrochrome in sulphuric acid, optionally with the addition of catholyte and/or anolyte overflow from the electrolysis, PA0 b) removing undissolved constituents by filtration, PA0 c) adding a reducing agent in a quantity more than equivalent to the quantity of iron(III) and chromium(IV) in the solution, PA0 d) precipitating chromium(III) hydroxide by raising the pH to about 4-6 by the addition of a base while maintaining the reducing conditions in the solution, PA0 e) separating the precipitated chromium hydroxide while maintaining the reducing conditions, PA0 f) working up the aqueous solution containing iron by oxidation; precipitating iron(III) hydroxide or iron(III) oxide and optionally isolating the sulphate in the solution as sodium sulphate, ammonium sulphate or calcium sulphate, PA0 g) dissolving the separated chromium hydroxide in chromic acid and optionally sulphuric acid where either a single solution in chromic acid is produced or two solutions are produced, one in chromic acid and another in sulphuric acid, PA0 h) separating the solution(s) from undissolved constituents and PA0 i) employing the …