Process for the preparation of sodium dichromate

US5273735A · kind A · utility

Assignee

• BAYER HEALTHCARE LLC · DE

Inventors

• Rainer Weber · Leverkusen, DE
• Bernd Rosenow · Leverkusen, DE
• Hans-Dieter Block · Cologne, DE
• Norbert Lonhoff · Leverkusen, DE

Key dates

• Filing date: Nov 23, 1992
• Grant date: Dec 28, 1993
• Expiry date: Nov 23, 2012

Classification

• Technology area (CPC C): Chemistry; Metallurgy
• CPC primary: C01G37/14
• WIPO field: Materials, metallurgy
• WIPO sector: Chemistry

Abstract

A process for the preparation of sodium dichromate and sodium dichromate solutions by alkaline oxidizing roasting of chromium ores, leaching resulting roast with water, adjustment of the pH to 7 to 9.5, removal of the insoluble constituents by filtration, a sodium monochromate solution containing 300 to 400 g/l of Na.sub.2 CrO.sub.4 being obtained, conversion of the monochromate ions of this solution into dichromate ions by addition of an acid and/or by electrolysis and/or by reaction with carbon dioxide under pressure and crystallization of sodium dichromate by concentration of this solution. The improvement wherein before the conversion into a sodium dichromate solution, the sodium monochromate solution is concentrated to contents of 700 to 1000 g/l of Na.sub.2 CrO.sub.4, the monochromatic ions, the solution is subsequently freed as far as possible from sodium sulphate by cooling to a temperature of below 0.degree. C. and filtration, and the residual monochromate ions which remain in the solution are converted into dichromate ions by electrolysis and/or by reaction with carbon dioxide and/or with chromic acid.