Process for making calciummonohydrogen phosphate dihydrate

US4483837A · kind A · utility

Assignee

• Hoechst GmbH · DE

Inventors

• Josef Cremer · Hürth, DE
• Josef Holz · Lechenich, DE
• Hans Haas
• Friedrich Schulte · Mechernich, DE

Key dates

• Filing date: Jun 24, 1983
• Grant date: Nov 20, 1984
• Expiry date: Jun 24, 2003

Classification

• Technology area (CPC C): Chemistry; Metallurgy
• CPC primary: C01B25/322
• WIPO field: Materials, metallurgy
• WIPO sector: Chemistry

Abstract

The disclosure relates to a process for making calciummonohydrogen phosphate dihydrate with a high degree of whiteness from pure phosphoric acid and naturally occurring calcium carbonates. More particularly, a fine-particulate calcium carbonate is suspended in water and the suspension is mixed at temperatures between 0.degree. and 60.degree. C. with phosphoric acid so as to establish a Ca/P-ratio of 0.20 up to 0.57. The phosphoric acid is added in quantities per unit time preventing the resulting mixture from foaming over. Next, solid matter constituents are separated from the mixture, after CO.sub.2 has ceased to evolve, with the resultant formation of a clear colorless acid solution. This solution and an aqueous suspension or solution of pure alkali metal and/or alkaline earth metal carbonates and/or hydroxides, are jointly introduced into a reaction zone at a reaction temperature of 20.degree. to 45.degree. C. so as to establish a pH-value initially of 2.0 to 5.0 and then, towards the end of the reaction of 6.0 to 8.0. Finally, the reaction product is filtered off, washed out, and dried in known fashion.