Ecc International Limited

Ecc America Inc.

Vasant D Chapnerkar

Vijay K Mathur

Vicente B Lasmarias

Mohan N Badgujar

A process for producing rhombic or barrel shaped precipitated calcium carbonate. Quicklime is slaked in an aqueous solution containing about 0.1% to about 2% by weight of a sugar, based upon the weight of the CaCO.sub.3 to be produced. Carbon dioxide is added to the slaked lime slurry at a preferred temperature of about 50.degree. F.-70.degree. F. until the pH drops from about 11-12 to about 7-8.

Process for production of rhombic shaped precipitated calcium carbonate

A method for preparing an acid resistant calcium carbonate pigment. An aqueous slurry of particulate calcium carbonate is provided at a pH of from about 11.0 to 12.0 and having from 2 to 5 g/l of excess calcium hydroxide. The slurry temperature is brought to the range of about 75.degree. to 80.degree. C., and sodium silicate solution is slowly mixed therewith to provide on a solid dry weight ratio from about 5 to 10% sodium silicate to calcium carbonate. Gaseous carbon dioxide is added to bring the slurry pH to the range of about 10.2 to 10.7, and the slurry is cooled to about 25.degree. to 30.degree. C. Finally zinc chloride is added to the cooled slurry to bring the pH to within the range of 7.5 to 8.0.

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Tampa, FL, United States of America

Vasant D Chapnerkar