Method for preparing acid resistant calcium carbonate pigments
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United States of America Patent
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Nov 17, 1992
Grant Date -
N/A
app pub date -
Apr 8, 1991
filing date -
Apr 8, 1991
priority date (Note) -
Expired
status (Latency Note)
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Abstract
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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