Patent ID: 6221146
Filing Date: 2001-04-24
Classification: C01F,C01P,D21H

Abstract:
A method of producing a precipitated calcium carbonate (pcc) product which has a coarse crystalline form which comprises the steps of:(a) preparing a suspension in an aqueous medium of calcium hydroxide particles which partially dissolve as calcium ions in the aqueous medium, the aqueous medium also incorporating an agent which promotes release into solution in the aqueous medium of calcium ions from the calcium hydroxide;(b) adding carbon dioxide to the aqueous medium to react with the calcium ions therein to produce a suspension in the aqueous medium of a precipitate of calcium carbonate crystals;(c) concentrating the suspension of the precipitate by a dewatering process; and(d) adding to the suspension of the precipitate a dispersing agent for the precipitate;wherein in step (a) the calcium hydroxide particles of the suspension of calcium hydroxide particles have a specific surface area measured by the BET nitrogen method of less than 33 m.sup.2 /g and the said agent comprises a water soluble organic compound present in an amount of from about 0.01% to about 0.20% by weight based on the dry weight of calcium carbonate to be produced from the calcium hydroxide in the aqueous medium, and in step (b) the carbon dioxide is first added to the aqueous medium when the temperature of the aqueous medium is in the range from about 5.degree. C. to about 12.degree. C. and is added at a rate such that the average rate of reaction of carbon dioxide and calcium ions expressed as weight of precipitate per unit time per unit volume of aqueous medium is in the range from about 0.4 g/min/L to about 2.0 g/min/L.