Precipitated calcium carbonate and method for the production thereof
AssigneeFP-Pigments Oy
InventorPentti Virtanen
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Abstract
The invention concerns precipitated calcium carbonate products containing polynuclear regular agglomerates having a number of calcium carbonate particles (aggregates) attached to each other and having a particle size of about 40 to 200 nm. According to the invention, these products are prepared by adjusting the Z potential of the calcium carbonate suspension to −1 . . . −20 mV by adjusting the pH of the suspension to 6.5 . . . 9.5. The pH of the calcium carbonate slurry obtained by causticizing is adjusted to a desired value in a box filter, where after the suspension is stirred by a heavy-duty mixer such that it is subjected to differences of about 50 to 200 m/s in peripheral speed. The products according to the invention have good opacity and are very well suited for coating paper.
Claims13
Precipitated calcium carbonate agglomerates containing a number of spherical calcium carbonate particles which are attached to each other and have a particle size of approximately 40 to 200 nm, wherein the particles are spherical with a deviation of less than about 10%.
A method for preparing calcium carbonate, which comprises:
- reacting a calcium oxide containing starting material with carbonate ions by adjusting a Z potential to −1 to −20 mV in a suspension by lowering a pH to 8.4±0.5;
- and
- recovering calcium carbonate in the form of agglomerates whose size is approximately 0.1 to 10 μm and which contain calcium carbonate particles having a size of approximately 40 to 200 nm, and the calcium carbonate particles are spherical with a deviation of less than about 10%.
Dependencies are inferred from the claim text.