| 摘要 |
PROBLEM TO BE SOLVED: To produce precipitated calcium carbonate high in whiteness and opacity and low in wearability by using paper making industry sludge discharged as a waste material in a waste paper recycle process. SOLUTION: The sludge from paper industry obtained after de-pulped and de-inked in the waste paper recycle process is heat-treated. A fired material, from which the particles having high hardness or large particle diameter are removed, is obtained by performing the heat treatment at a temp. equal to or below the decomposition temp. of calcium carbonate with excess air or classifying after the heat treatment. The fired material is mixed with a calcium hydroxide aq. suspension and is aged at a temp. higher than the normal temp. Next, precipitated calcium carbonate is prepared by passing carbon dioxide or a carbon dioxide-containing gas through the aq. suspension to carbonate. Precipitated calcium carbonate bulky and high in opacity is obtained by passing through the prescribed aging process before the carbonation. A paper using the calcium carbonate as filler or pigment has a performance not inferior than a paper using the conventional calcium carbonate.
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