PRECIPITATED CALCIUM CARBONATE PRODUCT HAVING IMPROVED BRIGHTNESS AND METHOD OF PREPARING THE SAME

摘要

A method of significantly improving the brightness and shade properties of a high quality PCC product. The method includes providing a calcium containing feed source that contains discoloring impurities. The calcium containing fee d source is formed into an aqueous slurry of calcium carbonate. Thereafter, th e slurry is fine screened through a 325 mesh screen in order to yield a slurry of filler grade calcium carbonate. The filler grade calcium carbonate slurry is wet milled in order to liberate the discoloring impurities and reduce the median particle size of the calcium carbonate to less than 2 microns. The discoloring impurities are then magnetically separated from the milled calci um carbonate slurry by subjecting the slurry to a high intensity magnetic field . After the magnetic separation step, the purified slurry may be de-watered to yield a dry powder; or alternatively, the slurry may be retained in aqueous form. In any event, the resultant calcium carbonate product has a median particle size of less than 2 microns and a TAPPI brightness of greater than 96.