Abstract: Novel precipitated calcium carbonate particles of varying size and shape, are prepared by adding gaseous carbon dioxide to an aqueous slurry containing basic calcium carbonate under a selectively controlled reaction environment. In its preferred embodiment precipitated calcium carbonate particles having a prismatic shape and an average equivalent spheroidal diameter of between about 1.5 and about 6.5 microns; large irregularly shaped particles having an average equivalent spherical diameter of between about 15 and about 25 microns; and multi-faceted spheroidal particles having an average equivalent spherical diameter of between 5 and about 15 microns, are provided. The reaction environment includes temperatures of between 0° C. and 60° C. and a surface active polyphosphate additive present in amounts of from about 0.1 and about 1.0 percent by weight.

Abstract: Novel precipitated calcium carbonate particles of varying size and shape, are prepared by adding gaseous carbon dioxide to an aqueous slurry containing basic calcium carbonate under a selectively controlled reaction environment. In its preferred embodiment precipitated calcium carbonate particles having a prismatic shape and an average equivalent spheroidal diameter of between about 1.5 and about 6.5 microns; large irregularly shaped particles having an average equivalent spherical diameter of between about 15 and about 25 microns; and multi-faceted spheroidal particles having an average equivalent spherical diameter of between 5 and about 15 microns, are provided. The reaction environment includes temperatures of between 0.degree. C. and 60.degree. C. and a surface active polyphosphate additive present in amounts of from about 0.1 and about 1.0 percent by weight.

Abstract: An aggregated synthetic hydrotalcite having a substantially spheroidal shape and an average diameter of up to about 60 .mu.m is disclosed. The aggregates are composed of individual platy particles having plate diameters of from about 0.05 to about 10 .mu.m. The material has a low tapped density, a high pore volume and a high specific surface area. A process for producing the product is also disclosed. Product particle size is determined by controlling process parameters including reaction temperature and pH, stirring speed of the reaction mixture, and reactant addition rates and concentrations, including aqueous solutions of soluble magnesium and aluminum salts, which are mixed in a molar ratio of from about 2.5:1 to 4:1, and a basic solution containing excess carbonate and base to maintain the reaction mixture at a pH of from about 8.5 to about 9.5.

Abstract: An aggregated synthetic hydrotalcite having a substantially spheroidal shape and an average diameter of up to about 60 .mu.m is disclosed. The aggregates are composed of individual platy particles having plate diameters of from about 0.05 to about 10 .mu.m. The material has a low tapped density, a high pore volume and a high specific surface area.A process for producing the product is also disclosed. Product particle size is determined by controlling process parameters including reaction temperature and pH, stirring speed of the reaction mixture, and reactant addition rates and concentrations, including aqueous solutions of soluble magnesium and aluminum salts, which are mixed in a molar ratio of from about 2.5:1 to 4:1, and a basic solution containing excess carbonate and base to maintain the reaction mixture at a pH of from about 8.5 to about 9.5.