Patent ID: 8809582

Claim:
A process for preparing a surface-reacted calcium carbonate having a desired specific BET surface area, the process comprising the following steps: a) providing a calcium carbonate; b) providing 5 wt.-% to 50 wt.-%, based on the weight of calcium carbonate, of at least one acid having a pK a of less than or equal to 2.5, wherein the corresponding acid anion is capable of forming water-insoluble calcium salts; c) providing gaseous CO 2 ; d) providing at least one water soluble non-polymeric organic and/or inorganic weak acid and/or a hydrogen salt of said at least one water soluble non-polymeric organic and/or inorganic weak acid; e) contacting said calcium carbonate with said at least one acid having a pK a of less than or equal to 2.5 of step b), with said gaseous CO 2 of step c) and with said at least one water soluble non-polymeric organic and/or inorganic weak acid and/or hydrogen salt of said at least one water soluble non-polymeric organic and/or inorganic weak acid of step d), in a manner to provide surface-reacted calcium carbonate having a desired specific BET surface area; and f) optionally drying the surface-reacted calcium carbonate; wherein the at least one water soluble non-polymeric organic and/or inorganic weak acid has a pK a of greater than 2.5 and wherein its corresponding acid anion is capable of forming water-insoluble calcium salts.