PCC with reduced portlandite content

A process for producing an aqueous suspension of precipitated calcium carbonate having a low portlandite content comprising the steps of:

• i) providing a calcium oxide containing material having a calcium oxide content of at least 90 wt.-%,
• ii) providing a precipitation enhancer selected from the group consisting of calcium carbonate nanoparticles, a water-soluble calcium salt, and a mixture thereof, wherein the calcium carbonate nanoparticles have a number based median particle size d50 of from 30 to 70 nm, and a portlandite content of less than 1 wt.-%, based on the total dry weight of the calcium carbonate nanoparticles,
• iii) preparing a milk of lime by mixing, in any order, water, the calcium oxide containing material of step i), and the precipitation enhancer of step ii), wherein the precipitation enhancer is included in an amount from 0.01 to 25 wt.-%, based on the total weight of the calcium oxide containing material, and
• iv) carbonating the milk of lime obtained from step iii) until an aqueous suspension of precipitated calcium carbonate having a portlandite content of less than 1 wt.-%, based on the total dry weight of the precipitated calcium carbonate, is obtained.