Process for producing nano precipitated calcium carbonate

1 . A process for producing nano precipitated calcium carbonate (nano-PCC) comprising the steps of:

a) providing a calcium oxide containing material,

b) providing water in an amount of up to 200 wt.-%, based on the total dry weight of the calcium oxide containing material,

c) providing a carbon dioxide source,

d) preparing nano-PCC in a crystal form as a particle of calcite by simultaneously carrying out the following steps (i) and (ii):

(i) simultaneously mixing and milling the calcium oxide containing material of step a) with the water of step b), and

(ii) adding under simultaneously mixing and milling the carbon dioxide source of step c) in an amount which corresponds to a mole ratio of the calcium oxide in the calcium oxide containing material of step a) to the carbon dioxide in the carbon dioxide source of step c) of 1:1 to 1:3.5.

2 . The process of claim 1 , wherein the process further comprises the step of e) separating the nano precipitated calcium carbonate from the mixture obtained from step d).

3 . The process of claim 1 , wherein process does not involve a drying step and the nano precipitated calcium carbonate obtained in step d) has a residual total moisture content of from 0.1 wt.-% to 10 wt.-%, based on the total dry weight of the nano precipitated calcium carbonate.

4 . The process of claim 1 , wherein calcium oxide containing material provided in step a) has

i) a minimum calcium oxide content of at least 75 wt.-% based on the total weight of the calcium oxide containing material and/or

ii) a weight median particle size d 50 of between 1.0 and 300 μm.

5 . The process of claim 1 , wherein carbon dioxide source of step c) comprises between 4 and 99.8 vol.-% carbon dioxide based on the total volume of the carbon dioxide source.

6 . The process of claim 1 , wherein in step d) the mole ratio of the calcium oxide in the calcium oxide containing material of step a) to the carbon dioxide in the carbon dioxide source of step c) is 1:1 to 1:2.

7 . The process of claim 1 , wherein d) the amount of water added in step ii) is from 1 wt.-% to 180 wt.-%, based on the total dry weight the calcium oxide containing material.

8 . The process of claim 1 , wherein precipitated calcium carbonate obtained in step d)

i) has a specific surface area from 5.0 to 80.0 m 2 /g measured using nitrogen and the BET method according to ISO 9277:2010 and/or

ii) is in form of particles having a number-based median particle size d 50 of below 900 nm and/or

iii) is in form of particles having a number-based top cut particle size d 98 of below 1000 nm and/or

iv) has a residual total moisture content of from 0.1 wt.-% to 10 wt.-%, based on the total dry weight of the nano precipitated calcium carbonate.

9 . The process of claim 1 , wherein process is performed in at least one dry mill.

10 . The process of claim 1 , wherein calcium oxide containing material provided in step a) has

i) a minimum calcium oxide content of at least 95 wt.-% based on the total weight of the calcium oxide containing material and/or

ii) has a weight median particle size d 50 of between 6 and 80 μm.

11 . The process of claim 1 , wherein carbon dioxide source of step c) comprises between 8 and 25 vol.-% carbon dioxide based on the total volume of the carbon dioxide source; and

that in step d) the mole ratio of the calcium oxide in the calcium oxide containing material of step a) to the carbon dioxide in the carbon dioxide source of step c) is 1:1.4 to 1:1.6; and

the amount of water added in step ii) is from 70 wt.-% to 90 wt.-%, based on the total dry weight the calcium oxide containing material.