Preparation of iron (III) oxide pigment

A process for producing haematite pigments, the process comprising:

• contacting iron, an aqueous haematite nucleus suspension containing haematite nuclei which have a particle size of 100 nm or less and a specific BET surface area of 40 m2/g to 150 m2/g (measured in accordance with DIN 66131), and an iron(II) nitrate solution, in the presence of at least one oxygen-containing gas at temperatures of 70 to 99° C. to produce a suspension comprising haematite pigment,
• wherein the aqueous solution of the iron, the haematite nucleus suspension, and the iron(II) nitrate solution is mixed by means of hydraulic mixing;
• wherein the hydraulic mixing is carried out by means of at least one pump which takes a liquid phase from a reactor at an outlet and feeds it back into the reactor at another place by an inlet, and
• wherein the at least one oxygen-containing gas is introduced into the aqueous solution with a gas introduction volume of 6 m3 of gas volume/m3 of batch volume/hour or less.