Titanium dioxide pigments are produced commercially using two different processes. The older sulfate process starts with a digestion reaction of the titanium-containing raw material (ilmenite or titanium slag) with concentrated sulfuric acid at 150-220 °C resulting in the,,black liquor“. Relatively pure TiO2 dihydrate is precipitated by hydrolysis of this sulfate solution, which contains colored heavy metal sulfates, sometimes in high concentration. Impurities are largely removed in further purification stages. The titanium oxyhydrate is then calcined, ground, and coated with inorganic compounds.
In the chloride process, the titanium-containing raw materials ilmenite, leucoxene, rutile, titanium slag, or anatase are chlorinated at 700-1200 °C. The TiCl4 is oxidized at temperatures of900-1400 °C to form TiO2. This raw pigment is ground and coated with inorganic compounds.
2.1.3.1