Sodium Chloride and Chloralkali

Titanium dioxide exists in two major crystal forms, rutile and anatase. Rutile is more closely packed and therefore denser than anatase. Compared with anatase, it has a higher refractive index and higher opacity. Because of its brilliant whiteness, excellent covering power, and resistance to color change, rutile is a valuable pigment for a broad range of applications in paints, plastics, inks, and paper. Anatase has a bluer undertone and is less abrasive than rutile. It is often preferred for applications in paper, ceramics, rubber, and fibers. 

Titanium dioxide has higher opacity than other white pigments. Rutile is about 15% higher than anatase but more than double that of zinc sulfide, more than three times that of antimony oxide, and more than ten times that of calcium carbonate. 

In the sulfate process, titanium ore is digested with sulfuric acid to form titanium sulfate (Ti0S04). The titanium sulfate is then hydrolyzed, filtered, washed, and calcined to give titanium dioxide. 

In the chloride process, dried ore reacts with chlorine gas to produce titanium tetrachloride. The titanium tetrachloride is purified chemically and by distillation and then reacted with oxygen to form titanium dioxide and chlorine. The chlorine is recycled. Prior to the oxidation, a minor amount of aluminum chloride is added to promote rutile formation [22]. The rutile is preferred because it is more durable and has a higher refractive index. Untreated titanium dioxide is used, but more commonly a surface treatment is done to improve specific end-use property requirements such as ability to disperse or weather resistance. 

The chlorine used for titanium dioxide production is prepared by electrolysis of sodium chloride. Like titanium ore, sodium chloride is mined. 

---