**1. Introduction**

Since the discovery of titanium in 1791, TiO2 has been used commercially for over 100 years. Compared with other white pigments, such as ZnS, BaSO4, ZnO, etc., TiO2 is a nontoxic, stable pigment [1]. It shows high hiding power, refractive index, whiteness, and other excellent physical properties (**Table 1**) [2]. As a result, TiO2 is widely used in printing ink, plastics, paper, coating materials, and cosmetics. It is also an indispensable raw material for the light industry, electronic industry, and other fields [3]. TiO2 is produced by the sulfate and chloride process. The quality of TiO2 produced by the two processes is different (**Table 2**) [2, 4]. Upmarket TiO2 is mainly produced by the chloride process [5].


### **Table 1.**

*Technical index comparison of white pigment [2].*


### **Table 2.**

*Comparison of different processes [2, 4].*
