Method advantages than gas phase method, liquid phase method, titanyl sulfate and titanium tetrachloride most industrial chemical precipitation potential. Combined with the advantages of China's sulfuric acid method titanium dioxide manufacturers, mature technology and rich experience, it is more advantageous to develop liquid phase titanyl sulfate chemical precipitation method to produce nano-TiO 2 . As for the scale of production, the demand for nano-TiO 2 in China is considered to be around 10,000 tons/year; some people think it is below 1,000 tons/year. The author believes that the latter view may be more in line with domestic realities. In this way, the domestic nano-TiO 2 production capacity has been able to meet the needs of the existing market. However, with the popularity of nano-TiO 2 and the change of people's consumption concept and the rapid and steady development of China's overall economy, nano-TiO 2 will usher in a broader market space.
The chemical precipitation method can be divided into a uniform precipitation method, a direct precipitation method, and a coprecipitation method. The uniform precipitation method has the characteristics of simple process, good product quality and easy operation, and is a preparation method with the most industrial development prospect. Evenly released, in this method, the precipitant added to the solution does not immediately react with the precipitated component, but the chemical reaction causes the precipitant to slowly form in the entire solution, so that the precipitate is slowly formed by the chemical reaction in the solution. As long as the speed of generating the precipitant is controlled, the concentration unevenness can be avoided, the supersaturation can be controlled within an appropriate range, thereby controlling the growth rate of the particles, and obtaining nanoparticles with uniform, compact, easy washing and high purity. Commonly used uniform precipitants are urea and the like. The reaction principle of preparing titanium TiO 2 with titanium oxysulfate as precursor and urea as precipitant is that urea aqueous solution starts to hydrolyze at about 70 ° C. The reaction formula is as follows:
CO(NH 2 ) 2 +3H 2 O===2NH 3 ·H 2 O+CO 2 ↑
Since the decomposition rate of urea is controlled by the heating temperature and the urea concentration, the urea decomposition rate can be lowered to a low level to obtain nano TiO 2 having a uniform particle size distribution and a small particle diameter. The decomposition products of urea, CO 2 and NH 3 , are gases after reaction or calcination, which are volatile and do not affect the purity and quality of the product. The precipitated agent NH 3 ·H 2 O is uniformly distributed in the TiOSO 4 solution, and the concentration is low, so that the precipitate TiO(OH) 2 is uniformly formed, and the reaction formula is as follows
TiOSO 4 +2NH 3 ·H 2 O===TiO(OH) 2 ↓+(NH 4 ) 2 SO 4
TiO(OH) 2 ===TiO 2 +H 2 O
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