Is Titanium Dioxide Safe To Consume-How Is Titanium Dioxide Manufactured
Titanium dioxide (TiO2) is a white pigment used in a variety of products, including paints, coatings, plastics, paper, and sunscreen. The manufacturing process of titanium dioxide typically involves one of two major production methods: the sulfate process and the chloride process.
### Sulfate Process
The sulfate process is the older and more traditional method of producing titanium dioxide. Here’s a general outline of the steps involved:
1. **Raw Material Extraction**: The process begins with the extraction of ilmenite (a titanium ore) or rutile (a pure form of titanium dioxide). Ilmenite is usually the more abundant and cheaper source.
2. **Pulverization**: The ore is then crushed and ground to a fine powder.
3. **Extraction of Titanium Dioxide**: The powdered ore is mixed with sulfuric acid, which dissolves the titanium dioxide and converts the other components into water-soluble compounds. This mixture is then heated to increase the reaction rate.
4. **Separation**: The resulting slurry is filtered to separate the titanium dioxide from the other compounds. The titanium dioxide is in the form of a sulfate.
5. **Purification**: The titanium sulfate is purified by removing impurities through processes such as solvent extraction or fractional crystallization.
6. **Hydrolysis**: The purified titanium sulfate solution is hydrolyzed to convert it back into titanium dioxide. This process involves adding water to the solution, which causes the titanium dioxide to precipitate out of the solution.
7. **Calcination**: The precipitated titanium dioxide is then heated to a high temperature (calcination) to remove any remaining moisture and volatile substances, and to convert it into a pigmentary form.
8. **Pigment Production**: The calcined titanium dioxide may be milled and surface-treated to optimize its properties for different applications.
### Chloride Process
The chloride process is a more modern method that is considered to be more environmentally friendly and efficient:
1. **Raw Material Preparation**: Rutile or upgraded ilmenite is used as the raw material. It is usually melted in an electric furnace to remove impurities.
2. **Reaction with Chlorine**: The molten material is then reacted with chlorine at high temperatures to produce titanium tetrachloride (TiCl4).
3. **Purification**: The titanium tetrachloride is purified by fractional distillation to remove any remaining impurities.
4. **Oxidation**: The purified titanium tetrachloride is oxidized in an oxygen-fired reactor to convert it back into titanium dioxide. This process also results in the production of chlorine, which can be recycled back into the process.
5. **Separation and Calcination**: The titanium dioxide is separated from the reaction gases and then calcined to remove moisture and volatile substances, similar to the sulfate process.
6. **Pigment Production**: The calcined titanium dioxide is then milled and surface-treated as needed for its intended use.
Both processes require careful control of conditions to ensure the quality of the final titanium dioxide product. The chloride process is favored for producing high-purity grades of titanium dioxide and is more energy-efficient, but it requires a higher initial investment in technology and infrastructure compared to the sulfate process.