What is titanium dioxide, and what are its properties?
Titanium dioxide is one of the most essential inorganic materials modern industry consumes. It is widely used in the contemporary world and is the primary commercial product of the titanium production sector. How is titanium dioxide manufactured and utilized? We will discuss it in this article along with other relevant aspects.
Pure titanium dioxide (TiO2) is a colorless, crystalline solid substance. When heated, its crystals turn yellow, and upon cooling, they regain their colorless appearance.
Modifications of titanium dioxide include:
- Rutile (cubic syngony, 85-90% of global production);
- Brookite (orthorhombic syngony);
- Anatase (tetragonal syngony, 10-15%);
- Rhombic IV and hexagonal V modifications.
Titanium dioxide is produced in two forms: rutile (R-type) and anatase (A-type).
Rutile titanium dioxide
It scatters light approximately 30% better than anatase, and it has better hiding power (the ability of titanium dioxide to cover the color of the painted surface).
Rutile titanium dioxide is preferred in paints, coatings, plastics, and cosmetics production.
Anatase form
It is less resistant to atmospheric conditions than rutile and provides less protection against UV radiation. Anatase pigments find their application in producing paper, rubber, and soap.
Use of titanium depending on its properties
Traditionally, the vast majority (about 95%) of all produced titanium dioxide is used in making paints and coatings.
The leading role of titanium dioxide among white pigments is predetermined by its high level of quality. This product is characterized by its ability to disperse, as well as its thermal and chemical resistance, whitening capability, resistance to atmospheric conditions, high refractive index, and more. These properties depend on the size of raw material particles and are significantly enhanced by their nanostructuring.
In the paint and coatings industry, the primary function of TiO2 is to impart paints with a white color and brightness and to enhance hiding power. It also protects against harmful ultraviolet rays and prevents film aging and yellowing of painted surfaces.
Titanium dioxide is a stable substance (the most stable one among all known white pigments). It is non-volatile and insoluble in acids, alkalis, and solutions under normal conditions.
Titanium dioxide is amphoteric, meaning it has basic and acidic properties (although it reacts with concentrated acids). It demonstrates high chemical stability towards various compounds, including those that may be toxic and present in the environment. Due to its inertness, titanium dioxide is non-toxic and generally considered a very safe substance. It can come into contact with packaged products and even be used as a food coloring in certain concentrations.
It may even enter the body as an aerosol through inhalation or ingestion. It is non-flammable.
Specific properties of titanium dioxide make it indispensable in various industries, contributing to the rapid growth of the global titanium dioxide market.
World Market of Titanium Dioxide Pigment Production.
There is a high demand for titanium dioxide in the global market, which is expected to continue growing. Additionally, there is a constant increase in the worldwide need for inorganic pigments. According to experts’ estimates, in recent years, titanium dioxide pigment accounted for 65-70% of the total consumption of inorganic pigments and over 90% of the consumption of white pigments.
In 2021, the titanium dioxide market was estimated to be more than 6 million tons, and it is projected that from 2022 to 2027, the market will demonstrate an average annual growth rate of over 6%. In the short term, the rapidly growing demand from the paint and coatings industry will be the primary driver of titanium dioxide market growth.
Titanium dioxide pigment is produced in 15 countries, with 33% of production capacity located in the USA. Additionally, almost 40% of production is in China, Ukraine, Germany, the United Kingdom, Finland, Saudi Arabia, Japan, France, Australia, and other countries.
The global titanium dioxide production distribution is as follows:
China has the largest titanium dioxide production capacity, producing approximately 3 million tons annually.
The largest world producers are the following companies: DuPont Titanium Technologies (USA), National Titanium Dioxide Co., Ltd. Cristal (Saudi Arabia), Huntsman Pigments (USA), Tronox, Inc. (USA), Kronos Worldwide, Inc. (USA), Sachtleben Chemie GmbH (Germany; Rockwood Holdings own 100% of the shares), Ishihara Sangyo Kaisha, Ltd. (Japan).
Raw materials for production of titanium dioxide pigment
A crucial aspect of the titanium dioxide manufacturing process is the supply of high-quality titanium ore. Despite titanium being one of Earth’s most abundant chemical elements, it occurs in deficient natural concentrations. Therefore, to establish an adequate supply of titanium ore capable of meeting the economic demands of TiO2 production, it is essential to implement rational methods of extraction and refinement of this mineral.
Read more about titanium ore mining and processing.
Ilmenite concentrate (FeTiO3)
The primary raw material in the titanium dioxide production process is ilmenite concentrate (FeTiO3), produced by mining and processing. Ilmenite is an ore that, from a chemical perspective, is a mixture of oxides, the majority of which are titanium and iron oxides.
Titanium slag
The second most significant raw material for the tio2 manufacturing process is titanium slag, containing 75-90% TiO2 and 5-7% FeO.
Read also our article on titanium slag production process.
Other raw material sources
Natural and synthetic rutile, as well as ore fines, have secondary importance.
Applications of titanium dioxide.
Due to its very high whiteness and fine particle size, titanium dioxide has found wide application as a white pigment in the paint and coatings industry. Among its advantages are non-toxicity, high optical properties (ability to scatter light), availability, chemical inertness, resistance to atmospheric conditions, and more. Gone are the days when paints were made using zinc or lead-containing white pigments.
Paint and coatings industry
It is the primary industry using titanium dioxide pigment. But not the last one.
TiO2 is widely used as a white pigment in the pulp and paper industry for producing synthetic fibers, rubber products, plastics, heat-resistant and optical glass, ceramic dielectrics, etc.
Applications of titanium dioxide other than pigment production are as follows:
Production of fiber optic products
Titanium dioxide, with a chemical purity of 99.9998%, is used in producing optical fiber products, medical equipment, and the radio-electronic industry. In manufacturing ultra-pure glasses, titanium dioxide serves as a purity reference.
Synthetic fibers and textiles
For matting twisted fibre.
Cosmetics
For protection against ultraviolet radiation in sunblock creams, for higher whitening effect of toothpastes, soaps, etc.
Food industry
For higher whitening effect in products, for protection of product package color (plastics) against ultraviolet radiation.
Pharmaceutical industry
For higher whitening effect in pharma products.
Printing paint
To increase weather resistance of coatings.
Catalyst
Photocatalyst and inert ceramic base material for active components.
Nanotechnology
Titanium dioxide nanopowders are used for air purification in cities, in producing nanofiber paper based on TiO2, in hydrogen energy, etc.
Manufacture of rubber products
Production of refractories
Coating of welding electrodes and coatings of casting molds.
Technologies of titanium dioxide production
In global practice, high-dispersion titanium dioxide pigment is produced by the sulfate (sulfuric acid) and chloride methods.
The sulfate method is based on the decomposition of ilmenite concentrates containing 45-56% TiO2 or titanium slags with a content of 75-80% TiO2, with subsequent conversion of titanium sulfates into dioxide.
The chloride method involves the chlorination of natural rutile concentrates, synthetic rutile, or titanium slags with a TiO2 content of 85% and higher, as well as special slags that have undergone additional processing and contain over 92% TiO2.
Considering specific features of both processes of the TiO2 production process, the primary criterion for choosing between the sulfate and chloride methods is the possibility of providing raw materials of the appropriate quality and environmental-related issues.
Both methods make it possible to obtain high-quality products with identical properties.
The approximate distribution of production technologies among manufacturers worldwide is 45% by the sulfate method and 55% by the chloride method.
The main stages of the TiO2 process by the sulfate and chloride methods are presented in the table.
| Sulfate (sulfuric acid) method | Chloride method |
|---|---|
| Drying, grinding concentrate | Drying, grinding concentrate |
| Decomposition | Drying, grinding of coke |
| Reduction of iron 3+ to iron 2+ | Burden mix melting in ore-thermal furnaces |
| Solution purification | Hot metal and slag casting into moulds |
| Pan crystallization | Cooling and water herdening |
| Centrifugal removal of copperas | Slag crushing and grinding |
| Vacuum-evaporating | Slag mixing with tar |
| Hydrolysis | Slag briquetting |
| White filtration | Slag chlorination |
| Whitening and salt treatment | Capture of TiCl4 in refrigerators |
| Calcination | 1st rectifivation of TiCl4 |
| Dry grindin | 2nd rectifivation of TiCl4 |
| Wet grinding | TiCl4 burning |
| Hydraulic classification | TiO2 and Cl2 capture |
| Surface treatment | Surface treatment |
Sulfate (sulfuric acid) method of TiO2 production
The sulfate method was applied in industry in 1931 to produce the anatase form of titanium dioxide and later, in 1941, for production of the rutile form. In this method, the initial raw material – ilmenite concentrate or titanium slag – is dissolved in sulfuric acid, resulting in titanium, iron, and other metal sulfate solutions. Then, basic TiO2 with the necessary particle size is formed after a series of technological transformations, including chemical reduction, purification, precipitation, washing, and calcination. The crystal structure (anatase or rutile form) is controlled during nucleation and calcination.
The equation describes the sulfate method of the titanium dioxide process:
FeTiO3 + 2H2SO4 → TiOSO4 + FeSO4 + 2H2O TiOSO4 + H2O → TiO2 + H2SO4.
The process diagram of TiO2 production using the sulfate method (with ilmenite as a raw material)
The process diagram of titanium dioxide production using the sulfate method (with titanium slag as a raw material).
Chloride method of TiO2 production
The chloride method was invented in 1950 to produce the rutile form of TiO2.
The chloride method converts rutile (natural or synthetic) or titanium slag into titanium tetrachloride (TiCl4) through chlorination in the presence of petroleum coke. Any resulting impurities of other metal chlorides are subsequently removed. The following equation describes the chloride method for obtaining TiO2:
2FeTiO3 + 7CI2 + ЗС → 2TiCI4 + 2FeCI3 + 3CO2TiCI4 + O2 → TiO2 + 2CI2.
The most crucial operation in TiO2 production by the chloride method is the combustion of titanium tetrachloride. It is carried out at temperatures between 900-1000°C with burners of a particular design.
The titanium tetrachloride combustion reaction is as follows:
TiCl4 + O2= TiO2 + 2С12.
The released chlorine can be returned to the production process to obtain titanium tetrachloride.
Three main methods for obtaining titanium dioxide from its titanium tetrachloride:
- Hydrolysis of aqueous solutions of titanium tetrachloride (followed by heat treatment of the sediment);
- Vapor-phase hydrolysis of titanium tetrachloride (is based on the interaction of titanium tetrachloride vapors with water vapors). The process is typically carried out at temperatures of 900-1000°C;
- Heat treatment of tetrachloride (combustion in a stream of oxygen).
Titanium pigments obtained by combustion of titanium tetrachloride may contain up to 0.6% adsorbed chlorine. The aqueous suspension of such a product has a pH of less than 7 and is unsuitable for producing paints. Desorption of chlorine from the pigment can be achieved by heating it at temperatures 300-900 °C. The chlorine concentration is reduced to 0.1% in this process. Such a product is suitable for manufacturing paints and enamels but requires surface treatment with silicon and aluminum compounds to obtain higher-quality pigments.
The chloride method is selective and demanding in terms of raw materials. Due to the use of chlorine and high temperatures, it requires corrosion-resistant equipment.
Comparative characteristics of two methods of titanium dioxide production
In both technological processes – sulfate and chloride – the intermediate products are accumulations of TiO2 crystals of pigment size, which need to be separated (ground) to achieve optimal optical characteristics.
Depending on the end-user requirements, various processing methods are used to modify TiO2, including sedimentation of oxides of silicon, aluminum, zirconium, or zinc onto the surface of pigment fractions.
Particular processing methods may be used to optimize operational characteristics for specific applications utilizing oxides in aqueous or anhydrous environments or various combinations thereof. Additionally, organic additives can be introduced by multiple methods to enhance particular characteristics of the pigment.
Advantages of the chloride method:
- High TiO2 quality;
- Reduced number of production stages and waste compared to the sulfate method.
Disadvantages of the chloride method:
- High requirements for raw materials – the use of natural rutile concentrates, synthetic rutile or titanium slags with a TiO2 content of 85% or more as raw materials, as well as special slags that have undergone additional processing and contain more than 92% TiO2;
- Extremely complicated organization of work with chlorine and the need to take measures to prevent chlorine losses;
- The complexity of organizing and recycling ferric chloride and impurities found in the slag;
- Acute need to use equipment made of expensive corrosion-resistant materials.
Advantages of the sulfate method:
- The quality of the finished product is not worse than the quality of products produced by the chloride method (by using modern technological solutions at the stage of washing chromophore impurities from hydrated TiO2);
- “Zero” waste production – the possibility of completely recycling all production waste into marketable products. Today, waste disposal after the sulfate method is quite sophisticated. At some factories, sales of products obtained from production waste are comparable to sales volumes of commercial products;
- Manufacturing of main equipment and technological devices is cheaper than implementing the chloride method of TiO2 production.
Disadvantages of the sulfate method:
- Influence of chromophore impurities on the finished product quality indicators;
- Inability to use natural (or artificial) rutile as a raw material;
- Use of modified and slightly modified ilmenite concentrates as raw materials.
Which Process is More Efficient in Your Case? Find Out the Best Solution With Our Experts
Enterprises in Ukraine with sulfate technology, successfully operated for many years:
«SUMYCHIMPROM» PJSC
«Crimean Titan» PJSC
M HEAVY TECHNOLOGY offers design services for an entire complex of technological processes for pigment titanium dioxide production, using the sulfate method at a high modern level.
Modern methods of additional processing of titanium dioxide pigment.
Practically, there are hardly any industrially produced pigments made of pure TiO2. Most of them undergo inorganic and, in some cases, organic treatment applied to the surface of TiO2 particles through sedimentation, mechanical mixing, or some other method.
Such surface treatment methods improve one or even several operational properties of the pigment, including ease of dispersion, resistance to atmospheric influences, or color stability.
A universal surface treatment method for obtaining a pigment suitable for any practical application has yet to be found. Therefore, the goal of ongoing research is to continue developing new grades of TiO2 that would meet the constantly changing requirements of modern industry.
Titanium dioxide production is a fascinating scientific and technical research and innovation area. Recently, a technology for producing TiO2 has been developed in which ammonium fluoride is used as the primary reagent and is safer than sulfuric acid. Besides, this reagent can be reused, leading to a reduction in waste. One disadvantage of the fluoride technology is that it results in a coarser-dispersed pigment powder compared to the chloride method.
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Which Process is More Efficient in Your Case? Find Out the Best Solution With Our Experts
Conclusions
- Titanium dioxide is one of the most widely used inorganic materials in modern industry, the main commercial product of the titanium industry.
- Titanium dioxide pigment production is economically profitable and technologically feasible. Titanium dioxide production is a reliable business, because in the modern world, the need for inorganic pigments is constantly growing and the global titanium dioxide market is rapidly developing.
- The main raw materials for titanium dioxide production are ilmenite concentrate and titanium slag, containing 75-90% TiO2 and 5-7% FeO.
- The main application field of titanium dioxide pigment as a white pigment is paint and varnish industry. Other applications are also wide and equally important.
- In world practice, highly dispersed titanium dioxide pigment is produced by two methods – sulfate (sulfuric acid) and chloride. Both methods allow you to obtain a high-quality product with identical properties.
- The main criterium for choosing between sulfate and chloride methods is the possibility of ensuring production with raw materials of appropriate quality and meeting environmental requirements.
- «M HEAVY TECHNOLOGY» offers services for designing a full complex of technological processes for pigment titanium dioxide production, using the sulfate method at a state-of-the-art level.
Author of the article: Larisa Sokol
