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Titanium (Ti) and water

Titanium and water: reaction mechanisms, environmental impact and health effects

Seawater contains 1 ppb of titanium. In phytoplankton titanium concentrations up to 30 ppm (dry mass) were discovered. River water contains only 3 ppb. In dissolved form the element in mainly present as non-ionic Ti(OH)4.

In what way and in what form does titanium react with water?

Titanium metal contains a surface layer of titanium oxide that prevents chemical reactions. When the layer is damaged it is usually restored rapidly. This not only occurs when it comes in contact with air, but also when it comes in contact with water. This reaction forms both titanium oxide and highly flammable hydrogen gas, according to the following reaction mechanism:

Ti (s) + 2H2O (g) -> TiO2 (s) + 2H2 (g)

Some titanium compounds undergo hydrolysis reactions in water, for example titanium chloride.

Solubility of titanium and titanium compounds

Titanium only reacts with water after its protective titanium oxide surface layer is destroyed. It is therefore water insoluble. Titanium compounds generally are not very water soluble. Examples include titanium carbide and titanium oxide.

Why is titanium present in water?

Titanium is a component of various types of rock, such as rutile, anatase, ilmenite, titanite and brookite, and is therefore abundant in soils. Titanium oxide and other titanium compounds are among the most stable soil components. Consequently, only small amounts of titanium end up in water from rock weathering.
The metal is durable and is not excreted by the body, because of its protective titanium oxide surface layer. Consequently, it is applied in artificial joints and pacemakers that need not be replaced within the first 20 years. The oxide layer protects against most chemicals. Titanium is also applied in chemical installations. The larger part of produced metal is applied in plane and car engines, because its stability resembles that of steel and weighs 45% less. This results in an excellent strength-weight relation. Titanium is added to alloys, for example in stainless steel production.
Its durability and non-magnetic properties cause titanium to be an option for building submarines.
A commercially significant titanium compound is titanium dioxide, which is applied as a pigment in paint, synthetics, paper, fiber and cosmetics production. However, titanium application does lead to the production of water pollutants that disable direct discharge of wastewater. Titanium carbide is applied in cutting tool production, and titanium chloride is applied as a catalyzer and basic product for artificial mist, titanium- and titanium dioxide pigments.

What are the environmental effects of titanium in water?

Titanium is not a dietary requirement. It may have a biological function, because it positively influences grain growth and nitrogen fixation by Leguminosae. Plants contain 1 ppm titanium (dry mass) on average. In soils titanium solutions dissolve rapidly. Consequently, concentrations up to 5000 ppm are tolerated. The element in non-water hazardous, whereas halogenated titanium compounds may pose a risk in water. These are toxic to small water organisms and are harmful because they alter pH values. Elementary titanium is a risk in other environmental compartments, as well.
During titanium dioxide pigment production, sulphuric acids or iron vitriol may form, depending on the process. Sulphuric acid formation in seas probably negatively influences sea ecology. This also applies to rivers and other surface waters.
The LD50 value for tetra isopropyl ortho titanate is known and is 7460 mg/kg for rats at oral intake.
Titanium naturally contains five non-radioactive isotopes, and eight instable isotopes.

What are the health effects of titanium in water?

The human body contains approximately 700 mg titanium, and our daily intake is approximately 0.8 mg. Only a small part of the total daily intake is absorbed by the body. Titanium does not play a significant role in any body functions. It is relatively non-toxic, because the body can tolerate relatively high doses and it does not accumulate. Existing hazards related to titanium are ascribed to the accompanying anion. For example, titanium halogen intake causes nausea and vomiting, and acidifies the body after resorption. Corrosion occurs at eye or skin contact, or when it comes in contact with mucous membranes.
One health effect of titanium not related to its presence in water is breathing in titanium dioxide particles with a very small particle size, leading to lung disease.

Which water purification technologies can be applied to remove titanium from water?

Titanium is present as a cation in acidic solutions and can therefore be removed by means of ion exchange. Iron vitriol that is formed in titanium dioxide pigment production is processes to acid or oxide and can than be applied as a precipitant in water purification.

Literature and the other elements and their interaction with water

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