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. |
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)
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.
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.
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.
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.
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.