Tin (Sn) and water
Tin and water: reaction mechanisms, environmental impact and health effects
|On average seawater contains 1-10 ppt of tin, and river water contains 6-40 ppt. The Lacuta seaweed generally contains 12 ppb of tin, and mussles contain up to 160 ppb (dry mass). Dissolved in water tin generally occurs as SnO(OH)3-, and in both seawater and freshwater mono-, di- and trimethyltin compounds can be found. This are partially decomposed to volatile compounds. |
Under normal circumstances tin is stable in water. When it comes in contact with hot water vapour a reaction results, forming tinoxide and hydrogen:
Sn + 2 H2O -> SnO2 + 2 H2
Some tin compounds hydrolyse in water. Examples include tin (IV) chloride, which forms tinoxide when heated.
Elementary tin does not dissolve in water under normal conditions (T = 20oC and pressure = 1 bar). Most tin compounds do not dissolve in water either, examples include tin (IV) oxide, tin (II) hydroxide, tin (IV) sulphide and tributyltin (TBT). Other tin compounds such as tin (II) chloride are water soluble. Organotin compounds are relatively badly water soluble, but may adsorb to sediments.
A number of tin minerals occur naturally, of which only cassiterite plays a role in commercial processes. Its main constituent tin (IV) oxide is water soluble and thereby weathering is prevented. The naturally occurring amount of tin in soils and water is relatively small. The release of tin from anthropogenic processes exceeds tin release from geological processes 110 times.
Tin is possibly a dietary requirement for a number of organisms. This may be caused by its presence in gastrine, a stomach and intestinal hormone.
The human body contains approximately 0.2 ppm of tin. There is no concrete evidence that suggests a dietary requirement of tin, except for the fact that it is a constituent of the gastrine hormone (see earlier). A number of literature sources mention that tin deficits may lead to hair loss, anorexia and acne.
Like any other metal tin may be removed from water by ion exchange.