Strontium (Sr) and water
Strontium and water: reaction mechanisms, environmental impact and health effects
|Seawater contains 8 ppm strontium on average. River water generally contains about 50 ppb of strontium and in oyster tissue 10 ppm of strontium (dry mass) was found. |
When dissolved in water strontium mainly occurs as Sr2+ (aq). One other possible form is SrOH+ (aq).
Strontium reacts with water slowly, generally to strontium hydroxide and hydrogen gas. It reacts with water quicker than calcium, which is placed directly above strontium in the periodic chart, and slower than barium, placed directly below strontium.
The following reaction mechanism is applicable:
Sr (s) + 2H2O (g) -> Sr(OH)2 (aq) + H2 (g)
Strontium is water insoluble, but it does react with water. Strontium compounds can be water soluble. Examples include strontium carbonate with a water solubility of 10 mg/L, and strontium chromate with a water solubility of 9 mg/L.
The most significant strontium mineral is celestite (strontium sulphate; SrSO4), followed by strontianite (strontium carbonate; SrCO3). At least 140,000 ton is exploited annually. This may produce strontium metal, which is not applied widely, but it may extract residue air from vacuum tubes. As a carbonate strontium is mainly applies for TV-screen production. This is the main application of the element. It insulates X-rays that occur from electric radiation in the cathode ray tube. This is however required less and less because of the increasing popularity of the flat screen TV. Strontium is applied for alloy refinery, and strontium sulphate was applied as imitation diamond. Because of its red inflammation it is suitable for application in fireworks. Strontium ferrite is applied in permanent ceramic magnets that are highly coercive and can be applied in small engines because of its resistance to heat and corrosion.
Strontium is only a dietary requirement in a few exceptional cases. A number of deep sea organisms apply strontium sulphate in shells, and stone corals also have a requirement for the element. Plants contains between 3 and 400 ppm strontium (dry mass). Strontium is usually immobile in the environment, because of rapid precipitation as strontium carbonate, or because it is applied in shells. The highest strontium concentrations are found in deserts and forest soils.
The human body contains approximately 4.6 ppm strontium. It has no specific function, but it is absorbed because of its similarity to calcium. Consequently, the larger part of absorbed strontium is inserted in bones.