Magnesium thiosulfate has the molecular formula of
MgS2O3 and the molecular weight of 136.4352 g/mol.
It is also known as “hyposulfite”. It can be prepared
by the reaction of sodium thiosulfate upon the chloride
in water:
MgCl2+Na2S2O3? MgS2O3+2NaCl
Since magnesium thiosulfate is soluble in water
(50 g/100 ml at 20°C), the solution must be evaporated
at a low temperature to crystallize the product (salt-out
temperature ～15°F (-9.4°C). A hexahydrate, MgS2O3·
6H2O, is the result.
These are colorless crystals that lose water at 170°C to
form the trihydrate. Further heating to 420°C then
forms the anhydrate. Further heating to 600°C will
cause the production of magnesium sulfate, sulfur and
oxides of sulfur:
2MgS2O3+2O2+heat? 2MgSO4+S+SO2
Magnesium thiosulfate is considered to have a low
toxicity to humans. It has been used to remove ozone
from either a water stream, such as a drinking water
or wastewater stream being treated with ozone, or
scrubbing ozone from a gaseous stream by contacting
the gaseous stream with solid magnesium thiosulfate.
It has also been used to remove chlorine gas from a water
stream by contacting the stream with magnesium thiosulfate
solution. In yet another aspect, a method of
scrubbing chlorine from a gaseous stream comprises
contacting the gas stream with solid magnesium
thiosulfate.
Magnesium thiosulfate is not commonly referenced
in scientific literature. The few articles that prevail
discuss technically specific physical properties of the
end product itself. Synthetic methods are described in
some Japanese patents and there is mention of MgTS
in a short German description in Handbuch der Anorganischen
Chemie, vol. 11, 1984. Both refer to adding
sulfur to magnesium sulfite to produce magnesium
thiosulfate. Neither reference describes the pH nor
physical consistency of the “sulfite” intermediate,
although the German article does note the “color
change” observed as SO2 is purged into MgO: the slurry
becomes yellow.
