White, crystalline powder. Slightly
soluble in water; insoluble in alcohol.
Magnesium sulfite has found usage in the “Kawasaki
process” as first developed in Japan. Although magnesium sulfite has found a number of
usages in industry, it is the bisulfite compound that is
used extensively in the wood-pulping process.Dolomite can contain
up to 40% magnesium and it was determined that
calcium was more proficient in the “sulfite process”
whereas magnesium bisulfite is used in the “Kraft
process” of making wood pulp used to manufacture
paper and cardboard products used extensively today.
Manufacture of paper pulp (as bisulfite).
Magnesium Sulfite can be prepared
by the reaction of a magnesium hydroxide slurry and
SO2 gas:
Mg(OH)2＋ SO2(gas) ＋H2O→MgSO3·6H2O
If the solution temperature is kept below 40°C, the
hexahydrate results. Above 40°C, the trihydrate,
MgSO3·3H2O, is the usual product. Magnesium sulfite
may also be prepared by adding a solution of sodium
sulfite to a solution of magnesium chloride. The mix is
kept at 25°C for 1–2 h and the solid phase which forms
is separated and washed with isopropanol and dried at
60°C. Again, the hexahydrate results.
