MAGNESIUM SULFITE Chemical Properties

Density 

1.725 g/cm3

Water Solubility 

g/100g solution H2O: 0.338 (0°C), 0.646 (25°C), 0.615 (98°C); solid phase, MgSO3 · 6H2O (0°C, 25°C), MgSO3 ·3H2O (98°C) [KRU93]

Solubility Product Constant (Ksp)

pKsp: 2.50

EPA Substance Registry System

Sulfurous acid, magnesium salt (1:1) (7757-88-2)

MAGNESIUM SULFITE Usage And Synthesis

Chemical Properties

White, crystalline powder. Slightly soluble in water; insoluble in alcohol.

Uses

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.

Uses

Manufacture of paper pulp (as bisulfite).

Preparation

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.

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