Magnesium sulfite is the magnesium salt of sulfurous acid with the molecular formula MgSO3. Its most common hydrated form has 6 water molecules, making it the hexahydrate MgSO3 6H2O. When heated above 40 °C (104 °F), it dehydrates to magnesium sulfite trihydrate, or MgSO3 3H2O. The anhydrous form is hygroscopic, meaning it readily absorbs moisture from the air.
Magnesium sulfite has been used in the "Kawasaki method" first developed in Japan. While magnesium sulfite has several uses in industry, it is the bisulfite compound that is widely used in the wood pulping process. Dolomite contains up to 40% magnesium, and calcium has been determined to be more proficient in the "sulfite process" and magnesium bisulfite is used in the "sulfate process" used to make wood pulp that is widely used today Paper and board products used.
Magnesium sulfite can be prepared by reacting magnesium hydroxide slurry with SO2 gas:
Mg(OH)2+SO2(gas)+H2O→MgSO3·6H2O
If the temperature of the solution is kept below 40°C, the hexahydrate will form. Above 40°C, the trihydrate MgSO3 3H2O is a common product. Magnesium sulfite can also be prepared by adding sodium sulfite solution to magnesium chloride solution. The mixture was kept at 25 °C for 1-2 h, the solid phase formed was separated and washed with isopropanol and dried at 60 °C. Again hexahydrate is produced.
Experimental Study on Catalytic Oxidation of MgSO3 in Magnesium Desulfurization
The catalytic oxidation of magnesium sulfite (MgSO3) to magnesium sulfate (MgSO4) is essential for the recovery of magnesium in the desulfurization process. In this paper, laboratory-scale experiments were performed to compare the catalytic activities of different catalysts, and the results showed that cobalt ions (Co2+) are highly effective in catalyzing the oxidation of MgSO3. In addition, pilot-scale tests were performed to verify the main reaction conditions affecting the Co2+ catalytic performance, such as air flow rate, pH, temperature, and Co2+ concentration. The possible reaction mechanism and reaction kinetics of MgSO3 oxidation catalysis are discussed and explained respectively.
