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The oxidation rate of magnesium sulfite

  • Magnesium sulfite is the magnesium salt of sulfurous acid with the formula MgSO3. Its most common hydrated form has 6 water molecules making it a hexahydrate, MgSO3·6H2O. When heated above 40 °C (104 °F), it is dehydrated to magnesium sulfite trihydrate, or MgSO3·3H2O.[1] The anhydrous form is hygroscopic, meaning that it readily absorbs water from the air.
    Literature data of solubility of MgSO3 in water and in aqueous solutions of MgSO4 have been correlated. Magnesium sulfite forms hexahydrate (stable below 40°C) and trihydrate (above 40°C), nevertheless, metastable hexahydrate can precipitate at temperatures significantly higher than this transition temperature. Magnesium sulfate increases the solubility of the sulfite.
    Magnesium sulfite is the magnesium salt of sulfurous acid with the formula MgSO 3. Its most common hydrated form has 6 water molecules making it a hexahydrate, MgSO 3·6H 2O. When heated above 40°C (104°F), it is dehydrated to magnesium sulfite trihydrate, or MgSO 3·3H 2O. The anhydrous form is hygroscopic, meaning that it readily absorbs water from the air.
    Oxidation of magnesium sulfite is important for recycle of byproduct in the magnesium desulfurization. The oxidation rate of magnesium sulfite, prepared by vacuum evaporation method, was investigated in a bubbling tank in presence of transition metal catalysts, which shows cobalt is the most effective. The general reaction orders with respect to cobalt, magnesium sulfite, and oxygen are 0.44, 0, and 0.46, respectively, and the apparent activity energy is 17.43 KJ·mol. The catalytic performance of cobalt compared with other metals was also analyzed employing the ion potential theory. Integrated with the three-phase reaction model, we inferred that the general oxidation rate of magnesium sulfite is controlled by mass transfer of oxygen. Further, the intrinsic kinetics was predicted, indicating that the reaction orders with respect to cobalt and oxygen are 1.0 and 0, respectively. The results are helpful for the recycle of magnesium sulfite in magnesia desulfurization.
    Catalytic oxidation of magnesium sulfite (MgSO3) into magnesium sulfate (MgSO4) is essential for recycling and utilization in the magnesium desulfurization processes. In this paper, laboratory-scale experiments were carried out to compare catalytic activity of different catalysts, which showed that cobalt ions (Co2+) were highly efficient for MgSO3 oxidation catalysis. Moreover, Pilot-scale tests were conducted to validate the major reaction conditions influencing catalytic performance of Co2+, such as air flow rate, pH, temperature, and Co2+ concentrations. Possible reaction mechanism and reaction kinetics of MgSO3 oxidation catalysis was discussed and interpreted, respectively. The MgSO3 oxidation by catalysis has much potential application in the industrial field of the magnesium desulfurization.