Rate of isothermal reduction of MgO with Al

Isothermal reduction of magnesium oxide with aluminum was carried out by use of an insertion tube charged with pellets composed of magnesium oxide and aluminum powders. Since the temperature in the tube increased rapidly during inserting the tube into the high temperature zone in the graphite crucible and decreased quickly during lifting up the tube to the low temperature zone, the isothermal reduction condition was essentially satisfied by the present method. The reduction rate was increased with increasing temperature, carrier gas flow rate and pellet-forming pressure. Even a little carrier gas could greatly increase the reduction rate of magnesium oxide. The XRD patterns of pellets at the different reduction stages confirmed that the aluminothermic reduction of magnesium oxide can be roughly classified into two stages. At the first stage, spinel, alumina and magnesium vapor were mainly produced; at the second stage, the spinel was further reduced by aluminum to produce alumina and magnesium vapor and the excessively added MgO was also reduced. A kinetic model is established to describe the reduction rate of magnesium oxide. The apparent rate constant in the kinetic model increases with increasing temperature, carrier gas flow rate and pellet forming pressure. The apparent activation energy of the reduction is determined to be 109 kJ/mol.