Mechanism of resulfurization in magnesium desulfurization process of molten iron

摘要

During magnesium desulfurization of molten iron, the desulfurization product of MgS floats up to the melt surface. After magnesium supply terminates, resulfurization tends to take place because of the transfer of sulfur from MgS into the melt. In the present study, a simplified experiment was designed to clarify this resulfurization mechanism. With MgS powders added onto the melt surface, the transfer rate of sulfur from MgS into the melt was measured. Two kinds of mechanisms are revealed to be responsible for the resulfurization in the magnesium desulfurization process. One is decomposition of MgS under the inert atmosphere; the other is oxidation of MgS under the oxidative atmosphere. It is also found that increasing temperature and oxygen partial pressure in the atmosphere increased the transfer rate of sulfur into the melt and the resulfurization ratio. But the increase in the added amount of MgS did not change the resulfurization ratio largely under the present experimental conditions. The resulfurization rate was smaller by using MgO crucible than that by using AI_2O_3 crucible. Addition of CaO and the activated charcoal powders onto the melt surface could significantly prevent sulfur of MgS on the melt surface from transferring into the melt. With a simplified first-order rate equation, the calculated capacity coefficient for transfer of sulfur from MgS to melt is increased with increasing the temperature and the oxygen partial pressure in the atmosphere, but does not change with adding different amounts of MgS onto the melt surface.