Kinetics of Resulfurization in Magnesium Desulfurization Process of Molten Iron

摘要

A simplified experiment was conducted in place of actual magnesium desulfurization process to study its resulfurization mechanism. The magnesium desulfurization products, MgS powders, were added onto the iron melt, and then the transfer rate of sulfur from MgS on the melt surface into the melt was studied. The effects of temperature, oxygen partial pressure in the atmosphere, initial sulfur concentration and materials of crucible on the resulfurization were investigated, the methods of prevention of resulfurization were proposed, and the resulfurizaiton rates were analyzed kinetically. There are two kinds of mechanisms that are responsible for the resulfurization in the magnesium desulfurization process. Under the inert atmosphere, the resulfurization takes place by decomposition of MgS. Under the oxidative atmosphere, the resulfurization proceeds by oxidation of MgS. With increasing temperature and oxygen partial pressure in the atmosphere, the transfer of sulfur into the melt was enhanced and the resulfurization ratio (xi_S) was increased. A larger amount of MgS added onto the melt surface did not change the xi _S value a lot under the present experimental conditions. Using MgO crucible could decrease the transfer rate of sulfur into the melt in comparison with using Al_2O_3 crucible. Addition of CaO onto the melt surface was proved to be an effective method to prevent sulfur form transferring into the melt. This is because MgS was transformed into a more stable sulfide of CaS. 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.