Yoshie Nakai

Development of Slag Recycling Process in Hot Metal Desulfurization with Mechanical Stirring

In order to develop an environment-friendly steelmaking process, a slag recycling process for hot metal desulfurization by mechanical stirring was designed. The process was developed with 70 kg-scale hot metal experiments and actual plant tests. The recycled slag has a 70% desulfurization ability compared with that of virgin flux (CaO-5%CaF2). The lower efficiency of the recycled slag was caused by SiO2 contamination carried over from the previous process. There is no particular size requirement for the recycled slag, as the effect of the recycled slag size on the desulfurization ability is small. The ratio of CaO in the recycled slag to total CaO should be less than 60% in order to prevent an increase in the amount of slag. Slag recycling operation can be repeated more than twice when the optimum conditions are applied. The slag recycling process was established in an industrial operation, and consumption of desulfurization flux decreased by 40% with the process compared with that without slag recycling. Slag hot recycling was adopted at another plant where consumption of desulfurization flux decreased by 50% compared to operation without slag recycling. The positive effect of hot slag recycling is estimated to be a result of the temperature of the recycled slag.

Fundamental Investigation of Reduction and Dissolution Behavior of Manganese Ore at High Temperature

The high temperature reduction behavior of manganese ore was investigated with the aim of utilizing ore as a more economical manganese source in the steelmaking process. The melting temperature and phase change behaviors of raw and sintered manganese ores were measured by high temperature X-ray diffraction and DTA in the temperature range from 303K to 1773K under atmospheric and vacuum conditions. The melting temperatures of the raw and sintered manganese ores were 1688K and 1732K, respectively. The main manganese compounds in the raw and sintered manganese ores were CaMn6SiO12 and MnO, Mn3O4 respectively. Under a vacuum (0.13kPa), both the raw and sintered manganese ores were reduced to MnO above 1473K, whereas under the atmospheric condition (101.3kPa), the manganese ores were reduced to Mn3O4 rather than MnO. The obtained results were discussed from a thermodynamic viewpoint.