Abstract
An investigation has been made on the abnormal swelling during prereduced pellet firing.Ten kinds of iron ore and 3 kinds of solid reductant were tested.When pellet contained a reactive reductant, abnormal swelling occurred in some kinds of ore.This was found to be due to the growth of metallic filament in a pellet, which grew abruptly in the reduction at about 1000°C.
The swelling was related to the unstable phase during reduction, or this may be attributed to (1) laminated structure, (2) strain within crystals, (3) weathering of ore, (4) incomplete recrystallization and so forth.
From the experiment in which 2% of pyrite or 1% of sulphonic acid (S15.9%) was mixed with ores, it was found that sulphur addition was effective to prevent from swelling.However, sulphur addition was disadvantage with respect to pellet quality, because sulphur remained in pellet after reduction.
