1967 Volume 53 Issue 14 Pages 1553-1560
In spite of adding no flux to the raw materials, the pellets of some kinds of ores were beoded with low melting slags by firing under an oxidizing condition. These slag formations were assorted into two cases. As seen in Marcona pellets of both hematite and magnetite ores, one was caused by the reaction between the gangue mineral and ferrous oxide, dissociated from ferric oxide by the promoting effect of MgO in actinolite. The firing temperature changed the volume and fluidity of the liquid slag and brought about the various forms of bonding. At nearly 1150°C the aggregates of the fine gangue and iron oxide particles combined the coarse ones, at 1200°C the liquid slag was formed at the contact points between the coarse gangue and iron oxide particles and combined them firmly, and above 1200°C the liquid phase sintering proceeded predominantly in the pellet.
The other occured typically in the firing of the pellet of Hanaoka pyrite cinder. Up to 1050°C the porous are particles were bonded with hematite. Above 1100°C, however, the molten slag formed from the gangue minerals (as sericite, chlorite etc) combined firmly the iron oxide particles.
In high temperature range the porosity of these pellets were increased by the gases generated in the thermal decompositions of ferric oxide in Marcona pellets and of calcium sulfate in Hanaoka.