1967 Volume 53 Issue 14 Pages 1561-1568
The pulverized Brazilian hematite are and the ground magnetic concentrates of Swedish and Marcona ores were pelletized and fired under various conditions. By investigating the packing states of the are particles in the dry balls and their behavior in firing processes, the followings were clarified. In the pelletizing of the hematite ore, the very fine particles (under 1-2μ), which coated the coarser ones, contributed a great deal to the increase in the density of the green pellet. In firing, the fine particles combined the coarser ones by forming bridges between them and the bridges grew with firing time resulting in strong pellets. After the size of the bridges exceeded several microns, the strength of the pellet increased rapidly without a remarkable decrease in the porosity.
While, the fine particles in the magnetic concentrates were unable to play the important part in pelletizing by reason of the formation of the magnetic flocks, which were not broken up by grinding. The strength of the pellets, in the first stage of the oxidizing firing, depended on the size and number of the hematite bonds (i. e. the oxidation degree of the magnetite and the content of the fine particles). However, the degree of the grain growth of the hematite came to determine the strength in the latter. The formation of the compact hematite shell, which hindered the permeation of oxygen gas into the pellet, was prevented by oxidizing previously the magnetite more than fifty percent at the lower temperature range.