Characterization of bonding and crystalline phases in fluxed pellets using peat moss and bentonite as binders

Abstract

Pellets in the basicity range of 0.2 to 1.6 were produced from specular hematite concentrates using bentonite or peat moss as a binder. Specific pellet basicities were achieved through the addition of (1) limestone and (2) a combination of dolomite and limestone. Mineralogical study and microanalysis of the bonding and crystalline phases were done using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). In limestone-fluxed pellets with bentonite as a binder, although formation of calcium ferrite was noted at the basicity of 0.8, its formation in appreciable quantities was delayed until the basicity of 1.6. For the pellets produced with a combination of dolomite and limestone, even at the basicity of 1.6, only minor amounts of this phase were present. In these pellets, some magnesioferrites were formed which did not conform to the stoichiometric composition (MgOFe₂O₂), but they were quite deficient in MgO. The silicate glass phases, which essentially provided the bonding in the pellets, showed a two-zone structure: (1) magnesian-ferruginous and (2) glass containing high quantities of Si and Ca. However, in pellets with only limestone addition, the zoned structure was less prevalent, probably due to low Mg content. The results indicate that using peat moss in conjunction with limestone, pellet sticking can be minimized at higher basicities. The factors influencing the pellet bonding and the change in the physical and chemical properties of these pellets are discussed.