Sintering tests, involving airflow measurements before and after bed ignition, were carried out on three optimized iron ore blends-containing only hematite (HAEM), hematite with pisolite (PISO), and hematite with pisolite and hematite-goethite (PIMM)-to assess the resistance of the flame front and associated regions. Results showed that post-ignition airflow rates for the three blends were comparable for the same pre-ignition airflow rate, indicating that reactive ores i.e. pisolite and hematite-goethite ores, did not have an adverse effect on flame front resistance. For the PIMM blend, increasing the level of fines (minus 0.15 mm fraction) also did not have any effect on the flame front resistance. Reducing the coke level in all the three blends and increasing basicity decreased the value of the resistance. The resistance was shown to be a strong function of green bed airflow velocity and semi-empirical equations, with single variables, were derived to characterize the 'sinterability' of iron ore mixes.KEY WORDS: hematite-goethite ores; sintering; flame front; airflow rates. Fig. 1. Flow streams to and from a sinter machine.

The properties of melts formed in the flame front during iron ore sintering determine the structure of the ensuing sinter bonding phases. The tumble strength of sinter particles and yield from a sinter strand are largely determined by the inherent strength and structure of the bonding phases present. In this study, bench-scale tests were carried out to study the effect of melt chemical composition and sintering conditions on bonding phase micro-structure. The study showed that phosphorus, silica, alumina and magnesia levels, sinter basicity and maximum sintering temperature influenced bonding phase structure through the reshaping and coalescing of the melt and bubbles. Information in the literature indicates that some of the observed changes in pore properties can be explained by changes in viscosity and surface tension of the melts. The inability to explain all the changes are most likely related to the differences in chemical compositions between melts considered in the literature and the sintering melts formed in this study. The study also showed that image analysis could used to provide a reliable objective description of the obtained sinter micro-structures.KEY WORDS: iron ore sintering; melt chemical composition; machine yield; sinter micro-structure.

In iron ore sintering, the properties of the flame front are clearly critical as they determine the heat imparted to the particulate bed and, hence, the strength of the formed sinter. This study explores the factors that influence flame front temperature and also the speed at which it descends down a bed. These two properties are dependent on post-ignition airflow rate and the properties of the sinter mix. Post-ignition airflow rate is a strong function of the pre-ignition airflow rate and the flow resistance of the flame front. This study reiterates the strong dependence of flame front resistance on gas flow velocity, flame front temperature and applied suction. Dense ores produce higher bulk density and lower porosity beds and, as a consequence, they have the effect of slowing down and broadening the flame front. The influence of flame front speed on flame front properties for different ores was also established. For comparable flame front properties results show that sinter basicity has a large influence on sinter strength and yield. Studies of coke combustion efficiency show decreasing values with increasing flame front speed and values increased significantly when sintering YANDI ore. Many of the obtained quantitative dependences will be used to verify a sintering mathematical model that is under development.