# Rudomain Iron Ore Treatment by High-Temperature Reduction
## 3 Results and Discussion
### Material Research of Metallised DRI pellets
The main parts of the DRI 3 sample consisted of relatively small zones of metallic iron, low-carbon iron carbide (Fe\({}_{2}\)C\({}_{0.05}\)), and ferrosilicon with a low silica content (Fe\({}_{3}\)Si). The microstructure of the DRI 3 sample also exhibited the contents of silica (SiO\({}_{2}\)), cristobalite (SiO\({}_{2}\)) and grains of hematite and wustite. The microstructure did not contain any melted grains, which also explains the low hardness of the produced metallised product. Furthermore, DRI pellets exhibited also a relatively large amount of unreacted charcoal. The microstructure of the DRI 3 sample also contained the signs of the reduction mechanism (Figure 14 down), in particular silica and carbon from the reducing agent located on the iron sphere produced by the reduction. The present silica (or a high-temperature form of cristobalite) inhibits the reduction of iron oxides. A standardised methodology prescribed by STN ISO 540 [27] was applied using a high-temperature microscope in the examination of changes in the surface and volume of the analysed samples of Rudomain R7 iron ore and the metallised pellets produced from  
Figure 13: An EDX analysis of the DRI 1 sample (original structure). it (DRI 1 and DRI 3). During the heating process, with a gradient of 10 \({}^{\circ}\)C/min and in an air atmosphere at temperatures of up to \(\sim\)1520 \({}^{\circ}\)C, geometrical changes were examined in the samples pressed into small cylinders (l = 3 mm; d = 3 mm) with the aim of identifying boundary temperatures. The melting point of Rudomain iron ore (1450 \({}^{\circ}\)C) indicated the high effectiveness of the reduction processes with the use of gaseous CO and H\({}_{2}\), which is the basic principle of the production of DRI or hot briquetted iron (HBI). In the study [19], the melting interval of the input materials for reduction was found to be approximately 1350-1410 \({}^{\circ}\)C. The results of the visual analysis for the identification of melting points indicated that DRI 1 and DRI 3 metallised pellets melted at a temperature that is higher than the melting point of the input Rudomain ore (Figure 15, Table 9). The DRI 3 sample melted at the temperature interval from 1492 to 1513 \({}^{\circ}\)C, whereas the DRI 1 sample did not melt even at the maximum operating temperatures available in the high-temperature microscope (\(\sim\)1510-1520 \({}^{\circ}\)C) (Figure 15). Since the metallised DRI products contained primarily metallic Fe and a high-temperature form of silica (cristobalite) with the melting point above 1500 \({}^{\circ}\)C, the high-temperature observations confirmed the chemical and mineralogical composition as well as the EDX analysis. The DRI 3 sample had a less intensive reduction and melted at the temperature interval of 1492-1513 \({}^{\circ}\)C; this confirms that the sample also contained iron oxides that did not fully undergo the reduction process. Figure 14: _Cont._  
Figure 14: An EDX analysis of DRI 3 samples (original structure). Figure 15: High-temperature observation of DRI 1 and DRI 3 iron ore samples before (R10) and after metallisation. NA—not analyzed at higher temperatures due to temperature limit reached, maximum about 1515 \({}^{\circ}\)C.  
Following the metallisation process, the average-representing sample Rudomain R7 (FeTOTAL of 59 wt%) achieved a FeTOTAL content of ~78%. Figure 16 shows a graphical simulation of the equilibrium composition in the metallisation of Rudomain R7. The simulation indicated that at a temperature of 1200 \({}^{\circ}\)C, the metallised product DRI should have the following chemical composition: FeTOTAL 78%; SiO2 18% (silica 9% + cristobalite 9%); C 2%; and other components representing 2%. The DRI 1 sample, which was made of Rudomain R7 and exhibited the best result of reduction conducted in a laboratory, had the following chemical composition: FeTOTAL 78.08%; SiO2 19.05%; C 0.68%; and other components representing 2.19% (Table 6).