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A ferrous burden loses its permeability in the cohesive zone of a Blast Furnace (BF), where the iron burden materials soften and melt. A tailor-made, high-temperature furnace named ARUL (Advanced Reduction under Load) was used here to study the reduction-softening behaviour of acid and olivine pellets and basic sinter under simulated BF gas, temperature and pressure conditions.The ARUL test showed the best reduction-softening properties for the basic sinter. The sinter sample resisted up to 1 329°C and achieved a reduction degree of 90.2% until a gas-impermeable structure was formed in a packed bed, whereas the acid pellet lost its permeability at 1 160°C and only reduced to a reduction degree of 48.7%. The olivine pellet had intermediate reduction-softening properties with a final temperature of 1 252°C and a final reduction degree of 68.7%. The differences between the test materials were assessed as being caused mainly by different chemistry, but it was also revealed that the sinter sample remained its macro-porosity markedly better in relation to the pellets, providing routes for reducing gases.The experimental results were compared to the phase diagrams calculated with the computational thermodynamic software FactSage. Phase diagrams for the 5-component FeO-SiO 2 -CaO-MgO-Al 2 O 3 systems with constant CaO, MgO and Al 2 O 3 contents were used to estimate the formation of liquid phases in the test materials. The computed phase diagrams gave an estimate of the liquid formation; however, some limitations were also found in the utilization of the computations because of the need to define the system in certain simplicity.

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Recycling of fine sized iron-rich by-products back to blast furnace (BF) process in the form of cementbonded briquettes has become a common procedure in steel plants. Replacing part of the cement by Ground Granulated Blast Furnace Slag (GGBFS) is also a common method to reduce cement consumption. When the briquettes are subjected to high temperature and reducing atmosphere in the BF, the cement phases decompose and the iron oxides undergo a series of phase transformations. To avoid early disintegration and to improve the performance of the briquettes, it is necessary to study these reactions during the reduction. In the present study the reduction behavior of the BF briquette samples was studied by experimental methods in a laboratory scale furnace, which simulates the conditions of the BF shaft in a CO-CO2-N2 atmosphere. With interrupted experiments the composition of the briquette was studied in different reduction stages of the BF shaft. The effect of GGBFS as a binder material on the reduction was studied with GGBFS containing briquette samples. The reduction of briquettes was compared to an olivine pellet which was used as a reference sample. Considerably higher reduction rate was detected with the briquettes compared to the pellet at 1 100°C when reduced to metallic iron. 25-50 vol-% swelling in the briquette samples was detected during the wüstite-iron reduction step at 900-1 000°C. X-ray diffraction (XRD) was used to observe the phase transformations in the Fe-Fe2O3-CaO system of the briquette and the results are in agreement with the theory.