Insights into the formation of iron ore sinter bonding phases

During the iron ore sintering process, iron ore fines (<6.3mm) are mixed with limestone flux and coke breeze and heated to ~1300ºC. This results in partial melting of the mixture, converting the loose raw materials into a porous but physically strong composite material in which the iron-bearing minerals are bonded together by a range of complex ferrite-like phases known collectively as 'SFCA' (Silico-Ferrite of Calcium and Aluminium). These 'SFCA' phases can be divided on the basis of composition and morphology into two main types: a low-Fe form that is simply referred to as SFCA, and a second high-Fe, low-Si form called SFCA-I. SFCA and SFCA-I are believed to be the most desirable bonding phases in iron ore sinter because of their high reducibility, high mechanical strength and low reduction degradation, all of which are significant factors in determining the efficiency of the blast furnace. Despite their importance in controlling the quality of iron ore sinter, the stability range and mechanisms of 'SFCA' formation from precursor phases are not well understood. CSIRO has attempted to improve understanding of phase relations within iron ore sinter by; a) conducting experimental phase equilibria studies within the Fe2O3-CaO-SiO2 (FCS) and Fe2O3-Al2O3-CaO-SiO2 (FACS) model sinter systems to establish the key thermal and compositional parameters that influence the bonding phase chemistry and stability, and, b) conducting in situ X-ray diffraction experiments to determine the formation mechanisms of SFCA and SFCA-I under simulated sintering conditions. The combination of techniques will provide insights into sinter formation mechanisms which are important in designing strategies to counter some of the key problems facing the Australian iron ore industry

Corrosion behavior of nickel ferrite-based ceramics for aluminum electrolysis cells

NiFe2O4-based ceramic materials of different compositions were fabricated from NiO and Fe2O3 using a solid-state synthesis technique at elevated temperatures. The materials were tested in a stirred finger test apparatus at 980°C in synthetic cryolite-based melts. The factors affecting corrosion rates of the materials were investigated experimentally under various conditions, including composition and porosity of the materials, duration of testing, Al2O3 content of the electrolytes, bath ratio, CaF2 addition and test atmosphere. The materials and bath, before and after testing, were characterized by combined XRD, XRF and EPMA. The results indicated that corrosion resistances of the NiFe2O4-based ceramic against the baths are very high. The mechanism of corrosion of the material is also discussed

Exploratory Study of Separation of Sulphidised Chrome Spinels from Reduced Ilmenite

The removal of chromium-containing impurities, such as chrome spinel (ZCr2O4 where Z = Fe, Mg, Mn) from ilmenite (FeTiO3) concentrates through selective sulphidation, has been investigated by the authors. Laboratory experimental studies using sulphur added to ilmenite concentrates under Becher-type reduction conditions showed it is possible to selectively sulphidise chrome spinels from different ilmenite deposits. In this paper, processes to remove the sulphidised chrome spinels from the bulk ilmenite concentrates were investigated using flotation and magnetic separation techniques. Clustering or fusing of the reduced ilmenite (RI) and sulphidised chrome spinel grains was found to have a detrimental effect on flotation performance and made it difficult to have clear separation. A light wet grind was effective for breaking the clustering, but it caused the sulphide rim to spall off from chrome spinel surfaces, which reduces flotation efficiency. The preliminary results obtained after a magnetic separation (0.7 A) of a demetallised sulphidised RI sample show that the sulphidised chrome spinels preferentially report to the magnetic fraction. Additional magnetic separation of the non-magnetic fraction at a lower current (0.3 A) improved the recovery of sulphidised chrome spinels. The demetallisation process followed by a magnetic separation provided insights into a potential route for the removal of chrome spinels from reduced ilmenite concentrates. These two steps simulate the aeration stage of the Becher process. Further studies are required to optimise the process parameters

Exploratory Study of Separation of Sulphidised Chrome Spinels from Reduced Ilmenite

The removal of chromium-containing impurities, such as chrome spinel (ZCr2O4 where Z = Fe, Mg, Mn) from ilmenite (FeTiO3) concentrates through selective sulphidation, has been investigated by the authors. Laboratory experimental studies using sulphur added to ilmenite concentrates under Becher-type reduction conditions showed it is possible to selectively sulphidise chrome spinels from different ilmenite deposits. In this paper, processes to remove the sulphidised chrome spinels from the bulk ilmenite concentrates were investigated using flotation and magnetic separation techniques. Clustering or fusing of the reduced ilmenite (RI) and sulphidised chrome spinel grains was found to have a detrimental effect on flotation performance and made it difficult to have clear separation. A light wet grind was effective for breaking the clustering, but it caused the sulphide rim to spall off from chrome spinel surfaces, which reduces flotation efficiency. The preliminary results obtained after a magnetic separation (0.7 A) of a demetallised sulphidised RI sample show that the sulphidised chrome spinels preferentially report to the magnetic fraction. Additional magnetic separation of the non-magnetic fraction at a lower current (0.3 A) improved the recovery of sulphidised chrome spinels. The demetallisation process followed by a magnetic separation provided insights into a potential route for the removal of chrome spinels from reduced ilmenite concentrates. These two steps simulate the aeration stage of the Becher process. Further studies are required to optimise the process parameters

Selective sulfidising roasting for the removal of chrome spinel impurities from weathered ilmenite ore

With high-grade ilmenite (FeTiO3) ores becoming scarce, there is a need to process lower-grade and more weathered ilmenite ores. These alternative sources provide complexities in terms of physical characteristics, mineral compositions, and impurity levels, all of which can significantly affect the subsequent processing route. In the production of high purity white pigment from ilmenite, chromia (Cr2O3)-containing impurities such as chrome-rich spinets need to be removed from the ilmenite concentrates down to commercially accepted levels. Existing magnetising roast processes currently used in the industry do not allow a clean separation of the chrome-rich spinets from the ilmenite due to overlapping physical properties. It has been suggested that selective sulfidation of chrome-rich spinels could be a potential route for chromia separation from ilmenite. However, the detailed conditions under which the selective sulfidation can occur are not well known. This work focuses on a systematic study of selective sulfidation of chromite FeCr2O4 (one end member of the spinel series) for the purpose of chromia impurity removal from a weathered ilmenite concentrate. Detailed thermodynamic assessment and experimental studies have been carried out to determine the conditions at which selective chrome spinel sulfidation occurs. The results suggest that there are two regimes (Area-1 and Area-2) where selective chrome spinel sulfidation is possible. Area-1 is in the range of pO(2) approximate to 2.37 x 10(-09) atm to 5.01 x 10(-15) atm, while Area-2 is at lower pO(2) (<= 6.92 x 10(-19) atm) and pS(2) (<= 1 x 10(-06) atm) region relative to Area-1. Targeted experimental analyses of the two regimes revealed that selective sulfidation of chrome spinel occur only under the reaction conditions at Area-2. It is suggested that the lack of selective chrome spinel sulfidation under Area-1 conditions is the change in activity of iron (a(Fe)) due to weathering action on chrome spinet grain

Phase formation in iron ore sintering

During the iron ore sintering process, iron ore fines (<6 mm) are mixed with limestone flux and coke breeze and heated to ~1300&#0186;C. This results in partial melting of the mixture, and converts the loose raw materials into a porous but physically strong composite material in which the iron bearing minerals are bonded together by a range of complex ferrite-like phases known collectively by the acronym 'SFCA' (Silico-Ferrite of Calcium and Aluminium). These 'SFCA' phases can be divided on the basis of composition and morphology into two main types: one is a low-Fe form that is simply referred to as SFCA, and the second is a high-Fe, low-Si form called SFCA-1. SFCA and SFCA-1 are believed to be the most desirable bonding phases in iron ore sinter because of their high reducibility, high mechanical strength and low reduction degradation, all of which are significant factors in determining the efficiency of the blast furnace