Change of Sinter Minerals and Final Fractional Reduction in the Reduction Stage from Hematite to Magnetite with CO-CO<SUB>2</SUB>-N<SUB>2</SUB> Gas Mixture

Abstract

To examine the reduction behavior of commercial sinter in the initial stage, the following analyses were done : Quantitative analysis of sinter before reduction was done by EPMA and the contents of hematite, calcium ferrite (CF) , magnetite and slag were determined. Comparison between EPMA surface analyses of sinter before reduction and reduced to magnetite stage at 1 133 K suggests that CF breaks up into magnetite and slag during reduction. Quantitative analysis of sinter minerals during reduction to magnetite stage was done by the X-ray internal standard method using the above-stated contents. Variations in the amount of hematite, CF and magnetite with fractional reduction are revealed ; CF is reduced to magnetite at 1 033 and 1 133 K but is not at 933 nor 983 K. Microstructures of samples reduced up to magnetite stage show that CF is reduced at 1 033 K but not at 983 K. Final fractional reduction in the hematite to magnetite stage under rising temperature conditions up to 1 173 K, Ff', was measured after measuring the one at a predetermined temperature, Ff; below about 1 003 K, CF is hardly reduced and Ff# 0.7 when oxygen reducible in this stage is assumed to come from hematite and CF. The ratio Ff/Ff' is given as a function of reduction temperature.

Gaseous Reduction Model for Sinter in Consideration of Calcium Ferrite Reaction Process (Unreacted-core Shrinking Model for Six Interfaces)

“…The present model is effective as long as CF exists in sinter, while its necessity increases as the ratio of CF rises. In the case of the measured example shown in Section 3·3, the mass ratio of Fe 2 O 3 in CF is 0.693, 22) and therefore, the reducible oxygen ratio in CF becomes less than the value of Y. Still, it is easy to guess the occurrence of fatal error in the previous analyses, in which CFw was treated to be reducible in the thermal reserve zone irrespective of irreducible one there; the mass ratio of the irreducible oxygen is about 20 up to 30%.…”

“…In section 3·3 for apparent molar density of reducible oxygen, the evaluation is exemplified on the basis of both EPMA and XRD analyses reported previously. 22) In this EPMA quantitative analysis, columnar shape CF was chosen partly because wider uniform area could be obtained and partly because main part of CF was columnar shape. Therefore, this EPMA quantitative analysis data are considered to be affected by the composition difference due to the structure difference.…”

“…In the case of Sinter A, the initial magnetite in the sinter product, Im, is evaluated as 14.71 mass% and moreover (Fe 2 O 3 ) = 65.84 mass% can be divided between hematite (%h) and Fe 2 O 3 contained in CF (%x), namely, %h + %x = 65.84. From the evaluation based on EPMA quantitative analyses reported previously, 22) mass ratio of Fe 2 O 3 in CF was obtained as 0.693, and mass ratio of (h + Im):CF can be observed as 0.74:0.26 by using the triangle figure 22) among mass ratios of h, m and CF quantitatively determined by the X-ray diffraction internal standard method. From these relations, the apparent molar density of reducible oxygen ρ O at each reduction step can be calculated.…”

Characterisation of iron ore sinter and its behaviour during non-isothermal reduction conditions

“…[23][24][25][26] There are two aspects in the study of sinter behaviour in the blast furnace. [27][28][29] The first aims at characterising the behaviour of the sinter in the shaft zone between the stockline and the start of burden softening of [27][28][29][30][31][32][33][34][35] the second deals with the behaviour of the sinter in the cohesive and dropping zones where ores soften and melt. [36][37][38][39][40][41][42] The position, shape and thickness of the cohesive zone have a critical influence on blast furnace operation and depend on the properties of sinter.…”