Photon Factory Activity Report 2017 #35 (2018)

BL-15A1/2014G707, 2015S2-002, 2016S2-001

Chemical state mapping of iron in heterogeneous reduction of iron-ore sinters
Masao KIMURA1,2, Yasuo TAKEICHI1,2, Reiko MURAO3
1
Photon Factory, Institute of Materials Structure Science, High Energy Accelerator ResearchOrganization, 1-1 Oho, Tsukuba, 305-0801, Japan2
Department of Materials Structure Science, School of High Energy Accelerator Science,SOKENDAI (The Graduate University for Advanced Studies), 1-1 Oho, Tsukuba, 305-0801, Japan
3
Advanced Technology Research Laboratories, Nippon Steel & Sumitomo Metal Co.,
Chiba 293-8511, Japan
1 Introduction
Iron-ore sinters constitute the major component of theiron-bearing burden in the blast furnace in most countries
in the Asia-Pacific region. Iron-ore sinters are formed byliquid-sintering at T > 1500K, and are composed of ironoxide phase (mainly α-Fe2O3 and partially Fe3O4) andcalcium-ferrites (CFs)[1]. In industrial process, it isrequired to optimize the speed of reduction and tominimize the degradation due to mechanical strength
during reduction. Therefore it is of great importance tounderstand where the reduction starts and how it
progresses among sinters. We tried to reveal the reduction
process in terms of iron chemical state changes (FeIII, FeII,and Fe0).
2 Experiment
Macroscopic chemical mapping in 2D was carried out
based on X-ray absorption measurements obtained byscanning the specimen (Fig. 1).
The sinter was embedded in resin and sliced into
specimens with a thickness of 20–30 µm. X-ray
absorption near-edge structure (XANES) spectra were
measured using ion chambers before and after absorption
by the specimen. The XANES spectrum at each point isassumed to be expressed as the linear combination of
those of FeIIO and FeIII2O3 and the ratios were determinedby least squares fitting. X-ray fluorescence was alsomeasured using a silicon drift detector (SDD) in order todetermine the chemical composition of iron and calcium.
Experiments were carried out at the synchrotron
undulator beamline BL-15A1 of the Photon Factory,
IMSS, KEK in Japan [2].
3 Results and Discussion
Figure 2 shows the results of iron chemical statemapping in 2D and compositional mapping of iron ore
sinter before and after reduction. Before the reduction,
most areas show a chemical state of FeIII (red) andFeIII+FeII (pink) corresponding to α-Fe2O3 and Fe3O4,respectively. Some areas with a high calcium
concentration show a chemical state between FeIII and FeII
(white) corresponding to CFs.
Areas with a low calcium concentration changed toFeIII (a typical areas is shown by a blue arrow in Fig. 2),
while areas with a high calcium concentration remained

as FeIII (red; shown by a red arrows in Fig. 3) or between
FeIII and FeII (white) [3].
It was observed that reduction was more likely toproceed in areas with low calcium concentration, which
can be explained by experimental results using powder
specimens of individual phases that iron oxides are moreeasily reduced than calcium ferrites [2]. The
heterogeneous reduction is easily expected to cause crack
formation and deteriorates the mechanical strength of thesinter. The relationship is now being studied.

Fig. 1 Schematic diagram of the experimental
setup for chemical mapping at BL-15A1 in PF

Fig. 2 Results of iron chemical state mapping (right) andcompositional mapping (left) of iron ore sinter afterreduction.
Acknowledgement
Part of this work carried out by MK and YT wassupported by the Cross-Ministerial Strategic Innovation
Promotion Program (SIP SM4I, units D66) operated by
the Cabinet Office of Japan.
References[1] S. N. Ahsan et al. Ironmaking and Steelmaking
10, 54 (1983).
[2] M. Kimura et al., J. Phys.: Conf. Ser. 712, 012077(2016).
[3] M. Kimura et al., J. Phys.: Conf. Ser. 849, 012015(2017).
* masao.kimura＠kek.jp