1. Industrial Applications of In Situ Diffraction Analysis – Iron Ore Sinter Phase Formation
Nathan A.S. Webster1, Mark I. Pownceby1, Rachel Pattel and Justin A. Kimpton2
1 CSIRO Mineral Resources, Private Bag 10, Clayton South, VIC, 3169, Australia 2 Australian Synchrotron, 800 Blackburn Rd, Clayton, VIC, 3168, Australia
CSIRO Mineral Resources
Understanding the formation mechanisms of Ca-rich ferrites has the potential to impact upon the iron-making process. In situ X-ray diffraction (XRD) and subsequent QPA is impacting this understanding.
Research Background
Iron ore sinter, a composite material comprised of iron ore fines bonded by a matrix of complex Ca-rich ferrite phases (Fig. 1b[1]), is a major component of blast furnace feed material.
Most of the Ca-rich ferrites contain silica and alumina and are known collectively by the acronym ‘SFCA’ (silico-ferrite of calcium and aluminium). These SFCA phases impart desirable physical properties of high strength, high reducibility and low reduction degradation to iron ore sinter.
‘SFCA’ is divided into two main types: SFCA (low Fe, columnar morphology), and SFCA-I (high Fe, low Si, platy morphology). Both have complex triclinic crystal structure.[2] SFCA-I is the more desirable phase.
Our research[3-8] is significantly impacting fundamental understanding of the formation of SFCA and SFCA-I from precursor phases. In recent work the impact of titanomagnetite addition, alumina source (i.e. gibbsite vs kaolinite vs aluminous goethite) and millscale addition on their formation has been determined. The goal is to maximise SFCA-I formation. Mill scale, mostly wüstite, magnetite and hematite, is a waste product formed on the surface of steel that occurs during continuous casting, reheating and hot-rolling operations.
Titanomagnetite Addition
Increasing Fe2.73Ti0.27O4-based ironsand addition causes a decrease in SFCA-I concentration (undesirable) with a corresponding increase in SFCA. The SFCA crystal structure is more accommodating to Ti. a
CaCO3 flux a b
2 wt% b
12 wt% c b
Ore
~1300°C
Pore
Coke
Ore
SFCA and SFCA-I phases, other Ca-rich ferrites, calcium silicates, glass, Fe3O4/Fe2O3
Figure 4: a) Accumulated in situ S-XRD data for a sinter mixture containing 12 wt%; and QPA results showing phase concentrations as a function of temperature for sinter mixtures containing a) 2 wt% and b) 12 wt% titanomagnetite ironsand.
Ultra-fine coating
Figure 1: Schematic showing a) a typical mixture of iron ore fines, flux and coke; and b) typical iron ore sinter product.[1]
Alumina Source
Iron ores containing kaolinite as the primary source of alumina were found to promote the formation of a greater amount of SFCA-I than iron ores containing primarily aluminous goethite or gibbsite.
The intermediate gehlenite phase appears highly reactive to hematite leading to the formation of SFCA-I at temperatures as low as 1050°C. a b
In Situ XRD – Simulating Sintering Conditions
Synthetic sinter mixtures, with bulk compositions in the SFCA and SFCA-I domains (Fig. 2), modelled the ultra-fine coating component of an industrial mixture (Fig. 1a).
In situ XRD data were collected on the powder diffraction beamline at the Australian Synchrotron, and in the laboratory on an INEL diffractometer, under simulated sintering conditions (Fig. 3).
Gibbsite
Kaolinite
Figure 5: QPA results for sinter mixtures containing a) gibbsite, and b) kaolinite, as the primary source of alumina.
Millscale Addition
Preliminary results suggest minimal effect on phase chemistry with increasing millscale addition.
SiO2
+ 0-5wt% Al2O3
Anton Paar chamber
CaSiO3
Ca4Si3O10
Ca2SiO4
SFCA
CaFe6O10
Ca2Fe2O5
X-ray
optics
CaO
Fe2O3
CaFe2O4
SFCA-I
Figure 2: Location of the SFCA and SFCA-I compositional domains in the Fe2O3-CaO-SiO2 system.
Figure 3: Experimentation on the INEL diffractometer.
Figure 6: Accumulated in situ S-XRD data for sinter mixtures containing a) 3 and b) 24 wt% millscale.
FOR FURTHER INFORMATION
REFERENCES
[1] M. Sasaki, Y. Hida, Tetsu-To-Hagane, 1982, 68, ,
[2] W.G. Mumme et al., Neues Jahrb. Miner. Abh., 1998, 173,
[3] N.A.S. Webster et al., Metall. Mater. Trans. B, 2012, 43,
[4] N.A.S. Webster et al., ISIJ Int., 2013, 53,
ACKNOWLEDGEMENTS
BHP-Billiton is acknowledged for financial support for some of this research. This research was partially undertaken on the powder diffraction beamline (10BM1) at the Australian Synchrotron, Victoria, Australia, under beamtime award AS132/PD6321.
Dr Nathan Webster e p
[5] N.A.S. Webster et al., ISIJ Int., 2013, 53,
[6] N.A.S. Webster et al., Metall. Mater. Trans. B, 2014, 45,
[7] N.A.S. Webster et al., ISIJ Int., 2016, 56, 1715–1722.
[8] N.A.S. Webster et al., ISIJ Int., 2017, 57, 41–47