Effect of Aluminum Dissolved in Hematite
on Formation of Calcium Ferrites at 1473 K
HUI GUO and XING-MIN GUO
Silico-ferrite of calcium and aluminum (SFCA) is a primary bonding phase, which determines
the quality of high basicity sinter used widely as raw materials in blast furnace ironmaking.
Calcium ferrite containing aluminum (CFA) is a key precursor during the formation process of
SFCA and is inﬂuenced by Al
content in iron ore ﬁnes. In this work, the experiment was
conducted to investigate the eﬀect of the aluminum occurrence state on the formation of calcium
ferrite by the simulating sintering process of diﬀerent types of aluminum-bearing hematite at
1473 K. X-ray diﬀraction, optical microscope, scanning electron microscopy, and
energy-dispersive spectroscopy were used to characterize the mineral change in sintered
samples. The result shows that the formation of CFA was promoted by both granular Al
wrapped in Fe
and aluminum dissolved in Fe
solid solution, especially for the latter, due
to the formation of the CFA directly from the reaction between Fe
solid solution and
CaO, and the aluminum content in CFA formed was inﬂuenced obviously by the solid solution
amount of alumina into Fe
as raw materials.
Ó The Minerals, Metals & Materials Society and ASM International 2018
basicity sinter is a major iron-bearing raw
material in blast furnaces in the Asia-Paciﬁc region.
The eﬃciency of the blast furnace for iron-making
strongly depends on the strength and reducibility of the
which are mainly inﬂuenced by the nature,
abundance, and morphology of minerals.
showed that the quality of sinter is associ-
ated with the calcium ferrite-bonding phase due to
relatively higher strength and better reducibility. In a
large number of silico-ferrite of calcium and aluminum
(SFCA) formation mechanism studies,
that the formation of SFCA can be improved when
alumina consists in raw materials of the sinter.
The strength and reducibility, especially low-temper-
ature reduction degradation of sinter,
enced obviously by the alumina content in iron ore ﬁnes.
However, there are few studies concerning the diﬀerence
on the occurrence state of Al
as a ganguelike gibbsite
] and kaolinite [Al
] in the raw
materials or as a solid solution such as the aluminum
dissolved in hematite and goethite.
In most studies,
the gibbsite or Al
pure reagent was adopted as the
source of aluminum to show that excessive content of
deteriorates the sinter quality, leading to low-tem-
perature reduction degradation, but Al
promote the formation of SFCA and SFCA-I.
In recent years, numerous studies have been done on
the formation mechanism of SFCA. The calcium ferrite
system is divided into two primary types. The ﬁrst one is
SFCA-I with a high Fe and low Si content, and it shows
a characteristic morphology as platy, needlelike, or
acicular. The other one is SFCA with a relatively low Fe
and high Si content, which usually presents columnar,
blocky, or lath morphology.
The in-situ X-ray
diﬀraction (XRD) method was used to investigate the
formation mechanism of SFCA and SFCA-I. Scarlett
found in the reaction sequences involved in
formation of the two types that the main calcium ferrite
phase is CaOÆFe
before the formation of SFCA and
SFCA-I, but the formation temperature of SFCA-I and
SFCA is lowered with adding Al
, so it promotes the
formation of desirable bonding phase of high basicity
sinter in the sintering process of iron ore ﬁnes. Webster
also studied the calcium ferrite containing
aluminum (CFA) phase, indicating that it is a kind of
complex calcium ferrite without Si as a precursor of
SFCA and SFCA-I. The CFA was observed at ﬁrst by
as a ternary compound in a quaternary
system of CaO-Al
. Lister and Glasser
pointed out the chemical formula of this compound as
determined the structure consisting
and designated as SFCA-II.
HUI GUO and XING-MIN GUO are with the School of
Metallurgical and Ecological Engineering, University of Science and
Technology Beijing, 30 Xueyuan Road, Haidian District, Beijing
100083, P.R. China. Contact email: firstname.lastname@example.org
Manuscript submitted December 15, 2017.
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