UTILISATION D'OLIVINE SYNTHETIQUE POUR LA PRODUCTION D'AGGLOMERE DE MINERAI DE FER

USE OF SYNTHETIC OLIVINE IN THE PRODUCTION OF IRON ORE SINTER

Abrégé anglais

ABSTRACT OF THE DISCLOSURE
An improved iron ore sinter for use in a blast furnace is
made from a raw sinter mix comprising: iron-bearing
materials; basic fluxes including a source of CaO and a
source of MgO; and solid carbon-bearing material usually
coke breeze, used as a heat-generating combustible. To
produce the sinter, the raw sinter mix is subjected to a
sintering treatment at a high temperature in order to cause
the iron-bearing materials, fluxes and carbon-bearing
material to agglomerate and sinter by incipient fusion; an
air-cooling treatment in order to produce a hard lumpy
substance having a porous cellular structure; and a
mechanical treatment to break the lumpy substance into a
specific size range. The improvement to the above sinter
lies in that the source of MgO in the raw sinter mix
exclusively consists of synthetic olivine obtained by
calcination of serpentinite. Such a use of synthetic
olivine has numerous and unexpected advantages over the use
of natural olivine as a source of MgO in the manufacture of
iron ore sinter for blast furnace, especially in terms of
enhanced sinter strength, improved sinter reduction
properties and productivity.

Revendications

The embodiments of the invention in which an exclusive
property or privilege is claimed are defined as follows:
1. In an iron ore sinter for use in a blast furnace, said
sinter being made from a raw sinter mix comprising:
iron-bearing materials;
basic fluxes including a source of CaO and a source of
MgO; and
solid carbon-bearing material used as a heat-generating
combustible,
said raw sinter mix being subjected to:
a sintering treatment at a high temperature in order to
cause said iron-bearing materials, fluxes and carbon-bearing
material to agglomerate and sinter by incipient fusion;
an air-cooling treatment in order to produce a hard
lumpy substance having a porous cellular structure; and
a mechanical treatment to break the lumpy substance
into sinters of a given size,
the improvement wherein the source of MgO in the raw sinter
mix consists of synthetic olivine, exclusively.
2. The improved iron ore sinter according to claim 1,
wherein the raw sinter mix is selected so that the resulting
iron-ore sinter has the following chemical composition:
Fe - from 48 to 60%
CaO - from 7 to 15%
SiO2 - from 3 to 8%
MgO - from 1 to 5%
Al2O3 from 0.3 to 3%
the percentage being expressed by weight and the balance
consisting of FeO, Mn, S and moisture, with the provision
that the basicity ratio of this composition, defined as :

<IMG>
ranges between 1.5 and 2.6.
3. The improved iron ore sinter according to claim 2,
wherein the iron-bearing materials comprise up to 50% by
weight of fine iron ore concentrates.
4. The improved iron ore sinter according to claim 2,
wherein the source of CaO in the raw sinter mix is
limestone.
S. The improved iron ore sinter according to claim 2,
wherein the solid carbon-bearing material is selected from
the group consisting of coke breeze, petroleum coke, coal or
mixture thereof.
6. The improved iron ore sinter according to claim 2,
wherein
- the iron-bearing materials comprise up to 50% by
weight of fine iron ore concentrates;
- the source of CaO in the raw sinter mix is limestone;
and
- the solid carbon-bearing material is selected from
the group consisting of coke breeze, petroleum coke, coal or
mixture thereof.
7. The improved iron ore sinter according to claim 1,
wherein the synthetic olivine is a fibrous-like synthetic
forsterite obtained by calcination of chrysotile asbestos
fibres at a temperature of from 650°C to 1,450°C, said
synthetic forsterite having an MgO:SiO2 ratio lower than
1.1, a raw loose density of from 3 to 40 pcf, a thermal

conductivity "k" factor of from 0.25 to 0.40 BTU. in/hr.
°F.ft2 and a fusion point of from 1,600° to 1,700 C.
8. The improved iron ore sinter according to claim 2,
wherein the synthetic olivine is a fibrous-like synthetic
forsterite obtained by calcination of chrysotile asbestos
fibres at a temperature of from 650°C to 1,450°C, said
synthetic forsterite having an MgO:SiO2 ratio lower than
1.1, a raw loose density of from 3 to 40 pcf, a thermal
conductivity "k" factor of from 0.25 to 0.40 BTU. in/hr.
°F.ft and a fusion point of from 1,600° to 1,700 C.
9. The improved iron ore sinter according to claim 3,
wherein the synthetic olivine is a fibrous-like synthetic
forsterite obtained by calcination of chrysotile asbestos
fibres at a temperature of from 650°C to 1,450°C, said
synthetic forsterite having an MgO:SiO2 ratio lower than
1.1, a raw loose density of from 3 to 40 pcf, a thermal
conductivity "k" factor of from 0.25 to 0.40 BTU. in/hr.
°F.ft and a fusion point of from 1,600° to 1,700 C.
10. The improved iron ore sinter according to claim 4,
wherein the synthetic olivine is a fibrous-like synthetic
forsterite obtained by calcination of chrysotile asbestos
fibres at a temperature of from 650°C to 1,450°C, said
synthetic forsterite having an MgO:SiO2 ratio lower than
1.1, a raw loose density of from 3 to 40 pcf, a thermal
conductivity "k" factor of from 0.25 to 0.40 BTU. in/hr.
F.ft and a fusion point of from 1,600° to 1,700 C.
11. The improved iron ore sinter according to claim 5,
wherein the synthetic olivine is a fibrous-like synthetic
forsterite obtained by calcination of chrysotile asbestos
fibres at a temperature of from 650°C to 1,450°C, said

synthetic forsterite having an MgO:SiO2 ratio lower than
1.1, a raw loose density of from 3 to 40 pcf, a thermal
conductivity "k" factor of from 0.25 to 0.40 BTU. in/hr.
°F.ft2 and a fusion point of from 1,600° to 1,700°C.
12. The improved iron ore sinter according to claim 6,
wherein the synthetic olivine is a fibrous-like synthetic
forsterite obtained by calcination of chrysotile asbestos
fibres at a temperature of from 650°C to 1,450°C, said
synthetic forsterite having an MgO:SiO2 ratio lower than
1.1, a raw loose density of from 3 to 40 pcf, a thermal
conductivity "k" factor of from 0.25 to 0.40 BTU. in/hr.
°F.ft2 and a fusion point of from 1,600° to 1,700°C.

Description

2~2993~
B~CKGROUND OF THE INVENTION
a) Field of the Invention
The present invention relates to an improved iron ore sinter
for use in a blast furnace. More particularly, it relates
to an improved iron ore sinter wherein the improvement
consists in using synthetic olivine in place of natural
olivine or dolomite as a source of MgO.
' 10
- b) Brief Descr tion of the Prior Art
" lp
As is well known in the art of metallurgy, four basic
ingredients have to be fed into a blast furnace to produce
iron by chemical reduction of iron oxides and/or other iron-
bearing substances, namely:
a) the iron oxides and/or iron-bearing substances per
se, in the form of sinters, pellets, briquettes or any other
type of agglomerates, or occasionally lumpy raw ores;
b) basic fluxes including a source of CaO and a source
of MgO selected amongst for example, limestone, dolomite,
natural olivine and the like, whose purpose is to form a
slag by reaction with the acid gangue constituents of the
feed;
c~ metallurgical coke used as a heat-generating
, combustible and as a reducing agent when it is transformed
into carbon monoxide by controlled combustion with air; and
d) air to provide oxygen and thus support the
combustion and slag formation.
All of these basic ingredients may be fed lnto the blast
furnace one at a time, in predetermined amounts, to form
successive layers of iron oxides, fluxes and coke through
which air is blown. As the coke burns, the iron oxides or

202993~
other iron-bearing substances melt and are reduced to form
the desired iron in molten form. The impurities are
"collected" in the liquid slag formed by the fluxes and can
be separated from the iron and removed from the furnace.
In recent years, it has been suggested to combine all of
these ingredients together in the form of agglomerates,
especially pellets or sinters, in order to improve the
permeability of the charge and thus permit higher gas flow
and better gas-solid contact within the furnace. In this
connection, reference can be made, by way of exadlple, to
U.S. patent no. 4,518,428 issued in 1985 to International
Minerals & Chemical Corp., or U.S. patent no. 4,651,584
issued in 1987 to U.S. Steel Corp.
The main advantage of using pellets or sinters in which all
the basic ingredients are combined (except air) is that such
a use substantially reduces, not to say eliminates the
introduction of basic fluxes in raw form into the furnace.
As a result:
1) substantial savings are obtained in the consumption
of expensive metallurgical coke, which would otherwise be
required to calcine the raw fluxes, and
2) blast furnace productivity (expressed in tons/m2 of
hearth area) is increased by as much as 50~.
As already indicated hereinabove, the fluxes used in the
blast furnace must include a source of CaO and a source of
MgO. In operation, both of these oxides react with the acid
gangue usually found in the iron-bearing substances used as
an iron source, which gangue includes SiO2, A1203 and other
impurities such as sulphur and phosphorous, the product of
this reaction being the slag.

202~39
In practice, the formation of a slag of proper chemistry and
fluidity is of a great importance to activate smooth
operation of the blast furnace. Indeed, the volume and
chemistry of the slag whose purpose is to carry the unwanted
impurities and help in the separation of iron in the hearth
of the furnace and subsequent removal of this iron from the
furnace are both known to influence the thermal balance and
the partition of sulphur between the slag and the molten
iron.
.' 10
The major chemical constituents and composition of the slags
of most of the existing blast furnaces presently in
- operation, are as follows:
TABLE I
,
% CaO % MgO %A12O3 %SiO2
34-47 4-12 10-22 31-39
,:,
As can be seen, MgO is an important ingredient of the slag.
In practice, when use is made of iron ore sinters, the MgO
found in the slag comes from the sinter into which the basic
fluxes are incorporated. Wherever necessary, but to a
lesser extent, additional MgO may be introduced in the form
of fluxed pellets or through direct addition o dolomite,
natural olivine (see U.S. patent 4,518,428), periclase (see

202~3~
U.S. patent no. 4,657,584) or similar material.
As already indicated thereinabove, the practice of adding an
MgO-containing material directly into the blast furnace has
largely been discontinued because of economic and
metallurgical considerations. Therefore, the iron-bearing
agglomerates that are presently used in the form of sinters
and pellets invariably contain certain amounts of MgO, which
usually vary between 1 and 3% by weight and in special
cases, up to 10%.
The incorporation of MgO directly into the agglomerates
(sinters or pellets) has many advantages, some of which are:
- improved resistance to low-temperature degradation,
leading to a decrease in flue dust losses;
- improved high-temperature reduction characteristics,
maintaining the structure of agglomerates for good
reduction;
- reduction in the range of softening and meltdown
temperature and increase in t4e respective temperatures;
- reduction of hanging and scaffolding;
- good desulphurizing properties and strong affinity for
sulphur;
- minimlzation of Fe 108g in the ~lag; and
- for high aluminou~ blast furnace slags, increase in the
fflag fluidity.
5",
In e~sence, the incorporation of MgO in agglomerates such as
sinters or pellets, leads to smooth and economic blast
furnace operation and improved hot metal quality.
Presently, the MgO incorporated into the agglomerates comes
from dolomite, natural olivine, dunite, burnt dolomite etc.
The use of such "natural" materials as source~ of MgO is

~029~3~
dictated p~imarily by cost, quality, and proximity to the
source, despite the fact that the quality of sinter may
substantially vary depending on the source -of the MgO-
containing material. It has been found however in many
European and Australian steel plants, that the use of
natural olivine as a source of MgO is better than the use of
any other material from the standpoint of productivity and
as well as quality of the agglomerates. The use of natural
olivine is suggested in U.S. patent no. 4,518,428 but is
rather limited in North America because of its non-
availability and high importation cost, although it isadmitted that the addition of natural olivine to the blast
furnace increases the MgO content of the slag and the
fluidity range of the slag, and makes it less sensitive to
other chemical impurities or to temperature variation.
On the other hand, it is also known that the viscosity of
the slag is dependent on the basicity ratio. The basicity
ratio of the sinter,(CaO + MgO) to (SiO2 ~ A12O3), should
remain preferably between 1.5 and 2.6. Since olivine is a
mineral of general formula Mg2SiO4, one can see that the
addition of olivine as a source of MgO in a blast furnace is
particularly interesting since, with such a mineral, SiO2 is
added at the same rate as MgO in the furnace, thereby
leaving the basicity ratio substantially unaffected.
:,
In practice, olivine added to the blast furnace as a "trim",
is of the same size as the other raw materials, i.e. 10-50
mm with less than 10~ of the particles below 10 mm. A good
lump size is important in the blast furnace where
permeability must be maintained in order to prevent poor gas
flow and the build up o back pressure. In turn, good
permeability is advantageous to ensure a continuous blast of
gas which results in an efficient furnace operation with the
-- 5

202~3~
attendant reduction in coke rate (volume of coke required
per ton of hot metal being produced).
Dolomite, extensively used in the past as a source of MgOj
is steadily decreasing in popularity because, on the one
hand, it requires the addition of silica to maintain the
basicity ratio of the slag and, on the other hand, it must
be calcined prior to being used.
Therefore, the use of lump olivine as a trim represents a
less costly single step procedure, provided that the mineral
is readily available.
SUMMARY OF THE INVENTION
The present invention is based on the discovery that the use
of synthetic olivine obtained by calcination of
serpentinite, has numerous and unexpected advantages over
the use of natural olivine as a source of MgO in the
manufacture of iron ore sinter for blast urnace, especially
in terms of enhanced sinter strength, improved sinter
reduction properties and productivity.
~herefore, the invention provides an improved iron ore
sinter for use in a blast furnace, said sinter being made
from a raw sinter mix comprising:
iron-bearing materials;
basic fluxes including a source of CaO and a source of
MgO; and
solid-carbon bearing materials, usually co~e breeze,
used as a heat-generating combustible and reducing agent,
the raw sinter mix being subjected to:
a cintering treatment at a high temperature in order to
cause the iron-bearing materials, fluxes and carbon-bearing

202~3~
materials to agglomerate and sinter by incipient fusion;
an air-cooling treatment in order to produce a hard
lumpy substance having a porous cellular structure; and
a mechanical treatment to break the lumpy substance
into a specific size range.
In accordance with the invention, the improvement to the
above sinter lies in that the source of MgO in the raw
sinter mix consists of synthetic olivine, exclusively.
,. 10
The improved iron-ore sinter that is so obtained may be used
as feed material in an iron reduction process. It is
however mainly intended to be used as a iron-bearing
material for use in a blast furnace for the production of
iron.
In addition to obtaining a sinter meeting all the usually
required quality criteria, the use of synthetic olivine as a
source of MgO improves the sinter strength and its reduction
properties, especially when compared with dolimite which is
presently the most conventional material u~ed for the
production of sinter. Improvement in sinter productivity is
also noted.
Preferably, the raw sinter mix is selected so that the
resulting iron-ore sinter has the following chemical
composition:
Fe - from 48 to 60
CaO - from 7 to 15%
SiO2 - from 3 to 8%
MgO - from 1 to 5%
A123 from 0.3 to 3%

2029~3~
the percentage being expressed by weight and the balance
consisting of FeO, Mn, S and moisture, with the provision
that the basicity ratio of this composition, defined as :
S CaO ~ MgO
SiO2 + A1203
be ranging between 1.5 and 2.6.
Preferably also, the iron-bearing materials comprise up to
50~ by weight of fine iron ore concentrates and the source
of CaO in the raw sinter mix is limestone.
As usual, the carbon-bearing material may be selected from
the group consisting of coke breeze, petroleum coke, coal or
mixture thereof.
GENERAL DESCRIPTION OF THE INVENTION
A - SYNTHETIC OLIVINE
As indicated thereinabove, the iron-ore sinter according to
the invention comprises synthetic olivine as source of MgO.
Synthetic olivine may be in granular or fiber-like form
depending on the kind of material used as starting material
for its production.
Whatever be its structure, synthetic olivine is a derivative
of ~erpentinite which is ound in nature under two different
forms, namely a granular form and a fibrous form which is
called chrysotile, or asbestos fibre. Both these minerals
are monoclinic and have roughly the same chemical
composition but different crystallographic forms (grains or
-- 8 --

~02~3~
fibers). They both crystalli2e in synthetic olivine when
they are subjected to high temperatures (greater than
700C).
,
Olivine as such, is a group of minerals ranging between two
extremes, namely magnesium olivine called forsterite, of
formula Mg2SiO4, and a ferrous olivine called fayalite, of
formula Fe2SiO4, which crystallize in the orthorhombic
- system. Between these two extremes, there are other
minerals containing both Fe and Mg in various amounts, which
are also called olivine. Typically, such intermediate
minerals may be of formula (MgFe)2SiO4.
Granular synthetic ~livine
Granular synthetic olivine can be obtained by calcination of
serpentinite rocks rejected as tailings in the asbestos
mines.
When heated at a high temperature (greater than 750C), the
crushed serpentinite mineral looses all its water and
recrystallizes in forsterite, which occurs in orthorhombic
crystallographic form. The presence of minor amounts of
magnetite or hematite in the serpentinite causes the
formation of ferric forsterite, which, as aoresaid, is also
called olivine. If the temperature is increased above
1,000C, another magnesium mineral called enstatite (MgSiO3)
appears in the olivine mix.
In practice, granular synthetic olivine is usually made at
high temperatures (1,250 to 1,350C) and the chemical
transformation that occurs during calcination can be
schematically represented as follows:

~2g939
3.MgO.2SiO22H2O ~ heat/time > MgSiO3 + Mg2SiO4 + 2H2O
(serpentinite) ~enstatite) (forsterite)
Depending on the chemical composition of the starting
material being used, the chemical composition of the
granular synthetic olivine which is obtained is as
follows tthe percentages being expressed by weight):
MgO 45-48
SiO2 42-45~
Fe23 7-10%
A123 1- 2%
CaO and other ~ 1%
lS As can be seen, this synthetic material has a high MgO
concentration. It also contains iron and has substantially
the same physical aspect as sand, with a bulk density of 90-
110 lbg/pi3.
To date, granular synthetic olivine has been used as foundry
sand (see U.S. patent no. 4,604,140 issued in 1986 to
Soci~t~ Nationale de l'Amiante), sandblasting agent ~see
U.S. patent no. 4,519,811 issued in 1985 to Soci~t~
Nationale de l'Amiante) or refractory sand. To the
A~pllcant's knowledge, it has never been suggested to use
this material as a source of MgO in the production of sinter
for blast furnaces, although it is known that it contains a
high MgO concentration and that large quantities of crushed
and finely ground serpentinite are available for use as
initial raw material.
- 10 --

2~2~93~
Fibrous-like synthetic forsterite
This other type of synthetic olivine is obtained by
calcination of chrysotile asbestos fibers at a temperature
of from 650C to 1,450C. This synthetic material has an
MgO:SiO2 ratio lower than l.l, a raw loose density of from 3
to 40 pcf, a thermal conductivity "k" factor of from 0.25 to
0.40 BTU. in/hr. F.ft2 and a fusion point of from 1,60~ to
1,700 C. It is obtained in a fibrous like form and
maintains this form even when it is processed.
Fibrous-like synthetic forsterite, hereinafter called
FRITMAG (trademark) is disclosed in U.S. patent application
serial no. 07/246,198 filed on September 16, 1988 in the
name of the Applicant. Its chemical composition is as
follows (the percentages being expressed by weight):
MgO 47%
Si2 ~ 47%
Fe23
A123 1. 0%
CaO and other 2.0%
As can be seen, FRITMAG also has a high MgO concentration.
To date, it has been suggested to use FRITMAG for the
manufacture of insulation products, fibrous cement
composition or brake linings, or in some vacuum forming
processes. To the Applicant's knowledge, it has never been
suggested so far to use FRITMAG as a source of MgO in the
production of sinter for blast furnaces, although it has a
high MgO content.

2~29~31~
B - SINTER VERSUS PELT.ETS FOR USE IN BLAST E~JRNACES
.
Sinter production
S As explained hereinabove, the primary iron-bearing materials
used for the production of iron in a blast furnace are iron
ore agglomerates in the form of sinter or pellets. On a
world-wide basis, sinters are preferred over pellets
approximately in the proportion of 65:35, because of the
main advantages of the sintering process in terms of cost-
effectiveness and ability to utilize a majority of the
recyclable materials produced in steel plants, which is
quite desirable from an environmental point of view.
The sintering process basically consists in converting iron-
containing materials of fine particle size (0.1 - 10 mm)
into coarse agglomerates by incipient fusion o~ the ore
particles at their contact surfaces, due to the combustion
of premixed solid fuel.
In the steel industry, the iron-bearing material~ used for
the production of sinter, usually con&ist of iron ore fines
and/or concentrates and revert materials such aq mill scale,
flue dust, processed iron fines from iron and steelmaking
operations, sinter returns, sinter and pellets screenings
and other recovered waste materials containing different
amounts of iron.
The basic fluxes necessary to the operation of the blast
furnace are incorporated advantageously into the sinter. As
was already explained in the preamble of the present
disclosure, the incorporation of the basic fluxes in the

2~2~!~39
sinter mix is a very cost-efficient method inasmuch as it
saves a substantial amount of expensive metallurgical coke.
The basic fluxes contain ~gO and CaO which react with the
acid constituents of iron ore fines and concentrates, coke
ash, etc. and act as slag formers. The source of CaO in the
fluxes may be crushed limestone or dolomite. Sometimes,
acid components such as quartz, alumina-bearing materials
- may also be deliberately added to the sinter mix so that
- when the sinter is charged in the blast furnace, the
- 10 resulting blast furnace slag that is formed has some desired
properties or compositions.
The solid carbon-bearing material that is incorporated into
the sinter mixture is intended to be used as a fuel and may
consist of coke breeze, petroleum coke, coal or other
carbonaceous material capable of causing incipient fusion of
the ore particles by combustion.
The aforesaid materials i.e. the iron-bearing materials,
basic fluxes and carbon-bearing material are mixed usually
with 4 - 6.5% moisture to cause the particles to adhere to
each other and forms a raw sinter mix that may be subjected
to micropelletization in known devices such as rotary drums
or disks.
A ~uitably micropelletized feed will provide good bed
permeability during sintering and will result in an
increased sintering rate.
The sintering is usually carried out in a DWIGHT-LLOYD-type
continuous travelling grate machine.
The coke breeze on the top of the bed is subjected to
combustion by burning oil or natural gas through burners in
- 13 -

202~3~
the ignition hood of the machine. Combustion is maintained
by continuous suction of air through the charge from below.
Burning of the coke breeze causes incipient fusion of ore
particles at the contact surfaces resulting in agglomeration
of the particles into coarse lumpy and porous structure.
The hot sinter is then cooled and sized usually into
particles of ~ - 2". The resulting product forms the blast
furnace sinter.
Sinter quality
; A smooth and efficient operation of the blast furnace
requires sinter with certain properties. Ideally, the
sinter should have the following characteristics:
1) It must be strong enough to resist disintegration
during handling so that the breakdown between the
sinter plant and the blast furnace is minimized.
2) It must also be strong enough to withstand the
abrasive and compressive forces that it faces
during the descent *hrough the blast furnace.
3) A close Qize range with minimum amount of fines
(-5 mm) is reguired in order to have a good burden
permeability for better gac-to-solid contact.
4) Furthermore, the sinter must be sufficiently
",
reducible to ensure that it does not pass down to
, "
i?~?~? the bosh zone virtually unchanged, since this
would lead to a large percentage of reduction by
solid carbon, i.e. an endothermic reaction,
increasing the coke consumption.
5) Good low-temperature breakdown properties in the
upper stack region of the furnace ensure an
efficient operation of the furnace.
6) A high initial softening temperature with complete
softening occurring over a narrow temperature
- 14 -

- 2~2993~
range is required so that bosh hanging is
minimized.
Testing of sinter in relevance to iron making practice
Sinter quality specifications have been developed through a
number of laboratory tests by several standards
organizations and in some user industries themselves.
In assessing the properties of a burden material, one must
consider all the properties of that particular material, the
proportion of the material in the burden, the overall
properties of other burden constituents, the relevant
furnace practice and the financial implications.
Laboratory tests developed by some of the organizations show
that the results can be correlated to furnace performance,
although for some- parameters, precise quantitative
relationships are not yet available.
These laboratory tests that were developed by the
International Standards Organization (ISO) and are
essentially ln line with the current trends, can be
classified as follows:
1) handling properties (tumbler test)
f 2) reducibility
, ,,
3) porosity
4) behaviour in the upper stack of the blast furnace
(low-temperature disintegration test)
5) behaviour in the lower stack of the blast furnace
(softening and melt down tests)
- 15 -

2~2~939
C - USE OF SYNTHETIC OLIVINE (or FRITMAG) AS SOURCE OF MgO
IN A BLAST FURNACE SINTER
As e~plained hereinabove, the invention is based on the
discovery that the use of synthetic olivine, either in the
form of granular synthetic olivine or in the form of
FRITMAG, as a source of MgO in the production of iron ore
sinter, has numerous and unexpected advantages, as compared
to the use of dolomite or natural olivine.
- More particularly, the invention is based on the discovery
that the use of synthetic olivine as source of MgO leads to
the production of an iron ore sinter which has the following
advantages, as compared to sinter obtained with natural
olivine or dolomite:
better impact resistance (tumbler strength)
better abrasion resistance
higher reducibility
and
more "consistent" chemistry because the synthetic
production of olivine allows proper adjustment of the
chemical constituents of the resulting product by blending
of the serpentinite material used as starting material with
other raw material(s) whenever necessary.
The synthetic olivine is preferably added as a fine powder
in the raw sinter mix. The size of the powder particles is
not critical, although higher surface area facilitates the
formation of micropellets.
The amount of synthetic olivine is preferably selected so
that the obtained sinter comprises from 1 to 5% by weight of
MgO, preferably 2%. The respective amounts of the other
constituents may be selected as is known in the art. All
- 16 -

202~3~ -
these amounts should be balanced proper~y so that the
basicity ratio CaO + MgO/SiO2 ~ Al2O3 of the sinter be
ranging between 1.5 and 2.6.
D - COMPARATIVE EXAMPLE
In this example, use was made of a raw sinter mix comprising
, iron-bearing materials including steel plants reverts, basic
fluxes and a carbonaceous fuel. The basic composition of
- 10 this mix is given in the following Table II.
'
TABLE II
wt.~
Specularite 24.5
Pellet fines 13.7
Mill scale 8.8
Iron fines 7.6
Return fines 30.0
FRITMAG 1.5
Limestone 8.9
Flue dust (fuel)5.0
Sinters were prepared from this raw mix, after addition
thereto of different sources of MgO, namely
~,"
- FRITMAG
- natural olivine
- dolomite
Each sinter mixture that was so prepared was mixed/
micropelletized for 3 minutes using a disk and then charged
into a sinter pot. The sintering was performed as is done
industrially. During the preparation of all the samples,
- 17 -

~2~39
the bed height, suction etc. were kept constant. After the
sintering was complete, each sinter cake was cooled to a
suitable temperature and subjected to a shatter test by
dropping it from a height of 6'. Subsequently, the sinter
lumps were crushed to -2" and screened to various size
fractions for testing. The results of the various tests are
given in Table III.
Table III - Comparison of test data obtained with various
MgO-bearing sources at basicity of 2.0, and MgO level of
3.0%
Source of MgO Tumbler strength Reducibility RDI
'T' index 'A' index dr (%-min 1) (+3.15 mm)
(%,+6.3mm)(%,-0.59mm) dt40
Fritmag65.2 5.2 1.33 83.0
Natural olivine 62.5 6.4 1.25 85.2
Dolomite52.2 6.9 1.20 84.8
The outline of the test procedures and indications of the
results obtained are described below.
....
Tumbler te~t
This was conducted on a sinter sample of 25 lbs in the +3/8"
to -2" ;ractions in a ASTM tumbler drum at 25 rpm for 8
minutes (i.e. 200 revolutions) and subsequently screened to
determine the tumbler as 'T' index ~+6.35 mm) and abrasion
or 'A' indax (-0.59 mm).
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2~2~9~3
The 'T' index (+6.35 mm or +~") reflects the impact
resistance of the sinter during handling. The higher is the
value, the better is the strength.
.
S The 'A' index (-0.589 mm) expresses the resistance of sinter
due to abrasion during handling. A lower value of the 'A'
index indicates better resistance to abrasion.
The data presented in Table III clearly indicate that the
impact resistance obtained with FRITMAG is better than with
natural olivine and much better than with dolomite. The
data also indicate that the resistance to abrasion with
FRITMAG is much better than with natural olivine or
dolomite.
Reducibility
The reducibility was determined using ISO test procedure.
This test is carried out at an elevated temperature under a
reducing gas atmosphere simulating blast furnace reduction
conditions.
The gas reducibility of the burden, i.e. the ease with which
oxygen can be removed from the iron-bearing materials in the
blast furnace stack, by means of the ascending gases is an
important parameter affecting the efficiency of the
ironmaking process as reflected by the coke rate and the
rate at which iron can be produced. A highly reducible
burden implies a faster driving and a shorter residence time
in the stack and high productivity of the blast furnace.
A high reducibility of sinter, therefore, reflects good
reduction properties of the sinter.

~2~3~
The data reported in Table III show that the sinters
produced with FRITMAG are more easily reducible as compared
to those produced with natural olivine or dolomite.
Low-temperature reduction strength (RDI)
The low-temperature reduction strength (RDI) of the sinters
was determined by the ISO test procedure of static reduction
followed by tumbling. This test simulates the blast furnace
conditions in the upper stack regions where it is mildly
reducing and temperatures are relatively low. A high +3.15
mm fraction following the tumbling is considered good (+3.15
mm ~ 80%).
The RDI reflects the resistance to degradation of the sinter
in the upper stack of the blast furnace under mildly
reducing conditions at low temperatures.
Following the tests, if the ~3.15 mm fraction is high
( > ~0%), the sinter is considered to have met the low-
temperature reduction strength requirement specified by mostsinter plants.
The data reported in Table III shows' that all the sinters
that were produced meet the RDI requirement.
, ....
E ~ ADVANTAGES OF SYNTHETIC OLIVINE OVER NATURAL OLIVINE
AND/OR DOLOMITE AS SOURCE OF MgO
Sinter strength
- better tumbler strength (high value)
- better abrasion resistance (low value)
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2~2~93~ `
Possible reasons: Because of finer size material, the MgO
gets more uniformly distributed. in the
mix and consequently in the sinter
matrix. This probably has made, the
sinter structure more stable.
Reducibility
- better reducibility
, 10 Possible reasons: Right mineralogical assemblage - sinters
' have more acicular calcium ferrites with
uniform distribution of pores, making
the reduction gas easily accessible to
the iron oxides for removal of oxygen.
As a MgO source
- higher surface area (finer-sized material) helping
in the formation of micropellets.
_ consistent chemis.try; since the material is
synthetically produced, the % of chemical
constituents can be maintained through proper
blending with other raw materials.