U.S. patent application number 14/908055 was filed with the patent office on 2016-06-16 for method for manufacturing agglomerate and reduced iron.
This patent application is currently assigned to Kabushiki Kaisha Kobe Seiko Sho (Kobe Steel, Ltd.. The applicant listed for this patent is KABUSHIKI KAISHA KOBE SEIKO SHO(KOBE STEEL, LTD.). Invention is credited to Hidetoshi TANAKA, Osamu TSUCHIYA.
Application Number | 20160168654 14/908055 |
Document ID | / |
Family ID | 52393037 |
Filed Date | 2016-06-16 |
United States Patent
Application |
20160168654 |
Kind Code |
A1 |
TSUCHIYA; Osamu ; et
al. |
June 16, 2016 |
METHOD FOR MANUFACTURING AGGLOMERATE AND REDUCED IRON
Abstract
A process for producing an agglomerate comprising heat treating
an iron oxide-containing powder at a heating temperature of 900 to
1,200.degree. C., and granulating an obtained heat treated powder,
as a raw material, thereby producing an agglomerate, wherein the
iron-oxide-containing powder has a 50% particle diameter of 2 .mu.m
or less.
Inventors: |
TSUCHIYA; Osamu; (Hyogo,
JP) ; TANAKA; Hidetoshi; (Chuo-ku, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KABUSHIKI KAISHA KOBE SEIKO SHO(KOBE STEEL, LTD.) |
Hyogo |
|
JP |
|
|
Assignee: |
Kabushiki Kaisha Kobe Seiko Sho
(Kobe Steel, Ltd.
Hyogo
JP
|
Family ID: |
52393037 |
Appl. No.: |
14/908055 |
Filed: |
May 26, 2014 |
PCT Filed: |
May 26, 2014 |
PCT NO: |
PCT/JP14/63829 |
371 Date: |
January 27, 2016 |
Current U.S.
Class: |
75/359 ;
75/751 |
Current CPC
Class: |
C22B 1/16 20130101; C22B
1/02 20130101; C21B 13/146 20130101; C21B 13/0046 20130101; C21B
13/0066 20130101; C22B 1/2406 20130101 |
International
Class: |
C21B 13/14 20060101
C21B013/14; C22B 1/02 20060101 C22B001/02; C22B 1/16 20060101
C22B001/16; C21B 13/00 20060101 C21B013/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 25, 2013 |
JP |
2013-154793 |
Claims
1. A process for producing an agglomerate, comprising heat-treating
an iron-oxide-containing powder having a 50% particle diameter of 2
.mu.m or less at a heating temperature of 900 to 1,200.degree. C.,
and granulating an obtained heat-treated powder, as a raw material,
thereby producing an agglomerate.
2. The process according to claim 1, wherein the granulation is
conducted by a rolling granulation method.
3. The process according to claim 1, wherein the heat treatment is
conducted so that the heat-treated powder has a 50% particle
diameter of 4 .mu.m or larger.
4. The process according to claim 1, wherein the heat treatment is
conducted for a heating period of 30 minutes or longer.
5. The process according to claim 1, wherein the heat treatment is
conducted while rolling the iron-oxide-containing powder.
6. The process according to claim 1, wherein the
iron-oxide-containing powder is a tailing.
7. The process according to claim 6, wherein the tailing is a
residue which has remained after Ni recovery from a Ni-containing
ore.
8. A process for producing a reduced iron, wherein the agglomerate
obtained by the process according to claim 1 is heated, thereby
producing a reduced iron.
9. The process according to claim 8, wherein the agglomerate
further contains a carbonaceous reducing agent.
10. The process according to claim 2, wherein the heat treatment is
conducted so that the heat-treated powder has a 50% particle
diameter of 4 .mu.m or larger.
11. The process according to claim 2, wherein the heat treatment is
conducted for a heating period of 30 minutes or longer.
12. The process according to claim 2, wherein the heat treatment is
conducted while rolling the iron-oxide-containing powder.
13. The process according to claim 2, wherein the
iron-oxide-containing powder is a tailing.
14. The process according to claim 13, wherein the tailing is a
residue which has remained after Ni recovery from a Ni-containing
ore.
15. A process for producing a reduced iron, wherein the agglomerate
obtained by the process according to claim 2 is heated, thereby
producing a reduced iron.
Description
TECHNICAL FIELD
[0001] The present invention relates to a technique for effectively
utilizing a fine iron-oxide-containing powder having a 50% particle
diameter of 2 .mu.m or less as an iron source.
BACKGROUND ART
[0002] As a process for producing reduced iron from an
iron-oxide-containing substance such as an iron ore, for example, a
gas reduction method in which natural gas is utilized is known. As
production processes of reduced-iron which were developed in recent
years, examples thereof include the FASTMET process in which
agglomerates obtained by mixing an iron-oxide-containing substance
with a carbonaceous reducing agent, e.g., a carbonaceous material,
are heated at a high temperature of 1,300.degree. C. or more to
produce reduced agglomerates, and the ITmk3 process in which the
reduced agglomerates are further heated and melted and the melt is
separated into reduced iron and slag to produce granular reduced
iron.
[0003] For producing reduced iron from an iron-oxide-containing
substance in the manner described above, use is made of
agglomerates having a diameter of 13 to 18 mm obtained by mixing
the iron-oxide-containing substance as a raw material with water
and a binder in a mixer and granulating the mixture with a
granulator.
[0004] As methods for agglomerating a powder, for example, a
pelletizing method and a sintering method are known. Granulation
methods suitable as pretreatments for powder particle size ranges
have been prescribed for (for example, Non-Patent Document 1).
Specifically, a 50% particle diameter of 4 .mu.m or larger is
recommended for the rolling granulation method as one example of
the pelletizing method, and a 50% particle diameter of about 0.11
to 3 mm is recommended for the sintering method.
[0005] Meanwhile, examples of valuable metals other than iron
include Ni, Al, Ti, etc. These valuable metals are being separated
and recovered as Ni, Al, and Ti from Ni-containing ores such as
saprolite, Al-containing ores such as red mud, Ti-containing ores
such as ilmenite, etc. For example, the high pressure acid leach
(HPAL) process is known as a process for separating and recovering
Ni from an Ni-containing ore. In this process, Ni can be extracted
and recovered by stably reacting an Ni-containing ore with sulfuric
acid kept in a high-temperature high-pressure state. After the
extraction and recovery of Ni, a product of sedimentation
separation is yielded as a residue. This residue contains iron
oxides in a large amount, and these oxides are mainly accounted for
by hematite (Fe.sub.2O.sub.3). This residue has a water content of
20% or higher, is in a muddy state, and has a 50% particle diameter
as small as about 0.6 .mu.m.
PRIOR ART DOCUMENT
Non-Patent Document
[0006] Non-Patent document 1: "Tetsutohagane", Relation between
Ore-Grindability and Optimum Size for Pelletizing Nihon Tekko
Kyokai-shi, 49th year (1963), No. 3, pp. 346-348
SUMMARY OF THE INVENTION
Problems that the Invention is to Solve
[0007] These are cases where the residues (hereinafter often
referred to as tailings) which have remained after desired
components were recovered by beneficiation operations contain iron
oxides such as hematite in a large amount as stated above. It is
hence conceived that the iron oxides contained in the tailings are
reduced, i.e., are utilized as an iron source. However, since the
tailings usually are exceedingly fine, it is difficult to
agglomerate the tailings by the rolling granulation method to
obtain granules usable as an ironmaking raw material. The reason
for this is as follows. In the case where the particles are
exceedingly fine, the particles readily stick to one another during
stirring within a mixer to form pseudo-particles. Upon granulation
with a granulator, these pseudo-particles bond to one another to
grow, thereby forming pellets each having projections on the
surface like konpeito. Pellets of such a shape are uneven in
internal structure and low in strength and, hence, cannot be used
as in ironmaking raw material. It is therefore difficult to
effectively utilize the tailings as an iron source by agglomerating
the tailings to obtain an ironmaking raw material.
[0008] The present invention has been achieved under such
circumstances. An object thereof is to provide a process for
producing agglomerates by granulating a fine iron-oxide-containing
powder having a 50% particle diameter of 2 .mu.m or less to produce
agglomerates usable as an ironmaking raw material. Another object
of the present invention is to provide a technique for producing
reduced iron from the agglomerates obtained by agglomeration.
Means for Solving the Problems
[0009] The present inventors diligently made investigations in
order to agglomerate a fine iron-oxide-containing powder and use
the agglomerates as an ironmaking raw material. As a result, the
present inventors have found that when an iron-oxide-containing
powder having a 50% particle diameter of 2 .mu.m or less is
heat-treated at a given temperature, the particles are enlarged
through sintering to each other and thus become able to be
agglomerated, making it possible to produce agglomerates. The
present invention has been thus completed.
[0010] That is, the process for producing an agglomerate which can
solve the above problems in the present invention includes: a step
of heat-treating an iron-oxide-containing powder having a 50%
particle diameter of 2 .mu.m or less at a heating temperature of
900 to 1,200.degree. C., and a step of granulating an obtained
heat-treated powder, as a raw material, thereby producing an
agglomerate.
[0011] The granulation may be conducted by a rolling granulation
method.
[0012] The heat treatment may be conducted so that the heat-treated
powder has a 50% particle diameter of 4 .mu.m or larger. For
example, the heat treatment may be conducted for a heating period
of 30 minutes or longer. The heat treatment is preferably conducted
while rolling the iron-oxide-containing powder.
[0013] As the iron-oxide-containing powder, a tailing can be used.
As the tailing, for example, a residue which has remained after Ni
recovery from a Ni-containing ore can be used.
[0014] In the present invention, a process for producing a reduced
iron, in which the agglomerate obtained by the above process is
heated, thereby producing a reduced iron, is included. The
agglomerate may further contain a carbonaceous reducing agent.
Effects of the Invention
[0015] According to the present invention, by subjecting an
iron-oxide-containing powder having a 50% particle diameter of 2
.mu.m or less to a heat treatment at a heating temperature of 900
to 1,200.degree. C., the particles can be enlarged. The resultant
particles can be agglomerated by conventional methods, and
spherical agglomerates can be produced therefrom. The agglomerates
obtained can be utilized as an ironmaking raw material.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is a photograph, as a drawing substitute, of a
heat-treated powder obtained by a heat treatment conducted at a
heating temperature of 400.degree. C.
[0017] FIG. 2 is a photograph, as a drawing substitute, of a
heat-treated powder obtained by a heat treatment conducted at a
heating temperature of 1,200.degree. C.
[0018] FIG. 3 is graphs which show the particle size distributions
of heat-treated powders.
[0019] FIG. 4 is a photograph, as a drawing substitute, of
agglomerates produced from the heat-treated powder obtained by a
heat treatment conducted at a heating temperature of 400.degree.
C., by disaggregating the heat-treated powder with a ball mill and
then granulating the particles.
[0020] FIG. 5 is a photograph, as a drawing substitute, of
agglomerates produced from the heat-treated powder obtained by a
heat treatment conducted at a heating temperature of 1,200.degree.
C., by pulverizing the heat-treated powder with a ball mill and
then granulating the particles.
EMBODIMENTS FOR CARRYING OUT THE INVENTION
[0021] The process in the present invention includes
[0022] a step of heat-treating an iron-oxide-containing powder
having a 50% particle diameter of 2 .mu.m or less at a heating
temperature of 900 to 1,200.degree. C. (hereinafter often referred
to as heat treatment step) and
[0023] a step of granulating an obtained heat-treated powder, as a
raw material, thereby producing an agglomerate (hereinafter often
referred to as agglomeration step). Each step is explained below in
detail.
[0024] [Heat Treatment Step]
[0025] In the process in the present invention, it is essential to
use an iron-oxide-containing powder having a 50% particle diameter
of 2 .mu.m or less. This process is intended to be used for
granulating such a fine iron-oxide-containing powder to obtain
agglomerates and effectively utilizing the agglomerates as an iron
source.
[0026] As the iron-oxide-containing powder having a 50% particle
diameter of 2 .mu.m or less, tailings can be used. The term
"tailing(s)" means the residue which has remained after desired
components were recovered by a beneficiation operation, and the
kind of the ore to be beneficiated is not particularly limited. As
the tailings, examples thereof include the residue resulting from
beneficiation of an iron ore, the residue which has remained after
recovery of Al from an Al-containing ore, the residue which has
remained after recovery of Ti from a Ti-containing ore, the residue
which has remained after recovery of Ni from an Ni-containing ore,
or the like.
[0027] Use is being made of red mud as an Al-containing ore,
ilmenite as a Ti-containing ore, saprolite as an Ni-containing ore,
or the like. For example, the HPAL process described above is known
as a process for recovering Ni from an Ni-containing ore, and the
residue which has remained after the separation and recovery of Ni
has a 50% particle diameter of 2 .mu.m or less.
[0028] In the heat treatment step, the iron-oxide-containing powder
having a 50% particle diameter of 2 .mu.m or less is heat-treated
at a heating temperature of 900 to 1,200.degree. C. By
heat-treating the fine iron-oxide-containing powder at a
temperature within that range, the iron-oxide-containing powder is
oxidized and enlarged through sintering. As a result, the particles
can be grown to such a size that the enlarged particles can be
agglomerated in the step which will be described later. In case
where the heating temperature is lower than 900.degree. C., the
enlarging effect is not obtained and the resultant particles cannot
be agglomerated or can be agglomerated to only give agglomerates
which are not spherical. Consequently, the heating temperature is
900.degree. C. or higher, preferably 950.degree. C. or higher, more
preferably 1,000.degree. C. or higher. However, in case where the
heating temperature exceeds 1,200.degree. C., a problem arises in
that coarse agglomerates are formed or agglomerates adhere to the
surface of the heat treatment device. Consequently, the heating
temperature is 1,200.degree. C. or lower, preferably 1,150.degree.
C. or lower, more preferably 1,100.degree. C. or lower.
[0029] The heating temperature may be controlled by inserting a
thermocouple into the furnace to measure the temperature of the
atmosphere at the center of the furnace and regulating the heating
temperature on the basis of the measured temperature.
[0030] In the heat treatment, the heating period may be controlled,
while taking account of the heating temperature, so that the
resultant heat-treated powder has a 50% particle diameter of 4
.mu.m or larger. It is preferable that the heating period should
be, for example, 30 minutes or longer. The heating period is more
preferably 40 minutes or longer, even more preferably 50 minutes or
longer. There is no particular upper limit on the heating period.
However, even when the heating period is prolonged, not only the
effect of increasing the particle diameter is not enhanced any more
but the productivity decreases. Because of this, the heating period
may be, for example, 60 minutes or less.
[0031] The heat treatment may be conducted in an oxidizing
atmosphere. For example, the treatment may be conducted in the
air.
[0032] It is preferable that the heat treatment should be conducted
while rolling the iron-oxide-containing powder, in order to evenly
heat the powder. As the heating furnace, a rotary heating furnace
may be used. The term "rotary heating furnace" means a furnace in
which the furnace surface which is the heating surface is rotating
on an axis of rotation and this axis of rotation lies at an angle
in the range of from the horizontal to less than the vertical.
[0033] [Agglomeration Step]
[0034] In the agglomeration step, the heat-treated powder obtained
in the heat treatment step is used as a raw material and this
heat-treated powder is agglomerated to produce agglomerates.
[0035] Examples of methods for granulating the heat-treated powder
include a rolling granulation method.
[0036] It is preferred to agglomerate the heat-treated powder so
that the agglomerates have a particle diameter of, for example, 10
to 16 mm.
[0037] Prior to the granulation, the heat-treated powder may be
disaggregated or pulverized. As a disaggregating machine or
pulverizer, a known one can be used. For example, use can be made
of a ball mill, roller mill, roll crusher or the like.
[0038] [Others]
[0039] The agglomerates obtained in the agglomeration step can be
used as an ironmaking raw material. For example, the agglomerates
obtained are subjected to a thermal hardening treatment and then
introduced into a blast furnace. Alternatively, the thermally
hardened agglomerates obtained by the thermal hardening treatment
are further heated in a reducing gas atmosphere. Thus, the iron
oxide can be reduced to produce reduced iron.
[0040] Reduced iron can be produced also by further adding a
carbonaceous reducing agent, a binder, etc. to the heat-treated
powder, forming the mixture into agglomerates, and heating the
agglomerates in a heating furnace.
[0041] As described above, according to the present invention, an
iron-oxide-containing powder having a 50% particle diameter of 2
.mu.m or less can be enlarged to a particle diameter which renders
granulation possible, by heat-treating the powder at a temperature
within a given range. Consequently, when the heat-treated powder
obtained by the heat treatment is agglomerated as a raw material,
the particles of the heat-treated powder grow at a rapidly
accelerating rate and agglomerates having an even structure can be
produced.
[0042] This application claims a right of priority based on
Japanese Patent Application No. 2013-154793 filed on Jul. 25, 2013.
The entire contents of the description of Japanese Patent
Application No. 2013-154793 are incorporated herein by
reference.
[0043] The present invention will be explained below in more detail
by reference to Example. However, the present invention should not
be construed as being limited by the following Example, and can of
course be modified so long as the modifications do not depart from
the spirit which was described above or will be described later.
Such modifications are all included in the technical range of the
present invention.
Example
[0044] An iron-oxide-containing powder having a 50% particle
diameter of 2 .mu.m or less was heat-treated, and the heat-treated
powder obtained was agglomerated to produce agglomerates. A
detailed explanation thereof is given below.
[0045] As the iron-oxide-containing powder having a 50% particle
diameter of 2 .mu.m or less, use was made of a residue which had
remained after Ni recovery from an Ni-containing ore. This residue
was tailings and had a water content of about 27%. The component
composition of the residue which had remained after Ni recovery is
shown in Table 1 below. In Table 1, LOI means ignition loss.
[0046] The tailings were placed outdoors and exposed to sunlight to
reduce the water content to about 19%. The tailings having a water
content regulated to about 19% were reddish brown. A 2 kg portion
thereof was introduced into a rotary heating furnace. The tailings
were heat-treated, while being allowed to roll, and were dried and
sintered thereby. For the heat treatment, a heating temperature of
400.degree. C., 800.degree. C., 1,100.degree. C., or 1,200.degree.
C. was used as shown in Table 2. The heating period was about 60
minutes in the case where the heating temperature was 400.degree.
C., and was about 30 minutes in the case where the heating
temperature was 800.degree. C., 1,100.degree. C., or 1,200.degree.
C., as shown in Table 2. With respect to the heating atmosphere,
the heat treatment was conducted in an air stream.
[0047] The powder obtained through the heat treatment remained
reddish brown in the case where the heating temperature was
400.degree. C., 800.degree. C., or 1,100.degree. C. However, the
powder changed to blackish brown in the case where the heating
temperature was 1,200.degree. C. For reference, a photograph of the
powder obtained through the heat treatment at a heating temperature
of 400.degree. C. is shown as a drawing substitute in FIG. 1. A
photograph of the powder obtained through the heat treatment at a
heating temperature of 1,200.degree. C. is shown as a drawing
substitute in FIG. 2.
[0048] Next, after the heat treatment, each heat-treated powder
cooled to room temperature was disaggregated or pulverized with a
ball mill to obtain a sample to be agglomerated. With respect to
the heat-treated powders obtained through the heat treatment at a
heating temperature of 400.degree. C., 800.degree. C., or
1,100.degree. C., each powder was disaggregated with a ball mill
for about 30 seconds. Meanwhile, the heat-treated powder obtained
through the heat treatment at a heating temperature of
1,200.degree. C. was pulverized with a ball mill for about 20
minutes.
[0049] The particle size distribution of each heat-treated powder
was measured, and the results thereof are shown in FIG. 3. The
abscissa of FIG. 3 indicates particle diameter (.mu.m), while the
ordinate thereof indicates the integrated mass of minus-sieve
particles (mass %). As shown in FIG. 3, when the particle size
distribution of a heat-treated powder is determined, with the mass
of the whole powder being taken as 100%, the particle diameter
corresponding to the point where the integrated mass of minus-sieve
particles reaches 50% is called 50% particle diameter.
[0050] The 50% particle diameter (.mu.m), the integrated mass of
minus-sieve particles having a particle diameter of less than 1
.mu.m (mass %), and the integrated mass of minus-sieve particles
having a particle diameter of less than 10 .mu.m (mass %) were each
calculated, and the results thereof are shown in Table 2 below.
[0051] As apparent from FIG. 3 and Table 2, the powders obtained
through the heat treatment conducted at a heating temperature of
400.degree. C. or 800.degree. C. each had substantially the same
50% particle diameter as the raw material powder which had not been
heat-treated, and the integrated mass of minus-sieve particles
having a particle diameter of less than 1 .mu.m thereof was also
substantially the same as that of the raw material powder. It was
thus found that the raw material powder and the powders obtained
through the heat treatment conducted at a heating temperature of
400.degree. C. or 800.degree. C. each had a particle diameter of
less than 10 .mu.m and had substantially the same particle size
configuration. In contrast, the powder obtained through the heat
treatment conducted at a heating temperature of 1,100.degree. C.
had a 50% particle diameter which was about 8.6 times that of the
raw material powder which had not been heat-treated, showing that
the particles have enlarged due to the heat treatment. Meanwhile,
the powder obtained through the heat treatment conducted at a
heating temperature of 1,200.degree. C. had a 50% particle diameter
which was about 53.5 times that of the raw material powder which
had not been heat-treated, and the integrated mass of minus-sieve
particles having a particle diameter of less than 1 um was able to
be reduced to 4.4 mass %. It can be found that the particles have
enlarged due to the heat treatment.
[0052] The enlargement of particles can be seen from not only the
results concerning the integrated mass of minus-sieve particles
having a particle diameter of less than 1 .mu.m but also the
results concerning the integrated mass of minus-sieve particles
having a particle diameter of less than 10 .mu.m. Namely, the raw
material powder and the powders obtained through the heat treatment
conducted at a heating temperature of 400.degree. C. or 800.degree.
C. each were composed only of particles having a particle diameter
of less than 10 .mu.m, whereas the heat treatment conducted at a
heating temperature of 1,200.degree. C. was able to reduce the
proportion of particles having a particle diameter of less than 10
.mu.m to 20.9% and to increase the proportion of coarse particles
having a particle diameter of 10 .mu.m or larger to about 80%.
[0053] Next, the specific surface area (cm.sup.2/g) of each
heat-treated powder was determined by calculation on the basis of
the particle size distribution values thereof for respective
particle size ranges on the assumption that each particle diameter
was spherical. The results thereof are shown in Table 2 given
later.
[0054] As apparent from Table 2, the powders obtained through the
heat treatment conducted at a heating temperature of 400.degree. C.
or 800.degree. C. each had a specific surface area (calculated
value) of 27,400 to 29,380 cm.sup.2/g. In contrast, the powder
obtained through the heat treatment conducted at a heating
temperature of 1,100.degree. C. had a specific surface area
(calculated value) of 8,520 cm.sup.2/g, and the powder obtained
through the heat treatment conducted at a heating temperature of
1,200.degree. C. had a specific surface area (calculated value) of
1,920 cm.sup.2/g. It can be found from these results that as the
heating temperature was elevated, the specific surface area became
smaller and the particles became larger.
[0055] Next, each heat-treated powder was introduced into a
granulator made of a rubber tire having a diameter of about 35 cm,
and an appropriate amount of water was added thereto to conduct
granulation. As a result, in the case where a powder obtained by
disaggregating the heat-treated powder obtained through the heat
treatment at a heating temperature of 400.degree. C. or 800.degree.
C. was used, the resultant pellets did not have a spherical shape
and had surface projections like konpeito. A photograph of the
agglomerates produced by granulating the powder obtained by
disaggregating the heat-treated powder obtained through the heat
treatment at a heating temperature of 400.degree. C. is shown as a
drawing substitute in FIG. 4.
[0056] In contrast, in the case where a powder obtained by
pulverizing the heat-treated powder obtained through the heat
treatment at a heating temperature of 1,100.degree. C. or
1,200.degree. C. was used, the resultant pellets had a spherical
shape. A photograph of the pellets produced by granulating the
powder obtained by pulverizing the heat-treated powder obtained
through the heat treatment at a heating temperature of
1,200.degree. C. is shown as a drawing substitute in FIG. 5.
[0057] Next, the pellets obtained by granulating the heat-treated
powder obtained through the heat treatment conducted at a heating
temperature of 1,100.degree. C. or 1,200.degree. C. were examined
for water content (%), crushing strength (kg) per pellet, and
porosity (%).
[0058] The crushing strength was determined by placing one pellet
between two flat plates, applying a load to the flat plates so as
to compress the pellet, and measuring the load at the time when the
pellet fractured (hereinafter the load is also called crushing
load; unit, kg), with a strength tester. The measurement of
crushing load was made on ten pellets, and an average thereof was
determined. The results thereof are shown in Table 2.
[0059] The porosity (%) was determined through calculation from the
value of apparent specific gravity, which was determined on the
basis of the buoyancy of a pellet immersed in mercury, and from the
value of true specific gravity of the raw material powder mixed.
The results thereof are shown in Table 2.
[0060] It was able to be ascertained that in the case where the
heat-treated powder obtained through the heat treatment conducted
at a heating temperature of 1,100.degree. C. or 1,200.degree. C.
was agglomerated, the pellets obtained had substantially the same
water content, crushing strength, and porosity as the green pellets
produced in conventional pelletizing plants.
[0061] By subjecting these pellets to a thermal hardening treatment
and then heating the pellets, for example, in a reducing gas
atmosphere, reduced iron can be produced. Reduced iron can be
produced also by adding a carbonaceous reducing agent, a binder,
etc. to the heat-treated powder to prepare pellets and heating the
pellets.
[0062] As described above, according to the present invention, an
iron-oxide-containing powder having a 50% particle diameter of 2
.mu.m or less can be made to have a particle size which renders
granulation possible, by heat-treating the powder at a heating
temperature of 900 to 1,200.degree. C., and agglomerates can be
produced therefrom. These agglomerates can be effectively utilized
as an iron source.
TABLE-US-00001 TABLE 1 Component composition (mass %) T.Fe FeO CaO
SiO.sub.2 Al.sub.2O.sub.3 S Cr Ni LOI 62.02 0.06 0.01 2.65 0.62
1.05 1.46 0.02 4.82
TABLE-US-00002 TABLE 2 Heat Heat 50% Smaller Smaller Specific
Properties of wet pellets treatment treatment particle than than
surface Shape Water Crushing temperature period diameter 1 .mu.m 10
.mu.m area of content strength Porosity No. (.degree. C.) (min)
(.mu.m) (mass %) (mass %) (cm2/g) agglomerates (%) (kg) (%) 1 raw
material -- 0.6 98.8 100 -- -- -- -- -- 2 400 60 0.5 95.7 100 27400
konpeito -- -- -- shape 3 800 30 0.4 98.8 100 29380 konpeito -- --
-- shape 4 1100 30 5.2 25.6 52.1 8520 spherical 16.5 2.0 38.4 5
1200 30 32.1 4.4 20.9 1920 spherical 10.2 2.5 32.8
* * * * *