U.S. patent application number 16/484618 was filed with the patent office on 2020-01-23 for metal oxide smelting method.
The applicant listed for this patent is SUMITOMO METAL MINING CO., LTD.. Invention is credited to Yukihiro Goda, Takashi Iseki, Jun-ichi Kobayashi, Shuji Okada.
Application Number | 20200024685 16/484618 |
Document ID | / |
Family ID | 63108191 |
Filed Date | 2020-01-23 |
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United States Patent
Application |
20200024685 |
Kind Code |
A1 |
Iseki; Takashi ; et
al. |
January 23, 2020 |
METAL OXIDE SMELTING METHOD
Abstract
Provided is a smelting method in which, for example, a metal
oxide such as a nickel oxide ore including nickel oxide is used as
a source material and is reduced with a carbonaceous reducing agent
to obtain a reduced product, with which method efficient processing
can be achieved. This metal oxide smelting method is, for example,
a nickel oxide ore smelting method. Specifically, the method
includes a reduction process step S3 that has: a drying step S31 in
which a mixture that was obtained by mixing a metal oxide and a
carbonaceous reducing agent is dried; a preheating step S32 in
which the dried mixture is preheated; a reduction step S33 in which
the preheated mixture is reduced using a rotary hearth furnace 1, a
hearth of which rotates; and a cooling step S35 in which the
obtained reduced product is cooled.
Inventors: |
Iseki; Takashi;
(Niihama-shi, JP) ; Goda; Yukihiro; (Niihama-shi,
JP) ; Kobayashi; Jun-ichi; (Niihama-shi, JP) ;
Okada; Shuji; (Niihama-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SUMITOMO METAL MINING CO., LTD. |
Tokyo |
|
JP |
|
|
Family ID: |
63108191 |
Appl. No.: |
16/484618 |
Filed: |
January 31, 2018 |
PCT Filed: |
January 31, 2018 |
PCT NO: |
PCT/JP2018/003273 |
371 Date: |
August 8, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C22B 1/244 20130101;
C22B 1/245 20130101; C22B 23/021 20130101; C22B 1/243 20130101;
C22B 5/10 20130101; C22B 1/216 20130101; C22B 23/023 20130101 |
International
Class: |
C22B 5/10 20060101
C22B005/10; C22B 23/02 20060101 C22B023/02; C22B 1/216 20060101
C22B001/216; C22B 1/243 20060101 C22B001/243 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 9, 2017 |
JP |
2017-022523 |
Claims
1. A metal oxide smelting method comprising a reduction treatment
step including: a drying step in which a mixture obtained by mixing
a metal oxide and a carbonaceous reducing agent is dried; a
preheating step in which the dried mixture is preheated; a
reduction step in which the preheated mixture is reduced using a
rotary hearth furnace, a hearth of which rotates; and a cooling
step in which the obtained reduced product is cooled.
2. The metal oxide smelting method according to claim 1, wherein
the reduced product obtained through the reduction step is
subjected to a temperature maintenance step in which the reduced
product is maintained at a prescribed temperature in the rotary
hearth furnace, and after maintained for a prescribed time, the
reduced product is supplied to the cooling step.
3. The metal oxide smelting method according to claim 2, wherein
the rotary hearth furnace has a structure capable of partitioning
the respective steps, and a treatment in the reduction step and a
treatment in the temperature maintenance step are performed using
the same rotary hearth furnace.
4. The metal oxide smelting method according to claims 2, wherein
the reduced product is maintained at a temperature of 1300.degree.
C. or higher and 1500.degree. C. or lower in the temperature
maintenance step.
5. The metal oxide smelting method according to claim 1, wherein in
the reduction step, reduction is performed while a reducing
temperature is set to 1200.degree. C. or higher and 1450.degree. C.
or lower.
6. The metal oxide smelting method according to claim 1, wherein
the mixture to be dried in the drying step is obtained through a
mixing treatment step in which at least a metal oxide and a
carbonaceous reducing agent are mixed to obtain a mixture, and a
pretreatment step in which a treatment of forming the obtained
mixture into a lump product or a treatment of filling the mixture
in a prescribed container is performed.
7. The metal oxide smelting method according to claim 1, further
comprising a separating step in which the reduced product cooled in
the cooling step in the reduction treatment step is separated into
a metal and slag and the metal is recovered.
8. The metal oxide smelting method according to claim 1, wherein
the metal oxide is nickel oxide ore.
9. The metal oxide smelting method according to claim 1, wherein
the reduced product contains ferronickel.
10. The metal oxide smelting method according to claims 3, wherein
the reduced product is maintained at a temperature of 1300.degree.
C. or higher and 1500.degree. C. or lower in the temperature
maintenance step.
11. The metal oxide smelting method according to claim 2, wherein
in the reduction step, reduction is performed while a reducing
temperature is set to 1200.degree. C. or higher and 1450.degree. C.
or lower.
12. The metal oxide smelting method according to claim 3, wherein
in the reduction step, reduction is performed while a reducing
temperature is set to 1200.degree. C. or higher and 1450.degree. C.
or lower.
13. The metal oxide smelting method according to claim 2, wherein
the mixture to be dried in the drying step is obtained through a
mixing treatment step in which at least a metal oxide and a
carbonaceous reducing agent are mixed to obtain a mixture, and a
pretreatment step in which a treatment of forming the obtained
mixture into a lump product or a treatment of filling the mixture
in a prescribed container is performed.
14. The metal oxide smelting method according to claim 3, wherein
the mixture to be dried in the drying step is obtained through a
mixing treatment step in which at least a metal oxide and a
carbonaceous reducing agent are mixed to obtain a mixture, and a
pretreatment step in which a treatment of forming the obtained
mixture into a lump product or a treatment of filling the mixture
in a prescribed container is performed.
15. The metal oxide smelting method according to claim 2, further
comprising a separating step in which the reduced product cooled in
the cooling step in the reduction treatment step is separated into
a metal and slag and the metal is recovered.
16. The metal oxide smelting method according to claim 3, further
comprising a separating step in which the reduced product cooled in
the cooling step in the reduction treatment step is separated into
a metal and slag and the metal is recovered.
17. The metal oxide smelting method according to claim 2, wherein
the metal oxide is nickel oxide ore.
18. The metal oxide smelting method according to claim 3, wherein
the metal oxide is nickel oxide ore.
19. The metal oxide smelting method according to claim 2, wherein
the reduced product contains ferronickel.
20. The metal oxide smelting method according to claim 3, wherein
the reduced product contains ferronickel.
Description
TECHNICAL FIELD
[0001] The present invention relates to a metal oxide smelting
method and relates to a smelting method in which, for example,
nickel oxide ore or the like is used as a source material and is
reduced with a carbonaceous reducing agent to obtain a reduced
product.
[0002] BACKGROUND ART
[0003] As methods for smelting nickel oxide ore which is called
limonite or saprolite, known are a dry smelting method for
producing nickel matte using a flash smelting furnace, a dry
smelting method for producing ferronickel using a rotary kiln or a
moving hearth furnace, a HPAL process that is a hydrometallurgical
method for obtaining nickel-cobalt mixed sulfide (mixed sulfide)
using an autoclave by adding a high pressure acid leach sulfating
agent, and the like.
[0004] Among the various methods mentioned above, particularly, in
a case where nickel oxide ore is reduced and smelted using a dry
smelting method, a treatment for forming nickel oxide ore of a
source material into a lump product by crushing the nickel oxide
ore into a proper size and the like, a treatment for forming a
slurry, or the like is performed as a pretreatment.
[0005] Specifically, when nickel oxide ore is formed into a limp
product, that is, a lump is formed from a powdery or granular ore,
it is general that the nickel oxide ore is mixed with other
components, for example, a binder or a reducing agent such as coke
to obtain a mixture and the mixture is further subjected to
moisture adjustment and the like, then charged into a lump product
manufacturing machine, and formed into a lump product referred to
as a pellet or a briquette (hereinafter, collectively simply
referred to as the "pellet") having, for example, one side or a
diameter of about 10 mm to 30 mm.
[0006] Further, the pellet is required to exhibit gas permeability
to a certain degree in order to "emit" the moisture contained.
Furthermore, the composition of the reduced product to be obtained
is non-uniform and a trouble that metal is dispersed or unevenly
distributed is caused when the reduction does not uniformly proceed
in the pellet. For this reason, it is important to uniformly mix
the mixture and maintain the temperature as constant as possible
when the pellet is subjected to the reduction treatment.
[0007] In addition, it is also a significantly important technique
to coarsen the ferronickel to be generated by reduction. The reason
for this is that, in a case where the generated ferronickel has a
fine size of, for example, several tens of .mu.m to several
hundreds of .mu.m or less, it is difficult to separate the
ferronickel from slag to be generated at the same time, and thus a
recovery rate (yield) as ferronickel greatly decreases. For this
reason, a treatment for coarsening the reduced ferronickel is
required.
[0008] Further, it is also an important technical problem how the
smelting cost can be suppressed low, and a continuous treatment
that can be operated in a compact facility is desired.
[0009] For example, Patent Document 1 discloses a technique
relating to a method for producing ferronickel, and particularly to
a method for producing ferronickel or a source material for
smelting ferronickel from nickel oxide ore of a low grade with high
efficiency. Specifically, disclosed is a method including a mixing
step of mixing a source material containing nickel oxide and iron
oxide with a carbonaceous reducing material to obtain a mixture, a
reduction step of reducing the mixture in a moving hearth furnace
by heating to obtain a reduced mixture, and a melting step of
melting the reduced mixture in a melting furnace to obtain
ferronickel.
[0010] Herein, Patent Document 1 describes that by setting the
metallized rate of Ni in the reduced mixture to 40% or more,
preferably 85% or more, heat required for reducing nickel oxide
remaining in the reduced mixture in the melting furnace is
decreased so that energy consumption in the melting furnace can be
reduced. However, even if the heat required for the reduction in
the melting furnace is decreased by increasing the metallized rate
of Ni in the reduced mixture (hereinafter, also referred to as the
"metallized rate"), the heat quantity itself required for
metallizing Ni is the same, the energy consumption is not reduced
when considered as a whole, and accordingly, the smelting cost is
not reduced.
[0011] Further, Patent Document 1 describes that a reduced lump
product (reduced mixture) reduced in the moving hearth furnace is
generally cooled to about 1000.degree. C. with, for example, a
radiant cooling plate or a refrigerant spraying machine provided in
the moving hearth furnace and then is discharged with a discharger.
However, upon the reduced lump product is cooled to about
1000.degree. C. or lower and discharged and recovered from the
moving hearth furnace, the moving hearth furnace is cooled, and
energy for increasing the temperature again for the reduction is
needed, which incurs cost. Further, when cooling and heating are
repeated, thermal shock to the furnace increases to shorten the
life span of the device, which also causes an increase in cost.
[0012] As described above, there are many problems in order to
obtain ferronickel by mixing and reducing nickel oxide ore and
continuously performing smelting at low cost.
DISCLOSURE OF THE INVENTION
Problems to be Solved by the Invention
[0013] The present invention has been made in view of such
circumstances, and provides a smelting method in which, for
example, a metal oxide such as nickel oxide ore including nickel
oxide or the like is used as a source material and is reduced with
a carbonaceous reducing agent to obtain a reduced product, with
which method an efficient treatment can be achieved.
Means for Solving the Problems
[0014] The present inventors have conducted intensive
investigations to solve the above-mentioned problems. As a result,
it has been found that an efficient smelting treatment can be
performed by subjecting a mixture containing a source material of a
metal oxide to a reduction treatment in which a drying step, a
preheating step, a reduction step using a rotary hearth furnace,
and a cooling step are sequentially performed, whereby the present
invention has been completed.
[0015] (1) A first invention of the present invention is a metal
oxide smelting method including a reduction treatment step
including: a drying step in which a mixture obtained by mixing a
metal oxide and a carbonaceous reducing agent is dried; a
preheating step in which the dried mixture is preheated; a
reduction step in which the preheated mixture is reduced using a
rotary hearth furnace, a hearth of which rotates; and a cooling
step in which the obtained reduced product is cooled.
[0016] (2) A second invention of the present invention is the metal
oxide smelting method in the first invention, in which the reduced
product obtained through the reduction step is subjected to a
temperature maintenance step in which the reduced product is
maintained at a prescribed temperature in the rotary hearth
furnace, and after maintained for a prescribed time, the reduced
product is supplied to the cooling step.
[0017] (3) A third invention of the present invention is the metal
oxide smelting method in the second invention, in which the rotary
hearth furnace has a structure capable of partitioning the
respective steps, and a treatment in the reduction step and a
treatment in the temperature maintenance step are performed using
the same rotary hearth furnace.
[0018] (4) A fourth invention of the present invention is the metal
oxide smelting method in the second or third invention, in which
the reduced product is maintained at a temperature of 1300.degree.
C. or higher and 1500.degree. C. or lower in the temperature
maintenance step.
[0019] (5) A fifth invention of the present invention is the metal
oxide smelting method in any one of the first to fourth inventions,
in which in the reduction step, reduction is performed while a
reducing temperature is set to 1200.degree. C. or higher and
1450.degree. C. or lower.
[0020] (6) A sixth invention of the present invention is the metal
oxide smelting method in any one of the first to fifth inventions,
in which the mixture to be dried in the drying step is obtained
through a mixing treatment step in which at least a metal oxide and
a carbonaceous reducing agent are mixed to obtain a mixture, and a
pretreatment step in which a treatment of forming the obtained
mixture into a lump product or a treatment of filling the mixture
in a prescribed container is performed.
[0021] (7) A seventh invention of the present invention is the
metal oxide smelting method in any one of the first to sixth
inventions, further including a separating step in which the
reduced product cooled in the cooling step in the reduction
treatment step is separated into a metal and slag and the metal is
recovered.
[0022] (8) An eighth invention of the present invention is the
metal oxide smelting method in any one of the first to seventh
inventions, in which the metal oxide is nickel oxide ore.
[0023] (9) A ninth invention of the present invention is the metal
oxide smelting method in any one of the first to eighth inventions,
in which the reduced product contains ferronickel.
Effects of the Invention
[0024] According to the present invention, it is possible to
provide a smelting method in which, for example, a metal oxide such
as nickel oxide ore including nickel oxide or the like is used as a
source material and is reduced with a carbonaceous reducing agent
to obtain a reduced product, with which method an efficient
treatment can be achieved.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] FIG. 1 is a process diagram illustrating an example of the
flow of a method for smelting nickel oxide ore.
[0026] FIG. 2 is a process diagram illustrating a treatment step to
be performed in a reduction treatment step.
[0027] FIG. 3 is a diagram (plan view) illustrating a configuration
example of a rotary hearth furnace, a hearth of which rotates.
PREFERRED MODE FOR CARRYING OUT THE INVENTION
[0028] <<1. Overview of Present Invention>>A metal
oxide smelting method according to the present invention is a
smelting method in which a metal oxide is used as a source material
and a reduction treatment is performed by a carbonaceous reducing
agent at a high temperature to obtain a reduced product. For
example, there is mentioned a method for producing ferronickel by
using nickel oxide as a metal oxide or nickel oxide ore including
iron oxide or the like as a source material and reducing the source
material for smelting using a carbonaceous reducing agent under a
high temperature.
[0029] Specifically, the metal oxide smelting method according to
the present invention includes reduction treatment step that
includes a drying step in which a mixture obtained by mixing a
metal oxide and a carbonaceous reducing agent is dried, a
preheating step in which the dried mixture is preheated, a
reduction step in which the preheated mixture is reduced using a
rotary hearth furnace, a hearth of which rotates, and a cooling
step in which the obtained reduced product is cooled.
[0030] In this manner, according to the present invention, the
mixture containing metal oxide as a source material is subjected to
the treatment in each step mentioned above, and further the
treatment in the reduction step is performed using the rotary
hearth furnace, a hearth of which rotates, so that the metal
contained in the metal oxide can be effectively metallized and an
efficient smelting treatment can also be performed.
[0031] Hereinafter, as a specific embodiment of the present
invention (hereinafter, referred to as the "present embodiment"), a
method for smelting nickel oxide ore will be described as an
example. The nickel oxide ore serving as a source material for
smelting contains at least nickel oxide. In this method for
smelting nickel oxide ore, ferronickel (iron-nickel alloy) can be
produced by reducing nickel oxide and the like contained in the
source material.
[0032] Incidentally, in the present invention, the metal oxide is
not limited to nickel oxide ore and the smelting method is also not
limited to a method for producing ferronickel from nickel oxide ore
containing nickel oxide and the like. Further, various
modifications can be made without changing the gist of the present
invention.
<<2. Method for Smelting Nickel Oxide Ore>>
[0033] The method for smelting nickel oxide ore according to the
present embodiment is a method for generating ferronickel, which is
a metal, and slag by mixing and kneading nickel oxide ore serving
as a source material for smelting with a carbonaceous reducing
agent or the like to obtain a mixture and subjecting the mixture to
a reduction treatment. Incidentally, ferronickel, which is a metal,
can be recovered from a mixture containing a metal and slag
obtained through the reduction treatment by separating the
metal.
[0034] FIG. 1 is a process diagram illustrating an example of the
flow of a method for smelting nickel oxide ore. As illustrated in
FIG. 1, this method for smelting nickel oxide ore includes a mixing
treatment step S1 in which nickel oxide ore and a material such as
a carbonaceous reducing agent are mixed to obtain a mixture, a
reduction charging pretreatment step S2 in which the obtained
mixture is formed into a lump product or filled in a prescribed
container, a reduction treatment step S3 in which the mixture is
reduced at a prescribed temperature (reducing temperature), and a
separating step S4 in which the metal is separated and recovered
from the mixture containing the metal and slag generated by the
reduction treatment.
<2-1. Mixing Treatment Step>
[0035] The mixing treatment step S1 is a step in which source
material powders including nickel oxide ore are mixed to obtain a
mixture. Specifically, in the mixing treatment step S1, nickel
oxide ore serving as a source material for smelting and source
material powders, such as iron ore, a flux component, a binder, or
a carbonaceous reducing agent, having a particle diameter of, for
example, about 0.2 mm to 0.8 mm are mixed at a prescribed ratio to
obtain a mixture.
[0036] The nickel oxide ore serving as an ore of a source material
for smelting is not particularly limited, but limonite ore,
saprolite ore, and the like can be used.
[0037] As the iron ore, for example, iron ore having an iron grade
of about 50%, hematite to be obtained by hydrometallurgy of nickel
oxide ore, and the like can be used.
[0038] An example of compositions (% by weight) of nickel oxide ore
serving as a source material and iron ore is presented in the
following Table 1. Incidentally, the composition of the source
material is not limited thereto.
TABLE-US-00001 TABLE 1 Source material [% by weight] Ni
Fe.sub.2O.sub.3 C Nickel oxide ore 1~2 50~60 -- Iron ore -- 80~95
--
[0039] Further, examples of the binder may include bentonite, a
polysaccharide, a resin, water glass, and dehydrated cake. Further,
examples of the flux component may include calcium oxide, calcium
hydroxide, calcium carbonate, and silicon dioxide.
[0040] The carbonaceous reducing agent is not particularly limited,
and examples thereof include coal powder and coke. Incidentally,
this carbonaceous reducing agent preferably has a size equivalent
to the particle size of the nickel oxide ore of the source material
ore. Further, the amount of the carbonaceous reducing agent mixed
can be adjusted such that the proportion of carbon amount is 5% or
more and 60% or less when the total value (also conveniently
referred to as the "total value of chemical equivalents") of a
chemical equivalent required for reducing the entire amount of
nickel oxide contained in the mixture to be formed into nickel
metal and a chemical equivalent required for reducing ferric oxide
contained in the pellet into iron metal is regarded as 100%.
[0041] In the mixing treatment step S1, a mixture is obtained by
uniformly mixing source material powders including nickel oxide ore
as described above. Upon this mixing, kneading may be performed at
the same time as mixing or kneading may be performed after mixing.
In this manner, by mixing and kneading the source material powders,
the contact area between the source materials increases and by
decreasing voids, the reduction reaction is likely to occur and the
reaction can be uniformly conducted. Accordingly, the reaction time
of the reduction reaction can be shortened and variation in the
quality is diminished. As a result, a highly productive treatment
can be performed and high quality ferronickel can be produced.
[0042] Further, after kneading the source material powders, the
mixture may be extruded using an extruder. By extruding the mixture
using an extruder in this manner, a still higher kneading effect
can be obtained, the contact area between the source material
powders increases, and voids can be decreased. Accordingly, high
quality ferronickel can be efficiently produced.
<2-2. Reduction Charging Pretreatment Step (Pretreatment
Step)>
[0043] The reduction charging pretreatment step S2 is a step in
which the mixture obtained in the mixing treatment step S1 is
formed into a lump product or filled in a container. That is, in
this reduction charging pretreatment step S2, the mixture obtained
by mixing the source material powders is molded such that the
mixture is easily charged into a furnace used in the reduction
treatment step S3 described later and the reduction reaction
efficiently occurs.
(Forming Mixture into Lump Product)
[0044] In the case of forming the obtained mixture into a lump
product, the mixture is formed (granulated) into a lump product.
Specifically, moisture is added to the obtained mixture in a
prescribed amount required for forming the mixture into a lump
product and the mixture is molded into a lump (hereinafter, also
referred to as the "pellet") using, for example, a lump product
manufacturing apparatus (such as a tumbling granulator, a
compression molding machine, or an extrusion molding machine) or
the like.
[0045] The shape of the pellet is not particularly limited, and the
shape of the pellet can be, for example, a spherical shape. By
adopting a spherical pellet, the reduction reaction easily proceeds
relatively uniformly, which is preferable. Further, the size of the
lump product to be formed into a pellet is not particularly
limited, but for example, the size (the diameter in the case of a
spherical pellet) of the pellet to be charged into a smelting
furnace, which is used for performing the reduction treatment
(reduction step S33), through the drying treatment (drying step
S31) and the preheating treatment (preheating step S32) can be set
to about 10 mm to 30 mm. Incidentally, the reduction step and the
like will be described in detail later.
(Filling of Mixture in Container)
[0046] In the case of filling the obtained mixture in a container,
the mixture can be filled in a prescribed container while being
kneaded by an extruder or the like. In this manner, after the
mixture is filled in the container, the reduction treatment may be
performed in the subsequent step of the reduction treatment step S3
without any changes, but the mixture filled in the container is
compressed by a press or the like. By compressing and molding the
mixture in the container, the density of the mixture can be
increased, the density becomes uniform, the reduction reaction
easily proceeds more uniformly, and ferronickel having small
variation in the quality can be produced.
[0047] The shape of the mixture to be filled in the container is
not particularly limited, but for example, the shape is preferably
a rectangular parallelepiped shape, a cubic shape, a cylindrical
shape, or the like. Further, the size thereof is not also
particularly limited, but for example, if the shape is a
rectangular parallelepiped shape or a cubic shape, the inside
dimensions of the height and the width is preferably approximately
500 mm or less. With such a shape and such a size, the variation in
the quality becomes small and highly productive smelting can be
performed.
[0048] <2-3. Reduction Treatment Step>
[0049] In the reduction treatment step S3, the source material
powders are mixed in the mixing treatment step S1 and the mixture
formed into a lump product or filled in the container in the
reduction charging pretreatment step S2 is reduced and heated at a
prescribed reducing temperature. By the reduction and heat
treatment of the mixture in the reduction treatment step S3, the
smelting reaction proceeds and a metal and slag are generated.
[0050] FIG. 2 is a process diagram illustrating a treatment step to
be performed in the reduction treatment step S3. As illustrated in
FIG. 2, the reduction treatment step S3 in the present embodiment
includes a drying step S31 in which the mixture is dried, a
preheating step S32 in which the dried mixture is preheated, a
reduction step S33 in which the mixture is reduced, and a cooling
step S35 in which the obtained reduced product is cooled. Further,
preferably, the reduction treatment step S3 includes a temperature
maintenance step S34 in which the reduced product obtained through
the reduction step S33 is maintained in a prescribed temperature
range.
[0051] Herein, the treatment in the reduction step S33 is performed
using a rotary hearth furnace, a hearth of which rotates. Further,
in a case where the temperature maintenance step S34 in which the
reduced product is maintained in a prescribed temperature range is
performed, at least the treatment in the reduction step S33 and the
treatment in the temperature maintenance step S34 are performed in
the rotary hearth furnace.
[0052] In this manner, by performing those treatments in the rotary
hearth furnace, the temperature in the rotary hearth furnace can be
maintained at a high temperature, so that it is unnecessary to
increase or decrease the temperature every time the treatments in
the respective steps are performed, and energy cost can be
considerably reduced. Further, according to the treatment using the
rotary hearth furnace, the control or management of the temperature
is easily conducted. According to these, high quality ferronickel
can be continuously stably
[0053] produced at high productivity. (1) Drying Step
[0054] In the drying step S31, the mixture obtained by mixing the
source material powders is subjected to the drying treatment. This
drying step S31 is mainly intended to extract moisture or
crystalline water in the mixture. [0055] A large amount of moisture
or the like is contained in the mixture obtained in the mixing
treatment step S1, the moisture evaporates and expands at a time by
a sharp increase to a high temperature like a reducing temperature
at the time of the reduction treatment in this state, the mixture
formed into a lump product is broken, or depending on the cases, is
broken into fragments, and thus it is difficult to perform a
uniform reduction treatment. For this reason, before the reduction
treatment is performed, the mixture is subjected to the drying
treatment to remove moisture so that breakage of the pellet or the
like is prevented.
[0056] The drying treatment in the drying step S31 is preferably
performed in the form of being connected to a rotary hearth
furnace. The drying treatment is also considered to be performed
while an area in which the drying treatment is conducted (drying
area) is provided in the rotary hearth furnace, but in such a case,
the drying treatment in the drying area is limited so that the
treatment in the reduction step S33 and the treatment in the
temperature maintenance step S34 may be affected.
[0057] Therefore, it is preferable that the drying treatment in the
drying step S31 is performed in a drying chamber which is provided
outside the furnace of the rotary hearth furnace and is connected
to the rotary hearth furnace. Incidentally, although will be
described in detail later, FIG. 3 illustrates a configuration
example of a rotary hearth furnace 1 and a drying chamber 20
connected to the rotary hearth furnace 1. In this manner, by the
drying chamber 20 being provided outside the furnace of the rotary
hearth furnace 1, a drying chamber can be designed quite separately
from steps such as preheating, reduction, and cooling described
later, and desirable drying, preheating, reduction, and cooling
treatments are easily performed, respectively. For example, in a
case where a large amount of moisture remains in the mixture
depending on the source material, since it takes time to perform
the drying treatment, the entire length of the drying chamber 20
may be designed to be long or the transfer speed of the mixture in
the drying chamber 20 may be designed to be decreased.
[0058] As the drying treatment in the drying chamber 20, for
example, a treatment can be performed so that the solid content in
the mixture is about 70% by weight and the moisture is about 30% by
weight. Further, the drying method is not particularly limited, but
the drying can be performed by blowing hot air to the mixture
transferred in the drying chamber 20. Further, the drying
temperature is not particularly limited, but from the viewpoint
that the reduction reaction is not started, the drying temperature
is preferably set to 500.degree. C. or lower and it is preferable
to perform uniform drying at the temperature of 500.degree. C. or
lower. An example of the composition (parts by weight) of the solid
content in the drying-treated mixture is presented in the following
Table 2. Incidentally, the composition of the mixture is not
limited thereto.
TABLE-US-00002 TABLE 2 Composition of solid content in dried
mixture (pellet) [Parts by weight] Ni Fe.sub.2O.sub.3 SiO.sub.2 CaO
Al.sub.2O.sub.3 MgO Binder Others 0.5~1.5 50~60 8~15 4~8 1~6 2~7
About 1 Balance
(2) Preheating Step
[0059] In the preheating step S32, the mixture after the moisture
has been removed by the drying treatment in the drying step S31 is
preheated (preliminarily heated).
[0060] When the mixture is charged into the rotary hearth furnace
and heated rapidly to a high temperature of a reducing temperature,
the mixture cracks due to thermal stress or becomes powders.
Further, the temperature of the mixture does not uniformly
increase, variation in the reduction reaction occurs, and the
quality of the metal to be generated may deteriorate. Therefore, it
is preferable that the mixture is preheated to a prescribed
temperature after the mixture is subjected to the drying treatment,
and according to thus, the breakage of the mixture and the
variation in reduction reaction can be suppressed.
[0061] The preheating treatment in the preheating step S32 is
preferably performed in the treating chamber provided outside the
furnace of the rotary hearth furnace, similarly to the drying
treatment, and the preheating treatment is preferably performed in
a preheating chamber connected to the rotary hearth furnace.
Incidentally, FIG. 3 illustrates a configuration example of a
preheating chamber 30 connected to the rotary hearth furnace 1, and
the preheating chamber 30 is provided outside the furnace of the
rotary hearth furnace 1 and is provided continuously from the
drying chamber 20 in which the drying treatment is performed. In
this manner, by performing the preheating treatment in the
preheating chamber 30 provided outside the furnace of the rotary
hearth furnace 1, the temperature in the rotary hearth furnace 1 in
which the reduction treatment is performed can be maintained to be
a high temperature and energy required for heating can be
considerably saved.
[0062] The preheating treatment in the preheating chamber 30 is not
particularly limited, but it is preferable to perform the
preheating treatment while a preheating temperature is set to
600.degree. C. or higher and it is more preferable to perform the
preheating treatment while a preheating temperature is set to
700.degree. C. or higher and 1280.degree. C. or lower. By
performing the treatment at a preheating temperature in such a
range, energy required for reheating to the reducing temperature in
the subsequent reduction treatment can be considerably reduced.
(3) Reduction Step
[0063] In the reduction step S33, the mixture preheated in the
preheating step S32 is subjected to a reduction treatment at a
prescribed reducing temperature. Specifically, the reduction
treatment in the reduction step S33 is performed using a rotary
hearth furnace, a hearth of which rotates. In this manner, by
performing the reduction treatment using the rotary hearth furnace,
the temperature in the furnace can be maintained in a high
temperature range, it is unnecessary to increase or decrease the
temperature, and energy cost can be considerably reduced. Further,
the control or management of the temperature is easily conducted
and high quality ferronickel can be stably generated.
[Configuration of Rotary Hearth Furnace]
[0064] Herein, FIG. 3 is a diagram (plan view) illustrating a
configuration example of a rotary hearth furnace, a hearth of which
rotates. As illustrated in FIG. 3, the rotary hearth furnace 1 has
a region 10 in which the hearth rotates and the region 10 is
divided into four so that respective divided regions form treating
chambers (10a, 10b, 10c, and 10d). Specifically, in this rotary
hearth furnace 1, for example, all of the four treating chambers
denoted by Reference Numeral "10a" to "10d" can be used as reducing
chambers in which the reduction treatment is performed. Further, in
the case of performing the temperature maintenance step S34
described later after the treatment in the reduction step S33, for
example, the treating chambers "10a, " "10b, " and "10c" can be
used as reducing chambers and the treating chamber "10d" can be
used as a temperature maintaining chamber in which the treatment in
the temperature maintenance step S34 is performed.
[0065] In order to strictly control the reaction temperature so as
to suppress energy loss, a configuration in which the respective
steps, that is, the respective treating chambers are partitioned by
a partition wall is preferably employed. In this manner, according
to the rotary hearth furnace having a structure capable of
partitioning the respective steps, as described later, the
treatment in the reduction step S33 and the treatment in the
temperature maintenance step S34 can be performed using the same
rotary hearth furnace while energy loss is suppressed. However, if
the partition wall is a fixed type, there is a possibility that
transferring between the steps, and particularly, charging and
discharging to and from the rotary hearth furnace become difficult,
so that the partition wall preferably has a structure which can
open and close to the degree that does not affect the movement of a
material to be treated.
[0066] Incidentally, the number of treating chambers formed by
dividing the region 10 in which the hearth rotates is not limited
to four illustrated in FIG. 3. Further, the number of reducing
chambers and the number of temperature maintaining chambers are
also not limited to the aforementioned examples and can be
appropriately set depending on treatment time or the like.
[0067] The rotary hearth furnace 1 includes, as described above, a
hearth which rotationally moves on the plane, and when the hearth
on which the mixture is placed rotationally moves at a prescribed
speed, the mixture passes through the respective treating chambers
(10a, 10b, 10c, and 10d) and the treatment is performed at the time
of the mixture passing through the treating chambers. Incidentally,
an arrow on the rotary hearth furnace 1 in FIG. 3 indicates a
rotation direction of the hearth and indicates a moving direction
of a material to be treated (mixture).
[0068] Further, the rotary hearth furnace 1 is connected to the
drying chamber 20 and the preheating chamber 30 which are provided
outside the furnace, and as described above, after the mixture is
subjected to the drying treatment in the drying chamber 20, the
dried mixture is transferred to the preheating chamber 30 and
subjected to the preheating treatment and the preheating-treated
mixture is sequentially transferred to the inside of the rotary
hearth furnace 1. Further, the rotary hearth furnace 1 is connected
to a cooling chamber 40 provided outside the furnace, and the
reduced product obtained through the reducing chamber or the
temperature maintaining chamber (10d) is subjected to the cooling
treatment in the cooling chamber 40 (cooling step S35 described
later).
[Reduction Treatment in Rotary Hearth Furnace]
[0069] In the reduction treatment using the rotary hearth furnace
1, it is preferable that nickel oxide, which is a metal oxide
contained in nickel oxide ore, is completely reduced as much as
possible; meanwhile, iron oxide, which is derived from iron ore or
the like mixed as source material powder with nickel oxide ore, is
partially reduced such that ferronickel having a target nickel
grade is obtainable.
[0070] Specifically, the reducing temperature is not particularly
limited, but is preferably set in a range of 1200.degree. C. or
higher and 1450.degree. C. or lower and more preferably set in a
range of 1300.degree. C. or higher and 1400.degree. C. or lower. By
performing reduction in such a temperature range, the reduction
reaction can uniformly occur, and metal (ferronickel metal) in
which variation in the quality is suppressed can be generated.
Further, more preferably, when reduction is conducted at a reducing
temperature in a range of 1300.degree. C. or higher and
1400.degree. C. or lower, a desired reduction reaction can occur in
a relatively short time.
[0071] Upon the reduction treatment, the internal temperature of
the reducing chamber in the rotary hearth furnace 1 is increased to
a reducing temperature in the aforementioned range, and after the
temperature increases, the temperature at this time is
maintained.
[0072] Further, in the reduction treatment, in order to prevent the
mixture sample from being difficult to recover when the mixture
sample reacts with the hearth and is not peeled off, a reaction
suppressing material such as ash may be spread on the hearth of the
rotary hearth furnace 1 to be used and the mixture sample may be
placed on the reaction suppressing material. For example, as the
ash serving as the reaction suppressing material, ash having
SiO.sub.2 as a main component and containing a small amount of an
oxide such as Al.sub.2O.sub.3 or MgO as other components can be
used.
[0073] (4) Temperature Maintenance Step
[0074] Although not an essential aspect, the temperature
maintenance step S34 in which the reduced product obtained through
the reduction step S33 is maintained in a prescribed high
temperature condition in the rotary hearth furnace may be
performed. In this manner, when the reduced product obtained by the
reduction treatment at a prescribed reducing temperature in the
reduction step S33 is not cooled immediately but is maintained in a
high temperature atmosphere, a metal component generated in the
reduced product can be settled and coarsened.
[0075] In a case where the metal component in the reduced product
is small in the state of being obtained by the reduction treatment,
for example, in a case where the metal component is a bulk-form
metal having a size of about 200 .mu.m or less, it is difficult to
separate the metal and the slag in the subsequent separating step
S4. Therefore, as necessary, by the reduced product being
maintained at a high temperature over a certain time continuously
after the reduction reaction is finished, the metal in the reduced
product having a larger specific gravity than that of the slag is
settled and aggregated to coarsen the metal.
[0076] Incidentally, in a case where the metal is coarsened to a
level that does not cause any problem in production by the
reduction treatment in the reduction step S33, particularly, this
temperature maintenance step S34 is not necessarily provided.
[0077] Specifically, the maintaining temperature of the reduced
product in the temperature maintenance step S34 is preferably set
in a high temperature of 1300.degree. C. or higher and 1500.degree.
C. or lower. By maintaining the reduced product at a high
temperature in such a range, the metal component in the reduced
product can be efficiently settled to obtain coarse metal.
Incidentally, when the maintaining temperature is lower than
1300.degree. C., since a large part of the reduced product becomes
a solid phase, the metal component is not settled, or even if the
metal component is settled, it takes time for that, which is not
preferable. On the other hand, when the maintaining temperature is
higher than 1500.degree. C., reaction between the obtained reduced
product and a hearth material proceeds, so that there is a case
where the reduced product cannot be recovered or the furnace is
damaged.
[0078] Herein, the treatment in the temperature maintenance step
S34 is performed in the rotary hearth furnace 1 used in the
reduction step S33 continuously to the reduction treatment. That
is, as described using FIG. 3, in the rotary hearth furnace 1, for
example, the treating chambers "10a, " "10b, " and "10c" are used
as reducing chambers, the treating chamber "10d" is used as a
temperature maintaining chamber in which the treatment is performed
in the temperature maintenance step S34, and the reduced product
obtained by passing through the reducing chambers (10a, 10b, and
10c) is maintained in a prescribed temperature range in the
temperature maintaining chamber (10d).
[0079] In this manner, by continuously performing, using the rotary
hearth furnace 1, the treatment in which the reduced product
obtained through the reduction treatment is maintained at a
prescribed temperature, the metal component in the reduced product
can be efficiently settled and coarsened. Moreover, when the
treatment in the reduction step S33 and the treatment in the
temperature maintenance step S34 are not performed in separate
furnaces but performed continuously using the rotary hearth furnace
1, heat loss between the respective treatments can be reduced and
an efficient operation can be performed.
[0080] (5) Cooling Step
[0081] In the cooling step S35, the reduced product obtained
through the reduction step S33 or the reduced product maintained at
a high temperature over a prescribed time in the temperature
maintenance step S34 is cooled to a temperature at which the
reduced product can be separated and recovered in the subsequent
separating step S4.
[0082] Since the cooling step S35 is a step in which the reduced
product obtained as mentioned above is cooled, the cooling step S35
is preferably performed in the cooling chamber connected to the
outside of the furnace of the rotary hearth furnace 1.
Incidentally, although FIG. 3 illustrates the configuration example
of the cooling chamber 40 connected to the rotary hearth furnace 1,
this cooling chamber 40 is provided to be connected to the outside
of the furnace of the rotary hearth furnace 1. In this manner, by
performing the cooling treatment in the cooling chamber 40 provided
outside the furnace of the rotary hearth furnace 1, the internal
temperature of the rotary hearth furnace 1 can be prevented from
decreasing, and energy loss can be suppressed. According to this,
efficient ferronickel generation can be conducted.
[0083] The temperature in the cooling step S35 (hereinafter, also
referred to as the "temperature at the time of recovering") is a
temperature at which the reduced product is handled substantially
as a solid, and the temperature is preferably a high temperature as
much as possible. By increasing the temperature at the time of
recovering as much as possible, even when the hearth, which
rotationally moves, of the rotary hearth furnace 1 returns to the
connect place with the preheating chamber 30 in which the
preheating step S32 is performed, energy loss can be reduced, and
energy required for reheating can be still more saved.
Specifically, the temperature at the time of recovering is
preferably set to 600.degree. C. or higher. By setting the
temperature at the time of recovering to a high temperature in this
manner, energy required for reheating can be considerably reduced,
and an efficient smelting treatment can be performed at low cost.
Further, by decreasing a difference in temperature inside the
rotary hearth furnace 1, thermal stress to be applied to the
hearth, the furnace wall, or the like can be decreased, and the
life span of the rotary hearth furnace 1 can be largely expanded.
Furthermore, failures during operation can also be considerably
decreased.
<2-4. Separating Step>
[0084] In the separating step S4, the metal (ferronickel metal) is
separated and recovered from the reduced product generated in the
reduction treatment step S3. Specifically, in the separating step
S4, the metal phase is separated and recovered from a mixed product
(reduced product) which contains a metal phase (metal solid phase)
and a slag phase (slag solid phase) which is obtained by the
reduction and heat treatment of the mixture.
[0085] As a method for separating the metal phase and the slag
phase from the mixed product which is composed of the metal phase
and the slag phase and is obtained as a solid, for example, methods
such as separation by specific gravity and separation by magnetic
force can be utilized in addition to removal of unnecessary
substances by sieving. Further, the metal phase and the slag phase
thus obtained can be easily separated since these exhibit poor
wettability, and it is possible to easily separated the metal phase
and the slag phase from the mixed product by imparting an impact to
the large mixed product, for example, falling down the large mixed
product at a prescribed falling distance or applying a prescribed
vibration to the large mixed product at the time of sieving.
[0086] The metal phase is recovered by separating the metal phase
and the slag phase in this manner, and thus a product of
ferronickel can be obtained.
EXAMPLES
[0087] Hereinafter, the present invention will be described in more
detail by means of Examples, but the present invention is not
limited to the following Examples at all. (Mixing Treatment
Step)
[0088] Nickel oxide ore serving as a source material ore, iron ore,
silica sand and limestone which are flux components, a binder, and
coal powder which is a carbonaceous reducing agent (carbon content:
85% by weight, average particle diameter: about 190 .mu.m) were
mixed using a mixer while adding an appropriate amount of water to
obtain a mixture. Incidentally, the carbonaceous reducing agent was
contained in an amount corresponding to the amount of carbon of 33%
when the total value of a chemical equivalent required for reducing
nickel oxide and iron oxide (Fe.sub.2O.sub.3) into metal without
being in excess or short was regarded as 100%.
[0089] Then, the mixture obtained by mixing with the mixer was
kneaded by a biaxial kneader.
(Reduction Charging Pretreatment Step)
[0090] Then, the mixture obtained by kneading was classified into
nine, and each mixture sample was molded using a pan granulator
into a spherical pellet of .phi.19 .+-.1.5 mm.
(Reduction Treatment Step)
[0091] Then, the respective mixture samples classified into nine
were subjected to a reduction treatment using a rotary hearth
furnace 1 as illustrated in FIG. 3 while treatment conditions were
changed. As the rotary hearth furnace 1, as illustrated in FIG. 3,
a hearth furnace in which a drying chamber 20 drying the pellet, a
preheating chamber 30 provided continuously to the drying chamber
20, and a cooling chamber 40 cooling a reduced product obtained
through treating chambers 10a to 10d in the furnace are connected
to the outside of the furnace was used.
[0092] Specifically, nine pellet samples were charged into the
drying chamber 20 connected to the outside of the furnace of the
reduction hearth furnace 1 and then subjected to a drying
treatment. The drying treatment was performed in a nitrogen
atmosphere substantially not containing oxygen by blowing hot air
set at 250.degree. C. to 350.degree. C. to the pellets such that
the solid content in the pellet would be about 70% by weight and
the moisture would be about 30% by weight. The solid content
compositions (excluding carbon) of the drying-treated pellet are
presented in the following Table 3.
TABLE-US-00003 TABLE 3 Composition of solid content in dried
pellet[% by mass] Ni Fe.sub.2O.sub.3 SiO.sub.2 CaO Al.sub.2O.sub.3
MgO Others 1.6 53.3 14.0 5.4 3.2 5.7 Binder, carbonaceous reducing
agent
[0093] Subsequently, the drying-treated pellet was transferred to
the preheating chamber 30 provided continuously to the drying
chamber 20 and the pellet was subjected to a preheating treatment
while the temperature in the preheating chamber 30 was maintained
in a range of 700.degree. C. or higher and 1280.degree. C. or
lower.
[0094] Subsequently, the preheating-treated pellet was transferred
to the inside of the rotary hearth furnace 1 and subjected to a
reduction treatment and a temperature maintenance treatment.
Specifically, as the rotary hearth furnace 1, a region 10 in which
the hearth rotationally moves was divided into four to provide four
treating chambers, among the four treating chambers, the treating
chambers 10a to 10c were used as reducing chambers in which the
reduction treatment is performed and the treating chamber 10d was
used as a temperature maintaining chamber in which the reduced
product is maintained at a high temperature.
[0095] In the hearth of the rotary hearth furnace 1, in order to
prevent the sample from being difficult to recover when the sample
reacts with the hearth and is not peeled off, from the viewpoint of
suppressing the reaction between the hearth and the sample as much
as possible, the hearth was paved in advance with ash (having
SiO.sub.2 as a main component and containing a small amount of an
oxide such as Al.sub.2O.sub.3 or MgO as other components).
[0096] Incidentally, in Examples in the aspect in which the
treatment of maintaining the reduced product at a high temperature
is not performed, the internal temperature of the temperature
maintaining chamber was set to 0.degree. C. and the mixture passed
only through the temperature maintaining chamber. Further, the
reduced product obtained through the reduction treatment or the
reduction treatment and the temperature maintenance treatment was
transferred to the cooling chamber connected to the rotary hearth
furnace 1, cooled rapidly to room temperature while allowing
nitrogen to flow, and then taken out into the air. Incidentally,
the recovery of the reduced product from the rotary hearth furnace
was performed in the form of the reduced product being transferred
to the cooling chamber 40, and the reduced product was recovered
along a guide installed at the cooling chamber 40 by the guide.
[0097] Conditions of the reduction treatment and the temperature
maintenance treatment in the reduction treatment step are presented
in the following Table 4.
[0098] Further, the nickel grade of the sample taken was analyzed
by an ICP emission spectroscopic analyzer (SHIMAZU S-8100 model)
and the metallized rate of nickel and the nickel content rate in
the metal were calculated, respectively. Incidentally, the
metallized rate of nickel was calculated by the following Equation
(i) and the nickel content rate in the metal was calculated by the
following Equation (ii).
Metallized rate of nickel=amount of metallized Ni in pellet/(amount
of entire Ni in pellet).times.100 (%) (i)
Nickel content rate in metal=amount of metallized Ni in pellet
(total amount of metallized Ni and Fe in pellet).times.100 (%)
(ii)
[0099] Further, the recovered samples were pulverized by wet
treatment and then the metal (ferronickel metal) was recovered by
magnetic separation. Then, the recovery rate of Ni metal was
calculated from the Ni content rate and the charged amount of the
nickel oxide ore charged, and the amount of the recovered Ni.
Incidentally, the recovery rate of Ni metal was calculated from the
following Equation (iii).
Recovery rate of Ni metal=amount of recovered Ni/+(amount of ore
charged.times.proportion of Ni contained in ore).times.100 Equation
(iii)
TABLE-US-00004 TABLE 4 High temperature Recovery Reducing Reducing
maintaining Metallized Content of rate of temperature time
temperature rate of Ni Ni in metal metal Sample (.degree. C.)
(Min.) (.degree. C.) (%) (%) (%) 1 1210 55 0 98.0 18.0 90.0 2 1255
45 0 98.2 18.2 90.2 3 1300 35 0 98.8 18.4 90.4 4 1350 18 0 99.3
18.6 90.6 5 1395 14 0 99.7 18.8 90.7 6 1445 8 0 99.7 19.0 90.9 7
1230 50 1310 99.3 18.5 90.6 8 1230 50 1400 99.8 18.9 91.1 9 1230 50
1480 99.9 19.3 92.2
[0100] As understood from Table 4, by the mixture containing the
source material ore being subjected to the reduction treatment step
having at least the drying step, the preheating step, the reduction
step in which the reduction is conducted using a rotary hearth
furnace, a hearth of which rotates, and the cooling step in which
the obtained reduced product is cooled, ferronickel of a high
nickel grade could be obtained, and nickel at a high recovery rate
of 90% or more as the recovery rate could be recovered.
[0101] Further, by performing the reduction treatment or the
reduction treatment and the temperature maintenance treatment using
the rotary hearth furnace, the internal temperature of the rotary
hearth furnace could be maintained to a high temperature, energy
required for reheating was suppressed, and an efficient smelting
treatment could be performed.
EXPLANATION OF REFERENCE NUMERALS
[0102] 1 ROTARY HEARTH FURNACE [0103] 10 REGION [0104] 10a, 10b,
10c, 10d TREATING CHAMBER (REDUCING CHAMBER, TEMPERATURE
MAINTAINING CHAMBER) [0105] 20 DRYING CHAMBER [0106] 30 PREHEATING
CHAMBER [0107] 40 COOLING CHAMBER
* * * * *