AU2018218643B2

AU2018218643B2 - Metal oxide smelting method

Info

Publication number: AU2018218643B2
Application number: AU2018218643A
Authority: AU
Inventors: Yukihiro GODA; Takashi Iseki; Jun-Ichi Kobayashi; Shuji Okada
Original assignee: Sumitomo Metal Mining Co Ltd
Current assignee: Sumitomo Metal Mining Co Ltd
Priority date: 2017-02-09
Filing date: 2018-01-31
Publication date: 2020-11-12
Anticipated expiration: 2038-01-31
Also published as: JP2018127693A; WO2018147145A1; US20200024685A1; PH12019501782A1; AU2018218643A1; JP6900695B2

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. Additionally, the reduced product that was obtained through the reduction step S33 is preferably subjected to a temperature maintenance step S34 in which the reduced product is maintained at a prescribed temperature within the rotary hearth furnace 1.

Description

METAL OXIDE SMELTING METHOD TECHNICAL FIELD

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.

BACKGROUND ART

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.

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.

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

mm.

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.

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 pm to several hundreds of pm 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.

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.

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.

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.

Further, Patent Document 1 describes that a reduced lump

product (reduced mixture) reduced in the moving hearth furnace

is generally cooled to about 10000C 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 10000C 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.

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.

Patent Document 1: Japanese Unexamined Patent Application,

Publication No. 2004-156140

DISCLOSURE OF THE INVENTION

The present invention seeks 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.

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.

(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.

(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.

(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.

(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

13000C or higher and 15000C or lower in the temperature

maintenance step.

(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 12000C or

higher and 14500C or lower.

(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.

(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.

(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.

(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.

According to a further aspect, the present invention

provides 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 at a temperature of 2500C or high and 3500C or

lower; a preheating step in which the dried mixture is

preheated at a temperature of 7000C or higher and 12800C or

lower; 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.

Effects of the Invention

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.

7A

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a process diagram illustrating an example of

the flow of a method for smelting nickel oxide ore. Fig. 2 is

a process diagram illustrating a treatment step to be

performed in a reduction treatment step. 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

<<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.

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.

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.

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.

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>>

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.

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 Si 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>

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.

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.

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.

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 1]

Source material Ni Fe 2 0 C

[% by weight] 3

Nickel oxide ore 1~2 50-60

Iron ore - 80-95

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.

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%.

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.

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)>

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)

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.

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)

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.

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.

<2-3. Reduction Treatment Step>

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.

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.

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.

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 produced at high productivity.

(1) Drying Step

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.

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.

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.

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.

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 5000C or lower and it is preferable to perform uniform drying at the temperature of 5000C 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 2]

Composition of solid content in Ni Fe 20 3 SiO 2 CaO A1 2 0 3 MgO Binder Others dried mixture (pellet) 0.5-1.5 50-60 8-15 4-8 1-6 2~7 About 1 Balance

[Parts by weight]

(2) Preheating Step

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).

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.

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

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.

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

6000C or higher and it is more preferable to perform the

preheating treatment while a preheating temperature is set to

7000C or higher and 12800C 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

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]

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.

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.

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.

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).

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]

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.

Specifically, the reducing temperature is not

particularly limited, but is preferably set in a range of

12000C or higher and 14500C or lower and more preferably set

in a range of 13000C or higher and 14000C 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 13000C or

higher and 14000C or lower, a desired reduction reaction can

occur in a relatively short time.

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.

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 2 as a main component and containing a small amount of an oxide such as A1 2 0 3 or MgO as other components can be used.

(4) Temperature Maintenance Step

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.

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 pm

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.

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.

Specifically, the maintaining temperature of the reduced

product in the temperature maintenance step S34 is preferably

set in a high temperature of 13000C or higher and 15000C 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 13000C, 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 15000C, 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.

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).

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.

(5) Cooling Step

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.

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.

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 6000C 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>

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.

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.

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

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)

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 pm) 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 (Fe203) into metal without being in excess

or short was regarded as 100%.

Then, the mixture obtained by mixing with the mixer was

kneaded by a biaxial kneader.

(Reduction Charging Pretreatment Step)

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 p1 9 ± 1.5 mm.

(Reduction Treatment Step)

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 cooling a reduced product obtained through treating chambers 10a to 10d in the furnace are connected to the outside of the furnace was used.

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 2500C to 3500C 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 3]

Composition of solid content in dried pellet[% by mass]

Ni Fe 2 0 3 Si0 2 CaO A1 2 0 3 MgO Others

Binder, 1.6 53.3 14.0 5.4 3.2 5.7 carbonaceous reducing agent

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 7000C or higher and 12800C or lower.

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.

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 Si0 2 as a main component and

containing a small amount of an oxide such as A1 2 0 3 or MgO as

other components).

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 OOC 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.

Conditions of the reduction treatment and the temperature

maintenance treatment in the reduction treatment step are

presented in the following Table 4.

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) x 100 (%) - (i)

Nickel content rate in metal = amount of metallized Ni in

pellet + (total amount of metallized Ni and Fe in pellet) x

100 (%) •••(ii)

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 x proportion of Ni contained in ore) x 100

- Equation -. (iii)

[Table 4]

High Reducing Reducing temperature Metallized Content of Recovery Sample temperature time maintaining rate of Ni Ni in metal ra (°C) (Min.) temperature (%) (%) Mt (°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

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.

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.

Throughout this specification and the claims which follow,

unless the context requires otherwise, the word "comprise",

and variations such as "comprises" or "comprising", will be

understood to imply the inclusion of a stated integer or step

or group of integers or steps but not the exclusion of any

other integer or step or group of integers or steps.

The reference in this specification to any prior

publication (or information derived from it), or to any matter

which is known, is not, and should not be taken as, an

acknowledgement or admission or any form of suggestion that

that prior publication (or information derived from it) or

known matter forms part of the common general knowledge in the

field of endeavour to which this specification relates.

EXPLANATION OF REFERENCE NUMERALS

1 ROTARY HEARTH FURNACE

REGION

a, 10b, 10c, 10d TREATING CHAMBER (REDUCING CHAMBER,

TEMPERATURE MAINTAINING CHAMBER) DRYING CHAMBER PREHEATING CHAMBER COOLING CHAMBER

Claims

The claims defining the invention are as follows:

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 at a

temperature of 2500C or high and 3500C or lower;

a preheating step in which the dried mixture is preheated

at a temperature of 7000C or higher and 12800C or lower;

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 claim 2 or 3,

wherein the reduced product is maintained at a temperature of

13000C or higher and 15000C or lower in the temperature

maintenance step.

5. The metal oxide smelting method according to any one of

claims 1 to 4, wherein in the reduction step, reduction is

performed while a reducing temperature is set to 12000C or

higher and 14500C or lower.

6. The metal oxide smelting method according to any one of

claims 1 to 5, 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 any one of

claims 1 to 6, 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 any one of

claims 1 to 7, wherein the metal oxide is nickel oxide ore.

9. The metal oxide smelting method according to any one of

claims 1 to 8, wherein the reduced product contains

ferronickel.