U.S. patent application number 10/495577 was filed with the patent office on 2005-02-10 for method for producing titanium oxide containing slag.
Invention is credited to Harada, Takao, Kobayashi, Isao, Miyahara, Itsuo, Sugitatsu, Hiroshi, Tanaka, Hidetoshi, Uemura, Hiroshi.
Application Number | 20050028643 10/495577 |
Document ID | / |
Family ID | 32089193 |
Filed Date | 2005-02-10 |
United States Patent
Application |
20050028643 |
Kind Code |
A1 |
Tanaka, Hidetoshi ; et
al. |
February 10, 2005 |
Method for producing titanium oxide containing slag
Abstract
The present invention provides a method for efficiently
manufacturing a titanium oxide-containing slag from a material
including titanium oxide and iron oxide, wherein a reduction of
titanium dioxide is suppressed and the electric power consumption
is minimized. The method includes the steps of: heating a raw
material mixture including titanium oxide, iron oxide, and a
carbonaceous reductant, or the raw material mixture further
including a calcium oxide source, in a reducing furnace; reducing
the iron oxide in the mixture to form reduced iron; feeding the
resultant mixture to a heating melting furnace; heating the
resultant mixture in the heating melting furnace to melt the
reduced iron and separate the reduced iron from a titanium
oxide-containing slag; and discharging and recovering the titanium
oxide-containing slag out of the furnace.
Inventors: |
Tanaka, Hidetoshi; (Hyogo,
JP) ; Miyahara, Itsuo; (Hyogo, JP) ; Uemura,
Hiroshi; (Hyogo, JP) ; Harada, Takao; (Hyogo,
JP) ; Sugitatsu, Hiroshi; (Hyogo, JP) ;
Kobayashi, Isao; (Hyogo, JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND, MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Family ID: |
32089193 |
Appl. No.: |
10/495577 |
Filed: |
May 14, 2004 |
PCT Filed: |
August 29, 2003 |
PCT NO: |
PCT/JP03/11003 |
Current U.S.
Class: |
75/435 |
Current CPC
Class: |
C21C 5/54 20130101; C21B
13/105 20130101; C21B 13/006 20130101; C21B 13/14 20130101; Y02P
10/134 20151101; C21B 13/008 20130101; C21B 13/143 20130101; C22B
34/1281 20130101; Y02P 10/216 20151101; C21B 13/0006 20130101; Y02P
10/136 20151101; Y02P 10/23 20151101; Y02P 10/20 20151101; C22B
34/1218 20130101 |
Class at
Publication: |
075/435 |
International
Class: |
C21B 003/04 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 8, 2002 |
JP |
2002-294830 |
Claims
1. A method for manufacturing a titanium oxide-containing slag,
comprising the steps of: (A) heating a raw material mixture
including titanium oxide, iron oxide, and a carbonaceous reductant
in a reducing furnace; (B) reducing the iron oxide in the mixture
to form reduced iron; (C) feeding the resultant mixture to a
heating melting furnace; (D) heating the resultant mixture in the
heating melting furnace to melt the reduced iron and separate the
reduced iron from a titanium oxide-containing slag; and (E)
discharging and recovering the titanium oxide-containing slag out
of the furnace.
2. The method according to claim 1, wherein, in step (C), the
resultant mixture is fed to the heating melting furnace without
substantial cooling.
3. The method according to claim 1, wherein the reducing furnace is
a rotary hearth furnace.
4. The method according to claim 1, wherein the raw material
mixture is an agglomerated compact.
5. The method according to claim 1, wherein the raw material
mixture further comprises a calcium oxide source.
6. A method for manufacturing a titanium oxide-containing slag,
comprising the steps of: (A) heating a raw material mixture
including titanium oxide, iron oxide, and carbonaceous reductant in
a reducing-melting furnace; (B) reducing the iron oxide in the
mixture to form reduced iron; (c) further heating the resultant
mixture to melt the reduced iron and separate the reduced iron from
a titanium oxide-containing slag; and (D) discharging and
recovering the titanium oxide-containing slag out of the furnace,
wherein the reducing-melting furnace is a moving hearth
reducing-melting furnace.
7. The method according to claim 6, wherein the moving hearth
reducing-melting furnace is a rotary hearth furnace.
8. The method according to claim 6, wherein the reducing-melting
furnace has at least two sections in a moving direction of the
hearth; one of the section being upstream of the hearth in the
moving direction is a reduction section, the other section being
downstream of the hearth in the moving direction is a heating
melting section; and the temperature of each section is separately
controlled.
9. The method according to claim 8, wherein the temperature of the
reduction section is in the range of 1200.degree. C. to
1500.degree. C.; the temperature of the heating melting section is
in the range of 1300.degree. C. to 1500.degree. C.; and the
temperature of the heating melting section is 100.degree. C. to
300.degree. C. higher than that of the reduction section.
10. The method according to claim 6, wherein the raw material
mixture is an agglomerated compact.
11. The method according to claim 6, wherein the raw material
mixture further comprises a calcium oxide source.
Description
TECHNICAL FIELD
[0001] The present invention relates to a method for manufacturing
a titanium oxide-containing slag, in particular, to a method for
efficiently manufacturing a titanium oxide-containing slag by
reducing iron oxide, for example, in a crude ore in advance.
BACKGROUND ART
[0002] A method for manufacturing a titanium oxide-containing slag
whereby iron is separated from an ore, such as ilmenite, including
titanium oxide and iron oxide is known. As exemplified in FIG. 4,
ilmenite and a carbonaceous reductant (for example, coke or charred
coal) are fed to a submerged arc furnace (hereinafter referred to
as SAF) 9 through a feeding line of materials 1 and a feeding line
of carbonaceous reductant 2, respectively with controlling each of
the feed rates by a regulating unit for feed rate 3. The iron oxide
is reduced and melted. Molten iron is then tapped, and titanium
oxide-containing slag is tapped from an output port disposed at the
furnace wall.
[0003] Methods described below are known in the art. In a method,
ilmenite is mixed with a carbonaceous reductant such as coke and a
small amount of calcium oxide flux, and then the mixture is
agglomerated. The resultant mixture is charged in an electric
furnace and is heated, thereby separating molten iron and molten
titanium oxide-containing slag.
[0004] In another method, a required amount of molten iron is
stored in a melting furnace, and a carbonaceous material, such as
coke, pitch, or heavy oil is added to the molten iron bath, while
blowing with oxygen, thereby evaporating the carbonaceous material.
Simultaneously, titanium raw material such as magnetite sand or
titaniferous iron ore is charged in the iron bath. Metal oxides
such as iron oxide and chromium oxide in the titanium raw material
are selectively reduced, thereby increasing the content of titanium
oxide in a slag and concentrating the titanium oxide.
[0005] In the conventional method wherein separation of the iron
and the titanium oxide-containing slag is performed by reduction
and melting the iron oxide in a raw material using a melting
furnace such as the SAF, the temperature in the furnace drops due
to the action of the reductive reaction of the iron oxide, which is
an endothermic reaction. Thus, a large quantity of electric power
is required to keep the furnace temperature constant. Furthermore,
a large amount of molten FeO is generated during the process. The
molten FeO seriously damages refractories in the furnace;
therefore, it is difficult to manufacture the titanium
oxide-containing slag efficiently using the SAF. In addition, the
furnace has to be kept in a highly reducing atmosphere so as to
reduce the iron oxide. Unfortunately, the titanium oxide is also
reduced in the reducing atmosphere.
DISCLOSURE OF INVENTION
[0006] In view of the above conventional art, it is an object of
the present invention to provide a method for manufacturing a
titanium oxide-containing slag from a raw material including
titanium oxide and iron oxide, wherein the reduction of titanium
dioxide can be suppressed, the electric power consumption can be
minimized, and the titanium oxide-containing slag can be
efficiently manufactured.
[0007] In view of the above problems, according to an aspect of the
present invention, a method for manufacturing a titanium
oxide-containing slag includes the steps of: (A) heating a raw
material mixture including titanium oxide, iron oxide, and
carbonaceous reductant, or the raw material mixture further
including a calcium oxide source in a reducing furnace; (B)
reducing the iron oxide in the mixture to form reduced iron; (C)
feeding the resultant mixture to a heating melting furnace; (D)
heating the resultant mixture in the heating melting furnace to
melt the reduced iron and separate the reduced iron from a titanium
oxide-containing slag; and (E) discharging and recovering the
titanium oxide-containing slag out of the furnace.
[0008] According to the method, in the above step (C), the
resultant mixture is preferably fed to the heating melting furnace
without substantial cooling, i.e., the resultant mixture is not
preferably cooled actively. Specifically, the temperature of the
reduced mixture preferably does not drop to 350.degree. C. or less,
more preferably 650.degree. C. or less, most preferably 900.degree.
C. or less.
[0009] The reducing furnace is preferably a rotary hearth furnace.
Since the rotary hearth furnace readily controls the furnace
temperature, the reduction of the titanium dioxide to a low-valence
oxide can be suppressed and the iron oxide can be efficiently
reduced.
[0010] According to another aspect of the present invention, a
method for manufacturing a titanium oxide-containing slag includes
the steps of: (A) heating a raw material mixture including titanium
oxide, iron oxide, and carbonaceous reductant, or the raw material
mixture further including a calcium oxide source in a
reducing-melting furnace; (B) reducing the iron oxide in the
mixture to form reduced iron; (C) further heating the resultant
mixture to melt the reduced iron and separate the reduced iron from
a titanium oxide-containing slag; and (D) discharging and
recovering the titanium oxide-containing slag out of the furnace,
wherein the reducing-melting furnace is a moving hearth
reducing-melting furnace.
[0011] According to the present invention, the moving hearth
reducing-melting furnace preferably includes a rotary hearth
furnace.
[0012] Furthermore, according to the present invention, the furnace
preferably has at least two sections in a moving direction of the
hearth. One of the sections being upstream of the hearth in the
moving direction may be a reduction section and, the other section
being downstream of the hearth in the moving direction may be a
heating melting section. The temperature of each section is
preferably controlled separately.
[0013] During the steps, the temperature of the reduction section
may be in the range of 1200.degree. C. to 1500.degree. C., the
temperature of the heating melting section may be in the range of
1300.degree. C. to 1500.degree. C. Furthermore, the temperature of
the heating melting section is preferably 100.degree. C. to
300.degree. C. higher than that of the reduction section.
[0014] In terms of handling, the raw material mixture according to
the present invention is preferably an agglomerated compact. When
the agglomerated compact is used, heat transfer efficiencies in the
reducing-melting furnace or the reducing furnace can be enhanced,
thereby achieving a high productivity.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is a schematic view of an example according to an
embodiment of the present invention;
[0016] FIG. 2 is a schematic view of another example according to
an embodiment of the present invention;
[0017] FIG. 3 is a schematic view of another example according to
an embodiment of the present invention; and
[0018] FIG. 4 is a schematic view of an embodiment according to the
conventional art.
REFERENCE NUMERALS
[0019] 1 feeding line of raw materials (titanium oxide and iron
oxide)
[0020] 2 feeding line of carbonaceous reductant
[0021] 3 regulating unit for feed rate
[0022] 4 mixing unit
[0023] 5 agglomerator
[0024] 6 rotary hearth furnace (reducing furnace)
[0025] 7 cooling equipment
[0026] 8 rotary hearth furnace (reducing-melting furnace)
[0027] 9 heating melting furnace
BEST MODE FOR CARRYING OUT THE INVENTION
[0028] The present inventors have found that the above object could
be achieved by a following method, and have accomplished the
present invention. Accordingly, in a method for manufacturing a
titanium oxide-containing slag (hereinafter referred to as titanium
slag) from a raw material mixture including titanium oxide, iron
oxide, and carbonaceous reductant, or the raw material mixture
further including a calcium oxide source; a moving hearth
reducing-melting furnace is used. A method according to the present
invention includes the steps of: charging the raw material in a
reduction furnace; heating and reducing the iron oxide; charging
the resultant mixture in a heating melting furnace; and melting the
resultant mixture.
[0029] In the conventional art, a raw material mixture is charged
in a melting furnace, and the iron oxide is simultaneously reduced
and melted. As described above, according to the present invention,
the iron oxide in the raw material mixture is sufficiently reduced
in advance, and then the resultant mixture is heated and melted.
Accordingly, electric power consumption to keep the furnace
temperature can be drastically curtailed, and consumption of
electrodes can be suppressed. The generation of molten FeO can be
also reduced and wear of refractories used for the furnace walls
can be considerably suppressed. Furthermore, the problem that
titanium dioxide is reduced during the reduction of iron oxide can
be solved.
[0030] The raw material mixture used in the present invention has a
mixture including titanium oxide, iron oxide, and a carbonaceous
reductant, or the mixture further including a calcium oxide source.
The kinds of titanium oxide and iron oxide are not particularly
limited. For example, not only natural ores such as titaniferous
iron ore (ilmenite), titaniferous magnetite, and pseudobrookite,
but also byproducts during manufacturing process of titanium oxide
or titanium can be used. For example, a residue resulting from a
separation by a centrifuge, a residue resulting from a filtration
by sulphate process, and a separated residue in a chlorination
furnace in a manufacturing process of titanium oxide by chloride
process are useful. If necessary, these raw materials may be mixed.
For example, adding iron ore and steel mill waste may control the
amount of iron oxide. Adding, for example, rutile, anatase, and
synthetic rutile may control the amount of titanium oxide. Steel
mill waste is preferably blast furnace flue dust, which includes
carbon and iron oxide, because not only iron oxide but also
carbonaceous reductant can be added to the raw materials at the
same time. An example of raw material mixture including ilmenite
and carbonaceous reductant will now be described. The natural
ilmenite may be used. The ratios of titanium and iron are not
limited.
[0031] Ilmenite generally includes 40 to 60 percent by weight of
titanium oxide, and 30 to 50 percent by weight of iron oxide. The
content of iron oxide in the raw material mixture is preferably
1/20 or more, more preferably 3/20 or more so as to manufacture the
titanium slag efficiently. In that case, the melting energy of the
titanium oxide in a melting furnace can be reduced preferably by
10% or more, more preferably by 30% or more.
[0032] Natural ilmenite includes gangue, such as any amount of
SiO.sub.2. Since the gangue, such as SiO.sub.2, Al.sub.2O.sub.3,
CaO, and MgO mixed in the titanium slag degrades the purity of
titanium, the content of the gangue in the raw material mixture is
preferably small.
[0033] The carbonaceous reductant is not limited and any material
including carbon may be available. For example, coal, charred coal,
coke, oil coke, charcoal, carbide from organic material, and waste
plastics may be used. Although the composition of the carbonaceous
reductant is not limited, the amount of the carbonaceous reductant
is preferably changed so that the iron oxide is sufficiently
reduced. For example, the number of moles of the fixed carbon in
the raw material mixture is preferably same or more of that of the
oxygen combined with the iron oxide. The amount of the carbon may
be suitably controlled, because the utilization rate of the carbon
depends on the raw material and the carbonaceous reductant. The
surplus carbon for the reductive reaction can be used for
carburizing the reduced iron and is included in the resultant pig
iron. The surplus carbon can be also used for a heat source, with
burning in the melting furnace. The carbonaceous reductant may be
charged in the furnace as the mixture, or may be disposed on the
hearth in advance. Preferably, a sufficient amount of the
carbonaceous reductant may be mixed in the mixture with the other
raw material. In that case, the vicinity of the iron oxide can be
kept in a highly reducing atmosphere during reduction, thereby
suppressing reoxidation of the reduced iron.
[0034] The method for mixing the raw material mixture is not
limited. The above raw materials may be ground and may be mixed
with any mixing unit, such as a mixer to prepare the raw material
mixture. The resultant mixture may be used as powders. In terms of
easy handling, the raw material mixture may be preferably
agglomerated to form an agglomerated compact, for example, a
briquette, a pellet, and a plate by use of any forming method, such
as briquette press, tumbling agglomeration, and extrusion.
According to the present invention, a compact formed as a briquette
(hereinafter referred to as material compact) will be described as
an example.
[0035] In manufacturing material compacts, a proper amount of a
calcium oxide source, for example slaked lime or limestone, is
preferably mixed in the material compacts. In that case, the
composition of a component for titanium slag in the material
compact, i.e. a component including titanium oxide and slag
components such as SO.sub.2, Al.sub.2O.sub.3, and CaO, which are
gangue components in a material ore, and which are ash residues in
a carbonaceous material, is controlled. Accordingly, the melting
point of the titanium slag, which is formed during melting of the
reduced iron, drops and fluidity of the titanium slag increases,
thereby readily separating the titanium slag from molten iron. The
calcium oxide source may exist during the melting process. For
example, calcium oxide may be added to the raw material mixture and
then may be agglomerated to form the material compacts. The calcium
oxide source may be added to the material compacts and then the
compacts may be oxidized. Furthermore, additional calcium oxide
source may be charged in the melting process.
[0036] If the calcium oxide source is not mixed with the raw
material in the melting process, a titanium slag having high purity
in titanium is formed, because of low content of the gangue.
However, the furnace temperature has to be increased to a high
melting point of the slag, for example 1650.degree. C. to
1750.degree. C. Unfortunately, energy consumption increases,
refractories are seriously damaged, and consumption of electrodes
is increased. Accordingly, the manufacturing cost is increased.
Therefore, if necessary, the calcium oxide source may be used
depending on a product quality and the manufacturing cost.
[0037] In the agglomerating of the material compact, binders, such
as bentnite, starch, slaked lime, and organic binder may be used,
if necessary.
[0038] The reducing-melting furnace and the reducing furnace
according to the present invention are preferably a moving hearth
reducing-melting furnace and a moving hearth reducing furnace. The
moving hearth furnaces are not limited, and any furnace including a
movable hearth is useful. All kinds of moving hearth
reducing-melting furnaces and moving hearth reducing furnaces, for
example, a straight grate furnace and a rotary hearth furnace are
useful.
[0039] The moving hearth furnace is advantageous in that it can
control temperatures easily. In more detail, the moving hearth
furnace allows iron oxide to be reduced selectively and
time-efficiently, while maintaining a temperature lower than with a
conventional melting furnace or reducing furnace, i.e., a
temperature low enough to prevent reduction of titanium oxide. In
particular, a rotary hearth furnace is preferable in that a space
for installing the rotary hearth furnace is relatively small.
Furthermore, the rotary hearth furnace can control atmospheres
easily. Accordingly, while the reduction of titanium dioxide is
suppressed, a high rate of reduction of iron oxide can be
achieved.
[0040] Although an example wherein a rotary hearth furnace is used
for a reducing-melting furnace or a reducing furnace will now be
described, the method of the present invention is not limited to a
method using the rotary hearth furnace.
[0041] In operating the rotary hearth furnace, a rotary hearth is
rotated at a predetermined rate, and then material compacts may be
fed onto the rotary hearth from a charger such that the material
compacts are stacked to have an appropriate thickness. While moving
in the furnace, the material compacts charged in the rotary hearth
are heated and are reduced with combustion heat and radiation heat
by a combustion unit, for example, a combustion burner disposed at
the furnace walls. The furnace is kept in a highly reductive
atmosphere due to a large amount of CO gas, which is generated by
combustion of the carbonaceous reductant in the material compacts
by combustion heat and radiation heat. Accordingly, the iron oxide
is reduced and the gas in the furnace can be easily controlled.
Furthermore, the carbonaceous reductant enhances a reductive
potential around the material compacts, then burns in the furnace.
Accordingly, the carbonaceous reductant also functions as a fuel,
thereby reducing the consumption of a burner fuel, such as natural
gas.
[0042] When the rotary hearth furnace is used for a reduction
furnace, the iron oxide in the material compacts is completely
reduced under the reductive atmosphere in the furnace, and then is
preferably scraped with a discharger, for example, a scraper or a
screw type discharger disposed at a downstream side of the hearth
in the moving direction.
[0043] As described above, the iron oxide in the material compacts
is reduced to form reduced iron, and then the reduced iron is
heated and melted. If the iron oxide is not sufficiently reduced,
i.e., a large amount of iron oxide remains during the melting
process, molten FeO is generated, or the furnace temperature may
drop due to an endothermic reaction involved in reduction of the
iron oxide (smelting reduction or solid reduction). The endothermic
reaction during the melting process causes an increase of the
electric power consumption so as to maintain the furnace
temperature. The consumption of electrodes is also increased
herewith. Furthermore, the molten Feo seriously damages
refractories in the furnace. Accordingly, the iron oxide is
preferably reduced as much as possible before the melting process.
Specifically, if a rate of reduction of iron oxide is less than
30%, the problem due to the endothermic reaction may be occur
during heating and melting. However, if the rate of reduction of
iron oxide is preferably 60% or more, more preferably 70% or more,
most preferably 85% or more, during heating and melting, the
decrease of temperature due to the endothermic reaction is
suppressed. Accordingly, the furnace can be operated continuously
and stably without increasing the electric consumption. Of course,
decrease of the total amount of iron oxide results in decreasing
the amount of molten FeO, thereby suppressing the damage of the
refractories in the furnace as much as possible.
[0044] In order to achieve a high rate of reduction of iron oxide,
i.e., preferably 60% or more, more preferably 70% or more, most
preferably 85% or more, the furnace temperature is preferably kept
at a range of 1200.degree. C. to 1500.degree. C., more preferably
at a range of 1200.degree. C. to 1400.degree. C. The iron oxide can
be selectively and effectively reduced without reducing titanium
oxide at the temperature ranging from 1200.degree. C. to
1500.degree. C.
[0045] If the reduction temperature is below 1200.degree. C., the
reductive reaction of the iron oxide proceeds slowly. Accordingly,
the iron oxide has to be held in the furnace for a long time, which
decreases the productivity. On the other hand, if the reduction
temperature is above 1500.degree. C., titanium dioxide is also
reduced; accordingly, the recovery rate of the titanium slag is
decreased. In that case, a low melting point slag including FeO is
bled out during the reduction process. Since the slag seriously
damages the refractories used for the hearth, continuous operation
of the furnace is difficult. Although the bleeding phenomenon may
occur at the temperature ranging from 1400.degree. C. to
1500.degree. C. in some compositions of the material compacts, the
frequency and the possibility are relatively small. Accordingly,
the temperature during the reducing process is preferably
1200.degree. C. to 1500.degree. C., more preferably 1200.degree. C.
to 1400.degree. C. In the practical operation, the furnace
temperature can be set at 1200.degree. C. or less at the early step
of the reduction, and then the temperature can be increased in the
range of 1200.degree. C. to 1500.degree. C. to proceed with the
reduction.
[0046] Although the time required for completing the reduction of
iron oxide depends on the ratio of iron oxide, titanium oxide, and
the kinds of the carbonaceous material, all of which compose the
material compacts, the time for the reduction generally ranges from
five minutes to twenty minutes.
[0047] After the above reduction of the material mixture, a mixture
(hereinafter referred to as material for manufacturing titanium
slag), wherein titanium oxide is scarcely reduced while most of the
iron oxide is reduced, is formed. The shape of material for
manufacturing titanium slag does not always have the original shape
and includes various types. For example, the shape includes a shape
wherein a part of the components, such as a slag, is separated, and
a shape wherein a part of reduced iron is separated. The shape
depends on, for example, the composition of the material mixture
and the reduction condition.
[0048] Since the material for manufacturing titanium slag prepared
by the reduction of the present invention includes a small amount
of iron oxide, the above problems due to iron oxide during melting
process are suppressed. Specifically, the electric consumption is
curtailed, the consumption of electrodes is suppressed, the damage
of the refractories in the furnace is decreased, and the reduction
of the titanium dioxide is suppressed. Furthermore, since the
melting of the reduced iron is proceeded in a short time, the
reduction of titanium dioxide due to a long time process can be
avoided, thereby manufacturing a titanium oxide-containing slag
efficiently.
[0049] As described above, according to the present invention,
since iron oxide in the material is sufficiently reduced before the
heating and melting process, the resultant reduced iron melts in a
relatively short time in the heating and melting process.
Accordingly, the reduction of the titanium dioxide can be
suppressed.
[0050] If most of the carbonaceous reductant mixed in the material
compacts is consumed in the reduction process of the iron oxide,
the emission of CO gas is decreased in the melting process. In that
case, an oxidizing gas reoxidizes the reduced iron. In order to
avoid this problem, additional carbonaceous reductant may be
charged in the melting process to regulate the atmosphere in the
furnace. Keeping the reductive atmosphere in the furnace
accelerates the reduction of the remaining iron oxide; furthermore,
the melting point of the reduced iron drops due to carburizing to
the reduced iron, thereby melting the reduced iron at a relatively
low temperature. If the carbon content is not enough, the melting
point of the reduced iron does not drop sufficiently. Accordingly,
the temperature for heating and melting has to be increased to
1500.degree. C. or more. In a commercial furnace, the operation
temperature is preferably as low as possible so as to reduce a
thermal load to the refractories of the hearth. Furthermore, in
view of the melting point of the generating slag, the operation
temperature is preferably about 1500.degree. C. or less.
[0051] Accordingly, in order to rapidly melt the reduced iron at a
temperature ranging from 1300.degree. C. to 1500.degree. C., the
gas composition in the atmosphere is preferably controlled suitably
in the melting process.
[0052] In the heating and melting process described above, the
material for manufacturing titanium slag, which is manufactured in
the reduced furnace, may be charged in a heating melting furnace
such as an electric furnace, which is used for manufacturing a
conventional titanium slag, and then may be carburized and melted.
The material compacts may be charged in a moving hearth
reducing-melting furnace and reduced in the furnace, and may be
heated and melted successively.
[0053] In a process wherein the material mixture is heated in the
reducing furnace and the iron oxide in the mixture is reduced to
form reduced iron and then the resultant mixture is fed to the
heating melting furnace, the material for manufacturing titanium
slag prepared by the reduction of the iron oxide is preferably fed
to the heating melting furnace without substantial cooling.
[0054] Even though the material for manufacturing titanium slag
discharged from the reducing furnace is cooled to a temperature
below the melting point, the temperature of the material is still
in the range of about 900.degree. C. to 1300.degree. C. If the
material is cooled to room temperature and is fed to the heating
melting furnace, the thermal energy is wasted. On the other hand,
if the material is kept at the high temperature, and is fed to the
heating melting furnace, the loss of the thermal energy is reduced
and the method is very practical. The heat is substantially used
for a heat source of the melting furnace, thereby reducing the
consumption energy for heating the melting furnace. The reducing
furnace may be directly linked to the heating melting furnace by a
chute. The material may be transferred once to a container covered
with refractory, then may be charged to the heating melting
furnace. In that case, the "without substantial cooling," intends
the mixture is not cooled actively. For example, a secondary
cooling such as cooling of an apparatus component, e.g., a chute is
not included.
[0055] The heating melting furnace includes, for example, an
electric furnace and a smelting furnace using fossil fuels. Any
melting furnace used for manufacturing the titanium slag is
useful.
[0056] The heating melting furnace is preferably an arc heating
melting furnace, i.e., arc furnace, efficiently heats molten iron
by arc heat without forced stirring. Furthermore, using the arc
furnace efficiently allows reduction and melting, while suppressing
the melting damage of the refractories disposed inside of the
furnace. The arc includes a submerged arc generated by
electrification by plunging electrodes into a titanium slag, which
floats on the molten iron in the melting furnace. A material
charger is preferably disposed around an arc heating portion, i.e.,
insertion portion of the electrodes such that the material for
manufacturing titanium slag, which is charged in the arc furnace,
is rapidly reduced and melted with arc heat. A charger for
additionally charging the carbonaceous reductant may be disposed
toward the charging position of the material for manufacturing
titanium slag.
[0057] In the arc furnace, the charged material for manufacturing
titanium-slag is melted and generates molten iron. The molten iron
is incorporated one after another to molten iron, which is already
generated and retained. Gangue and titanium oxide, both of which
coexist in the compacts, form molten titanium slag. The molten
titanium slag flows together with the molten slag floating on the
molten metal. Accordingly, at a time that the molten iron and the
molten titanium slag are stored at a predetermined amount in the
arc furnace, the molten iron may be discharged one after another
from a lower position of the melting furnace, and the molten
titanium slag may be suitably discharged from a position a little
above the boundary face between the molten titanium slag and the
molten iron. The molten titanium slag and/or molten iron may be
discharged by tilting the furnace.
[0058] The molten titanium slag is cooled. Then the titanium slag
may be used as it is. Furthermore, the titanium slag may be
crushed, and then titanium oxide may be separated from other slag
components by screening. The resultant molten iron metal may be
used as a material for iron manufacture.
[0059] The reduction process and the melting process can be also
performed as a continuous process with a moving hearth furnace, for
example, a rotary hearth furnace. After the reduction process in
the rotary hearth furnace, the furnace temperature is increased in
the range of 1300.degree. C. to 1500.degree. C. to perform the
melting process. In the above two-step heating process, remaining
iron oxide is reduced and the reduced iron is melted. In that case,
both reduced iron and titanium oxide are manufactured stably and
efficiently. In the two-step heating process the rotary hearth
furnace is, for example, preferably separated to at least two
sections in the moving direction of the hearth by partition walls.
One section being disposed upstream is a reduction section; the
other section being disposed downstream is a heating melting
section. The temperature of each section and the gas composition in
the atmosphere of each section are preferably separately
controlled. The furnace may be separated to four sections or more,
by three partition walls or more, thereby controlling the
temperature and gas composition in the atmosphere precisely. Any
number of sections is possible depending on the scale and the
structure of a moving hearth reducing-melting furnace. Furthermore,
cooling equipment including any cooling unit can be installed to
cool and solidify the molten iron. Accordingly, the resultant
material is readily scraped by a discharger disposed at the
downstream portion. In this case, although a generated slag is also
discharged as a titanium slag, the slag may be separated by any
separating unit such as crushing and screening.
[0060] In order to perform the reduction and melting more smoothly
and more efficiently, the temperature in the furnace during the
melting is preferably 100.degree. C. to 300.degree. C., more
preferably 120.degree. C. to 250.degree. C. higher than that during
the reduction.
[0061] In using the reducing-melting furnace, the titanium slag may
not be melted. When the discharged products are recovered as a
mixture including iron granules and slag granules, the mixture is
crushed after discharging from the furnace and is sorted out by any
method such as magnetic separation, thereby manufacturing a slag
including a large amount of titanium.
[0062] The method for manufacturing a titanium oxide-containing
slag according to the present invention is also applied to a
vanadium oxide-containing slag and a niobium oxide-containing slag.
The material containing vanadium oxide includes a magnetite
containing titanium and vanadium, a dust by a boiler operation, and
a waste catalyst. For example, a mixture including a material,
which contains vanadium oxide and iron oxide, and a carbonaceous
reductant is charged in the reducing furnace to reduce the iron
oxide. Then the resultant mixture is melted in the melting furnace.
Vanadium oxide-containing slag is manufactured by the above method.
The material containing niobium oxide includes niobium ores such as
pyrochlore and columbite. For example, a mixture including a
material, which contains niobium oxide and iron oxide, and a
carbonaceous reductant is charged in the reducing furnace to reduce
the iron oxide. Then the resultant mixture is melted in the melting
furnace. Niobium oxide-containing slag is manufactured by the above
method. Of course, the reducing-melting furnace is useful for
performing the reduction and the melting.
EXAMPLE 1
[0063] Referring to FIG. 1, crushed carbonaceous reductant (coal,
fixed carbon: 74.0%, volatile matter: 15.5%, ash: 10.5%) and
ilmenite (TiO.sub.2: 44.4%, total Fe: 31.3% (FeO: 36.7%), SiO.sub.2
and others: rest) were fed to regulating unit for feed rate 3
through a feeding line of carbonaceous reductant 2 and a feeding
line of raw materials 1, respectively and were mixed with a mixing
unit 4 (mixer) (mixing ratio: coal 10.2 parts by weight, ilmenite
89.8 parts by weight). Molasses (about 3%) was added as a binder
and slaked lime (about 1%) was further added as a calcium oxide
source and a binder. The mixture was pressed by an agglomerator 5
(briquette press) to form briquette compacts (volume: 5.5
cm.sup.3), then the compacts were charged into a rotary hearth
furnace 6. The furnace was heated by burners disposed at the
furnace wall so that the temperature therein ranges from
1200.degree. C. to 1500.degree. C. The compacts were held in the
furnace from 5 minutes to 12 minutes on average, thereby heating
and reducing iron oxide. The conditions for heating and reducing
were controlled such that about 85% of the iron oxide was reduced
to iron. The composition of the material for manufacturing titanium
slag was as follows: TiO.sub.2: 46.03%, FeO: 6.34%, total Fe:
32.45%, and others: rest. The shape of the discharged material for
manufacturing titanium slag was briquette shape.
EXAMPLE 2
[0064] Referring to FIG. 1, the material for manufacturing titanium
slag charged from the rotary hearth furnace according to Example 1,
was continuously fed to a heating melting furnace 9, i.e., an arc
heating melting furnace disposed adjacent to the rotary hearth
furnace, so that the material does not contact the air as much as
possible, maintaining a high temperature (900.degree. C.). Then the
material was heated and melted. In the heating and melting process,
a fixed amount of molten iron was kept in the melting furnace, and
a submerged arc method was employed. Specifically, electrodes for
arc heating were plunged into the molten slag layer then were
electrically charged. The material for manufacturing titanium slag
was charged toward the vicinity of the arc heating portion, and
then melted by arc heating. According to the present embodiment,
since the material for manufacturing titanium slag discharged from
the reducing furnace included necessary carbon and calcium oxide,
additional carbonaceous reductant and flux were not required. When
a predetermined amount of molten iron was produced in the furnace,
the molten iron was discharged from a tapping hole to a ladle, and
molten titanium slag was suitably discharged from a slag outlet
disposed at a sidewall of the furnace, thereby controlling the
molten titanium slag remaining in the furnace. A resultant molten
pig iron included 4.0% carbon. The resultant titanium slag included
70.0% TiO.sub.2. According to this Example, an electric power
consumption in the arc heating electrodes was about 1340 KWh/tmi
(mi: molten iron for manufacturing).
EXAMPLE 3
[0065] The material for manufacturing titanium slag according to
Example 1 was melted in the arc heating melting furnace 9 using the
same condition in Example 2, except in that the resultant material
was stood to cooling to a room temperature in cooling equipment 7
shown in FIG. 2. Then molten titanium slag and molten iron were
manufactured.
[0066] The composition of the molten iron and the composition of
the titanium slag were the same as in Example 2. According to this
Example, however, the electric power consumption in the arc heating
electrodes was about 2020 KWh/tmi (mi: molten iron for
manufacturing).
COMPARATIVE EXAMPLE 1
[0067] The briquette compacts used in Example 1 were charged into
the heating melting furnace 9 used in Example 2, instead of being
charged into the rotary hearth furnace. That is, the iron oxide in
the compacts was not reduced in advance. Then molten titanium slag
and molten iron were manufactured from the compacts, using the same
conditions in Example 2. A resultant molten pig iron included 4.0%
carbon. The resultant titanium slag included 69.0% TiO.sub.2. A
part of the refractories used for the furnace walls was damaged.
According to this Comparative Example, the electric power
consumption in the arc heating electrodes was about 3430 KWh/tmi
(mi: molten iron for manufacturing).
EXAMPLE 4
[0068] Referring to FIG. 3, the briquette compacts used in Example
1 were reduced in the rotary hearth furnace 8 and then melted in
the same furnace. The rotary hearth furnace 8 includes two
sections, i.e., a reduction section and a heating melting section
separated by a partition wall. Iron oxide was reduced in the
reduction section using the same conditions in Example 1, and then
the resultant material was melted in the heating melting section at
a temperature in the furnace ranging from 1300.degree. C. to
1500.degree. C. The resultant molten iron and titanium slag were
cooled to about 1000.degree. C. to solidify, then were discharged
out of the furnace by a discharger. The process from charging to
discharging the material required about 8 minutes to 15 minutes.
The resultant reduced iron was a high-grade iron, which included
about 96% iron. The resultant titanium slag also included high
content of titanium (TiO.sub.2: 70%).
EXAMPLE 5
[0069] In this Example, the material including titanium oxide and
iron oxide was a residue resulting from a centrifugal separation
process during titanium oxide manufacturing by a sulphate process.
The main composition of the residue was as follows: Total Fe: 15%
to 20%, H.sub.2SO.sub.4: 10% to 15%, Mg: 1% to 2%, TiO.sub.2: 4% to
7%, and others: rest. The residue was roasted to remove moisture
and volatile components. The iron and magnesium were oxidized in
the roasted residue. The roasted residue and a carbonaceous
reductant, i.e., coal were mixed (mixing ratio: residue 80 parts by
weight, coal 20 parts by weight). The mixture was pressed by an
agglomerator to form briquette compacts. Slaked lime (0.6 parts by
weight) was added to the compacts such that basicity was 1.1, i.e.,
CaO/SiO.sub.2=1.1, thereby preparing the material compacts (100.6
parts by weight). The material compacts were fed into the rotary
hearth furnace having a hearth moving at a constant speed, such
that the material compacts were stacked to have a uniform
thickness. The iron oxide in the material was reduced at a furnace
temperature ranging from 1200.degree. C. to 1500.degree. C. Then
the resultant material was discharged from the furnace. The
material for manufacturing titanium slag was prepared (65 parts by
weight). The composition of the material for manufacturing titanium
slag was as follows: Total Fe: 70%, C: 6%, TiO.sub.2: 10%, MgO: 4%,
CaO: 1%, SiO.sub.2: 1%, and Al.sub.2O.sub.3: 1%. The material for
manufacturing titanium slag (65 parts by weight) was melted with
the arc heating melting furnace 9 as in Example 2.
[0070] After the melting process, molten pig iron (45 parts by
weight) and titanium slag (13 parts by weight) were discharged from
the melting furnace. The molten pig iron included 96% iron. The
titanium slag included 51% titanium oxide.
INDUSTRIAL APPLICABILITY
[0071] As described above, according to the present invention, iron
oxide can be reduced in a short time. Accordingly, while the
reduction of titanium dioxide is suppressed, a high rate of
reduction of iron oxide can be achieved. The material for
manufacturing titanium slag described above includes low content of
iron oxide. Accordingly, the drop in furnace temperature due to the
reductive reaction of iron oxide can be suppressed; therefore,
electric power consumption to keep the furnace temperature can be
curtailed. The generation of molten FeO can be also reduced,
thereby suppressing the damage of refractories in the furnace.
Unlike a conventional process, since a highly reductive atmosphere
in the furnace is not required, the reduction of the titanium oxide
can be suppressed. Furthermore, when the material for manufacturing
titanium slag according to the present invention is heated, the
material starts melting within a short time. Accordingly, reduction
of the titanium oxide due to a long time process can be avoided,
thereby manufacturing a titanium oxide-containing slag
efficiently.
[0072] According to the method of the present invention, the
titanium slag is efficiently manufactured from a material such as
ilmenite, including titanium oxide and iron oxide.
* * * * *