U.S. patent application number 14/915811 was filed with the patent office on 2016-07-28 for zinc production method using electric furnace dust as raw material.
This patent application is currently assigned to Kinotech Solar Energy Corporation. The applicant listed for this patent is KINOTECH SOLAR ENERGY CORPORATION. Invention is credited to Masaaki IOSAKI, Shuji MORI, Yuzuru SATO.
Application Number | 20160215407 14/915811 |
Document ID | / |
Family ID | 52586779 |
Filed Date | 2016-07-28 |
United States Patent
Application |
20160215407 |
Kind Code |
A1 |
IOSAKI; Masaaki ; et
al. |
July 28, 2016 |
ZINC PRODUCTION METHOD USING ELECTRIC FURNACE DUST AS RAW
MATERIAL
Abstract
A zinc production method including a chlorination step 101 at
which crude zinc chloride vapor 3 and an oxygen gas 2 are obtained
by bringing electric furnace dust 1 containing zinc oxide or
secondary dust 1 generated at the time of reducing the electric
furnace dust in a reduction furnace into contact with a mixed gas
containing a chlorine gas 8 and an oxygen-containing gas 10,
converting a zinc oxide component in the electric furnace dust 1 or
the secondary dust 1 into zinc chloride, and vaporizing the zinc
chloride. The zinc production method further includes purification
steps 102, 104, and 105 at which a zinc chloride component
contained in the crude zinc chloride vapor 3 is separated from
components 5 and 7 other than zinc chloride contained in the crude
zinc chloride vapor 3 to obtain a purified zinc chloride melt 6,
and an electrolysis step 103 at which the purified zinc chloride
melt 6 is electrolyzed to obtain a zinc melt 9 and the chlorine gas
8.
Inventors: |
IOSAKI; Masaaki;
(Nagareyama-shi, Chiba, JP) ; MORI; Shuji;
(Fujisawa-shi, Kanagawa, JP) ; SATO; Yuzuru;
(Sendai-shi, Miyagi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KINOTECH SOLAR ENERGY CORPORATION |
Tokyo |
|
JP |
|
|
Assignee: |
Kinotech Solar Energy
Corporation
Tokyo
JP
|
Family ID: |
52586779 |
Appl. No.: |
14/915811 |
Filed: |
September 1, 2014 |
PCT Filed: |
September 1, 2014 |
PCT NO: |
PCT/JP2014/072931 |
371 Date: |
March 1, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C22B 7/02 20130101; C25B
1/26 20130101; Y02P 10/20 20151101; C25C 3/34 20130101; Y02P 10/212
20151101; C22B 19/30 20130101; C22B 19/20 20130101; C22B 19/32
20130101 |
International
Class: |
C25C 3/34 20060101
C25C003/34; C25B 1/26 20060101 C25B001/26; C22B 19/20 20060101
C22B019/20; C22B 7/02 20060101 C22B007/02; C22B 19/32 20060101
C22B019/32; C22B 19/30 20060101 C22B019/30 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 2, 2013 |
JP |
2013-181287 |
Claims
1. A zinc production method comprising: a chlorination step of
obtaining crude zinc chloride vapor by bringing electric furnace
dust containing zinc oxide or secondary dust generated at a time of
reducing the electric furnace dust in a reduction furnace into
contact with a mixed gas containing a chlorine gas and an
oxygen-containing gas, converting a zinc oxide component in the
electric furnace dust or the secondary dust into zinc chloride, and
vaporizing the zinc chloride; a purification step of obtaining
purified zinc chloride by separating a zinc chloride component
contained in the crude zinc chloride vapor from components other
than zinc chloride contained in the crude zinc chloride vapor; and
an electrolysis step of obtaining a zinc melt and a chlorine gas by
electrolyzing a molten salt electrolytic bath in which the purified
zinc chloride is melted.
2. The zinc production method according to claim 1, wherein the
purification step includes a distillation purification step of
obtaining the purified zinc chloride by distilling a melt
containing the zinc chloride component contained in the crude zinc
chloride vapor.
3. The zinc production method according to claim 1, wherein the
purification step includes a reduction purification step of
obtaining the purified zinc chloride by adding a reducing agent to
a melt containing the zinc chloride component contained in the
crude zinc chloride vapor.
4. The zinc production method according to claim 1, wherein the
purification step includes a distillation purification step of
obtaining primary purified zinc chloride by distilling a melt
containing the zinc chloride component contained in the crude zinc
chloride vapor and a reduction purification step of obtaining
secondary purified zinc chloride by adding a reducing agent to a
melt of the primary purified zinc chloride obtained at the
distillation step.
5. The zinc production method according to claim 1, wherein the
chlorine gas is obtained by electrolysis at the electrolysis
step.
6. The zinc production method according to claim 1, wherein air is
used as the oxygen-containing gas.
7. The zinc production method according to claim 3, wherein the
reducing agent is powdered metal zinc.
8. The zinc production method according to claim 3, wherein at the
reduction purification step, the reducing agent is added to molten
salt in which the zinc chloride component contained in the crude
zinc chloride vapor and alkali chloride or alkaline earth chloride
are mixed and melted.
9. The zinc production method according to claim 1, wherein at the
electrolysis step, the molten salt electrolytic bath in which the
purified zinc chloride and alkali chloride or alkaline earth
chloride are mixed and melted is electrolyzed.
Description
TECHNICAL FIELD
[0001] The present invention relates to a zinc production method,
and more particularly relates to a zinc production method using, as
a raw material, electric furnace dust generated at the time of
melting and refining of scraps in an electric furnace method, being
one of iron-making processes, or dust generated in a reduction
furnace at the time of recycling electric furnace dust as an
iron-making raw material, a non-ferrous material, or a cement
extender (hereinafter, "secondary dust").
BACKGROUND ART
[0002] Generally, in the electric furnace method, being one of the
iron-making processes, electric furnace dust is generated as
industrial waste containing zinc oxide components in an amount of
about 1.5% to 2.0% of steel production at the time of melting and
refining of scraps. It is reported that 7 million tons of electric
furnace dust are generated globally, and 0.5 million tons of
electric furnace dust are generated in Japan.
[0003] Most of iron scraps are from discarded electric appliances
or discarded automobiles. A surface for painting of the discarded
electric appliances or discarded automobiles is galvanized. Scraps
contain paint, plastic, and an oil content. Therefore, the electric
furnace dust contains hazardous organic matter such as chloride and
dioxin, in addition to heavy metals such as zinc and lead. On the
other hand, the electric furnace dust contains about 20% to 30%
iron and 20% to 30% zinc. Accordingly, the electric furnace dust is
very useful as resources.
[0004] However, it is difficult to directly use the electric
furnace dust as a raw material for aqueous electrolysis, which is a
mainstream of the current zinc production method. This is because
free iron oxide that is soluble in sulfuric acid is contained in a
large amount in the electric furnace dust, while most of zinc in
the electric furnace dust is zinc ferrite, which is a compound of
zinc oxide and iron oxide and is hardly soluble in sulfuric acid.
In addition, the electric furnace dust also contains halogen such
as chlorine, which is harmful for aqueous electrolysis. Due to
these reasons, such a zinc production method has been used that
reduces the electric furnace dust once, recovers the electric
furnace dust as crude zinc oxide, and performs electrolytic
treatment.
[0005] As mainstream recycling techniques for obtaining crude zinc
oxide from the electric furnace dust, there can be mentioned Wells
furnace method, plasma method, electric melting reduction method,
MF furnace method, or rotating bed furnace method. Currently, crude
zinc oxide produced by these recycling techniques is used as a raw
material for dry and wet zinc refining.
[0006] Under such circumstances, Patent Document 1 relates to a
zinc recovery method, and discloses a metal zinc recovery method of
recovering metal zinc from electric furnace dust containing zinc
oxide, which is generated from an iron scrap smelting furnace using
an electric furnace method or the like. Specifically, Patent
Document 1 discloses a process of mixing and kneading electric
furnace dust or secondary dust with metal iron-containing powder, a
reducing agent, a binding agent, and water, and thereafter, molding
and firing the kneaded product in a reduction furnace. Accordingly
in Patent Document 1, zinc oxide in the electric furnace dust or in
the secondary dust is recovered as metal zinc vapor.
PRIOR ART DOCUMENT
Patent Document
[0007] Patent Document 1: Japanese Patent Application Laid-open
Publication No. 2002-105550
SUMMARY OF THE INVENTION
Problem to be Solved by the Invention
[0008] However, according to studies made by the present inventors,
in the configuration disclosed in Patent Document 1, zinc oxide in
the electric furnace dust or in the secondary dust is recovered as
metal zinc vapor. Because crude zinc oxide contains a chlorine
component, removal of the chlorine component is costly at the time
of generating zinc bare metal from the crude zinc oxide. Therefore,
there is still room for improvement.
[0009] Furthermore, in the configuration disclosed in Patent
Document 1, the composition of metal zinc to be recovered has a
purity of 3N at most, and there is still room for improvement in
the purity.
[0010] According to further studies made by the present inventors,
in an electrolytic method in wet refining using crude zinc oxide as
a raw material, aqueous electrolysis of dilute sulfuric acid is
used. The current density thereof is as low as 500 A/m.sup.2.
Further, zinc bare metal grown on a cathode surface needs to be
recovered by detaching the cathode. Therefore, recovery work and
equipment therefor are required, and thus there is room for
improvement. Accordingly, in the electrolytic method in wet
refining, the size of the plant tends to become large in order to
achieve economies of scale to reduce the cost. That is, in the
current zinc production method using electric furnace dust,
electric furnace dust can be transferred to an intermediate
material, being crude zinc oxide. However, there is no other choice
but to transport crude zinc oxide into a large-scale zinc smelter,
bearing the cost of transportation.
[0011] As described above, crude zinc oxide is produced as the
secondary dust from the electric furnace dust by using large-scale
equipment and much energy. In the aqueous electrolysis, being the
mainstream of the current zinc production method, one of the
reasons for not being able to use the electric furnace dust
directly is that most of zinc in the electric furnace dust is zinc
ferrite, which is hardly soluble in sulfuric acid. If zinc in the
electric furnace dust can be directly treated, large energy saving
can be realized.
[0012] The present inventors have found that the problems described
above can be solved by extracting a zinc component in the electric
furnace dust or in the secondary dust by a chlorination process,
and then refining and treating the zinc component according to a
molten salt electrolysis method, thereby completing the present
invention.
[0013] The present invention has been achieved in view of the above
problems, and an object of the present invention is to provide a
zinc production method, which is suitable for treatment of electric
furnace dust or the like containing chlorine in a large amount
without requiring any additional cost for dechlorination, can
produce zinc bare metal having a high purity of 4N or more, and can
be operated with a compact apparatus.
Means for Solving the Problem
[0014] The basic content of the present invention is to obtain zinc
bare metal having a high purity of 4N or more by a configuration in
which electric furnace dust or secondary dust is brought into
contact with a mixed gas containing a chlorine gas and an
oxygen-containing gas, a zinc oxide component in the electric
furnace dust or the secondary dust is converted into zinc chloride
and vaporized, and then extracted as crude zinc chloride vapor.
Thereafter, the crude zinc chloride vapor is purified to obtain
purified zinc chloride in a molten state, and further treated by a
molten salt electrolysis method.
[0015] At a chlorination step of the present invention, by bringing
the electric furnace dust or the secondary dust containing zinc
oxide into contact with the mixed gas containing a chlorine gas and
an oxygen-containing gas, an iron component in the electric furnace
dust or the secondary dust is chlorinated only in a trace amount,
and most of the iron component remains as a solid. Therefore, the
zinc component in the electric furnace dust or the secondary dust
can be selectively chlorinated and vaporized.
[0016] In chlorination of the secondary dust containing mainly
crude zinc oxide, chlorination by using either only the chlorine
gas or the mixed gas containing the chlorine gas and the
oxygen-containing gas is possible. However, in a case of the
electric furnace dust, zinc ferrite needs to be chlorinated. In
this case, it is desired to chlorinate a zinc oxide component
preferentially, without chlorinating most of the iron oxide
component and free iron oxide present singly in zinc ferrite. In
the present invention, it has been found by thermodynamic studies
that the zinc oxide component can be preferentially chlorinated by
using the mixed gas containing the chlorine gas and the
oxygen-containing gas, and this fact has been confirmed by
experiments.
[0017] Furthermore, at a purification step of the present
invention, the zinc chloride component contained in the crude zinc
chloride vapor obtained at the chlorination step is separated from
components other than zinc chloride contained in the crude zinc
chloride vapor, thereby enabling to obtain purified zinc chloride.
As the components other than zinc chloride, iron chloride produced
by chlorination of a part of iron oxide, lead chloride and alkali
chloride derived from raw materials, and the like can be
considered.
[0018] As the purification step, it is preferable to adopt a
distillation step or a reduction step. Further, the distillation
step and the reduction step can be combined to adopt multiple
purification steps to be performed in this order.
[0019] When the distillation step is adopted as the purification
step, purified zinc chloride is obtained by distilling a melt
containing a zinc chloride component contained in the crude zinc
chloride vapor. Accordingly, the zinc chloride component in the
crude zinc chloride vapor is separated from metal chloride
components other than zinc chloride by using a vapor pressure
difference therebetween. As a result, the zinc chloride component
can be purified.
[0020] When the reduction step is adopted as the purification step,
by adding a reducing agent to a melt of crude zinc chloride, or
mixed molten salt of crude zinc chloride and alkali chloride or
alkaline earth chloride, a metal impurity component more noble than
zinc can be reduced and deposited, thereby purifying the zinc
chloride component. When the mixed molten salt is used, a metal
component less noble than zinc may be contained therein.
[0021] When the distillation step and the reduction step are
combined to adopt multiple purification steps to be performed in
this order, the zinc chloride component in the crude zinc chloride
vapor can be purified in a mode with a higher purity due to a
synergistic effect thereof.
[0022] At the electrolysis step of the present invention, because
the molten salt electrolytic bath contains chloride, even if the
raw material contains a chlorine component, an additional cost for
dechlorination required in the conventional method is not required.
Therefore, the electrolysis step is advantageous for treatment of
electric furnace dust or the like containing chlorine in a large
amount.
[0023] Furthermore, at the electrolysis step of the present
invention, the molten salt electrolysis method of zinc chloride is
used. Therefore, as compared to existing aqueous electrolysis in
which the current density is about 500 A/m.sup.2 per 1 m.sup.2 of
the surface area of an electrode, productivity as high as 5000
A/m.sup.2, which is 10 times that of the existing aqueous
electrolysis, can be achieved, and thus the equipment can be made
compact. Further, in the molten salt electrolysis method, if the
temperature of the electrolytic bath is set to a melting point or
higher of metal zinc, zinc bare metal to be electrolyzed and
deposited can be extracted in a molten state from the bottom of an
electrolytic cell, by using known methods such as a gas lift method
by means of an inert gas such as a nitrogen gas, a vacuum suction
method, and a method using a solid centrifugal pump. Accordingly,
detachment work of a cathode such as in the aqueous electrolysis is
not required, thereby enabling energy saving. Therefore, in a place
where electric furnace dust is generated, an on-site zinc smelter
that uses, as a raw material, electric furnace dust containing a
halogen component can be realized.
[0024] That is, in order to achieve the above object, a first
aspect of the present invention is to provide a zinc production
method including a chlorination step of obtaining crude zinc
chloride vapor by bringing electric furnace dust containing zinc
oxide or secondary dust into contact with a mixed gas containing a
chlorine gas and an oxygen-containing gas, converting a zinc oxide
component in the electric furnace dust or the secondary dust into
zinc chloride, and vaporizing the zinc chloride. The zinc
production method also includes a purification step of separating
the zinc oxide component contained in the crude zinc chloride vapor
from components other than zinc chloride contained in the crude
zinc chloride vapor to obtain purified zinc chloride, and an
electrolysis step of electrolyzing a molten salt electrolytic bath,
in which the purified zinc chloride is melted, to obtain a zinc
melt and a chlorine gas. As a specific example of the purification
step, a method of condensing and liquefying the crude zinc chloride
vaporized and separated from the electric furnace dust or the like
at the chlorination step at a specific condensation temperature,
for example, in a temperature range of about 380 .quadrature.
5.quadrature.C near the melting point of zinc chloride is
preferably used. Further, a method of purifying a part or all of
the purified zinc chloride that has been once condensed and
liquefied by repeating re-evaporation and condensation is also used
preferably, in order to obtain high purity zinc chloride. At the
purification step, one or a plurality of cooling units in order to
perform condensation and liquefaction, or condensation and
liquefaction and reflux inside a chlorination reaction device, and
a receiver arranged so that the crude zinc chloride is not mixed in
can be used. When the cooling units and the receiver arranged
corresponding to each of the cooling units are used, a temperature
different from each other can be set, thereby enabling to perform
separation and purification highly accurately. Further, the crude
zinc chloride vaporized and discharged from the chlorination
reaction device can be condensed and/or distilled in another device
separate from the chlorination reaction device.
[0025] According to a second aspect of the present invention, in
addition to the first aspect, the purification step includes a
distillation purification step of obtaining the purified zinc
chloride by distilling a melt containing the zinc chloride
component contained in the crude zinc chloride vapor.
[0026] According to a third aspect of the present invention, in
addition to the first aspect, the purification step includes a
reduction purification step of obtaining the purified zinc chloride
by adding a reducing agent to a melt containing the zinc chloride
component contained in the crude zinc chloride vapor.
[0027] According to a fourth aspect of the present invention, in
addition to the first aspect, the purification step includes a
distillation purification step of obtaining primary purified zinc
chloride by distilling a melt containing the zinc chloride
component contained in the crude zinc chloride vapor and a
reduction purification step of obtaining secondary purified zinc
chloride by adding a reducing agent to a melt of the primary
purified zinc chloride obtained at the distillation step.
[0028] According to a fifth aspect of the present invention, in
addition to any of the first to fourth aspects, the chlorine gas is
obtained by electrolysis at the electrolysis step.
[0029] According to a sixth aspect of the present invention, in
addition to any of the first to fifth aspects, air is used as the
oxygen-containing gas.
[0030] According to a seventh aspect of the present invention, in
addition to any of the third to sixth aspects, the reducing agent
is powdered metal zinc.
[0031] According to an eighth aspect of the present invention, in
addition to any of the third to seventh aspects, at the reduction
purification step, the reducing agent is added to molten salt in
which the zinc chloride component contained in the crude zinc
chloride vapor and alkali chloride or alkaline earth chloride are
mixed and melted.
[0032] According to a ninth aspect of the present invention, in
addition to any of the first to eighth aspects, at the electrolysis
step, the molten salt electrolytic bath in which the purified zinc
chloride and alkali chloride or alkaline earth chloride are mixed
and melted is electrolyzed.
Effect of the Invention
[0033] According to the zinc production method of the first aspect
of the present invention, the zinc oxide component can be
preferentially chlorinated at the chlorination step, without
chlorinating most of the iron oxide component and free iron oxide
present singly in zinc ferrite. At the distillation purification
step, the zinc chloride component contained in the crude zinc
chloride vapor obtained at the chlorination step is separated from
components other than zinc chloride contained in the crude zinc
chloride vapor, thereby enabling to obtain a purified zinc chloride
melt. At the electrolysis step, the molten salt electrolysis method
can be performed by using the purified zinc chloride melt obtained
at the purification step. Accordingly, it is possible to realize
the zinc production method that is suitable for treatment of
electric furnace dust or the like containing chlorine in a large
amount without requiring any additional cost for dechlorination,
can produce zinc bare metal having a high purity of 4N or more, and
can be operated with a compact apparatus.
[0034] According to the zinc production method of the second aspect
of the present invention, at the distillation purification step,
zinc chloride and metal chloride other than the zinc chloride are
separated from each other by using a vapor pressure difference
therebetween, and the zinc chloride component contained in the
crude zinc chloride vapor can be purified. Accordingly, purified
zinc chloride can be obtained easily and efficiently.
[0035] According to the zinc production method of the third aspect
of the present invention, at the reduction purification step, the
metal impurity component more noble than zinc in the zinc chloride
melt can be reduced and deposited as a solid, thereby enabling to
purify the zinc chloride component contained in the crude zinc
chloride vapor. Accordingly, purified zinc chloride can be obtained
easily and efficiently.
[0036] According to the zinc production method of the fourth aspect
of the present invention, the reduction purification step is
provided at a subsequent stage of the distillation purification
step and at a previous stage of the electrolysis step. At the
reduction purification step, by adding the reducing agent to zinc
chloride in a molten state, having been subjected to the
distillation purification step, a heat quantity to be consumed and
a consumed amount of the reducing agent at each step can be
complemented mutually and optimized. Accordingly, purified zinc
chloride having a higher purity can be obtained at a low cost.
[0037] According to the zinc production method of the fifth aspect
of the present invention, the chlorine gas is obtained by
electrolysis at the electrolysis step. Accordingly, a closed-cycle
zinc production method can be used, thereby enabling to reduce
generation of waste.
[0038] According to the zinc production method of the sixth aspect
of the present invention, by using air as the oxygen-containing
gas, there is no necessity of separately providing an oxygen-gas
supply source. The ambient air can be introduced easily at the
chlorination step via a supply pump.
[0039] According to the zinc production method of the seventh
aspect of the present invention, the reducing agent is the powdered
metal zinc. Therefore, the metal impurity component more noble than
zinc in the zinc chloride melt can be reduced and deposited and
separated reliably, thereby enabling to purify the zinc chloride
component contained in the crude zinc chloride vapor.
[0040] According to the zinc production method of the eighth aspect
of the present invention, at the reduction purification step, the
reducing agent is added to the molten salt in which the zinc
chloride component contained in the crude zinc chloride vapor and
alkali chloride or alkaline earth chloride are mixed and melted.
Accordingly, the alkali chloride or the alkaline earth chloride
functions as supporting salt in the molten salt electrolytic bath
at the electrolysis step at the subsequent stage. As a result, the
viscosity, the electric resistance, and the vapor pressure of the
molten salt electrolytic bath can be optimized, thereby enabling to
improve the electrolysis efficiency.
[0041] According to the zinc production method of the ninth aspect
of the present invention, at the electrolysis step, the molten salt
electrolytic bath in which the purified zinc chloride and alkali
chloride or alkaline earth chloride are mixed and melted is used.
Accordingly, the alkali chloride or the alkaline earth chloride
functions as supporting salt in the molten salt electrolytic bath.
As a result, the viscosity, the electric resistance, and the vapor
pressure of the molten salt electrolytic bath can be optimized,
thereby enabling to improve the electrolysis efficiency.
BRIEF DESCRIPTION OF THE DRAWINGS
[0042] FIG. 1 is a process chart of a zinc production method
according to an embodiment of the present invention.
[0043] FIG. 2 is a process chart of a modification of the zinc
production method according to the embodiment of the present
invention.
[0044] FIG. 3 is a process chart of another modification of the
zinc production method according to the embodiment of the present
invention.
EMBODIMENT FOR CARRYING OUT THE INVENTION
[0045] Embodiments of a zinc production method according to the
present invention will be explained below in detail with reference
to the accompanying drawings.
[0046] First, a zinc production method according to an embodiment
of the present invention is described in detail with reference to
FIG. 1.
[0047] FIG. 1 is a chart showing a process of the zinc production
method according to the embodiment of the present invention.
[0048] As shown in FIG. 1, first, at a chlorination step 101, a
mixed gas containing a chlorine gas 8 and an oxygen-containing gas
10 is brought into contact with electric furnace dust 1 or
secondary dust 1 in a chlorination furnace (not shown), thereby
obtaining a zinc oxide component in the electric furnace dust 1 or
the secondary dust 1 as crude zinc chloride vapor 3. On the other
hand, an iron component in the electric furnace dust 1 or in the
secondary dust 1 is not chlorinated and remains as a solid. The
chlorination step 101 is a reaction step to obtain the crude zinc
chloride vapor 3 from the zinc oxide component in the electric
furnace dust 1 or the secondary dust 1. The composition of the
secondary dust 1 is shown in Table 1 below.
TABLE-US-00001 TABLE 1 Zn Un- (%) Pb (%) Fe (%) Cu (%) Cd (%) Sn
(%) Si (%) melted 62.90 3.63 0.67 0.089 0.13 0.082 0.062 Trace
[0049] Specifically, at the chlorination step 101, the powdered
electric furnace dust 1 or the powdered secondary dust 1 is stored
in the chlorination furnace, and the chlorine gas or a mixed gas
containing the chlorine gas 8 and the oxygen-containing gas 10 is
caused to flow therein from a bottom side of the stored powdered
electric furnace dust 1 or powdered secondary dust 1. At the
chlorination step 101, a reaction to substitute an oxygen component
constituting metal oxide in the electric furnace dust 1 or the
secondary dust 1 with chlorine proceeds to obtain the crude zinc
chloride vapor 3, and an oxygen gas 2 is produced as a by-product.
Regarding a metal component such as iron contained in the electric
furnace dust 1 or the secondary dust 1, a part thereof is extracted
together with a zinc component and mixed in the crude zinc chloride
vapor 3 as an iron chloride gas, and the remainder thereof is
separated as a residue 4.
[0050] As an experimental example of the chlorination step 101, a
chlorination experiment was carried out by using zinc ferrite
(chemical composition formula: ZnFe.sub.2O.sub.4) synthesized from
zinc oxide and ferric oxide. Specifically, in the experimental
example, synthesized zinc ferrite was pulverized to obtain a
sample, which was stored in a reaction tube made of quartz with a
filter. A chlorine gas was then fed thereto via the filter. The
temperature at that time was 800.quadrature.C, and the chlorine gas
had a composition containing chlorine and air with a volume ratio
of 3:10. Salt was discharged as vapor due to the reaction at that
time, which was then collected. At this time, the solid sample did
not react completely and a part thereof remained. The obtained salt
and the remaining solid sample (residue) were analyzed by an ICP
emission spectrometer, to determine a molar ratio Fe/Zn of iron and
zinc. This analysis result is shown in Table 2 below.
TABLE-US-00002 TABLE 2 Object Synthesized ferrite Residue Collected
salt Fe/Zn 1.99 15.4 0.0032
[0051] As shown in Table 2, in the synthesized ferrite, Fe/Zn is
1.99, which approximately matches the stoichiometric ratio of 2.0.
Meanwhile, in the residue, iron oxide was condensed, and in the
collected salt, iron was about 0.3% of zinc. Accordingly, it is
obvious that zinc has been selectively chlorinated.
[0052] Furthermore, it became clear from calculation based on the
composition of the residue and salt that about 84% of the zinc
component in zinc ferrite was chlorinated. The chlorination
efficiency in the experiment is not so high. However, if it is
taken into consideration that the grain size of the pulverized
sample was coarse, and the temperature was relatively low, it is
assumed that the chlorination efficiency close to 100% can be
obtained by optimizing the conditions.
[0053] Further, the residue containing iron in a large amount may
be able to be used as a raw material at the time of producing pig
iron. In this case, waste can be effectively recycled.
[0054] Subsequently, at a purification step (distillation
purification step) 102, the crude zinc chloride vapor 3 obtained
through the chlorination step 101 is distilled and purified, to
obtain a purified zinc chloride melt 6.
[0055] Specifically, at the distillation purification step 102, the
crude zinc chloride vapor 3 is stored in a distillation apparatus
(not shown) lined with ceramics such as alumina and silicon carbide
having corrosion resistance against high-temperature metal
chloride. The purified zinc chloride melt 6 is separated by
utilizing a vapor pressure difference due to the difference in the
chloride. At this time, a metal chloride component 5 having a lower
boiling point than zinc chloride and a metal chloride component 7
having a higher boiling point than zinc chloride are separated from
the zinc chloride vapor 3.
[0056] Subsequently, at an electrolysis step 103, the purified zinc
chloride melt 6 obtained through the distillation purification step
102 is stored and electrolyzed in an electrolytic cell (not shown),
thereby obtaining a metal zinc melt 9, and also the chlorine gas 8
as a by-product. The result shown in Table 3 below was obtained by
analyzing the composition of the metal zinc obtained in this
manner. For the electrolytic cell used at the electrolysis step
103, as an example, an electrolytic cell housing a carbon electrode
in a container lined with ceramics can be used.
TABLE-US-00003 TABLE 3 Zn (%) Pb (%) Fe (%) Cu (%) Cd (%) Sn (%) Si
(%) 99.99 0.0002 0.0008 0.001 0.0001 0.0002 --
[0057] In the present embodiment, in terms of reducing generation
of waste by realizing a closed-cycle zinc production method, a
chlorine gas produced as a by-product in an anode at the
electrolysis step 103 can be used, as the chlorine gas 8 to be used
at the chlorination step 101.
[0058] Furthermore, as the oxygen-containing gas 10 to be used at
the chlorination step 101, ambient air easily supplied by a pump or
the like can be used instead of providing any particular oxygen gas
source.
[0059] Further, a heating furnace (a reaction distillation still)
having a configuration in which a reactor used at the chlorination
step 101 and a distillation still used at the distillation
purification step 102 are shared, which can change the gas
temperature therein in a stepwise manner can be used. In this case,
the produced crude zinc chloride vapor 3 is introduced therein, and
a low-boiling point component such as iron chloride (FeCl.sub.3) is
accumulated as a liquid or a solid in a low-temperature portion of
the heating furnace. A high-boiling point component such as sodium
chloride, potassium chloride, and lead chloride (PbCl.sub.2) is
accumulated in a high-temperature portion of the heating furnace.
In an intermediate portion between the low-temperature portion and
the high-temperature portion of the heating furnace, zinc chloride
can be condensed and produced.
[0060] At the electrolysis step 103, a molten salt electrolytic
bath in which the purified zinc chloride melt 6 and alkali chloride
or alkaline earth chloride are mixed and melted can be used.
Accordingly, in the molten salt electrolytic bath, the alkali
chloride or the alkaline earth chloride functions as supporting
salt, and the viscosity, the electric resistance, and the vapor
pressure of the molten salt electrolytic bath can be optimized,
thereby enabling to improve the electrolysis efficiency. Further,
as the alkali chloride or the alkaline earth chloride, it is more
preferable to use sodium chloride, in regards to cost and its
property as supporting salt.
[0061] According to the zinc production method of the present
embodiment, a zinc production method that is suitable for treatment
of electric furnace dust or the like containing chlorine in a large
amount without requiring any additional cost for dechlorination,
can produce zinc bare metal having a high purity of 4N or more, and
can be operated with a compact apparatus can be realized.
Particularly, at the chlorination step 101, by bringing the
electric furnace dust 1 into contact with a mixed gas containing
the chlorine gas 8 and the oxygen-containing gas 10, zinc oxide in
zinc ferrite contained in the electric furnace dust 1 can also be
chlorinated. Therefore, most of an iron component 4 is not
chlorinated and remains as a solid, thereby enabling to chlorinate
and vaporize the zinc component selectively.
[0062] In the zinc production method according to the present
embodiment, various modifications can be considered. Particularly,
the distillation purification step 102 can be replaced by a
reduction purification step 104. This modification is described in
detail with reference to FIG. 2.
[0063] FIG. 2 is a process chart of the modification of the zinc
production method according to the present embodiment.
[0064] As shown in FIG. 2, according to a zinc production method of
the present modification, the main difference from the present
embodiment is that the distillation purification step 102 of the
present embodiment described above is replaced by the reduction
purification step 104. Remaining steps are identical to those of
the present embodiment.
[0065] That is, according to the zinc production method of the
present modification, the crude zinc chloride vapor 3 obtained
through the chlorination step 101 is reduced and purified, to
obtain a purified zinc chloride melt 6'.
[0066] Specifically, at the reduction purification step 104, by
adding a reducing agent 11 to the zinc chloride melt obtained from
the crude zinc chloride vapor 3 obtained through the chlorination
step 101, and reducing and depositing a metal impurity component 12
more noble than zinc to remove the precipitate, the purified zinc
chloride melt 6' is obtained. The reducing agent 11 is preferably
powdered metal zinc, with the object of separating the metal
impurity component 12 more noble than zinc in the zinc chloride
melt by reduction and deposition efficiently and reliably.
[0067] At the electrolysis step 103, the purified zinc chloride
melt 6' obtained through the reduction purification step 104 is
electrolyzed to obtain the metal zinc melt 9, and also the chlorine
gas 8 as a by-product. Further, by cooling and solidifying the zinc
melt 9, metal zinc having a purity of 4N or more was obtained.
[0068] At the reduction purification step 104, it is preferable to
add a reducing agent to the molten salt in which alkali chloride or
alkaline earth chloride is added and melted in the zinc chloride
melt. Accordingly, in the molten salt electrolytic bath at the
electrolysis step 103 at the subsequent stage, the alkali chloride
or the alkaline earth chloride functions as supporting salt, and
the viscosity, the electric resistance, and the vapor pressure of
the molten salt electrolytic bath can be optimized, thereby
enabling to improve the electrolysis efficiency. Further, as the
alkali chloride or the alkaline earth chloride, it is more
preferable to use sodium chloride, in regards to cost and its
property as supporting salt.
[0069] Furthermore, in terms of realizing a closed-cycle zinc
production method and the like, at the reduction purification step
104, electrolytic tailing salt having been subjected to the
electrolysis step 103 is mixed with the zinc chloride melt can be
used.
[0070] As another modification of the zinc production method
according to the present embodiment, a reduction purification step
105 can be added subsequent to the distillation purification step
102. This modification is described in detail with reference to
FIG. 3.
[0071] FIG. 3 is a process chart of another modification of the
zinc production method according to the present embodiment.
[0072] As shown in FIG. 3, according to a zinc production method of
the present modification, the main difference from the present
embodiment is that the reduction purification step 105 is provided
between the distillation purification step 102 and the electrolysis
step 103 in the present embodiment described above. Remaining steps
are identical to those of the present embodiment.
[0073] That is, in the zinc production method of the present
modification, the purified zinc chloride melt 6 (primary purified
zinc chloride melt) obtained through the distillation purification
step 102 is reduced and purified, to obtain a purified zinc
chloride melt 6'' (secondary purified zinc chloride melt).
[0074] Specifically, at the reduction purification step 105, the
reducing agent 11 is added to the primary purified zinc chloride
melt 6 obtained through the distillation purification step 102 to
precipitate and remove the metal impurity component 12 more noble
than zinc, thereby obtaining the secondary purified zinc chloride
melt 6''. The reduction purification step 105 is identical to the
reduction purification step 104 in the modification described
above.
[0075] At the electrolysis step 103, the secondary purified zinc
chloride melt 6'' obtained through the reduction purification step
105 is electrolyzed, to obtain the metal zinc melt 9, and also the
chlorine gas 8 as a by-product. Further, by cooling and solidifying
the zinc melt 9, metal zinc having a purity of 4N or more was
obtained. In the present modification, the consumed amount of heat
and the reducing agent at each of the distillation purification
step 102 and the reduction purification step 105 can be
complemented mutually and optimized. Accordingly, purified zinc
chloride having a higher purity can be obtained at a low cost.
[0076] An experimental example of the present modification is
described here.
[0077] At the chlorination step 101 in the present experimental
example, electric furnace dust having a composition shown in Table
4 below was brought into contact with a mixed gas containing the
chlorine gas 8 and the oxygen-containing gas 10, in a vertical
tubular furnace, being a reaction tube, in which the reaction
temperature was maintained at 900.quadrature.C. At the chlorination
step 101, a zinc component was mainly extracted as zinc chloride
from the electric furnace dust in the tubular furnace, and
vaporized and separated. A non-volatile residue containing iron
oxide as the main component remained at a bottom portion of the
tubular furnace.
TABLE-US-00004 TABLE 4 Cd Zn (%) Pb (%) Fe (%) Cu (%) (%) Sn (%) Si
(%) Mn (%) 34.00 1.74 22.00 0.223 0.11 0.063 1.22 1.58 K Al (%) Cr
(%) Ni (%) Na (%) (%) Ca (%) Mg (%) Cl (%) 0.416 0.267 0.023 ND 0.8
1.72 0.318 4.91
[0078] Subsequently, at the distillation purification step 102,
vapor containing zinc chloride obtained at the chlorination step
101 as the main component was caused to pass through a porous body
made of ceramics at a top portion of the tubular furnace, in which
the temperature thereof was controlled to be maintained at
380.quadrature.C .quadrature. 5.quadrature.C, to be condensed and
liquefied. Accordingly, the primary purified zinc chloride melt 6
was obtained. The composition of the primary purified zinc chloride
melt 6 obtained at the distillation purification step 102 is shown
in Table 5 below, and the composition of the residue containing the
non-volatile iron oxide as the main component, which remained at
the bottom portion of the tubular furnace at the chlorination step
101 is shown in Table 6 below.
TABLE-US-00005 TABLE 5 Cu Zn (%) Pb (%) Fe (%) (%) Cd (%) Sn (%) Si
(%) Mn (%) 42.80 1.9 0.546 0.428 0.0001 0.0001 0.004 0.148 Na Al
(%) Cr (%) Ni (%) (%) K (%) Ca (%) Mg (%) Cl (%) 0.005 ND 0.013 ND
0.08 ND ND 44.5
TABLE-US-00006 TABLE 6 Cd Zn (%) Pb (%) Fe (%) Cu (%) (%) Sn (%) Si
(%) Mn (%) 0.50 0.058 45.8 0.028 0.12 0.075 6.16 3.39 K Al (%) Cr
(%) Ni (%) Na (%) (%) Ca (%) Mg (%) Cl (%) 2.69 1.05 0.028 0.146 ND
4.04 3.38 1.5
[0079] Subsequently, at the reduction purification step 105, the
primary purified zinc chloride melt 6 obtained at the distillation
purification step 102 was held in a heated molten state by
maintaining the temperature at 500.quadrature.C, in a crucible
housed in a muffle furnace in which the pressure of a gas phase was
set to a range from (atmospheric pressure--10) Pa to (atmospheric
pressure--200) Pa. With respect to the primary purified zinc
chloride melt 6 in the heated molten state, zinc powder
corresponding to about 1% by weight was added and stirred while
causing a nitrogen gas to flow therein. The top clear layer of the
melt obtained at this time was collected as the secondary purified
zinc chloride melt 6''. The composition of the secondary purified
zinc chloride melt 6'' is shown in Table 7 below.
TABLE-US-00007 TABLE 7 Zn (%) Pb (%) Fe (%) Cu (%) Cd (%) Sn (%) Al
(%) 47.60 0.0002 0.0006 0.00004 0.0007 0.001 ND Ca (%) Cr (%) Ni
(%) 0.0035 0.00003 0.00007
[0080] Finally, at the electrolysis step 103, the secondary
purified zinc chloride melt 6'' obtained through the reduction
purification step 105 was electrolyzed in an electrolytic cell, in
which the bath temperature was set to 500.quadrature.C and a carbon
electrode was stored therein, to obtain the metal zinc melt 9, of
which composition is shown in Table 8 below.
TABLE-US-00008 TABLE 8 Zn (%) Pb (%) Fe (%) Cu (%) Cd (%) Sn (%) Al
(%) 99.99 0.0001 0.001 0.0001 0.0007 0.0026 0.0004 Ca (%) Cr (%) Ni
(%) 0.0032 0.0002 0.0003
[0081] The electrolytic bath of the electrolytic cell is a mixed
salt bath in which sodium chloride is added to the secondary
purified zinc chloride melt 6'', and the composition thereof is
shown in Table 9 below.
TABLE-US-00009 TABLE 9 Zn (%) Pb (%) Fe (%) Cu (%) Cd (%) Sn (%) Al
(%) 36.73 0.00015 0.0005 0.00004 0.0007 0.001 ND Ca (%) Cr (%) Ni
(%) 0.0032 0.00003 0.00006
[0082] In the present invention, the shapes, the arrangements, the
numbers, and the like of constituent elements are not limited to
those described in the above embodiments, and it is needless to
mention that changes can be appropriately made without departing
from the scope of the invention, such as replacing these
constituent elements with other elements having equivalent
operational effects.
INDUSTRIAL APPLICABILITY
[0083] As described above, according to the present invention, it
is possible to provide a zinc production method that is suitable
for treatment of electric furnace dust or the like containing
chlorine in a large amount, without requiring any additional cost
for dechlorination and also containing zinc components in ferrite,
which is difficult to be treated in wet refining, can produce zinc
bare metal having a high purity of 4N or more, and can be operated
with a compact apparatus. Therefore, because of its general
purposes and universal characteristics, applications of the present
invention can be expected in a wide range in a zinc production
method using, as a raw material, electric furnace dust generated at
the time of melting and refining of scraps in an electric furnace
method, being one of iron-making processes or secondary dust.
* * * * *