U.S. patent application number 14/705419 was filed with the patent office on 2015-08-20 for system and method for carbon dioxide solidification.
The applicant listed for this patent is Hyundai Motor Company, Kia Motors Corporation. Invention is credited to Sung Yeup Chung, Tae Young Kim, Ki Chun Lee.
Application Number | 20150232344 14/705419 |
Document ID | / |
Family ID | 47911505 |
Filed Date | 2015-08-20 |
United States Patent
Application |
20150232344 |
Kind Code |
A1 |
Kim; Tae Young ; et
al. |
August 20, 2015 |
SYSTEM AND METHOD FOR CARBON DIOXIDE SOLIDIFICATION
Abstract
Disclosed is a method for solidifying carbon dioxide into
carbonate, in which carbon dioxide is stably converted into and
solidified into carbonate (mineral facies) by using steel slag or
natural mineral by extracting an alkali component by supplying an
ammonium salt solvent as an extraction solvent to raw slag and
injecting carbon dioxide into an extract solution supplied to a
carbonation reactor to produce carbonate precipitate from the
extract solution through the induction of a conversion reaction of
the carbon dioxide into the carbonate precipitate. Then after the
above two step are performed at least one an acetic acid solvent is
supplied as an extraction solvent to the raw slag so as to finally
extract an alkali component; and carbon dioxide is injected into an
extract solution to produce carbonate precipitate from the extract
solution through the induction of a conversion reaction of the
carbon dioxide into the carbonate precipitate.
Inventors: |
Kim; Tae Young; (Suwon,
KR) ; Chung; Sung Yeup; (Seoul, KR) ; Lee; Ki
Chun; (Seoul, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Hyundai Motor Company
Kia Motors Corporation |
Seoul
Seoul |
|
KR
KR |
|
|
Family ID: |
47911505 |
Appl. No.: |
14/705419 |
Filed: |
May 6, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
13302197 |
Nov 22, 2011 |
9051189 |
|
|
14705419 |
|
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Current U.S.
Class: |
422/608 |
Current CPC
Class: |
C01B 32/60 20170801;
B01J 2219/24 20130101; C01D 7/00 20130101; C01F 11/18 20130101;
C01D 7/16 20130101; C01F 5/24 20130101; C01D 7/07 20130101; B01J
19/06 20130101; C01F 11/181 20130101 |
International
Class: |
C01B 31/24 20060101
C01B031/24; B01J 19/06 20060101 B01J019/06 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 28, 2011 |
KR |
10-2011-0098545 |
Claims
1-6. (canceled)
7. A system for solidifying carbon dioxide into carbonate, the
system comprising: an extraction reactor configured to extract an
alkali component by supplying an ammonium salt solvent as an
extraction solvent to raw slag; a carbonation reactor configured to
inject carbon dioxide into an extract solution supplied to the
carbonation reactor from the extraction reactor to produce
carbonate precipitate from the extract solution through induction
of a conversion reaction of the carbon dioxide into the carbonate
precipitate, the extract solution containing the alkali component,
wherein the extraction reactor is further configured to supply an
acetic acid solvent as an extraction solvent to the raw slag so as
to finally extract an alkali component supply ammonium salt solvent
as an extraction solvent to raw slag and injecting carbon dioxide
into an extract solution at least one time; and extraction reactor
to be configured to the reactor itself to supply the acetic acid or
ammonium salt or wherein the carbonation reactor is further
configured to inject carbon dioxide into an extract solution
supplied to the carbonation reactor to produce carbonate
precipitate from the extract solution through induction of a
conversion reaction of the carbon dioxide into the carbonate
precipitate, the extract solution containing the alkali component
extracted using the acetic acid solvent.
8. The system of claim 7, wherein ammonium salt solvent is supplied
as an extraction solvent to raw slag and carbon dioxide injected
into an extract solution several times or more, and then the acetic
acid solvent is supplied to the raw slag collected after completion
of thereof.
9. The system of claim 7, wherein the ammonium salt is any one
selected from the group including ammonium chloride, ammonium
nitrate, and ammonium acetate.
10. The system of claim 7, wherein the raw slag separately
discharged from the extract solution containing the alkali
component is collected and recycled.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims under 35 U.S.C. .sctn.119(a) the
benefit of Korean Patent Application No. 10-2011-0098545 filed on
Sep. 28, 2011, the entire contents of which are incorporated herein
by reference.
BACKGROUND
[0002] (a) Technical Field
[0003] The present invention relates to a system and method for
solidifying carbon dioxide into carbonate. More particularly, the
present invention relates to a system and method for solidifying
carbon dioxide into carbonate in which carbon dioxide is stably
converted into and solidified into carbonate (mineral facies) by
using steel slag or natural mineral.
[0004] (b) Background Art
[0005] A solidification technology of carbon dioxide into carbonate
is a system and method for disposing of separated/collected carbon
dioxide, which has been raised as an alternative technology for
geological/deep zone storage. The ultimate object of the technology
is to produce a carbon component through conversion of carbon
dioxide, and convert the produced carbon component into fuel or a
basic compound required for industrial processes.
[0006] In other words, the conversion of carbon dioxide into
another material such as carbonate provides an environmentally
friendly advantage because it removes carbon dioxide from the air
which causes global warming. Furthermore, the conversion allows
carbon dioxide to be applied as a raw material for industrial basic
materials.
[0007] As shown in FIG. 1, in conventional solidification of carbon
dioxide into carbonate by using steel slag or natural mineral, in
order to extract an alkali metal component such as calcium, acetic
acid has been used as an extraction solvent. Beneficially, it is
possible to maximize the total amount of solidified carbon dioxide
since the calcium extraction ratio of acetic acid is much higher
than those of other solvents.
[0008] However, in solidification of carbon dioxide into carbonate,
when a large amount of acetic acid is used as an extraction solvent
for extracting an alkali metal component, it is difficult to handle
the acetic acid due to strong olfactory acridity. Also, in this
case, other components of slag besides calcium may be eluted, and
thus many other impurities may be precipitated together with a
conversion reaction of carbon dioxide into carbonate. Further,
since it is required to add a large amount of sodium hydroxide
(NaOH) as a pH adjuster for a carbonate conversion reaction, an
additional cost is required. The use of sodium hydroxide
excessively produces calcium hydroxide (Ca(OH).sub.2), and thus
produces suspended solids, which interferes with the conversion of
calcium into calcium carbonate (CaCO.sub.3). Thus, the purity of
the converted calcium carbonate is low thereby requiring a lot of
additional purifying steps. This lowers economical efficiency.
[0009] In order to improve the above described problems, in the
solidification of carbon dioxide into carbonate, acetic acid has
been conventionally substituted by ammonium salt, etc. Then, the
use condition of ammonium salt has been optimized so that carbon
dioxide can be stably solidified into carbonate.
[0010] Ammonium salt is not acrid, unlike acetic acid, and is easy
to handle. Especially, in this case, the calcium extraction
selectivity is high, and thus during the extraction of calcium from
slag, other components except for calcium are hardly eluted. Also,
there is an advantage in that since a pH of a solution is increased
after the extraction, a carbonate conversion reaction can be
efficiently carried out without the addition of sodium hydroxide
during the carbonate conversion reaction. Furthermore, there is an
advantage in that since there are no other impurity components, it
is possible to collect high purity CaCO.sub.3. Thus, it is expected
to improve the economical efficiency according to a reduction of
the consumption amount of sodium hydroxide, and the collection of
high purity calcium carbonate.
[0011] However, the above described ammonium salt has a low calcium
extraction ratio, thereby reducing the ratio of solidification of
carbon dioxide. Also, the conventional method for solidifying
carbon dioxide into carbonate, as shown in FIG. 2, induces a
reaction for extracting an alkali component by using ammonium salt
at a very low concentration. Thus, the extraction ratio of calcium
from slag is very low.
[0012] Also, in the conventional method for solidifying carbon
dioxide into carbonate, as shown in FIG. 2, carbon dioxide is
injected immediately after calcium extraction without a pH
adjusting step, thereby inducing the carbonate conversion reaction.
Thus, the final amount of converted carbonate is also not large
enough.
[0013] The above information disclosed in this Background section
is only for enhancement of understanding of the background of the
invention and therefore it may contain information that does not
form the prior art that is already known in this country to a
person of ordinary skill in the art.
SUMMARY OF THE DISCLOSURE
[0014] The present invention has been made in an effort to solve
the above-described problems associated with the prior art. The
present invention provides a system and method for solidifying of
carbon dioxide into carbonate. In the system and method, the use of
high concentration ammonium salt increases the calcium extraction
selectivity, and increases a pH of an extract solution. This
minimizes the amount of sodium hydroxide, and induces an efficient
carbonate conversion reaction. Also, in the system and method, the
use of acetic acid for final extraction of an alkali component
increases the amount of solidified carbon dioxide. This not only
induces an efficient carbonate conversion reaction but also
maximizes the amount of solidified carbon dioxide.
[0015] In one aspect, the present invention provides a system and
method for solidifying carbon dioxide into carbonate, the method
including the steps of: (a) extracting an alkali component by
supplying an ammonium salt solvent as an extraction solvent to raw
slag; (b) injecting carbon dioxide into an extract solution
supplied to a carbonation reactor to produce carbonate precipitate
from the extract solution through induction of a conversion
reaction of the carbon dioxide into the carbonate precipitate, the
extract solution containing the alkali component; (c) supplying an
acetic acid solvent as an extraction solvent to the raw slag so as
to finally extract an alkali component; and (d) injecting carbon
dioxide into an extract solution supplied to the carbonation
reactor to produce carbonate precipitate from the extract solution
through induction of a conversion reaction of the carbon dioxide
into the carbonate precipitate, the extract solution containing the
alkali component extracted in step (c).
[0016] Preferably, the steps (a) and (b) are carried out once or
are repeated several times or more, and then the steps (c) and (d)
are carried out by supplying the acetic acid solvent to the raw
slag collected after completion of the steps (a) and (b). Also,
preferably, between the steps (a) and (b), a pH adjuster may be
selectively added in order to increase the pH of the extract
solution containing the alkali component from 8.about.9 to 12.
[0017] Also, the ammonium salt may be any one selected from the
group including ammonium chloride, ammonium nitrate, and ammonium
acetate, and the raw slag may be separately discharged from the
extract solution containing the alkali component is collected and
recycled.
[0018] Other aspects and exemplary embodiments of the invention are
discussed infra.
[0019] In the inventive method for solidifying of carbon dioxide
into carbonate, only an alkali component such as calcium from raw
slag is selectively extracted in a solution phase, and is
solidified into carbonate precipitation through a reaction with
carbon dioxide in a gas phase. Thus, it is possible to reduce
carbon dioxide and also effectively produce and collect calcium
carbonate as precipitation.
[0020] Also, in the present invention, it is possible to collect
high purity carbonate by using ammonium salt as an extraction
solvent. Thus, it is possible to reduce a process time and a cost
for purifying, compared to conventional low purity carbonate
obtained by physical pulverization. Furthermore, it is possible to
make at least several times higher profit than that of the low
purity carbonate. Finally, in the present invention, it is possible
to reduce the cost for disposal of slag by collecting low-basicity
slag and recycling it as aggregate.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] The above and other features of the present invention will
now be described in detail with reference to certain exemplary
embodiments thereof illustrated in the accompanying drawings which
are given hereinbelow by way of illustration only, and thus are not
limitative of the present invention, and wherein:
[0022] FIG. 1 is a flow chart schematically showing a
solidification method of carbon dioxide into carbonate, according
to a conventional method;
[0023] FIG. 2 is a flow chart schematically showing a
solidification method of carbon dioxide into carbonate, according
to another conventional method; and
[0024] FIG. 3 is a flow chart schematically showing a
solidification method of carbon dioxide into carbonate, according
to the exemplary embodiment of the present invention.
[0025] It should be understood that the appended drawings are not
necessarily to scale, presenting a somewhat simplified
representation of various preferred features illustrative of the
basic principles of the invention. The specific design features of
the present invention as disclosed herein, including, for example,
specific dimensions, orientations, locations, and shapes will be
determined in part by the particular intended application and use
environment.
DETAILED DESCRIPTION
[0026] Hereinafter reference will now be made in detail to various
embodiments of the present invention, examples of which are
illustrated in the accompanying drawings and described below. While
the invention will be described in conjunction with exemplary
embodiments, it will be understood that the present description is
not intended to limit the invention to those exemplary embodiments.
On the contrary, the invention is intended to cover not only the
exemplary embodiments, but also various alternatives,
modifications, equivalents and other embodiments, which may be
included within the spirit and scope of the invention as defined by
the appended claims.
[0027] The present invention provides an optimum solidification
method, in which high concentration ammonium salt is used so as to
increase the selective extraction ratio of calcium, and to increase
the pH of an extract solution. This minimizes the amount of sodium
hydroxide to be used, thereby inducing an efficient carbonate
conversion reaction. Meanwhile, ammonium salt is effective in the
collection of high purity carbonate, but shows a lower calcium
extraction ratio than acetic acid. Thus, the total amount of
solidified carbon dioxide is small. In order to complement this
disadvantage, in the final extraction of an alkali component from
raw slag, acetic acid is used instead, thereby increasing the
amount of solidified carbon dioxide. This not only induces an
efficient carbonate conversion reaction but also increases the
total amount of solidified carbon dioxide.
[0028] Accordingly, in the present invention, two kinds of solvents
including ammonium salt and acetic acid are sequentially used so
that calcium carbonate of good quality can be collected from a
limited amount of slag (steel by-product) or natural minerals, and
the total amount of solidified carbon dioxide can be maximized.
[0029] For this, in the present invention, when natural minerals,
steel slag, and electric arc furnace slag, which contain alkali
components such as calcium, magnesium, are used to solidify carbon
dioxide, high concentration ammonium salt is used to extract
calcium ions and to obtain an extract solution of pH 8 or more
during extraction and carbonation reaction processes at room
temperature and atmospheric pressure. Then, a small amount of a pH
adjuster is added to adjust the pH of the extract solution supplied
to a carbonation reactor, and carbon dioxide is injected into the
extract solution, thereby inducing an effective carbonate
conversion reaction.
[0030] In the present invention, since a slag used for solidifying
carbon dioxide through carbonation includes electric arc furnace
slag as well as steel slag, it is possible to recycle the electric
arc furnace slag which typically is wasted. Also, in the use of
ammonium salt during the process at room temperature and
atmospheric pressure, high concentration ammonium salt of 80 g/L is
used as an extraction solvent. This increases the extraction ratio
of calcium, compared to a conventional technology. Furthermore, the
pH is increased up to 12 by the addition of a small amount of the
pH adjuster, and then a carbonation reaction of carbon dioxide is
induced. Accordingly, it is possible to collect a large amount of
calcium carbonate of good quality, compared to a conventional
technology.
[0031] Also, in the final step of the present invention, acetic
acid is used as an extraction solvent so as to increase the
extraction ratio of calcium. This allows the total amount of
solidified carbon dioxide to be maximized.
[0032] In other words, since the calcium extraction selectivity of
ammonium salt is high, it is possible to obtain high purity calcium
carbonate. Also, due to the use of high concentration ammonium
salt, the pH of the extraction solution is increased, which allows
a carbonate conversion reaction to be effectively carried out.
Subsequently, acetic acid is used as an extraction solvent, thereby
increasing the extraction ratio of an alkali component. This
increases the total amount of solidified carbon dioxide.
[0033] Hereinafter, the present invention will be described in
detail with reference to FIG. 3.
[0034] First, in an alkali component extraction reactor 10, a
process for extracting an alkali component is carried out. For
example, a raw mineral or slag (e.g., all slags produced by an iron
manufacturing process, and an electric arc furnace steelmaking
process) are supplied to the alkali component extraction reactor 10
while a high concentration extraction solvent is supplied. Then,
stirring is carried out for a predetermined time.
[0035] In the alkali component extraction reactor 10, in order to
extract an alkali component such as calcium from the slag (a
by-product of an iron manufacturing process), various kinds of
slags and extraction solvents may be used. As the extraction
solvents, high concentration ammonium salt (ammonium chloride,
ammonium nitrate, and ammonium acetate) and acetic acid may be
sequentially used.
[0036] Herein, first, in order to produce and collect high purity
carbonate from a mineral and slag, high concentration ammonium salt
is used as an extraction solvent, thereby efficiently inducing a
carbonation reaction. Then, subsequently while extracting an alkali
metal component, acetic acid is used as an extraction solvent,
thereby increasing the amount of solidified carbon dioxide. Thus,
the slag (with reduced basicity) from which the alkali metal
component has been extracted and separated can be recycled as
aggregate.
[0037] Ammonium salt has a pH of 6. When raw slag together with
high concentration ammonium salt is added to the alkali component
extraction reactor 10 and stirred, a solution including an extract
of an alkali component such as calcium (Ca), that is, an alkali
component-containing extract solution extracted from the slag by
the ammonium salt as an extract solvent, has a pH of 8.about.9. In
other words, the slag introduced into the alkali component
extraction reactor 10 is stirred until an extract solution of pH
8.about.9 is obtained.
[0038] In order to adjust the pH of the extract solution from
8.about.9 to 12, before the extract solution is supplied to the
carbonation reactor 20, sodium hydroxide (NaOH) as a pH adjuster is
added to the extract solution.
[0039] Meanwhile, since the extract solution has a relatively high
pH of 8.about.9, in some cases, it may be directly used for the
carbonation reaction without a pH adjusting step. In other words,
without a step for adjusting the pH of the extract solution from
8.about.9 to 12, the extract solution may be directly supplied to
the carbonation reactor 20.
[0040] Then, the solution containing an extracted alkali component,
with a pH of 12, that is, the extract solution, is supplied to the
carbonation reactor 20 while carbon dioxide is supplied from a
carbon dioxide supplying means 30 to the carbonation reactor 20.
Accordingly, the extract solution (containing an alkali metal
component) of pH 12 flows into the carbonation reactor 20 while
carbon dioxide is injected and converted into carbonate precipitate
through reaction with the extract solution. In this manner, the
carbonate reaction is induced within the carbonation reactor 20
while the carbonate precipitate is produced from the extract
solution. In other words, carbon dioxide in gas phase is directly
injected into the carbonation reactor 20, is reacted with alkali
ions at pH 12, and becomes dissolved carbonate. Then, through
separation of precipitate/solution, precipitated high purity
carbonate is obtained. Herein, the extract solution from which
carbonate has been separated has a pH of 6.about.7.
[0041] As described above, the extract solution containing an
alkali metal component extracted from slag is subjected to a
carbonation reaction at room temperature and atmospheric pressure,
and thereby carbon dioxide can become carbonate with a high
conversion ratio and can be fixed. Then, the raw slag, which is
separated from the extract solution and discharged from the alkali
component extraction reactor 10, is collected again into the alkali
component extraction reactor 10 for recycling.
[0042] The above described process for producing and obtaining high
purity carbonate by using ammonium salt as an extract solution may
be carried out once or may be repeated several times or more. Then,
after the process for producing high purity carbonate by the
ammonium salt is completed, acetic acid is finally used as an
extract solvent so as to produce an extract solution (pH 4)
containing an alkali metal component extracted from the slag at a
high extraction ratio.
[0043] In the treatment of carbon dioxide with acetic acid as an
extraction solvent, first, the raw slag recycled into the alkali
component extraction reactor 10 is added with acetic acid, and
stirred. Then, a solution including an extract of an alkali
component such as calcium (Ca), that is, an alkali
component-containing extract solution extracted from the slag by
the acetic acid as an extract solvent, is produced. The slag
collected into the alkali component extraction reactor 10 is
stirred until an extract solution of pH 4 is obtained.
[0044] In order to adjust the pH of the extract solution from 4 to
12, before the extract solution with pH 4 is supplied to a
carbonation reactor 21, sodium hydroxide (NaOH) as a pH adjuster is
added to the extract solution. Then, the extract solution with an
adjusted pH of 12 is supplied to the carbonation reactor 21 while
carbon dioxide is supplied from a carbon dioxide supplying means 31
to the carbonation reactor 21.
[0045] Accordingly, the extract solution (containing an alkali
metal component) of pH 12 flows into the carbonation reactor 21
while carbon dioxide is injected and converted into carbonate
precipitate through reaction with the extract solution. In this
manner, the carbonate reaction is induced within the carbonation
reactor 21 while the carbonate precipitate is produced from the
extract solution. In other words, carbon dioxide in gas phase is
directly injected into the carbonation reactor 21, is reacted with
alkali ions at pH 12, and becomes dissolved carbonate. Then,
through separation of precipitate/solution, precipitated carbonate
is obtained. Herein, the extract solution from which carbonate has
been separated has a pH of 6.about.7.
[0046] As described above, the extraction reaction is carried out
with high efficiency by using acetic acid as a solvent so as to
greatly reduce the alkali component within raw slag. Then, through
the carbonation reaction induced by injection of carbon dioxide
into the extract solution, it is possible to maximize the total
amount of solidified carbon dioxide. Also, the finally collected
slag can have an appropriate low basicity and can be recycled as
aggregate.
Examples
[0047] The following examples illustrate the invention and are not
intended to limit the same.
[0048] Hereinafter, the present invention will be described in
detail with reference to Examples, but the Examples do not limit
the scope of the present invention. For example, the slag used in
Examples below is only intended to explain a specific embodiment,
and in actuality, various kinds of slags can be used.
Example
[0049] A carbonation reaction for converting carbon dioxide into
carbonate was carried out by using steel slag as a raw material and
using ammonium chloride as a solvent. First, 100 g of steel slag
was introduced into an alkali component extraction reactor, and 1 L
of an ammonium chloride solution including ammonium chloride
dissolved in water was introduced as an extract solvent in the
extraction reactor. Herein, ammonium chloride was used in an amount
of 93.5 g/1.74 mol % with respect to 100 g of steel slag, and the
pH of the solution was about 6.
[0050] Then, in the alkali component extraction reactor, the slag
and the solution were stirred by using an impeller at 150 rpm for
about 30 minutes, and then, an extract solution containing a
calcium component eluted from the slag, and the slag were
separately discharged by using a filter. Herein, the pH of the
extract solution ranged from 8 to 9, and sodium hydroxide as a pH
adjuster was added so as to adjust the pH to 12.
[0051] Next, in a carbonation reactor, carbon dioxide in a gas
phase was directly injected at a flow rate of 2 L/min into the
extract solution containing the calcium component, and thereby a
reaction producing calcium carbonate was induced through a reaction
of carbon dioxide with calcium ions. While carbon dioxide was
injected to the extract solution, precipitate of calcium carbonate
was produced within the carbonation reactor. The reaction was
carried out until the pH of the extract solution became 7 to 6.
Then, the injection of carbon dioxide was finished, and the
precipitate was separated from the solution so as to provide high
purity calcium carbonate.
[0052] After the first extraction reaction as described above, the
amount of extracted calcium was only 15.about.20% of calcium oxide
(CaO) of the initial steel slag. Thus, the basicity of the slag was
not sufficiently lowered. In order to complement the lower calcium
extraction ratio with respect to acetic acid, the slag which has
been already used was collected and used for a re-extraction
reaction. In other words, the first calcium extraction reaction
using ammonium chloride was repeatedly carried out once more so as
to carry out the carbonation reaction of carbon dioxide.
[0053] The amount of calcium extracted by repeating the calcium
extraction reaction using ammonium chloride as an extraction
solvent several times was not large. However, after the extraction,
the calcium extraction selectivity was high during the conversion
reaction of carbon dioxide into carbonate. Thus, it was possible to
obtain calcium carbonate of good quality through a direct reaction
of calcium ions and carbon dioxide.
[0054] In this manner, by repeating the alkali metal component
extraction reaction using ammonium salt as an extraction solvent
several times, it is possible to produce and collect high purity
calcium carbonate.
[0055] Next, in order to improve the amount of solidified carbon
dioxide by finally increasing the extraction ratio of calcium from
slag, in a last calcium extraction process, acetic acid with a
calcium extraction ratio of 90% or more was used as a solvent while
the component of calcium oxide of slag was greatly reduced by an
extraction reaction in an alkali component extraction reactor.
Then, the extract solution with an adjusted pH of 12 was introduced
into a carbonation reactor, and carbon dioxide was injected
thereto. Through a carbonation reaction, carbon dioxide was
solidified. In other words, by the extract solution containing the
extracted calcium content at a high concentration, carbon dioxide
was carbonated, so that the total amount of solidified carbon
dioxide was maximized.
[0056] The slag separately discharged during calcium extraction
using acetic acid had a low basicity appropriate for recycling as
an aggregate due to the great reduction of calcium oxide because
calcium was extracted with a high extraction ratio.
[0057] In the Example above, the alkali component extraction
reaction using ammonium salt as an extraction solvent was repeated
twice, and finally, acetic acid was used as an extraction solvent
so as to increase the amount of solidified carbon dioxide. Thus, it
was possible to produce and collect calcium carbonate with a high
purity, and maximize the total amount of solidified carbon
dioxide.
[0058] According to the kinds of extraction solvent (such as
ammonium salt and acetic acid) for extraction of an alkali metal
component, a calcium extraction ratio and a calcium carbonate
conversion ratio were noted in Table 1 below.
TABLE-US-00001 TABLE 1 Ca CaCO.sub.3 extraction conversion kind of
solvent ratio ratio ammonium chloride 15~20% 93% (ammonium salt)
acetic acid 90% or more 25%
[0059] As noted above, in the present invention, for the initial
extraction of an alkali component, ammonium salt having a high
extraction selectivity of the alkali component is used as a
solvent, and thus, other components are hardly eluted from the
slag. Furthermore, the pH of the extract solution becomes 8 or more
during the process, thereby reducing the amount of a pH adjuster by
up to 50% or more. Accordingly, the amount of operating time and
cost is reduced. Also, the suspended solids caused by the
production of calcium hydroxide (Ca(OH).sub.2) (a residual product
of sodium hydroxide (NaOH)) are eliminated. Thus, high-purity and
high-quality calcium carbonate precipitate without an additional
post-treatment and an additional purifying step are obtained. This
makes it easy to produce calcium carbonate henceforth.
[0060] As described above, the subsidence high-purity calcium
carbonate obtained by chemical precipitation achieves economical
efficiency at least several times higher than conventional calcium
carbonate obtained by physical pulverizing. However, in the case
where only the conventional ammonium salt is used as a solvent, the
extraction selectivity of an alkali component is high while the
extraction ratio of the alkali component is very low with respect
to acetic acid. Furthermore, the amount of solidified carbon
dioxide is small, and the reduction extent of basicity of slag is
low. Thus, it is difficult to recycle the slag as an aggregate.
[0061] Accordingly, in the present invention, in order to increase
the amount of solidified carbon dioxide, first, the step of
collecting high purity carbonate from slag by using ammonium salt
is carried out at least once, and then, in the final step, acetic
acid is used to increase the usability of slag as an aggregate and
the amount of solidified carbon dioxide.
[0062] As described above, in the present invention, in solidifying
carbon dioxide through carbonation, ammonium salt and acetic acid
are sequentially used. Thus, the effect of a conventional acetic
acid solvent is maintained while the disadvantage of an ammonium
salt solvent is complemented. This causes additional effects such
as the collection of high purity carbonate, and the reduction of an
amount of a pH adjuster. Then, finally, economical efficiency is
also improved.
[0063] The invention has been described in detail with reference to
exemplary embodiments thereof. However, it will be appreciated by
those skilled in the art that changes may be made in these
embodiments without departing from the principles and spirit of the
invention, the scope of which is defined in the appended claims and
their equivalents.
* * * * *