CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims priority under 35 USC § 119 to Korean Patent Application
No.
10-2012-0051834 filed on May 16, 2012 in the Korean Intellectual Property Office (KIPO), the entire disclosure of which
is incorporated by reference herein in its entirety.
BACKGROUND
1. Field
[0002] Example embodiments of the present invention relate to methods and systems for recovering
a metal. More particularly, example embodiments of the present invention relate to
methods for recovering a metal from solution, systems for recovering a metal from
solution, and systems for recovering lithium from salt water.
2. Description of the Related Art
[0003] Lithium (Li) is widely utilized in various industries such as glasses, ceramics,
alloys, lubricating oils, pharmaceutics, etc. Particularly, a lithium secondary battery
has been recently highlighted and developed for a power supply of a hybrid vehicle
and an electric vehicle. A demand for the lithium secondary battery is expected to
surge up to about 100 times a demand in a compact battery market for, e.g., a cell
phone, a laptop computer, etc.
[0004] Further, a demand for lithium may be increased drastically as global environmental
restrictions are becoming strengthened, and an application of lithium may be expanded
to various industries of 21
st century including electronic, chemical and energy industries as well as the hybrid
and electric vehicles industry.
[0005] A source of lithium may include a mineral, a brine or a sea water. The mineral may
include spodumene, petalite and lepidolite which contain a relatively large amount
of lithium in a range of about 1 % to about 1.5 %. However, an extraction of lithium
from the mineral may require many complex processes such as a floatation, an annealing,
a grinding, an acid mixing, an extraction, a purification, an concentration, a precipitation,
etc., and thus large cost and energy may be spent during the processes. Further, an
environmental pollution may be caused by an acid used in the extraction of lithium.
[0006] When lithium is recovered from the sea water, a recovery device including an adsorbent
may be introduced into the sea water so that lithium may be selectively adsorbed,
and then lithium may be recovered by an acid treatment. However, a concentration of
lithium in the sea water is as small as about 0.17 ppm, and thus the recovery from
the sea water may be limited from an economical aspect.
[0007] Considering the above problems, lithium is mainly recovered from the brine. For example,
a salt lake is used as a crude source of lithium, and other salts including Mg, Ca,
B, Na or K co-exist therein together with lithium.
[0008] A concentration of lithium in the brine may range from about 0.3 g/L to about 1.5
g/L, and lithium in the brine may be extracted as a form of lithium carbonate. A solubility
of lithium carbonate may be about 13 g/L. Even though lithium in the brine is assumed
to be completely converted into lithium carbonate, a concentration of lithium carbonate
in the brine may range from about 1.59 g/L to about 7.95 g/L which is smaller than
the solubility of lithium carbonate. Thus, precipitated lithium carbonate may be re-dissolved
thereby to reduce a recovery ratio of lithium.
[0009] Accordingly, a conventional method for recovering lithium in the brine as the form
of lithium carbonate includes pumping the brine from a natural salt lake and storing
in an evaporation pond, naturally vaporizing the brine for a long period more than
a year to concentrate lithium as great as several ten times, and removing impurities
such as Mg, Ca or B by a precipitation so that lithium may be recovered at an amount
greater than the solubility of lithium carbonate.
[0010] However, the conventional method requires much time for the vaporization and the
concentration of the brine to reduce an overall productivity. Further, lithium may
be precipitated together with the impurities during the vaporization and the concentration
steps to cause a loss of lithium, and the method is limited in a rainy season.
SUMMARY
[0011] Example embodiments of the present invention provide a method for efficiently recovering
various metals from a solution.
[0012] Example embodiments of the present invention provide a system for recovering various
metals from a solution.
[0013] Example embodiments of the present invention provide a system for recovering various
metals such as lithium from a salt water.
[0014] According to an aspect of the present inventive concepts, there is provided a method
for recovering a metal from a solution. In the method, a first electrode that includes
a metal for recovery and a second electrode that includes a metal different from the
metal for recovery are prepared. The first electrode and the second electrode are
immersed in a first solution that includes a metal ion for recovery. The metal ion
for recovery in the first solution is combined with the first electrode. The first
electrode and the second electrode are charged while immersing the first and second
electrodes in a second solution different from the first solution so that the metal
ion for recovery is separated from the first electrode. The metal for recovery is
recovered from the second solution.
[0015] In example embodiments, in combining the metal ion for recovery in the first solution
with the first electrode, the first electrode and the second electrode which are positively
and negatively charged, respectively, may be electrically connected to induce a discharge.
[0016] In example embodiments, the metal for recovery may include lithium, the first electrode
may include a lithium manganese oxide, and the second electrode may include silver,
zinc, copper and/or mercury.
[0017] According to an aspect of the present inventive concepts, there is provided a system
for recovering a metal from a solution. The system includes a first electrode including
a first metal, a second electrode including a second metal different from the first
metal, and a power source for charging the first and second electrodes. The first
electrode is discharged in a first solution that includes a first metal ion to be
combined with the first metal ion and is charged in a second solution different from
the first solution to release the first metal ion. The second electrode is discharged
in the first solution to be combined with a first anion of the first solution and
is charged in the second solution to release the first anion.
[0018] In example embodiments, the first electrode may include a lithium manganese oxide,
and the second electrode may include silver, zinc, copper and/or mercury.
[0019] In example embodiments, the first electrode may include LiMn
2O
4 having a spinel phase.
[0020] In example embodiments, the first electrode may further include a carbon electrode,
and the lithium manganese oxide may be coated on a surface of the carbon electrode.
[0021] In example embodiments, the system may further include a battery capable of repeating
charge and discharge processes. An electric energy generated when the first and second
electrodes are discharged may be stored in the battery, and the battery may be connected
to the power source to provide the stored electric energy.
[0022] According to an aspect of the present inventive concepts, there is provided a system
for recovering lithium from a salt water. The system includes a first electrode including
a lithium manganese oxide, a second electrode including silver, a power source for
charging the first and second electrodes, and a battery capable of repeating charge
and discharge processes. The first electrode is discharged in a salt water that includes
a lithium ion and a chlorine ion to be combined with the lithium ion and is charged
in a charging solution different from the salt water to release the lithium ion. The
second electrode is discharged in the salt water to be combined with the chlorine
ion and is charged in the charging solution to release the chlorine ion. The battery
stores an electric energy generated when the first electrode is discharged and is
connected to the power source to provide the stored electric energy.
[0023] In example embodiments, the first electrode may include LiMn
2O
4 having a spinel phase.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] Example embodiments will be more clearly understood from the following detailed description
taken in conjunction with the accompanying drawings.
FIG. 1 is a flow chart illustrating a method for recovering a metal from a solution
in accordance with example embodiments;
FIGS. 2 and 3 are schematic views illustrating a system for recovering a metal from
a solution in accordance with example embodiments;
FIG. 4 is a graph showing concentration changes of a lithium ion and a sodium ion
present in a discharging solution while repeating charge and discharge processes in
a lithium recovery process of Example 1;
FIG. 5 is a graph showing concentration changes of a lithium ion, a calcium ion, a
potassium ion, a magnesium ion and a sodium ion present in a discharging solution
while repeating charge and discharge processes in a lithium recovery process of Example
2; and
FIG. 6 is a graph showing a concentration change of a lithium ion present in a charging
solution while repeating charge and discharge processes in a lithium recovery process
of Example 2.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0025] Various exemplary embodiments will be described more fully, in which some exemplary
embodiments are shown. The present inventive concept may, however, be embodied in
many different forms and should not be construed as limited to the exemplary embodiments
set forth herein. Rather, these exemplary embodiments are provided so that this description
will be thorough and complete, and will fully convey the scope of the present inventive
concept to those skilled in the art.
[0026] The terminology used herein is for the purpose of describing particular example embodiments
only and is not intended to be limiting of the present inventive concept. As used
herein, the singular forms "a," "an" and "the" are intended to include the plural
forms as well, unless the context clearly indicates otherwise. It will be further
understood that the terms "comprises" and/or "comprising," when used in this specification,
specify the presence of stated features, integers, steps, operations, elements, and/or
components, but do not preclude the presence or addition of one or more other features,
integers, steps, operations, elements, components, and/or groups thereof.
[0027] Example embodiments are described herein with reference to cross-sectional illustrations
that are schematic illustrations of idealized example embodiments (and intermediate
structures). As such, variations from the shapes of the illustrations as a result,
for example, of manufacturing techniques and/or tolerances, are to be expected. Thus,
example embodiments should not be construed as limited to the particular shapes of
regions illustrated herein but are to include deviations in shapes that result, for
example, from manufacturing. For example, an implanted region illustrated as a rectangle
will, typically, have rounded or curved features and/or a gradient of implant concentration
at its edges rather than a binary change from implanted to non-implanted region. Likewise,
a buried region formed by implantation may result in some implantation in the region
between the buried region and the surface through which the implantation takes place.
Thus, the regions illustrated in the figures are schematic in nature and their shapes
are not intended to illustrate the actual shape of a region of a device and are not
intended to limit the scope of the present inventive concept.
[0028] Unless otherwise defined, all terms (including technical and scientific terms) used
herein have the same meaning as commonly understood by one of ordinary skill in the
art to which this inventive concept belongs. It will be further understood that terms,
such as those defined in commonly used dictionaries, should be interpreted as having
a meaning that is consistent with their meaning in the context of the relevant art
and will not be interpreted in an idealized or overly formal sense unless expressly
so defined herein.
Methods for Recovering a Metal from a Solution
[0029] FIG. 1 is a flow chart illustrating a method for recovering a metal from a solution
in accordance with example embodiments.
[0030] Referring to FIG. 1, in step S10, a first electrode and a second electrode may be
immersed in a first solution containing a metal ion for recovery, and the metal ion
in the first solution may be combined with the first electrode. In example embodiments,
the first electrode and the second electrode may be positively and negatively charged,
respectively, and the first and second electrodes may be electrically connected to
cause a discharge so that the metal ion for recovery in the first solution may be
combined with the first electrode.
[0031] Preferably, before electrically connecting the first and second electrodes, the first
electrode may be positively charged and the second electrode may be negatively charged.
[0032] A metal for recovery may not be specifically limited, however, may include, e.g.,
lithium, sodium, potassium, magnesium, calcium, strontium, manganese, etc.
[0033] The first solution may be obtained, e.g., a sea water or a highly concentrated brine
(or a salt water). The first solution may further include other metal ions and anions
in addition to the metal ion for recovery. For example, if the metal for recovery
is lithium, the first solution may include cations of lithium, sodium, potassium,
magnesium, calcium, strontium, manganese, etc., and a chlorine anion (Cl
-).
[0034] The first electrode may include the metal for recovery. For example, if the metal
for recovery is lithium, the first electrode may also include lithium. Preferably,
the first electrode may have a selectivity for the metal for recovery. For example,
if the metal for recovery is lithium, the first electrode may include a lithium manganese
oxide (LMO). Specifically, the LMO may include LiMn
2O
4, LiMnO
6, etc., and these may be used alone or in a combination thereof. The selectivity for
a lithium ion of the LMO may vary according to a phase of the LMO. Preferably, the
LMO may have a spinel phase.
[0035] Preferably, the second electrode may include a metal different from the metal for
recovery. Further, the metal of the second electrode may have an ionization tendency
greater than that of the metal for recovery. Thus, when the first and second electrodes
are electrically connected to each other, the first electrode may serve as an anode
(positive electrode) and the second electrode may serve as a cathode (negative electrode).
Preferably, the metal of the second electrode may be selected in consideration of
the ionization tendency of the metal for recovery, for example, may include silver,
zinc, copper, mercury, etc. The second electrode may preferably include the metal
that may be combined with and separated from an anion reversibly and repeatedly in
charge and discharge processes. Thus, silver may be used as the metal of the second
electrode in consideration of the reversibility and an environmental aspect.
[0036] When the first and second electrodes are electrically connected to each other, the
discharge may occur. In the discharge, electrons may be moved from the first electrode
to the second electrode. The metal ion for recovery in the first solution may accept
the electron to be combined with the first electrode, and the metal of the second
electrode may lose the electron to be combined with an anion in the first solution.
In an embodiment, the first electrode may include LiMn
2O
4, the second electrode may include silver, and the first solution may include the
lithium cation and the chlorine anion. In this case, a reaction represented by Chemical
Equation 1 may occur in the first electrode, and a reaction represented by Chemical
Equation 2 may occur in the second electrode.
[Chemical Equation 1] Li
1-xMn
2O
4 + xLi+ + xe
- → LiMn
2O
4
[Chemical Equation 2] xAg + xCl
- → xAgCl + xe
-
[0037] As indicated in the above equations, the lithium ion in the first solution may be
combined with the LMO of the first electrode, and the chlorine ion in the first solution
may be combined with silver of the second electrode to generate silver chloride. As
a result, concentrations of the lithium and chlorine ions in the first solution may
be reduced.
[0038] In example embodiments, the LMO included in the first electrode may have the selectivity
for lithium, and thus lithium may be selectively separated from the first solution
containing the different metal ions.
[0039] In example embodiments, the positively charged first electrode and the negatively
charged second electrode may be electrically connected to each other for discharging
the first and second electrodes. However, alternatively, a power source may be connected
to the first and second electrodes, the first electrode may be negatively charged
(electrons may be provided), and the second electrode may be positively charged so
that the lithium ion in the first solution may be combined with the first electrode.
[0040] Subsequently, in step S20, the first and second electrodes may be immersed in a second
solution different from the first solution and may be charged so that the metal ion
for recovery may be separated from the first electrode. The second solution may be
an aqueous solution including suitable electrolytes.
[0041] In a case that the first electrode includes LiMn
2O
4 and the second electrode includes silver chloride, the first and second electrodes
may be charged such that the first electrode may be positively charged and the second
electrode may be negatively charged to cause a reaction represented by Chemical Equation
3 in the first electrode and a reaction represented by Chemical Equation 4 in the
second electrode.
[Chemical Equation 3] LiMn
2O
4 → Li
1-xMn
2O
4 + xLi+ + xe
-
[Chemical Equation 4] xAgCl + xe
- → xAg + xCl
-
[0042] As a result, the LMO of the first electrode may lose the lithium ion, and silver
chloride of the second electrode may lose the chlorine ion to be reduced into silver.
Accordingly, the second solution may include the lithium cation and the chlorine anion.
[0043] Subsequently, in step S30, the metal for recovery may be recovered from the second
solution. Various conventional methods may be implemented for recovering the metal.
[0044] For example, when the second solution includes the lithium cation and the chlorine
anion, the second solution may be heated to obtain a solid-state lithium chloride.
Lithium chloride may be non-toxic and chemically stable, and thus easily stored and
managed. Additionally, lithium chloride may be directly used as an electrolyte of
a lithium secondary battery.
[0045] In other examples, the second solution including the lithium cation and the chlorine
anion may be treated by an electrolysis to collect lithium.
[0046] Before recovering the metal, the discharge process in the first solution and the
charge process in the second solution described above may be repeated so that a concentration
of the metal for recovery in the second solution may be increased. The first electrode
may be positively charged and the second electrode may be negatively charged by the
charge process in the second solution. The first and second electrodes may be taken
out from the second solution, and immersed and electrically connected to each other
again in the first solution so that the lithium ion in the first solution may be combined
again with the first electrode by the discharge process. If the concentration of the
metal for recovery in the second direction becomes increased, a recovery efficiency
of the metal may be improved.
[0047] According to example embodiments of the present invention, a metal may be efficiently
recovered from a solution. Specifically, highly concentrated lithium may be obtained
in a short time compared to conventional methods using vaporization/concentration
of brine and adsorption from a sea water. Further, the method in accordance with example
embodiments may include simple processes and may be relatively free from an environmental
pollution. Additionally, an electric energy generated from the discharge process may
be stored and reused to minimize an energy consumption.
[0048] The method in accordance with example embodiments may be used for recovering a metal
from a sea water or a highly concentrated brine, and may be also used for recovering
a metal from an industrial wastewater.
[0049] Hereinafter, a system for implementing the method for recovering a metal from a solution,
and a system for recovering lithium from a brine are described in detail with reference
to accompanying drawings.
Systems for Recovering a Metal from a Solution and Systems for Recovering Lithium
from a Brine
[0050] A system for recovering a metal from a solution according to example embodiments
may comprise a first electrode including a first metal and a second electrode including
a second metal different from the first metal. The first and second electrodes may
be electrically connected to each other. The first electrode may be discharged in
a first solution including a first metal ion to be combined with the first metal ion,
and may be charged in a second solution different from the first solution to release
the first metal ion. The second electrode may be discharged in the first solution
to be combined with a first anion of the first solution, and may be charged in the
second solution to release the first anion. The system may include a power source
for charging the first and second electrodes.
[0051] FIGS. 2 and 3 are schematic views illustrating a system for recovering a metal from
a solution in accordance with example embodiments.
[0052] Referring to FIG. 2, a first solution 30 may be accommodated in a first bath 40.
A first electrode 10 and a second electrode 20 may be immersed in the first solution
30. For example, the first electrode 10 and the second electrode 20 may be partially
immersed in the first solution 30 such that upper portions thereof may be exposed
from the first solution 30. In some embodiments, the first and second electrodes 10
and 20 may be entirely immersed in the first solution 30.
[0053] The first solution 30 may include a metal ion for recovery. In example embodiments,
a metal for recovery may be lithium. The first solution 30 may be a sea water or a
highly concentrated brine (or salt water), and may further include sodium, potassium,
magnesium, calcium, strontium, manganese, etc., in addition to lithium. The first
solution 30 may also include an anion. If the first solution 30 is the sea water or
the highly concentrated brine, the first solution may mainly include a chlorine anion
(Cl
-).
[0054] The first electrode 10 may include the metal for recovery. For example, if the metal
for recovery is lithium, the first electrode 10 may also include lithium. Preferably,
the first electrode 10 may have a selectivity for the metal for recovery. For example,
if the metal for recovery is lithium, the first electrode 10 may include a lithium
manganese oxide (LMO). Specifically, the LMO may include LiMn
2O
4, LiMnO
6, etc., and these may be used alone or in a combination thereof. The selectivity for
a lithium ion of the LMO may vary according to a phase of the LMO. Preferably, the
LMO may have a spinel phase.
[0055] The LMO may have a relatively low conductivity. Thus, the first electrode 10 may
further include an additional material having a relatively strong conductivity. For
example, the first electrode 10 may include a carbon electrode containing graphite,
carbon nanotube, graphene, etc., and the LMO may be at least partially coated on a
surface of the carbon electrode. A wire for electrically connecting the first electrode
10 and the second electrode 20 may be connected to the carbon electrode.
[0056] Specifically, the first electrode 10 may include a mixture of powders of the LMO
and graphite, and the mixture may be at least partially coated on the surface of the
carbon electrode. For example, a positive electrode material composition including
the LMO, the powder of graphite, a binding agent and a solvent may be coated on the
carbon electrode, and dried to obtain the first electrode 10. For example, the binding
agent may include polyvinyliden fluoride (PVDF), polyvinyl alcohol (PVA), polyurethane
(PU), etc. These may be used alone or in a combination thereof. For example, the solvent
may include an alcohol such as methanol, ethanol, propanol, butanol, etc. These may
be used alone or in a combination thereof.
[0057] The second electrode 20 may include a metal different from the metal for recovery.
Further, the metal of the second electrode 20 may have an ionization tendency greater
than that of the metal for recovery. Thus, when the first and second electrodes 10
and 20 are electrically connected to each other, the first electrode 10 and the second
electrode 20 may serve as an anode and a cathode, respectively. Preferably, the metal
of the second electrode 20 may include silver, zinc, copper, mercury, etc. In example
embodiments, the second electrode 20 may include silver.
[0058] The first and second electrodes 10 and 20 may be electrically connected to each other
through the wire for a discharge process. Preferably, before electrically connecting
the first and second electrodes 10 and 20, the first electrode 10 may be positively
charged, and the second electrode 20 may be negatively charged to result in the discharge
process of the first and second electrodes 10 and 20.
[0059] In example embodiments, the first electrode 10 may include LiMn
2O
4, the second electrode 20 may include silver, and the first solution 30 may include
the lithium cation and the chlorine anion. Therefore, when the first and second electrodes
10 and 20 are electrically connected to each other, the lithium cation of the first
solution 30 may be combined with the LMO of the first electrode 10, and the chlorine
anion of the first solution 30 may be combined with silver of the second electrode
20 to generate silver chloride. As a result, concentrations of the lithium and chorine
ions may be reduced in the first solution 30.
[0060] The first and second electrodes 10 and 20 may be connected to a battery 50. An electric
energy generated from the discharge process may be stored in the battery 50. The battery
50 may be also used as a power source in a charge process described below. The battery
50 may include any conventional battery capable of repeating charge and discharge
processes of an electric energy. For example, a lead storage battery, a mercury battery,
a lithium ion battery, a lithium polymer battery, etc., may be used as the battery
50.
[0061] Referring to FIG. 3, the first and second electrodes 10 and 20 after the discharge
process may be immersed in a second solution 60 accommodated in a second bath 70.
[0062] When the first and second electrodes 10 and 20 are positively and negatively charged,
respectively, by charging the first and second electrodes 10 and 20, the LMO of the
first electrode 10 may lose the lithium ion and silver chloride of the second electrode
20 may lose the chlorine ion to be reduced into silver. Accordingly, the second solution
60 may include the lithium cation and the chlorine anion.
[0063] The first and second electrodes 10 and 20 may be connected to a suitable power source
for charging the first and second electrode 10 and 20. The power source may be connected
to the battery 50, and the electric energy stored in the battery may be utilized so
that an energy efficiency may be improved.
[0064] By repeating the charge and discharge processes illustrated in FIGS. 2 and 3, a highly
concentrated lithium ion may be achieved, and lithium may be recovered as a form of,
e.g., a lithium salt from the lithium ion solution.
[0065] In example embodiments, the first and second bath 40 and 70 may be separated from
each other. However, the discharge process may be performed in the first solution,
and then the first solution may be replaced with the second solution to perform the
charge process continuously in a single container.
[0066] According to example embodiments, highly concentrated lithium may be obtained in
a short time compared to conventional methods using vaporization/concentration of
brine and adsorption from a sea water. Further, the method or the system in accordance
with example embodiments may include simple processes and may be relatively free from
an environmental pollution. Additionally, an electric energy generated from the discharge
process may be stored and reused to minimize an energy consumption.
[0067] Hereinafter, a method for recovering a metal from a solution, a system for implementing
the method, and a system for recovering lithium from a brine are described in detail
with reference to specific Examples.
Example 1
[0068] A silver electrode of 3x3 cm
2, and a graphite electrode of the same size were prepared. A powder of LiMn
2O
4, Super-P (manufactured by Timcal, Swiss) as a graphite powder, and PVDF as a binder
resin were mixed in a mixing ratio of about 80:10:8 to form a mixture. The mixture
was dispersed in ethanol, coated on the graphite electrode and dried to prepare an
electrode for lithium recovery.
[0069] The electrode for lithium recovery and the silver electrode were immersed with a
distance of about 1 cm therebetween in a charging solution of about 90 ml including
lithium chloride of about 25 mM. A power source was connected to the electrodes to
provide a charging voltage of about 1.2 V for about 20 minutes. Accordingly, the electrode
for lithium recovery was positively charged, and the silver electrode was negatively
charged.
[0070] Subsequently, the electrode for lithium recovery and the silver electrode were immersed
in a discharging solution of about 90 ml including lithium chloride of about 25 mM
and sodium chloride of about 25 mM. The electrode for lithium recovery and the silver
electrode were connected through a wire to be discharged for about 30 minutes.
[0071] The charge and discharge processes were repeatedly performed three times. On completion
of each cycle (including one charge process and one discharge process), a sample of
about 1 ml was extracted from the discharging solution, and concentration changes
of lithium and sodium ions were measured using a ion-chromatography apparatus, DX-120
(manufactured by DIONEX). The results are shown in FIG. 4.
Example 2
[0072] A silver electrode of 3x3 cm
2, and a graphite electrode of the same size were prepared. A powder of LiMn
2O
4, Super-P (manufactured by Timcal, Swiss) as a graphite powder, and PVDF (weight average
molecular weight: ∼ 534,000, glass transition temperature: -38 °C, density at 25 °C:
1.74 g/ml, manufactured by Sigma Aldrich, USA) as a binder resin were mixed in a mixing
ratio of about 80:10:8 to form a mixture. The mixture was dispersed in ethanol, coated
on the graphite electrode and dried to prepare an electrode for lithium recovery.
[0073] The electrode for lithium recovery and the silver electrode were immersed with a
distance of about 1 cm therebetween in a charging solution of about 80 ml including
lithium chloride of about 30 mM. A power source was connected to the electrodes to
provide a charging voltage of about 1.2 V for about 20 minutes. Accordingly, the electrode
for lithium recovery was positively charged, and the silver electrode was negatively
charged.
[0074] Subsequently, the electrode for lithium recovery and the silver electrode were immersed
in a discharging solution of about 80 ml including lithium chloride of about 30 mM,
sodium chloride of about 30 mM, potassium chloride of about 30 mM and magnesium chloride
of about 30 mM. The electrode for lithium recovery and the silver electrode were connected
through a wire to be discharged for about 40 minutes.
[0075] The charge and discharge processes were repeatedly performed four times. On completion
of each cycle (including one charge process and one discharge process), a sample of
about 1 ml was extracted from the discharging solution, and concentration changes
of lithium, potassium, calcium, magnesium and sodium ions were measured using a ion-chromatography
apparatus, DX-120 (manufactured by DIONEX). The same amount of a sample was extracted
from the charging solution, and a concentration change of a lithium ion was measured.
The results are shown in FIGS. 5 and 6.
[0076] FIG. 4 is a graph showing concentration changes of the lithium ion and the sodium
ion present in the discharging solution while repeating the charge and discharge processes
in Example 1. FIG. 5 is a graph showing concentration changes of the lithium ion,
the calcium ion, the potassium ion, the magnesium ion and the sodium ion present in
the discharging solution while repeating the charge and discharge processes in Example
2. FIG. 6 is a graph showing a concentration change of the lithium ion present in
the charging solution while repeating the charge and discharge processes in Example
2.
[0077] Referring to FIG. 4, the concentration of the lithium ion was continuously decreased
while repeating the charge and discharge processes in Example 1, however, the concentration
of the sodium ion was substantially maintained without a reduction. Therefore, it
can be acknowledged that the lithium ion may be selectively recovered from a mixture
with the sodium ion using the method and the system for recovering a metal from a
solution according to example embodiments.
[0078] Referring to FIG. 5, the concentration of the lithium ion was continuously decreased
while repeating the charge and discharge processes in Example 2, however, the concentrations
of the calcium ion, the potassium ion and the sodium ion were substantially maintained
without a reduction. The concentration of the magnesium ion was decreased in a first
cycle, and then substantially maintained without a reduction in the subsequent cycles.
Referring to FIG. 6, the concentration of the lithium ion was continuously increased
in the charging solution while repeating the charge and discharge processes. Therefore,
it can be acknowledged that the lithium ion may be selectively recovered from a mixture
with the sodium ion, the potassium ion, the calcium ion and the magnesium ion using
the method and the system for recovering a metal from a solution according to example
embodiments.
[0079] The sodium and magnesium ions are significantly present in the sea water and the
highly concentrated brine which may be sources of lithium. Particularly, magnesium
may have a solubility similar to that of lithium, and thus may not be easily separated
by a vaporization method. The presence of these ions may be a main factor reducing
an efficiency in a lithium recovery process. Therefore, the method and the system
for recovering a metal from a solution according to example embodiments may be implemented
to efficiently recover lithium from the sea water and the highly concentrated brine.
[0080] The foregoing is illustrative of example embodiments and is not to be construed as
limiting thereof. Although a few example embodiments have been described, those skilled
in the art will readily appreciate that many modifications are possible in the example
embodiments without materially departing from the novel teachings and advantages of
the present inventive concept. Accordingly, all such modifications are intended to
be included within the scope of the present inventive concept as defined in the claims.
Therefore, it is to be understood that the foregoing is illustrative of various example
embodiments and is not to be construed as limited to the specific example embodiments
disclosed, and that modifications to the disclosed example embodiments, as well as
other example embodiments, are intended to be included within the scope of the appended
claims.