This invention relates to a method and apparatus for extracting lithium,
particularly a method and an apparatus for efficiently extracting only a lithium
component from a solution containing lithium and impurities.
In recent years metallic lithium or lithium compounds such as lithium
salts, have been used in various fields. Their application typically includes lithium
batteries, lithium-containing ceramic materials, coolant adsorbents, pharmaceuticals,
aluminum alloying materials, and nuclear fusion fuel materials, and the like. The
metallic lithium or lithium compounds have been obtained from Li-containing ore,
such as spodumene, amblygonite, petalite, and lepidolite; brine; or geothermal
water. For example, the lithium is extracted from these raw materials, in the form
of a lithium salt, by adsorption using an adsorbent (e.g., aluminum hydroxide)
or electrolysis using an ion-exchange membrane made of resin. Having found a use
as a power source of small-sized appliances, such as watches, cameras, calculators,
and IC cards, lithium batteries have been enjoying a drastically increasing demand,
and used lithium batteries have been increasing concomitantly. Accordingly, attention
has been paid to the reuse or recycle of the lithium component from the used lithium
batteries.
Of the above-mentioned extraction methods, the adsorption method
hardly produces high purity lithium salts due to the low extraction efficiency
so that a step of purification is needed. Therefore, this method may be disadvantageous
from the standpoint of labor and cost. On the other hand, the electrolysis method
is a technique in which lithium (Li) ions are electrically moved through an ion-exchange
membrane made of resin. The efficiency by the electrolysis method is not satisfactory
because not only Li ions but hydrogen ions pass through the ion-exchange membrane
.
An object of the present invention is to provide a method and apparatus
for extracting lithium at high purity and high efficiency from aqueous solution
containing lithium.
Another object of the present invention is to provide a method and
apparatus for concentrating or rather condensing a lithium-containing liquid.
A still another object of the present invention is to provide a method
and apparatus for efficiently refining a liquid containing lithium and impurities.
A further object of the present invention is to provide a method
and apparatus for efficiently purifying an aqueous solution containing lithium.
A still further object of the invention is to provide a method and
apparatus for accelerating extraction of lithium ions from an aqueous solution.
A still further object of the invention is to provide a method and
apparatus for efficiently and inexpensively producing a lithium salt of high purity
from an aqueous solution containing lithium.
According to an aspect of the present invention, the foregoing and
the other objects are attained by the method and apparatus, wherein a lithium-ion
conducting solid electrolyte is utilized as a partition (or rather separator) which
separates an aqueous solution containing lithium (ie the crude liquid from which
lithium is to be extracted) from a lithium-collecting solution and wherein a means
for applying an electric field (or rather voltage) across said partition is so
arranged that only lithium ions are forced to transfer through said partition from
said crude solution to said lithium-collecting solution. More specifically, the
present invention provides a method for extracting lithium from a crude liquid
containing at least lithium ions; which comprises bringing the crude liquid into
contact with one side of the partition constituted mainly of a lithium-ion conducting
solid electrolyte (hereinafter referred to as an Li solid electrolyte or simply
as a solid electrolyte) while bringing another liquid (hereinafter referred to
as recovery liquid) into contact with the other side of the partition, and applying
an electrical field across the partition in such a manner that the crude liquid
side is positive and the recovery liquid side is negative thereby to selectively
extract the lithium from the crude liquid through the partition into the recovery
liquid.
The apparatus for carrying out the method of the present invention
basically comprises (1) the partition constituted mainly of the Li solid electrolyte,
(2) a chamber (hereinafter referred to as a feed chamber), formed on one side of
the partition, into which feed chamber the crude liquid containing at least lithium
ions is introduced so as to come into contact with the partition , (3) another
chamber(hereinafter referred a recovery chamber) for collecting lithium, formed
on the other side of the partition, into which recovery chamber a liquid for collecting
lithium (hereinafter referred to as a recovery liquid) is introduced so as to
come into contact with the partition , and (4) a means for applying an electrical
field (or voltage) across the partition in such a manner that the crude liquid
is positive and the recovery liquid is negative thereby to selectively allow the
lithium in the form of ions of the crude liquid to pass through the partition
into the recovery chamber .
In the above-described method, the Li solid electrolyte comprises
a perovskite-type solid electrolyte represented by the formula: (Lax,Liy)TiOz,
wherein x=2/3a, y=3a-2b, z=3-b, 0<a≤1/6, 0≤b≤0.06, and y>0, or
the perovskite-type solid electrolyte with part of the La ions substituted with
metal ions having a larger ionic radius than that a La ion.
According to one aspect of the present invention, only Li ions but
no other ions are transferred through the Li solid electrolyte because other element
ions can not pass through the partition . The perovskite type Li
ion solid electrolyte is better than other solid electrolytes for accomplishment
of the invention because the perovskite type Li ion solid electrolyte as defined
above does not deteriorate and does not chemically react with water even under
an electric field.
With the aid of an electric field (voltage) applied across partition
separating the crude and recovery liquids, extraction of a high purity lithium
or lithium component is accelerated and condensation of lithium in the recovery
liquid is attained to the extent that a lithium concentration in the recovery
liquid is higher than that of in crude liquid. The perovskite-type solid electrolyte
exhibits excellent Li ion selectivity and has a high bulk ion conductivity even
at room temperature. Besides, it is activated stably even in the presence of water.
Therefore, according to the invention, the industrialization of efficient
extraction of lithium from aqueous solution, including refinement, condensation
and recovery or recycling is attained efficiently, easily and/or precisely. Further,
by reacting the extracted lithium with other compounds such as CO2 a
lithium salt, such as Li2CO3
can be easily mass produced at
high purity.
Fig. 1 is a model showing the crystal structure of a lithium ion
conducting solid electrolyte of perovskite type to be utilized in the present invention.
Fig. 2 is a schematic drawing illustrating a imaginary mechanism
of lithium ion conduction in the-lithium-ion conducting solid electrolyte.
Fig. 3(a) is a sectional view of essential part of the apparatus
according to the present invention, which uses a lithium ion conducting solid electrolyte
as a partition along which mesh electrodes are arranged, illustrating a basic mechanism
of a selective extraction of lithium from a crude solution containing lithium
and other components through the partition.
Fig(3)b shows a chemical reactions of lithium ions with other components,
in a crude liquid and a recovery liquid respectively.
Fig. 4 is a schematic vertical sectional view of an example of the
apparatus according to the invention.
Fig. 5(a) is a schematic vertical sectional view of another example
of the apparatus according to the invention.
Fig.5(b) is a schematic vertical sectional view of the apparatus
for obtaining lithium in a form of lithium salt, according to an embodiment of
the invention.
Fig. 6(a) is a schematic structure of a partition comprising plates
made of lithium-ion conducting solid electrolyte, used in one of the embodied apparatus
according to the invention.
Fig.6(b) is a vertical sectional view of the partition of Fig5 (a),
assembled with mesh electrodes across which electric field is applied to cause
lithium ions to pass through the partition.
Fig. 7 is a schematic vertical sectional view of still another example
of the apparatus of the invention, wherein a tube of lithium ion solid electrolyte,
having one end closed but the other end open, is used as a partition separating
a crude lithium liquid from a lithium recovery liquid.
Fig. 8 is a perspective exploded view of the partition and the mesh
electrodes of the apparatus as shown in Fig. 7.
Fig. 9 (a) shows an assembly of a plurality of the tubular partitions
of Fig.8 used in the apparatus embodied according to the invention.
Fig.9(b) is a perspective view and a vertical sectional view of an
apparatus using the plurality of partitions as shown in Fig.9 (a), embodied according
to the invention. Fig. 10 is a perspective view of another partition having a honeycomb
structure usable in the apparatus according to the invention.
Fig. 11(a) is a schematic vertical section showing yet another example
of the apparatus in which the partition of Fig. 10 is used.
Fig.11(b) is a schematic plan view showing a top portion of the apparatus
shown in Fig. 11(a).
Fig. 12 is a schematic vertical section showing a modification of
the apparatus of Fig. 11, in which the recovery liquid is made to flow along the
wall of the partition.
The lithium-extracting apparatus according to the present invention
takes the following three basic inventive elements in combination.
The first inventive element is characterized by that the partition
made of lithium-ion conducting solid electrolyte is used for extracting lithium
only from the crude liquid containing lithium.
The partition used here can have the form of a plate as shown by
the reference numeral 2 in Fig.3 (a), on one surface of which the feed chamber
3 is formed, and on the other surface of which the recovery chamber 4 is provided.
The partition 2 of such a simple shape as plate can be prepared by, for example,
firing a ceramic green sheet composed of stoichiometric mixture of raw materials.
The electrodes 5,6 covering over the surface of the plate partition 3 may be made
of a metallic mesh. As shown in Figs. 6 (a) and 6 (b), the partition 2 may be made
up of a plurality of segments 41 with gaps between them. Every gap between the
adjacent segments 41 being sealed so as to prevent the liquids from passing through
and mixed up. By such a manipulation, the partition having such a large area as
could hardly be formed of an integral Li solid electrolyte can easily be made up.
There is no fear of the two liquids' mixing up if the gaps between the segments
are sealed completely. The sealing 42 may be done by integrally molding the segments
with plastic material to form the integral partition 2.
In this first inventive element, instead of the plate partition 2
as described above, as shown in Fig. 8 or Fig. 9(a), a pipe or tubular partition
2 with the one end closed and the other end open, may be preferably used, because
the inside of the tubular partition 2 can be used as either the feed chamber or
the recovery chamber. When the crude or recovery liquid is put in the inside of
such tubular chamber, the liquid is surrounded by the partition and therefore,
it is easy and handy to form a radial and uniform electric field cross the partition
2,which leads to an improved efficiency of lithium extraction in comparison to
the plate partition. If the tubular partition 2 with its both open ends is used
as shown in Fig.12 and either one of the crude and recovery liquids is flown in
succession through the inside thereof by means of continuously feeding the lithium-containing
liquid, the continuous extraction of lithium may be easily attained in a recovery
chamber contacting the outside or inside surface of the partition. The partitions
in total can be made in a shape of honeycomb as shown in Fig. 10, in which hollows
of the honeycomb can be used as the crude or recovery chambers and the walls made
by honeycomb hollows 47 may be used as the partitions. By using the honeycomb-shaped
partition in the apparatus for extracting lithium in the form of ions, high efficient
extraction or transfer of lithium from the crude solution to the recovery liquid
is attained because most of the wall of honeycomb hollows can be utilized as the
partitions which allow lithium ions to pass through them, as shown in Fig. 11(b).
The second inventive element composed in the apparatus of the invention
is characterized in that the electrodes across which an electric voltage is applied
are placed along the surfaces of the partition which has two surfaces opposing
each other, contacting either the crude liquid or the recovery liquid and separating
the two liquids. In this configuration when extraction of lithium is desired in
acceleration, the electrode placed along the partition which contacts the crude
liquid is set electrically positive and the other electrode placed along the other
surface of the partition which contacts the recovery liquid is set electrically
negative as shown in Fig. 3(a).
In an aspect of the second inventive element, the electric field
caused by the voltage applied across the electrode can be uniformly made across
the liquids existing between the electrodes intervened with the partition, if the
shape of the electrode(s) are net or mesh as shown by the reference numeral 6d
of Fig.8 and if they cover the surfaces of the partition in a uniform distance
as shown in Figs.6(b), 7 and 8. As a result of this, the partition 2 made up of
the Li solid electrolyte of perovskite type can be made full use of, thereby securing
a further increased efficiency of lithium extraction.
The third inventive element of the apparatus is characterized by
forming at least one chamber, with the portion the partition made of the Li-conducting
solid electrolyte. If the plate partition is used to make a part of the inside
wall surface of the chamber contacting the crude liquid, the other surface of
the wall becomes a part of another chamber contacting the recovery liquid. If the
partition in the form of cup-shape or pipe- shape having its one end closed, either
one of the feed and recovery chambers may be unnecessary because the partition
itself forms a chamber. If the partition is made like a honeycomb as previously
described, each of the honeycomb hollows surrounded by a honeycomb wall can be
either the feed or recovery chamber to which the crude or recovery liquid is introduced
respectively.
The apparatus of the present invention may further comprise the forth
inventive element which is characterized in that a means for feeding and discharging
the crude liquid to or from the feed chamber and a means for continuously feeding
and discharging the recovery liquid. These means are for instance, pumping motors
flow meters, valves for some openings etc. necessary to feed or discharge the
liquids to or from the chambers, by which the feed and discharge of the crude liquid
and the recovery liquid can be carried out in a continuous manner so that even
a large quantity of a crude liquid and recovery liquid can be treated with good
efficiency.
More specifically in regard to a preferred embodiment of , the above
forth inventive element, the apparatus further having the following structure is
preferable; i. e., the crude liquid fed from a feed opening of the feeding means
is made to flow along the wall of the partition and then discharged from a discharge
opening of the discharging means. By this structure, even though a deposit may
adhere to the partition or the electrode contacting the crude liquid in the feed
chamber , the flow of the crude liquid effects washing away the deposit and thereby
prevents reducing an electrical current efficiency through the partition. The
apparatus may be preferably provided with a circulating means for recycling the
crude liquid discharged from the feed chamber to the feed opening thereof. In this
way the crude liquid is repeatedly brought into contact with the partition by the
circulation so that the lithium can be extracted from the crude liquid to the recovery
liquid efficiently without waste.
The apparatus may also preferably have a similar structure in the
recovery chamber; the recovery liquid fed from an opening of the feeding means
is made to flow along the wall of the partition and then discharged from a discharge
opening of the feed chamber by the discharging means. For example, where an aqueous
solution including water is used as a recovery liquid, the extracted Li component
produces LiOH in the recovery side, which tends to be deposited on the partition
and/or the electrode in the recovery side. According to the above structure the
flow of the recovery liquid along the wall of the partition washes off the deposit
such as LiOH, thereby to prevent reducing the electrical current efficiency through
the partition. Similar to the feed chamber, the circulating means for returning
the discharged recovery liquid to the recovery chamber is effective for the recovery
chamber. Thus, the recovery liquid can be repeatedly brought into contact with
the partition by the circulation means to efficiently increase (or rather condense)
the lithium concentration of the liquid in the recovery chamber.
In order to obtain a purified lithium salt efficiently, the method
and apparatus of the present invention may preferably need a fifth inventive element,
i.e.; a precipitant capable of reacting with the extracted lithium existing as
lithium ions in the recovery chamber may be added to the recovery liquid. The
lithium component in LiOH of the recovery liquid is immobilized as a result of
the precipitation, and the concentration of the dissolved lithium component in
the liquid is reduced. By this, the deposit of LiOH, stuck on the partition or
electrode is inhibited. Useful precipitants for this use include carbon dioxide(CO2)
which reacts with a dissolved lithium component to form a soluble lithium carbonate
(Li2CO3). The recovery chamber may be provided with a means
for bubbling the recovery liquid by the gas of CO2. The recovery chamber
may also have another means for separating the lithium-containing precipitate from
the recovery liquid, thereby facilitating to renew the liquid by circulation.
The means for separating the precipitate may be a structure having a filter which
passes the recovery liquid but collects the precipitate.
The Li solid electrolyte which is used as the partition in the present
invention includes a perovskite-type solid electrolyte represented by the formula:
(Lax,Liy)TiOz, wherein x=2/3-a, y=3a-2b, z=3-b,
0<a≤1/6, 0≤b≤0.06, and y>0. This perovskite-type solid electrolyte,
as previously described, exhibits the excellent Li ion selectivity and high bulk
ion conductivity even at the room temperature. Besides, it acts stably even in
the presence of water. Therefore, the extraction of Li ions, particularly from
the aqueous solution can be achieved precisely and efficiently, as this electrolyte
is utilized as the partition to filtrate Li ions only for extraction, concentration,
and purification of lithium and for lithium salt production etc. in the embodiments
of the invention.
In the above formula representing the perovskite-type solid electrolyte,
the a is adjusted at 1/6 or less (exclusive of zero). If the a is
more than 1/6, there will be crystal phases (e.g., Li2TiO3
and Li2Ti3O7) different from the perovskite structure,
resulting in decrease of the Li ion conductivity of the partition and impairment
of the lithium extraction effect thereof. If the a is zero, there is no
Li ion as a conducting carrier per formula weight, and the compound to be used
as the partition no longer functions as a Li ion conductor.
The b in the above formula is adjusted at 0.06 or less. The
value b is a parameter specifying the vacancy content created in the site of oxygen
ions forming the skeleton of a perovskite-type crystal structure as hereinafter
described. If the b exceeds 0.06, the vacancy content increases excessively, tending
to make the perovskite-type crystal structure instable. Then, it may follow that
the Li ion conductivity is reduced to ruin the Li extraction effect.
In order for a solid electrolyte to retain the perovskite-type crystal
structure to be used for the method and apparatus of the invention, the numbers
of La ions and Li ions per formula weight should be represented by x=2/3-a and
y=3a-2b, respectively. Taking the values a and b into account, x
should preferably range from 1/2 to 2/3 (excluding 2/3), and y should preferably
range from 0 to 1/2 (excluding 0). If the x exceeds 2/3, the relative amount of
Li ion decreases considerably , resulting in reduction of Li ion conductivity of
the partition, which leads to an impractical reduction of the Li extraction effect.
If the x is less than 1/2, different phases having a crystal structure other than
the perovskite structure appear, tending to reduce the Li ion conductivity of the
partition. The value x in a preferable range is from 0.5 to 0.6. As to the y ,
if it exceeds 1/2, there will be different phases having a crystal structure other
than the perovskite structure, and if the y is 0, the oxide compound no longer
functions as an Li ion conductor for the partition. The value y inin a preferable
range is 0.1 to 0.4.
The partition made of the Li conducting solid electrolyte as shown
above can be prepared by, for example, the process comprising the following steps
as numbered (1),(2) and (3),
- (1) Oxides of metallic elements or their compounds (such as nitrates and carbonates)
that are convertible to corresponding oxides on heat treatment in an oxidizing
atmosphere are blended to prepare a raw material mixed powder having a stoichiometric
composition for the solid electrolyte. For instance, the mixed powder of La2O3,
Li2CO3, and TiO2 may be preferably made by this
The mixed powder is then heated to 800 to 1100°C, preferably 900 to 1000°C, to
synthesize a perovskite-type compound powder .
- (2) The perovskite-type powder is then formed into an unfired green body of
a predetermined shape by a known forming method such as pressing (inclusive of
cold hydrostatic pressing), injection molding, extrusion molding, slip casting
(forming step). Before the forming, a small amount of a binder may be added to
the powder to easily form the green body for the unfired partition.
- (3) The resulting unfired partition (green body) is then fired at 1100 to 1400°C,
by a general sintering method including hot pressing and hot isostatic pressing.
Without preparing a perovskite type compound as shown in the above
step (1), the raw material mixed powder after being formed in a desired shape of
unfired partition can be sintered to obtain the fired perovskite type lithium ion
conducting solid.
It is considered that the above-described perovskite-type solid electrolyte
exhibits Li ion conductivity based on the following mechanism. Fig. 1 schematically
illustrates a unit cell of the solid electrolyte with an idealized perovskite
structure. In the unit cell, Ti ions are in the sites corresponding to the apices
of a cubic lattice (hereinafter referred to as B-sites), and an La or Li ion is
in the site corresponding to the centroid of the cubic lattice (hereinafter referred
to as A-site). Six oxygen ions are coordinated around each Ti ion to form a regular
octahedron, and the TiO6 octahedra are linked three-dimensionally to
build up crystals. Taking into consideration sharing of ions by adjacent unit cells
and adjacent oxygen octahedra, a unit cell comprises one La or Li ion, one Ti ion
and three oxygen ions, giving a chemical formula (La, Li)TiO3, which
is equivalent to the above formula wherein x=y=0.5 and z=3.
In an ideal perovskite structure, the total number of La and Li ions
per formula weight (i.e., x+y) ought to be 1. However in this structure, it is
possible to make (x+y) less than 1 by controlling the x and y values while maintaining
electrical neutrality of the whole crystal, thereby to provide a vacancy in A-site.
Formation of the vacancy in A-site necessarily causes generation of a vacancy in
the oxygen ion sites so as to maintain the electrical neutrality of the whole crystal.
Accordingly, by using the parameter a which decides the Li ion content and
also using the parameter b which decides the vacancy content generated
in the oxygen ion sites, the aforesaid solid electrolyte can be represented by
the formula (Lax,Liy) TiOz wherein x=2/3-a, y=3a-2b,
z=3-b, 0<a≤1/6, 0≤b≤0.06, and y>0.
Fig. 2 shows an ion arrangement in the (100) plane of the above-described
crystal structure, (corresponding to the plane surrounded by the dotted broken
lines in Fig. 1). Assuming that Li ions migrate in the crystal, the narrowest interstitial
passageway called "bottlenecks" on the (100) plane is located in the sites sandwiched
in between two oxygen ions (the sites surrounded by four oxygen ions when seen
three-dimensionally). Compared with an La ion, an Li ion has a smaller radius and
is capable of passing through the bottlenecks as referenced as Wn in Fig.2. If
Li ions and vacancies are linked from one end of the crystal to the other via the
bottlenecks, there is provided an ion conduction channel. On an electrical field
being applied across the crystal, Li ions are considered to migrate along the channel
so that the crystal achieves ionic conduction. It seems that La ions make no contribution
to the ionic conduction because it has too large a ionic radius to pass through
the bottleneck Wn .
Most of the metallic ions have a larger ionic radius than that of
Li ion and hardly pass through the bottlenecks, failing to cause the ion conduction
channel. This seems to be a reason for the excellent Li-ion selectivity of the
solid electrolyte against other metallic ions. Further, the solid electrolyte to
be utilized for the invention is excellent in property of blocking hydrogen ions
(protons), probably because that the hydrogen ions are generally present in the
aqueous solution in the form of oxonium ions (H3O+) which
are too large in their sizes of ions to enter the ionic channels.
From the standpoint of vacancy concentration, the solid electrolyte
can also be represented by the formula; La(Li1-Q[ ]Q)TiOz-J,
wherein J is a parameter of oxygen defect; [ ] is a vacancy, and Q is a vacancy
ratio. If the total number of Li ion sites, i.e., the number of the sites occupied
by Li ions and the number of the vacant sites, is about 0.31 or less, the absolute
sum of the Li ions and vacancies tends to be insufficient for the Li ions to be
linked via vacancies to make ion- conduction channels from end to end of the crystal.
As a result, the channels for ion conduction is insufficient in number for assuring
a satisfactory ion conductivity of the solid electrolyte. Accordingly, the total
value of the Li ion sites is desirable to be larger than the above value of 0.31.
If the Li ion concentration is too high, i.e., if the value a in the above
formula exceeds 1/6, the Li ions tend to enter B-sites where they are energetically
more stable than in A-sites, and cause to generate a different phase having a
crystal structure other than a perovskite structure in the solid electrolyte ,and
accordingly the reduction of its ion conductivity ensues . If the a is 0,
the number y of Li ions, representing a conducting carrier per formula weight,
becomes 0, causing the loss of the Li ion conductivity.
In some cases, addition of an element to the electrolyte material
is effective in dilating the bottleneck of the solid electrolyte, resulting in
improving the ion conductivity and Li ion extraction efficiency. More specifically,
it is effective to substitute part of La ions with metallic ions having a larger
ionic radius, for example, Sr ions. With the La ions substituted by other metallic
ions as described above a frame of the surrounding oxygen ions is expanded. It
seems accordingly to follow that the size of the bottleneck Wn (see Fig. 2) is
increased to allow Li ions to pass more easily. In the case of using Sr, La is
preferably substituted with Sr in a proportion of not more than 30 atm%. If the
degree of substitution exceeds 30 atm%, the ion conductivity tends to decrease.
A more preferable degree of the La substitution with other metallic ions is 10
to 20 atm%.
Various inventive elements that may be added appropriately to the
lithium extraction apparatus according to the present invention will hereinafter
be described in detail.
Both the crude liquid and recovery liquid may mainly comprise water.
The Li solid electrolyte such as the above-described perovskite-type Li solid electrolyte
acts stably in the presence of water. For example, an Li ion-containing aqueous
solution such as sea water can be used as a crude liquid, and distilled water
as a recovery liquid.
The ion conductivity of the solid electrolyte and the Li ion extraction
efficiency of the present device can be improved by increasing the temperatures
of the crude liquid and the recovery liquid from the room temperature. Note however
that too high the temperatures of the crude liquid and recovery liquid may raise
a problem of liquid evaporation. Where both the liquids mainly comprise aqueous
solution like water, therefore, the elevated temperature may be preferably controlled
below the boiling point of the aqueous solution by a temperature control means.
While a heater may be separately provided as such a temperature control means,
Joule's heat generated in the partition may be utilized instead for heating the
crude liquid and recovery liquid,which leads to simplification of the apparatus
and cost reduction.
The means for applying an electrical field comprises a pair of electrodes
set in contact or close to and sandwiching the partition, by which the electrical
field is applied across the thickness of the partition i.e. across a pair of the
electrodes. The electrodes and the partition can be separately prepared, and can
be assembled together in the actual use.
The electrodes are preferably set close to both surfaces of the partition
thereby the contact of the crude liquid and the recovery liquid with the partition,
ie assured, and at least one of the electrodes is placed covering along the surface
of the partition.
According to this structure, the an electrical field can be uniformly
applied to the partition. The distance between the electrode and the partition
is preferably in the range of 1-30mm, more preferably 5-15 mm. As a result, the
partition made of the Li solid electrolyte can be made full use of, thereby securing
a further increased efficiency of lithium extraction.
The partition can have the form of a plate having two major surfaces,
on one of which a feed chamber is formed and on the other of which a recovery chamber
is provided. A partition of such a simple plate can easily be prepared by, for
example, firing a ceramic green sheet having a stoichiometric composition for the
perovskite Li conducting solid electrolyte if fired. For this partition , the
electrodes may be made of a metallic mesh covering the surface of the plate.
where it is difficult to make the partition having a large area,
the partition can be made up of a plurality of segments with the spaces between
every two adjacent segments being sealed so as to obstruct the passage of liquid.
The partition can have a cylindrical form with its one end closed.
In this structure, an electrode is set inside and outside the cylinder while assuring
the contact of the crude liquid and the recovery liquid with the partition. The
electrode set outside the cylinder can be a mesh covering the outer wall of the
partition. Such a mesh electrode is effective in uniformly applying an electrical
field to the partition. The cylindrical partition is put with its end downward
into a tank containing a crude liquid or a recovery liquid. There are thus provided
two chambers, inside and outside the cylindrical partition, one for the crude liquid
and the other for the recovery liquid. This structure embraces an embodiment in
which a plurality of cylindrical partitions are put in the same tank to attain
a further increased contact efficiency between the crude liquid and the recovery
liquid via the partition.
The uniformity of electrical field application across the partition
can further be improved by providing a mesh electrode along the inner wall of the
cylindrical partition as well as along the outer wall. In this case, a feed pipe
made of metal for feeding a crude liquid or a recovery liquid can be inserted in
the inside of the chamber made with the cylindrical partition in the axial direction
of the cylinder. The feed pipe can be electrically connected to the inside mesh
electrode to serve as an electrical collector for electricity flowing from or to
the mesh electrode. This will be a compact means for applying an electrical field
across the partition and supplying electricity across the electrode..
The partition can also have a honeycomb structure composed of a plurality
of spaces each elongated in a direction are adjoined to each other in a plane intersecting
to the elongated direction. The partition portion surrounding each of the spaces
constitutes the above cylindrical part, thereby providing many spaces serving
as the chambers. About half of the chambers are used as feed chambers for containing
a crude liquid, and the chambers adjacent to the feed chambers are used as recovery
chambers for containing a recovery liquid. According to this structure, the contact
efficiency between the crude liquid and-the recovery liquid is further increased,
resulting in increased efficiency in lithium recovery. More specifically, the honeycomb
structure can be composed of a plurality of hollow columns having a square section,
arranged in a chessboard pattern. The feed chambers and recovery chambers are
arranged alternately in the chessboard pattern. Thus, most of the partitions in
the honeycomb shape can make effective the selective extraction of lithium, bringing
a further increased efficiency in lithium recovery.
In the above honeycomb structure, the means for applying an electrical
field comprises a plurality of wire or rod electrodes connected in series each
inserted into each feed chamber from one end of the respective column chamber in
the axial direction and a plurality of wire or rod electrodes connected in series
each inserted in each recovery chamber in the axial direction from one end of
the respective column chamber opposite to the end from which the electrodes for
the feed chambers are inserted. A voltage is applied across the electrode in the
feed chamber and the electrode in the recovery chamber adjacent to the feed chamber
and thereby an electric field occurs through the part of the partition separating
these two chambers. According to this structure, the electrical filed can be applied
uniformly through all of the partition, and the electrodes used can be of a simple
structure and easily prepared.
The apparatus can have a feeding means for continuously feeding a
crude liquid to the feed chamber and a discharging means for continuously discharging
the crude liquid having its lithium component concentration reduced by lithium
extraction into the recovery side. The apparatus can also have a means for continuously
feeding a recovery liquid to the recovery chamber and a discharging means for continuously
discharging the liquid having an increased lithium component concentration. According
to this structure, feed and discharge of the crude liquid and recovery liquid
can be carried out efficiently in a continuous manner, and large quantities of
a crude liquid can be treated for extraction to a recovery liquid with good efficiency.
The apparatus having the above structure is designed so that the
crude liquid fed from the opening of the feeding means is made to flow along the
wall of the partition and is then discharged from the opening of the discharging
means. In this case, even though a deposit adheres to the partition on the side
of the feed chamber or the electrode formed along the partition, the flow of the
crude liquid is effective in washing away the deposit and thereby preventing the
partition from being reduced in its electrical current efficiency by the deposit.
The apparatus can also be provided with a circulating means for returning the liquid
discharged from the feed chamber to the feed chamber. The crude liquid can be
repeatedly brought into contact with the partition by the circulation so that lithium
can be extracted from the crude liquid continuously without waste.
The apparatus can also have a structure that the recovery liquid
fed from the opening of the feeding means is made to flow along the wall of the
partition and then discharged from the opening of the discharging means. For example,
where lithium is extracted into an aqueous recovery solution, the extracted Li
produces LiOH in the recovery solution, which LiOH tends to be deposited on the
partition or the electrode in the recovery solution. According to this structure,
the flow of the recovery liquid along the wall of the partition washes away the
deposit such as LiOH, thereby preventing reduction of the electrical current efficiency
of the partition. Further, the apparatus can be provided with a circulating means
for recycling the recovery liquid which has been discharged from the recovery chamber
by the discharging means to the recovery chamber. Thus, the recovery liquid can
be repeatedly brought into contact with the partition by the circulation to increase
the lithium concentration in the liquid in the recovery chamber.
A precipitant capable of reacting with the extracted lithium component
to form a precipitate can be added to the recovery liquid. In this case, the lithium
component in the recovery liquid is immobilized as a precipitate, and the concentration
of the dissolved lithium component in the liquid is reduced. As a result, deposition
of LiOH, etc. on the partition or electrode is inhibited. Useful precipitants include
carbon dioxide, which reacts with a dissolved lithium component to form sparingly
soluble lithium carbonate (Li2CO3). The recovery chamber
can be provided with a means for bubbling carbon dioxide through the recovery liquid.
The recovery chamber can also have a means for separating the lithium-containing
precipitate from the liquid, thereby facilitating the circulation of the liquid.
The means for separating the precipitate can be a structure having a filter for
collecting the precipitate from the liquid.
The present invention will further be illustrated in greater detail
by way of Examples with reference to the accompanying drawings.
Fig. 3(a) is a schematic figure depicting the mechanism of the lithium
extraction according to the present invention. The Li extraction apparatus 1 shown
in Fig. 3 (a) has a partition 2 made of an Li solid electrolyte, a feed chamber
3 formed on one side of the partition 2 in which a crude liquid CL containing an
Li component and impurities such as Na is introduced so as to come into contact
with the partition 2, and a recovery chamber 4 formed on the opposite side of the
partition 2 in which a recovery liquid EL is introduced so as to come into contact
with the partition 2. On both sides of the partition 2 are set mesh electrodes
5 and 6 made of noble metal such as Ag, Pt, and an alloy thereof, to cover the
wall of the partition 2. The electrode 5 in the feed chamber 3 is connected to
the positive pole of a direct current power source 7, while the electrode 6 in
the recovery chamber 4 is connected to the negative pole of the power source 7.
The electrodes 5 and 6 and the direct current power source 7 constitute a means
for applying an electrical field. In this Example, the crude liquid CL is an aqueous
solution containing LiCl and, as an impurity, NaCl, and the recovery liquid EL
is distilled water.
The Li solid electrolyte forming the partition 2 is a perovskite-type
solid electrolyte represented by the formula: (Lax, Liy)TiOz,
wherein x=2/3-a, y=3a-2b, z=3-b, 0<a≤1/6, 0≤b≤0.06, and y>0. The
perovskite-type solid electrolyte represented by the above formula can be prepared
as follows. Oxides of the constituent metallic elements or compounds of the elements
capable of being converted to corresponding oxides in an oxidative atmosphere
(such as nitrates and carbonates) are blended to prepare a mixed powder having
a prescribed composition. The mixed powder is heated to 800 to 1100°C, preferably
900 to 1000°C, to synthesize a perovskite-type compound powder. The resulting powder,
if necessary, mixed with an appropriate amount of a binder is formed into a partition
of a prescribed shape by a known forming method, such as pressing (inclusive of
cold hydrostatic pressing), injection molding, extrusion molding, slip casting,
and the like. The resulting green body is sintered at 1100 to 1400°C.
Upon applying an electrical field by means of the electrodes 5 and
6 and the power source 7 in such a manner that the crude liquid side of the partition
is positive and the recovery liquid side of the partition is negative, Li+
in the crude liquid CL passes through the partition 2 into the recovery liquid
EL. On the other hand, Na+ as an impurity cannot pass through the partition
2 and remains in the crude liquid CL side. Thus only Li ions of the crude liquid
CL can be extracted into the recovery liquid EL. Application of an electrical field
to the partition 2 is accompanied by Joule's heat generation in the partition 2,
which can be utilized for heating both the crude liquid CL and recovery liquid
EL above room temperature. As a result, the solid electrolyte of the partition
2 exhibits increased ion conductivity to achieve improved extraction efficiency.
In this case, the partition is to function as a heating means as well. The heating
temperature of the crude liquid CL and the recovery liquid EL is preferably not
higher than their boiling point, i.e., not higher than 100°C, most preferably from
70 to 90°C. It is also possible to provide heaters 8 and 9 in the feed chamber
3 and the recovery chamber 4, respectively, as a separate heating means with which
the crude liquid CL and the recovery liquid EL are heated.
In order to increase the rate of Li ion extraction, it is effective
to increase the electric voltage (current) applied across the partition 2. This
can be done by (1) increasing the voltage as far as water does not undergo electrolysis
(in the case of using an aqueous crude liquid). (2) setting the electrodes 5 and
6 as close as possible to the partition 2, (3) increasing the facing area of the
electrodes 5 and 6 to the partition 2, and (4) reducing the thickness of the partition
2 as long as the strength is not impaired to decrease the electrical resistance
of the partition 2 against the current. The thickness of the partition 2 is preferably
0.1 to 2 mm. If it is less than 0.1 mm, the partition is liable to break due to
insufficient strength. If it exceeds 2 mm, the electrical resistance of the partition
is too high to obtain a sufficient current density, resulting in reduction of
Li extraction efficiency.
Fig. 3(b) shows the reactions occurring in the crude liquid CL side
and the recovery liquid EL side during extraction with using of a crude liquid
(CL) containing LiCl. As lithium ions are extracted into the recovery liquid EL
side, chlorine gas (Cl2) evolves. It is desirable therefore that a venting
means 3f for discharging and collecting chlorine gas be provided in the feed chamber
3. In the recovery liquid EL side, on the other hand, a reaction between the extracted
Li ions and water produces LiOH and hydrogen gas (H2). It is desirable
therefore that a venting means 4f for discharging hydrogen gas be provided in the
recovery chamber 4.
Various other embodiments of the Li extraction apparatus 1 according
to the invention are described below with reference to Figs. 4 through 12.
The apparatus 1 shown in Fig. 4 comprises a tank 10 and a cylinder
11 with an open end 11a which pierces one side of the tank 10 so that the open
end 11a is in the recovery chamber 4. The inside space of the tank 10 is used as
a recovery chamber 4, and that of the cylinder 11 as a feed chamber 3. Into the
opening 11a of the cylinder 11 is fitted a plate of an Li solid electrolyte to
form a partition 2. Mesh electrodes 5 and 6 each connected to a direct current
power source 7 are set on each side of the partition 2.
A feed opening 12 for feeding a crude liquid CL to the feed chamber
3 and a discharge opening 13 for discharging the crude liquid CL from the feed
chamber 3 are provided at the end of the cylinder 11 opposite to the end 11a where
the partition 2 is fitted. The discharged crude liquid CL passes through a circulating
pipe 14 and returns to the feed chamber 3 through the feed opening 12 by means
of a circulating pump 15 provided in the middle of the pipe 14. That is, the circulating
pipe 14 and the pump 15 compose a feeding means, a discharging means, and a circulating
means for the crude liquid. The circulating pipe 14 can have a discharge pipe
20 with a valve 21 and a feed pipe 22 with a valve 23. When the lithium concentration
of the circulating crude liquid CL decreases to a given level as a result of continuous
lithium extraction, the valve 21 is opened to discharge the treated CL through
the discharge pipe 20, and then the valve 23 is opened to supply an untreated crude
liquid to the crude liquid CL system,
The tank 10 has a feed opening 16 for feeding a recovery liquid EL
to the recovery chamber 4 and a discharge opening 17 for discharging the recovery
liquid EL from the recovery chamber 4. The discharged recovery liquid EL passes
through a circulating pipe 18 and returns to the recovery chamber 4 by means of
a circulating pump 19 provided in the middle of the pipe 18. That is, the circulating
pipe 18 and the pump 19 compose a feeding means, a discharging means, and a circulating
means for the recovery liquid. The circulating pipe 18 can have a discharge pipe
24 with a valve 25 and a feed pipe 26 with a valve 27. When the lithium concentration
of the circulating recovery liquid EL increases to a desired level as a result
or continuous lithium extraction, the recovery liquid EL is discharged through
the discharge pipe 24, and then a fresh recovery liquid is supplied from the feed
pipe 26 to the recovery system.
The apparatus 1 shown in Fig. 5(a) comprises a tank 30 that is partitioned
with a partition 2 into a feed chamber 3 and a recovery chamber 4. A circulating
pipe 14 is connected to the feed chamber 3 in the same manner as described above
so that a crude liquid CL can be circulated by means of a pump 15 provided in the
middle of the pipe 14. A reservoir tank 31 for reserving the crude liquid CL is
provided on the route of the circulation pipe 14. A recovery liquid EL is continuously
fed from a feed tank 32 through a feed pipe 33 to the recovery chamber 4 by means
of a pump 34 provided in the middle of the pipe 33. The recovery liquid EL is
continuously discharged from the recovery chamber 4 through a discharge pipe 35
by means of a pump 36 (The recovery liquid EL is not circulated).
As shown in Fig. 5(b), the recovery chamber 4 is further partitioned
with a wall 4c into a precipitation chamber 4a on the side of the partition 2 and
a pre-discharge chamber 4b on the other side of the wall 4c. A fresh recovery liquid
EL is fed to the precipitation chamber 4a. The precipitation chamber 4a is equipped
with a bubbling nozzle 38 having a number of jet nozzles. carbon dioxide (CO2)
is fed to the nozzle 38 through a feed pipe 39 whereby CO2 bubbles up
the recovery liquid EL in the precipitation chamber 4a.
Lithium ions extracted into the recovery liquid EL become LiOH. If
the LiOH concentration in the recovery liquid EL increases, there are cases in
which LiOH is deposited and adhered to the partition 2 and the electrode 6 to hinder
the passage of electricity. Where the recovery liquid EL is bubbled by CO2
as described above, LiOH reacts with CO2 to become sparingly soluble
Li2CO3 which precipitates in the precipitation chamber 4a,
and is thus separated from the recovery liquid EL. The precipitated Li2CO3
can be collected through a pipe 40 provided at the bottom of the precipitation
chamber 4a. The recovery liquid EL from which the lithium component has been separated
overflows the wall 4c into the pre-discharge chamber 4b and is continuously discharged
from the discharge pipe 35 by means of the pump 36. Li2CO3,
if remaining in the recovery liquid EL in the chamber 4b, is trapped by a filter
unit 37 provided on the discharge pipe 35.
If it is difficult to make a partition of an integral solid electrolyte
having large area, the partition can be made up of a plurality of segments as shown
in Fig. 6. The partition 2 of Fig. 6 is composed of a plurality of plate segments
41 made of an Li solid electrolyte which are arranged on the same plane and a
sealing part 42 which fills every gap among the segments 41 to block the passage
of liquid through the gaps. The sealing part 42 is, for example, a plastic frame
integrally molded with the segments 41 by injection molding, etc. The sides of
each segment 41 can have a mating protrusion 42a (e.g., a line protrusion) for
biting into the sealing part 42 or a mating cut (e.g., a groove) into which the
sealing part 42 bites so that the segments 41 may not fall off the sealing part
42.
In the apparatus shown in Fig. 7, a partition 2 having a cylindrical
form with its bottom closed is inserted in a tank 10 with its closed bottom down
to provide two chambers; one surrounded by the inner wall of the tank 10 and the
outer surface of the partition 2, which can serve as a recovery chamber 4; and
the other formed inside the partition 2, which can serve as a feed chamber 3.
The tank 10 is composed of an open-top main body 10a having a flange 10c around
its opening 10b and a shield 10f that covers the opening 10b of the main body 10a
with watertightness. The shield 10f is removably fitted to the flange 10c with
a fixture 10e, e.g., a bolt and a nut, via a gasket 10d made of rubber, etc.
The shield 10f has a through-hole 10g in its thickness direction.
The upper part of the inner wall of the through-hole 10g ie cut out to make a terrace
10h, on which a gasket 10i whose inner diameter is slightly smaller than the outer
diameter of the partition 2 is fitted. The partition 2 has a closed bottom having
a semispherical shape and an open top 2a having a flange 2b. The partition 2 is
inserted into the tank 10 through the hole 10g and fixed to the upper side of the
shield 10f at its flange 2b via the gasket 10i. The partition 2 having the above-mentioned
shape can be prepared by, for example, casting a slurry of a raw material powder
mixture into a liquid-absorbing mold (called slip casting) and firing the resulting
green cast body.
A mesh electrode 6 shaped along the outside of the partition 2 is
set to cover almost the entire outer wall of the partition 2. Similarly, a mesh
electrode 5 shaped along the inner wall of the cylindrical partition 2 is set inside
the partition 2 to cover almost the entire inner wall of the partition 2. As shown
in Fig. 8, the mesh electrode 6 is composed of a metal frame 6c and metal meshes
6d that are fixed to the frame 6c to cover it. The metal frame 6c is constructed
of a plurality of ring members 6a which are concentric with the partition 2 and
are set at a prescribed interval in the axial direction of the partition 2 and
a plurality of linking members 6b that are parallel to the axial direction of
the partition 2 and link the ring members 6a,
The mesh electrode 5 is constructed in almost the same manner as
for the mesh electrode 6. A feed pipe 43 for feeding a crude liquid CL to the feed
chamber 3 is inserted through the inside of the metallic frame 5c. The feed pipe
43 is made of metal and is electrically connected to ring members 5a with radially
arranged linking members 5e. As shown in Fig. 7, the opening 2a of the partition
2, while having inserted therein the mesh electrode 5 and the feed pipe 43, is
sealed watertightly with a stopper 44 made of rubber, etc. The feed pipe 43 and
a discharge pipe 45 for the crude liquid CL pierce the stopper 44 and extend outside
the partition 2.
A recovery liquid EL is fed from the feed opening 16 into the recovery
chamber 4 and discharged from the discharge opening 17, while a crude liquid CL
is fed through the feed pipe 43 to the feed chamber 3 and discharged through the
discharge pipe 45. In this situation, a power source (not shown) is turned on to
apply an electrical field to the partition 2 via the mesh electrodes 5 and 6 in
such a manner that the feed chamber side is positive and the recovery chamber side
is negative, whereby Li ions in the crude liquid CL selectively migrate through
the partition 2 into the recovery liquid EL. In the above-described structure,
electricity from the power source runs through the metallic feed pipe 43 and flows
to the mesh electrode 5 in the crude liquid chamber 3. That is, the feed pipe 43
also serves as an electric collector for transmitting electricity to the mesh electrode
5.
The apparatus can have a plurality of the cylindrical partitions
2 as shown in Fig. 9(a). In this case, the shield 10f has a plurality of through-holes
10g for inserting the partitions 2 therethrough. As in the example shown in Fig.
9(b), the crude liquid CL discharged from every feed chamber 3 can overflow the
respective discharge pipes 45, spread over the upper surface of the shield 10f,
and be discharged from an outlet 46 provided at the upper part of the main tank
body 10a. In this example, the shield 10f is fixed to the main body 10a by fitting
its periphery into a groove 10k via a gasket 101, the groove 10k being made on
the upper inner wall of the main body 10a at a prescribed depth from the top of
the wall.
In Fig. 10 is illustrated a partition 2 having a honeycomb structure.
The honeycomb structure of the partition 2 is comprised of a plurality of spaces
47 (hereinafter sometimes referred to as column) each elongated in a direction
adjoined to each other in a plane intersecting to the elongated direction, each
serving like a cylindrical partition as referred to above. More specifically,
the columns 47 each have a square section and are arranged in a chessboard pattern,
thus providing a plurality of spaces, in which feed chambers 3 and recovery chambers
4 alternate as shown in Fig. 11(b). The partition having such a honeycomb structure
can be prepared by, for example, mixing a raw material powder mixture with a binder
to prepare a compound, molding the compound by extrusion or injection molding,
and firing the resulting green body.
Fig. 11 schematically illustrates an Li extraction apparatus 1 constructed
with the above-described honeycomb partition 2. Both the upper and lower openings
of all the columns are sealed watertightly with stoppers 48 made of plastic, metal,
etc. via sealing members (gaskets) 49. A wire or rod electrode 5 (electrode for
a feed chamber) is inserted into each column serving as a feed chamber from one
of the ends through the stopper 48 in the axial direction. The plurality of the
electrodes 5 are connected in series and led to the positive pole of a direct current
power source (not shown). Similarly, a wire or rod electrode 6 (electrode for
a recovery chamber) is inserted into each column serving as a recovery chamber
from the opposite end of the column (opposite to the end from which the electrode
5 is inserted) through the stopper 48 in the axial direction. The plurality of
the electrodes 6 are connected in series and led to the negative pole of the direct
current power source. In each feed chamber and each recovery chamber, a feed opening
12 or 16 and a discharge opening 13 or 17 are provided through the stopper 48 at
the end opposite to the end from which the electrode 5 or 6 is inserted. A crude
liquid CL and a recovery liquid EL are fed to the respective chambers from the
feeding opening 12 or 16, respectively, and discharged from the discharge opening
13 or 17, respectively.
A voltage from the direct current power source is applied to the
part of the partitions 2 separating each feed chamber 3 and each recovery chamber
4 by way of each pair of electrodes 5 and 6 put in these chambers, whereby Li ions
are extracted into a recovery liquid EL in each recovery chamber 4 from the crude
liquid in all the surrounding feed chambers 3 through the surrounding partition
2 as depicted in Fig. 11(b).
As shown in Fig. 12, a feed opening 16 for feeding a recovery liquid
can be formed near the border of the recovery chamber 4 (i.e., near the partition
2), and the discharge opening 17 for discharging the recovery liquid can be formed
near the opposite border. In this case, the recovery liquid EL fed from the feed
opening 16 is made to flow along the wall of the partition 2 and then discharged
from the discharge opening 17. The flow of the recovery liquid EL along the wall
of the partition 2 is effective to wash away a deposit on the wall, such as LiOH
that is formed from the extracted lithium component. The same manipulation can
be applied to the feed chamber to make a flow of the crude liquid CL along the
wall of the partition 2.
While the invention has been described in detail and with reference
to specific examples thereof, it will be apparent to one skilled in the art that
various changes and modifications can be made therein without departing from the
scope thereof.