U.S. patent application number 13/989476 was filed with the patent office on 2013-10-31 for leaching solution and metal recovery method.
The applicant listed for this patent is Masahide Okamoto, Yasuko Yamada, Yoshihide Yamaguchi. Invention is credited to Masahide Okamoto, Yasuko Yamada, Yoshihide Yamaguchi.
Application Number | 20130287654 13/989476 |
Document ID | / |
Family ID | 46145565 |
Filed Date | 2013-10-31 |
United States Patent
Application |
20130287654 |
Kind Code |
A1 |
Yamada; Yasuko ; et
al. |
October 31, 2013 |
LEACHING SOLUTION AND METAL RECOVERY METHOD
Abstract
A valuable metal recovery method of recovering metals from a
lithium ion battery without using complicate steps and by a
relatively simple and convenient facility is intended to be
provided. For attaining the purpose, lithium is leached selectively
from a positive electrode active material containing a composite
oxide of lithium and transition metal elements by using a solution
showing a weak acidity at a pH of 4 to 7 so that the high Li/Co
selectivity is high and a Li recovery rate is high, and lithium is
recovered from the leaching solution. By using a solute that the
acidity of the acidic solution spontaneously disappears due to
evolution of a gas after leaching of lithium, neutralization step
is no more required and the volume of liquid wastes is
decreased.
Inventors: |
Yamada; Yasuko; (Sagamihara,
JP) ; Yamaguchi; Yoshihide; (Yokohama, JP) ;
Okamoto; Masahide; (Yokohama, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Yamada; Yasuko
Yamaguchi; Yoshihide
Okamoto; Masahide |
Sagamihara
Yokohama
Yokohama |
|
JP
JP
JP |
|
|
Family ID: |
46145565 |
Appl. No.: |
13/989476 |
Filed: |
November 11, 2011 |
PCT Filed: |
November 11, 2011 |
PCT NO: |
PCT/JP2011/006308 |
371 Date: |
June 17, 2013 |
Current U.S.
Class: |
423/179.5 ;
252/186.1 |
Current CPC
Class: |
Y02W 30/84 20150501;
C22B 26/12 20130101; H01M 10/54 20130101; H01M 10/052 20130101;
Y02T 10/70 20130101; C22B 7/007 20130101; H01M 6/52 20130101; Y02E
60/10 20130101; Y02P 10/20 20151101 |
Class at
Publication: |
423/179.5 ;
252/186.1 |
International
Class: |
C22B 26/12 20060101
C22B026/12 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 25, 2010 |
JP |
2010-261905 |
Jun 9, 2011 |
JP |
2011-128806 |
Claims
1. A metal recovery method of recovering metals from a positive
electrode active material of a lithium ion battery containing
lithium and transition metal elements, comprising: leaching
valuable metals contained in the positive electrode active material
into an acidic solution; and recovering lithium from the acidic
solution where the valuable metals are leached, wherein the acidic
solution is at pH of 4 to 7.
2. A metal recovery method according to claim 1, wherein the acidic
solution contains a redox potential controller.
3. A metal recovery method according to claim 2, wherein the acidic
solution further contains a pH controller.
4. A metal recovery method according to claim 2, wherein the redox
potential controller comprises hydrogen peroxide.
5. A metal recovery method according to claim 2, wherein the redox
potential controller comprises ozone.
6. A metal recovery method according to claim 3, wherein the pH
controller comprises carbon dioxide.
7. A metal recovery method according to claim 1, wherein one of the
solute of the acidic solution, the redox potential controller or
the pH controller is a material that spontaneously disappears from
the solution.
8. A metal leaching solution of leaching metals from a positive
electrode active material of a lithium ion battery containing
lithium and transition metal elements, wherein pH of the solution
is from 4 to 7 and the solute of the solution is a spontaneously
disappearing solute.
9. A metal recovery method of recovering metals from a positive
electrode active material of a lithium ion battery containing
lithium and transition metal elements, comprising: leaching lithium
contained in the positive electrode active material into an acidic
solution containing a spontaneously disappearing oxidizer and a
buffer solution; and recovering lithium from the acidic solution in
which lithium is leached.
10. A metal recovering method according to claim 9, wherein the
buffer solution contains a carboxylic acid and a salt thereof as a
solute.
11. A metal recovering method according to claim 10, wherein the
carboxylic acid is an aliphatic carboxylic acid having a carboxyl
group and not containing an aromatic ring.
12. A metal recovering method according to claim 11, wherein the
carboxylic acid has a number of carbon atoms of 1 to 4 (excluding
carbon atoms in the carboxyl group).
13. A metal recovering method according to claim 10, wherein the
carboxylic acid is an organic acid or glycine.
14. A metal recovering method according to claim 9, wherein the
buffer solution contains phosphoric acid and a salt thereof as a
solute.
15. A metal recovering method according to claim 9, wherein the
spontaneously disappearing oxidizer comprises ozone or aqueous
hydrogen peroxide.
16. A metal recovering method according to claim 9, wherein the
acidic solution in the leaching step is at a pH of 4 to 7.
17. A metal leaching solution of leaching metals from a positive
electrode active material of a lithium ion battery containing
lithium and transition metal elements, wherein the leaching
solution contains a spontaneously disappearing oxidizer and a
buffer solution and a pH of the solution is 4 to 7.
Description
TECHNICAL FIELD
[0001] The present invention concerns a metal recovery technique of
recovering metals from lithium ion batteries simply and
conveniently.
BACKGROUND
[0002] Along with recent progress in portability of electronic
equipment, use of secondary batteries has been increased rapidly.
As application of the secondary batteries extends not only to
equipment of relatively low power consumption such as mobile phones
or portable music players but also to equipment requiring high
power such as electric tools, electric bicycles, and electric
automobiles, lithium ion batteries capable of providing high energy
density have attracted attention. Along with increasing application
to high power equipment, necessity for recovering of valuable
materials from waste batteries has been increasing and various
techniques have been proposed for the recovery of valuable metals
from the lithium ion batteries.
[0003] A recycling technique for lithium ion batteries is featured
and a method of recovering valuable metals constituting lithium ion
batteries is described systematically, for example, by Jinqiu Xu et
al., "A review of processes and technologies for the recycling of
lithium-ion secondary batteries", Journal of Power Sources, vol.
177, pp. 512-527 (2008) (non-patent document 1). According to a
typical recycling method described in the non-patent document 1,
waste lithium ion batteries are subjected to mechanical treatments
such as unsealing, disassembling, and pulverization, then a
positive electrode active material containing valuable metals is
entirely dissolved by acid leaching, from which desired ingredients
are separated and recovered for every ingredient by a treatment,
for example, of separating them for every ingredient and
precipitating by utilizing the difference of dissolving properties
for every ingredient, or subjecting a desired ingredient
preferentially to solvent extraction.
[0004] Further, Japanese Patent No. 3675392 discloses a technique
of recovering copper and cobalt by diaphragm electrolysis using a
solution formed by dissolving valuable metals obtained by acid
leaching as a cathode solution and using a cation exchange film as
a diaphragm. In the present specification, a liquid before treating
the valuable metal is referred to as a leaching solution and a
liquid after treating the valuable metal is referred to as a
dissolved solution.
SUMMARY
[0005] In the non-patent document 1 by Jinqiu Xu et al., it is
intended to attain a compatibility between improvement in the
recovery rate of the valuable materials and high purity of
recovered products, but there is a large room for the improvement
since treatment steps are complicate, as well as an enormous
investment cost is necessary for treating a great amount of waste
batteries.
[0006] Further, Japanese Patent No. 3675392 specifically uses a
facility of utilizing ion selectivity of a cationic exchange film
(diaphragm electrolysis cell illustrated in FIG. 2 of JP No.
3675392) and diffusion dialysis equipment utilizing the anion
selectivity of an anion selection membrane (with no explanatory
view). Referring more specifically, main valuable metals can be
recovered by a series of treatments including electrodeposition
recovery of Cu by diaphragm electrolysis.fwdarw.pH
control.fwdarw.electrodeposition recovery of cobalt by diaphragm
electrolysis.fwdarw.pH control.fwdarw.settling recovery of
Fe(OH).sub.3 and Al(OH).sub.3.fwdarw.recovery of Li.sub.2Co.sub.3
by adding a carbonate salt. According to the technique, since
copper (bivalent ions) and cobalt (trivalent ions) are recovered by
electrochemical reduction, metals at high purity can be obtained.
However, there is still a room for improvement in that enormous
amount of electricity should be applied in a case of treating a
great amount of waste batteries.
[0007] For example, for recovering of about 100 kg of cobalt, it is
necessary to continuously supply a current of 1 ampere for about
100 hours. However, since an approximately equal electric amount is
applied also in the preceding copper electroanalysis, unexpected
labors are necessary for recovering entire metals only by the
diaphragm electrolysis. Further, since the amount of liquid
increases for every pH control in a multi-stage, a lithium
concentration is lowered when Li.sub.2CO.sub.3 is recovered at the
final stage in the series of treatments, and it is considered that
the recovery rate of lithium is not always high even when a
carbonate salt is added. This is because unrecovered ingredients
increase more as the amount of liquid becomes larger since the
saturated solubility of lithium carbonate is as high as 1.3 wt % at
20.degree. C. In order to avoid such disadvantage, treatment, for
example, addition of a concentration step is necessary. Further,
since Fe(OH).sub.3 and Al(OH).sub.3 tend to be gelled in a weakly
acidic to neutral aqueous solution, operation for the step of
recovering Fe(OH).sub.3 or Al(OH).sub.3 by filtration based on the
technique of Japanese Patent No. 3675392 is not easy. On the other
hand, when the liquid is diluted for facilitating the filtration
operation, the lithium recovery rate is lowered. Further, since the
surface of gelled settling such as Fe(OH).sub.3 and Al(OH).sub.3
also has a property of adsorbing lithium ions, it is difficult to
greatly improve the lithium recovery rate also from this view
point.
[0008] A typical example of the inventions disclosed in the present
application is to be described briefly as below.
[0009] Lithium is leached selectively from a positive electrode
active material containing lithium and transition metal elements by
using a weakly acidic leaching solution (pH at 4 to 7), to separate
them into transition metal element ingredients as a not-leached
solid content and a lithium ingredient in the leaching solution.
Since an acidic solution in which a solute disappears spontaneously
to lower the concentration is used, this treatment is a liquid
waste-free process.
[0010] The present invention can provide a valuable metal recovery
method of recovering valuable metals from lithium ion batteries at
a high efficiency simply and conveniently.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 illustrates compositions of leaching solutions
according to examples of the present invention and a Li/Co ratio as
a result of analysis for the solution obtained by treatment with a
leaching solution;
[0012] FIG. 2 illustrates a schematic step flow for recovery of
valuable metals in the examples according to the invention;
[0013] FIG. 3 illustrates plots showing correlation between pH and
redox potential due to concentration of an aqueous-hydrogen
peroxide according to the example of the invention;
[0014] FIG. 4 illustrates compositions of leaching solutions
according to the example of the present invention, and Li/Co ratio
for the result of analysis on dissolved solution obtained by
treatment with the leaching solution; and
[0015] FIG. 5 illustrates plots showing the relation between
leaching time and dissolved oxygen concentration according to the
example of the invention.
DETAILED DESCRIPTION
[0016] Preferred embodiments of practicing the present invention
are to be described.
First Embodiment
[0017] The outline of a method of recovering valuable metals
according to this embodiment is to be described with reference to
FIG. 2. FIG. 2 is a schematic step flow for recovering valuable
metals from a waste lithium battery (hereinafter referred to as
waste battery) of this embodiment. First, respective constituent
components obtained by disassembling a waste battery (S101) are
sorted for every component (S102), and only the electrode active
material containing valuable metals at a high concentration is
taken out. The thus taken out electrode active material is treated
by a solution for selectively leaching lithium (lithium selective
leaching: S103) to form a solution in which lithium is leached. The
solution containing selectively leached lithium and the not-leached
content is put to solid-liquid separation (S104). When a carbonate
salt or gaseous carbon dioxide is mixed with a solution A
containing lithium (S105), lithium can be recovered as lithium
carbonate Li.sub.2CO.sub.3 (S106). In the solid-liquid separation,
a solid ingredient B is recovered (S107). When multiple transition
metals are contained, they are recovered by filtration by
precipitating and settling them sequentially as hydroxides by a
simple and convenient operation of pH control after dissolving the
solid ingredients B (S108). The valuable metals can be recovered
from waste battery by the series of operations described above.
[0018] The valuable metal recovery flow is to be described more
specifically in accordance with the steps illustrated in FIG. 2.
For recovering valuable metals from a waste battery, it is at first
necessary to disassemble the battery. The battery is discharged
before disassembling since there may be a possibility that electric
charges still remain in the battery. In this embodiment, charges
remaining in the battery are discharged by immersing the battery in
an electroconductive liquid containing an electrolyte.
[0019] Since lithium ions dispersed in the battery can be
concentrated into the inside of the positive electrode active
substance by the discharging operation, the amount of lithium
recovery can be maximized. Further, lithium selectivity in the
leaching treatment is at the maximum by ensuring a state in which
lithium is taken into a specified crystal structure. When the
positive electrode active substance is LiCoO.sub.2, since it is
said that when the positive electrode active material is
LiCoO.sub.2, it exists as Li.sub.0.4CoO.sub.2 in the completely
charged state and as LiCoO.sub.2 in the completely discharged
state, there may be a worry of causing lithium recovery loss of
about 60% at the maximum if the discharging treatment is not
applied. Naturally, the discharging treatment also provides an
advantage capable of ensuring safety in the battery disassembling
step and the pulverization step.
[0020] In this embodiment, a mixed solution of sulfuric
acid/.gamma.-butyrolactone was used as a conductive liquid
containing the electrolyte. Since the sulfuric acid acts as an
electrolyte in the mixed solution, electroconductivity (reciprocal
to resistance value) can be controlled by controlling the
concentration of the sulfuric acid. In this embodiment, when the
electric resistance of the solution was actually measured from the
rightmost end to the leftmost end of a discharging vessel, it was
100 k.OMEGA.. If the resistance of the solution is excessively low,
discharging progresses excessively rapidly to induce a danger and,
on the other hand, if the resistance is excessively high,
discharging takes much time to deteriorate practicability. In this
embodiment, the solution resistance is preferably in a range of
about 1 k to 1000 k.OMEGA. and the concentration of the electrolyte
is preferably controlled so that the resistance value is within the
range.
[0021] The waste battery used in this embodiment includes, in
addition to so-called spent batteries which have reached the limit
of predetermined charge/discharge cycles and the charge capacity
has been lowered, semi-processed goods occurring due to failure in
the battery manufacturing steps and old type inventory adjustment
products occurring due to change of specification of products.
[0022] A waste battery after the discharge treatment is
disassembled at S101. Battery constituent components of the waste
battery after the discharge treatment such as casings, packings,
safety valves, circuit devices, spacers, collectors, separators,
and positive electrode and negative electrode active materials are
disassembled and sorted for every component by using an appropriate
method.
[0023] Since the waste lithium ion battery is often in a
pressurized state with the gas being filled fully inside the
battery, operational safety should be taken into consideration. In
this embodiment, wet pulverization was performed while cooling them
in a state dipped into the conductive liquid containing the
electrolyte. The battery could be pulverized safely without
scattering gases filled in the batteries into the atmospheric air
by adopting the wet pulverization under cooling.
[0024] Further, for promoting peeling of the positive electrode
active material and the negative electrode active material coated
and formed on the surface of collectors from the surface of the
respective collectors, the composition of the
electrolyte-containing electroconductive liquid may be controlled.
Electroconductivity is an important property to be noted in the
electroconductive liquid used for the discharging step, and
properties such as viscosity and dielectric constant should be
noted in the electroconductive liquid used in the wet pulverization
step. Since required specifications are different between the
discharging step and the wet pulverization step, composition of the
conductive liquid used may be changed for every step. In this case,
two or more kinds of conductive liquids have to be prepared. In
this embodiment, the electroconductive liquid had an identical
composition with a view point of simplification and suppression of
labors and cost.
[0025] The wet pulverization method usable in this embodiment
includes, for example, a method of using a ball mill but this is
not restrictive. A sieving treatment is applied after pulverizing
the battery under the condition of preferentially pulverizing the
electrode active material of the positive electrode (hereinafter
referred to as positive electrode active material) and the
electrode active material of negative electrode (hereinafter
referred to as a negative electrode active material) among the
constituent components such as casings, packings, safety valves,
circuit devices, spacers, collectors, separators, and electrode
active materials. Thus, the positive electrode active material and
the negative electrode active material are sorted and recovered
such that positive electrode active material and the negative
electrode active material are undersize pulverizates and other
materials are oversize pulverizates (S102).
[0026] While sieving was used in this embodiment, since the
components are pulverized in the wet process, a slurry obtained by
wet pulverization can be sorted as it is by a filtration treatment
using a filter of a relatively large mesh. A recovery rate may be
possibly improved by adopting a continuous treatment of wet
pulverization-filtration. Casings, packings, safety valves,
collectors (aluminum foil, copper foil), etc. have larger
extendability and, accordingly, a larger rapture strength than the
positive electrode active material (typically LiCoO.sub.2) or
negative electrode active material (typically graphite). Due to the
property, pulverizates of the electrode active material have a size
smaller than pulverizates obtained from other components and, as a
result, can be easily sorted and recovered by sieving or
filtration.
[0027] The under size pulverizates obtained by the treatment
described above are subjected to a leaching treatment by a weakly
acidic leaching solution (S103).
[0028] In this embodiment, a spent lithium ion battery for digital
camera was disassembled. The positive electrode active material of
the waste battery used in this embodiment was a lithium compound
mainly comprising LiCoO.sub.2 but it may also contain positive
electrode active materials of other compositions such as iron
phosphate, nickel, manganese, etc. The positive electrode active
material was mixed with a weakly acidic leaching solution and
stirred at a room temperature for one hour to leach lithium. In
this embodiment, the reaction temperature and the reaction time in
the lithium selective leaching step were controlled, and the
leaching treatment was stopped specifically at a reaction ratio of
80% or less before complete dissolution of the positive electrode
active material. With a practical point of view, the reaction rate
is most preferably, about 70 to 75%. If it exceeds 80%,
deterioration of the selectivity in the selective lithium leaching
reaction may possibly increase and, on the other hand, if it is
below 70%, the recovery rate is lowered to deteriorate economy.
[0029] In this embodiment, the leaching solution and the residue
are separated for terminating the leaching treatment (S104). For
the separation method, centrifugal separation, filtration, etc. can
be adopted. In this embodiment, separation and recovery were
performed by centrifugal separation at a room temperature, under
15,000 rpm, for 15 minutes. Separation between the leaching
solution and the residue is facilitated at a higher number of
rotations.
[0030] FIG. 1 illustrates the Li/Co molar ratio of the obtained
dissolved solutions. As illustrated in FIG. 1, when the positive
electrode active material was completely leached by using the
strongly acidic leaching solution by the method described in the
non-patent document 1 by Jinqiu Xu, et al, the Li/Co molar ratio of
the dissolved solution before dialysis was about 1. When leaching
is performed under a strongly acidic condition at pH.ltoreq.1, the
Li/Co molar ratio is approximately 1.0. This is because the entire
composition of lithium cobaltate is dissolved and, if dissolution
is terminated in the course of the process, the Li/Co molar ratio
scarcely changes. On the other hand, in this embodiment, the Li/Co
molar ratio is improved to 4 or more when a weakly acidic leaching
solution at pH 4.ltoreq.1.ltoreq.7 is used. This is because Li is
dissolved preferentially to Co (although detailed reaction
mechanism is not apparent). The weakly acidic leaching solution may
also be a buffer solution with addition of a material having a
buffering effect to pure water. The Li/Co molar ratio was 4 in a
case of a phthalic acid buffer solution (mixture of phthalic acid
and potassium phthalate) adjusted to pH at 4. The Li/Co selectivity
is further improved when a redox potential controller is added to
the weakly acidic solution. When a treating solution prepared by
adjusting an aqueous hydrogen peroxide to a weak acidity of pH at 4
was used as the leaching liquid, the Li/Co molar ratio was improved
greatly as 335. Further, the Li/Co molar ratio was as high as 121
also in a case of adding carbon dioxide to ozonized water.
[0031] For the lithium selective leaching solution in this
embodiment, an aqueous solution prepared by dissolving, for
example, ozone, hydrogen peroxide, or peracetic acid, can be used.
Such a solute acts as an oxidizer. Generally, in the recovery of
the valuable metals from batteries, a mineral acid at high
concentration is used for leaching lithium cobaltate to perform
complete dissolution. In this embodiment, the mineral acid at a
high concentration is not used and, further, the upper limit of the
leaching temperature is defined as 30.degree. C. If the temperature
is much higher than 30.degree. C., the rate of spontaneous
decomposition of ozone or hydrogen peroxide increases to form a
solute not contributing to the dissolution of the positive
electrode active material and the solute is consumed
wastefully.
[0032] When a leaching solution at a pH of 4 to 7 and a redox
potential of 0.3 to 0.4 V is used, a high Li/Co molar ratio tends
to be obtained. When the value of pH becomes less than 4, the
dissolution rate of the positive electrode active material
increases to increase the Li dissolution rate and the recovery rate
tends to be higher. However, the Co dissolution rate also
increases, tending to lower the Li/Co molar ratio. In a range of
the concentration of hydrogen peroxide in this embodiment
illustrated in FIG. 3, leaching of cobalt starts to increase where
the concentration of the aqueous hydrogen peroxide is higher than
15%. The Li/Co molar ratio is high in a region where the
concentration of the aqueous hydrogen peroxide is lower than 20%.
In this embodiment, since a redox potential is 0.3 V at the
concentration of aqueous hydrogen oxide of 15% and a redox
potential is 0.4 V at the concentration of aqueous hydrogen
peroxide of 20%, it has been found that a high Li/Co molar ratio is
obtained in a range of the redox potential of 0.3 to 0.4 V.
[0033] In the recovered solution (A) obtained by selective
leaching, lithium is leached selectively and the solute used in the
leaching solution (specifically, hydrogen peroxide or ozone)
spontaneously disappears. Spontaneous disappearing means that a
concentration of a certain effective ingredient lowers to about
one-half or lower of an initial concentration without adding any
chemical material for promoting neutralization or decomposition.
For example, hydrogen peroxide is spontaneously decomposed into
water molecules and oxygen molecules and ozone is spontaneously
decomposed into oxygen molecules. Most of generated oxygen
molecules are released out of the solution. Further, carbon dioxide
is vaporized and released out of the solution. Accordingly, since
the solution becomes neutral by spontaneous disappearing, a
conventional neutralization treatment used after the acid leaching
is no more necessary (S105).
[0034] Referring to the succeeding operation, since the solution of
the valuable metals obtained after the leaching treatment is a
solution of a strong acid at a high concentration in the method
proposed in the non-patent document 1 Jinqiu Xu, et al, a so-called
pH control of mixing a great amount of an alkali is inevitable
before the recovery of lithium as lithium carbonate. However,
ozonized water or aqueous hydrogen peroxide used in this embodiment
is a spontaneously disappearing solution and the pH of the
recovered solution (A) after the leaching treatment of lithium
cobaltate is weakly alkaline, that is, at a pH of about 9 to 11.
When the thus obtained recovered solution (A) is treated, for
example, by mixing an alkali metal-free carbonate such as calcium
carbonate or gaseous carbon dioxide without neutralization such as
pH adjustment, lithium can be precipitated and recovered as an
alkali metal-free lithium carbonate (S106).
[0035] Since not only the neutralization is unnecessary but also
ozone, hydrogen peroxide, gaseous carbon dioxide, or the like
spontaneously disappears and the solution left after lithium
recovery becomes water, it can be utilized again for aqueous
hydrogen peroxide or ozonized water and, as a result, a liquid
waste-free metal recovery method can be constructed.
[0036] Transition metal ingredients are recovered from a residue
(B) obtained in the separation of Li and transition metal at S104
(S107). In this embodiment, since the positive electrode active
material mainly comprising lithium cobaltate is treated, the
residue (B) obtained by the treatments so far contains a small
amount of leached lithium and cobalt. When they are separated at a
high purity or when the residue contains transition materials other
than cobalt and they are intended to be separated and recovered for
every kind of metals, they can be separated and recovered for every
kind of transition metal elements by treatment utilizing the
difference in the dissolution property of hydroxides of respective
metal elements, basically, by repeating pH control.fwdarw.settling
and recovery (S108). Co, Ni, Mn, and Fe can be separated as
hydroxides, and precipitated and recovered by pH control of the
solution also in a case where the positive electrode contains
lithium compounds other than LiCoO.sub.2, for example, olivine type
positive electrode active material such as LiNiO.sub.2,
LiMnO.sub.2, Li(Ni.sub.1/3Co.sub.1/3Mn.sub.1/3) O.sub.2,
LiCoPO.sub.4, LiFePO.sub.4, LiCoPO.sub.4F, and LiFePO.sub.4F.
Second Embodiment
[0037] The outline for the method of recovering valuable metals in
this embodiment is to be described. The method of recovering the
valuable metals in this embodiment is basically identical with that
of the first embodiment. This embodiment is different from the
first embodiment in that a spontaneously disappearing oxidizer and
a buffer solution of suppressing the spontaneous disappearing rate
of the oxidizer are used as a weakly acidic leaching solution in
the leaching treatment at S103 in FIG. 2. This can attain
compatibility between a high Li/Co molar ratio and a high Li
recovery rate in the lithium leaching reaction.
[0038] As the leaching solution in this embodiment, a mixture, for
example, of an ozonized water at a dissolved ozone concentration of
150 ppm as a spontaneously disappearing oxidizer, and an acetic
acid buffer solution (0.1M, pH 4.7) or a phthalic acid buffer
solution (0.1M, pH 4.0) as a buffer solution comprising a
carboxylic acid and a salt thereof can be used, but the kind of the
oxidizer, the kind of the carboxylic acid, and the concentration
thereof are not restricted to them. A positive electrode active
material is added to the mixed solution of the ozonized water and
the buffer solution, and stirred for about 20 minutes to leach
lithium (S103).
[0039] In this embodiment, the leaching solution and the residue
are separated for terminating the leaching treatment (S104). As the
separation method, centrifugal separation, filtration, etc. can be
adopted. Separation and recovery are possible in the centrifugal
separation by treating, for example, at a room temperature, under
10,000 rpm, for 30 seconds.
[0040] The recovery solution (A) formed by the selective leaching
described above is obtained as a lithium concentrate (S105) in
which the oxidizer (ozone) used in the leaching solution disappears
spontaneously. The Li/Co molar ratio in the recovery solution (A)
obtained in this embodiment was 4243 in a case of using an acetic
acid buffer solution and a high Li/Co molar ratio was obtained in
the same manner as in the first embodiment. Further, as illustrated
in FIG. 4, while the lithium recovery rate was 18% in a case of
using only the ozonized water as the leaching solution, it is
improved to 28% in a case of using the ozonized water and the
phthalic acid buffer solution and, further, value as high as 98% is
obtained in a case of using a mixture of the ozonized water and the
acetic acid buffer solution. As described above, a lithium recovery
method at a high lithium recovery rate and a high Li/Co molar ratio
can be established by using the ozonized water and the buffer
solution.
[0041] In the recovery of lithium, it is more preferred that both
of the lithium recovery rate and the Li/Co molar ratio in the
recovered ingredients are higher and it is preferred that the
former is about 100%. The reason why such high lithium recovery
rate can be obtained by the spontaneously disappearing oxidizer and
the buffering solution is to be described specifically later.
[0042] Phthalic acid is dissociated in an aqueous solution in
accordance with the chemical formula 1 and the chemical formula 2
shown below. The acid dissociation constant kPa (logarithm of the
reciprocal of the dissociation constant) in the chemical formula 1
is 2.94 and pKa in the chemical formula 2 is 5.41. In a preferred
pH range of: 4<pH<7 described in the first embodiment,
equilibrium in the chemical formula 1 shifts to the right
substantially completely. In the chemical formula 2, it shifts to
the right or the left depending on pH, or ingredients in the both
sides are present each in an meaningful amount. When the phthalic
acid buffer solution is used, pH is kept in a preferred range by
the equilibrium reaction depending on pH and the ozone
decomposition is suppressed to improve the lithium recovery rate
from 18% to 28%.
C.sub.6H.sub.4(COOH).sub.2C.sub.6H.sub.4(COOH)COO.sup.-+H.sup.+
(Chemical formula 1)
C.sub.6H.sub.4(COOH)COO.sup.-C.sub.6H.sub.4(COO.sup.-).sub.2+H.sup.+
(Chemical formula 2)
[0043] In this embodiment, when an acetic acid buffer solution is
used as the buffer solution, the lithium recovery rate is
outstandingly improved. The reason is to be described below.
[0044] In the preferred pH range described above, most of phthalic
acid components are dissociated. When the phthalic acid is
dissociated into C.sub.6H.sub.4(COOH)COO.sup.-, an electron density
on carboxyl groups is higher. Since the carboxylate ion is an
electron donating group, the electron density on an aromatic ring
increases as a result. Further, since the phthalic acid has an
aromatic ring in the molecular structure as a weak electron
attracting group, the electron density tends to increase. When the
electron density on the aromatic ring is high, the electrons tend
to be deprived by an oxidizer. Accordingly, when dissociated
phthalate ions and ozone as the oxidizer are present together,
ozone may sometimes oxidize a portion of the phthalate ions. In
this case, ozone after oxidizing the phthalic acid is consumed
without reaction to LiCoO.sub.2. Further, the oxidized phthalic
acid becomes a neutral radical and, since the radical cannot
contribute to the reactions in the chemical formula 1 and the
chemical formula 2, an effective concentration of ions constituting
the buffer solution is lowered to lower the buffering effect of the
solution. When the reaction of leaching LiCoO.sub.2 proceeds in a
state where the buffering function is lowered, OH.sup.- is formed
and therefore pH of the reaction solution shifts to the alkaline
side. When the reaction solution becomes alkaline, a portion of
ozone is decomposed without reaction to LiCoO.sub.2.
[0045] As the result described above, the reaction of leaching
LiCoO.sub.2 no more proceeds. The buffering solution providing the
same effect includes, for example, benzoic acid.
[0046] Compared with the phthalic acid, since an acetic acid has no
site where the electron density increases locally in the molecular
structure as the aromatic ring, electrons are less deprived by the
oxidizer, the acetic acid is less oxidized even when ozone as the
oxidizer is present together. That is, since the acetic acid is
less decomposed, the buffering effect in the reaction solution can
be maintained for a long time.
[0047] Further, since the acetic acid buffer solution can maintain
the buffering effect in the reaction solution and the pH of the
reaction solution does not become alkaline even when the dissolving
reaction of the positive electrode active materials occurs, ozone
can be suppressed from disappearing spontaneously due to increase
of pH and, as a result, ozone is utilized effectively to the
leaching reaction of LiCoO.sub.2 and a high lithium recovery rate
can be attained.
[0048] FIG. 5 illustrates a result of actually measuring the change
of a dissolved ozone concentration in the leaching reaction of
LiCoO.sub.2. As seen in FIG. 5, when the positive electrode active
material is dissolved only by ozonized water, the dissolved ozone
concentration lowers abruptly in initial several minutes and the
dissolved ozone concentration is lowered to about 5 ppm for a
leaching time of 10 minutes. On the other hand, when an acetic acid
buffer solution is added to the ozonized water, the dissolved
oxygen concentration at the leaching time described above is 50 ppm
and it can be seen that lowering of the dissolved oxygen
concentration is suppressed. That is, when the positive electrode
active material is leached, lowering of the dissolved ozone
concentration can be suppressed to maintain the concentration by
the addition of the acetic acid buffer solution to the ozonized
water. Then, by maintaining the dissolved ozone concentration at a
high level for a long time, the leaching reaction of lithium from
the positive electrode active material can be performed
efficiently.
[0049] As will be apparent from the consideration described above,
the effect of the acetic acid is not restricted only to that
obtained by the acetic acid but may be obtained also by any other
carboxylic acid having a carboxyl group and containing an aromatic
ring.
[0050] In this embodiment, while the result for the acetic acid
buffer solution is shown, other aliphatic monocarboxylic acids such
as propionic acid, butanoic acid, and pentanoic acid can be used
according to the study made by the present inventors. Acid having
the number of carbon atoms constituting the carbon chain larger
than that of the acids described above are not suitable to the
practical use since the solubility to water is lowered. The
concentration of the buffer solution used herein is generally about
0.1 mol/L and the concentration is preferably 0.001 mol/L or higher
at the lowest. The solubility of materials having a small number of
carbon atoms (values at 20.degree. C. shown by the mass of a solute
dissolved in 100 g of water and a molar concentration in this
state) is 37 g/100 g (0.005 mol/L) for propionic acid, 5.6 g/100 g
water (0.032 mol/L) for butanoic acid, and 2.4 g/100 g water (0.075
mol/L) for pentanoic acid. The oxidative decomposition rate of
aliphatic monocarboxylic acids is in the order of: butanoic acid
>propionic acid >acetic acid. The oxidative decomposition
rate is lower as the number of carbon atoms is smaller, and the
performance capable of attaining compatibility between a high
Li/transition metal separability and a high lithium recovery rate
is more excellent as the number of carbon atoms is smaller.
However, those acids having a number of carbon atoms of 0 in other
portion than the carboxyl group are not preferred. For example,
formic acid has an aldehyde group. Since the aldehyde group is
oxidized by the oxidizer and the oxidizer is consumed in the
reaction of oxidizing the buffer solution, formic acid is not
suitable. Oxalic acid is not suitable since pKa is as low as 1.25
and oxalic acid is classified as a strong acid. For polyhydric
aliphatic carboxylic acids, oxalic acid, succinic acid, tartaric
acid, citric acid, malic acid, and malonic acid can be used, in
view of pKa and solubility. Further, a customary glycine may also
be used as the buffer solution.
[0051] As described above, buffer solutions comprising materials
having the number of carbon atoms of 1 to 4 (not including carbon
atoms in the carboxyl group) and the acid dissociation constant of:
4<pH<7 are preferred with a view point of the solubility.
[0052] When the buffer solutions described above are used,
compatibility can be attained between high Li/transition metal
separability and high Li recovery rate.
[0053] For example, Chinese Patent Laid-Open No. CN101673859A
(Patent document 2) discloses a method of recovering lithium and
cobalt by using an organic acid such as citric acid, succinic acid,
malic acid, etc. for a solution of leaching a positive electrode
active material. However, since the buffer solution is not used, pH
is low and for example, pH is 1 or less in a solution of citric
acid at a concentration of 1.25 mol/L described in Example 1 of the
Patent document 2. Accordingly, LiCoO.sub.2 is entirely dissolved
and recovered lithium and cobalt are at a low purity, and a
separation operation is necessary for recovering only lithium. On
the other hand, as a result of studies made by the inventors, in
the embodiment, a weakly acidic leaching solution is suitable and
obtained metals can be purified to a high level by selectively
leaching only lithium from the positive electrode active material
and leaving only cobalt in the residue after leaching by leaching
at a weakly acidic state.
[0054] Further, as the buffer solution, not only the carboxylic
acid but also other buffer solutions may be used providing that the
buffer solution exhibits an acidity (4<pH<7). As other buffer
solutions than the carboxylic acid, a buffer solution, for example,
of phosphoric acid and a salt thereof can be used. They include,
for example, a buffer solution comprising sodium dihydrogen
phosphate and disodium hydrogen phosphate but they are not
restrictive but other compositions may also be used. When phosphor
is recovered after recovering Li from the acidic solution in which
Li is dissolved selectively, phosphor can be utilized again as a
solute of the buffer solution. The phosphor separation and recovery
method includes separating operations such as methods of using
dialysis membrane separation, acid retardation, and ion exchange
resin.
[0055] Further, while ozone was used as the spontaneously
disappearing oxidizer in this embodiment, aqueous hydrogen peroxide
may also be used instead.
[0056] While LiCoO.sub.2 was used as the positive electrode
material in this embodiment, when the positive electrode active
material contains lithium compounds other than LiCoO.sub.2, for
example, olivine type positive electrode active materials such as,
LiNiO.sub.2, LiMnO.sub.2, Li (NiCoMn)O.sub.2, LiCoPO.sub.4,
LiFePO.sub.4, LiCoPO.sub.4F, and LiFePO.sub.4F, etc., Co, Ni, Mn,
and Fe can be separated as hydroxides and recovered by
precipitation by pH control of the liquid. The operation of
recovering transition metals in this case is performed by the same
treatments as those in S107 and S108 of the first embodiment, and
the method is identical with that of the first embodiment.
[0057] As described above, a metal recovery method capable of
attaining compatibility between the high Li/transition metal
separability and the high lithium recovery rate can be provided by
the combined use of the oxidizer and the buffer solution having the
effect of suppressing the spontaneous disappearing rate of the
oxidizer and selectively leaching lithium.
* * * * *