U.S. patent application number 11/033899 was filed with the patent office on 2005-07-21 for method for producing indium-containing aqueous solution.
This patent application is currently assigned to SUMITOMO CHEMICAL COMPANY, LIMITED. Invention is credited to Fujiwara, Shinji, Koyama, Kazuya, Saegusa, Kunio.
Application Number | 20050155870 11/033899 |
Document ID | / |
Family ID | 34752116 |
Filed Date | 2005-07-21 |
United States Patent
Application |
20050155870 |
Kind Code |
A1 |
Koyama, Kazuya ; et
al. |
July 21, 2005 |
Method for producing indium-containing aqueous solution
Abstract
As an effective method for reusing ITO sintered bodies, there is
provided a method for producing an aqueous solution containing
indium ions which comprises a step of subjecting an acidic solution
containing indium ions and tin ions to an electrolytic treatment to
precipitate metallic tin and a step of removing or re-dissolving
the precipitated metallic tin.
Inventors: |
Koyama, Kazuya; (Tsukuba,
JP) ; Fujiwara, Shinji; (Tsukuba, JP) ;
Saegusa, Kunio; (Yawara, JP) |
Correspondence
Address: |
SUGHRUE MION, PLLC
2100 PENNSYLVANIA AVENUE, N.W.
SUITE 800
WASHINGTON
DC
20037
US
|
Assignee: |
SUMITOMO CHEMICAL COMPANY,
LIMITED
NATIONAL INSTITUTE OF ADVANCED INDUSTRIAL SCIENCE AND
TECHNOLOGY
|
Family ID: |
34752116 |
Appl. No.: |
11/033899 |
Filed: |
January 13, 2005 |
Current U.S.
Class: |
205/705 ;
205/704 |
Current CPC
Class: |
C22B 7/007 20130101;
Y02P 10/234 20151101; Y02P 10/20 20151101; C22B 25/06 20130101;
C22B 58/00 20130101; C22B 25/04 20130101; C22B 3/045 20130101; Y02P
10/228 20151101 |
Class at
Publication: |
205/705 ;
205/704 |
International
Class: |
C25F 001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 19, 2004 |
JP |
2004-010241 |
Jan 19, 2004 |
JP |
2004-010242 |
Claims
1. A method for producing an aqueous solution containing indium
ions which comprises a step of subjecting an acidic solution
containing indium ions and tin ions to an electrolytic treatment to
precipitate metallic tin and a step of removing or redissolving the
precipitated metallic tin.
2. A method according to claim 1, wherein the current quantity for
the electrolytic treatment is a quantity with which the tin ions
can be substantially precipitated from the acidic solution by
converting the tin ions to metallic tin; and the precipitated
metallic tin is removed.
3. A method according to claim 2, wherein the current density in
the electrolytic treatment is not less than 50 Am.sup.-2 and not
more than 800 Am.sup.-2.
4. A method according to claim 1, wherein the acidic solution
contains indium ions and tetravalent tin ions and the content of
the tetravalent tin ions exceeds 50% by weight in the total tin
ions; the current quantity for the electrolytic treatment is half
or more of the current quantity with which tetravalent tin ions can
be precipitated as metallic tin so that the content of divalent tin
ions reaches 50% by weight or more in the total tin ions; and the
precipitated metallic tin is redissolved.
5. A method according to claim 4, wherein the current density in
the electrolytic treatment is not less than 50 Am.sup.-2 and not
more than 2000 Am.sup.-2.
6. A method according to claim 1, wherein the electrolytic
treatment is carried out by passing a current through an aqueous
sulfuric acid solution in an anode chamber of an electrolytic cell
and an acidic solution containing indium ions and tin ions in a
cathode chamber of the electrolytic cell which are partitioned with
a cation exchange membrane.
7. A method according to claim 1, wherein the acidic solution
containing indium ions and tin ions is obtained by dissolving a
compound containing indium, tin and oxygen in hydrochloric acid.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a method for producing an
aqueous solution containing indium ions.
[0003] 2. Description of Related Art
[0004] An aqueous solution containing indium ions is used for
producing an indium tin oxide (hereinafter sometimes referred to as
"ITO") sintered body. An ITO sintered body is used as a target for
producing an ITO thin film by a sputtering method. An ITO thin film
is utilized as a transparent electric conductive film for a liquid
crystal display because of its high electric conductivity and
excellent transparency.
[0005] When an ITO sintered body is used as a target in a
sputtering method, the ITO sintered body is eroded with progress of
sputtering. The erosion proceeds not uniformly, but locally. When
the erosion progresses, penetrated holes are formed through the ITO
sintered body, and hence the ITO sintered body is exchanged for a
new one before the formation of holes. ITO sintered bodies which
have some still usable portions are not abandoned as they are, but
are reused, and various methods are proposed for the reuse of ITO
sintered bodies.
[0006] These proposals all employ complicated steps in an attempt
to recover high purity metallic indium or indium oxide.
[0007] For example, JP-A-2000-169991 discloses a method for
electrolytic extraction of metallic indium having a purity of
99.9999% or higher after precipitating and removing impurities as
hydroxides and sulfides.
[0008] JP-A-8-91838 discloses a method for recovery of an indium
oxide powder of 99.99% in purity by repeating extraction and back
extraction according to a solvent extraction method.
[0009] JP-A-10-204673 discloses a method for recovery of metallic
indium of 99.99% in purity by carrying out dissolving treatment of
an ITO target, replacement precipitation of impurity, and
subsequent electrolytic extraction of the metallic indium.
[0010] The recovered metallic indium of high purity is reused as a
raw material for preparation of an indium oxide powder. Indium
oxide prepared in this way or recovered as mentioned above is mixed
with tin oxide at a given ratio, and the mixture is press molded
and sintered to obtain an ITO sintered body (sintered body
producing method 1 disclosed in JP-A-3-207858).
[0011] Metallic indium or indium oxide recovered by any of these
methods is very high in purity and hence complicated steps are
required and production cost is high. Furthermore, tin in the ITO
sintered body is not reused.
[0012] As a method of producing an ITO sintered body, there is a
method which comprises co-precipitating indium hydroxide and tin
hydroxide, recovering the resulting particles, molding the
particles and sintering the molded particles (sintered body
producing method 2 disclosed in JP-A-7-247162). According to the
method disclosed in the patent document, In(NO.sub.3).sub.3 and
SnCl.sub.4.5H.sub.2O were used as the material for the
co-precipitation of indium hydroxide and tin hydroxide, and the tin
ion was tetravalent and the co-precipitated particles were
In(OH).sub.3--Sn(OH).sub.4.
BRIEF SUMMARY OF THE INVENTION
[0013] The inventors have conducted a research on a more effective
method for reuse of ITO sintered bodies and accomplished the
present invention.
[0014] That is, the present invention relates to a method for
producing an aqueous solution containing indium ions which
comprises a step of subjecting an acidic solution containing indium
ions and tin ions to an electrolytic treatment to precipitate
metallic tin and a step of removing or redissolving the
precipitated metallic tin. The method of the present invention
includes an electrolytic treatment as a main step, being different
from conventional methods.
[0015] According to the method of the present invention in which
metallic tin is removed, being different from the conventional
methods of reuse including complicated steps, indium is not
recovered as metallic indium or indium oxide of extremely high
purity, but is recovered by a simple electrolytic treatment in a
purity of such an extent as capable of being effectively utilized
at the subsequent steps for producing ITO sintered body. The method
is very simple, requires low production cost and is industrially
advantageous.
[0016] Furthermore, according to the method of the present
invention in which metallic tin is re-dissolved, tin in the ITO
sintered body is also reused. Moreover, there is obtained an
aqueous solution which contains indium ions and is high in the
content of divalent tin ions, and when this aqueous solution is
used, an ITO sintered body of high density can be obtained, which
is suitable for producing an ITO thin film having a high electric
conductivity. In addition, the compositional ratio of indium and
tin in the original sintered body is nearly reproduced, and thus
the method is industrially advantageous.
DETAILED DESCRIPTION OF THE INVENTION
[0017] The present invention relates to a method for producing an
aqueous solution containing indium ions which comprises a step of
subjecting an acidic solution containing indium ions and tin ions
to an electrolytic treatment to precipitate metallic tin and a step
of removing or re-dissolving the precipitated metallic tin.
The First Embodiment
[0018] In a preferred embodiment of the present invention, the
current quantity for the electrolytic treatment is such one as
capable of substantially precipitating tin ions from the acidic
solution by converting tin ions to metallic tin. The precipitated
metallic tin is removed.
[0019] Being different from conventional methods, this method does
not recover indium as metallic indium or indium oxide of extremely
high purity, but recovers indium by a simple electrolytic treatment
in a purity of such an extent as capable of being effectively
utilized at the subsequent steps for producing ITO sintered body.
The method is very simple, requires low production cost and is
industrially advantageous.
[0020] The current quantity for the electrolytic treatment is such
one with which the tin ions can be substantially precipitated from
the acidic solution by converting tin ions to metallic tin, and is
preferably not less than 1-fold and not more than 3-fold, more
preferably not less than 1-fold and not more than 2-fold of the
current quantity actually needed for converting 80% of tin ions
contained in the acidic solution to metallic tin. If the current
quantity is too much, metallic indium is precipitated, resulting in
reduction of indium ion concentration. The precipitated tin which
deposits on an electrode upon the completion of the electrolytic
treatment can be separated together with the electrode and the
precipitated tin which is liberated from the electrode can be
separated by filtration or the like. When the electrolytic
treatment is stopped, dissolution of the precipitated metallic tin
spontaneously begins and hence it is preferred to carry out the
removal of the electrode or the filtration immediately after
completion of the electrolytic treatment.
[0021] The current density in the electrolytic treatment is
preferably not less than 50 Am.sup.-2 and not more than 800
Am.sup.-2, more preferably not less than 100 Am.sup.-2 and not more
than 700 Am.sup.-2, further preferably not less than 400 Am.sup.-2
and not more than 600 Am.sup.-2. If the current density exceeds 800
Am.sup.-2, metallic indium tends to be also precipitated in
addition to the metallic tin. If the current density is less than
50 Am.sup.-2, a long time may be required for the precipitation of
metallic tin.
[0022] The amount of tin ions remaining in the aqueous solution is
preferably 2% by weight or less, more preferably 1% by weight or
less based on the total amount of indium ions and tin ions.
[0023] The thus obtained aqueous solution containing indium from
which tin ions are substantially removed may be utilized in the
following manner. That is, metallic indium may be precipitated by
further electrolyzing the aqueous solution. Furthermore, an indium
oxide powder may be produced by oxidizing the metallic indium, and
an ITO sintered body may be produced by mixing the powder with a
tin oxide powder, molding the mixture and sintering the molded
mixture.
[0024] Moreover, an aqueous solution containing divalent tin ions
is added to the indium-containing aqueous solution from which tin
ions are substantially removed, thereby to prepare an aqueous
solution containing indium ions and mainly divalent tin ions, and
an ITO sintered body may be produced from the aqueous solution as
mentioned hereinafter.
[0025] In any of these methods, the amount of the tin oxide powder
added and the amount of the tin ions added can be determined in
relation with the concentration of indium ions depending on the
amount of tin contained in the final ITO powder. The amount of tin
contained in the ITO powder in terms of oxide is 2-20% by weight,
usually 10-20% by weight based on the total amount of indium oxide
and tin oxide.
The Second Embodiment
[0026] In another preferred embodiment of the present invention,
the electrolytic precipitated metallic tin is redissolved.
[0027] In an aqueous solution, tin is present in the state of being
divalent or tetravalent. According to the present invention,
tetravalent tin ions are precipitated as metallic tin in preference
to divalent tin ions by the electrolytic treatment, and the
precipitated metallic tin redissolves in the aqueous solution as
divalent tin ions. Therefore, the amount of divalent tin ions with
respect to the total tin ions in the aqueous solution can be
increased without substantial increase of tin ions.
[0028] The inventors have found that when precipitates of
hydroxides of indium and tin are produced from an aqueous solution
containing indium ions and tin ions and containing divalent tin
ions in an amount of 50% by weight or more of the total tin ions
(total of divalent tin ions and tetravalent tin ions), an ITO
sintered body obtained therefrom has a high density, and when this
sintered body is used as a sputtering target, an ITO thin film
having a high electric conductivity can be obtained (Japanese
Patent Application No. 2003-319439). In the above invention, the
inventors have proposed a method for producing an aqueous solution
containing divalent tin ions in an amount of 50% by weight or more
of the total tin ions by adding metallic tin to an acidic solution
containing mainly tetravalent tin ions which is obtained by
dissolving the ITO sintered body in an acid, thereby decreasing
tetravalent tin ions and increasing divalent tin ions in accordance
with the following formula (1):
Sn+Sn.sup.4+.fwdarw.2Sn.sup.2+ (1)
[0029] According to this method, the amount of the total tin ions
in the aqueous acidic solution increases and the amount of tin ions
with respect to indium ions increases.
[0030] On the other hand, in the method of the present invention,
it is utilized that tetravalent tin ions are precipitated as
metallic tin by the electrolytic treatment in preference to
divalent tin ions, and the precipitated metallic tin is redissolved
as divalent tin ions. Therefore, an aqueous solution containing
divalent tin ions in an amount of 50% by weight or more of the
total tin ions can be simply produced without substantial increase
of tin ions.
[0031] The indium-containing aqueous solution obtained by this
method is low in the content of tetravalent tin ions, and when
substantially all of the precipitated tin is dissolved, the
solution has tin ion and indium ion at nearly the same
compositional ratio as in the original sintered body. An ITO
sintered body may be produced by a known method by co-precipitating
these ions and calcining the precipitate and molding the calcined
powder and sintering. The ITO sintered body produced using the
indium-containing aqueous solution obtained by the method of the
present invention has a high density and is suitable as a
sputtering target for producing a transparent electric conductive
film. Moreover, the present invention is also industrially
advantageous in view of the facts that tin in the ITO sintered body
is also reused and nearly the same compositional ratio of indium
and tin as in the original sintered body can be reproduced.
[0032] It is preferred that the acidic solution used contains
indium ions and tin ions and the content of tetravalent tin ions
exceeds 50% by weight in the total tin ions. For example, tin ions
contained in an acidic solution obtained by dissolving an ITO
sintered body in an acid are mainly tetravalent, and such an acidic
solution can be suitably used.
[0033] The current quantity passed in the electrolytic treatment is
preferably half or more of the current quantity required for
precipitating tetravalent tin ions as metallic tin so that the
content of divalent tin ions reaches 50% by weight or more of the
total amount of tin ions. Since at least a part, preferably,
substantially all of the precipitated metallic tin is redissolved
as divalent tin ions, the current quantity is half or more of the
current quantity required for precipitating tetravalent tin ions as
metallic tin. Specifically, first the amount of tetravalent tin
ions necessary for decreasing the proportion of tetravalent tin
ions in the total tin ions to less than 50% by weight in the acidic
solution is calculated, and then a current quantity necessary to
reduce the tetravalent tin ions to metallic tin is calculated. The
current quantity passed in the electrolytic treatment is not less
than 0.5-fold, preferably not less than 0.5-fold and not more than
10-fold, more preferably not less than 0.5-fold and not more than
5-fold of the current quantity obtained above. If the current
quantity is too much, metallic indium is precipitated subsequent to
metallic tin. When the electrolytic treatment is discontinued, all
of the precipitated metallic indium may be dissolved in the acidic
solution, and, therefore, after completion of dissolution of all
the metallic indium, the indium ion concentration in the acidic
solution does not change from the concentration before the
electrolytic treatment, but energy efficiency lowers.
[0034] The current density in the electrolytic treatment is
preferably not less than 50 Am.sup.-2 and not more than 2000
Am.sup.-2, more preferably not less than 100 Am.sup.-2 and not more
than 1500 Am.sup.-2, further preferably not less than 400 Am.sup.-2
and not more than 600 Am.sup.-2. If the current density exceeds
2000 Am.sup.-2, hydrogen gas is sometimes generated from cathode.
If it is less than 50 Am.sup.-2, a long time is required for the
precipitation of metallic tin.
[0035] At the stage of completion of the electrolytic treatment,
the proportion of divalent tin ions in the total tin ions in the
acidic solution sometimes already reaches 50% by weight or more.
Furthermore, all of the metallic tin precipitated at the stage of
completion of the electrolytic treatment may be present on the
cathode or may be present in the state of being partly liberated in
the solution.
[0036] Then, the precipitated metallic tin and, if present, the
liberated tin are dissolved and tetravalent tin ions remaining in
the acidic solution is reduced to divalent tin ions in accordance
with the formula (1). The dissolution of metallic tin spontaneously
begins immediately after discontinuation of the electrolytic
treatment.
Sn+Sn.sup.4+.fwdarw.2Sn.sup.2+ (1)
[0037] The precipitated metallic tin may be separated from the
acidic solution without using it and metallic tin separately
prepared may be added to the acidic solution and dissolved therein,
but it is preferred to use the precipitated metallic tin because
the amount of tin ions in the acidic solution does not change from
the amount before the electrolytic treatment.
[0038] The reduction treatment with dissolution of metallic tin is
preferably carried out in an inert gas atmosphere such as N.sub.2
or Ar, more preferably carried out in an inert gas atmosphere while
stirring the acidic solution.
[0039] The temperature at the time of dissolution of the metallic
tin is not particularly limited and may be optionally selected
within the industrially usually employed range. The dissolution is
usually carried out at a temperature of not lower than 0.degree. C.
and not higher than 90.degree. C., and the higher temperature is
preferred since the reduction of tetravalent tin ions by the
dissolution of the metallic tin is accelerated. The time of the
reduction treatment by the dissolution of the metallic tin is not
necessarily limited since it varies depending on the reaction
temperature or the proportion of divalent tin ions in the aqueous
solution to be finally obtained, and it is usually 1 hour or more,
preferably 3 hours or more, more preferably 5 hours or more.
[0040] In case a part of metallic tin remains in undissolved state
after the reduction treatment by the dissolution of metallic tin,
such metallic tin may be separated from the aqueous solution by a
method such as filtration.
[0041] Furthermore, only one electrolytic operation and one
operation of dissolution of metallic tin are described above, but
also, for example, the electrolytic operation and the operation of
dissolution of metallic tin may-be repeatedly carried out several
times.
[0042] The proportion of divalent tin ions in total tin ions in the
aqueous solution obtained as mentioned above is 50% by weight or
more, preferably 70% by weight or more, further preferably 80% by
weight or more.
[0043] If necessary, concentrations of indium and tin may be
adjusted by further adding an aqueous solution containing divalent
tin ions or an aqueous solution containing indium ions. In this
case, the concentrations of indium and tin may be determined in
relation with the concentration of indium depending on the amount
of tin contained in the ITO powder to be obtained finally. The
amount of tin contained in the ITO powder is 2-20% by weight,
usually 10-20% by weight in terms of an oxide based on the total
amount of indium oxide and tin oxide.
[0044] The resulting aqueous solution containing indium and
divalent tin ions is easily oxidized, for example, by leaving it in
the air, and the divalent tin ions change to tetravalent tin ions.
Therefore, the aqueous solution is preferably stored in an inert
atmosphere in a container sealed hermetically.
[0045] When electrolysis is started, metallic tin is usually
deposited on a cathode electrode. However, if the current density
is low and the temperature of the acidic solution is high, it
sometimes occurs that the precipitation of metallic tin cannot
visually be observed and the precipitated metallic tin is
immediately dissolved. Therefore, the above method includes the
case where the precipitation of metallic tin is not visually
observed. Further, precipitation of metallic tin and dissolution of
metallic tin sometimes proceed simultaneously, and the present
invention also includes this case.
[0046] Electrolytic Treatment
[0047] Conditions of electrolytic treatment and others which are
common to the above embodiments 1 and 2 are as follows.
[0048] The method of electrolytic treatment may be either of
constant current method and constant voltage method (constant
potential method), but the constant current method is preferred. In
the case of using the constant current method, the electrolytic
treatment is carried out with the current density as mentioned
above.
[0049] In the case of using the constant voltage method, the
cathode potential is -0.6 V or higher, preferably -0.45 V or
higher, more preferably -0.4 V or higher according to standard
hydrogen electrode. If the potential is lower than -0.6 V, hydrogen
gas may be generated from the cathode electrode plate.
[0050] Materials of the electrode used for the electrolytic
treatment are preferably insoluble platinum, indium, dimensionally
stable electrode or carbon electrode plate as an anode electrode,
and tin, copper, titanium or platinum as a cathode electrode. When
the electrolysis is started, metallic tin is deposited on a cathode
electrode.
[0051] The temperature of the electrolyte during electrolytic
treatment is not particularly limited and may be optionally
selected within the range which is usually employed for industrial
electrolytic treatment. The electrolytic treatment is usually
carried out at a temperature of 0.degree. C. or higher and
80.degree. C. or lower.
[0052] Since the divalent tin ions are gradually oxidized to
tetravalent tin ions with oxygen in the air, the electrolytic
treatment is preferably carried out in an inert gas atmosphere such
as N.sub.2 or Ar. More preferably, the electrolytic treatment is
carried out in an inert gas atmosphere while stirring the acidic
solution.
[0053] When hydrochloric acid is contained in the acidic solution,
chlorine gas may be generated from the anode electrode. In this
case, it is preferred to partition the electrolytic cell with a
cation exchange membrane and to carry out the electrolytic
treatment by passing a current through an aqueous sulfuric acid
solution in the anode chamber and the acidic solution containing
indium ions and tin ions in the cathode chamber.
[0054] When dissolution of metallic indium as the anode electrode
is allowed to preferentially take place, generation of chlorine gas
can sometimes be inhibited even hydrochloric acid is contained in
the acidic solution. In this case, the electrolytic treatment may
be carried out without using the cation exchange membrane.
[0055] As the acidic solution containing indium ions and tin ions,
mention may be made of, for example, an acidic solution prepared by
dissolving a compound containing indium, tin and oxygen, such as
ITO or an indium hydroxide-tin hydroxide mixture in an acid such as
hydrochloric acid, sulfuric acid or nitric acid. The acidic
solution is not limited to the above examples. Industrially, the
present invention is effectively employed for reusing ITO sintered
bodies removed from used ITO targets, ITO powders below quality
standards, ITO sintered bodies below quality standards, cutting
wastes of ITO sintered bodies, etc.
[0056] A method using a used ITO target will be explained
below.
[0057] Since a used ITO target is recovered in such a state that an
ITO sintered body is adhered to a backing plate made of copper by
indium soldering and the like, the recovered target is heated to
about 150-200.degree. C. and the ITO sintered body is peeled off
from the backing plate. In some case, the indium solder used for
adhering the ITO sintered body to the backing plate may attach to
the ITO sintered body peeled off and removed. The indium solder
sometimes contains impurities such as Cu and Pb, and, besides,
extraneous substances containing Si, Al, Fe, etc. sometimes attach
to the surface of the ITO sintered body. Therefore, it is preferred
to wash the ITO sintered body with an acid to remove the indium
solder or extraneous substances.
[0058] It is preferred that the ITO sintered body is previously
ground for improving dissolution rate into acid. The grinding
method is not particularly limited, and there can be used a jaw
crusher, roll crusher, disk mill, vibration mill and the like which
are industrially usually employed. The material of a part of these
grinding machines which contacts with the ITO sintered body to be
ground is preferably ceramics such as alumina, zirconia or tungsten
carbide which is hardly worn. In the case of the above material
being metal, the metal sticks to the ground ITO sintered body to
cause contamination, and it sometimes become necessary to remove
metal impurities from a solution prepared by dissolving the ITO
sintered body (hereinafter sometimes referred to as merely
"solution"). The size of the ITO sintered body after grinding is
preferably 20 mm or less, more preferably 2 mm or less, most
preferably 0.5 mm or less.
[0059] The acid for dissolving the ITO sintered body includes, for
example, hydrochloric acid, sulfuric acid, nitric acid or the like.
Hydrochloric acid which is high in dissolution rate of ITO is
preferred. A case of using hydrochloric acid will be explained
below. The dissolution method is not particularly limited, and
mention may be made of, for example, a method of charging
hydrochloric acid and the ground ITO sintered body in a reaction
vessel, followed by stirring.
[0060] The temperature and time for dissolving the ITO sintered
body with acid are not particularly limited, and industrially
advantageous temperature and time can be selected. The temperature
is usually 40.degree. C. or higher and 100.degree. C. or lower,
preferably 60.degree. C. or higher and 80.degree. C. or lower, and
the dissolution time is usually 100 hours or less, preferably 50
hours or less, further preferably 24 hours or less. The indium
concentration in the solution obtained by dissolving the ITO
sintered body is preferably not less than 50 g/L and not more than
350 g/L, more preferably not less than 100 g/L and not more than
350 g/L.
[0061] In the resulting solution, there sometimes remain fragments
of undissolved ITO sintered body or ceramics particles incorporated
from the parts of the grinding machines. In this case, these solids
are removed by a solid-liquid separation such as filtration and
only the liquid is recovered.
[0062] Furthermore, Zr, Al, Si, Fe and the like are sometimes
contained as impurities. In this case, it is preferred to add a
step of allowing the solution to contact with an ion exchange resin
such as a cation exchange resin or an anion exchange resin to
remove these impurities. Especially, when a solution obtained by
grinding an ITO sintered body and dissolving the ground ITO
sintered body is used, there is a high possibility of containing
Zr, Al, Si, Fe and the like as impurities, and it is preferred to
add a step of allowing the solution to contact with an ion exchange
resin to remove these impurities. The tin ions contained in the
thus obtained ITO solution are tetravalent, and there are contained
ion species similar to those in an aqueous solution obtained by
dissolving indium chloride and stannic chloride. The above step may
be carried out before or after the electrolytic treatment, and may
be carried out after the reduction treatment.
[0063] Having thus generally described the present invention, the
following specific examples are provided to illustrate the
invention. The examples are not intended to limit the scope of the
invention in any way.
EXAMPLES
[0064] As the acidic solution containing indium ions and tin ions,
the following solutions were used in Examples 1-4.
[0065] [Acidic solution A]: A used ITO target was ground to about
1-4 mm by a jaw crusher and dissolved in hydrochloric acid having a
concentration of 35% by weight. The resulting solution was diluted
with pure water to obtain an acidic solution A having an In
concentration of 167.2 g/L and an Sn concentration of 17.7 g/L.
[0066] [Acidic solution B]: A used ITO target was ground to about
1-4 mm by a jaw crusher and dissolved in hydrochloric acid having a
concentration of 35% by weight. The resulting solution was diluted
with pure water and passed through a column packed with a cation
exchange resin to remove impurity Zr, thereby obtaining an acidic
solution B having an In concentration of 159.6 g/L and an Sn
concentration of 14.8 g/L.
[0067] The indium and tin ion concentrations were measured by ICP
spectrometry.
Example 1
[0068] In a 100 mL beaker was charged 98 mL of the acidic solution
A, followed by stirring while blowing N.sub.2 gas into the beaker.
An electrolytic treatment was carried out using a metallic indium
plate of 30.times.20 mm as an anode electrode and a metallic tin
plate of 30.times.30 mm as a cathode electrode at a current density
of 780 Am.sup.-2 at room temperature (about 25.degree. C.) for 60
minutes. Concentrations of indium ions and tin ions in the
resulting aqueous solution were 182.9 g/L (indium ion concentration
increased over the concentration before the electrolytic treatment
since there occurred dissolution of metallic indium used as the
anode) and 2.5 g/L respectively. The tin ion concentration after
the electrolytic treatment was 14% of the tin ion concentration
before the electrolytic treatment (1.3% by weight of the total
metal ions).
Example 2
[0069] 50 mL of the acidic solution B was charged in a cathode
electrode chamber of an electrolytic cell partitioned with a cation
exchange membrane, followed by stirring while blowing N.sub.2 gas
thereinto. Furthermore, sulfuric acid of 1 N in concentration was
charged in an anode electrode chamber. An electrolytic treatment
was carried out using a metallic copper plate of 36.times.25 mm as
a cathode electrode and a platinum plate of 30.times.20 mm as an
anode electrode at a current density of 200 Am.sup.-2 at room
temperature (about 25.degree. C.) for 3 hours. Concentrations of
indium ions and tin ions in the resulting aqueous solution were
158.7 g/L and 2.8 g/L respectively. The tin ion concentration after
the electrolytic treatment was 19% of the tin ion concentration
before the electrolytic treatment (1.7% by weight of the total
metal ions).
Example 3
[0070] 50 mL of the acidic solution B was charged in a cathode
electrode chamber of an electrolytic cell partitioned with a cation
exchange membrane, followed by stirring while blowing N.sub.2 gas
thereinto. Furthermore, sulfuric acid of 1 N in concentration was
charged in an anode electrode chamber. An electrolytic treatment
was carried out using a Cu plate of 36.times.25 mm as a cathode
electrode and a platinum plate of 30.times.20 mm as an anode
electrode at a current density of 400 Am.sup.-2 at room temperature
(about 25.degree. C.) for 2 hours. The indium ion concentration and
tin ion concentration in the resulting aqueous solution were 155.6
g/L and 1.5 g/L respectively. The tin ion concentration after the
electrolytic treatment was 10% of the tin ion concentration before
the electrolytic treatment (0.95% by weight of the total metal
ions).
Example 4
[0071] 50 mL of the acidic solution B was charged in a cathode
electrode chamber of an electrolytic cell partitioned with a cation
exchange membrane, followed by stirring while blowing N.sub.2 gas
thereinto. Furthermore, 1 N sulfuric acid was charged in an anode
electrode chamber. An electrolytic treatment was carried out using
a metallic copper plate of 36.times.25 mm as a cathode electrode
and a platinum plate of 30.times.20 mm as an anode electrode at a
current density of 600 Am.sup.-2 at room temperature (about
25.degree. C.) for 2 hours. The indium ion concentration and tin
ion concentration in the resulting aqueous solution were 145.8 g/L
and 0.3 g/L respectively. The tin ion concentration after the
electrolytic treatment was 2% of the tin ion concentration before
the electrolytic treatment (0.2% by weight of the total metal
ions).
[0072] As the acidic solution containing indium ions and
tetravalent tin ions, the following solutions were used in Examples
5-8. The solutions substantially do not contain divalent tin
ion.
[0073] [Acidic solution B]: A used ITO target was ground to about
1-4 mm by a jaw crusher and dissolved in an aqueous hydrochloric
acid solution having a concentration of 35% by weight. The
resulting aqueous solution was diluted with pure water and allowed
to contact with a cation exchange resin to remove the impurity Zr,
thereby obtaining an acidic solution A having an indium ion
concentration of 159.6 g/L and a tetravalent tin ion concentration
of 14.8 g/L.
[0074] [Acidic solution C]: Stannic chloride pentahydrate
(SnCl.sub.4.5H.sub.2O) was added to an acidic solution obtained by
dissolving metallic indium in an aqueous hydrochloric acid solution
having a concentration of 35% by weight to prepare an acidic
solution B containing indium ions and tetravalent tin ions and
having an indium ion concentration of 334.7 g/L and a tetravalent
tin ion concentration of 36.3 g/L.
[0075] [Acidic solution D]: Stannic chloride pentahydrate
(SnCl.sub.4.5H.sub.2O) was added to an acidic solution obtained by
dissolving metallic indium in an aqueous hydrochloric acid solution
having a concentration of 35% by weight to prepare an acidic
solution C containing indium ions and tetravalent tin ions and
having an indium ion concentration of 346.2 g/L and a tetravalent
tin ion concentration of 36.5 g/L.
[0076] [Acidic solution E]: A used ITO target was ground to about
1-4 mm by a jaw crusher and dissolved in an aqueous hydrochloric
acid solution having a concentration of 35% by weight to prepare an
acidic solution D containing indium ions and tetravalent tin ions
and having an indium ion concentration of 333.4 g/L and a
tetravalent tin ion concentration of 34.3 g/L.
[0077] The indium ion concentration in the acidic solution was
measured by ICP spectrometry, the total tin ion concentration
(concentration of divalent tin ions+tetravalent tin ions) was
measured by iodometric titration or ICP spectrometry, and the
divalent tin ion concentration was measured by iodometric
titration.
Example 5
[0078] 50 mL of the acidic solution B was charged in the cathode
electrode chamber of an electrolytic cell partitioned with a cation
exchange membrane, followed by stirring while blowing N.sub.2 gas
into the acidic solution. Furthermore, 50 mL of 1 N aqueous
sulfuric acid solution was charged in the anode electrode chamber.
An electrolytic treatment was carried out using a copper plate of
36.times.25 mm as a cathode electrode and a platinum plate of
30.times.20 mm as an anode electrode at a current density of 400
Am.sup.-2 at room temperature (about 25.degree. C.) for 55 minutes.
Then, the electrolytic treatment was stopped and the content was
left to stand for 5 hours to obtain an acidic solution having an
indium ion concentration of 157 g/L, a total tin ion concentration
of 10.5 g/L and a divalent tin ion concentration of 6.4 g/L. The
proportion of divalent tin ions in the tin ions in this acidic
solution was 61% by weight.
Example 6
[0079] 50 mL of the acidic solution C was charged in the cathode
electrode chamber of an electrolytic cell partitioned with a cation
exchange membrane, followed by stirring while blowing N.sub.2 gas
thereinto. Furthermore, 50 mL of 1 N aqueous sulfuric acid solution
was charged in the anode electrode chamber. An electrolytic
treatment was carried out using a copper plate of 36.times.25 mm as
a cathode electrode and a platinum plate of 30.times.20 mm as an
anode electrode at a current density of 600 Am.sup.-2 at room
temperature (about 25.degree. C.) for 55 minutes. Then, the
electrolytic treatment was stopped and the content was left to
stand for 5 hours to obtain an acidic solution having an indium ion
concentration of 331 g/L, a total tin ion concentration of 34.7 g/L
and a divalent tin ion concentration of 29.8 g/L. The proportion of
divalent tin ions in the tin ions in this acidic solution was 86%
by weight.
Example 7
[0080] 100 mL of the acidic solution D was charged in the cathode
electrode chamber of an electrolytic cell partitioned with a cation
exchange membrane, and N.sub.2 gas was blown into the acidic
solution at 200 mL/min. Furthermore, 100 mL of 1 N aqueous sulfuric
acid solution was charged in the anode electrode chamber. An
electrolytic treatment was carried out using an Sn plate of
38.times.30 mm as a cathode electrode and a platinum plate of
38.times.30 mm as an anode electrode at a current density of 350
Am.sup.-2 at room temperature (about 25.degree. C.) for 4 hours.
Then, the electrolytic treatment was stopped and the content was
left to stand for 4 hours to obtain an acidic solution having an
indium ion concentration of 287.5 g/L, a total tin ion
concentration of 31.1 g/L and a divalent tin ion concentration of
31.0 g/L. The proportion of divalent tin ions in the tin ions in
this acidic solution was more than 99% by weight. The impurity
concentration in this acidic solution was measured by an ICP
spectrometric apparatus to find that concentrations of Al, Si, Fe,
Cu and Zn were less than 1 wt ppm and that of Pb was less than 2 wt
ppm.
Example 8
[0081] 100 mL of the acidic solution E was charged in the cathode
electrode chamber of an electrolytic cell partitioned with a cation
exchange membrane, followed by stirring. In this case, N.sub.2 gas
was blown into the cathode chamber at 200 mL/min. Furthermore, 100
mL of 1 N aqueous sulfuric acid solution was charged in the anode
electrode chamber. An electrolytic treatment was carried out using
an Sn plate of 38.times.30 mm as a cathode electrode and a platinum
plate of 38.times.30 mm as an anode electrode at a current density
of 260 Am.sup.-2 at room temperature (about 25.degree. C.) for 35
minutes. Further electrolytic treatment was carried out at a
current density of 310 Am.sup.-2 for 235 minutes. Then, the
electrolytic treatment was stopped and the content was left to
stand for 4 hours to obtain an acidic solution having an indium ion
concentration of 289.6 g/L, a total tin ion concentration of 28.6
g/L and a divalent tin ion concentration of 27.5 g/L. The
proportion of divalent tin ions in the tin ions in this acidic
solution was 96% by weight.
* * * * *