U.S. patent application number 09/795481 was filed with the patent office on 2002-06-13 for method for separating metal ions.
This patent application is currently assigned to National Institute for Research in Inorganic Materials. Invention is credited to Komatsu, Yu, Tsurubou, Shigekazu.
Application Number | 20020070171 09/795481 |
Document ID | / |
Family ID | 18792390 |
Filed Date | 2002-06-13 |
United States Patent
Application |
20020070171 |
Kind Code |
A1 |
Komatsu, Yu ; et
al. |
June 13, 2002 |
Method for separating metal ions
Abstract
A method for separating metal ions, which comprises adding a
selective capturing agent to an aqueous solution containing plural
types of metal ions, said selective capturing agent being a cyclic
compound and forming a complex with metal ions having ion radii
suitable for the size of the ring alone, so that unnecessary metal
ions are held by the selective capturing agent in the aqueous
solution, and bringing said aqueous solution into contact with an
ion exchange solid phase so as to transport desired metal ions
alone to the solid phase.
Inventors: |
Komatsu, Yu; (Ibaraki,
JP) ; Tsurubou, Shigekazu; (Ibaraki, JP) |
Correspondence
Address: |
OBLON SPIVAK MCCLELLAND MAIER & NEUSTADT PC
FOURTH FLOOR
1755 JEFFERSON DAVIS HIGHWAY
ARLINGTON
VA
22202
US
|
Assignee: |
National Institute for Research in
Inorganic Materials
No. 1, Namiki 1-chome, Tsukuba-shi, Ibaraki Japan
Tsukuba-shi
JP
|
Family ID: |
18792390 |
Appl. No.: |
09/795481 |
Filed: |
March 1, 2001 |
Current U.S.
Class: |
210/660 ;
210/656; 423/157 |
Current CPC
Class: |
C22B 3/304 20210501;
C22B 26/20 20130101; B01J 39/04 20130101; Y02P 10/20 20151101 |
Class at
Publication: |
210/660 ;
423/157; 210/656 |
International
Class: |
B01D 015/08; C22B
026/20 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 13, 2000 |
JP |
2000-312887 |
Claims
What is claimed is:
1. A method for separating metal ions, which comprises adding a
selective capturing agent to an aqueous solution containing plural
types of metal ions, said selective capturing agent being a cyclic
compound and forming a complex with metal ions having ion radii
suitable for the size of the ring alone, so that unnecessary metal
ions are held by the selective capturing agent in the aqueous
solution, and bringing said aqueous solution into contact with an
ion exchange solid phase so as to transport desired metal ions
alone to the solid phase.
2. The method for separating metal ions according to claim 1,
wherein the plural types of metal ions are in the same Group.
3. The method for separating metal ions according to claim 2,
wherein the plural types of metal ions are at least two types
belonging to alkaline earth metal ions.
4. The method for separating metal ions according to claim 1,
wherein the selective capturing agent is a cryptand or a crown
ether.
5. The method for separating metal ions according to claim 2,
wherein the selective capturing agent is a cryptand or a crown
ether.
6. The method for separating metal ions according to claim 3,
wherein the selective capturing agent is a cryptand or a crown
ether.
Description
METHOD FOR SEPARATING METAL IONS
[0001] The present invention relates to a method for separating
metal ions. More particularly, the present invention relates to a
method for separating metal ions by separating a specific type of
metal ions while preventing inclusion of impurities to obtain metal
ions with a high purity.
[0002] As a method for separating metal ions, an ion exchange
method and a solvent extraction method are well known as
representative examples.
[0003] The ion exchange method is a separation method utilizing a
reaction wherein metal ions in an aqueous solution replace ions in
an ion exchanger and undergo phase transition. The reaction amount
is determined by the ratio of the amount of the ion exchanger to
the amount of the aqueous solution, and the separative power shows
a constant value depending upon the ion exchanger.
[0004] The solvent extraction method is a separation method
utilizing a reaction wherein metal ions in an aqueous solution
react with an extracting agent or a synergistic extracting agent
dissolved in an organic solvent and undergo phase transition into
an organic phase. The amount of the metal ions to be extracted
depends on the type of the extracting agent or the synergistic
extracting agent, and the separative power shows a constant value
characteristic to the extracting agent or the synergistic
extracting agent.
[0005] However, by either of the ion exchange method and the
solvent extraction method as representative examples of the method
for separating metal ions, inclusion of impurities is inevitable,
and complete or substantially complete separation of desired metal
ions is difficult.
[0006] Specifically, separation of alkaline earth metal ions will
be explained as an example. In the ion exchange method, when a
titania hydrate is employed as an ion exchanger, for example, in
separation of Ca and Sr which are alkaline earth metal ions
adjacent to each other, so much as 16% of impurities will be
mixed.
[0007] Further, in the solvent extraction method, as the separative
power is determined by the type of the extracting agent or the
synergistic extracting agent, depending upon the type of the
extracting agent or the synergistic extracting agent, inclusion of
at least 1% of impurities may be inevitable in separation of Ca and
Sr.
[0008] Under these circumstances, the present invention has been
made to overcome the above drawbacks of conventional methods for
separating metal ions, and it is an object of the present invention
to provide a method for separating metal ions, which comprises
separating a specific type of metal ions while preventing inclusion
of impurities to obtain metal ions with a high purity.
[0009] The present invention provides a method for separating metal
ions, which comprises adding a selective capturing agent to an
aqueous solution containing plural types of metal ions, said
selective capturing agent being a cyclic compound and forming a
complex with metal ions having ion radii suitable for the size of
the ring alone, so that unnecessary metal ions are held by the
selective capturing agent in the aqueous solution, and bringing
said aqueous solution into contact with an ion exchange solid phase
so as to transport desired metal ions alone to the solid phase.
[0010] The present invention further provides the above method
wherein the plural types of metal ions are in the same Group. The
present invention further provides the above method wherein the
plural types of metal ions are at least two types belonging to
alkaline earth metal ions. The present invention still further
provides the above method wherein the selective capturing agent is
a cryptand or a crown ether.
[0011] Now, preferred embodiments of the method for separating
metal ions of the present invention will be explained in further
detail below.
[0012] In the method for separating metal ions of the present
invention, a selective capturing agent which selectively captures
specific types of metal ions is used. This selective capturing
agent is a cyclic compound, and forms a complex with metal ions
having ion radii suitable for the size of the ring alone.
[0013] In the method for separating metal ions of the present
invention, the above selective capturing agent is added to an
aqueous solution containing plural types of metal ions, and the
aqueous solution is brought into contact with an ion exchange solid
phase.
[0014] The selective capturing agent forms a metal complex with
specific metal ions alone in the aqueous solution. This reaction
takes place in accordance with a theoretical equilibrium value, and
the metal ions forming a metal complex are held in the aqueous
solution even after the reaction. Accordingly, in the aqueous
solution, metal ion species forming a metal complex with the
selective capturing agent and metal ion species not forming a metal
complex are present, and there is a significant difference in the
ion radius between them. Metal ions capable of being held in the
aqueous solution are determined by the type of the selective
capturing agent and the size of the metal ions, and the amount of
metal ions held shows a characteristic value depending on the type
of the selective capturing agent and the type of the metal
ions.
[0015] When the aqueous solution in such a state is brought into
contact with an ion exchange solid phase, the metal ion species not
forming a metal complex alone transfers to the solid phase. The
metal ion species forming a metal complex and having a large ion
radius does not transfer. Based on this principle, in the method
for separating metal ions of the present invention, unnecessary
metal ions are held by the selective capturing agent in the aqueous
solution, and desired metal ions alone are transferred to the solid
phase. Accordingly, metal ions to be brought in the solid phase as
impurities will drastically decrease. Therefore, according to the
method for separating metal ions of the present invention, a
specific type of metal ions can be completely or substantially
completely separated while preventing inclusion of impurities, and
metal ions with a high purity can be obtained. Further, the
separation efficiency of metal ions will improve.
[0016] Here, in the method for separating metal ions of the present
invention, it is possible to separate metal ions in the same Group.
Metal ions in the same Group have the same reaction mechanism in an
ion exchange reaction, and are likely to move to the ion exchange
solid phase. However, metal ions other than desired ones are held
by the selective capturing agent in the aqueous solution, whereby
inclusion of impurities into the solid phase will be inhibited.
[0017] The selective capturing agent may optionally be determined
depending upon the ion radii of metal ions to be held, and a
cryptand or a crown ether may, for example, be mentioned. In order
to improve complex-forming ability of the selective capturing
agent, in the method for separating metal ions of the present
invention, a water-soluble organic solvent such as propanol may be
added to the aqueous solution.
[0018] Now, the present invention will be described in detail with
reference to Examples. However, it should be understood that the
present invention is by no means restricted to such specific
Examples. Further, the type of metal ions, the type of the
selective capturing agent and reaction conditions are not limited
thereto.
EXAMPLE
[0019] Into an aqueous solution containing both ions of Ca and Sr
as alkaline earth metals, cryptand [2.2.2] as a selective capturing
agent was added and dissolved, and this aqueous solution was
brought into contact with Amberlite 200CT as an ion exchange resin.
After equilibrium was reached, the amounts of metal ions in the
liquid phase and the solid phase were measured, and the results
were compared with a case where an aqueous solution containing Ca
and Sr ions was brought into contact with Amberlite 200CT without
addition of cryptand [2.2.2]. Further, the results were compared
with separation of Ca and Sr by conventional ion exchange method
and solvent extraction method. In the ion exchange method, titania
hydrate was used as the ion exchanger, and in the solvent
extraction method, TTA (thenoyltrifluoroacetone) was used as an
extracting agent, and TOPO (trioctylphosphineoxide) was used as a
synergistic extracting agent.
[0020] The results are shown in the following Tables 1 and 2.
1 TABLE 1 pH of aqueous solution 5 6 6.3-7.8 8 9 Retention of Sr
(%) Cryptand [2.2.2]added 27 88 100 88 33 Cryptand [2.2.2]not 0 0 0
0 0 added
[0021]
2 TABLE 2 Inclusion ratio of Sr (%) Present separation method 0.00
(pH 6.3-7.8) Ion exchange method 16.00 Solvent extraction method
1.01
[0022] As shown in Table 1, Sr ions having a large ion radius
undergo a complex-forming reaction with cryptand [2.2.2] and are
held in the aqueous solution. On the contrary, Ca ions having a
small ion radius do not react with cryptand [2.2.2] and move to the
ion exchange resin as the solid phase. Cryptand [2.2.2] has Sr
capturing properties in a pH of the aqueous solution of from 4 to
9, and particularly in a pH of from 6.3 to 7.8, it can capture 100%
of Sr. Accordingly, when the aqueous solution is neutral or has a
pH in the vicinity thereof, separation of Ca and Sr can be carried
out completely or substantially completely.
[0023] When cryptand [2.2.2] is not added, both Ca ions and Sr ions
move to the solid phase, and when the aqueous solution has a pH of
from 2 to 12, 100% of both metal ions move to the solid phase.
Accordingly, separation of Ca and Sr is impossible.
[0024] Further, as shown in Table 2, inclusion of impurities is
inevitable in the conventional ion exchange method and solvent
extraction method, whereas in the method for separating metal ions
of the present invention, metal ions with a high purity, without
inclusion of impurities, can be obtained.
[0025] As explained above, according to the method of the present
invention, metal ions with a high purity can be obtained by
separating a specific type of metal ions while preventing inclusion
of impurities.
* * * * *