JP3310730B2 - Adsorbent for separation of rare earth metals - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an adsorbent for efficiently separating one or several kinds of rare earth metals from an aqueous solution containing rare earth metals.

[0002]

2. Description of the Related Art Rare earth metals are the core raw materials of various new materials that support modern advanced technology, and their use and demand are expected to expand further in the future.
Along with this, the demand for very high purity is growing rapidly. The rare earth metal is a general term for 17 kinds of elements obtained by adding yttrium and scandium to 15 kinds of lanthanide elements from lanthanum to thulium. These elements are similar in chemistry and their separation is very difficult. Therefore, there is a strong demand for the development of separation and purification techniques for producing high-purity rare earth metals.

At present, solvent extraction and ion exchange are mainly used for the separation and purification of rare earth metals. Among them, the former is suitable for continuously processing a large amount of raw materials, but it is necessary to use several dozen stages of mixer settler for advanced separation.

The latter is a method in which rare earths as raw materials are collectively adsorbed on a cation exchange resin, and eluted and developed into individual elements using a complexing agent having a selective elution function such as EDTA. That is, in this case, the cation exchange resin used for the adsorption of the rare earth metal has no function of individually and selectively adsorbing the individual rare earth metals, and the separation into the individual rare earth metals is carried out by using an eluent such as EDTA. This is performed using the selective elution property of the complexing agent. In this method, since a complexing agent used for elution is expensive, it has been desired to develop an adsorbent having a selective adsorption function for expressing selectivity at the stage of adsorption. If such an adsorbent can be used,
Elution can be performed with an inexpensive inorganic acid, and the cost of separation can be greatly reduced.

[0005] Recently, as such an adsorbent, an extractant such as bis (2-ethylhexyl) phosphoric acid or PC-88A, which has a high selectivity and is used as a rare earth solvent extraction reagent, is used in XAD.
A material impregnated with a porous resin such as -7 has attracted attention and is widely used. However, such an impregnated resin has a problem that the impregnated extraction reagent gradually leaks over a long period of use, and the adsorption function is deteriorated.

An object of the present invention is to provide an inexpensive adsorbent which has the ability to identify and select individual rare earth metals.

That is, the adsorbent according to the present invention uses one of the hydrogen atoms of the amino group bonded to the C ₂ position of chitosan as (C
ＯO) CH ₂ N (CH ₂ COOH) CH ₂ CH ₂ N (C
It comprises chemically modified chitosan substituted with a polyaminocarboxyl group represented by (H ₂ COOH) CH ₂ CH ₂ N (CH ₂ COOH) ₂ , thereby solving the above problem.

The adsorbent of the present invention has a high selectivity having a polyaminocarboxylic acid functional group similar to EDTA conventionally used as an eluent as described above, and the polyaminocarboxylic acid has a high functional group. It is chemically bonded to the parent of the molecule, and does not cause the above-mentioned leakage problem even during long-term use.

The adsorbent of the present invention can be produced at low cost because the base polymer is chitosan obtained from shrimp and crab shells as biomass waste.

Formula 1 shows the chemical structure of chitosan as a raw material of the adsorbent of the present invention, and Formula 2 shows the chemical structure of the adsorbent of the present invention. Such an adsorbent of the present invention can be obtained by simply stirring the raw material chitosan represented by the formula 1 and diethylene triamine pentaacetic acid in a mixed aqueous solution of acetic acid and methanol at a molar ratio of 1: 3 for about 12 hours at room temperature. It can be easily synthesized. This adsorbent is a fine powder with an average particle size of 0.5 mm or less, similar to the raw material chitosan, but has a particle size of several mm using existing technology so that it can be easily used as a filler. Can also be processed into particles.

[0011]

(Equation 1)

[0012]

(Equation 2)

[0013]

Example 1 5 g in 200 ml of a 2% by volume dilute aqueous acetic acid solution
Dissolve chitosan, add methanol and add 500ml
100 ml of methanol in which 33 g of anhydrous diethylenetriaminepentaacetic acid was suspended was added to the solution, and methanol was further added to obtain a 750 ml solution. After the solution was stirred overnight at room temperature, the precipitate was filtered and washed with a 0.5 M aqueous sodium hydroxide solution to remove unreacted diethylenetriaminepentaacetic acid. It was washed with distilled water and a 0.1N aqueous sulfuric acid solution, and finally washed again with distilled water until the effluent became neutral. Vacuum drying was performed to obtain 5.3 g of a white powder. The amount of carboxyl groups in the solid powder was determined by neutralization titration, and the introduction rate of the functional groups was determined to be 22%.

[0014]

Example 2 0.05 g of the adsorbent synthesized in Example 1
Was shaken in an Erlenmeyer flask maintained at 30 ° C. with various concentrations of a dilute sulfuric acid aqueous solution containing various kinds of rare earth metals at a concentration of about 0.1 mmol / dm ³ , and a distribution coefficient as shown in FIG. 1 was obtained. The relationship between pH and pH was obtained. The separation coefficients obtained from the distribution coefficient values of each metal at pH = 2 are as follows. That is, Ce / La: 7.76, Pr /
Ce: 1.95, Nd / Pr: 2.27, Y / Nd:
2.14, Sm / Y: 1.69, Eu and Gd / S
m: 2.09 and Dy / Gd: 1.48. When these are compared with those of D2EHPA widely used as a solvent extraction reagent, Ce / La: 2.98, Pr / C
e: 2.06, Nd / Pr: 1.38, Pr / C
e has almost the same separation coefficient as D2EHPA,
The separation coefficients for e / La and Nd / Pr are quite large. From this, it is clear that the present adsorbent has a particularly excellent function for separating light rare earths from each other.

[0015]

[Comparative Example] Using a polystyrene manufactured by REANAL as a base material and 0.1 g of a chelating resin LIGNDEX-E having a functional group of ethylenediamine triacetic acid, about 0.4 g was used.
1m, including a variety of rare earth metals concentration of mmol / dm ³
ol / dm ³ aqueous solution of sodium nitrate 10ml
When the mixture was shaken in an Erlenmeyer flask maintained at a temperature of, the relationship between the partition coefficient and the pH of each rare earth metal shown in FIG. 2 was obtained. Although there are some variations, the plots of the six kinds of rare earth metals shown in the figure are almost on the same line, and it is clear that it is impossible to separate the rare earth metals using this chelate resin.

[0016]

According to the present invention as described above, it has high discrimination and selectivity for individual rare earth metals, and can be separated and eluted into individual components with an inexpensive inorganic acid. An inexpensive adsorbent suitable for effective high-level separation and durable for a long period of time is obtained, and the effect is great.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between the distribution coefficient (D) and the pH in the adsorption of various rare earth metals by the adsorbent of the present invention.

FIG. 2 Distribution coefficient (D) and pH in adsorption of various rare earth metals by LIGNDEX-E resin used in Comparative Example
FIG.

────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Ryuji Niihara 12-12 Onimarucho, Saga City, Saga Prefecture Nindai Apartment Room 6 (72) Inventor Norio Nakashi Ebisu Building 406, Nakamachi 2-chome, Omuta-shi, Fukuoka Prefecture (72) Inventor Takashi Hashida 210 Shirokane Heights 202, Shirokanecho, Omuta-shi, Fukuoka Prefecture (72) Koki Domoto Inventor 247-6, Oike, Miike, Omuta-shi, Fukuoka Prefecture (58) Field surveyed (Int.Cl. ⁷ , DB name) C22B 1 / 00-61/00 B01D 15/00 B01J 20/24

Claims (1)

(57) [Claims] 1. One of the hydrogen atoms of an amino group bonded to the C ₂ position of chitosan is replaced with (C ＝ O) CH ₂ N (CH ₂ COO
_{H) CH 2 CH 2 N (} CH 2 COOH) CH 2 CH 2 N
An adsorbent for separating rare earth metals comprising chemically modified chitosan substituted with a polyaminocarboxyl group represented by (CH ₂ COOH) ₂ .