JPH07100371A - Adsorbent for removing rare earth element and adsorption separation method using the same - Google Patents

Abstract

PURPOSE:To obtain an adsorbent for rate earth elements using carbamylmethylenephosphoric acid as an extracting agent and having superior adsorbing performance at ordinary temp., especially an adsorbent effective in removing rare earth elements such as transuranium elements from radioactive waste liquor and to provide an adsorption separation method using the adsorbent. CONSTITUTION:A mixture of carbamylmethylenephosphoric acid with carbamylmethylenephosphoric ester is impregnated into a porous carrier to obtain the objective adsorbent and the objective method for adsorbing and separating rare earth elements with the adsorbent is provided. Since the extracting agent impregnated into the adsorbent has low viscosity even at ordinary temp. and has superior extracting ability to rare earth elements, the rate of adsorption of rare earth elements is high and the elements can selectively and efficiently be adsorbed and separated. Since the adsorbed rare earth elements are easily desorbed, the adsorbent can be used in plural treating processes.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a rare earth element adsorbent,
In particular, the present invention relates to an adsorbent that is effective in removing rare earth elements such as transuranium elements from radioactive waste liquid generated in a radioactive waste reprocessing plant, and an adsorption separation method using the same.

[0002]

2. Description of the Related Art In Japan, a method has been adopted for recovering spent nuclear fuel by reprocessing U and Pu and vitrifying the remaining radioactive waste liquid. In this radioactive liquid waste, in addition to fission products such as Cs, Sr, and Ru, a trace amount of transuranium elements (T, such as Tp, Am, and Cm (T
RU). Among these TRUs are:
There are α-emitters, such as ²⁴³ Am and ²⁴⁵ Cm, that have a half-life of 5000 years or more. Therefore, it is possible to separate TRU contained in radioactive waste liquid and effectively store and manage or appropriately dispose of it. is required.

A process for removing TRU from radioactive waste liquid has been developed so far, and a bidentate organic compound capable of efficiently trapping a lanthanoid element in a nitric acid aqueous solution and a rare earth element such as an actinide element containing TRU. It is known that a solvent extraction process using a phosphoric acid extractant, particularly carbamylmethylene phosphoric acid ester (abbreviated as CMP), carbamylmethylene phosphoric acid (abbreviated as CMPO), is effective.
However, since this process is a solvent extraction method by liquid / liquid contact, not only the apparatus becomes very large-scaled, but also a large amount of secondary waste liquid is generated.

In order to deal with such a problem, CMP
Development of a process using an adsorbent obtained by impregnating a polymer carrier with an extractant such as CMPO or CMPO is in progress. The present inventors have found that dihexyl diethylcarbamyl methylene phosphate ester (in a swellable porous polymer carrier having a specific pore diameter and pore volume, such as a low-crosslinking degree styrene-divinylbenzene copolymer). Patent applications have already been filed for adsorbents for removing transuranic elements impregnated with CMP (abbreviated as DHDECMP) (JP-A-3-225299 and JP-A-3-264899). By using this adsorbent, TRU can be efficiently adsorbed and separated from the radioactive waste liquid.

On the other hand, CMPO is known to have a large adsorption capacity for rare earth elements including TRU. By impregnating the CMPO with the above-mentioned porous polymer carrier or the like, an adsorbent having a further excellent adsorption performance is obtained. Was expected to be obtained. However, this CMPO has a high melting point. For example, even if the porous carrier is impregnated at a temperature exceeding the melting point, the adsorbent is packed in a column, for example, 30
When adsorption separation is performed by the column method at about ℃, CMPO
Has a high viscosity, there is a problem that the moving speed of the rare earth element to be adsorbed and removed in the CMPO is slow and a high adsorption speed cannot be obtained.

[0006]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an adsorbent which uses CMPO as an extractant and has a high adsorption rate even at room temperature. In the present specification, the extractant refers to a substance having the ability to selectively capture rare earth elements, and the adsorbent means a solid extractant in which the extractant is immobilized on, for example, a porous carrier. And

[0007]

[Means for Solving the Problems]
This can be solved by a rare earth element removing adsorbent characterized by impregnating a mixture of CMP with CMP in a porous carrier. The adsorbent for rare earth elements of the present invention will be described in detail below. The rare earth element adsorbent of the present invention (hereinafter abbreviated as an adsorbent) is formed by impregnating a porous carrier with an extractant composed of a mixture of CMPO and CMP.

Here, CMPO and CMP are carbamylmethylene phosphoric acid and its derivative which are bidentate organophosphorus compounds having excellent extraction performance for trivalent rare earth elements, and carbamylmethylene phosphoric acid ester and its derivative. Means each. Examples of CMPO include octyl (phenyl) -N, N-diisobutylcarbamyl methylene phosphoric acid (abbreviated as oφD (iB) CMPO), dihexyl-N,
N-diethylcarbamyl methylene phosphoric acid (DHDECMP
And the like, and as CMP, dihexyl-N, N-diethylcarbamylmethylene phosphate (abbreviated as DHDECMP) and the like are preferable.

For example, as CMPO, oφD (iB) C
When MPO is used and DHDECMPO is used as CMP, the melting point of CMPO is 45 ° C., so that it is solid at room temperature and its viscosity is 10 ⁴ cp even at 50 ° C. On the other hand, CMP has a low viscosity of 25 cp at room temperature (25 ° C.). In the adsorbent of the present invention, a mixture of CMPO and CMP at a ratio such that the mixture has fluidity at room temperature is used as an extractant. The mixing ratio is not particularly limited, but it is preferable that CMPO is contained at about 10% to 90%. When CMPO is 90% or more, the viscosity of the extractant cannot be lowered, and when it is 10% or less, excellent extraction performance of CMPO cannot be exhibited.

The CMP used in the present invention is not limited to the above-mentioned DHDECMPO, but other CMs.
P derivatives are also preferably used. Further, instead of CMP, a substance that is liquid at room temperature and that can dilute CMPO to reduce its viscosity may be used. As such a substance, T
Those having an ability to capture a rare earth element such as RU and enhancing the extraction effect of a rare earth metal in cooperation with CMPO are preferable. Examples of such substances include, in addition to CMP isomers, tributyl phosphate (TBP), triacrylphosphine oxide (TOPO), tri-n-octyl ammonium nitrate (TOAHNOS), bis (2,6-dimethyl-4). -Heptyl) phosphoric acid (HD (DIBM) P), di-2-ethylhexyl dithioic acid (D2EHDTP), dibutyl-
N, N-diethylcarbamylphosphonate (DBDEC
P), methylenebisdihexylphosphine oxide (M
HDPO) and the like.

A porous polymer carrier or the like is preferably used as the porous carrier to be impregnated with the extractant composed of such a mixture of CMPO and CMP. The porous polymer carrier may be composed of a polymer resin having either hydrophobic or hydrophilic property. For example, a styrene-divinylbenzene copolymer having a low degree of cross-linking, whose pore size and particle size are easily adjusted, is used. Polymers (abbreviated as SDB), acrylic ester resins, and the like are preferable. The shape of the porous polymer carrier is not particularly limited, but a granular shape is preferable in consideration of the packing efficiency in the column. In particular, the smaller the particle size, the larger the contact area with the liquid to be treated, and the more preferable it is because the rare earth element such as TRU can be adsorbed and separated in a short time.

[0012] The porous polymer carrier is preferably one having a low degree of cross-linking and an appropriate pore diameter and pore volume so that the extractant can be impregnated in a large amount and uniformly. For example, when SDB particles are used, the degree of crosslinking is 3% to 30%, the average pore diameter is 700 angstroms to 3000 angstroms, and the average pore volume is 0.7 ml / g to 2.2 ml / g. preferable. If the degree of crosslinking is less than 3%, S
If the strength of the DB particles decreases and the degree of crosslinking exceeds 30%, the swelling property decreases, and it becomes difficult to uniformly impregnate the extractant. On the other hand, if the average pore diameter is 3000 angstroms or more, the pore volume in the SDB particles becomes too large and the strength decreases, and if it is less than 700 angstroms, the impregnated amount of the extractant decreases. Further, when the average pore volume is 2.2 ml / g or more, the strength is lowered and
When it is less than 7 ml / g, when the extractant is impregnated and the adsorbent particles are swollen, there are no voids that serve as passages for the liquid to be treated, and the adsorption rate is reduced.

In order to produce the adsorbent of the present invention as described above, first, a porous polymer carrier made of a polymer resin having an appropriate degree of crosslinking, particle size, pore size and pore volume is suspended, for example. It is produced by the turbid polymerization method or the like. As the method for producing the porous polymer carrier, a method conventionally used for producing porous polymer particles is used in addition to the suspension polymerization method, and the method is not particularly limited. For example, when the porous polymer carrier is granular, it is disclosed in JP-A-61-25.
The double nozzle vibration method and the like as described in JP-A-2202, JP-A-3-225299 and JP-A-3-264899 are preferably used.

Next, the porous polymer carrier is immersed in the above-mentioned extractant to impregnate the porous polymer carrier with the extractant. The impregnation conditions are appropriately selected depending on the type of porous polymer carrier, the physical properties, the type of extractant, and the like. For example, SDB particles are used as the porous polymer carrier and oφ is used as the extraction agent.
When a 1: 1 mixture of D (iB) CMPO and DHDECMP was used, the SDB particles were immersed in the extractant and stirred at 70 ° C. for about 24 hours, then the SDB particles were filtered off and The excess extractant in the pores of the SDB particles is removed by washing with water twice. Then, for example, in a vacuum drying furnace, 60
The adsorbent of the present invention is obtained by drying at 0 ° C. for about 3 hours.

Next, the adsorption separation method for rare earth elements using this adsorbent will be described. FIG. 5 is a diagram showing an embodiment of the adsorption separation method of the present invention, in which 1 is the adsorbent of the present invention. First, the adsorbent 1 is packed in a column 2 for column chromatography. Next, with the cock 3 of the column 2 closed, the liquid to be treated 10 containing a rare earth element is flown in from the column inlet 4. Then, the rare earth element is extracted and captured by the extractant from the liquid to be treated 10 that is in contact with the adsorbent 1. Next, when the cock 3 is opened,
From the column outlet 5, the liquid to be treated in which the rare earth metal such as TRU is adsorbed and separated flows out. For example, the liquid to be treated 10
Is a radioactive waste liquid containing TRU, TRU is removed by the adsorptive separation method of the present invention, and the adsorbent on which TRU is adsorbed is reduced in volume by dry distillation or the like and disposed of according to a predetermined method.

Further, in the present invention, one adsorption / separation operation is completed, and distilled water is caused to flow through a column filled with an adsorbent in which a rare earth element such as TRU is adsorbed, thereby adsorbing the adsorbent. It is preferable to desorb the rare earth element adsorbed on the column and let it flow out together with distilled water. For example, by flowing distilled water in an amount of about 30 times the column volume at 30 ° C., the rare earth element adsorbed on the adsorbent can be almost completely desorbed. In the adsorbent of the present invention, the extractant impregnated in the porous polymer carrier is hardly lost even after such desorption operation, and therefore the adsorbent is used for the second adsorption. Even if the separation operation is performed, the adsorption separation performance is not deteriorated. Therefore, it is preferable to repeat the operations of adsorption separation and desorption a plurality of times and then reduce the volume of the adsorbent of the present invention by dry distillation or the like as described above.

In the above description, the adsorption separation method using the column chromatography method has been described, but the adsorption separation method of the rare earth element of the present invention is not limited thereto.
Any method may be used as long as the adsorbent of the present invention and the liquid to be treated containing the rare earth element can be brought into solid / liquid contact. Since the adsorbent of the present invention is obtained by impregnating an extracting agent in a porous polymer carrier, it can be used for separating not only TRU but also rare earth elements that can coordinate with the extracting agent, such as lanthanoid element and actinoid element. Needless to say, it can be used.

As described above, the adsorbent of the present invention contains C
Since the mixture of MPO and CMP is used as the extractant, the extractant has a low viscosity even at around room temperature and has an excellent extractability for rare earth elements such as TRU. Therefore, the adsorbent of the present invention obtained by impregnating the extractant into a porous carrier has a high adsorption rate of rare earth elements and can efficiently adsorb and separate TRU from a radioactive waste liquid containing TRU, for example. Further, the adsorbent of the present invention can desorb the adsorbed rare earth element simply by flowing distilled water, and
Since the extractant is not easily lost even by the desorption treatment, it can be used for a plurality of treatments.

The present invention will be described in more detail below with reference to examples. (Example 1) oφD (iB) CMPO was used as CMPO, DHDECMPO was used as CMP, and these were mixed at a weight ratio of 1: 1 to obtain an extractant.
The extractant was liquid at room temperature. Next, SDB particles were prepared by a suspension polymerization method as a porous polymer carrier. The degree of crosslinking of the porous polymer carrier is 5%, the particle size is 100 to 200 μm, and the average pore volume is 1.5 ml / g.
Met. The SDB particles are dipped in the above extractant,
The extractant was impregnated into the SDB particles by stirring at 0 ° C. for 24 hours. After the SDB particles impregnated with this extractant were filtered off, the excess extractant was removed by washing several times with hot water at 70 ° C. and dried in a vacuum drying oven at 60 ° C. for 3 hours to obtain the product of this example. An adsorbent was obtained. The content of the extractant in the obtained adsorbent is
It was 1.9 to 2.0 g per 1 g of SDB particles.

Example 2 The adsorbent prepared in Example 1 was packed in a cylindrical column chromatography column having an inner diameter of 15 mm and a length of 1 m as shown in FIG. Cerium was used as the rare earth element to be adsorbed and separated. That is, 1 mo containing Ce (NO ₃ ) ₃ at a concentration of 240 ppm
A 1 / l Al (NO ₃ ) ₃ aqueous solution was used as the liquid to be treated. The liquid to be treated was flown into the above column at 30 ° C. to adsorb and separate cerium in the liquid to be treated. The cerium concentration in the liquid flowing out from the column outlet was measured by optical emission analysis. FIG. 1 is called a breakthrough curve, and is a plot of the cerium concentration in the effluent with respect to the flow rate of the liquid to be treated. The breakthrough curve obtained in this example is shown in FIG.

Example 3 Cerium was adsorbed and separated in the same manner as in Example 2 except that the adsorbent of Example 1 was used and the temperature at the time of adsorption separation was 50 ° C. Figure 2 shows the breakthrough curve.
It shows in (a).

Comparative Example 1 An adsorbent was prepared by impregnating CMPO as an extractant with SDB particles as in Example 1. Using the adsorbent, cerium was adsorbed and separated at 30 ° C. and 50 ° C. in the same manner as in Examples 2 and 3. The breakthrough curves obtained are shown in FIG. 1 (b) and FIG. 2 (b), respectively.

Comparative Example 2 An adsorbent was prepared by impregnating SMP particles with CMP as an extractant and impregnating it with SDB particles. Using the adsorbent, 3 as in Examples 2 and 3
Cerium was separated by adsorption at 0 ° C and 50 ° C. The breakthrough curves obtained are shown in FIG. 1 (c) and FIG. 2 (c), respectively.

From the results of Comparative Example 1 in which the adsorbent impregnated with CMPO alone as the extractant was used, it was found that the adsorption rate of this adsorbent at 30 ° C. was slow, and cerium that was not adsorbed would flow out from the start of outflow. . However, 50 ℃
In Example 1, cerium did not flow out up to about 50 times the column volume, and beyond that, the concentration of cerium in the effluent increased sharply. This is because CMP
It is considered that the adsorption rate was improved by lowering the viscosity of O and increasing the moving rate of cerium.

In Comparative Example 2 using an adsorbent containing only CMP as an extractant, cerium was completely adsorbed and separated up to about 40 times the column volume, and the effluent did not contain cerium. However, beyond that, the cerium concentration in the effluent rapidly increased, and the cerium concentration was about the same as that of the liquid to be treated at about 100 times. That is, about 100 times
It is considered that the cerium extraction ability of CMP impregnated with the adsorbent was saturated. Also, this behavior is 50 even at 30 ° C.
The same was true at ° C. It is considered that CMP is a liquid in this temperature range and the viscosity hardly changes.

On the other hand, in Example 2 using an adsorbent impregnated with a 1: 1 mixture of CMPO and CMP as an extractant, 1
Cerium does not flow out until more than 00 times the amount of liquid to be treated passes, and a breakthrough curve that rises sharply thereafter is obtained.
The breakthrough curve at C (Example 3) was almost the same. From this, it can be understood that the viscosity of CMPO was lowered by mixing with CMP, the moving speed of cerium was increased, and the adsorption speed was improved. Further, referring to FIG. 2, the breakthrough curve of Example 3 is on the higher liquid volume side than the breakthrough curve of Comparative Example 2 using CMPO having a reduced viscosity. That is, CMPO
It is considered that, by mixing CMP with CMP, they exert a synergistic effect and exhibit higher extraction performance than that of CMPO alone.

Example 4 Distilled water was introduced at 30 ° C. into a column used for adsorption separation of cerium in Example 2 and filled with an adsorbent having cerium adsorbed to desorb cerium. . Measure the cerium concentration in the effluent,
It plotted with respect to the liquid volume of the flowing distilled water. The result is shown in Figure 3.
It shows in (a).

Example 5 The column used for the adsorption separation of cerium in Example 3 was used, and the temperature of distilled water was 50 ° C.
Then, cerium was desorbed in the same manner as in Example 4. The results are shown in Fig. 4 (a).

(Comparative Example 3) With respect to the adsorbent of Comparative Example 1 in which only CMPO was used as an extractant, cerium was desorbed in the same manner as in Examples 4 and 5. The results at 30 ° C are shown in Fig. 3 (b).
The results at 50 ° C. are shown in FIG.

(Comparative Example 4) With respect to the adsorbent of Comparative Example 2 using only CMP as an extractant, cerium was desorbed in the same manner as in Examples 4 and 5. The results at 30 ° C. are shown in FIG.
The results at 50 ° C. are shown in FIG.

From these results, when the adsorbent impregnated with the CMPO-only extractant was used, the desorption rate was slow and the desorption could not be completed without passing about 50 times the column volume of distilled water. However, in the case of CMP alone, desorption occurs immediately when passing distilled water, and desorption can be performed by passing about 10 times the amount of distilled water. On the other hand, in the case of using the adsorbent of the present invention, the desorption rate can be improved as compared with CMPO by mixing CMP and lowering the viscosity, and at 30 ° C., the desorption rate is about 30 times, and at 50 ° C. The adsorbed cerium could be desorbed by passing 20 times the amount of distilled water.

Since the adsorbent of the present invention uses a mixture of CMPO and CMP as an extractant, the extractant has a low viscosity even at room temperature and has an excellent extractability for rare earth elements such as TRU. . Therefore, the adsorbent of the present invention obtained by impregnating the extractant into a porous carrier has a high adsorption rate of rare earth elements, and can selectively and efficiently remove TRU from a radioactive waste liquid containing, for example, TRU. . In addition, the adsorbent of the present invention can desorb the adsorbed rare earth element simply by flowing distilled water, and since the extractant is not easily lost by the treatment, it should be used for a plurality of waste liquid treatments. You can Further, the adsorbent of the present invention, since both the porous polymer carrier and the extractant are organic compounds, the volume can be easily reduced by an operation such as carbonization, and a secondary waste liquid may be generated. Absent.

[Brief description of drawings]

FIG. 1 (a) 1: 1 mixture of CMPO and CMP,
It is a figure which shows the breakthrough curve at the time of carrying out the adsorption separation of the cerium in a to-be-processed liquid at 30 degreeC using the adsorbent which used (b) CMPO and (c) CMP as an extractant.

FIG. 2 (a) 1: 1 mixture of CMPO and CMP,
It is a figure which shows the breakthrough curve at the time of carrying out the adsorption separation of the cerium in a to-be-processed liquid at 50 degreeC using the adsorbent which used (b) CMPO and (c) CMP as an extractant.

Figure 3: (a) 1: 1 mixture of CMPO and CMP,
It is a graph which shows the cerium density | concentration change of the effluent at the time of desorbing the cerium adsorbed by the distilled water of 30 degreeC from the adsorbent which used (b) CMPO and (c) CMP as an extractant.

FIG. 4 (a) 1: 1 mixture of CMPO and CMP,
It is a graph which shows the cerium density | concentration change of the effluent at the time of desorbing the cerium adsorbed by the distilled water of 50 degreeC from the adsorbent which used (b) CMPO and (c) CMP as an extractant.

FIG. 5 is a diagram showing an example of the rare earth element adsorption separation method of the present invention.

[Explanation of symbols]

 1 adsorbent 2 column 3 cock 4 column inlet 5 column outlet 10 liquid to be treated

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Kenji Takeshita Kenji Takeshita 1201 Takada, Kashiwa-shi, Chiba Institute of Industrial Creation, Kashiwa Laboratory In Toyosu General Office Co., Ltd. (72) Inventor Chisato Takahashi 3-2-16 Toyosu, Koto-ku, Tokyo Ishikawajima Harima Heavy Industries Co., Ltd. In Toyosu General Office

Claims (2)

[Claims] 1. An adsorbent for removing a rare earth element, which is obtained by impregnating a mixture of carbamyl methylene phosphoric acid and carbamyl methylene phosphoric acid ester into a porous carrier. 2. A column is filled with the adsorbent according to claim 1, and a liquid to be treated containing a rare earth element is flown into the column to adsorb the rare earth element to the adsorbent for separation. Rare earth element adsorption separation method.