JP3957405B2 - Method for producing metal element adsorbent - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a metal element adsorbent which is difficult to crush, does not increase the loss of pressure and increases the treatment speed of liquid wastes when the adsorbent is filled into a column and waste treatment is conducted and make it possible to gain a metal element adsorbent where alkali metal does not remain as residue following the incineration of the adsorbent after the liquid waste is treated and, as a result of it, the quantity of wastes does not increase. SOLUTION: A gel composition is generated by dissolving powdery condensed tannin in an NaOH, KOH or LiOH water solution of pH 7 to 10, mixing the solution with an aldehyde water solution or a hexamethylene tetramine and heating the mixture. The stabilized gel composition is put in contact with nitric acid, hydrochloric acid or sulfuric acid whose concentration is both 0.01 N or more and below 2 N preferably. Consequently, Na, K or Li as a terminal atom of a molecule of the gel composition can be replaced with an H atom.

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a metal element adsorbent for adsorbing actinide elements such as uranium, thorium and transuranium elements, heavy metal elements including cadmium, lead, chromium, mercury and iron, or metal elements such as cobalt, cesium and strontium. It relates to a manufacturing method.
[0002]
[Prior art]
Waste liquids discharged in the process of handling nuclear fuel contain nuclear fuel elements such as uranium and thorium, heavy metal elements including cadmium, lead, chromium, mercury and iron, or metal elements such as cobalt, cesium and strontium. Yes. Conventionally, as a method for producing an adsorbent for adsorbing these metal elements, a condensed tannin powder is dissolved in an alkaline aqueous solution, and an aqueous aldehyde solution is mixed with this solution to produce a gel-like composition. A method is known in which a product is aged at room temperature or stabilized by heating (Japanese Patent Application Laid-Open No. 5-66291). The adsorbent obtained by this method can adsorb metal elements efficiently.
[0003]
[Problems to be solved by the invention]
However, after this conventional metal element adsorbent is packed in the column of the waste liquid treatment device, when the waste liquid containing the metal element is passed through the column and this waste liquid is treated, the adsorbent increases as the waste liquid passage speed increases. As a result, the pressure loss increases, the flow rate of the waste liquid becomes slow, and as a result, there is a problem that the passage speed of the waste liquid cannot be increased.
In addition, since alkali metal ions such as Na ions and K ions used in manufacturing the adsorbent remain in the adsorbent, when the waste liquid is alkaline, the alkali metal ion remains in the adsorbent after the waste liquid treatment. . Therefore, the alkali metal ion remaining in the adsorbent remains as a residue even after the adsorbent is incinerated after the waste liquid treatment, resulting in a disadvantage that the amount of waste increases.
[0004]
An object of the present invention is to provide a method for producing a metal element adsorbent capable of increasing the treatment speed of waste liquid without being crushed and increasing pressure loss when packed in a column and performing waste liquid treatment. is there.
Another object of the present invention is to provide a method for producing a metal element adsorbent that does not leave alkali metal as a residue after incineration of the adsorbent after waste liquid treatment, and thus does not increase the amount of waste. is there.
[0005]
[Means for Solving the Problems]
In the invention according to claim 1, a condensed tannin powder is dissolved in an aqueous solution of sodium hydroxide, potassium hydroxide or lithium hydroxide having a pH of 7 to 10, and an aldehyde aqueous solution or hexamethylenetetramine is mixed into this solution. A method for producing a metal element adsorbent, characterized in that nitric acid, hydrochloric acid or sulfuric acid is brought into contact with the gel composition in a method for producing a metal element adsorbent which produces a stabilized gel composition by heating is there.
In the invention according to claim 2, the condensed tannin powder is mixed with an aqueous hexamethylenetetramine solution, and an aqueous solution of sodium hydroxide, potassium hydroxide or lithium hydroxide is added to this mixed solution to adjust the pH to 7-10. In the method for producing a metal element adsorbent for dissolving a tannin powder and heating the solution to produce a stabilized gel composition, the gel composition is contacted with nitric acid, hydrochloric acid or sulfuric acid. It is a manufacturing method of a metal element adsorbent.
[0006]
In the invention which concerns on Claim 1 or 2, the said acid is made to contact a gel-like composition, The sodium, potassium, or lithium which is the terminal atom of the molecule | numerator of a gel-like composition can be substituted by the hydrogen atom.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
In this specification, the stabilization of the gel-like composition means making the gel-like composition insoluble in any of water, acid or alkali, and the stabilized gel-like composition means water, acid or It refers to a composition that is insoluble in any alkali. The tannin powder used in the present invention is condensed tannin. This condensed tannin is a proanthocyanidin that produces anthocyanidic pigments with acid, and does not contain astringency. Examples include quebraco tannin, wattle tannin, mangrove tannin, sprue tannin, gambir tannin, red catechin, oak bark tannin and the like.
[0008]
The gel composition before being treated with nitric acid, hydrochloric acid or sulfuric acid of the present invention is porous and has a network structure. When a sodium hydroxide solution is used as an alkaline aqueous solution as the terminal group of the molecules constituting this gel composition, as shown in FIG. 1 (a), the terminal atom becomes Na and has a large ion Na. The pore size of the composition has a large value of 1 to 2 μm. When the above acid is brought into contact with this gel composition, as shown in FIG. 1B, the exchange group changes from large ionic Na to small ionic H, so that the network structure of the gel composition shrinks and becomes dense. As a result, the pore size of the gel composition is reduced to 0.5 to 1 μm, and the mechanical strength of the gel composition is increased. As a result, when the column is filled with the metal element adsorbent of the present invention and the waste liquid treatment is performed, the adsorbent is less likely to be crushed, and as a result, pressure loss does not increase and the waste liquid treatment speed can be increased. it can.
As described above, when the gel-like composition is brought into contact with nitric acid, hydrochloric acid or sulfuric acid, Na, K or Li, which is the terminal atom of the molecule of the gel-like composition, is changed to the terminal atom of H. The concentration of nitric acid, hydrochloric acid or sulfuric acid is preferably 0.01N or more and less than 2N. More preferably, it is 0.1N or more and 1.5N or less. Since the gel-like composition exhibits weak alkalinity, when the acid concentration is less than 0.1N, the acid is neutralized by the gel-like composition and, as a result, is a terminal atom of the molecule of the gel-like composition. It becomes difficult to change Na, K or Li to the terminal atom of H. On the other hand, when the concentration of the acid is 2N or more, the gel composition is easily dissolved in the acid, which is not preferable.
[0009]
As a specific method of bringing the acid into contact with the gel composition, the gel composition is put into an acid solution, or the acid solution is injected into a container containing the gel composition at room temperature for 30 minutes or more. After stirring, dehydrate.
[0010]
Examples of the aldehyde aqueous solution commonly used in the inventions of claims 1 and 2 include formaldehyde aqueous solution, acetaldehyde aqueous solution, and glutaraldehyde aqueous solution. However, the aqueous solution is not particularly limited as long as it is an aldehyde aqueous solution. Among these, an aqueous formaldehyde solution is preferable because it accelerates the formation of the gel-like composition and increases the mechanical strength of the adsorbent that has become the gel-like composition.
The metal element adsorbent produced by the method of the present invention is an actinide element such as uranium, thorium, or transuranium element, or an element such as cadmium, lead, chromium, mercury, iron, or cobalt, cesium, Suitable for adsorption of elements such as strontium.
[0011]
In the invention according to claim 1, the condensed tannin powder is first dissolved in an aqueous solution of sodium hydroxide, potassium hydroxide or lithium hydroxide having a pH of 7-10. This is because if the pH is less than 7, the tannin powder is difficult to dissolve, and if the pH exceeds 10, the resulting gel composition is unstable and easily soluble in water. As for the mixing ratio of the tannin powder, the tannin powder is preferably mixed in the range of 1 to 40% by weight with respect to the aqueous solution of the alkali metal hydroxide. If it is less than 1% by weight, the tannin powder is difficult to gel, and if it exceeds 40% by weight, the viscosity becomes high and handling becomes difficult. This solution is mixed with an aqueous aldehyde solution or hexamethylenetetramine. Here, for example, in the case of a 37% by weight aqueous solution of formaldehyde, at least 1.39 mL is added and mixed with 50 mL of an aqueous solution in which tannin is dissolved. The mixed liquid is heated to produce a stabilized gel composition. By contacting nitric acid, hydrochloric acid, or sulfuric acid with this stabilized gel-like composition, a metal element adsorbent in which Na, K, or Li, which is the terminal atom of the molecule of the gel-like composition, has been changed to H atoms can be obtained.
[0012]
In the invention according to claim 2, first, the condensed tannin powder is mixed with the hexamethylenetetramine aqueous solution. The hexamethylenetetramine aqueous solution is an aqueous solution in which hexamethylenetetramine is dissolved at least 0.5% by weight. The mixing ratio of the tannin powder is the same as that of the first aspect. Next, when sodium hydroxide, potassium hydroxide or lithium hydroxide is added and the pH is adjusted to 8 or more, the tannin powder is completely dissolved. Thereafter, a stabilized gel-like composition is produced by heating in the same manner as in claim 1, and similarly treated with the acid to obtain a metal element adsorbent.
In order to increase the contact area with the metal element-containing solution, the metal element adsorbent of the gel composition obtained by the two methods described above is pulverized and subdivided into a desired size by a mechanical means such as a mixer. Used. Examples of a method for adsorbing and separating a metal element using this metal element adsorbent include a column method and a batch method.
[0013]
The metal element adsorbent of the present invention obtained by the above-described method is brought into contact with a solution containing uranium, thorium, transuranium element, or a metal element such as cadmium, lead, chromium, mercury, iron, cobalt, cesium, strontium. The adsorbent adsorbs metal elements very efficiently. This is presumably because the polyphenolic hydroxyl group possessed by the tannin constituting the gel composition of the adsorbent becomes a functional group to form a metal element and a chelate compound. In addition, the gel-like composition has a three-dimensional structure in which the functional group is easily coordinated with the metal element, and the gel-like composition is a very strong hydrophilic substance. It is considered to show performance.
[0014]
In particular, the metal element adsorbent obtained in the present invention is excellent in the adsorption performance of uranium, thorium and uranium in seawater generated from the nuclear fuel production process, as well as curium and americium which are superuranium elements generated from the reprocessing process. It has excellent adsorption performance for various elements such as cadmium, lead, hexavalent chromium, mercury, iron, cobalt, cesium and strontium generated from the process of handling neptunium, plutonium, and metal elements, and its utility value is extremely large.
Further, since the adsorbent of the present invention that has adsorbed metal can be incinerated without generating toxic gas, the volume of adsorbent can be greatly reduced by incineration to reduce the amount of solid waste generated.
[0015]
【Example】
Next, in order to show the concrete mode of the present invention, the example of the present invention is explained with a comparative example.
<Example 1>
8 g of Wattalanin powder, which is condensed tannin, was added to 50 mL of NaOH aqueous solution at pH 8.7 and dissolved. Since the pH of the solution gradually decreased as tannin powder was added, an aqueous NaOH solution was added as needed to keep the pH of the solution at 8. To this solution was then added 2.77 mL of a 37 wt% aqueous solution of formaldehyde, and the solution was heated at 70 ° C. for 1 hour. Thereby, gelation and stabilization were performed at the same time, and a stabilized gel composition was prepared. This gel composition was pulverized with a mixer and subdivided into particle sizes of about 1.0 to 2.4 mm, and then divided into two equal parts. One of the halves was brought into contact with a 0.1N nitric acid solution for 1 hour. That is, one of the two gel-like compositions divided into this nitric acid solution was added and stirred at room temperature for 1 hour. Thereafter, the gel composition was dehydrated to obtain the metal element adsorbent of Example 1.
[0016]
<Example 2>
The metal element adsorbent of Example 1 was further pulverized with a mixer and subdivided into particle sizes of about 0.5 to 1.2 mm to obtain the metal element adsorbent of Example 2.
[0017]
<Comparative Example 1>
The metal element adsorbent that was not washed with the nitric acid solution, that is, the remaining one of the two divided in Example 1 was used as the metal element adsorbent of Comparative Example 1.
[0018]
<Adsorption performance test example 1>
The metal element adsorbent of Example 2 and the metal element adsorbent of Comparative Example 1 were separately packed in a column having an inner diameter of 0.1 m at a height of 2 m. Pure water was supplied to these columns by upflow, the pressure at the column inlet and the column outlet was measured, and the pressure loss was determined from the difference. The relationship between the linear velocity and pressure loss was investigated by changing the linear velocity when the column was passed through. The result is shown in FIG.
As is clear from FIG. 2, the pressure loss is almost the same loose rate when the adsorbent of Example 2 is filled up to about 30 cm / min and when the adsorbent of Comparative Example 1 is filled. However, when the linear velocity exceeds 35 cm / min, the pressure loss of the adsorbent of Comparative Example 1 increases more rapidly, whereas the adsorbent of Example 2 has an increased rate of pressure loss. It can be seen that it is extremely small compared to Comparative Example 1.
[0019]
<Adsorption performance test example 2>
250 mL each of a pH 4 solution having a uranium concentration of 245 ppb was placed in two containers. To these solutions, 25 mg each of the metal element adsorbent of Example 1 and the metal element adsorbent of Comparative Example 1 were added in dry weight, stirred for about 2 hours to adsorb uranium, and the adsorption rate was measured. Furthermore, the uranium adsorption rate was measured by varying the pH of the uranium-containing solution in this test. That is, with respect to the metal element adsorbents of Example 1 and Comparative Example 1, the pH of the solution was set to 6, 8, and 10, respectively, and the uranium adsorption rate was measured in the same manner. The result is shown in FIG. Here, the adsorption rate α is Co when the uranium concentration of the stock solution before addition of the adsorbent is C, and Ct is the uranium concentration of the solution after adsorbent addition and uranium adsorption.
α = [(Co−Ct) / Co] × 100 (%)
Is a value calculated by.
As is apparent from FIG. 3, the adsorbent of Example 1 shows almost the same uranium adsorption rate as Comparative Example 1 in a wide range of pH 4 to 10, and it can be seen that there is no difference in adsorption performance depending on the presence or absence of washing with acid.
[0020]
【The invention's effect】
As described above, according to the method for producing a metal element adsorbent of the present invention, a stabilized gel-like composition is produced using condensed tannin powder as a raw material, and nitric acid, hydrochloric acid or Since Na, K, or Li, which is the terminal atom of the molecule, is changed to H atom by contacting sulfuric acid, the column is filled with the obtained metal element adsorbent, and when the waste liquid treatment is performed, adsorption It becomes difficult for the agent to be crushed, and as a result, the pressure loss does not increase, and the treatment speed of the waste liquid can be increased.
Moreover, after treating the waste liquid using the metal element adsorbent obtained in the present invention, when the adsorbent after the waste liquid treatment is incinerated, an alkali metal such as Na, K or Li does not remain as a residue, Therefore, there is an effect that the amount of waste can be reduced.
[Brief description of the drawings]
FIG. 1A is a view showing the state of terminal groups of molecules constituting a gel composition before acid contact.
(B) The figure which shows the state of the terminal group of the molecule | numerator which comprises the gel-like composition after an acid contact.
FIG. 2 is a graph showing the results of adsorption performance test example 1 of the present invention.
FIG. 3 is a graph showing the results of adsorption performance test example 2 of the present invention.

Claims (2)

Gel in which condensed tannin powder is dissolved in an aqueous solution of sodium hydroxide, potassium hydroxide or lithium hydroxide having a pH of 7 to 10, mixed with an aldehyde aqueous solution or hexamethylenetetramine, and the mixture is heated to stabilize the gel. In the method for producing a metal element adsorbent that produces a glass-like composition,
A method for producing a metal element adsorbent, comprising bringing the gel composition into contact with nitric acid, hydrochloric acid, or sulfuric acid. Condensed tannin powder is mixed with an aqueous solution of hexamethylenetetramine, and an aqueous solution of sodium hydroxide, potassium hydroxide or lithium hydroxide is added to the mixed solution to adjust the pH to 7 to 10, thereby dissolving the tannin powder. In the method for producing a metal element adsorbent that produces a gel composition stabilized by heating
A method for producing a metal element adsorbent, comprising bringing the gel composition into contact with nitric acid, hydrochloric acid, or sulfuric acid.

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