KR20180079539A - Washing method for uranium-contaminated materials - Google Patents

Abstract

The purpose of the present invention is to provide an efficient washing method of a material contaminated with uranium. To achieve the purpose, the washing method of a material contaminated with uranium comprises the following steps of: a step 1 of washing a material contaminated with uranium with acid; a step 2 of immersing metal ions except uranium by adjusting pH of a solution after washing in the step 1; and a step 3 of immersing uranium by adjusting pH of a solution from which the metal ions immersed in the step 2 are removed. The washing method of a material contaminated with uranium according to the present invention can remarkably reduce an amount of secondary waste by dividing pH of a washing solution for a material contaminated with uranium into two steps and adjusting the same. The reduction of secondary waste reduces an amount of final disposal target waste, thereby greatly reducing disposal costs. Further, addition of natural materials such as bentonite and zeolite removes trace amounts of uranium remaining after a treatment of a waste solution, thereby enabling more eco-friendly discharge.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a washing method for uranium-

The present invention relates to a method for cleaning materials contaminated with uranium.

Uranium waste obtained by pickling up soil or gravel generally contains a large amount of impurities other than uranium other than uranium itself. Therefore, when disposing the waste without any additional treatment, stabilization and increase of solidification treatment and disposal cost It is absolutely necessary to reduce the volume of radioactive waste to be disposed through the separation of uranium and non-radioactive materials from such waste.

The disposal cost of the domestic radioactive waste repository is about 15 million won per 200 L drum, so the disposal cost is very high. Therefore, it is very important to reduce the volume of the uranium-metal composite oxide from the viewpoint of reducing the disposal cost.

Typical examples of conventional uranium waste treatment techniques include washing, electrokinetic processes, electolytic decontamination, dry compaction, dissolution, heating and grinding, Thermal decomposition and oxidation.

A method for drying, repacking or compressing a radioactive grab, sludge, soil or the like generated in a uranium conversion process (drying of radioactive solid waste generated in a uranium conversion process, Bulk-feeling treatment by compression, etc .; Proceedings of the Korean Nuclear Society Spring Conference, 2003).

A conventional method for cleaning uranium pollutants is to wash contaminated materials with acid, neutralize the pH by adding a base to the solution, and precipitate the uranium dissolved in the solution. The precipitate is then removed and the solution reused. However, when the pH of the washing solution is directly neutralized, metal ions such as iron and aluminum precipitate and excess secondary waste is generated. In addition, the concentration of sodium, potassium, and calcium in the neutralization solution is increased, and if it is continuously used as the regeneration liquid, the cleaning efficiency of the contaminant decreases. In order to prevent this, the solution must be evaporated after a certain period of use, which requires a lot of energy and is therefore uneconomical. On the other hand, if a regenerated solution containing a small amount of uranium is released for a long period of time, the uranium may be deposited on the soil of a drainage channel, so that the uranium concentration in the solution should be minimized in order to discharge it to the outside.

The present inventors have devised an effective treatment method of minimizing the amount of radioactive waste to be disposed while overcoming the limitations of the conventional uranium pollutant cleaning method, The present invention has been accomplished on the basis of the above-mentioned findings. The present invention has been accomplished on the basis of this finding.

Bulk-sensitive treatment by drying, compression, etc. of radioactive solid waste generated in uranium conversion process, Proceedings of KAERI Spring Conference, 2003

It is an object of the present invention to provide a method for efficiently cleaning materials contaminated with uranium.

In order to accomplish the above object, the present invention provides a method for purifying a uranium-contaminated material, comprising the steps of: (1) washing a material contaminated with uranium with an acid; Adjusting the pH of the solution after washing according to step 1 to precipitate metal ions other than uranium (step 2); And adjusting the pH of the solution from which the precipitated metal ions have been removed in step 2 to precipitate uranium (step 3); And a method for cleaning uranium contaminated material.

The method of cleaning materials contaminated with uranium according to the present invention can significantly reduce the amount of secondary waste by adjusting the pH of the uranium pollutant washing liquid by dividing into two stages.

FIG. 1 is a photograph showing a change of a solution according to pH change of a washing solution,
2 is a graph showing solubility of metal ions with respect to pH change.

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. However, the embodiments of the present invention can be modified into various other forms, and the scope of the present invention is not limited to the embodiments described below. Further, the embodiments of the present invention are provided to more fully explain the present invention to those skilled in the art. In addition, "including" an element throughout the specification does not exclude other elements unless specifically stated to the contrary.

Hereinafter, the contents of the present invention will be described in detail.

The present invention relates to a method for cleaning materials contaminated with uranium, and more particularly to a method for cleaning a material contaminated with uranium with an acid (step 1); Adjusting the pH of the solution after washing according to step 1 to precipitate metal ions other than uranium (step 2); And adjusting the pH of the solution from which the precipitated metal ions have been removed in step 2 to precipitate uranium (step 3); And a method for cleaning uranium contaminated material.

Hereinafter, the present invention will be described in detail.

Step 1 of the cleaning method according to the present invention is a step of washing a material contaminated with uranium with an acid, specifically, dissolving uranium attached to the contaminated material with an acid to wash uranium from the target material.

At this time, the material contaminated with uranium may be gravel. However, the present invention is not particularly limited to this.

A large amount of gravel waste contaminated with radioactivity may be generated during decommissioning / restoration of the uranium conversion facility. Contaminated gravel contained in oil contaminated soil has been used for a long time and various technologies have been developed and some of them have been put into practical use. However, since radioactive contaminated gravel is generated only in nuclear facilities, many studies are not conducted There is a lack of basic data on cleaning. Therefore, it will take a lot of time and money to develop technologies for cleaning them. However, the development of the radioactive contaminated gravel waste cleaning method is very important from an environmental point of view as well as an economic point of view since a large amount of gravel will be generated in the future in the dismantling of nuclear facilities. At this time, gravels with low cleaning efficiency were crushed and washed to finally meet the allowable concentration (1.0 Bq / g or less based on natural uranium). In order to increase the efficiency of washing and shorten the washing time, the uranium contaminated gravel was crushed / ground and washed. As the particle size was smaller, the washing efficiency was higher and the permissible concentration of self - disposal was satisfied. Uranium is considered to be adsorbed in the form of UO ₂ ²⁺ or U (Ⅳ) in the case of gravels generated from uranium conversion facilities.

The acid used in step 1 is preferably at least one selected from the group consisting of sulfuric acid, hydrochloric acid, nitric acid, and acetic acid, but is not limited thereto.

Among the decontamination methods, the chemical decontamination method, especially the chemical wet decontamination method using acid, is a method that is typically used for decontamination of radioactive metal waste because it is cheap and relatively fast in terms of decontamination speed and effective compared with other decontamination methods.

In the present invention, the acid solution for chemical wet decontamination using the acid is preferably at least one selected from the group consisting of sulfuric acid, hydrochloric acid, nitric acid and acetic acid, but is not limited thereto.

In addition, the molar concentration of the acid solution of step 1 may be 0.5 M to 2 M. [ At this time, even if the molar concentration of the acid solution is made higher than 2 M, a significant improvement in the uranium dissolution rate may not be expected. If the acid solution has a molar concentration lower than 0.5 M, the uranium dissolution may not be sufficiently performed.

Next, Step 2 according to the present invention is a step of heating the iron (Fe ^{3 +} ) contained in excess in the solution after the washing according to Step 1, And adjusting the pH to selectively remove aluminum (Al ^< ^{3 + &} gt ^; ) to precipitate metal ions other than uranium. Specifically, the step of precipitating uranium Precipitating only the excluded metal ions, wherein the metal ions are predominantly trivalent metal ions.

In the conventional method of washing substances contaminated with uranium, there is a problem that the amount of waste is greatly increased by precipitating all the ions contained in the solution to be cleaned and treating the waste with waste. However, in the present invention, iron, aluminum and metal ions, which are dissolved in the gravel washing waste solution and occupy more than 2/3 of the alkali solution of pH 7 to pH 9, are first precipitated and discarded to thereby significantly reduce the amount of uranium contaminated waste It is effective.

As the metal ions other than the uranium in the solution after the washing with the first step is shown in Fig aluminum (Al ^{3 +),} iron (Fe ^{3 +),} manganese (Mn ^{3 +)} and trivalent ions may contain large amounts of have.

In the cleaning method of the material contaminated with uranium according to the present invention, the first precipitation and disposal of the metal ions means to remove the metal ions such as iron and aluminum precipitated first by adjusting the pH to 3 to 4 in the step 2 .

The pH may be controlled by one or more selected from the group consisting of sodium hydroxide, potassium hydroxide and ammonium hydroxide.

 Preferably, step 2 is carried out by adjusting the pH to 3 to 4. If the pH is lower than 3 in step 2, the metal ions are not sufficiently precipitated. If the pH is higher than 4, some uranium ions precipitate together.

Step 3 of the cleaning method according to the present invention is a step of precipitating uranium by adjusting pH of a solution in which metal ions precipitated in step 2 are removed. Specifically, the precipitate produced in step 2 contains almost no uranium, which can be disposed of by itself, so that the pH is adjusted only by the solution except for these precipitates.

The pH may be controlled by one or more selected from the group consisting of sodium hydroxide, potassium hydroxide and ammonium hydroxide.

pH KOH (g) The precipitate (g) U-238 (Bq / g) 3 1.83 0.59 1.52 4 2.15 0.75 1.50 5 2.32 0.94 0.036 6 2.35 0.95 0.023 7 2.41 0.97 Non-detection 8 2.44 1.09 Non-detection 9 2.48 1.13 Non-detection

The step 3 is preferably carried out by adjusting the pH to 7 to 9. [

As shown in Table 1, the radioactivity of uranium in the solution does not decrease until the pH of the waste solution is pH 4, but decreases rapidly at pH 5 and 6. However, since a small amount of uranium activity is still detected, it is preferable to control the range of pH 7 to pH 9 in which uranium radioactivity is not detected. If it is adjusted to pH 9 or above, more KOH is added than necessary, and the solubility of uranium increases in a strong base solution.

After the uranium precipitation in step 3, the remaining solution may be discharged to the outside or may be reused as a washing solution for removing uranium in gravel by adding an acid. Such reuse has an advantage that the generation of waste liquid can be reduced. In addition, it is possible to solve the problem that a small amount of uranium can be accumulated outside by additionally treating with an adsorbent to remove uranium and discharging it to the outside.

On the other hand, if the uranium-containing solution produced in step 3 is continuously used, the concentration of soluble ions such as K, Na, Ca, etc. in the solution is increased and the cleaning efficiency is decreased. Therefore, it is necessary to regenerate the washing solution several times and then treat this solution. As a method of treating the decontamination waste solution without regeneration, it is possible to consider the evaporation concentration treatment of the waste solution, the ion exchange treatment, the solution regeneration by electrolytic dialysis, and the like. The method of concentrating the waste solution by evaporation consumes a lot of energy and its processing speed is slow. Especially, when sulfuric acid is used, there is a problem that a lot of solid waste is generated even after the concentration treatment by the sulfur component.

If uranium is released for a long period of time, the uranium concentration in the solution should be reduced as much as possible in order to discharge the solution to the outside, since there is a possibility that the uranium may be deposited on the soil of the drainage channel.

Therefore, the pH of the waste solution other than the precipitate formed after step 3 is adjusted by using acid or base solution, and uranium adsorbent is added to adsorb and remove the residual uranium.

The acid or base solution may be sodium hydroxide, potassium hydroxide, sulfuric acid or nitric acid, but is not limited thereto.

The adsorbent may be bentonite, magnetite, zeolite, ion exchange resin, etc. In particular, it is preferable to use Na-bentonite which is excellent in the adsorption performance of uranium and inexpensive.

When the solution from which the uranium precipitate is removed after the step 3 is treated with the adsorbent, the uranium concentration corresponds to the self-disposal allowable concentration (1.0 Bq / g or less based on natural uranium).

In particular, bentonite or zeolite has the greatest adsorption power when a solution in which uranium precipitate is removed is adjusted to a pH of 5 to 7 and then used as an adsorbent. This makes it possible to efficiently remove uranium before the waste liquid is discharged even if expensive ion exchange resins are not used, and thus to have an economically advantageous effect.

For example, after the step 3 is performed, the uranium concentration in which the uranium precipitate is removed is adjusted to a pH of 5 to 7, treated with an adsorbent, and then discharged, is less than 50 μg / L. It is similar to the upper limit value of uranium concentration of 30 μg / L, which is prescribed by the WHO, and it corresponds to the permissible concentration of uranium (1.0 Bq / g or less based on natural uranium) The pH of the removed solution is not adjusted to a pH of 5 to 7, which is significantly lower than that of adsorbent treatment alone. For example, it corresponds to about 1/20 or less of the permissible concentration of the above-mentioned disposal.

In fact, some concentrations of groundwater in Korea are lower than natural water, compared to several tens to several hundred μg / L, so it will be discharged or treated as general industrial waste.

Therefore, the method of washing uranium contaminated material according to the present invention does not directly neutralize the pH of the washing liquid but divides the washing liquid twice, firstly removing metal ions except uranium, and secondly removing uranium to remove the amount of final disposal wastes This can significantly reduce disposal costs. In addition, by treating the waste liquid with an adsorbent, the concentration of the residual uranium can be reduced to the maximum extent possible by self-disposing.

Hereinafter, the present invention will be described more specifically with reference to Examples and Experimental Examples. The following examples and experimental examples are only illustrative of the present invention, and the scope of the present invention is not limited thereto.

≪ Example 1 >

Cleaning uranium contaminants 1

100 g of 1.0 M sulfuric acid was added to 50 g of crushed gravel contaminated with uranium, and washing was carried out at a temperature of 60 ° C for 3 hours. Then, 0.2 g of potash alum was added to the washing solution, and the pH of the solution was adjusted to 3 by adding potassium hydroxide (KOH) to precipitate the metal except uranium. The solution was then vacuum filtered to separate the precipitate and liquid, and the pH was adjusted to 5 by adding potassium hydroxide to the separated liquid to precipitate the uranium. The precipitated uranium and liquid were separated by vacuum filtering the solution and the separated liquid was released.

≪ Example 2 >

Cleaning uranium contaminants 2

The contaminants were washed in the same manner as in Example 1, except that potassium hydroxide was added to the liquid separated from the solution precipitated with metal except uranium in Example 1 to adjust the pH to 6.

≪ Example 3 >

Cleaning uranium contaminants 3

The contaminants were washed in the same manner as in Example 1, except that potassium hydroxide was added to the liquid separated from the solution precipitated with metal except uranium in Example 1, and the pH was adjusted to 7.

<Example 4>

Cleaning uranium contaminants 4

The contaminants were washed in the same manner as in Example 1, except that potassium hydroxide was added to the liquid separated from the solution in which the metal except uranium was precipitated in Example 1, and the pH was adjusted to 8.

&Lt; Example 5 >

Cleaning uranium contaminants 5

The contaminants were washed in the same manner as in Example 1, except that potassium hydroxide was added to the liquid separated from the solution precipitated with metal except uranium in Example 1, and the pH was adjusted to 9.

&Lt; Example 6 >

Cleaning uranium contaminants 6

100 g of 1.0 M sulfuric acid was added to 50 g of crushed gravel contaminated with uranium and washing was carried out at a temperature of 60 for 3 hours. Then, 0.2 g of potash alum was added to the washing solution and potassium hydroxide (KOH) was added to adjust the pH of the solution to 4 to precipitate the metal except for uranium. The solution was then vacuum filtered to separate the precipitate and liquid, and the pH was adjusted to 5 by adding potassium hydroxide to the separated liquid to precipitate the uranium. The precipitated uranium and liquid were separated by vacuum filtering the solution and the separated liquid was released.

&Lt; Example 7 >

Cleaning uranium contaminants 7

The contaminants were washed in the same manner as in Example 6, except that potassium hydroxide was added to the liquid separated from the solution in which the metal other than uranium was precipitated in Example 6, and the pH was adjusted to 6.

&Lt; Example 8 >

Cleaning uranium contaminants 8

The contaminants were washed in the same manner as in Example 6, except that potassium hydroxide was added to the liquid separated from the solution in which the metal except uranium was precipitated in Example 6, and the pH was adjusted to 7.

&Lt; Example 9 >

Cleaning uranium contaminants 9

In Example 6, contaminants were washed in the same manner as in Example 6, except that potassium hydroxide was added to the liquid separated from the solution in which the metal other than uranium was precipitated to adjust the pH to 8.

&Lt; Example 10 >

Cleaning uranium contaminants 10

The pollutants were washed in the same manner as in Example 6, except that potassium hydroxide was added to the liquid separated from the solution in which the metal except uranium was precipitated in Example 6, and the pH was adjusted to 9.

&Lt; Example 11 >

Cleaning uranium contaminants 11

100 g of 1.0 M sulfuric acid was added to 50 g of crushed gravel contaminated with uranium, and washing was carried out at a temperature of 60 ° C for 3 hours. Then, 0.2 g of potash alum was added to the washing solution, and the pH of the solution was adjusted to 3 by adding potassium hydroxide (KOH) to precipitate the metal except uranium. The solution was then vacuum filtered to separate the precipitate and the liquid. Potassium hydroxide was added to the separated liquid to adjust the pH to 8.2 to precipitate the uranium. The precipitated uranium and liquid were separated by vacuum filtering the solution and the separated liquid was released.

&Lt; Example 12 >

Cleaning uranium contaminants 12

The pollutants were washed in the same manner as in Example 11 except that the liquid separated in Example 11 was treated with Na-bentonite (Kanto Co.) and then discharged.

&Lt; Example 13 >

Cleaning uranium contaminants 13

The same procedure as in Example 12 was carried out except that the pH of the liquid was adjusted to 6.0 before being discharged from the liquid of Example 12 and discharged after being treated with Na-bentonite (Kanto Corp.) Respectively.

&Lt; Example 14 >

Cleaning uranium contaminants 14

The pollutants were washed in the same manner as in Example 12 except that Na-bentonite (manufactured by Wyoming) was used instead of Na-bentonite (Kanto) as an adsorbent in Example 12.

&Lt; Example 15 >

Cleaning uranium contaminants 15

Before discharging the liquid separated in Example 14, the pH of the liquid was adjusted to 6.0, treated with Na-bentonite (Wyoming), and then discharged. Respectively.

&Lt; Example 16 >

Cleaning of uranium contaminants 16

The pollutants were washed in the same manner as in Example 12, except that Ca-bentonite (domestic) was used instead of Na-bentonite (Kanto) as an adsorbent in Example 12.

&Lt; Example 17 >

Cleaning uranium contaminants 17

The pollutants were washed in the same manner as in Example 16, except that the pH of the liquid was adjusted to 6.0, treated with Ca-bentonite (domestic), and then discharged before discharging the liquid separated in Example 16 .

&Lt; Example 18 >

Cleaning uranium contaminants 18

The pollutants were washed in the same manner as in Example 12, except that the magnetite was used instead of Na-bentonite (Kanto Co.) as the adsorbent in Example 12.

&Lt; Example 19 >

Cleaning uranium contaminants 19

The pollutants were washed in the same manner as in Example 18, except that the pH of the liquid was adjusted to 6.0 before being discharged from the liquid of Example 18, treated with magnetite, and then discharged.

&Lt; Example 20 >

Cleaning uranium contaminants 20

The pollutants were washed in the same manner as in Example 12, except that zeolite A-3 was used instead of Na-bentonite (Kanto Corp.) as the adsorbent in Example 12.

&Lt; Example 21 >

Cleaning uranium contaminants 21

The pollutants were washed in the same manner as in Example 20, except that the pH of the liquid was adjusted to 6.0, treated with zeolite A-3, and then discharged before discharging the liquid separated in Example 20.

&Lt; Example 22 >

Cleaning uranium contaminants 22

The pollutants were washed in the same manner as in Example 12, except that zeolite A-4 was used instead of Na-bentonite (Kanto Corp.) as the adsorbent in Example 12.

&Lt; Example 23 >

Cleaning uranium contaminants 23

The pollutants were washed in the same manner as in Example 22, except that the pH of the liquid was adjusted to 6.0, treated with zeolite A-4, and then discharged before discharging the liquid separated in Example 22 above.

&Lt; Example 24 >

Cleaning uranium contaminants 24

The pollutants were washed in the same manner as in Example 12, except that the ion exchange resin (S-950) was used instead of Na-bentonite (Kanto Co.) as the adsorbent in Example 12.

&Lt; Example 25 >

Cleaning uranium contaminants 25

As in Example 24, except that the pH of the liquid was adjusted to 6.0, treated with an ion-exchange resin (S-950), and then discharged before discharging the liquid separated in Example 24, And washed.

&Lt; Comparative Example 1 &

Cleaning uranium contaminants 26

100 g of 1.0 M sulfuric acid was added to 50 g of crushed gravel contaminated with uranium and washing was carried out at a temperature of 60 for 3 hours. Then, 0.2 g of potash alum was added to the washing solution, and the pH of the solution was adjusted to 7 by adding potassium hydroxide (KOH) to precipitate the precipitate.

&Lt; Comparative Example 2 &

Cleaning uranium contaminants 27

The procedure of Comparative Example 1 was repeated except that the pH of the washing solution was adjusted to 8 in Comparative Example 1.

&Lt; Comparative Example 3 &

Cleaning uranium contaminants 28

The procedure of Comparative Example 1 was repeated except that the pH of the washing solution was adjusted to 9 in Comparative Example 1.

<Experimental Example 1>

Determine the amount of uranium contaminated waste

In order to confirm that the amount of the secondary waste can be significantly reduced when neutralizing the pH of the washing solution of the uranium pollutant in two stages, in Examples 1 to 10 and Comparative Example 1, Comparative Example 2 and Comparative Example 3 The following experiment was carried out.

The amount of uranium precipitate precipitated secondarily in Examples 1 to 10 and the amount of sediment precipitated in Comparative Examples 1 to 3 were compared by subtracting the amount of precipitate in which the metal other than uranium was precipitated from the amount of the total precipitate , And the results are shown in Table 2 below.

EXAMPLES / COMPARATIVE EXAMPLE Amount of uranium precipitate (g) Example 1 0.35 Example 2 0.36 Example 3 0.38 Example 4 0.5 Example 5 0.54 Example 6 0.19 Example 7 0.2 Example 8 0.22 Example 9 0.34 Example 10 0.38 Comparative Example 1 0.97 Comparative Example 2 1.09 Comparative Example 3 1.13

The amount of the secondary waste was 0.35 g, the amount of the secondary waste was 0.36 g in Example 2, 0.38 g in Example 3, 0.5 g in Example 4, the amount of secondary wastes in Example 5 , 0.19 g in Example 6, 0.2 g in Example 7, 0.22 g in Example 8, 0.34 g in Example 9, and 0.38 g in Example 10, respectively.

On the other hand, in Comparative Example 1, the amount of the secondary waste was 0.97 g, which was 1.09 g in Comparative Example 2, and 1.13 g in Comparative Example 3, do

According to Table 2, when the pH of the uranium washing solution is directly neutralized, the metal ions contained in the washing solution are precipitated together to generate excessive secondary wastes. In Examples 1 to 10, sediments in which metals other than uranium are precipitated are almost free from uranium and can be disposed of by themselves. Therefore, when pH is neutralized in order to remove uranium from the washing solution, it is possible to reduce the amount of the secondary waste, which is a precipitate, to about 1/3 by adjusting the pH of the washing solution to 3 to 4 and pH to 7 to 9 It can be seen that the method of cleaning materials contaminated with uranium according to the present invention can significantly reduce the amount of waste contaminated with uranium.

<Experimental Example 2>

Changes in Uranium Concentration by Adsorbent Added to Neutralizing Solution for Gravel Washing

In order to confirm that the concentration of the residual uranium can be reduced to a minimum by putting a small amount of adsorbent into the waste solution after the step 3, the following experiments were conducted with respect to Examples 11 to 25.

The amount of uranium precipitated in Examples 11 to 25 was filtered through a Whatman 4 or 0.45 μm syringe filter, and the amount of uranium in the filtrate was measured by ICP-AES. The results are shown in Table 3 below.

Example filter U
(μg / L) Example 11 Whatman4 400 Example 12
Whatman4 140 0.45 μm 90 Example 13 0.45 μm <50 Example 14 Whatman4 300 0.45 μm 280 Example 15 0.45 μm <50 Example 16 Whatman4 410 0.45 μm 200 Example 17 0.45 μm 310 Example 18 Whatman4 320 0.45 μm 340 Example 19 0.45 μm 50 Example 20 Whatman4 370 0.45 μm 380 Example 21 0.45 μm 350 Example 22 Whatman4 400 0.45 μm 400 Example 23 0.45 μm <50 Example 24 Whatman4 <50 0.45 μm <50 Example 25 0.45 μm <50

According to the above Table 3, when the filtrate was filtered with Whatman 4 filter in Example 11, the amount of uranium in the filtrate was 400 μg / L.

 In Example 12, the amount of uranium in the filtrate was 140 μg / L when filtered with Whatman 4 filter, and 90 μg / L when filtered with a 0.45 μm filter. In Example 13, the amount of uranium in the filtrate was less than 50 μg / L when it was filtered with a 0.45 μm filter filter. The amount of uranium in the filtrate was 300 μg / L when filtered with Whatman 4 filter in Example 14, and 280 μg / L when filtered with a 0.45 μm filter. In Example 15, the amount of uranium in the filtrate is less than 50 μg / L when it is filtered with a 0.45 μm filter filter. In Example 16, the amount of uranium in the filtrate was 410 μg / L when filtered with Whatman 4 filter, and 200 μg / L when filtered with a 0.45 μm filter. In Example 17, when the filtrate was filtered with a 0.45 μm filter, the amount of uranium in the filtrate was 310 μg / L. The amount of uranium in the filtrate was 320 μg / L when filtered with Whatman 4 filter in Example 18, and 340 μg / L when filtered with a 0.45 μm filter. In Example 19, when the filtrate was filtered with a 0.45 μm filter filter, the amount of uranium in the filtrate was 50 μg / L. In Example 20, the amount of uranium in the filtrate was 370 μg / L when filtered with Whatman 4 filter, and 380 μg / L when filtered with a 0.45 μm filter. In Example 21, the amount of uranium in the filtrate was 350 μg / L when it was filtered with a 0.45 μm filter filter. The amount of uranium in the filtrate was 400 μg / L when filtered with Whatman 4 filter in Example 22, and 400 μg / L when filtered with a 0.45 μm filter. In Example 23, the amount of uranium in the filtrate was less than 50 μg / L when it was filtered with a 0.45 μm filter filter. In Example 24, the amount of uranium in the filtrate was less than 50 μg / L in both the Whatman 4 filter and the 0.45 μm filter. In Example 25, the amount of uranium in the filtrate is less than 50 μg / L even when it is filtered with a 0.45 μm filter filter.

It can be seen from Experimental Example 2 that Na-bentonite, zeolite A-4 and S-950 ion exchange resins at pH 6 lowered the uranium concentration of 400 μg / L of neutralizing solution to 50 μg / L or less. This value is similar to the upper limit value of uranium concentration of drinking water standard prescribed by the World Health Organization (WHO), which is 30 μg / L, and the uranium emission standard value in drainage specified in Nuclear Safety Commission Notice No. 2014-34 ' (About 1 mg / L). In fact, some concentrations of groundwater in Korea are lower than natural water, compared to several tens to several hundred μg / L, so it will be discharged or treated as general industrial waste.

When the ion exchange resin is used as the adsorbent roll, the adsorption power is good. However, since the resin is an organic matter, it can not be thrown away, so there is a disadvantage that a regeneration process is required to reduce waste. However, natural products such as Na-bentonite and zeolite adsorbed uranium in solution, and even if the concentration is increased by a factor of 100, they fall below their own disposal stage (U-238 = 80 mg / L) In the acid solution below 3, the uranium adsorption coefficient is low, so they can be decontaminated in contaminated soil. Therefore, it is most economical and desirable to add Na-bentonite, which is good in adsorption power, to the neutralized solution of the waste solution, filter it, and discharge it.

 As a result of Experimental Example 2, when the waste liquid was discharged after the use of the cleaning method of the material contaminated with uranium according to the present invention for several times, the concentration of uranium in the discharged liquid was reduced by the adsorbent .

The present invention is not limited to the above-described embodiment and the accompanying drawings, but is intended to be limited by the appended claims. It will be apparent to those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. something to do.

Claims (12)

Washing the uranium contaminated material with acid (step 1); Adjusting the pH of the solution after washing according to step 1 to precipitate metal ions other than uranium (step 2); And adjusting the pH of the solution from which the precipitated metal ions have been removed in step 2 to precipitate uranium (step 3); Lt; RTI ID = 0.0 &gt; of uranium &lt; / RTI &gt; contaminated material.
The method of claim 1, wherein the material contaminated with uranium is gravel.
The method according to claim 1, wherein the acid used in step (1) is at least one selected from the group consisting of sulfuric acid, hydrochloric acid, nitric acid and acetic acid.
The method according to claim 1, wherein at least one selected from the group consisting of sodium hydroxide, potassium hydroxide and ammonium hydroxide is used to adjust the pH in the step 2 and the step 3. .
The method according to claim 1, wherein said step (2) is carried out with a pH of from 3 to 4.
The method according to claim 1, wherein the metal ions precipitated in step (2) are at least one selected from the group consisting of iron ions, aluminum ions and manganese ions.
The method according to claim 1, wherein said step (3) is carried out by adjusting the pH to 7 to 9.
The method according to claim 1, wherein, after step 3, a solution from which uranium precipitate has been removed is used for controlling the pH of step 2 or step 3.
The method according to claim 1, wherein after the step 3, the solution having the uranium precipitate removed is treated with an adsorbent and then discharged.
The method according to claim 9, wherein the adsorbent is at least one selected from the group consisting of bentonite, magnetite, zeolite, and ion exchange resin.
10. The method of claim 9, wherein the uranium concentration of the treated process liquid is a self-disposed permissible concentration (1.0 Bq / g or less based on natural uranium).
10. The method of claim 9, wherein the adsorbent treatment is performed after adjusting the pH of the solution to 5 to 7 before treating the solution from which the uranium precipitate is removed with the adsorbent.

Images