JPS58223798A - Method of processing concentrated salt liquid waste containing radioactive material - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a method (1) for treating concentrated salt waste liquid containing radioactive materials discharged from nuclear facilities.

[Technical background of the invention]

General 1 - Radioactive waste liquid discharged from facilities handling radioactive materials contains 184Cs, 187Cs, 60Co, 54
Since it contains radioactive nuclides such as Mn, 110mAg, 51cr, and 95Zr-95Nb, the waste liquid is concentrated by appropriate means and then solidified and stored in cement, asphalt, or plastic.

However, since the waste liquid contains a large amount of non-radioactive salts, this method of assimilating the concentrate produces a large amount of assimilates, for example, one solidified cement per m3 of seawater used. There are many problems in terms of volume reduction, such as the formation of (200 l).

In addition, methods of separating radioactive substances using agglomeration and sedimentation methods are widely used, such as 184Cs, 187Cs, 110
There is a drawback that nuclides that are difficult to coprecipitate, such as mAg, 51Cr, 65Zn, and 95Zr-95Nb, cannot be removed.

Name of the present invention: As a result of our research into a method for treating waste liquid that eliminates the drawbacks of these conventional methods and effectively removes radioactive substances with good volume reduction, we found that waste liquid 8; (a) Ni++, Co
++, Mn++ or Zn++, (b) ferrocyanate ion, (c) Fe+++, (d) OH-, (e) S-
We have developed a method in which radioactive substances and pollutants such as chromic acid are co-precipitated by crystallization by successively adding metal ions that react with S--, and (f) S-- to form a precipitate, and are recovered and removed from the waste liquid.

(Refer to Japanese Patent Application No. 57-65126) The above method uses 184Cs, 187Cs, and 60Co in the waste liquid.
, 58Co, 54Mn, 59Fe, 55Fe, 65Zn
, 95Zr-95Nb, 51Cr, 110mAg, etc. and pollutants such as chromic acid are recovered with good separation, and the remaining waste liquid containing a large amount of non-radioactive salts is discharged. This has an excellent effect in that the volume is reduced to 1/1000 compared to the case of evaporation and concentrated cement assimilation, while radioactive substances and chromic acid in the discharged waste liquid are below the detection limit.

However, if a chelating agent is present in the waste liquid to be treated, some of these nuclides will be skimmed and insufficient precipitate will be formed, which cannot be removed even with scavengers. Therefore, the above-mentioned crystallization coprecipitation method does not give satisfactory results for waste liquids containing chelating agents.

[Purpose of the invention]

The present invention has been made to solve the above-mentioned drawbacks, and is a treatment for concentrated salt solution containing radioactive substances that can be applied to waste liquid C2 containing a chelating agent and obtain satisfactory results. [Summary of the Invention] The present invention provides a method for isolating salt waste liquid containing radioactive substances.
) The waste liquid is treated by appropriately combining the treatment by crystallization coprecipitation described above and (B) the adsorption treatment by activated carbon.

C1 To be more specific, the present invention provides a solution to (A) (a) Ni++, Co++, Mn++, and Zn for waste water containing radioactive substances.
Step (b) of adding divalent metal ions selected from the group consisting of ++; Step (c) of adding ferrocyanate ions in an amount equivalent to or more than the 21 metal ions; and (c) adding excess of the ferrocyanate ions. Step (d) of adding ferric ions in an amount equivalent to or more; Step (e) of adding alkali to adjust the pH to 8.5 to 11; Step of gradually adding sulfide ions; and (f)
After sequentially performing the steps of adding metal ions that can react with sulfurized rice to form a precipitate, the step of separating the formed precipitate from the remaining waste liquid and recovering the precipitate; and (B) activating carbon C Nisutaki. Step (A), (
B) Both steps are carried out in an appropriate combination.

The chelating agents present in the waste liquid and interfering with crystallization are organic chelating agents which form complexes with many metal elements. This is particularly problematic because KDTA and its wire conductors form complexes with many types of metal elements and have a wide stable PH range. In addition, 1-nitrone-2-naphthol, 2-nitrone-1-naphthol, Congo red,
Dimethylglyoxime etc. form complexes with specific elements and interfere with crystallization.

Therefore, in the present invention, these chelating agents are removed by being adsorbed on activated carbon to effectively carry out crystallization coprecipitation.

Activated carbon treatment may be performed first or after crystallization and coprecipitation. If crystallization coprecipitation is performed after activated carbon treatment, radioactive substances can be completely removed. When performing activated carbon treatment first, good results can be obtained if the waste liquid is filtered or centrifuged in advance to remove suspended solids.

Since the amount of the chelating agent in the waste liquid is several ppm or less, the amount of activated carbon used may be small. Activated carbon treatment can be carried out by filling an activated carbon adsorption tower with activated carbon and flowing the liquid to be treated through the tower.

Precipitation of radionuclides in the crystallization coprecipitation step (A) is thought to be performed as follows.

First, in steps (a) and (b), precipitated crystals of berlinate are formed, and these precipitated crystals contain 184Cs and 18
7Cs is incorporated. The amount of the divalent metal salt (a) added at this time is several ppm to several hundred ppm, preferably N
It is 70 ppm for iSo4.7H2O. In addition, the amount of (b) added is 1.1 to 1.5 equivalents to the salt of (a), and when using potassium ferrocyanide trihydrate salt, it is 170 p.
Approximately pm is appropriate. Subsequently, the ferric ions added in step (c) and the remaining ferrocyanate ions react to form a Berlin blue precipitate, and during the formation of this precipitate, the present 184Cs and 187Cs are incorporated, Also 60C
A part of o is also taken in. The appropriate amount of diiron sulfate to be added is 1.1 to 1.5 equivalents relative to the excess ferrocyanate ion, and preferably diiron sulfate is used in an amount of about 220 ppm. Furthermore, in step (d), an alkali is added to precipitate excess ferric ions as ferric hydroxide. At this time, 54Mn, 59Fe, 95Zr-95
Sodium hydroxide or potassium hydroxide is used as the alkali into which the Nb, 51Cr, and 60Co nuclides are taken. The pH is preferably 9.5 to 10.3. In step (e), sulfide ions S-- are added to the alkaline solution in an amount ranging from several ppm to several 100 ppm. Preferably, sodium sulfide is added to 30 ppm. Next, in step (f), metal ions such as Ni++, Co++, Fe++ react with S-- to form a sulfide precipitate.
, Cu++, Zn++, etc., precipitates of sulfides of these metals are formed, and at this time, residual nuclides such as 110mAg and 65Zn are incorporated. The metal ions added in (f) are suitably 1.1 to 1.5 equivalents of sulfide ions, for example, N
An aqueous solution of iSO4.7H2O is used.

The precipitates formed in each of the above steps will redissolve if left for a long time, so care must be taken.For example, if left for a long time after the ferric hydroxide precipitate is formed, the previously precipitated berric acid salt and Berlin blue will decompose. Therefore, it is necessary to proceed to the next (θ) step 5 within 6 hours at the latest. In addition, if left for a long time after adding sulfide ions, berlinate,
Since Berlin Blue will be decomposed and redissolved, quickly proceed to the next step (
f) must proceed to the process.

By performing each step in sequence as described above, the precipitates are deposited one after another, and after all the precipitates have been precipitated, the precipitates are separated using a clad separator or a filter.

[Embodiments of the invention]

Next, examples of the present invention will be shown.

5 m3 of waste liquid is filtered or centrifuged to remove floating suspensions. Next, this waste liquid is passed through an activated carbon adsorption tower.

The adsorption tower has a cylindrical shape with a diameter of 500 mm and a height of 800 mm.
The towers are arranged in series C1. When one of the two towers breaks through, the latter tower becomes the first stage, and a new adsorption tower is installed at the latter stage.

The waste liquid that has passed through the activated carbon adsorption tower is subjected to crystallization and coprecipitation treatment.

This crystallization coprecipitation is carried out as follows.

NiSO4・7H2O 330 to the above activated carbon treated waste liquid
Add about 10 g to an aqueous solution over 5 to 20 minutes while stirring well. Next, potassium ferrocyanide K4 [Fe
850 g of (CN)6].3H2O is made into an approximately 10% aqueous solution and is added over 5 to IO minutes while stirring well. A colloid of berlinate is formed here. Next, Fe2(S
o4) Make 1100 g of B into an approximately 10% aqueous solution and add over 5-10 minutes with stirring. Next, NaOH12
00g and adjust the pH to 8.5-11, preferably 9.
．． Adjust to 5. Finish the adjustment in about 5 to 20 minutes and then add Na2
Add 400 g of S.9H2O as an approximately 10% aqueous solution. Complete the addition in 5 to 10 minutes while stirring well. Next, 600 g of NiSO4.7H2O was made into a 10% aqueous solution and added while stirring well. The entire process should not exceed 6 hours. The generated precipitate is separated using a clad separator or filter.

This completes the crystallization coprecipitation process, and the treated waste liquid is filtered or centrifuged again, passed through an activated carbon absorption tower, repeats the crystallization coprecipitation process, and then filtered or centrifuged again to neutralize it. . The waste liquid treated in this way is purified to below the detection limit of radioactivity and released.

As another example, the same treatment may be performed in the order of waste liquid → crystallization coprecipitation → filtration or centrifugation → activated carbon adsorption → crystallization coprecipitation → filtration or centrifugation → activated carbon adsorption → neutralization → release.

Note that if 110mAg is not present in the waste liquid to be treated, steps (e) and (f) can be omitted in crystallization coprecipitation treatment C, and if 184Cs and 187Cs are not present ( In some cases, step a) can be omitted. In the latter case, the addition of Fe+++ in step (c) is equivalent to (a
) increases by the amount of ions not added.

〔Effect of the invention〕

As congratulated above, according to the present invention, the following effects can be obtained.

(1) Even if a C nickelating agent is present in the waste liquid, the crystallization coprecipitation method can be used. In other words, when treated with the method of the present invention, chromic acid and radioactive substances can be removed from the waste liquid with good separation performance even in the presence of a chelating agent, and the sludge separated from the waste liquid is non-radioactive unlike the conventional concentration method. Since it does not contain large amounts of salt, its volume is extremely small.

The sludge is 1/200 or less of the original waste liquid, and can significantly reduce the susceptibility of assimilated products such as cement solidified products.

(About 1/1000 of the solid weight compared to the conventional concentration method)
This corresponds to a volume reduction of . (2) Since the amount of the chelating agent in the waste liquid is usually several ppm or less, the amount of activated carbon may be extremely small. Furthermore, the volume of activated carbon that has adsorbed chelate can be further reduced by incineration.

(3) Equipment and operation are simple.

Claims (1)

[Claims] (1) For concentrated salt waste liquid containing radioactive substances, (A) (
a) Step of adding divalent metal ions selected from the group consisting of Ni++, Co++, Mn++ and Zn++ (b) Step of adding 7-erocyanate ions in an amount greater than the above value to the divalent metal ions (c) Step (d) of adding ferric ions in an amount equivalent to or more than the excess amount of ferrocyanate ions; Step (e) of adding an alkali to adjust the pH to 8.5 to 11; and (e) adding sulfide ions. process and (f)
After carrying out one step of adding a metal ion that can react with the Mu ion to form a precipitate, a step of separating the formed precipitate from the remaining waste liquid and recovering the precipitate; and (B) for reactivation. A method for treating concentrated salt waste liquid containing radioactive substances, characterized in that both steps (A) and (B) of the adsorption step are carried out in an appropriate combination. (2) A method for treating a concentrated salt waste liquid containing a radioactive substance according to claim 1, wherein step (A) is carried out within 6 hours. (Before step 81(B), suspended matter in the waste liquid is removed by filtration or centrifugation.) Treatment method. (4) For concentrated salt waste liquids that do not contain 110 mAg. (A) Processes (θ) and (f) of steps (θ) and (f) are omitted. Processing method. (5) For concentrated salt waste liquids in which 184Cs and 187Cs are not present, step (a) of step (A) is omitted. .