JPS6039596A - Method of removing transition metal from solution containingcomplexing agent - 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 The present invention relates to a method for removing transition metals from solutions containing complexing agents.

In the cooling systems of nuclear reactors, deposits containing radioactive elements often occur. , these radioactive deposits must be removed in order to safely maintain and repair nuclear reactor cooling systems. This has been solved, for example, by using an oxidizing solution of alkali permanganate, followed by a decontamination solution of oxalic acid, citric acid, and ethylenediaminetetraacetic acid (EDTA). EDTA forms a complex with radioactive element ions in the deposit and solubilizes the deposit.

The contaminant removal solution is circulated through a cooling system and a cation exchange resin, which exchanges ions with the metal ions on the resin to liberate EDTA, which can then be used to solubilize the metal ions. Make it.

However, a major problem with this method is that EDTA does not easily exchange metal ions, especially iron ions, such as ferric ions, with cation exchange resins. Therefore, the metal ion-EDTA concentration in the decontamination solution increases until it is no longer effective in solubilizing the metal ions in the deposit.

When this concentration increase occurs, a new EDT A
must be added to the decontamination solution. That is, E.D.
The decontamination solution must be constantly monitored to determine if the TA is depleted and therefore more EDTA must be added.

Furthermore, one must be very careful about adding too much EDTA. That is, if EDTA does not form a complex with metal ions, EDTA is not very soluble and the precipitated EDTA itself is difficult to remove from the cooling system. In addition, if excess EDTA is added, not only is it a waste of EDTA, but the excess EDTA must be removed from the decontamination solution in subsequent steps when adding EDTA to large amounts of radioactive waste. .

Therefore, the present invention provides a method for removing transition metals from a solution containing a complexing agent in which the equilibrium constant of the ferric ion complex formation reaction is at least 1022. and a method for removing transition metals from a complexing agent-containing solution, characterized in that the solution is circulated through the anion exchange resin.

Preferably, the complexing agent is ethylenediaminetetraacetic acid or an alkali metal salt thereof.

The inventors have discovered a method for removing transition metal ions from a decontamination solution containing a selected complexing agent while simultaneously regenerating the complexing agent. Unlike conventional methods that use cation exchange resins, the present method uses anion exchange resins. For example, an EDTA anion is preloaded onto an anion exchange resin, and each metal ion-EDTA complex is subjected to ED treatment.
Deposit on TA-loaded anion exchange resin and release fresh EDTA from the anion exchange resin into solution. Therefore, the concentration of uncomplexed EDTA in solution is kept fairly constant, and monitoring the EDTA concentration in solution,
That is, it is not necessary to add new E L:) T A.

As described above, the method of the present invention can be applied to various solutions containing a complex of a transition metal and a complexing agent (complex forming agent) whose equilibrium constant in the ferric ion complex formation reaction is 1022 or more.

Examples of such complexing agents include ethylenediaminetetraacetic acid fi
(EDTA), trans, 1f2-diami/cycloA
These include san tetran1° acid (DCTA) and oxybis (ethylenediaminetetraacetic acid). Transition metals commonly found in nuclear reactor decontamination solutions include iron, cobalt,
Contains nickel and chromium. The temperature of the solution should be at least 4'C to keep the EDTA dissolved in solution and prevent it from precipitating.However, the temperature of the solution should be below about 100C. This is because if the temperature is higher than this temperature, the anion exchange resin and the complexing agent used in the solution may decompose.The pH of the solution is not particularly limited, but the acidity of the complexing agent present may Therefore, most contaminant removal solutions typically contain 2 to 2
．． It is 5.

Therefore, in the first step of the method of the invention, the anion exchange resin is loaded with EDTA. Any anion exchange resin is suitable and can be used in the present invention. The ion exchange resin should be loaded only with EDTA and not with any other additional complexing agents. This is because when the metal ion-EDTA complex is adsorbed onto the EDTA-loaded anion exchange resin, it releases other anions [i.e., nitrilotriacetic acid (NT A >, citric acid, or oxalic acid 1) into the solution. This is to reduce the EDTA concentration of.

Other complexing agents, such as NTA, or organic acids, such as citric acid or oxalic acid, form transition metal complexes that are much weaker than those formed by EDTA, and metals complexed with complexing agents other than EDTA are It is removed from the complexing agent-containing solution by the cation exchange resin. This is not the case for EDTA-metal complexes, and as a result, metal ions remain in solution when conventional removal methods are used.

EDTA can most conveniently be loaded onto an anion exchange If fat by preparing a solution of EDTA and passing this solution through an anion exchange resin. To load the anion exchange resin with EDTA, it is desirable to use an EDTA salt solution, preferably an alkali metal salt, such as sodium EDTA. This is because anion exchange resins release sodium hydroxide into solution rather than just water. NaO
Since H is highly alkaline (pH approximately 12-14), the pH of the solution exiting the column increases after the initial rise.
It drops again to a sodium pH (pH about 4-5).

This is because the few hydroxyl groups of the preferred strong base anion exchange resins are replaced by EDTA anions. Thus, by monitoring the I) I-1 of the solution leaving the resin, it can be determined whether the resin is fully loaded. pH is about 6 or less.

The resin should be considered completely loaded with EDTA anions. On the other hand, if the acid form of EDTA is used, it is more difficult to determine whether the resin is loaded with I+1. This is because there are no sodium ions present in the acid form of EDTA and the solution leaving the column is at approximately neutral pH (1+H approximately 7). Therefore, the difference between the pH value of the solution fed to the column (approximately 4.5) and the pH value of the solution leaving the column (approximately 7) is significantly smaller than when using sodium salts. Furthermore, acidic EDTA hardly dissolves in water. This means that the solution must be made more planar.

In the next step of the invention, a contaminant removal solution containing a metal ion-EDTA complex is placed between the anion exchange resin loaded with ED T'A and the cooling system of the nuclear reactor, or the cooling system to be decontaminated. For example, the steam generator of a pressurized water reactor or a boiling water reactor is circulated. As the Jk group ion-EDTA complex is adsorbed onto the ED'rA@ ion exchange resin, fresh EDTA is released into the decontamination solution. The solution is circulated until the metal ion concentration in the solution exiting the cooling system is substantially greater than the metal ion concentration in the solution entering the cooling system.

After the metal ion-EDTA complex is removed, the EDTA and the remaining ions in the solution are removed by passing the solution through a fresh anion exchange resin or a mixed anion-cation exchange resin, so that the solution is The water will be relatively pure. Pre-loaded anion exchange resin absorbs metal ions.
EDT, ~ Once saturated with precious wood, this resin is discarded as radioactive waste.

The present invention will be explained below based on Examples and Reference Examples.

Reference example diameter: 2.5 am (1 inch), length: 45.7'
am (18 inches) is a glass column made of strong basic polystyrene resin with a particle size of 15 to 50 mesh.
RA-400” anion exchange resin (R1+om nod
100 IIll (trade name, manufactured by Haas) was loaded. E
I) A solution of 100 g/l of T A's Fium salt was prepared. .

This solution having a pH of 4.38 was poured from the top of the column at a rate of 1 to 3 anion exchange resin bed volumes (bed body 81)/hour, and the pH of the solution flowing out from the bottom of the column was measured. Table 1 below shows the p of the solution flowing out from the column after the solutions of various anion exchange resin beds are passed through the column.
Indicates H.

Table 1 Bed body fi’ [p H O,511,85 1,012,86 1,512,9 (3 2,012,36 2,56,56 3,0,,5,90 3,55,64 4,05,47 4,55,29 5,0* 5.15 6.0 5,07 ' : pl (prepared a new solution of 4,49.

As shown in the table above, after the initial start-up time, the pH of the solution exiting the ion exchange resin dropped to near 1114 of the solution injected into the ion exchange resin.

This indicates that the column is almost saturated with EDTA.

Example 1 A 0.5% by weight solution of a commercially available contaminant removal reagent solution consisting of 30% citric acid, 30% Scheric acid, and 40% EDT A containing an inhibitor believed to be thiourea. Iron (magnetite) iron from Fe30+) 50 each
, 100, 150) m to prepare a simulated used contaminant removal solution. Each of these three solutions and the EDTA-loaded anion exchange resin prepared in Reference Example were mixed in a beaker at 54°C. These solutions were tested after 5 hours and found to contain 3.11 and 46 ppm iron, respectively. ``This confirmed that the EDTA-loaded anion exchange resin successfully removed iron from solution.

Example 2 An EDTA-loaded anion exchange resin was prepared in the same manner as in the reference example, and a 100 ml sample of this EDTA-loaded anion exchange resin was
, diameter 2.5 am (1 inch), length 45.7 cm
A +n (18 inch) glass column was loaded. iron 8
A commercially available f18 contaminant containing 0 ppm was passed from top to bottom and iron, oxalate, citrate, and EDT A concentrations exiting the column were measured. The following table shows these concentrations.

Table 2 EDTA after the initial start-up time as shown in the table above
The column loaded with 10% iron in the solution successfully flows out.
It is removed to below ppm.

Continuation of page 1 (Illustrator Lawrence Frederi Beck Betzker, Ju near

Claims (1)

[Claims] The equilibrium constant of the ferric ion complex formation reaction is at least 10
In the method for removing transition metals from a solution containing a complexing agent as described in No. 22, an anion exchange resin is loaded with the complexing agent or a salt thereof, and the solution is circulated through the anion exchange resin. A method for removing transition metals from a complexing agent-containing solution.