JPS6238247A - Method for regenerating ion exchange resin - Google Patents

Abstract

PURPOSE:To reduce the amount of regenerating chemicals and to prolong the life of an ion exchange resin, by regenerating a chelate agent forming a complex along with the metal ion adsorbed by the ion exchange resin by a solution containing regenerating chemicals in an amount equivalent to or slightly more than the metal ion. CONSTITUTION:The chelate agent forming a complex along with the main metal ion adsorbed by an ion exchange resin is regenerated by a solution containing regenerating chemicals in an amount equivalent to or slightly more than the aforementioned metal ion. For example, when the cation exchange resin of a condensation desalting device of a boiling water atomic power plant is regenerated, the amount of the chelate agent contained in the regenerated solution is set to one equal to or more than a mol number necessary for forming a neutral or negative complex along with the metal contained in said ion exchange resin to perform regeneration. The amount of the regenerating solution is suitably adjusted to 1/4-1/2 the amount of the ion exchange resin. Further, it is suitable to perform regeneration by stirring the ion exchange resin and the regenerating solution by air bubbles.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a method for regenerating an ion exchange resin used in a condensate demineralizer of a boiling water nuclear power plant, and particularly relates to a method for regenerating an ion exchange resin used in a condensate demineralizer of a boiling water nuclear power plant, and particularly relates to a method for regenerating an ion exchange resin used in a condensate desalination device of a boiling water nuclear power plant. The present invention relates to a method for regenerating ion exchange resins suitable for increasing chemical waste and reducing the amount of chemical waste generated.

[Background of the invention]

The conventional method for regenerating ion exchange resin in boiling water nuclear power plant condensate demineralizers is as described in JP-A-50-146570, after separating it into cation exchange resin and anion exchange resin. The ion exchange resin is regenerated with sulfuric acid, and a regeneration level of 100 g H2S04 per resin IQ and a concentration of 5% is commonly used. There were problems in that this amount was used regardless of the amount of ion loading on the cation exchange resin, and that at the above sulfuric acid concentration, iron regeneration efficiency was low and iron was difficult to remove. As a result of analyzing the cation load on the cation exchange resin used in the condensate demineralizer of a boiling water nuclear power plant, as shown in Figure 5, the majority of the cation load was iron ion load.

Therefore, the main purpose of regenerating the cation exchange resin is to remove iron ions. This adsorbed iron is the aforementioned sulfur
I1. In terms of degree and amount, the regeneration rate is about 25%, and a large amount remains in the resin. Therefore, iron ions accumulate year after year in the cation exchange resin that is used repeatedly, as shown in FIG. As a result, the effective ion exchange capacity remaining is reduced, and the condenser loses its ability to cope with seawater leakage, so it has to be discarded after a few years.

Further, the sulfuric acid solution used for regenerating the cation exchange resin is neutralized with the sodium hydroxide solution used for regenerating the anion exchange resin to form a sodium sulfate solution, concentrated in a waste liquid concentrator, and stored as waste. The system for concentrating waste liquid is shown in Figure 6. In FIG. 6, waste liquid 12 neutralized in the neutralization tank 11
is sent to the waste liquid concentrator 13 and heated and concentrated in the heater 14, but 1-lium sulfate produces a precipitate containing a large amount of water such as Na25o4.10H20, so there is a limit to the concentration that can be concentrated. was less than 20%, and if this concentration was not maintained, problems such as clogging of the pipe 15 due to precipitation of precipitates would occur.

For information related to this type of method, see Japanese Patent Application Laid-Open No. 51-0.
94035, JP-A-17781, JP-A-37
-7605 etc. are mentioned.

[Purpose of the invention]

The purpose of the present invention is to significantly reduce the amount of chemicals used in chemical regeneration of ion exchange resin in condensate desalination equipment of boiling water nuclear power plants, extend the life of ion exchange resin, and generate radioactive waste. To provide a method to reduce the amount.

[Summary of the invention]

The present invention was made based on the following study results.

The ion exchange reaction of cation exchange resin converts metal ions into M
″+, ion exchange resin is represented by R−, and if hydrogen ions (H+) are added to the ion exchange resin, M”+nH”R−=M” (R−), +nH” −(1
).

Here, [M]: Concentration of metal ion M''+ in the aqueous phase (w
oQ/Q), CM)-: Resin phase (71M'' (7) concentration CmoQ/(1-resin> (H): Hydrogen ion concentration of water phase (moQ/Q) [H],: Water iR of resin phase Ion concentration (moQ/2-resin) Ko: Ion exchange constant between hydrogen ions and metal ions M0.

Therefore, the distribution coefficient D of metal ions into the aqueous phase and the resin phase is
11 is represented by . Equation (3) shows that the smaller the distribution coefficient D'' is, the easier it is to regenerate the ion exchange resin.D
' can be reduced by increasing (H), but for example, if sulfuric acid is used as in the past, the amount of sulfuric acid increases, which is not preferable. So, D.

One possible way to reduce this is to reduce the metal ion concentration in the aqueous phase. A complexing agent (Y”-
) is added to the aqueous phase, [M″”)+ (Y”’−)−)
(mYnM) ・= (4) and [Ma+] decreases. There are many complexing agents that form complexes with iron ions, but Table 1 shows the stability constants of relatively inexpensive chemicals and their complexes.

Table 1 Iron complexing agents and their stability constants By the way, since the cation exchange resin must be regenerated in an acidic environment, it is desirable that the complexing agents in Table 1 have a small stability constant as an acid. The acid stability constants of the complexing agents in Table 1 are shown in Table 2.

Table 2 Stability constants of organic acids Also, iron ions adsorbed on a cation exchange resin used in a condensate demineralizer at a boiling water nuclear power plant are eluted with a sodium sulfate solution, and ammonium thiosulfate - absorbance As shown in Table 3, ferrous ions and ferric ions were present, and ferric ions accounted for approximately 70% of the total iron ions. Understood. As a result of regeneration under the cation exchange tree regeneration conditions actually carried out at the power plant, ferrous ions can be removed to some extent from the cation exchange resin.

It became clear that ferric ions were hardly removed, and it became clear that this was the cause of the poor regeneration efficiency in the actual machine.

Table 3 From this result and Tables 1 and 2, it is clear that in order to remove ferric iron from a cation exchange resin, oxidative acid, which forms a stable complex with ferric iron and has relatively low acid stability, is required. It can be seen that it is effective to play the The case where oxalic acid is used as an eluent will be discussed below.

The reaction in the elution of ferric iron with oxalic acid is 2 (R=Fe)
+3H, C, ○, -+ 6 (R-H)+Fe, Cc2
o4)z-(5) According to formula (3), here, L is C204-t αre(CzO4) is Fe
The side reaction coefficient for the reaction between *** and oxalic acid (Anders Ringbon: Complex Formation Reaction Industrial Library (1965)) If 0.1N oxalic acid is used as the eluent, from the stability constant in Table 2, [H ) (L) When the degree of dissociation α is determined, α=0.031, and the pH is 2.5. Also, α2. Find L.

αy−L= 1 +(L)β1+(L)”β2+(L)
The stability constant β of each of 3β1 is from the literature value (1).

/3. = 10", L= 10"-", β3= 1
The values of 0'''K were obtained through experiments and are shown in Table 4.

Table 4 Ion exchange capacity of cation exchange resin 1.8 eq/Q-
Assuming that 10% of Resin adsorbs ferric ions, and substituting the two series of values into equation (6), we get that most of the ferric iron will move into the solution and will not be adsorbed by the resin. . When eluted with sulfuric acid (IN), the result is as follows, and most of it is adsorbed on the resin. The same holds true for ferrous iron, which has a higher concentration in the solution than ferric iron. Next, the seventh
As shown in the figure, a resin column 16 is filled with a cation exchange resin 17 on which ferrous and ferric ions are adsorbed, and a regenerating liquid 18 contains 15% sulfur W and 0.2 N oxalic acid.
The flow rate was adjusted using the cock 19, and a fixed amount of the effluent liquid 20 was received in the container 21, and the ferrous and ferric iron in the effluent liquid 20 was analyzed to examine its elution behavior. . The results are shown in FIGS. 8 to 10. When sulfuric acid is used as the regeneration solution, ferrous iron is eluted, but a large amount of regeneration solution is required for complete regeneration, and ferric iron cannot be eluted.When oxalic acid is used as the regeneration solution 18, As shown in FIG. 8, both ferrous and ferric iron are eluted, and the amount of regenerating liquid can be reduced.

Although ferrous iron does not form a stable complex with oxalic acid, it is thought that as a result of ferric iron forming a complex with oxalic acid, the hydrogen ion concentration increased and the elution of ferrous iron was promoted.

Furthermore, if ferrous iron is converted to ferric iron using an oxidizing agent, all iron ions are considered to be effectively transferred to the regenerating liquid.

FIG. 10 shows the results when hydrogen peroxide was further added to the regeneration liquid. It can be seen that the addition of an oxidizing agent is effective.

[Embodiments of the invention]

Hereinafter, an embodiment of the present invention will be explained with reference to FIG. 1. A cation exchange resin 2 adsorbed with ferrous and ferric ions was placed in a regenerated cation exchange resin #F1.

The oxalic acid solution 3 is sent to the regeneration tower 1 from the tank 4 in which the oxalic acid solution 3 is stored. The oxidative acid solution 3 elutes iron ions from the cation exchange resin 2 and is sent to the waste liquid treatment tank 5. Oxidic acid solution 3
The volume of the cation exchange resin is twice the volume of the cation exchange resin, and the amount of oxalic acid in the oxalic acid solution 3 includes at least 1.5 times the equivalent of ferric iron adsorbed on the cation exchange resin.

According to this embodiment, more than 70% of the ferric ions adsorbed on the cations can be removed.

The second embodiment has the configuration of the first embodiment, but the modification shown in FIG. Add hydrogen peroxide solution to solution 3.

The amount of hydrogen peroxide added is at least the same equivalent as the ferrous ion adsorbed on the cation exchange resin.

According to this embodiment, since hydrogen peroxide changes ferrous iron to ferric iron, 7 of the total iron ions adsorbed on the cation exchange resin 6
It has the effect of removing more than 0%.

A third embodiment is shown in FIG. Oxalic acid and hydrogen peroxide are transferred from the condensate demineralization tower 7 of a boiling water nuclear power plant to the cation exchange resin regeneration tower 1 to regenerate the cation exchange resin 2 separated from the anion exchange resin. Regeneration liquid 3 containing
The cation exchange resin 2 is sent from the storage tank 2 to the regeneration tower 1.
The liquid is circulated through the liquid feed pump 6. Composition of circulating eluent 3.

The concentration is the same as in Example 2.

According to this embodiment, since the iron ion concentration in the resin and the iron concentration in the regenerating solution are in equilibrium, it is possible to remove 95% or more of the iron ions from the cation exchange resin.

A fourth embodiment is shown in FIG. In FIG. 2, the regenerating liquid is @circled, but in this example, a certain amount of the regenerating liquid 3 is sealed in the regenerating tower 1, and air 8 is introduced from the bottom of the cation exchange resin 2.
The cation exchange resin 2 and the regeneration liquid 3 are stirred with air bubbles. Oxalic acid and hydrogen peroxide in the regenerating solution in this case are the same as in Example 2.

According to this embodiment, since the amount of regenerating liquid can be reduced to 1/4 of the amount of resin, there is an effect that the discharge layer of the regenerating liquid can be reduced to 1/8 of that in the first and second embodiments.

A fifth embodiment is shown in FIG. Furthermore, in the fourth embodiment,
Heaters [9, 10] are added to keep the temperature of the regenerating liquid 3 and air 8 at 70°C.

In this case, the regenerating solution is oxalic acid, and its amount is equal to or more than the equivalent of ferric iron, which is the total amount of adsorbed ions and attached iron.

According to this embodiment, there is an effect that not only adsorbed iron ions but also attached iron oxide can be dissolved and removed.

〔Effect of the invention〕

According to the present invention, more than 90% of ferric ions and ferrous ions adsorbed on the cation exchange resin can be removed, and the amount of chemicals used for regeneration can be reduced, so the amount of waste generated from boiling water nuclear power plants can be reduced. This has the effect of reducing The effects are shown in Table 1.

[Brief explanation of the drawing]

Figure 4 is a diagram showing a method for regenerating a cation exchange resin according to an embodiment of the present invention, and Figures 2 to 4 are diagrams showing an application example of the present invention for regenerating a condensate demineralizer in a boiling type nuclear power plant. Figure 5 is a diagram showing the regeneration method in the column, Figure 5 is a diagram showing ion loading, Figure 6 is a waste liquid treatment system diagram, Figure 7 is a diagram showing the experimental method of column elution, Figures 8 to 10 are FIG. 3 is a diagram showing the elution behavior of iron ions in a column elution method. DESCRIPTION OF SYMBOLS 1... Cation exchange resin regeneration tower, 2... Cation exchange resin, 3... Regeneration liquid, 4... Tank, 5... Waste liquid receiving tank, 6... Circulation pump, 7... Condensate desalination tower, 8
... Air, 9 ... Air heater, 10 ... Regeneration liquid heater, 11 ... Waste liquid neutralization tank, 12 ... Waste liquid, 13
...Waste liquid concentrator. 14... Waste liquid heater, 15... Piping, 16... Column, 17... Ion exchange resin, 18... Regeneration liquid,
19... flow, <-

Claims (1)

[Scope of Claims] 1. In the chemical regeneration of cation exchange resin, a regenerated chemical solution containing a complexing agent that forms a complex with the main metal ion adsorbed on the ion exchange resin in an amount equivalent to or slightly in excess of the metal ion. A method for regenerating an ion exchange resin, the method comprising: regenerating an ion exchange resin. 2. A method for regenerating an ion exchange resin according to claim 1, characterized in that oxalic acid is used as a complexing agent to elute ferric iron. 3. A method for regenerating an ion exchange resin according to claim 2, characterized in that hydrogen peroxide is added to the regeneration chemical to oxidize ferrous iron to ferric iron to improve regeneration efficiency. 4. In claims 1 to 4, when applied to the regeneration of a cation exchange resin in a condensate demineralizer for boiling water nuclear power generation, the amount of complexing agent contained in the regeneration liquid is A method for regenerating an ion exchange resin, characterized in that the amount is equal to or greater than the number of moles necessary to form a neutral or negative complex with a metal contained in the exchange resin. 5. A method for regenerating an ion exchange resin according to claim 4, characterized in that the amount of the regenerating liquid is in the range of 1/4 to 2/1 of the amount of the ion exchange resin. 6. An ion exchange resin regeneration method according to claims 4 and 5, characterized in that the regeneration liquid is circulated through the resin in a regeneration tower. 7. An ion exchange resin regeneration method according to claims 4 and 5, characterized in that the ion exchange resin and regeneration liquid are regenerated by stirring with air bubbles. 8. A method for regenerating an ion exchange resin according to claim 7, characterized in that the regeneration is performed by heating the regeneration liquid and air to a temperature of 70 to 50°C.