JPS5852598A - Removal of organic compounds from radioactive waste liquid - 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] This invention relates to improvements in methods for reusing treated water.

Low-level radioactive waste liquid generated at nuclear power plant waste treatment facilities is evaporated and concentrated, and the concentrated waste liquid is solidified.
The evaporated water is condensed, treated with an ion exchange resin, and reused. However, anion exchange resins are generally not very stable against heat or radiation, and some of them decompose to produce amines (eg, trimethylamine) and alcohols (eg, methanol). Since these organic compounds enter the condensed water side during evaporation and concentration, they tend to accumulate gradually during the recycled use of the treated water and need to be removed.

The simplest method to remove organic compounds from water is to use an adsorbent such as activated carbon, but it has the disadvantage that low-boiling compounds such as trimethylamine and methanol mentioned above are difficult to adsorb. In the case of wastewater treatment, the adsorbent after use becomes secondary waste, and its disposal becomes a problem. 55
-4271.9), a large amount of air is required for sufficient removal, and if a high temperature is used to increase the removal rate, a considerable amount of wastewater will evaporate at once5, and the organic matter in the exhaust gas will be There is a risk of secondary pollution such as having a bad odor.

Another method for decomposing and removing organic matter in water is a technique that uses ultraviolet light and chlorine (which acts as an oxidizing agent). Although this method is good for treating general organic matter, it is not suitable for handling radioactive waste liquids because there is a great risk of corrosion of the equipment.

In view of the current situation, the present invention provides a technology for removing organic compounds with low adsorption properties contained in radioactive waste liquid while minimizing concerns about secondary pollution and corrosion of equipment. The purpose is to

The method of removing organic compounds from radioactive waste liquid of the present invention includes:
This is a method to oxidize and decompose organic compounds using a combination of ultraviolet rays and an oxidizing agent. First, the radioactive waste liquid containing organic compounds is irradiated with ultraviolet rays while ozone or hydrogen peroxide is added to the radioactive waste liquid. It is characterized in that it oxidizes and decomposes organic compounds.

Ultraviolet rays in the wavelength range of 1 x 102 to 5 x 102 m[mu] are particularly effective. There are a variety of mercury lamps on the market that generate ultraviolet light useful for photochemical reactions, and you can choose the appropriate one from them.

For irradiation, a method called an internal irradiation type in which a mercury lamp is placed in the liquid is advantageous because it has a high light utilization rate. If necessary, a suitable jacket may be used as shown later.

As the oxidizing agent, ozone or hydrogen peroxide is used as described above. Ozone is particularly effective as an electrophilic reagent such as an amine.

As is well known, ozone is generated by corona discharge in oxygen, so by supplying air to the discharge device, the ozone-containing air can be pumped into the waste liquid to be treated as bubbles through a suitable aeration tube. Bye.

When using hydrogen peroxide, its aqueous solution may be dropped into the waste liquid and stirred. The appropriate concentration is about 0.005 to 0.5%.

When used as an ozone oxidizing agent, it is effective to keep the pH of the waste liquid to be treated at approximately 7 or higher, that is, in the neutral to alkaline range, as shown in the examples shown later.

The amount of oxidizing agent required, whether using ozone or hydrogen peroxide, depends on the amount of UV radiation to be applied, as well as the type and concentration of organic compounds in the waste liquid to be treated, and the desired degree of removal. , those skilled in the art will be able to easily determine in each case by referring to the Examples described later and conducting some experiments if necessary.

Although the process of the present invention is conveniently carried out in batches on a conventional scale, it can also be operated continuously if sufficient residence time is available.

If radioactive waste liquid is treated according to the present invention, most of the organic compounds contained in it will be converted into harmless carbonic acid, oxidizing power divided by 1, and the treated water will be easy to use. There is little risk of corrosion of the equipment.Furthermore, after use, it decomposes into 02 and H20, so there is no need to worry about it accumulating in the treated water.

The apparatus used to carry out the treatment method described in - generally has the configuration shown in FIG. 1. That is, the waste liquid Rw to be treated is first sent to the filtration device 3 to remove solid content. This not only reduces the radioactivity level of the water to be treated, but also eliminates unnecessary consumption of oxidizing agents. It also prevents solid matter from adhering to the mercury lamp, which generates ultraviolet rays, and improves lamp efficiency. Benefits include being able to avoid a decline in

As already explained, the waste liquid that has passed through the filtration device enters the oxidation treatment tank 1, where it is exposed to ultraviolet rays from a mercury lamp 2, and organic compounds are oxidized under the action of the oxidizing agent Ox. . The mercury lamp 2 is housed in a suitable jacket 21 known as an internal irradiation type photochemical reaction device, and a liquid 10
It is preferable to use a tube inserted inside because it has a high light utilization rate.

The exhaust gas passes through the mist catcher 4 and the processing device 5 and is released into the atmosphere. The treated liquid is stored in a tank (not shown) and subjected to evaporation and concentration if necessary.
Reuse circularly.

If the concentration of organic compounds in the waste liquid to be treated is relatively high or if high-level removal is desired, oxidation using only an oxidizing agent may be performed prior to oxidation under ultraviolet irradiation. Recommended.

Therefore, the second method of removing organic compounds from radioactive waste liquid of the present invention is to apply ozone or hydrogen peroxide to the radioactive waste liquid containing organic compounds to oxidize and decompose some of the organic compounds. For the waste liquid after this oxidative decomposition,
It is characterized by oxidizing and decomposing remaining organic compounds by applying ozone or hydrogen peroxide while irradiating ultraviolet rays.

The configuration of the apparatus used for this implementation is typically shown in FIG. That is, the waste liquid from the filtration device 3 is first put into the oxidation tank (first tank) IA, and oxidized with only the oxidizing agent Ox.
The treated liquid 10 A is transferred to the next oxidation tank (second tank) I.
B, where it is oxidized with an oxidizing agent Ox under ultraviolet irradiation.

This two-step process, as shown in the example below,
A high decomposition rate of organic compounds can be obtained.

The method of removing organic compounds from radioactive waste liquid of the present invention includes:
It also includes a third method, in which the radioactive waste liquid containing organic compounds is irradiated with ultraviolet rays, and while applying ultrasonic vibrations, ozone or hydrogen peroxide is applied to remove the organic compounds. It is characterized by chemical decomposition.

Ultrasonic vibrations are provided by placing one or more vibrating elements in the outer wall, inner wall or waste liquid of the oxidation tank. Elements suitable for this purpose are readily available on the market. When using a plurality of elements, each element should be placed in a non-opposing relationship.

An example is shown in FIG. In the figure, three ultrasonic vibration elements 6 are attached to the inner wall of the oxidation tank 1 at non-opposed positions.

The significance of applying ultrasound to oxidation with an oxidizing agent under ultraviolet irradiation is that it contributes to improving the agitation of the waste liquid, and as shown in the example below, the speed of the oxidation reaction is slightly improved. Yes, and another reason is that it prevents the jacket of the mercury lamp from getting dirty and prevents a decrease in the efficiency of using ultraviolet rays.

The less dirty the lamp jacket is and therefore the need for cleaning, the more the potential for human exposure is reduced.

Conventionally, various mechanical and chemical methods have been used to clean lamps in photochemical reaction devices, but these methods pose risks such as increased human exposure, increased secondary waste, and corrosion of the device. It was not suitable for treating radioactive waste liquid. The present invention eliminates such problems.

A mercury lamp with an output of 100 W was placed in the center of a tank with a jacket of 100 W, and an aeration tube was provided at the bottom.

An apparatus having the configuration shown in FIG. 1 was assembled around this oxidation tank.

A radioactive waste liquid mainly containing 1.70 ppm of methanol as an organic compound was continuously fed into the tank at various flow rates within the range of 01~], Ot/min, and taken out in equal amounts at a temperature of 20'C. Organic compounds were oxidized by releasing ozone-containing air as bubbles from a diffuser tube. The amount of ozone supplied is 0.5 f/mi
It is n.

The methanol concentration in the effluent from the tank was measured and organized by residence time in the tank. The results are shown in the graph in Figure 4 (
03+UV). For comparison, oxidation was attempted by supplying only ozone without UV irradiation, and the results are shown in Figure 4 (03). It is clear that methanol decomposition does not progress much with ozone alone, but oxidation can be effectively carried out when combined with ultraviolet light.

The tank used in Example 1 was used as the second tank, and before that,
At t, a tank with only an aeration pipe at the bottom was provided as the first tank. Other than that, a device having the configuration shown in FIG. 2 was assembled in the same manner as in Example].

The treated waste liquid is methanol 1.501') rim.
and 1.50 ppm of trimethylamine. This waste liquid was supplied at a flow rate of 0.2 t/min, and after first being subjected to ozone oxidation in the first tank, the effluent was photo-osin oxidized in the second tank. The amount of ozone supplied to both the first tank and the second tank was 0.1 it'/min. This processing method is called the 12-step method.

For comparison, only the photo-osin oxidation as in Example 1 was performed in a tank with a volume of 12 tons under the conditions of an ozone supply rate of 0.2 f/min. This is called a two-stage method.

The decomposition rate in terms of the amount of residual organic compounds in the effluent was as follows.

Methanol 84% 95% i.Remethylamine 97 97 When trimethylamine is present, the decomposition rate itself is high, but there is a tendency to suppress the decomposition of methanol.

On the other hand, the results of the methanol decomposition rate organized by the residence time in the tank when the flow rate was varied are shown in FIG. According to the two-stage method, a high decomposition rate is quickly reached.

Example 3 An apparatus having the flow shown in FIG. 1 was assembled using an oxidation tank having the structure shown in FIG. 3, but with only one ultrasonic vibration element attached to the outer wall of the container.

The capacity of the tank is 10 tons, and the capacity of the tank is 100 tons.
A W 2 low-pressure mercury lamp 2 was used and protected with a Vycor glass jacket 21. Ultrasonic oscillator is 300W
, 25KHz.

Methanol 200ppm, suspended solid content 2001)I
) m containing waste liquid 10 is put into the tank 1, and the aeration pipe 4 at the bottom is put into the tank 1.
Air containing ozone was blown into the tank to oxidize it, and the decomposition rate of methanol was measured over time.

For comparison, an experiment was also conducted without applying ultrasonic vibration.

The results are shown in the graph of FIG. It can be seen that when the third method is followed (tJV+US), a higher decomposition rate is reached more quickly than in the case of ultraviolet irradiation alone (UV).

In addition, each batch of the waste liquid was treated for 2 hours, and the initial rate of methanol decomposition was tracked to obtain the graph shown in FIG.

It was observed that by applying ultrasonic vibration, the initial reaction rate could be maintained even if the number of processed batches increased, but otherwise the reaction rate gradually decreased. Needless to say, this is caused by a decrease in ultraviolet transmittance due to the adhesion of suspended matter to the lamp jacket.

Example 4 The apparatus used in Example 1 was provided with a supply port for hydrogen peroxide solution, and a pump was used to supply hydrogen peroxide solution so that the H3O2 concentration in the tank was 0.05%.

Only air was blown in from the ozone-containing air diffuser used earlier, and the waste liquid in the tank was stirred. Other operating conditions are the same as in Example 1.

The methanol concentration in the effluent from the tank was measured and the results, organized by residence time in the tank, are shown in Figure 8.

For comparison, data obtained when only hydrogen peroxide was supplied without ultraviolet irradiation are also shown in FIG.

As in Example 1, the effect of combined use is clear.

Example 5 Example 5 was repeated under the same conditions except that the initial pH of the waste liquid, that is, pi-1 when it flows into the tank, was variously changed. The decomposition rate of methanol after 60 minutes of residence in the tank was plotted, and the results shown in Figure 9 were obtained. It can be seen that during ultraviolet light-osine oxidation, the liquid quality of the waste liquid should be neutral or alkaline.

[Brief explanation of the drawing]

FIG. 1 is a flowchart 1 for explaining the first method of the present invention. FIG. 2 shows the first method for explaining the second method of the present invention.
It is a flowchart similar to the figure. FIG. 3 is a longitudinal sectional view showing the configuration of the main parts of an apparatus used for carrying out the third method of the present invention. FIG. 4 is a graph showing the effects of the present invention, showing the relationship between treatment time and methanol concentration in waste liquid. Figure 5 is a graph showing the effects of the second method of the present invention and the relationship between treatment time and methanol decomposition rate. Figure 6 is a graph showing the effects of the third method of the present invention. Fig. 7 is a graph showing the effect of the third method of the present invention from another perspective, showing the relationship between the processing time and the methanol decomposition rate. Figure 8 is a graph showing the effect of the present invention, and is a graph showing the relationship between treatment time and methanol decomposition rate. Figure 9 is a graph showing the effect of the present invention. It is a graph showing the influence of the pH of waste liquid on the decomposition rate of methanol. Rw... Raw waste liquid 1.0. IOA, IOB... Waste liquid Ox.
... Oxidizing agent 1 ... Oxidation treatment tank, IA...
・ Same (1st tank), 1B... Same (2nd tank) 2... Mercury lamp 3... Diffusion pipe 4... Ultrasonic vibration element patent applicant JGC Agent Co., Ltd. Patent Attorney Suga So Fusai 1 Figure 12 Figure 8 Figure 4 Figure Keyaki V Ginhan (Bessuku 5 Figure 0 20 40 60 80 10
0 Trade F+) ￥ If Left O 6 Figure 0 20 40 60 80 100 Gaginto (Clear) Off Figure 0 2 4 6 13 10 1
2 pins now several years old 8 figures push 9 counts n gin) Fang 0 figures H

Claims (1)

[Claims] (+1) An organic compound in a radioactive waste solution characterized by oxidizing and decomposing the organic compound by applying ozone or hydrogen peroxide to the radioactive waste solution containing an organic compound while irradiating the radioactive waste solution with ultraviolet rays. (2) Ozone or hydrogen peroxide is applied to radioactive waste liquid containing organic compounds to oxidize and decompose some of the organic compounds, and then the waste liquid after this oxidative decomposition is irradiated with ultraviolet rays. A method for removing organic compounds from a radioactive waste solution, which is characterized by oxidizing and decomposing the remaining organic compounds by applying ozone or hydrogen peroxide to the radioactive waste solution. A method for removing organic compounds in a radioactive waste liquid characterized by irradiating the organic compound with ultrasonic vibration and oxidizing and decomposing the organic compound by applying ozone or hydrogen peroxide. (4) The irradiated ultraviolet rays , lXIO2~5×102?y
The method according to any one of claims 1 to 3, which includes a wavelength range of lμ. (5) The method according to any one of claims 1 to 3, in which ozone is applied by blowing ozone-containing air into the radioactive waste liquid. (6) Claims 1 to 3 in which hydrogen peroxide acts by adding hydrogen peroxide to radioactive waste liquid.
Either way. (The method according to any one of claims 1 to 3, in which the waste liquid is filtered to remove solid content prior to the oxidative decomposition.) (8) The pH of the waste liquid is adjusted to 7 or higher, and the ozone The method according to any one of claims 1 to 3, which acts on the method.