JPS6367877B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention is directed to a radioisotope handling facility (hereinafter referred to as RI).
It is written as a facility. ) concerning a method for treating radioactive waste fluid generated from Conventionally, methods for treating the wastewater include a coagulation sedimentation method and an evaporation method. Although the coagulation-sedimentation method is a low-cost method, the decontamination factor [DF = (radioactivity concentration before treatment) / (radioactivity concentration after treatment)] is less than 50, and the volume reduction ratio [CF = (radioactivity concentration before treatment)] is less than 50. (amount of radioactive waste liquid)/(amount of radioactive waste liquid after treatment)] is less than 50, and although the evaporation method is a high-cost method, DF is 10 ³ to 10 ⁴ and CF is
100 or less, and each has its advantages and disadvantages. The present invention has relatively low cost and high DF.
The present invention also provides a method for treating radioactive waste fluid generated from RI facilities where CF is obtained. In other words, the present invention can reduce the pH of waste liquid containing radioactive substances.
3 or more and concentrate with an ultra-semi-permeable membrane, or adjust the waste liquid to pH 3 or higher, add an inorganic flocculant or an organic flocculant, concentrate with an ultra-semi-permeable membrane, and add a surfactant to the concentrated liquid. The present invention relates to a method for treating radioactive waste liquid, which is characterized in that the concentrated liquid is added and concentrated again using the ultrasemi-permeable membrane, and then the concentrated liquid is foamed and subjected to foam separation treatment. The accompanying drawings illustrate one embodiment of the method of the present invention. In the figure, radioactive waste liquid 5 first enters circulating liquid tank 1 while being mixed with alkaline agent 6. The alkaline agent 6 is injected so that the pH of the waste liquid becomes 3 or higher.
The circulating liquid tank 1 is fed under pressure (0.5 to 4 kg/cm ² ) to the ultrafiltration device 2 by the supply pump 4 . The ultrafiltration device 2 is a filtration device using a semipermeable membrane that allows salts in a solution and dissolved low-molecular substances to pass through, but does not allow suspended solids, colloids, and high-molecular substances to pass through. The size of the holes in the semipermeable membrane is preferably 1 to 10 mμ. The permeated liquid 8, which has partially passed through the ultrafiltration device 2, is discharged as decontaminated water. On the other hand, suspended substances, colloids, etc. are not permeated and are included in the circulating fluid 9. The circulating fluid 9 continues to be circulated in the order of the circulating fluid tank 1, the supply pump 4, and the ultrafiltration device 2, and suspended substances (including radioactive materials) are concentrated. This concentration operation is continued until the radioactivity concentration in the permeate 8 does not exceed a predetermined value (ie, the standard value of effluent water, 1×10 ⁻⁶ μCi/cc). At this time, the volume reduction ratio is usually 50 to 100.
As the concentration progresses and an appropriate volume reduction ratio is obtained (in addition,
When the radioactivity concentration in the permeated liquid 8 reaches the above standard value, a surfactant 7 (for example, dodecylbenzenesulfonic acid = DBS, etc.) is injected into the circulating liquid tank 1,
Continue the cycle. The injection rate of the surfactant 7 is 0.5 to 0.5 to the amount of concentrated liquid held in the circulating liquid tank 1.
It is preferable to set it to 10 ppm. After 5 to 10 cycles, the concentrate 10 is sent to the foam separator 3. The foam separator 3 is a device that foams the concentrated liquid 10 using air 13. The concentrated liquid 10 generates a large amount of foam on the liquid surface due to the DBS and air contained therein. At this time, suspended matter (including radioactive substances) contained in the concentrate 10 adheres to the bubble surface and is separated from the water in the concentrate 10 as scum 11. The separated water is returned to the circulating liquid tank 1 as a desorbed liquid 12. During this separation operation, most of the DBS in the concentrated liquid 10 is transferred to the scum 11 and is not contained in the desorbed liquid 12. Note that unless the surfactant 7 is added, the foam separator 3 will not produce effective foam. The above operations produce the following effects. (1) Radioactive substances are insolubilized by injecting alkaline agent 6 to make the waste liquid pH 3 or higher. For example, in the case of ⁶⁰ Co and ⁵⁹ Fe, the following reaction results in
Precipitates as hydroxide. ⁶⁰ Co ²⁺ +20H ^- → ⁶⁰ Co(OH) ₂ (precipitate) ⁵⁹ Fe ³⁺ +30H ^- → ⁵⁹ Fe(OH) ₃ (precipitate) (2) Ultrasemipermeable membrane with hole size 1 to 10 mμ By using this, the suspended solids in the waste liquid and the above-mentioned insolubilized radioactive substances are separated from the liquid. (3) Add surfactant 7 to 0.5 to 10 ppm based on the amount of concentrated liquid.
By adding , the effect of washing and desorbing suspended substances adhering to the semipermeable membrane surface, the foaming effect, and the adsorption effect of some radioactive substances are produced. (4) The liquid is foamed by blowing air, and suspended substances are attached to the surface of the bubbles. In addition to air blowing, there are other methods for foaming, such as surface aeration. (5) The foam separator 3 separates the generated air bubbles and the mixture scum such as suspended solids attached to the surface of the bubbles from the liquid. These actions can provide the following effects. High decontamination efficiency can be obtained by insolubilizing radioactive substances and separating them with a semipermeable membrane. By using a surfactant, most of the separated radioactive substances can be removed from the surface of the semipermeable membrane, thereby extending the life of the semipermeable membrane. Also, the semipermeable membrane can be used repeatedly. Surfactants increase decontamination efficiency by adsorbing some radioactive substances. Separation of foam significantly increases the concentration of radioactive substances in the liquid. In addition, in the method of the present invention, in addition to adding an alkali agent, an inorganic flocculant (for example, Al salt, Fe salt, etc.)
Alternatively, an organic polymer flocculant (eg, an acrylamide compound, etc.) may be added. In this case, the injection rate of the alkaline agent is determined so that the pH is 5 or higher, and the inorganic flocculant is used as a flocculant solution with a pH of 50~
It is preferable to add 200 ppm and 0.5 to 5 ppm of the organic polymer flocculant as a flocculant (powder). This operation produces the following effects. (i) Radioactive substances that have been insolubilized by injection of an alkaline agent are flocculated by an inorganic flocculant or an organic polymer flocculant. For example, in the case of an inorganic flocculant (Al salt), the following reaction occurs at pH 5 or higher. Al ³⁺ +30H ^- →Al(OH) ₃ (precipitate) The Al(OH) ₃ produced in the above equation aggregates with the insolubilized radioactive substance as a core, and the particle size increases. In addition, in the case of an organic polymer flocculant, the insolubilized radioactive substances coagulate together, increasing the particle size. (ii) Other effects are the same as in (1) to (5) above. Through these actions, the following effects can be achieved. ○…

Claims (1)

[Scope of Claims] 1 A waste liquid containing a radioactive substance is concentrated with an ultra-semi-permeable membrane to a pH of 3 or more, a surfactant is added to the concentrated liquid, and it is concentrated again with the ultra-semi-permeable membrane, and then the A method for treating radioactive waste liquid, characterized by foaming a concentrated liquid and performing foam separation treatment. 2. Adjust the waste liquid containing radioactive substances to PH3 or higher, add a non-flocculant or an organic flocculant, concentrate with an ultra-semi-permeable membrane, add a surfactant to the concentrated liquid, and re-concentrate it with the ultra-semi-permeable membrane. A method for treating radioactive waste liquid, which comprises concentrating it, and then foaming the concentrated liquid to perform a foam separation treatment.