JPS60394A - Method of treating radioactive waste liquor - 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 treating radioactive waste liquid.

(Prior Art) Conventional methods for treating radioactive waste include the coagulation-precipitation method, ion exchange method, and evaporation concentration method.

The coagulation-precipitation method is a method in which a coagulant (aluminum salt, iron salt, etc.) is added to the waste liquid, and radioactive substances are captured and co-precipitated in the process of forming coagulated flocs such as hydroxide. This method is suitable for processing large amounts of low-level radioactive waste liquid at low cost, but it is important to note that the decontamination coefficient (radioactivity concentration before treatment /
Since the radioactivity concentration after treatment is less than 102, it cannot be used for high-level radioactive waste liquid.

In the ion exchange method, the main radioactive substances in the waste liquid exist as cations, so these are removed by ion exchange resin. However, ion exchange resins are expensive, and there are problems such as resin deterioration, and this method is limited to cases where it can be used repeatedly with low-level radioactive waste liquid.

Although the decontamination coefficient is about 102 to 108, there is also a big problem in processing the recycled waste liquid.

The evaporative concentration method extracts a large amount of water from the waste liquid into evaporated water.

This method allows radioactive substances to remain in the waste liquid.

This method has a high decontamination coefficient of 103 to 107 because it can separate nonionic nuclides from water that cannot be removed by the above two methods, and is the best method.It is suitable for decontaminating small amounts of high-level radioactive waste liquid, but the processing cost is high. Since it is the most expensive, it is not suitable for treating low- to medium-level radioactive waste fluids generated in large quantities from nuclear power plants.

(Objective of the Invention) The object of the present invention is to treat large amounts of low-level to medium-V Pel radioactive waste discharged from nuclear power plants, radioisotope handling facilities, and uranium handling facilities at a lower cost than conventional methods. The object of the present invention is to provide a method for treating radioactive waste liquid that can be treated.

(Structure of the Invention) The gist of the present invention is to treat a radioactive waste liquid by concentrating it through a J-type outer filtration membrane treatment in which water glass and a solidification aid are added.

In a more preferred configuration of the present invention, the concentrate obtained by the ultrafiltration membrane treatment as described above is immediately concentrated and assimilated (
(e.g. asphalt assimilation, vitrification, evaporation to dryness, etc.)
(2) There is a method in which a surfactant is added to wash the ultrafiltration membrane, the resulting liquid is separated into foam, and then concentrated and solidified in the same manner as in (2) above.

Specific Example I This will be explained below with reference to the drawings.

In FIG. 1, 1 is a circulating fluid tank, 2 is an ultrafiltration device, 3 is a foam separator, 4 is a concentration solidification device, 5 is a pump that supplies liquid from the circulating fluid tank 1 to the ultrafiltration tank 2, and 6 is radioactive waste liquid,
7 is water glass, 8 is a solidification aid, 9 is a pH adjuster, 10 is a surfactant, 11 is a permeated liquid from the ultrapolar filtration device 2, and 12 is sent from the ultrapure filtration device 2 to the circulating liquid tank 1. Circulating fluid sent, 13
14 is the foam (cross) separated by the foam separator 3 and guided to the concentration solidification device 4; 15 is the foam separator 5; Yoshi foam 14'f! : Desorbed liquid after separation, 1
6i1: Air 517 supplied to the foam separator is concentrated and solidified assimilate, and 18 represents condensate obtained from the concentration and solidification device 4 and returned to the circulating liquid tank 1.

(1) Radioactive waste liquid 6 from nuclear power plants, facilities handling radioisotopes, etc. is mixed with whole water glass 7 and put into the circulating liquid tank 1. This waste liquid 6 usually contains non-volatile nuclides (
58Co, ”Co, S9F@.

54Mn, etc.), but due to the alkaline action of the water glass 7, the radionuclides react as shown in the following formulas (1) to (3) and are insolubilized.

Na2O+H20-+ 2Na +20H-(1)60
0o”−+20H−−+ 60Co(OH)2↓ −−
-(2)"Fe"+30H-→"Fe(OH)3↓
・-(3) Water glass 7 bottles J engineering S sodium citrate 1-3
It is commercially available as silicic acid gel (Na2O-nsi02 ・mH2O).
Product No. 3 (5to2/Na2O-3,
15 molar ratio) is preferably used. The amount of water glass 7 added is 1 to 20 wt% as SiO□ based on the amount of suspended matter in the waste liquid 6.

(2) A solidification aid 8 is further added to and mixed with the waste liquid 6 mixed with the water glass 7 in the circulating liquid tank 1. The following chemicals can be used as the solidification aid 8.

Inorganic compounds include sulfite (I(2so3)) and sulfuric acid (
H2SO4) r Hydrochloric acid (mat), nitric acid (H)J
O3) + HouN (F13BO3) + Charcoal e (Hz
OO3), inorganic acids such as phosphoric acid (H3P04),
Reducing inorganic acid salts such as sodium sulfite (Na2SOs) r sodium thiosulfate CN &28203), ammonium sulfate ((NH4)zsO<),
Inorganic acid salts such as sodium phosphate (NaH2PO4), -reducing gases such as carbon oxide (CO), sulfur dioxide (SO2), hydrogen sulfide (H2S), sodium sulfide (Na
m5), calcium chloride (OaC!t2
) rAlkaline earth metal salts such as Calcilla sulfate A (C!asO4), sodium aluminate A (Na2A4
04) rAluminum salts such as aluminum sulfate (A4(So,)3), sodium bicarbonate (NaHCO2)
Alkali carbonates such as, zinc hydroxide (Zn(OH)2
) can be used.

Examples of organic compounds include organic acids such as formic acid (ITOOOH), oxalic acid ((OOOH)2), and acetic acid (0H3000H), and organic acid salts such as sodium formate (HOOONa) and sodium acetate (0H300ONa).

Aldehyde compounds such as formaldehyde.

Monosaccharides and reducing oligosaccharides can be used.

Pour the solidification aid 8 into the water glass 7 so that it has a reaction equivalent of N A20, and if necessary, add the pH adjuster 9 to the circulating liquid tank 1.
Readjust the pH to about 15-9. Due to the complex reaction between the water glass 7, the heavy metal of the radionuclide, the solidification aid 8, and the pH adjuster 9, the silicic acid of the water glass becomes active, and the polymerized silicon 9
(n5i02・XH20) Generate. This reaction mechanism is complicated and has not been clarified, but at pH 5-9
It is known that some of the heavy metals mentioned above and polymerized silicic acid bond with each other in a very short time.

mH2O-+ in Na20-nsi02 n5102 xH2O+yH20+ZNaOH+++(
4) In the liquid mixed in this way, granular solids are formed and the liquid becomes suspended in about 1 to 5 minutes. This granular solid contains almost 100% radionuclides and has a particle size of approximately 10
It is 0 mμ or more. The polymerized silicic acid of formula (4) acts as a binder for suspended substances (including insolubilized radionuclides) in the waste liquid, and has the effect of increasing the particle size of the suspended substances. Polymerized silicic acid also has the ability to form a film on the surface of suspended matter.

(3) The suspension is sent from the circulating liquid tank 1 to the ultrafiltration device 2 by the supply pump 5. Liquid feeding pressure is 0.5~4k
It is about g7cm2. The ultrafiltration device 2 is a filtration device 4 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 diameter is about 1 to 10 mμ.

The ultrapolar membrane has the function of separating water from the HUB turbid substances (including insolubilized radionuclides) described in id (2) in the waste liquid.

A portion of the feed liquid flows out of the ultrafiltration device 2 as a permeate 11 . On the other hand, suspended matter 5 colloids and the like contained in the supplied liquid are not permeated and are included in the circulating liquid 12. Thus, the circulating fluid tank 1, the supply pump 5, the ultrafiltration membrane 2, and the circulating fluid 1
The circulation continues in the order of 2, and the suspended matter (including radioactive substances) contained in the waste liquid in the circulating liquid tank 1 is concentrated. As the radionuclides leaking into the permeate 11 gradually increases, this concentration operation is continued until the radioactivity level in the permeate does not exceed a predetermined value. At this time, the volume reduction ratio (yellow waste liquid before treatment / quantity after treatment) is usually 50 to 10.
It is about 0.

(4) In cases where the radioactive waste liquid 6 already contains a detergent (for example, it contains a surfactant from the beginning, such as washing φM waste water from nuclear power plants and facilities that handle R engineering), ultrafiltration can be used to properly remove the detergent. When a suitable volume reduction ratio is obtained, the surfactant contained in the concentrate 13 will be used in the next foam separation device
1 value, that is, 10 ppm or more,
In that case, the concentrated liquid 13 is immediately sent to the foam separator 3.

If the radioactive waste liquid 6 does not contain detergent or if the concentration of surfactant contained in the concentrated liquid 15 does not reach 10 ppm, use the surfactant 10? Inject into circulation fluid tank 1 and continue circulation. The surfactant 10 (for example, DBS sodium dodecylbenzenesulfonate) is added in an amount of 10 ppm or more to the concentrate 16.

By adding 10i of surfactant), the effect of cleaning and desorbing the suspended solids adhering to the ultraviolet membrane, the foaming effect, and the
・Has an adsorption effect on some radionuclides. The polymerized silicic acid produced also acts as a builder for surfactants (a builder by itself exhibits almost no i1'7j activity, but when used in combination with a surfactant, its surfactant power is enhanced). something that strengthens).

(5) The concentrated liquid 13 is then sent to the foam separator 6.

The foam separator 3 is a device that foams the concentrated liquid 11 and separates it into bubbles and liquid. A large amount of foam is generated on the liquid surface by the air 16, and the suspended matter, etc., is attached to the surface of the bubbles, thereby separating the suspended matter containing radionuclides from the solution.

Note that the foam 14 will not be effectively generated unless the concentration of the surfactant in the concentrated liquid 13 is 10 ppm or more. In addition to air blowing, there are other methods for foaming, such as surface aeration.
Either method can be used. At this time, the suspended matter containing the radioactive nuclear citron contained in the concentrated liquid 13 adheres to the surface of the bubbles, causing the bubbles 1
4 is separated from the solution from the concentrate 13. The separated solution is returned to the circulating liquid tank 1 as a desorbed liquid 15. During this separation operation, most of the surfactant in the concentrated liquid 13 is transferred to the scum and is hardly contained in the desorbed liquid 13.

(6) The foam 14 is solidified by the concentration and solidification device 4, and is filled and stored in a drum as a solidified product 17. At that time, foam 1
The moisture in 4 is recovered as condensate 18 and returned to the circulating liquid tank 1 for treatment. As the concentration and solidification device 4, known means such as asphalt solidification and vitrification can be used.

That is, in the case of asphalt solidification, the foam 14 is evaporated to dryness or immediately stirred and mixed with asphalt heated to about 120 to 160°C to fix solids in the asphalt647, and in the case of vitrification, the foam 14 is fixed in the asphalt. After evaporating to dryness, borax (Na2B2O, 1oz
o,) and Kui sand (mainly Sin,) 'i plus 90
A glass-like solid is obtained by melting at 0 to 1300°C and gradually removing heat. It is known that these asphalt solidified products and vitrified products are extremely safe because they dispose of radioactive materials.

Specific example■ In Figure 2, 1, 2.4~9, 11~13° and 1
7.18 is similar to that shown in FIG.

1. Mix the turbulent waste liquid 6 from a plant that handles uranium with water glass 7 and put it into the circulating liquid tank 1. This waste liquid 6
It is usually a uranium compound (UO2F).

etc.) and fluoride (HF etc.) as a by-product. As shown in the following formulas (5) to (7), the uranium compound is insolubilized by the alkaline action of water glass and hydrogen fluoride (HF) is fixed.

Na2O+H20-+ 2NaOH-(5)2UO11
'2 +6NaOH-+ Na2U207↓+4]1a
? -1-3H20...(6), HF+NaOH-4NaF+H20...(7) Water glass is sodium silicate No. 3 product (5i
O1/Nano-115) f is preferably used. The amount of water glass added is 5102 (10 to 100 wtLf) based on the amount of suspended solids produced in the waste liquid. This is because HF is present in this waste liquid, which is different from the case of Example I, and therefore Na2O is required in an amount greater than the reaction equivalent of UO□F2 and HF.

A solidification aid 8 is further added to and mixed with the waste liquid 6 mixed with the water glass 7 in the circulating liquid tank 1. As the chemicals that can be used as the solidification aid 8, the compounds described in Example 1 can be used, but in order to fix fluorine (F-) at the same time, it is convenient to use alkaline earth metal salts and aluminum salts. Alkaline earth metal salts react with fluoride and become insolubilized.

For example, calcium chloride (0a
When Ot2) is used, the reaction occurs as shown in the following formula (8).

0aO62+ 2NaF-4C! aF2↓+2NaC4
e + @ (8J The amount of solidification aid 8 added is the combined amount of reaction equivalent of Na2O of water glass 7 and reaction equivalent of fluorine (F-), and if necessary, add pH adjuster 9 to circulating liquid tank 1. p of
Readjust so that H is about 5 to 9.

Due to the combined reaction of the water glass with the above-mentioned uranium compound, solidification aid, and pH adjuster, the silicic acid of the water glass is liberated to produce polymerized silicic acid (ns1o2.XH, O). These reaction mechanisms are complex and have not been clarified, but the pH
In Nos. 5 to 9, the polymerized silicic acid is formed in a significantly short time,
It is known that r-metal contained in waste liquid and polymerized silicic acid bond.

The polymerized silicic acid acts as a binder for the suspended substances (sodium biuranate, calcium fluoride) in the waste liquid, and has the effect of increasing the particle size of the suspended substances. In the thus mixed liquid, granular solids are formed in about 1 to 5 minutes and the liquid becomes suspended. This granular solid material contains not only radionuclides but also calcium fluoride (0aF2)
Ylo.

5 particle diameters are approximately 20 mμ or more.

Polymerized silicic acid also forms a film on the surface of suspended matter.

Next, the liquid is sent from the circulating liquid tank 1 to the ultrafiltration device 2 by the supply bonder 5, and as in Example I, the above-mentioned suspended matter in the waste liquid and the waste liquid are separated and concentrated by the ultrafiltration membrane, and the volume is reduced. . The volume reduction ratio at this time is usually about 200 to 1000.

Polymerized silicic acid liberated from water glass has the effect of dispersing suspended substances in the liquid, and therefore has the effect of preventing the deposition of suspended substances on the membrane surface.

When an appropriate volume reduction ratio is obtained, the daughter condensate 13 is transferred to the concentrating and solidifying device 4.
send to As in Example I, known means can be used for the concentration and solidification device 4.

If it is desired to recover the uranium compound, the concentrated liquid 13 may be simply evaporated to dryness using the condensation solidification device 4, and then dissolved using known means, ie, nitric acid 52 (HNO3).

Example As Example 1 of the present invention, a waste liquid containing 60 (3o) was treated in the same manner as in Example 1, and as Example 2, a waste liquid containing a uranium compound was treated in the same manner as in Example (2). Treatment conditions, The obtained volume reduction ratio and decontamination coefficient are shown in Table 1. Furthermore, as a comparative example, the conditions and results of treating the same waste liquid as in Example 2 containing uranium compounds (UF) by the conventional ultrafiltration method are also shown in Table 1. Shown below.

Further, the treatment liquid obtained in Example 1 was subjected to asphalt solidification or glass assimilation.

Table 2 shows the assimilation conditions and the state of the obtained solidified product.

Table 1 (Note) The ultrafiltration supply pressure is 2.5 kg/crn2° and the permeation rate 'O1/m2-Hr. Since the particles are coarsened to a particle size that does not allow them to pass through, the ultrafiltration membrane can perform concentration and separation more efficiently than a simple ultrafiltration device 1 ton, and the decontamination coefficient can be significantly increased.

(2) Most radionuclides than ultrafiltration devices due to the interaction between surfactants and polymerized silicic acid produced from water glass? The 5-polymerized silicic acid is dispersed in the suspended substance in the liquid to prevent the substance from being deposited on the membrane surface, and the surfactant has the effect of cleaning the membrane and desorbing the substance, extending the life of the membrane, and further improving the membrane surface. to enable repeated use.

(3) The decontamination coefficient can be increased by the surfactant adsorbing some radionuclides.

(4) Foaming power is significantly enhanced by the interaction between the surfactant and the polymerized silicic acid produced from water glass. Therefore, the radionuclides in the liquid can be separated into bubbles with high efficiency.

(5) By separating the foam, the amount of liquid can be significantly reduced.

(6) When concentrating and solidifying with asphalt, the asphalt solidification rate is high because the suspended solids absorbed by the polymerized silicic acid easily stick to the asphalt.

(7) Polymerized silicic acid is a non-swelling gel, so it does not swell even if it absorbs a small amount of water fixed in asphalt.
Since it does not cause cracks in the solidified asphalt, it prevents the leaching of radionuclides and increases safety.

(3) In the case of vitrification, since polymerized silicic acid has the same composition as the glass component, glass assimilation is extremely easy, and the amount of silica sand required to be added is small.

(9) Since uranium compounds and fluorine are insolubilized and the polymerized silicic acid coarsens them to a particle size that does not allow them to pass through an ultrafiltration membrane, concentration and separation using an ultrafiltration membrane can be performed more efficiently than simple membrane separation. The decontamination coefficient can be significantly increased.

As described above, according to the method of the present invention, the decontamination coefficient can be significantly increased and the processing cost is lower than when simply passing the waste liquid through the limit. As a method for treating a large amount of low-to-medium level radioactive waste liquid, the present invention is more economical than the evaporative concentration method and has a higher decontamination coefficient than the coagulation-precipitation method.

[Brief explanation of drawings]

1 and 2 are flow sheets illustrating the method of the present invention. Acting agent 1) Meifuku agent Ryo Hagiwara -

Claims (1)

[Claims] A method for treating radioactive waste liquid, which is characterized by adding water glass and a solidification aid to the radioactive waste liquid and subjecting it to ultrafiltration.