JPS60395A - 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.

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.

The ion exchange method is a method in which the main radioactive substances in waste liquid exist as cations, and these are adsorbed and removed by an ion exchange resin. However, ion exchange resins are expensive, and there are problems such as resin deterioration, etc., and they are limited to cases where they can be used repeatedly with Bell radioactive waste liquid.

Although the decontamination coefficient is about 102 to 105, there is also a big problem in processing the recycled waste liquid.

The evaporative concentration method is a method in which a large amount of water is evaporated and separated from the waste liquid, and the radioactive materials remain in the waste liquid. This method has the best decontamination coefficient of 103 to 107 because nonionic nuclides that are difficult to remove with the above two methods can be separated from water.
Although it is suitable for decontaminating small amounts of high-level radioactive waste, it has the highest processing cost and is not suitable for treating large amounts of low- to intermediate-level radioactive waste generated from nuclear power plants and the like.

Therefore, the present inventor proposed a method using ultrafiltration as a method for inexpensively treating low-to-medium level radioactive waste liquid (Japanese Patent Application No. 55284/1984). This method is extremely effective when the number of types of radionuclides in the waste liquid is relatively small and is insoluble, but it is said that it cannot fully decontaminate nuclides that tend to form complex salts or are soluble. There's a problem.

The present invention has been devised to overcome the above-mentioned drawbacks and to treat all low-V to medium-V radioactive waste fluids discharged from facilities that handle radioisotopes and uranium.

The present invention is relatively low cost and has a higher decontamination coefficient than a simple membrane separation method (ultrafiltration or reverse osmosis), and can decontaminate even foamy waste liquid that cannot be reduced in volume with the evaporative concentration method.
To provide a method for treating radioactive waste liquid that can obtain an excellent decontamination coefficient even when it contains not only non-volatile radionuclides but also volatile radionuclides.

That is, the gist of the present invention is to add water glass and a solidification aid to radioactive waste liquid, perform ultrafiltration, and then subject the p-filtrate to reverse osmosis treatment.

The accompanying drawings illustrate exemplary embodiments of the method of the invention. In Figure 1, water glass 9 is added to radioactive waste liquid 8 and
Mix in soil circulation tank 1. This waste liquid 8 usually contains non-volatile nuclides (58Co, 60Co.

In addition to volatile nuclides (such as 59FB and 64Mn),
131 constructions.

106 Ru, etc.) may be included.

Water glass is JIS sodium silicate No. 1-5 Na2
It is commercially available as 0Na20-n5i02-),
In this case, it is preferable to use product No. 3 (8102/Na2O-5.15 molar ratio), which quickly forms citric acid gel (n81oz-xH20). The water glass addition meter is 1 to 20 wt% as 5102 based on the amount of suspended solids in the waste liquid.
Added.

After all of the water glass 9 has been added to the first circulating liquid tank 1, the solidification aid 10 is added thereto and mixed.

Chemicals that can be used as the solidification aid 10 are as follows.

Inorganic compounds include sulfite (H2"os) r sulfuric acid ("t"0<) r hydrochloric acid (Hal), nitric acid (H
NO3).

Boric acid (HsBOs) + carbonic acid ("b C03)
+ Inorganic acids such as phosphoric acid (H3P04), sodium sulfite (na2Soz), sodium thiosulfate A (
Reducing inorganic acid salts such as ammonium sulfate ((shellfish H4) 21904) Reducing gases such as hydrogen (H, S), sodium sulfide (Na
Sulfides such as z8), calcium chloride (CaO12)
, alkaline earth metal salts such as calcium sulfate (0aSO4), sodium aluminate (Na2At204) r
Aluminum salts such as aluminum sulfate (Az4(so4)a), alkali carbonates such as sodium bicarbonate (NaHCO2), and heavy metals such as zinc hydroxide (Zn(OH)2) can be used.

Examples of organic compounds include oxalic acid ((C00H)2) and acetic acid (CH3000H).
Organic acids such as sodium formate (HOOOlla)
, organic acid salts such as sodium acetate (0H300ONa), aldehyde compounds, monosaccharides, and reducing oligosaccharides can be used.

For waste liquids containing volatile radionuclides, any of the above substances can be used as the solidification aid 10, and for waste liquids containing only non-volatile radionuclides, any of the above substances can be used as the solidification aid 10.

The solidification aid 10 is injected in a reaction equivalent amount with Nano in the water glass 9, and if necessary, the pH of the first circulating liquid tank 1 is readjusted to about 15 to 9 using the pH adjuster 11a.

In the thus mixed liquid, granular solids are formed and the liquid becomes suspended in about 1 to 5 minutes. This granular solid material contains approximately 100 insoluble radionuclides and has a particle size of approximately 100 mμ or more.

The liquid is sent from the first circulating liquid tank 1 to the ultrafiltration device 2 by the supply pump 7a. Liquid feeding pressure is 05~4kg/crn2
That's about it.

Ultrafiltration device 2 This is a filtration device using a semipermeable membrane that allows salts and soluble low-molecular substances in the solution to pass through, but does not allow suspended solids, colloids, and polymeric substances to pass through. The size of the holes in the semipermeable membrane is about 1 to 10 mμ.

The feed liquid is separated in the ultrafiltration device 2 partly as a permeate 16 and mostly as a circulating liquid 14 .

The permeated liquid 13 contains soluble radionuclides in addition to soluble salts and low-molecular substances that have passed through the membrane. On the other hand, circulating fluid 1
4 contains suspended matter and colloids (including insoluble radionuclides) that could not pass through the membrane.

In this way, the circulation continues in the order of the first circulating liquid tank 1, the supply pump 7a, the ultrafiltration device 2, and the circulating liquid 14, and the suspended matter and colloids (insoluble radionuclides) contained in the waste liquid in the first circulating liquid tank 1 are ) are concentrated. As the radioactive nuclides leaking into the permeated liquid 13 gradually increase, this concentration operation is continued until the radioactivity level in the permeated liquid does not exceed a predetermined value.

The permeated liquid 13 flows into the second circulating tank 3 and is supplied to the reverse osmosis device 4 by the supply pump 7b. The reverse osmosis device 4 applies a pressure higher than the osmotic pressure of the permeated liquid 13 (usually about several tens of kg 7 cm2) to allow water, which is a solvent, to permeate through a semipermeable membrane, and solutes (soluble substances, ions, etc.) are removed at the membrane surface. It is a device to prevent this. Normally CLS blocks the permeation of ions and polymeric substances with a size of ~60 mμ.

Part of the supplied liquid (permeated liquid 13) flows out as permeated liquid 19 in the reverse osmosis device 4, and soluble salts and low molecular weight substances (including soluble radionuclides) contained in the supplied liquid are permeated. It is contained in the circulating fluid 20. Thus, the second circulating liquid tank 6,
Circulation continues in the order of the supply pump 7b5, reverse osmosis device 4, and circulating fluid 20, and the soluble salts and low molecular weight substances (including soluble radionuclides) contained in the waste fluid in the second circulating fluid tank 3 are concentrated. Ru. As the radionuclides leaking into the permeate liquid 19 gradually increases, this concentration operation
The treatment is continued until the radioactivity level in step 9 does not exceed a predetermined value.

Although it varies depending on the ion species, the reverse osmosis membrane is more permeable to anions than cations, and as the concentration operation progresses, the pH of the circulating fluid 20 gradually increases. In order to neutralize this, it is necessary to add pH adjuster 11b (acid).

Normally, the pH is adjusted to 4.0 to Z5 due to the characteristics of the reverse osmosis membrane.

The ultrafiltration concentrate 15 obtained as described above is sent to the foam separator 5. Note that in cases where the radioactive waste liquid 8 already contains detergent, the surfactant contained in the concentrated liquid 15 will exceed 10 q/cm when an appropriate volume reduction ratio is obtained, so immediately remove the concentrated liquid. 15 to the foam separator 5.

In cases where radioactive liquid 6 liquid 8 does not contain detergent,
If the surfactant contained in the concentrated liquid 15 does not reach 10 my/l, the surfactant 12 is injected into the first circulating liquid tank 1 and circulation is continued.

The injection amount of the surfactant (DBS!=sodium dodecylbenzene sulfonate, etc.) is 10 Zlv/or more per 15 parts of the concentrate. Thereafter, it is sent to the condensate liquid + sl foam separator 5.

The foam separator 5 is a device that can foam 15 feet of concentrated liquid using air, and a large amount of foam is generated on the liquid surface by the surfactant 12 contained in the concentrated liquid 15 and the air. In addition to air blowing, any method such as surface aeration can be used as a foaming method. At this time, suspended matter (including radionuclides) contained in the concentrate 15 adheres to the surface of the bubbles, and foam 16 is separated from the solution from the concentrate 15. Foam 16 flows into assimilation device 6 .

On the other hand, the solution V separated by the foam separator 5 is returned to the first circulating liquid tank 1 as a desorbed liquid 17. During this separation operation, most of the surfactant in the concentrated liquid 15 is transferred to the scum, and almost no surfactant is contained in the desorbed liquid 17.

The reverse osmosis concentrate 21 flows into the solidification device 6 together with the foam 16 obtained from the foam separator 5 .

The assimilation device 6 can use known means such as asphalt solidification and vitrification. That is, in the case of asphalt solidification, the foam 16 is evaporated to dryness, or immediately
It is used to identify solid substances (including radionuclides) in the asphalt by stirring and mixing it with asphalt heated to about 60℃.In the case of vitrification, after evaporating the foam to dryness,
Borax (Na2B407-10H,0) and silica sand (mainly 5tO2) are added, melted at 900 to 1300°C, and the heat is gradually removed to obtain a glassy solid. These asphalt solidified products and vitrified products are known to be extremely safe because they dispose of radioactive materials.

The above operations produce the following effects.

(1) Radionuclides are insolubilized by the alkaline action of water glass 9. For example, 6 [IC! In the case of 0.69yθ, the following reaction occurs and hydroxide is precipitated.

Na2O+H20-+ 2Na-4-20H-= (
1) 60Co"-1-20H-→"Co(OH)2↓
---(2)591? lθ3++30H-→59yθ
(OH)3↓ ... (3) (2) Due to the combined reaction of the water glass 9, the above radionuclide, and the solidification aid 10, the silicic acid of the water glass is liberated, resulting in polymerized silicic acid (n5i02 x H20)
generate. This reaction is carried out by adjusting the pH of the waste liquid using the pH adjuster 11a.
It is further significantly promoted by adjusting the value to 5 to 9. Although the reaction mechanism is not clear due to its complexity, it is known that some of the radionuclides mentioned above and polymerized silicic acid bind. The qualitative reaction is as follows.

Na20−nSiO2・mH2O −+nSiO2・xH2O+yH20+zNaOH−−
-(4) (3) The polymerized silicic acid acts as a binder for suspended solids (including insolubilized radionuclides) in the waste liquid, and increases the total particle size of the suspended solids.

Polymerized silicic acid also has the ability to form a film on the surface of suspended matter.

(4) By using an ultrafiltration membrane with a hole size of 1 to 10 mμ, the above-mentioned suspended substances and colloids (including insolubilized radionuclides) in the waste liquid are completely separated from the liquid.

(5) By adding surfactant 12, it has the effect of cleaning and desorbing suspended solids and colloids adhering to the surface of the ultrafiltration membrane, the foaming effect, and the effect of adsorbing some radionuclides (1 oz. /z or higher, this effect will be drastically reduced).

(6) Polymerized silicic acid also acts as a surfactant builder (a substance that exhibits almost no surface activity by itself, but strengthens its surface active power when used in combination with a surfactant).

(7) The reverse osmosis membrane completely separates the solution from the soluble salts and low-molecular substances (including all soluble radionuclides) that pass through the ultrafiltration membrane.

(8) In the foam separator 5, air is blown into the liquid to foam the liquid and cause suspended substances to adhere to the surface of the bubbles.

(9) 5 bubble separators Separate the generated bubbles and the suspended solids attached to their surfaces from the liquid.

00 The solidification device 6 evaporates the foam 16 from the foam separation device 5 and the concentrated liquid from the reverse osmosis device 4 to dryness, and removes the radionuclides therein.
Fix solid substances etc. in asphalt or glass.

These actions can provide the following effects.

■ The radioactive nucleus w4 is completely insolubilized and the polymerized silicic acid coarsens it to a particle size that does not allow it to pass through the ultrafiltration membrane, so concentration and separation with the ultrafiltration membrane can be carried out efficiently, and it can only be separated by an ultrafiltration membrane. In comparison, the decontamination coefficient is significantly increased.

■ Due to the interaction between the surfactant and the polymerized citric acid produced from water glass, the surface of the ultrafiltration membrane removes most of the radionuclides, extending the life of the membrane and allowing it to be used repeatedly.

■ The decontamination coefficient can be increased by the surfactant adsorbing some radionuclides.

(2) Because the nature of reverse osmosis membranes is that they must not contain suspended solids, it is extremely advantageous to use ultraviolet filtration M'x as a pretreatment for reverse osmosis membranes.

■ Since the reverse osmosis membrane blocks soluble salts and colloids (including soluble radioactive substances) that pass through the ultrafiltration membrane, the decontamination coefficient can be significantly increased.

■ Most of the radionuclides are removed using an ultrafiltration membrane,
Since the amount of radionuclides in the reverse osmosis membrane is small, the lifespan of the reverse osmosis membrane can be extended and the membrane can be used repeatedly.

■ Foaming power is significantly increased by the interaction between surfactant and polymerized silicic acid produced from water glass. Therefore, radioactive nuclides in the liquid can be efficiently separated into foam.

■ The volume of liquid can be significantly reduced (by dividing the foam).

■ Polymerized silicic acid 1d is a non-swelling gel, so it does not swell even if it absorbs the remaining water in asphalt, and does not cause cracks in solidified asphalt, preventing radioactive nuclides from leaching and increasing safety. .

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

A further example embodiment of the invention is shown in FIG.

In Figure 2, water glass 9 is added to radioactive i8 and the first
Mix in circulating liquid tank 1. This waste liquid 8 usually contains uranium compounds (such as UO2F2) and fluoride (I(
F, etc.) are included.

As the water glass, it is preferable to use sodium silicate No. 5 (13i02/Nano = 115 molar ratio) as in the case of FIG. The amount of water glass added varies greatly depending on the composition of the suspended solids in the waste liquid, but it is usually preferable to add 10 to 100 wt% of the amount of water glass as 5102. Unlike the case in FIG. 1, since H4F is present in the waste liquid, Na2O is required in an amount greater than the reaction equivalent of UO2F2 and HF. That is, if the amount of uranium compound (for example, Na2TJzOy) is large, a large amount of water glass can be added, and if the amount of uranium compound is small, strong particles can be formed by adding a small amount of water glass.

After adding water glass 9 in circulating liquid tank 1, solidification aid 1 is further added.
Add 0 and mix. All of the chemicals shown in the case of Figure 1 can be used as the solidification aid 10, but at the same time, it is convenient to use alkaline earth metal salts and aluminum salts in order to remove as much fluorine (F-) as possible. It is. The amount of solidification aid 10 to be added is based on the reaction equivalent of water glass with Na2O when using alkaline earth metal salts or aluminum salts, or the reaction equivalent of water glass with lla@O when using alkaline earth metal salts or aluminum salts. The total amount of the reaction equivalent amount and the reaction amount of fluorine (CF-) is taken as the total amount, and if necessary, the pH of the first circulating liquid tank 1 is readjusted to about 5 to 9 using the pH adjuster 11a.

In the liquid mixed in this way, granular solids are formed in about 1 to 5 minutes, and the liquid becomes suspended. These granular solids contain approximately 100% of insoluble radionuclides, and when alkaline earth metal salts or aluminum salts are used as solidification aids, most of the fluoride is contained. The diameter is about 20 mμ or more. When a solidification aid other than an alkaline earth metal salt or an aluminum salt is used, fluoride is hardly contained in the granular solid.

Next, the liquid is sent from the first circulating liquid tank 1 to the ultrafiltration device 2 by the supply pump 7a, and concentrated and volume-reduced in the same manner as in FIG. The decontamination coefficient at this time is 10 in the case of H.
3 to about 105, and the volume reduction ratio is usually about 50 to 100. In addition, the F concentration of the permeate 13 is Iri4 when an alkaline earth metal salt or aluminum salt is used as a solidification aid.
my/ is below, and in the case of other solidification aids, it was the same as the F- concentration in the radioactive waste liquid.

The permeated liquid 13 suddenly flows into the second circulation tank 3 and the supply pump 7
b is supplied to the furnace infiltration device 4. The reverse osmosis device 4 performs the net volume reduction in the same manner as in the first embodiment. At this time, the pH adjuster 11b (acid) is added to adjust the pH of the circulating fluid 20 to 4.0~
RIAI adjustment to 75.

The decontamination coefficient of the reverse osmosis device 74 obtained in this way is U, which is usually about 50 to 100.The volume reduction ratio is usually about 20 to 10.
The F concentration was about 0 and was below 0.5 to 0.

In the case where the radioactive waste liquid 8 already contains detergent, the superconcentrated liquid 15 obtained as described above contains 1 omy771 of surfactant at the stage where an appropriate volume reduction ratio is obtained.
Since it contains the above, immediately add 15 of the condensation solution to 2 of the reverse osmosis concentrate.
1 and sent to the assimilation device 6.

In cases where the radioactive waste liquid 8 does not contain a surfactant, or when the surfactant contained in the concentrated liquid 15 is
/ If the amount does not reach t, add surfactant 12 first.
Inject into circulation tank 1 and continue circulation. The amount of surfactant 12 injected is the same as in the case of FIG. Thereafter, the concentrated liquid 15 is sent to the solidification device 6.

As the solidification device 6, known means can be used in the same manner as in the case of FIG.

The above operations produce the following effects.

(i) Due to the alkaline action of the water glass 9, the following reaction occurs, and the uranium compound becomes insolubilized as sodium deuterate, and hydrogen fluoride becomes sodium fluoride.

Na2O+ H2O→ 2NaOH・- (5) 2U
O2Fg -1-61JaOH→Na2U207↓+4
NaF+H20...(6) HP+1laOH-) NaF-1-H2O=
(7) (11) When an alkaline earth metal salt is used as the solidification aid 10, it reacts with fluoride and becomes insolubilized.

For example, when 0a(3Q is used, calcium fluoride is precipitated by reaction as shown in the following formula.

C! aCt2+2NaF −+ 0aF2↓+2Nac
t...(8)(iii) The assimilation device 6 dries the concentrated liquid 15 and removes not only suspended substances (sodium diuranate, calcium fluoride, etc.) but also dissolved substances (sodium fluoride).
It has the function of fixing materials such as in asphalt or glass.

(V) All other effects are the same as those in (2) to (7) above.

The effects of these actions are as described below.

■ It is possible to completely prevent a decrease in the decontamination coefficient due to the tendency of complex ions to form due to the characteristics of uranium compounds.

■ Fluoride, which is a by-product of uranium compounds, can be removed to an extremely high degree.

(2) Other effects are the same as ω) 6) and (9) to 01 described above.

EXAMPLE As Example 1.2 according to the method of the invention, 60Co and l
The waste liquid containing SS was treated using the process shown in Figure 1. As Example 3, 235U f! : The waste liquid contained was treated according to the process shown in Figure 2. Table 1 summarizes the volume reduction ratio (amount of radioactive waste liquid before treatment/amount of radioactive waste liquid after treatment) and decontamination coefficient of each example. Further comparative example'? Table 1 also shows the conditions and results for processing only the waste liquid containing 60Co and 135Co.

When the concentrated liquids obtained in Examples 1 to 3 were subjected to asphalt solidification or vitrification under the solidification conditions shown in Table 2, the solidification state after cooling was good in all cases.

Table 2 (Note) The above examples used all the concentrated solutions of each example in Table 1.

As explained above, according to the method of the present invention, the decontamination coefficient is significantly increased compared to simple membrane separation methods such as ultrafiltration or reverse osmosis. It is an advantageous method that can reduce the volume, can also treat waste liquid containing volatile radionuclides, and has lower processing costs than conventional methods.

[Brief explanation of drawings]

1 and 2 of the accompanying drawings are diagrams showing the flow of the method of the present invention. Sub-agents 1) Akihiro’s agent Ryo Hagiwara −

Claims (1)

[Claims] A method for treating radioactive waste liquid, which comprises adding water glass and a solidification aid to radioactive waste liquid, ultrafiltering the liquid, and then subjecting the filtrate to reverse osmosis treatment.