JPH0810278B2 - Method for solidifying phosphate waste liquid - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for solidifying a phosphate waste liquid with an inorganic solidifying material. For example, radioactive sodium hydrogen phosphate waste liquid from a nuclear facility is treated with the inorganic solidifying material. A method suitable for use and solidification.

[Conventional technology]

The sodium hydrogen phosphate waste liquid is stored in a tank in the form of monosodium dihydrogen phosphate having a high solubility at room temperature, and when it is solidified, it is solidified by bitumen in the conventional practice.

[Problems to be solved by the invention]

However, the solidified material obtained by solidifying bitumen has problems in fire resistance and load resistance when considering land disposal. Therefore, it is desirable to carry out solidification treatment with an inorganic solidifying material such as cement or a mixture of cement and water glass instead of bitumen solidifying, but monosodium dihydrogen phosphate does not solidify at all with an inorganic solidifying material and forms a solidified body. I couldn't do that.

An object of the present invention is to solidify a sodium hydrogenphosphate waste liquid and other phosphate waste liquids with an inorganic solidifying material.

[Means for Solving the Problems] The above object is achieved by adjusting the pH of the phosphate waste liquid to 6 or more and then adding the inorganic solidifying material.

[Action]

The monosodium dihydrogen phosphate waste liquid has a pH of 4, and in this state, it does not solidify at all with the inorganic solidifying material, as described above. This is because cement or cement + glass gradually solidifies under alkaline conditions, but gelation proceeds rapidly under acidic conditions. Therefore, add an alkaline solution such as sodium hydroxide solution to the waste liquid.
When the pH is increased, most of the monosodium dihydrogen phosphate (NaH ₂ PO ₄ ) at pH 6 or higher and pH 8 to
At 8.8, everything is changed to disodium monohydrogen phosphate (Na ₂ HPO ₄ ).

NaH ₂ PO ₄ + NaOH → Na ₂ HPO ₄ + H ₂ O This disodium monohydrogen phosphate can be solidified by adding an inorganic solidifying material. In this case, when the addition of the inorganic solidifying material is carried out at 30 ° C. or higher, the solidification reaction proceeds in the state of monosodium phosphate or heptahydrate of disodium monohydrogen phosphate,
After that, when it becomes normal temperature, it is converted into dodecahydrate to take in free water in the inorganic solidification system, which has the effect of particularly increasing the strength of the solidified body. The same applies to other phosphate waste solutions.

〔Example〕

A monosodium dihydrogen phosphate aqueous solution, which is a waste liquid, is placed in a reaction tank, an aqueous sodium hydroxide solution is added thereto, and the pH of the liquid in the reaction tank is monitored by a pH meter. FIG. 3 shows this process. Of monosodium dihydrogen phosphate aqueous solution
The pH is 4, but as sodium hydroxide is added, it reacts sequentially and changes to disodium monohydrogen phosphate. An aqueous solution of sodium hydroxide was added to monosodium dihydrogen phosphate to give a solution of 0.
It becomes neutral when 6 to 0.7 molar equivalents are added. The pH of the aqueous solution changed to 100% disodium monohydrogen phosphate is 8 to 8.8.

Assuming a case where the starting waste liquid is a mixed liquid of monosodium dihydrogen phosphate and disodium monohydrogen phosphate, the two are mixed at various molar ratios and the pH of the aqueous solution is measured. It is shown in FIG. Since Fig. 3 and Fig. 4 are in good agreement, even if the starting waste liquid is a mixture of the above-mentioned two types of sodium hydrogen phosphate, it is necessary to grasp the approximate value of the composition ratio by measuring the pH. It turns out that is possible. Therefore, it is reasonable to monitor at pH.

In order to make a strong solidified body using an inorganic solidified material, an alkaline side with a pH of 6.5 or higher is good, but in order to make the most healthy solidified body, it is better to change it to disodium monohydrogen phosphate. good. That is, it is better that the pH is 8 to 8.8. For example p
If H shows 7, it is advisable to add 0.2 equivalent of sodium hydroxide to adjust the pH to 8 to 8.8.

The sodium hydrogen phosphate waste liquid having the pH thus adjusted is concentrated or dried into a powder, and an inorganic solidifying material such as cement or a mixture of cement and water glass is added to the solidifying treatment. The temperature of this solidification treatment will be described below.

FIG. 5 shows solubility curves of monosodium dihydrogen phosphate and disodium monohydrogen phosphate. Both of them increase in solubility with increasing temperature and lose crystal water. Taking the case of adding an inorganic solidifying material at 50 ° C or higher as an example, the following reaction occurs in the reaction tank, When the inorganic solidifying material is added, disodium monohydrogen phosphate is fixed to the inorganic solidifying material as a monohydrate. On the other hand, it is known that the inorganic solidified body becomes stronger as the free water inside is smaller, but there is a limit in reducing the mixing of water from the workability when adding the inorganic solidified material. But above Na ₂ HPO ₄
・ As the waste solidified with H ₂ O solidifies and cools to room temperature, Na ₂ HPO ₄・ H ₂ O → Na ₂ HPO ₄ / 7H ₂ O → Na ₂ HPO ₄・ 12H ₂ O and crystal water are taken in. It is thought that this will go, and this will be effective in maintaining a high degree of solidified soundness.

On the other hand, for example, if the inorganic solidifying agent is added at room temperature from the beginning, a large amount of water is required at the time of adding the solidifying agent because the waste itself first takes in water as a 12-hydrate salt. Not only will the strength be adversely affected, but it will not be possible to solidify under certain conditions.

The effects of the pH of the aqueous waste solution and the addition temperature of the inorganic solidifying agent on the solidified product were investigated and the results of the tests are shown in FIG. 6 and FIG. 7, respectively. pH 6 or higher, inorganic solidifying material addition temperature 30
A solidified body can be sufficiently obtained at a temperature of ℃ or above. When land disposal as radioactive waste is targeted, the pH is 6.5 or more and the kneading temperature is 35.
A solidified body that is sufficiently healthy can be obtained at a temperature of ゜ or higher.

In addition, the temperature when adding the inorganic solidifying material should be kept below 100 ° C because it will boil and lose water when it is above 100 ° C, and in the case of radioactive liquid waste, it will be below 80 ° C to prevent the radionuclide from flying. It is desirable to suppress it.

Hereinafter, two examples of the present invention in the case of treating an aqueous solution of monosodium dihydrogen phosphate as a radioactive waste liquid will be specifically described.

Example 1 In FIG. 1, a radioactive monosodium dihydrogen phosphate aqueous solution is introduced into a reaction tank 6 from a storage tank 1 through a valve 3. The reaction tank 6 is provided with a rotary blade 7 for stirring which is rotated by the power unit 4, and the temperature of the entire tank can be controlled by the heater 8. The progress of the reaction can be monitored with the pH meter 5. After the waste sodium monohydrogen phosphate aqueous solution is introduced, the sodium hydroxide aqueous solution is introduced from the tank 2 into the reaction tank through the valve 3. When the pH is adjusted to 6 or more by stirring in the reaction tank for a predetermined time, most of the monosodium dihydrogen phosphate is converted to disodium monohydrogen phosphate. Subsequently, this solution is introduced from the reaction tank 6 through the valve 3 into the concentration dryer 9. Here, it is concentrated or powdered. Then, through the lower valve 3, the waste solidification container 14
To be introduced. On the other hand, to explain the system of the solidifying material, an inorganic solidifying material (cement or a mixture of cement and water glass) is introduced from the tank 10 into the kneading tank 12 via the valve 3, and water is introduced from the tank 11 via the valve 3 into the kneading tank 12. Similarly kneading tank 12
And is kneaded uniformly by the rotary blades 7 which are rotated by the power unit 4 of the kneading tank 12. Subsequently, the kneaded product of the inorganic solidifying material and water is introduced into the waste solidifying container 14 via the valve 3.
A hardening agent 13 made of phosphate is introduced from a tank 13 into a waste solidification container 14 via a valve 3. Hardener 13 is a kneading tank
It is also possible to adopt a method of introducing into 12 and kneading with the inorganic solidifying material in advance. A rotary vane 7 which is rotated by the power machine 4 is introduced into the waste solidification container 14, whereby the waste, the solidifying material and the curing agent are uniformly mixed. Further, a heater 8 is provided around the waste solidification container 14, whereby kneading is performed at 30 ° C. or higher and 80 ° C. or lower. Alternatively, a heater may be introduced into the waste solidification container 14 during kneading. After kneading in the waste solidification container 14, the rotary blade 7 is removed from the container 14 and the contents are solidified as they are. In addition, it is a waste solidification container that is kneaded uniformly.
Instead of being carried out inside the waste solidification container 14, it may be carried out outside the waste solidification container 14, and in this case, one set of kneading tank and valve may be added.

Example 2 As shown in FIG. 2, the waste monosodium dihydrogen phosphate aqueous solution is introduced from the storage tank 15 into the reaction tank 19 via the valve 18. The reaction tank 19 is provided with a rotary blade 20 for stirring which is rotated by a power unit 17, and the temperature of the entire tank can be controlled by a heater 21. The reaction progress is pH.
Monitor with a meter. After the waste sodium dihydrogen phosphate aqueous solution is introduced into the reaction tank 19, the sodium hydroxide aqueous solution is introduced from the tank 16 through the valve 18 and stirred to accelerate the reaction. When the pH is adjusted to 6 or more by stirring in the reaction tank for a predetermined time, most of the monosodium dihydrogen phosphate is converted to disodium monohydrogen phosphate. Subsequently, this solution is introduced from the reaction tank 19 into the concentrating / drying device 22 via the valve 18 to be dried and powdered, and then introduced into the granulator 27 via the valve 18 to be pelletized. The waste that has become the pellets 29 is introduced into the waste solidification container 28. On the other hand, referring to the solidifying material system, the inorganic solidifying material is introduced from the tank 23 into the kneading tank 25 through the valve 18,
Here, the water added from the water tank 24 via the valve 18 is uniformly kneaded by the rotary blades 20 rotated by the power machine 17. Subsequently, the kneaded material of the inorganic solidifying material and water is introduced into the waste solidifying container 28 containing the waste pellets 29 via the valve 18, and the curing agent is also introduced from the tank 26 via the valve 18 and solidified. . Waste solidification container during solidification 28
The temperature is controlled at 30 ° C to 80 ° C by the heater 21 around the. The curing agent 26 is mixed with the kneading tank via the valve 18.
It may be introduced into the waste solidification container 28 in which the pellets 29 are filled, after being introduced into 25 and kneaded with the inorganic solidification material in advance.

The inorganic solidified bodies prepared by the methods of Examples 1 and 2 are 10 when the temperature at the time of adding the inorganic solidifying material is 30 ° C. or higher and less than 50 ° C.
0 kg / cm ^2, showed a strength of about 250 Kg / cm ² when a 50 ° C. or higher 80 ° C. or less, been made a better waste loading.

The inorganic solidifying material used was cement or cement + water glass, but a solidified body can also be made by using other hydraulic inorganic solidifying material.

In the above examples, the monosodium dihydrogen phosphate waste liquid was treated, but even when other phosphate waste liquids are treated, adjustment to the same pH adjustment value and the same inorganic solidification as above. By adding the material and the same addition temperature, it can be solidified by the inorganic solidification material. For example, other phosphate waste liquor, specifically potassium phosphate, potassium hydrogen phosphate,
Calcium phosphate, calcium hydrogen phosphate, cobalt phosphate, iron phosphate, nickel phosphate, chromium phosphate, manganese phosphate are also solidified according to the invention using an inorganic solidifying material which is cement or a mixture of cement and water glass. be able to. An appropriate alkaline solution such as sodium hydroxide, potassium hydroxide or calcium hydroxide may be used for pH adjustment.

〔The invention's effect〕

According to the present invention, since it is possible to solidify a monosodium dihydrogen phosphate waste liquid and other phosphate waste liquids, which were conventionally impossible to solidify with an inorganic solidifying material, with an inorganic solidifying material, a waste liquid storage space is saved and volume reduction storage is performed. At the same time, it is possible to avoid the problems of fire resistance and load resistance such as those of the conventional solidified bitumen.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention in the case of homogeneous solidification,
FIG. 2 is a diagram showing an embodiment of the present invention in the case of solidifying pellets, FIGS. 3 and 4 are diagrams showing results of a basic experiment for adjusting pH of a waste liquid, and FIG. 5 is a solubility curve of sodium hydrogen phosphate. FIG. 6 is a diagram showing the relationship between the pH of the waste liquid and the strength of the solidified body, and FIG. 7 is a diagram showing the relationship between the temperature of addition of the solidifying material and the strength of the solidified body. 1 ... Waste tank, 2 ... Sodium hydroxide tank 3 ... Valve, 4 ... Power machine 5 ... pH meter, 6 ... Reaction tank 7 ... Rotating blades, 8 ... Heater 9 ... Concentration dryer , 10 …… Solidifying material tank 11 …… Water tank, 12 …… Kneading tank 13 …… Hardener tank, 14 …… Waste solidifying container 15 …… Waste tank, 16 …… Sodium hydroxide tank 17 …… Power machine , 18 ...... Valve 19 ...... Reaction tank, 20 ...... Rotary blade 21 ...... Heater, 22 ...... Concentration dryer 23 ...... Solidification material tank, 24 ...... Water tank 25 ...... Kneading tank, 26 ...... Curing agent Tank 27 …… Granulator, 28 …… Waste solidification container 29 …… Pellets.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tsuneo Nemoto 1168 Moriyama-cho, Hitachi City, Ibaraki Prefecture, Hitachi Energy Research Institute Co., Ltd. Energy Research Institute (56) Reference JP-A-53-37179 (JP, A) JP-A-59-75197 (JP, A) JP-A-62-130395 (JP, A)

Claims (2)

[Claims] 1. An alkaline solution is added to a phosphate waste liquid to adjust the pH of the phosphate waste liquid to 6 or more, and the phosphate waste liquid after the adjustment is concentrated or dried into a powder, and the pH is adjusted to 30 ° C. More than 100
A method for solidifying a phosphate waste liquid, which comprises solidifying by adding an inorganic solidifying material under a temperature condition of less than ° C. 2. The method for solidifying a phosphate waste liquid according to claim 1, wherein the phosphate waste liquid is an aqueous solution containing monosodium dihydrogen phosphate as a main component.