Curing formula for high-boron-content concentrated solution and application

Abstract

The invention belongs to the technical field of nuclear power station radioactive waste treatment, and particularly relates to a curing formula for a high-boron-content concentrated solution and application, the curing formula comprises the following raw materials by weight: 90-100 parts of cement, 12-16 parts of epoxy resin, 6-8 parts of a curing agent, 17-19 parts of slaked lime, 2-2.5 parts of a modified molecular sieve, 0.5-0.7 part of calcium chloride, and 0.5-0.8 part of a water reducer. According to the curing formula disclosed by the invention, the boron inclusion rate can be improved, and the cured cement has good durability and mechanical properties.

Description

Technical Field

[0001] The invention belongs to the technical field of nuclear power plant radioactive waste treatment, and in particular relates to a solidification formula for high-boron concentrated liquid and its application. Background Art

[0002] A large amount of radioactive liquid waste is generated during the operation of nuclear power plants. Evaporation and concentration technology is usually used to treat it, but most of the radionuclides are concentrated in the concentrated waste liquid after treatment. It needs to be further treated to facilitate transportation and storage to radioactive solid waste disposal sites. After natural decay, its radioactivity level is reduced to a safe level and no longer harms the environment. Cement solidification is a relatively safe and commonly used method. The hydration of cement is used to make the mixed slurry form a cement solidified body with certain mechanical strength, durability and radionuclide adsorption capacity, thereby achieving the purpose of waste solidification and facilitating transportation.

[0003] Patent CN102800377B discloses a cement solidification method for nuclear power waste, comprising the steps of: using cement, lime and admixture as curing agent raw materials, adding admixture, lime and cement to nuclear power waste concentrate in sequence, stirring and standing to solidify to obtain a solidified body, which can reduce the volume of the cement solidified body and improve the nuclear power waste inclusion rate. The components need to be added in sequence, which is inconvenient to operate; Patent CN105741899A discloses a solidification treatment additive, solidification formula and process for radioactive boron-containing waste liquid. The additive uses cement as a solidification base material, uses fly ash, zeolite powder, silica fume and sodium aluminate to accelerate cement hardening, and then adds sodium silicate and carbon fiber powder to solidify polyborate. The obtained solidified body has a high inclusion rate for boric acid, but the patent requires that boric acid be converted into polyborate before solidification, which may cause leakage during the conversion process and pollute the environment.

[0004] Therefore, there is an urgent need to prepare a curing formula that is easy to operate and has a high boron inclusion rate. Summary of the invention

[0005] In order to overcome the above-mentioned deficiencies of the prior art, the present invention provides a curing formula which is easy to operate, has a high boron inclusion rate, and the cured cement body has good durability and mechanical properties.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] The first aspect of the present invention provides a curing formula for high-boron concentrated liquid, which comprises the following raw materials in parts by weight: 90-100 parts of cement, 12-16 parts of epoxy resin, 6-8 parts of curing agent, 17-19 parts of slaked lime, 2-2.5 parts of modified molecular sieve, 0.5-0.7 parts of calcium chloride, and 0.5-0.8 parts of water reducer.

[0008] Preferably, the purity of Ca(OH)2 in the slaked lime is ≥95%.

[0009] In some embodiments, the cement is 42.5 Portland cement.

[0010] Preferably, the 42.5 silicate cement has a 3-day compressive strength of ≥17 MPa, a 28-day compressive strength of ≥42.5 MPa, a 3-day flexural strength of ≥3.5 MPa, and an 8-day flexural strength of ≥6.5 MPa.

[0011] In some embodiments, the method for preparing the curing agent comprises the following steps:

[0012] (1) Add pentaerythritol and thionyl chloride to DMF, react at 0-5°C for 3-4 hours, extract, rotary evaporate, and dry to obtain a solid. Add the obtained solid, 3-butene-1-ol, and a catalyst to dichloromethane, react at 75-85°C for 35-37 hours, and extract to obtain intermediate 1;

[0013] (2) adding the intermediate 1 obtained in step (1) and an initiator to acrylic acid, reacting at 70-80° C., filtering with suction, and drying to obtain an intermediate 2 having a number average molecular weight of 600-700;

[0014] (3) The intermediate 2 obtained in step (2) and triphenylmethane triisocyanate are added to DMF, reacted at 60-70° C. for 5-6 h, rotary evaporated, and dried to obtain a curing agent.

[0015] In some embodiments, the mass ratio of the intermediate 1 to acrylic acid in the step (2) is 1:(0.8-1).

[0016] The invention prepares a curing agent for epoxy resin curing, and increases the density of cement after curing, and has good mechanical properties. The possible reason is that the self-made curing agent contains a plurality of isocyanate groups, which generate a cross-linking structure with the epoxy resin in the curing formula and the hydroxyl group in the modified molecular sieve, thereby increasing the hardness of the cement solidified body after curing. In addition, pentaerythritol is connected with 3-butene-1-ol through an ether bond after chlorination, and then polymerized with acrylic acid. The mass ratio of intermediate 1 and acrylic acid is further limited, so that the existence of a certain number of alkane segments and ether bonds in the obtained curing agent increases the compressive strength of the cement solidified body. In addition, in the curing process, part of the isocyanate groups may react with water to generate carbon dioxide, and the carbon dioxide dissolves in water to form carbonic acid, and the acidity of the carbonic acid is greater than that of boric acid. According to the principle of strong acid to weak acid, part of the boron in the system exists in the form of boric acid, the generation of calcium borate precipitation is accelerated, the curing is promoted, and the cross-linking structure can be stably present in the cement solidified body, thereby increasing the inclusion rate.

[0017] In some embodiments, the mass ratio of the intermediate 2 to triphenylmethane triisocyanate in step (3) is 1:(2.5-3).

[0018] The present invention limits the mass ratio of the intermediate 2 to triphenylmethane triisocyanate so that the reaction system has more free triphenylmethane triisocyanate, and most of the triphenylmethane triisocyanate molecules have only one isocyanate group that reacts with the intermediate 2, thereby ensuring that the obtained curing agent has a sufficient number of isocyanate groups to participate in curing.

[0019] In some embodiments, the method for preparing the modified molecular sieve comprises the following steps:

[0020] 1) The molecular sieve is heated to 490-510°C at a heating rate of 3-4°C / min, and calcined for 3-4h to obtain an activated molecular sieve, and a 0.95-0.12mol / LFe(NO3)3 solution is added to the activated molecular sieve, reacted at 75-85°C for 3-4h, centrifuged, dried, and then calcined at 490-510°C for 3-4h to obtain an ion-exchanged molecular sieve;

[0021] 2) adding the ion-exchanged molecular sieve obtained in step 1) into a nitric acid solution and reacting at 50-60° C. for 3-4 hours, then adding chitosan and reacting at 50-60° C. for 2-3 hours to obtain a modified molecular sieve.

[0022] Adding molecular sieves to the solidification formula helps to adsorb radionuclides, but conventional molecular sieves have limited adsorption capacity and are prone to leakage. The present invention increases the adsorption capacity of boron-containing waste liquid by modifying the molecular sieve, and at the same time increases the anti-leaching property of the cement solidified body. On the one hand, the possible reason is the coordination between the iron ions and the borate in the molecular sieve after ion exchange, which increases the adsorption amount of boron and reduces the amount of slaked lime added. On the other hand, it may be due to the gelling property and film-forming property of chitosan, which increases the anti-leaching property of radionuclides and accelerates the solidification of cement.

[0023] In some embodiments, the mass ratio of the molecular sieve to chitosan after ion exchange in step 2) is 1:(0.2-0.4).

[0024] The invention limits the mass ratio of the molecular sieve and chitosan after ion exchange, so that the chitosan can effectively contain radioactive nuclides, and will not block the pores of the molecular sieve and affect the adsorption amount of the radioactive nuclides.

[0025] In some embodiments, the water reducing agent is a polycarboxylic acid water reducing agent.

[0026] The second aspect of the present invention provides an application of a curing formula for a high-boron concentrated liquid. The curing formula is used to cure the high-boron concentrated liquid, comprising the following steps: adding cement, high-boron concentrated liquid, water reducer, epoxy resin, curing agent, slaked lime, modified molecular sieve and calcium chloride into a cement curing barrel, stirring evenly, standing for 23-25 ​​hours to cure, and obtaining a cement solidified body.

[0027] In some embodiments, the high-boron concentrated liquid is the evaporation and concentration product of radioactive waste liquid from a nuclear power plant, with a boron concentration of 44,000-50,000 ppm, and the mass ratio of cement to the high-boron concentrated liquid is (1.3-1.4):1.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] 1. The cement solidified body solidified by the solidification formula containing a solidifying agent and a modified molecular sieve in the present invention has good durability, inclusion rate, anti-leaching property and mechanical properties.

[0030] 2. The present invention prepares a curing agent for accelerating cement curing and increasing the density of the cement after curing, and has good mechanical properties. The possible reason is that the homemade curing agent contains multiple isocyanate groups, which, on the one hand, produce a cross-linked structure with the epoxy resin in the curing formula and the hydroxyl group in the modified molecular sieve, thereby increasing the hardness and compressive strength of the cement body after curing. In addition, during the curing process, some of the isocyanate groups may react with water to produce carbon dioxide, accelerating the formation of calcium borate precipitation, promoting curing, and being able to stably exist in the cement solidification body in the presence of a cross-linked structure, thereby improving the inclusion rate.

[0031] 3. The present invention modifies the molecular sieve, and the coordination effect between the iron ions and borate in the molecular sieve after ion exchange increases the adsorption of boron, while reducing the amount of slaked lime added. On the other hand, the gelling and film-forming properties of chitosan increase the anti-leaching property of radionuclides and accelerate the solidification of cement. DETAILED DESCRIPTION

[0032] The present invention will be described below in conjunction with specific embodiments. It should be noted that the following examples and comparative examples are examples of the present invention and are only used to illustrate the present invention, but not to limit the present invention. Other combinations and various modifications within the concept of the present invention may be performed without departing from the spirit or scope of the present invention.

[0033] In order to facilitate those skilled in the art to implement the present invention, some raw materials and manufacturers of the embodiments and comparative examples are described as follows: the compounds and related reagents used in the present invention can be purchased from the market, among which epoxy resin was purchased from Jinan Qiwei Chemical Co., Ltd., model E-51, viscosity 13350mpa·s (25°C), polycarboxylate water reducer CP1803 was purchased from Nanjing Qinghai Trading Co., Ltd., and molecular sieve was purchased from Raodong (Liaoning) New Materials Co., Ltd., model HY type.

[0034] Preparation Example 1

[0035] The preparation method of curing agent-1 comprises the following steps:

[0036] (1) 1.4 g of pentaerythritol and 2.5 g of thionyl chloride were added to 20 ml of DMF, reacted at 0° C. for 4 h, extracted, rotary evaporated, and dried to obtain a solid. 2.1 g of the obtained solid, 0.72 g of 3-butene-1-ol, and 0.03 g of NaBH4 were added to 20 ml of dichloromethane, reacted at 80° C. for 36 h, and extracted to obtain intermediate 1;

[0037] (2) adding 1 g of the intermediate 1 obtained in step (1) and 0.01 g of benzoyl peroxide to 0.9 g of acrylic acid, reacting at 75° C., filtering with suction, and drying to obtain an intermediate 2 having a number average molecular weight of 662;

[0038] (3) 1 g of the intermediate 2 obtained in step (2) and 2.9 g of triphenylmethane triisocyanate were added to 20 ml of DMF, reacted at 65° C. for 5.5 h, rotary evaporated, and dried to obtain curing agent-1.

[0039] Preparation Example 2

[0040] The preparation method of curing agent-2 is the same as that of Preparation Example 1, except that the amount of acrylic acid added is 0.5 g.

[0041] Preparation Example 3

[0042] The preparation method of curing agent-3 is the same as that of Preparation Example 1, except that the added amount of triphenylmethane triisocyanate is 2 g.

[0043] Preparation Example 4

[0044] The preparation method of curing agent -4 is the same as that of Preparation Example 1, except that the number average molecular weight of intermediate 2 is 841.

[0045] Preparation Example 5

[0046] The preparation method of modified molecular sieve-1 comprises the following steps:

[0047] 1) 5 g of molecular sieve was heated to 500°C at a heating rate of 3°C / min and calcined for 4 h to obtain an activated molecular sieve. 100 ml of 0.1 mol / L Fe(NO3)3 solution was added to the activated molecular sieve, reacted at 80°C for 4 h, centrifuged, dried, and then calcined at 500°C for 4 h to obtain an ion-exchanged molecular sieve;

[0048] 2) 1 g of the ion-exchanged molecular sieve obtained in step 1) was reacted with 10 ml of 65 wt% nitric acid solution at 55° C. for 3.5 h, and then 0.3 g of chitosan was added and reacted at 55° C. for 2.5 h to obtain modified molecular sieve-1.

[0049] Preparation Example 6

[0050] The preparation method of modified molecular sieve-2 is the same as that of Preparation Example 5, except that the amount of chitosan added in step 2) is 0.6 g.

[0051] Example 1

[0052] A curing formula for a high-boron concentrate comprises the following raw materials, measured by weight: 95 parts of 42.5 silicate cement, 14 parts of epoxy resin, 7 parts of curing agent-1, 18 parts of slaked lime, 2.3 parts of modified molecular sieve-1, 0.6 parts of calcium chloride, and 0.7 parts of polycarboxylate water reducer CP1803.

[0053] Example 2

[0054] A curing formula for a high-boron concentrate comprises the following raw materials, measured by weight: 90 parts of 42.5 silicate cement, 12 parts of epoxy resin, 6 parts of curing agent-1, 17 parts of slaked lime, 2 parts of modified molecular sieve-1, 0.5 parts of calcium chloride, and 0.5 parts of polycarboxylate water reducer CP1803.

[0055] Example 3

[0056] A curing formula for a high-boron concentrate comprises the following raw materials, measured by weight: 100 parts of 42.5 silicate cement, 16 parts of epoxy resin, 8 parts of curing agent-1, 19 parts of slaked lime, 2.5 parts of modified molecular sieve-1, 0.7 parts of calcium chloride, and 0.8 parts of polycarboxylate water reducer CP1803.

[0057] Example 4

[0058] A curing formula and a curing method for a high-boron concentrated solution. The specific implementation method is the same as that of Example 1, except that an equal amount of curing agent-1 is replaced by curing agent-2.

[0059] Example 5

[0060] A curing formula and a curing method for a high-boron concentrated solution. The specific implementation method is the same as that of Example 1, except that an equal amount of curing agent-1 is replaced by curing agent-3.

[0061] Example 6

[0062] A curing formula and curing method for a high-boron concentrated solution, the specific implementation method is the same as that of Example 1, except that an equal amount of curing agent-1 is replaced by curing agent-4.

[0063] Example 7

[0064] A solidification formula and solidification method for a high-boron concentrated solution. The specific implementation method is the same as that of Example 1, except that the modified molecular sieve-1 is replaced by modified molecular sieve-2 in equal amounts.

[0065] Comparative Example 1

[0066] A curing formula and curing method for a high-boron concentrated solution, the specific implementation method is the same as that of Example 1, except that an equal amount of curing agent-1 is replaced by triethylenetetramine.

[0067] Comparative Example 2

[0068] A solidification formula and solidification method for a high-boron concentrated solution, the specific implementation method is the same as that of Example 1, except that the modified molecular sieve-1 is replaced by molecular sieve in equal amounts.

[0069] Performance Testing

[0070] The curing formulas of the above embodiments and comparative examples are used to cure high-boron concentrates. The curing method is: cement, high-boron concentrates, water reducers, epoxy resins, curing agents, slaked lime, modified molecular sieves and calcium chloride are added to a cement curing barrel and stirred for 1 hour, and then allowed to stand for 24 hours to cure. The mass ratio of cement to high-boron concentrate is 1.35:1, and a cement solidified body is obtained. The cement solidified body is tested in accordance with GB14569.1 "Performance Requirements for Solidified Bodies of Low and Medium Level Radioactive Wastes - Cement Solidified Bodies" and GB7023 "Long-term Leaching Test for Solidified Bodies of Radioactive Wastes".

[0071] Table 1

[0072]

[0073] From the data comparison of Examples 1-3 in Table 1, it can be seen that the cement solidified body obtained by the curing formula has excellent compressive strength, boron inclusion rate, radiation resistance, leaching resistance and impact resistance; compared with Example 4 and Example 1, it can be seen that the ratio of acrylic acid to intermediate 1 in curing agent-2 is changed, resulting in a decrease in the compressive strength of the cement solidified body; compared with Example 1, it can be seen that the ratio of intermediate 2 to triphenylmethane triisocyanate in curing agent-3 is changed, which may reduce the crosslinking degree of epoxy resin, resulting in a decrease in the compressive strength of the cement solidified body and a decrease in the encapsulation rate; compared with Example 6 and Example 1, From the comparison of Example 1, it can be seen that the increase in the number average molecular weight of the intermediate 2 in the curing agent-4 may make the toughness of the cement solid body too large, resulting in a decrease in the anti-leaching property; from the comparison of Example 7 and the example, it can be seen that the change of the molecular sieve and chitosan after ion exchange in the modified molecular sieve-2 may reduce the adsorption capacity of the modified molecular sieve, resulting in a decrease in the boron inclusion rate; from the comparison of Example 1 and Comparative Example 1, it can be seen that when using conventional curing agents, the crosslinking density of the cement solid body is reduced, and various performances are reduced; from the comparison of Example 1 and Comparative Example 2, it can be seen that the use of molecular sieves leads to a decrease in the boron inclusion rate and anti-leaching property of the cement solid body.

[0074] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technician familiar with this profession can make some changes or modifications to equivalent embodiments of equivalent changes using the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A solidification formula for high-boron concentrated waste liquid, characterized in that: The invention comprises the following raw materials by weight: 90-100 parts of cement, 12-16 parts of epoxy resin, 6-8 parts of curing agent, 17-19 parts of slaked lime, 2-2.5 parts of modified molecular sieve, 0.5-0.7 parts of calcium chloride and 0.5-0.8 parts of water reducing agent.

2. The solidification formula for high-boron concentrate according to claim 1, characterized in that: The cement is 42.5 silicate cement.

3. The solidification formula for high-boron concentrated solution according to claim 1, characterized in that: The preparation method of the curing agent comprises the following steps: (1) Add pentaerythritol and thionyl chloride to DMF, react at 0-5°C for 3-4 hours, extract, rotary evaporate, and dry to obtain a solid. Add the obtained solid, 3-butene-1-ol, and a catalyst to dichloromethane, react at 75-85°C for 35-37 hours, and extract to obtain intermediate 1; (2) adding the intermediate 1 obtained in step (1) and an initiator to acrylic acid, reacting at 70-80° C., filtering with suction, and drying to obtain an intermediate 2 having a number average molecular weight of 600-700; (3) The intermediate 2 obtained in step (2) and triphenylmethane triisocyanate are added to DMF, reacted at 60-70° C. for 5-6 h, rotary evaporated, and dried to obtain a curing agent.

4. The solidification formula for high-boron concentrate according to claim 3, characterized in that: In the step (2), the mass ratio of the intermediate 1 to acrylic acid is 1:(0.8-1).

5. The solidification formula for high-boron concentrate according to claim 3, characterized in that: In the step (3), the mass ratio of the intermediate 2 to triphenylmethane triisocyanate is 1:(2.5-3).

6. The solidification formula for high-boron concentrated solution according to claim 1, characterized in that: The preparation method of the modified molecular sieve comprises the following steps: 1) The molecular sieve is heated to 490-510°C at a heating rate of 3-4°C / min, and calcined for 3-4h to obtain an activated molecular sieve, and a 0.95-0.12mol / L Fe(NO3)3 solution is added to the activated molecular sieve, reacted at 75-85°C for 3-4h, centrifuged, dried, and then calcined at 490-510°C for 3-4h to obtain an ion-exchanged molecular sieve; 2) adding the ion-exchanged molecular sieve obtained in step 1) into a nitric acid solution and reacting at 50-60° C. for 3-4 hours, then adding chitosan and reacting at 50-60° C. for 2-3 hours to obtain a modified molecular sieve.

7. The solidification formula for high-boron concentrated solution according to claim 6, characterized in that: In the step 2), the mass ratio of the molecular sieve after ion exchange to chitosan is 1:(0.2-0.4).

8. The solidification formula for high-boron concentrated solution according to claim 1, characterized in that: The water reducing agent is a polycarboxylic acid water reducing agent.

9. An application of a solidification formula for a high-boron-containing concentrated solution according to any one of claims 1 to 8, characterized in that: The curing formula is used to cure high-boron concentrate, and the curing method is: adding cement, high-boron concentrate, water reducer, epoxy resin, curing agent, slaked lime, modified molecular sieve and calcium chloride into a cement curing barrel, stirring for 0.5-1.5 hours, standing for 23-25 ​​hours to cure, and obtaining a cement solidified body.

10. The use of the solidification formula for high-boron concentrated liquid according to claim 9, characterized in that: The high-boron-containing concentrated liquid is the evaporation and concentration product of radioactive waste liquid from a nuclear power plant, with a boron concentration of 44000-50000 ppm. The mass ratio of cement to the high-boron-containing concentrated liquid is (1.3-1.4):1.

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