A method for removing Zr(IV) from radioactive waste liquid using molecular sieve

Abstract

The present invention belongs to the technical field of radioactive waste treatment, and relates to a method for removing Zr(IV) from radioactive waste liquid by using a molecular sieve. The method is to mix the molecular sieve with the radioactive waste liquid, adsorb and react for a period of time at a certain temperature, and remove the molecular sieve after filtering or centrifugal treatment; the molecular sieve is a HY type molecular sieve with a topological structure of FAU type. The method for removing Zr(IV) from radioactive waste liquid by using a molecular sieve of the present invention can efficiently remove Zr(IV) from radioactive waste liquid, and the molecular sieve used has strong acid resistance and radiation resistance.

Description

Technical Field

[0001] The invention belongs to the technical field of radioactive waste treatment and relates to a method for removing Zr(IV) from radioactive waste liquid by using molecular sieve. Background Art

[0002] At present, the PUREX process is a technology widely used in nuclear fuel reprocessing plants around the world. It is mainly based on the fact that the extraction ability of the extractant TBP for uranium, thorium, neptunium, plutonium and fragment elements in different oxidation states is significantly different, so as to purify and separate uranium, thorium, neptunium, plutonium and fragment elements. Studies have found that in the PUREX process, especially at the oil-water interface of the 1A tank during a cycle, an emulsion layer containing solids is often formed, which is usually also called "interface contamination". The formation of interface contamination not only affects the recovery rate of uranium and plutonium and the purity of the product, aggravates the degradation of the extractant, but also hinders normal production operations. When a large amount of interface contamination is formed, it may even make the entire process unable to operate normally. In addition, the high-level radioactive waste liquid discharged from the PUREX process also contains trans-plutonium elements and fission products, which will produce a third phase when the solvent extraction method is used to treat the high-level waste liquid. These problems are all related to Zr(IV). Therefore, pre-removal of Zr(IV) in the PUREX process is an effective way to cut off the generation pathway of interfacial contaminants and effectively alleviate the negative impact of interfacial contaminants.

[0003] The high-level waste liquid produced in the PUREX process contains long-lived fission products, activation products, neutron poisons, corrosion products and actinides, among which zirconium is a nuclide with a long half-life and a high fission yield. When the solvent extraction method is used to treat high-level waste liquid, the extractant TRPO has a strong ability to extract zirconium and easily forms a three-phase, making the process impossible. Therefore, Zr(IV) in the high-level waste liquid must be removed first to eliminate its interference with the process.

[0004] Domestic and foreign researchers have developed a variety of adsorbents for the removal of Zr(IV) from high-level radioactive liquid waste, such as ion exchange resin (Xu Y, Kim SY, S Usuda. Journal of Radioanalytical & Nuclear Chemistry, 2013, 297(1):91-96), chitosan (Li Fang, Zhang Cuige, Ding Chunmei. Journal of Xinyang Normal University: Natural Science Edition, 2009, 22(4):4), sodium alginate gel (Onishi T, Koyama SI, Mimura H. Progress in Nuclear Energy, 2015, 82:69-73), silica gel (Liu Xuegang, Liang Junfu, Xu Jingming et al. Atomic Energy Science and Technology, 2007, 41(1):6), and metal oxides such as iron oxide / tin oxide (Bao Borong. Atomic Energy Science and Technology, 1985, 000(005):614-614). Among them, organic ion exchange resin has good mechanical properties, strong regeneration ability, and relatively simple operation, but poor high temperature and radiation resistance, low adsorption capacity in strong acidic solutions, and easy to form secondary waste; the inorganic adsorbent currently used to remove Zr(IV) from high-level waste liquid is silica gel, which is acid-resistant, high temperature-resistant, and radiation-resistant, but has a long adsorption equilibrium time and low adsorption capacity. Therefore, there is currently no adsorption material that fully meets the requirements for efficient removal of Zr(IV) from radioactive waste liquid under high acid and strong radiation conditions.

[0005] Molecular sieves are hydrated aluminosilicate crystals composed of silicon-oxygen tetrahedrons and aluminum-oxygen tetrahedrons. Due to their good ion exchange capacity, rich pore structure, high specific surface area and irradiation stability, they have good potential application prospects in radioactive waste liquid treatment. Summary of the invention

[0006] The purpose of the present invention is to provide a method for removing Zr(IV) from radioactive waste liquid by using a molecular sieve, so as to efficiently remove Zr(IV) from the radioactive waste liquid, and the molecular sieve used has strong acid resistance and radiation resistance.

[0007] To achieve this object, in a basic embodiment, the present invention provides a method for removing Zr(IV) from radioactive waste liquid using a molecular sieve, wherein the method comprises mixing the molecular sieve with the radioactive waste liquid, adsorbing and reacting the mixture at a certain temperature for a period of time, and removing the molecular sieve after filtration or centrifugation; the molecular sieve is a HY type molecular sieve having a FAU topological structure.

[0008] The relevant principles of the present invention are as follows:

[0009] The size selectivity of the adsorbent material can be used to selectively separate Zr(IV). The molecular sieve topology selected in the present invention is FAU type, and its skeleton contains 12-membered rings (diameter ) composed of a super cage (diameter ) structure, which matches the size of the solvated Zr(IV) ions, so Zr(IV) can enter the molecular sieve and exchange ions with the cations in the cage, and coordinate with the oxygen atoms on the molecular sieve framework, thereby achieving efficient removal of Zr(IV) in radioactive waste liquid. The high specific surface area, negative charge on the skeleton channel structure and high stability of this molecular sieve are also conducive to the adsorption of Zr(IV) in radioactive waste liquid.

[0010] Figure 1 HY(SiO 2 / Al 2 O 3 =25), NaY(SiO 2 / Al 2 O 3 =5), K-CHA(SiO 2 / Al 2 O 3 =4) Adsorption kinetic curve of molecular sieve (Zr(IV) concentration in the solution is 100 mg / L, nitric acid concentration is 3 mol / L, experimental temperature is 25°C, and the mass volume ratio of the molecular sieve used to the solution is 1:100).

[0011] Description: Use K-CHA(SiO 2 / Al 2 O 3 =4) and NaY(SiO 2 / Al 2 O 3 =5) adsorption of Zr(IV) is used to react with HY(SiO 2 / Al 2 O 3 =25) adsorbed Zr(IV) for comparative experiments. It can be seen that in 3 mol / L nitric acid solution, HY(SiO 2 / Al 2 O 3 =25) has a higher equilibrium adsorption capacity for Zr(IV) than K-CHA(SiO 2 / Al 2 O 3 =4) and NaY(SiO 2 / Al 2 O 3 =5) of equilibrium adsorption capacity.

[0012] Figure 2 HY(SiO2 / Al 2 O 3 =25) molecular sieve adsorption curve of Zr at different nitric acid concentrations (adsorption time is 180min, experimental temperature is 25°C, Zr(IV) concentration in the solution is 100mg / L, and the mass volume ratio of the molecular sieve used to the solution is 1:100).

[0013] Note: The adsorption behavior of Zr(IV) on molecular sieves is closely related to the acidity of the solution and the hydrolysis form of Zr(IV) in the acidic solution. Depending on the concentration of Zr(IV) in the solution and the acidity of the solution, Zr(IV) can be hydrolyzed into monomers or polymers. When the concentration of nitric acid is 0.1 mol / L, Zr(IV) may exist mainly in the form of tetramers, accompanied by a small amount of monomers and multinuclear species. Due to the large volume of the hydrolysis products of Zr(IV), they may have difficulty entering the interior of the molecular sieve. Although H + The concentration is low, the competitive effect is low, but the equilibrium adsorption amount is also relatively low. When the nitric acid concentration is 0.5 mol / L, the Zr(IV) monomer content increases, and H + The competitive adsorption of H is weak, and the equilibrium adsorption capacity reaches the maximum value. + When the concentration increases further, H + The competitive effect is more obvious, and the equilibrium adsorption capacity shows a downward trend.

[0014] Figure 3 HY(SiO 2 / Al 2 O 3 =25) Molecular sieve and silicon-based material multi-level pore SiO 2 and SiO 2 (Aperture ) Comparison of the adsorption amount of Zr(IV) in 3 mol / L nitric acid (the adsorption time of HY type molecular sieve is 180 min, the adsorption time of silicon-based material is 8 h, the Zr(IV) concentration in the solution is 100 mg / L, the nitric acid concentration is 3 mol / L, the experimental temperature is 25°C, and the mass volume ratio of the molecular sieve used to the solution is 1:100).

[0015] Note: It can be seen that the adsorption effect of HY molecular sieve on Zr(IV) is better than that of silica gel on Zr(IV) under the same conditions.

[0016] Figure 4 HY(SiO 2 / Al 2 O 3=25) XRD pattern of molecular sieve (XRD detection uses CuKα as source, detection voltage is 40kV, current is 40mA, scanning angle is 4°-40°, step length is 0.05s -1 ).

[0017] Note: The experimental results are compared with the standard card JCPDS No.73-2313 to prove that HY(SiO 2 / Al 2 O 3 =25) The obvious diffraction peaks are consistent with the characteristic peaks of FAU type zeolite.

[0018] Figure 5 HY(SiO 2 / Al 2 O 3 =25) Selective adsorption diagram of molecular sieve for Zr(IV) in radioactive solution (adsorption time is 180 min, Zr(IV) concentration in radioactive solution is 610 mg / L, nitric acid concentration is 3 mol / L, experimental temperature is 25°C, and the mass volume ratio of molecular sieve used to solution is 1:100).

[0019] Note: It can be seen that HY(SiO 2 / Al 2 O 3 =25) has excellent selectivity for Zr(IV) in radioactive liquid.

[0020] Figure 6 HY(SiO 2 / Al 2 O 3 =25) of TEM electron microscope.

[0021] Description: HY molecular sieves are irregular in shape, with diameters ranging from hundreds of nanometers to 2μm.

[0022] In a preferred embodiment, the present invention provides a method for removing Zr(IV) from radioactive waste liquid using a molecular sieve, wherein the molecular sieve and the radioactive waste liquid are mixed in a mass volume ratio of 1:20-500.

[0023] In a preferred embodiment, the present invention provides a method for removing Zr(IV) from radioactive waste liquid using a molecular sieve, wherein the certain temperature is 25-50°C.

[0024] In a preferred embodiment, the present invention provides a method for removing Zr(IV) from radioactive waste liquid using a molecular sieve, wherein the period of time is 0.1-5 hours.

[0025] In a preferred embodiment, the present invention provides a method for removing Zr(IV) from radioactive waste liquid using a molecular sieve, wherein the radioactive waste liquid is high-level waste liquid generated by the PUREX process, low- and intermediate-level waste liquid generated during the treatment of high-level waste liquid, or radioactive waste liquid generated by a nuclear accident / leakage.

[0026] In a preferred embodiment, the present invention provides a method for removing Zr(IV) from radioactive waste liquid using a molecular sieve, wherein the concentration of nitric acid in the radioactive waste liquid is 0.1-5 mol / L.

[0027] In a preferred embodiment, the present invention provides a method for removing Zr(IV) from radioactive waste liquid using a molecular sieve, wherein the filtration is performed using a stainless steel filter column containing a sand core.

[0028] In a preferred embodiment, the present invention provides a method for removing Zr(IV) from radioactive waste liquid using molecular sieves, wherein the centrifugal speed is 5000-1000 rpm and the time is 5-20 min.

[0029] In a preferred embodiment, the present invention provides a method for removing Zr(IV) from radioactive waste liquid using molecular sieves, wherein the method further comprises determining the concentration of Zr(IV) in the radioactive waste liquid after filtration or centrifugation.

[0030] In a preferred embodiment, the present invention provides a method for removing Zr(IV) from radioactive waste liquid using molecular sieves, wherein the concentration of Zr(IV) in the radioactive waste liquid is determined using an ICP-AES.

[0031] The beneficial effect of the present invention is that the method of removing Zr(IV) from radioactive waste liquid by using molecular sieve of the present invention can efficiently remove Zr(IV) from radioactive waste liquid, and the molecular sieve used has strong acid resistance and radiation resistance.

[0032] The present invention proposes a method for removing zirconium from radioactive waste liquid using a HY type molecular sieve (with uniform pores) with a topological structure of FAU type. This molecular sieve can be used in high concentrations of HNO 3 It is stable in solution because of its topological structure of FAU type, and its skeleton consists of 12-membered rings (with a diameter of ) composed of a super cage (diameter ) structure, so Zr(IV) can coordinate with it well, thus achieving efficient removal of Zr(IV) in radioactive waste liquid. The high specific surface area, negative charge on the skeleton channel structure and high stability of this molecular sieve are also conducive to the adsorption of Zr(IV) in radioactive waste liquid. Therefore, at room temperature, in a 3 mol / L nitric acid solution, the removal rate of zirconium by this molecular sieve can reach up to 97.64%, K d It is 827.46mL / g.

[0033] The present invention can solve or alleviate the problem of interface contamination in the PUREX process, and simultaneously solve or alleviate the third phase problem in the process of solvent extraction treatment of high-level radioactive waste liquid. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 HY(SiO 2 / Al 2 O 3 =25), NaY(SiO 2 / Al 2 O 3 =5), K-CHA(SiO 2 / Al 2 O 3 =4) type molecular sieve adsorption kinetic curve of Zr in 3 mol / L nitric acid (corresponding to Example 1 and Comparative Examples 1 and 2).

[0035] Figure 2 HY(SiO 2 / Al 2 O 3 =25) type molecular sieve adsorption curve of Zr at different nitric acid concentrations (corresponding to Examples 1 and 4).

[0036] Figure 3 HY(SiO 2 / Al 2 O 3 =25) type molecular sieve and silicon-based material multi-level pore SiO 2 and SiO 2 (Aperture ) is a comparison chart of the adsorption amount of Zr in 3 mol / L nitric acid (corresponding to Example 1 and Comparative Example 3).

[0037] Figure 4 HY(SiO 2 / Al 2 O 3 =25) type molecular sieve XRD pattern (corresponding to Example 1).

[0038] Figure 5 HY(SiO 2 / Al2 O 3 =25) type molecular sieve and silicon-based material multi-level pore SiO 2 and SiO 2 (Aperture ) is a diagram of the selective adsorption of Zr(IV) in the radioactive liquid (corresponding to Example 5 and Comparative Example 4).

[0039] Figure 6 HY(SiO 2 / Al 2 O 3 =25) type molecular sieve TEM electron microscope image (corresponding to Example 1). DETAILED DESCRIPTION

[0040] The specific implementation of the present invention is further described below by way of examples. For simulated radioactive waste liquid, the common method steps in the following examples are as follows:

[0041] (1) Weigh a certain amount of HY molecular sieve (topological structure is FAU type) in a conical flask;

[0042] (2) according to a certain mass volume ratio of molecular sieve to solution (1:20-1:500), a certain volume of zirconium-containing radioactive nitric acid solution (wherein the concentration of nitric acid is 0.1-5 mol / L) is added, and then the conical flask is sealed and placed in a constant temperature water bath oscillator to maintain a certain temperature (25-50° C.) and oscillate for a period of time (0.1-5 h);

[0043] (3) After the adsorption reaches a certain time, the conical flask is removed from the water bath, and the feed solution in the conical flask is pumped into a stainless steel filter column containing a sand core by a peristaltic pump for filtration. After the adsorbent and the solution are separated, the concentration of Zr(IV) in the feed solution is determined by an ICP-AES.

[0044] Adsorption amount q, removal rate RE and distribution coefficient K d The calculation formula is:

[0045]

[0046]

[0047]

[0048] in:

[0049] C 0 is the initial Zr(IV) concentration in the aqueous phase, mg / L;

[0050] C e is the concentration of Zr(IV) in the aqueous phase after adsorption equilibrium, mg / L;

[0051] V is the volume of the solution, L;

[0052] m is the mass of the adsorbent, g.

[0053] Embodiment 1:

[0054] In a conical flask, add 0.05 g of FAU molecular sieve HY (SiO 2 / Al 2 O 3 =25), then add 5mL of simulated liquid containing 3mol / L nitric acid and 100mg / L Zr(IV), and place in a 25℃ constant temperature water bath shaker for shaking. After shaking for 180min, transfer the liquid in the conical flask to a centrifuge tube for centrifugation, and take the supernatant for testing. The ion concentrations before and after adsorption were measured by plasma emission spectrometry (ICP). According to the measurement results, the Zr(IV) removal rate was 78.5%, and K d It is 365.12mL / g.

[0055] Embodiment 2:

[0056] The experimental temperature was raised to 50 degrees, and the other experimental conditions were the same as those in Example 1. According to the measured results, the Zr(IV) removal rate was calculated to be 91.58%, K d It is 1088.12mL / g.

[0057] Embodiment 3:

[0058] The mass volume ratio of the molecular sieve to the solution was changed to 1:20, and the other experimental conditions were the same as those in Example 1. According to the measurement results, the Zr(IV) removal rate was calculated to be 97.64%, and K d It is 827.46mL / g.

[0059] Embodiment 4:

[0060] The nitric acid concentration in the simulated liquid used in the experiment was changed to 0.1 mol / L, and the other experimental conditions were the same as those in Example 1. According to the measurement results, the Zr(IV) removal rate was calculated to be 53.73%, and K d It is 116.10mL / g.

[0061] The nitric acid concentration in the simulated liquid used in the experiment was changed to 0.5 mol / L, and the other experimental conditions were the same as those in Example 1. According to the measurement results, the Zr(IV) removal rate was calculated to be 93.46%, and K d It is 1429.64mL / g.

[0062] The nitric acid concentration in the simulated liquid used in the experiment was changed to 1.0 mol / L, and the other experimental conditions were the same as those in Example 1. According to the measurement results, the Zr(IV) removal rate was calculated to be 88.19%, and K d It is 746.56mL / g.

[0063] The nitric acid concentration in the simulated liquid used in the experiment was changed to 2.0 mol / L, and the other experimental conditions were the same as those in Example 1. According to the measurement results, the Zr(IV) removal rate was calculated to be 82.41%, and K d It is 468.59mL / g.

[0064] The nitric acid concentration in the simulated liquid used in the experiment was changed to 4.0 mol / L, and the other experimental conditions were the same as those in Example 1. According to the measurement results, the Zr(IV) removal rate was calculated to be 67.11%, and K d It is 204.07mL / g.

[0065] The nitric acid concentration in the simulated liquid used in the experiment was changed to 5.0 mol / L, and the other experimental conditions were the same as those in Example 1. According to the measurement results, the Zr(IV) removal rate was calculated to be 54.04%, and K d It is 117.57mL / g.

[0066] Embodiment 5:

[0067] In a conical flask, add 0.1 g of FAU molecular sieve HY (SiO 2 / Al 2 O 3 =25), then add 10mL of radioactive liquid containing 3mol / L nitric acid and 610mg / L Zr(IV), and place in a 25℃ constant temperature water bath shaker for shaking. After shaking for 180min, separate the solid and liquid by filtering. The ion concentrations before and after adsorption were measured by plasma emission spectrometer (ICP). According to the measurement results, the Zr(IV) removal rate was 35.6%, and K d It is 55.22 mL / g (Table 1).

[0068] Table 1. Adsorption results of HY molecular sieve on high-level waste liquid

[0069]

[0070] Comparative Example 1: (Purpose: to compare with Example 1)

[0071] The molecular sieve used in Example 1 was replaced with FAU type molecular sieve NaY (SiO 2 / Al 2 O3 =5), and the other experimental conditions are the same as those in Example 1. According to the measurement results, the Zr(IV) removal rate is 28%, K d It is 38.89mL / g.

[0072] Comparative Example 2: (Purpose: to compare with Example 1)

[0073] The molecular sieve used in Example 1 was replaced with a CHA type molecular sieve K-CHA (SiO 2 / Al 2 O 3 =4), and the other experimental conditions are the same as those in Example 1. According to the measurement results, the Zr(IV) removal rate is 52.25%, K d It is 109.42mL / g.

[0074] Comparative Example 3: (Purpose: to compare with Example 1)

[0075] In a conical flask, add 0.05 g of multi-level porous SiO purchased from Jiangsu Xianfeng Nanomaterial Technology Co., Ltd. 2 Then add 5mL of simulated liquid containing 3mol / L nitric acid and 100mg / L Zr(IV) and place in a 25℃ constant temperature water bath shaker for shaking. After shaking for 8h, centrifuge at 8000rpm for 5min, and then separate the solid and liquid by filtering. The ion concentrations before and after adsorption were measured by plasma emission spectrometer (ICP). According to the measurement results, the Zr(IV) removal rate was 42.5%, and K d It is 73.91mL / g.

[0076] The multi-level porous SiO 2 The SiO2 was purchased from Jiangsu Xianfeng Nanomaterial Technology Co., Ltd. 2 (Aperture ), and the other experimental conditions remained unchanged. According to the measurement results, the Zr(IV) removal rate was calculated to be 37%, K d It is 58.73mL / g.

[0077] From the comparison results, it can be seen that the adsorption effect of silicon-based materials on Zr(IV) is not as good as that of HY type molecular sieves on Zr(IV).

[0078] Comparative Example 4: (Purpose: to compare with Example 5)

[0079] In a conical flask, add 0.1 g of SiO purchased from Jiangsu Xianfeng Nanomaterial Technology Co., Ltd. 2 (Aperture ), then add 10mL of radioactive liquid containing 3mol / L nitric acid and 610mg / L Zr(IV), and place in a 25℃ constant temperature water bath shaker for shaking. After shaking for 8h, solid-liquid separation is performed by filtration. The ion concentrations before and after adsorption are measured by plasma emission spectrometry (ICP). According to the measurement results, the Zr(IV) removal rate is 22.95%, and K d It is 29.79 mL / g (Table 2).

[0080] The SiO 2 The multi-level porous SiO 2 , and the other experimental conditions remain unchanged. According to the measured results, the Zr(IV) removal rate is 20.82%, K d It is 26.29 mL / g (Table 2).

[0081] From the comparison results, it can be seen that the removal effect of silicon-based materials on Zr(IV) in radioactive waste liquid is not as good as the removal effect of HY type molecular sieve on Zr(IV) in radioactive waste liquid under the same conditions.

[0082] Table 2. Adsorption results of high-level liquid waste by silicon-based materials

[0083]

[0084]

[0085] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these changes and variations. The above embodiments or implementations are merely illustrative of the present invention, and the present invention may also be implemented in other specific ways or other specific forms without departing from the gist or essential features of the present invention. Therefore, the described implementations should be considered illustrative rather than restrictive in any respect. The scope of the present invention should be described by the appended claims, and any changes equivalent to the intent and scope of the claims should also be included within the scope of the present invention.

Claims

1. A method for removing Zr(IV) from radioactive waste liquid using molecular sieves, characterized in that: The method comprises mixing the molecular sieve with the radioactive waste liquid, performing an adsorption reaction at a certain temperature for a period of time, and removing the molecular sieve after filtering or centrifugal treatment; the molecular sieve is a HY type molecular sieve with a FAU type topological structure; The mass volume ratio of the molecular sieve to the radioactive waste liquid is 1:20-100; The concentration of nitric acid in the radioactive waste liquid is 0.1-5 mol / L.

2. The method according to claim 1, characterized in that: The certain temperature is 25-50°C.

3. The method according to claim 1, characterized in that: The period of time is 0.1-5h.

4. The method according to claim 1, characterized in that: The radioactive waste liquid is high-level waste liquid generated by the PUREX process, medium- and low-level waste liquid generated during the treatment of high-level waste liquid, or radioactive waste liquid generated by nuclear accidents / leakages.

5. The method according to claim 1, characterized in that: The filtration is carried out using a stainless steel filter column containing a sand core.

6. The method according to claim 1, characterized in that: The centrifugal speed is 5000-1000rpm, and the time is 5-20min.

7. The method according to claim 1, characterized in that: The method also measures the concentration of Zr(IV) in the radioactive waste liquid after filtration or centrifugation.

8. The method according to claim 7, characterized in that: The concentration of Zr(IV) in the radioactive waste liquid was measured using a plasma emission spectrometer.

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