A method for preparing cobalt hydroxide colloid

Abstract

The invention discloses a method for preparing a cobalt colloid, comprising the steps of: adding a cobalt salt solution to a boric acid-lithium hydroxide solution, mixing uniformly to obtain a mixed solution; dropping a hydrazine solution into the mixed solution, and reacting to obtain a cobalt hydroxide colloid. The method for preparing the cobalt hydroxide colloid of the present invention, the prepared cobalt hydroxide colloid is close to the real cobalt hydroxide colloid composition and particle size of a primary circuit, and the preparation conditions are milder than the high temperature and high pressure operating conditions of a primary circuit, reducing the difficulty of preparing the cobalt hydroxide colloid.

Description

Technical Field

[0001] The invention specifically relates to a method for preparing cobalt hydroxide colloid in the existing form of cobalt in a primary loop system of a pressurized water reactor nuclear power plant. Background Art

[0002] The corrosion products on the surface of the fuel cladding of a PWR nuclear power plant may cause axial power offset (AOA) and corrosion under deposits (CILC), affecting the core safety of the reactor. In addition, during the commercial operation of a PWR nuclear power plant (normal operation and shutdown for refueling), 90% of the radioactive radiation dose of professional workers comes from activated corrosion products, that is, activated corrosion products are the main source of radiation exposure for PWR nuclear power plant workers.

[0003] In order to ensure the core safety of pressurized water reactor nuclear power plants and reduce the collective dose, it is necessary to study methods to reduce core corrosion products, from the perspectives of reducing sources (reducing the generation of corrosion products), reducing migration (changing water chemical conditions), reducing deposition (studying technologies that affect the morphology of corrosion products), and removing deposition (fuel ultrasonic cleaning, oxidation purification, and radioactive chemical decontamination technologies). At the same time, the system sets up a primary circuit purification system to treat ionic and suspended corrosion products in the primary circuit system to achieve the purpose of purifying the primary circuit.

[0004] However, in the primary loop system of a pressurized water reactor nuclear power plant, the corrosion products such as cobalt and iron contain a large amount of colloidal substances. Since most of the colloidal substances are charged, they are metastable substances and are very small in size, most of which are between 10 and 100 nm. For filters with a minimum filter diameter of 0.1 μm, they cannot be effectively intercepted. The colloids entering the subsequent ion exchange desalination bed may be adsorbed by the ion exchange resin and block the skeleton structure of the resin, resulting in an increase in the pressure difference. The pressure difference exceeds the standard and needs to be replaced before failure. At the same time, due to the metastable state, they may aggregate and deposit on the pipeline system, generate hot spots on the pipeline system, and generate radioactivity. Therefore, the study of the morphological transformation of colloidal corrosion products is also a key point in the chemical control of pressurized water reactors. According to the data of a nuclear power base, cobalt 60 accounts for the highest proportion in the primary loop system (RCP) and the residual heat removal system (RRA). It is necessary to carry out relevant research on the morphological transformation of cobalt. Therefore, it is necessary to develop a preparation method for cobalt hydroxide colloid to provide raw materials for related research. Summary of the invention

[0005] In view of this, in order to overcome the defects of the prior art, the object of the present invention is to provide a method for preparing cobalt colloid, which can prepare cobalt colloid particles of cobalt hydroxide.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A method for preparing cobalt hydroxide colloid comprises the following steps:

[0008] Adding the cobalt salt solution to the boric acid-lithium hydroxide solution and mixing them evenly to obtain a mixed solution;

[0009] A hydrazine solution is added dropwise to the mixed solution, and after reaction, cobalt hydroxide colloid is obtained.

[0010] According to some preferred embodiments of the present invention, the boric acid-lithium hydroxide solution is prepared by the following method: adding lithium hydroxide solution to the boric acid solution, adjusting the pH of the system to 7-7.5. The concentration of the boric acid solution is 5.72 g / L (corresponding to a boron concentration of 1000 ppm).

[0011] According to some preferred embodiments of the present invention, the pH value of the boric acid-lithium hydroxide solution is 7-7.5, preferably 7.2.

[0012] According to some preferred implementation aspects of the present invention, the concentration of the cobalt salt solution is 0.5-1.5 g / L, preferably 1 g / L, and the corresponding mass ratio of boric acid to cobalt salt is 65.6-196.8.

[0013] The concentration of the cobalt salt solution is related to the particle size of the generated colloid. The higher the concentration, the larger the particle size. Therefore, a suitable concentration of the cobalt salt solution is required. In some embodiments, by selecting the above concentration and pH, the volume of the boric acid-lithium hydroxide solution with a pH of 7-7.5 is 86 ml; the volume of the cobalt salt solution with a concentration of 1 g / L is 5 ml.

[0014] According to some preferred embodiments of the present invention, the cobalt salt is a soluble cobalt salt, preferably cobalt nitrate and / or cobalt chloride.

[0015] According to some preferred embodiments of the present invention, the mixing is carried out at a stirring speed of 350-450 rpm. -1 Stir for 15-25 minutes. Preferably, the speed is 400 rpm. -1 Stir for 20 min.

[0016] According to some preferred embodiments of the present invention, the mass concentration of the hydrazine solution is 45-55%, preferably 50%.

[0017] According to some preferred embodiments of the present invention, the hydrazine in the hydrazine solution and Co 2+The molar ratio is 300:0.5-1.5, preferably 300:1. Hydrazine is a reducing agent, and its molar ratio to Co affects the speed of the reaction, the degree of reaction, and the composition and particle size of the final product. The preferred molar ratio of 300:1 can obtain a cobalt hydroxide colloid with an average particle size of 100nm. In the preparation method of the present application, hydrazine cannot reduce Co to 2+ Reduction to metallic Co 0 , but due to the hydrolysis of hydrazine to produce OH - , by providing an alkaline environment, promoting Co 2+ β-Co(OH)2 is formed.

[0018] According to some preferred embodiments of the present invention, the reaction is carried out at 30-40°C for 1-3h, preferably at 35°C for 2h.

[0019] According to some preferred embodiments of the present invention, the hydrazine solution is added dropwise within 20s-60s.

[0020] According to some preferred embodiments of the present invention, the average particle size of the prepared cobalt hydroxide colloid is 90-110 nm, preferably 100 nm.

[0021] Due to the adoption of the above technical scheme, compared with the prior art, the advantages of the present invention are: the method for preparing cobalt hydroxide colloid of the present invention can prepare cobalt hydroxide colloid close to the composition and particle size of the real cobalt hydroxide colloid of the first loop, and the preparation conditions are milder than the high temperature and high pressure operating conditions of the first loop, thereby reducing the difficulty of preparing cobalt hydroxide colloid. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0023] Figure 1 a is a TEM image of cobalt hydroxide colloid prepared in a preferred embodiment of the present invention;

[0024] Figure 1 b is the EDS spectrum of the cobalt hydroxide colloid prepared in the preferred embodiment of the present invention;

[0025] Figure 2 The lattice fringes and electron diffraction pattern of the cobalt hydroxide colloid prepared in the preferred embodiment of the present invention. DETAILED DESCRIPTION

[0026] In order to enable those skilled in the art to better understand the technical solution of the present invention, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0027] The preparation method of the cobalt hydroxide colloid in this embodiment comprises the following steps:

[0028] Step 1) Add the cobalt salt solution to the boric acid-lithium hydroxide solution and mix well to obtain a mixed solution. The mixing speed is 400 rpm. -1 , stirring time 15-25min.

[0029] The pH value of the boric acid-lithium hydroxide solution is 7-7.5, preferably 7.2. The boric acid-lithium hydroxide solution is prepared by the following method: adding lithium hydroxide solution to the boric acid solution to adjust the pH of the system to 7-7.5. The concentration of the boric acid solution is 5.72 g / L (corresponding to a boron concentration of 1000 ppm).

[0030] The concentration of the cobalt salt solution is 0.5-1.5 g / L, preferably 1 g / L. The corresponding mass ratio of boric acid to cobalt salt is 65.6-196.8. The cobalt salt is a soluble cobalt salt, preferably cobalt nitrate and / or cobalt chloride.

[0031] When the above concentration and pH are selected, the volume of the boric acid-lithium hydroxide solution with a pH of 7-7.5 is 86 ml; the volume of the cobalt nitrate solution with a concentration of 1 g / L is 5 ml.

[0032] Step 2), heating the mixed solution to 30-40°C, adding hydrazine solution to the mixed solution, so that the molar ratio of hydrazine to Co in the system is 300:0.5-2, reacting at 35°C for 2h to obtain cobalt hydroxide colloid, and the average particle size of the prepared cobalt hydroxide colloid is 90-110nm.

[0033] The mass concentration of the hydrazine solution is 45-55%, preferably 50%. The speed of adding the hydrazine solution is controlled to be completed within 20s-60s. 2+ The molar ratio is 300:0.5-1.5, preferably 300:1, and cobalt hydroxide colloid with an average particle size of 100 nm can be obtained.

[0034] Example 1

[0035] The preparation method of the cobalt hydroxide colloid in this embodiment comprises the following steps:

[0036] Add 5 ml of 1 g / L cobalt nitrate solution to 86 ml of B-Li solution with a pH of 7.2 and heat at 400 rpm. -1 The mixture was stirred at a stirring speed of 20 min, and 333 μL of hydrazine solution was slowly added to keep it reducing, so that the molar ratio of hydrazine to Co was maintained at 300:1. The mixture was reacted at 35°C for 2 h to obtain cobalt hydroxide colloid with an average particle size of about 100 nm and a chemical form of β-Co(OH)2.

[0037] Example 2

[0038] The preparation method of the cobalt hydroxide colloid in this embodiment comprises the following steps:

[0039] Add 5 ml of 1 g / L cobalt nitrate solution to 86 ml of B-Li solution with a pH of 7.5 and heat at 400 rpm. -1 The mixture was stirred at a stirring speed of 20 min, and 333 μL of hydrazine solution was slowly added to keep it reducing, so that the molar ratio of hydrazine to Co was maintained at 300:1. The mixture was reacted at 35°C for 2 h to obtain cobalt hydroxide colloid with an average particle size of about 100 nm and a chemical form of β-Co(OH)2.

[0040] Example 3

[0041] The preparation method of the cobalt hydroxide colloid in this embodiment comprises the following steps:

[0042] Add 5 ml of 1 g / L cobalt nitrate solution to 86 ml of B-Li solution with a pH of 7.2 and heat at 400 rpm. -1 The mixture was stirred at a stirring speed of 20 min, and 333 μL of hydrazine solution was slowly added to keep it reducing, so that the molar ratio of hydrazine to Co was maintained at 300:1. The mixture was reacted at 40°C for 2 h to obtain cobalt hydroxide colloid with a particle size of about 100 nm and a chemical form of β-Co(OH)2.

[0043] Comparative Example 1

[0044] The difference between this comparative example and Example 1 is that the amount of hydrazine added in this comparative example is 33.3 μL, and the ratio of hydrazine to Co is 30:1. The remaining steps and parameters are basically the same as those in Example 1.

[0045] The experimental results did not detect the formation of cobalt hydroxide colloid.

[0046] Comparative Example 2

[0047] The difference between this comparative example and Example 1 is that the reaction temperature in this comparative example is 60° C. The remaining steps and parameters are basically the same as those in Example 1.

[0048] The experimental results showed that the main component of the generated cobalt colloid was cobalt element.

[0049] Comparative Example 3

[0050] The difference between this comparative example and Example 1 is that the pH of the boric acid-lithium hydroxide solution in this comparative example is 6.0. The remaining steps and parameters are basically the same as those in Example 1.

[0051] The experimental results did not detect the formation of cobalt hydroxide colloid.

[0052] Comparative Example 4

[0053] The difference between this comparative example and Example 1 is that the hydrazine is added dropwise at a fast speed in this comparative example, and is added dropwise in an instant. The remaining steps and parameters are basically the same as those in Example 1.

[0054] The experimental results showed that the average particle size of the generated cobalt hydroxide particles was much larger than 100 nm and could no longer be called a colloid.

[0055] Test Case

[0056] The cobalt hydroxide colloid prepared in Example 1 was measured for the microscopic morphology of the obtained colloidal sample using a high-resolution transmission electron microscope (HR-TEM), the elemental composition of the colloidal particles was determined by surface energy spectrum (EDS), and the chemical structure of the prepared cobalt hydroxide colloid was analyzed and verified by information such as electron diffraction and lattice diffraction fringes.

[0057] 1) If Figure 1 As shown, TEM clearly captures the cobalt hydroxide colloidal particles, which can prove that a colloidal form is indeed formed under the experimental conditions of the present invention, and the shape of the cobalt hydroxide colloidal particles is approximately spherical. The colloidal particle size is measured by a scale and is in the range of about 100 nm.

[0058] The surface element energy spectrum (EDS) analysis of the cobalt colloidal particles observed in TEM was further performed, and the results are as follows: Figure 1 As shown in (b), the cobalt hydroxide colloidal particles contain Co and O elements, which are evenly distributed in the particle structure, with a ratio of approximately O:Co=2:1.

[0059] 2) Using HR-TEM, clear lattice fringes and electron diffraction patterns of cobalt colloidal particles were observed. Figure 2As shown in the figure, the lattice fringes of the cobalt colloidal particles are clear and the diffraction spots are obvious, indicating that the particles are solid with a certain degree of crystallinity. By analyzing the lattice fringes, the crystal plane spacing d values ​​of the particles can be obtained to be 0.395nm, 0.383nm and 0.489nm respectively. Combined with the Bragg formula (Formula 1), the diffraction angle 2θ value of the cobalt colloidal particles can be calculated, which is listed in Table 1.

[0060] 2dsinθ=λ (1)

[0061] Table 1 Comparison of diffraction angle 2θ values ​​of cobalt colloidal particles and cobalt oxides and hydroxides

[0062]

[0063]

[0064] The diffraction results were compared with those of metallic cobalt and cobalt hydroxide, and it was found that the cobalt colloidal particles formed under the experimental conditions were consistent with β-Co(OH)2. Based on this, it can be judged that the cobalt colloidal particles obtained under this condition are cobalt hydroxide.

[0065] The method for preparing the cobalt hydroxide colloid in the above embodiment can obtain cobalt colloid in the prepared boric acid-lithium hydroxide medium under the condition of adding hydrazine, and the average particle size is about 100nm, and the chemical form is β-Co(OH)2. The preparation conditions are milder than the high temperature and high pressure operation conditions of the first circuit, which reduces the difficulty of preparing the cobalt hydroxide colloid.

[0066] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with the technology to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing cobalt hydroxide colloid, characterized in that: The steps include: Adding the cobalt salt solution to the boric acid-lithium hydroxide solution and mixing them evenly to obtain a mixed solution; Adding hydrazine solution dropwise to the mixed solution, and obtaining cobalt hydroxide colloid after reaction; The cobalt salt is cobalt nitrate; the mass concentration of the hydrazine solution is 45-55%; The hydrazine in the hydrazine solution and Co 2 + The molar ratio is 300:0.5-1.5; the reaction conditions are 1-3 hours at 30-40°C; the dripping speed of the hydrazine solution is to add it within 20s-60s; The average particle size of the prepared cobalt hydroxide colloid is 90-110 nm, and the chemical form of the cobalt hydroxide colloid is β-Co(OH)2.

2. The preparation method according to claim 1, characterized in that: The boric acid-lithium hydroxide solution is prepared by the following method: adding lithium hydroxide solution to the boric acid solution to adjust the pH of the system to 7-7.

5.

3. The preparation method according to claim 1, characterized in that: The concentration of the cobalt salt solution is 0.5-1.5 g / L.

4. The preparation method according to claim 1, characterized in that: The mixing is carried out at a stirring speed of 350-450 rpm -1 Stir for 15-25 min.

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