Preparation method of cadmium fluoride for thorium-based molten salt reactor

Abstract

The invention provides a preparation method of cadmium fluoride for a thorium-based molten salt reactor, aiming at overcoming the defect that the cadmium fluoride meeting the technical index requirements of the thorium-based molten salt reactor is difficult to industrially produce due to the reasons of raw material purity, process parameters and the like in the existing preparation method. The method comprises the following steps: dissolving and filtering cadmium oxide by using ammonia water to remove alkaline insoluble impurities, stabilizing the crystal form of cadmium fluoride by gradient drying, and removing protective ammonium bifluoride impurities at high temperature to obtain a cadmium fluoride product meeting the technical index requirements of a thorium-based molten salt reactor.

Description

Technical Field

[0001] The present invention relates to a method for preparing cadmium fluoride. Background Art

[0002] The applications of cadmium fluoride are mostly concentrated in high-tech industries. For example, in the metallurgical field, it can be used as an aluminum brazing flux to help remove the surface oxide film of aluminum and its alloys during the brazing process, improve the wettability and spreadability of the filler metal, and thus achieve a good welding effect; in the field of chemical catalysis, it can be used as a catalyst support to provide active sites for some organic synthesis reactions, helping to accelerate the reaction rate and improve the selectivity of the reaction; in the glass industry, it can be used as a glass additive to increase the abrasion resistance of the glass, improve the hardness and durability of the glass; in the nuclear industry, it can be used as a reactant in the molten salt of the thorium-based molten salt reactor to participate in the nuclear reaction process in the reactor, playing an important role in the operation and control of the reactor; in the electronic industry, it can be used to manufacture electronic components such as cathode ray tubes and phosphors, and can also be used as an insulator in high-frequency semiconductor technology.

[0003] Among them, for cadmium fluoride used in the thorium-based molten salt reactor, the requirements are that the content of F ions is 25 - 25.5%, the content of Cd ions is 74 - 74.5%, the content of O ions is less than 0.1%, the content of NH3 ions is less than 0.01%, the content of Fe ions is less than 0.001%, and the contents of Ca and Mg ions are both less than 0.001%. However, due to reasons such as the purity of raw materials and process parameters, existing preparation methods are difficult to industrially produce cadmium fluoride that meets the requirements of these technical indicators. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for preparing cadmium fluoride for a thorium-based molten salt reactor, so as to overcome the problem that existing preparation methods are difficult to industrially produce cadmium fluoride that meets the technical indicator requirements of the thorium-based molten salt reactor due to reasons such as the purity of raw materials and process parameters.

[0005] The technical solution of the present invention is as follows:

[0006] A method for preparing cadmium fluoride for a thorium-based molten salt reactor, characterized in that it includes the following steps:

[0007] Step 1: Prepare a cadmium ammonia solution;

[0008] Step 1.1: Add cadmium oxide with a particle size ≤ 20 μm and a content > 99% to excessive analytical pure ammonia water, and seal and stir to dissolve in a container to obtain a cadmium ammonia solution; the sealing here is to prevent the ammonia water from escaping during the dissolution reaction, and the excessive ammonia water is to enable better dissolution of cadmium oxide; the reaction equation is: CdO + 4NH4OH ==== (Cd(NH3)4)(OH)2 + 3H2O;

[0009] Step 1.2: Since impurities such as iron in cadmium oxide are insoluble, the cadmium ammonia solution is filtered to make the iron impurity content less than 0.5 ppm, obtaining a pure cadmium ammonia solution;

[0010] Step 2: Synthesize cadmium fluoride;

[0011] Step 2.1: Add the cadmium ammonia solution to electronic grade hydrofluoric acid for reaction, controlling the pH value of the reaction solution to be 2.5 - 3, obtaining a mixed solution of cadmium fluoride and ammonium bifluoride; the purpose of the pH value being 2.5 - 3 is as follows: 1) Prevent the hydrolysis of cadmium fluoride during the reaction; 2) Generate cadmium fluoride as completely as possible; 3) Ensure that what is obtained after subsequent heating and concentration is a mixture of ammonium bifluoride and cadmium fluoride; 4) Prevent the hydrolysis and oxidation of cadmium fluoride during subsequent drying; the reaction equation is: 10HF + (Cd(NH3)4)(OH)2 ==== CdF2·2H2O + 4NH4HF2

[0012] Step 2.2: Heat, stir, and concentrate the mixed solution of cadmium fluoride and ammonium bifluoride for reaction. After a large amount of crystals appear, filter, sediment, remove the supernatant, and collect the bottom precipitate for filtration to obtain a mixture of cadmium fluoride and ammonium bifluoride;

[0013] Step 3: Dry cadmium fluoride;

[0014] The mixed crystals of cadmium fluoride and ammonium bifluoride are gradient dried under the protection of high-purity nitrogen. First, dry at 200 - 250 °C for 2 - 3 hours to remove the water inside and outside the cadmium fluoride molecules, and then raise the temperature to 500 - 600 °C and dry for 2 - 3 hours to remove the excess ammonium bifluoride, obtaining the finished product of cadmium fluoride. The reaction equations are: CdF2·2H2O ==== CdF2 + 2H2O; NH4HF2 ==== NH3↑ + 2HF↑.

[0015] Use an XRF fluorescence spectrometer to detect the finished product of cadmium fluoride. Its F ion content is 25 - 25.5%, Cd ion content is 74 - 74.5%, O ion content is less than 0.1%, NH3 ion content is less than 0.01%, Fe ion content is less than 0.001%, and the contents of Ca and Mg ions are both less than 0.001%, meeting the requirements of cadmium fluoride for thorium-based molten salt reactors.

[0016] The advantages of the present invention are:

[0017] 1. The present invention uses ammonia water to dissolve and filter cadmium oxide, removing the alkaline insoluble impurities, stabilizing the crystal form of cadmium fluoride through gradient drying, and removing the protective ammonium bifluoride impurities at high temperature, obtaining a cadmium fluoride product that meets the technical index requirements of thorium-based molten salt reactors.

[0018] 2. The present invention can prepare a high-purity cadmium fluoride product that meets the requirements of thorium-based molten salt reactors under conventional conditions, which is easy to implement. Detailed implementation mode

[0019] The present invention will be further described in detail below through embodiments.

[0020] Embodiment 1

[0021] In this embodiment, cadmium fluoride for a thorium-based molten salt reactor is prepared through the following steps:

[0022] Step 1: Prepare a cadmium ammonia solution;

[0023] Step 1.1: Take cadmium oxide with a particle size ≤ 20 μm and a content > 99%, add it to analytical pure ammonia water for dissolution, with the molar ratio of cadmium to ammonia being 1:4.5, seal and stir in a container for 3 hours to obtain a cadmium ammonia solution, and let it stand for later use;

[0024] Step 1.2: Filter the cadmium ammonia solution obtained in Step 1.1 using a filter with a filtration accuracy of 1 μm to remove trace insoluble substances. When the iron impurity content in the solution is detected to be less than 0.5 ppm, a pure cadmium ammonia solution is obtained.

[0025] Step 2: Synthesize cadmium fluoride

[0026] Step 2.1: Take electronic-grade hydrofluoric acid with a mass fraction of 30% and add it to a tetrafluoride beaker. Add the cadmium ammonia solution obtained in Step 1.2 to it. When the pH value is adjusted to 2.8, a mixed solution of cadmium fluoride and ammonium bifluoride is obtained;

[0027] Step 2.2: Heat and raise the temperature of the mixed solution of cadmium fluoride and ammonium bifluoride obtained in Step 2.1 to 110 °C for stirring and concentration reaction. After a large amount of crystals are concentrated, filter, appropriately settle, remove the supernatant, collect the bottom precipitate for filtration, and obtain a mixture of cadmium fluoride and ammonium bifluoride.

[0028] Step 3: Dry cadmium fluoride;

[0029] Step 3.1: Put the cadmium fluoride and ammonium bifluoride crystals obtained in Step 2.2 into a platinum crucible, and perform gradient drying in an atmosphere furnace with high-purity nitrogen: first dry at 200 °C for 3 hours, and then raise the temperature to 500 °C and dry for 3 hours to obtain the finished cadmium fluoride product.

[0030] The finished cadmium fluoride product prepared in this embodiment is detected using an XRF fluorescence spectrometer. The detection results show that the F ion content is 25.232%, the Cd ion content is 74.189%, the O ion content is 0.079%, the NH3 ion content is less than 0.0087%, the Fe ion content is less than 0.0008%, the Ca ion content is 0.0007%, and the Mg ion content is 0.0002%, meeting the requirements of cadmium fluoride for a thorium-based molten salt reactor.

[0031] Example 2

[0032] In this example, cadmium fluoride for thorium-based molten salt reactors is prepared through the following steps:

[0033] Step 1: Prepare cadmium ammonia solution;

[0034] Step 1.1: Take cadmium oxide with a particle size ≤ 20 μm and a content > 99%, add it to analytical pure ammonia water for dissolution. The molar ratio of cadmium to ammonia is 1:5. Stir and dissolve it in a sealed container for 2 hours to obtain cadmium ammonia solution, and let it stand for later use;

[0035] Step 1.2: Filter the cadmium ammonia solution obtained in Step 1.1 using a filter with a filtration accuracy of 1 μm to remove trace insoluble substances. When the iron impurity content in the solution is less than 0.5 ppm, a pure cadmium ammonia solution is obtained.

[0036] Step 2: Synthesize cadmium fluoride;

[0037] Step 2.1: Take electronic-grade hydrofluoric acid with a mass fraction of 38% and add it to a tetrafluoro beaker. Add the cadmium ammonia solution obtained in Step 1.2 to it. When the pH value is adjusted to 2.5, a mixed solution of cadmium fluoride and ammonium bifluoride is obtained;

[0038] Step 2.2: Heat up the mixed solution of cadmium fluoride and ammonium bifluoride obtained in Step 2.1 to 120 °C for stirring and concentration reaction. After a large amount of crystals are concentrated, filter, appropriately settle, remove the supernatant, collect the bottom precipitate for filtration, and obtain a mixture of cadmium fluoride and ammonium bifluoride.

[0039] Step 3: Dry cadmium fluoride;

[0040] Step 3.1: Put the cadmium fluoride and ammonium bifluoride crystals obtained in Step 2.2 into a platinum crucible, and carry out gradient drying in an atmosphere furnace with high-purity nitrogen: first dry at 250 °C for 3 hours, then raise the temperature to 550 °C and dry for 3 hours to obtain the finished cadmium fluoride product.

[0041] Use an XRF fluorescence spectrometer to detect the finished cadmium fluoride product prepared in this example. The detection results show that the F ion content is 25.198%, the Cd ion content is 74.336%, the O ion content is 0.082%, the NH3 ion content is less than 0.0069%, the Fe ion content is 0.0007%, the Ca ion content is 0.0006%, and the Mg ion content is 0.0003%, meeting the requirements of cadmium fluoride for thorium-based molten salt reactors.

[0042] Example 3

[0043] In this example, cadmium fluoride for thorium-based molten salt reactors is prepared through the following steps:

[0044] Step 1: Prepare cadmium ammonia solution;

[0045] Step 1.1: Take cadmium oxide with a particle size ≤ 20 μm and a content > 99%, add it to analytical pure ammonia water for dissolution. The molar ratio of cadmium to ammonia is 1:5. Seal and stir in a container for 2.5 hours to obtain cadmium ammonia solution, and let it stand for use;

[0046] Step 1.2: Filter the cadmium ammonia solution obtained in Step 1.1 using a filter with a filtration accuracy of 1 μm to remove trace insoluble substances. When the iron impurity content in the solution is detected to be less than 0.5 ppm, a pure cadmium ammonia solution is obtained.

[0047] Step 2: Synthesize cadmium fluoride

[0048] Step 2.1: Take 50% by mass of electronic grade hydrofluoric acid and add it to a tetrafluoro beaker. Add the cadmium ammonia solution obtained in Step 1.2 to it. When the pH value is adjusted to 2.7, a mixed solution of cadmium fluoride and ammonium bifluoride is obtained;

[0049] Step 2.2: Heat the mixed solution of cadmium fluoride and ammonium bifluoride obtained in Step 2.1 to 130 °C for stirring and concentration reaction. After a large amount of crystals are concentrated, filter, appropriately settle, remove the supernatant, collect the bottom precipitate for filtration, and obtain a mixture of cadmium fluoride and ammonium bifluoride.

[0050] Step 3: Dry cadmium fluoride;

[0051] Step 3.1: Put the cadmium fluoride and ammonium bifluoride crystals obtained in Step 2.2 into a platinum crucible, and perform gradient drying in an atmosphere furnace with high-purity nitrogen: first dry at 250 °C for 2 hours, then raise the temperature to 600 °C and dry for 2 hours to obtain the finished cadmium fluoride product.

[0052] Use an XRF fluorescence spectrometer to detect the cadmium fluoride finished product prepared in this example. The detection results show that the F ion content is 25.318%, the Cd ion content is 74.233%, the O ion content is 0.072%, the NH3 ion content is less than 0.0081%, the Fe ion content is less than 0.0005%, the Ca ion content is 0.0009%, and the Mg ion content is 0.0001%, meeting the requirements of cadmium fluoride for thorium-based molten salt reactors.

[0053] Example 4

[0054] The cadmium fluoride for thorium-based molten salt reactors is prepared in the following steps in this example

[0055] Step 1: Prepare cadmium ammonia solution;

[0056] Step 1.1: Take cadmium oxide with a particle size ≤ 20 μm and a content > 99%, add it to analytical pure ammonia water for dissolution. The molar ratio of cadmium to ammonia is 1:4.7. Seal and stir in a container for 2.5 hours to obtain a cadmium-ammonia solution, and let it stand for later use.

[0057] Step 1.2: Filter the cadmium-ammonia solution obtained in Step 1.1 using a filter with a filtration accuracy of 1 μm to remove trace insoluble substances. When the iron impurity content in the solution is detected to be less than 0.5 ppm, a pure cadmium-ammonia solution is obtained.

[0058] Step 2: Synthesize cadmium fluoride

[0059] Step 2.1: Take electronic-grade hydrofluoric acid with a mass fraction of 45% and add it to a tetrafluoro beaker. Add the cadmium-ammonia solution obtained in Step 1.2 to it. When the pH value is adjusted to 3, a mixed solution of cadmium fluoride and ammonium bifluoride is obtained.

[0060] Step 2.2: Heat up the mixed solution of cadmium fluoride and ammonium bifluoride obtained in Step 2.1 to 125 °C for stirring and concentration reaction. After a large amount of crystals are concentrated, filter, appropriately sediment, remove the supernatant, collect the bottom precipitate for filtration, and obtain a mixture of cadmium fluoride and ammonium bifluoride.

[0061] Step 3: Dry cadmium fluoride;

[0062] Step 3.1: Put the cadmium fluoride and ammonium bifluoride crystals obtained in Step 2.2 into a platinum crucible, and perform gradient drying in an atmosphere furnace with high-purity nitrogen: first dry at 220 °C for 2.5 hours, then raise the temperature to 600 °C and dry for 2.5 hours to obtain the finished product of cadmium fluoride.

[0063] Use an XRF fluorescence spectrometer to detect the finished product of cadmium fluoride prepared in this example. The detection results show that the F ion content is 25.326%, the Cd ion content is 74.219%, the O ion content is 0.068%, the NH3 ion content is less than 0.0076%, the Fe ion content is less than 0.0006%, the Ca ion content is 0.0008%, and the Mg ion content is 0.0002%, meeting the requirements of cadmium fluoride for thorium-based molten salt reactors.

[0064] The above four examples illustrate that the preparation method provided by the present invention is very stable, the obtained products have high repeatability, and the indicators meet the requirements.

Claims

1. Preparation method of cadmium fluoride for thorium-based molten salt reactor, characterized in that, It includes the following steps: Step 1: Prepare cadmium ammonia solution; Step 1.1: Add cadmium oxide with a particle size ≤ 20 μm and a content > 99% into excessive analytical pure ammonia water, and seal and stir to dissolve in a container to obtain cadmium ammonia solution; Step 1.2: Filter the cadmium ammonia solution to make the iron impurity content therein less than 0.5 ppm to obtain a pure cadmium ammonia solution; Step 2: Synthesize cadmium fluoride; Step 2.1: Add the cadmium ammonia solution into electronic grade hydrofluoric acid for reaction, and control the pH value of the reaction solution to be 2.5 - 3 to obtain a mixed solution of cadmium fluoride and ammonium bifluoride; Step 2.2: Heat and stir and concentrate the mixed solution of cadmium fluoride and ammonium bifluoride for reaction. After a large amount of crystals appear, filter, sediment, remove the supernatant, collect the bottom precipitate for filtration to obtain a mixed crystal of cadmium fluoride and ammonium bifluoride; Step 3: Dry cadmium fluoride; Gradient dry the mixed crystal of cadmium fluoride and ammonium bifluoride under the protection of high-purity nitrogen. First, dry at 200 - 250 °C for 2 - 3 hours, and then raise the temperature to 500 - 600 °C and dry for 2 - 3 hours to obtain the finished product of cadmium fluoride.

2. The preparation method of cadmium fluoride for a thorium-based molten salt reactor according to claim 1, characterized in that, In Step 1.1, the molar ratio of cadmium oxide to ammonia water is 1:4.5 - 5, and seal and stir to dissolve for 2 - 3 hours.

3. The preparation method of cadmium fluoride for a thorium-based molten salt reactor according to claim 1, wherein In Step 1.2, a filter with a filtration accuracy of 1 μm is used for filtration.

4. The preparation method of cadmium fluoride for a thorium-based molten salt reactor according to claim 1, characterized in that, In Step 2.1, electronic grade hydrofluoric acid with a mass fraction of 30 - 50% is used to react with the cadmium ammonia solution.

5. The preparation method of cadmium fluoride for a thorium-based molten salt reactor according to claim 1, characterized in that, In Step 2.2, the mixed solution of cadmium fluoride and ammonium bifluoride is heated to 110 - 130 °C for stirring and concentrating reaction.

6. A cadmium fluoride for a thorium-based molten salt reactor, characterized in that, It is prepared by using the method according to any one of claims 1 - 5.