Preparation method and application of alumina powder with low radioactive element content

Abstract

The invention relates to the technical field of preparation of low-radioactivity aluminum oxide, in particular to a preparation method and application of aluminum oxide powder with low radioactive element content. The alumina powder contains uranium and thorium, and the preparation method comprises the following steps: carrying out slurry mixing and grinding on metallurgical-grade alumina to obtain an alumina slurry raw material with a preset median particle size; the method comprises the following steps: carrying out a neutralization reaction on an alumina slurry raw material by using a mixed gas containing carbon dioxide to obtain a mixed reaction slurry; the pressure of the mixed gas is greater than or equal to 0.5 MPa; carrying out solid-liquid separation on the mixed reaction slurry to obtain a first aluminum oxide solid phase containing uranyl ions and thorium ions; and carrying out solid-phase replacement reaction on the first aluminum oxide by using an extraction solvent containing a silane coupling agent to obtain the low-radioactivity aluminum oxide slurry. According to the preparation method, efficient separation of uranium and thorium ions and an aluminum oxide solid phase is achieved through a neutralization reaction and a replacement reaction, and the content of radioactive elements in a final aluminum oxide powder product is 5 ppb or below.

Description

Technical Field

[0001] The present application relates to the technical field of low-radioactive alumina preparation, and in particular to a preparation method of alumina powder with low radioactive element content and its application. Background Art

[0002] Highly conductive alumina is commonly used as a thermal filler. These materials can be used to create thermal interface materials, such as sheet-type gap fillers, liquid gap fillers, phase change thermal interface materials, thermal gels, and other polymeric thermal interface materials. These materials are typically used in consumer electronics, communication base stations, and power batteries. When alumina is used as a thermally conductive material, the concentrations of uranium (U) and thorium (Th) in thermally conductive alumina can reach hundreds of parts per billion (ppb). Uranium and thorium emit alpha radiation, and the concentrations of U and Th are directly related to the intensity of these alpha radiations. The presence of these alpha radiations can interfere with normal device signal transmission, leading to operational errors and "soft errors." This phenomenon is particularly severe in highly sealed devices. To prevent these "soft errors" during device signal transmission, strict control of the radioactive elements uranium (U) and thorium (Th) in the filler is essential.

[0003] At present, the methods for treating the radioactivity of alumina are as follows: (1) dispersing alumina in an acidic solution to obtain a dispersion; then using a solvent containing a silane coupling agent to replace the dispersion to obtain a replacement reaction solution; finally subjecting the replacement reaction solution to a high-temperature drying treatment to obtain a low-radioactive alumina powder, wherein the uranium content of the low-radioactive alumina powder can be reduced from 30 ppb to less than 5 ppb; (2) soaking an aluminum-containing raw material in an acid solution to obtain a wet aluminum-containing raw material; adding the wet aluminum-containing raw material to a reactor and performing a precipitation reaction under high temperature and high pressure conditions to fully dissolve and precipitate the uranium element in the aluminum-containing raw material to obtain a treated sample; filtering the obtained treated sample to obtain a filter residue; then grinding the filter residue to a desired particle size to obtain a fine-grained sample; taking out the fine-grained sample and washing it multiple times, and then putting the washed sample into a spheroidizing device for spheroidization treatment to obtain a low-radioactive spherical alumina product; the uranium content of the low-radioactive spherical alumina product is ≤5 ppb.

[0004] However, the low-radioactive alumina produced by the above method only reduces the uranium content and does not control the thorium content. Summary of the Invention

[0005] The present application provides a method for preparing alumina powder with low radioactive element content and its application to solve the following technical problem: how to simultaneously reduce the content of uranium and thorium in alumina.

[0006] In a first aspect, embodiments of the present application provide a method for preparing alumina powder with a low radioactive element content, wherein the alumina powder contains uranium and thorium, and the preparation method comprises:

[0007] Grinding the metallurgical grade alumina to obtain an alumina slurry raw material with a preset median particle size;

[0008] Using a mixed gas containing carbon dioxide, neutralizing the alumina slurry raw material, so that the uranium forms uranyl ions and the thorium element disperses to form thorium ions, to obtain a mixed reaction slurry; wherein the pressure of the mixed gas is ≥0.5 MPa;

[0009] performing solid-liquid separation on the mixed reaction slurry to obtain a first alumina solid phase containing uranyl ions and thorium ions;

[0010] The first alumina solid phase is subjected to a replacement reaction using an extraction solvent containing a silane coupling agent to separate the uranyl ions and thorium ions, thereby obtaining a low-radioactive alumina slurry.

[0011] Optionally, the volume of the carbon dioxide is 35% to 40% of the volume of the mixed gas; and / or

[0012] The mass of the silane coupling agent is 1% to 5% of the mass of the extraction solvent.

[0013] Optionally, the neutralization reaction temperature is 35° C. to 45° C., and the neutralization reaction time is ≥ 1 h; and / or

[0014] The replacement reaction time is 0.5h to 2h.

[0015] Optionally, the silane coupling agent includes hexamethyldisilazane and / or methyltrimethoxysilane.

[0016] Optionally, the neutralization reaction is carried out in a first stirring manner, wherein the first stirring speed is ≥180 r / min; and / or

[0017] The replacement reaction is carried out in a second stirring manner, and the rotation speed of the second stirring is ≥150 r / min.

[0018] Optionally, the slurry grinding of metallurgical-grade alumina to obtain an alumina slurry raw material having a preset median particle size comprises the following steps:

[0019] Performing a first tempering on the metallurgical grade alumina to obtain a first alumina slurry;

[0020] Grinding the first alumina slurry to a preset median particle size to obtain a second alumina slurry;

[0021] The second alumina slurry is subjected to a second tempering to obtain an alumina slurry raw material.

[0022] Optionally, the preset median particle size is 5 μm to 40 μm; and / or

[0023] The mass concentration of the first alumina slurry is 300 g / L to 400 g / L; and / or

[0024] The mass concentration of the alumina slurry raw material is ≤200g / L.

[0025] Optionally, the extraction solvent containing a silane coupling agent is used to perform a replacement reaction on the first alumina solid phase to separate the uranyl ions and thorium ions to obtain a low-radioactive alumina slurry, which then includes the steps of:

[0026] performing solid-liquid separation on the low-radioactive alumina slurry to obtain a second alumina solid phase;

[0027] The second aluminum oxide solid phase is calcined to obtain aluminum oxide powder with low radioactive element content.

[0028] Optionally, the calcination temperature is ≥1250° C., and the calcination time is 2 h to 2.5 h.

[0029] In a second aspect, an embodiment of the present application provides a thermally conductive filler, which includes alumina powder obtained by the preparation method described in the first aspect.

[0030] The above technical solution provided by the embodiment of the present application has the following advantages compared with the prior art:

[0031] An embodiment of the present application provides a method for preparing alumina powder with a low radioactive element content. The preparation method can refine the particle size of metallurgical-grade alumina through slurry grinding, so that the metallurgical-grade alumina can be dispersed and form a finer-grained alumina slurry raw material to improve the efficiency of subsequent neutralization reaction and replacement reaction; then, a mixed gas containing carbon dioxide is used to neutralize the alumina slurry raw material at a pressure of 0.5 MPa or above, so that the uranium in the alumina slurry raw material forms uranyl ions and enters the liquid phase of the alumina slurry raw material; in addition, since thorium generally exists in alumina in the form of oxides or complexes, these thoriums will be fully dispersed in a high-pressure environment and form thorium ions through the action of neutralization reaction, and these thorium ions can enter the liquid phase of the alumina slurry raw material. Then, an extraction solvent containing a silane coupling agent is used to displace the uranyl and thorium ions adsorbed by the first alumina solid phase into the silane coupling agent through a displacement reaction, separating these impurity ions from the first alumina solid phase. This reduces the content of radioactive elements in the first alumina solid phase and ultimately produces a low-radioactive alumina slurry. Therefore, this preparation method first refines the particle size of metallurgical-grade alumina through slurry grinding, and then, through the combined effects of a high-pressure mixed gas containing carbon dioxide and an extraction solvent containing a silane coupling agent, ultimately achieves the simultaneous reduction of both uranium and thorium radioactive elements. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application.

[0033] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following is a brief introduction to the drawings required for use in the embodiments or the description of the prior art. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0034] Figure 1 A schematic flow chart of a method for preparing alumina powder with low radioactive element content provided in an embodiment of the present application;

[0035] Figure 2 A schematic diagram of a detailed process for preparing a main body of alumina powder with low radioactive element content provided in an application example;

[0036] Figure 3 A schematic diagram of a detailed process for preparing alumina powder with low radioactive element content provided in an embodiment of the present application. DETAILED DESCRIPTION

[0037] To make the purpose, technical solutions, and advantages of the embodiments of this application more clear, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the drawings in the embodiments of this application. Obviously, the described embodiments are part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0038] The range descriptions described in this application, such as numerical ranges, ratio ranges, etc., include all possible sub-ranges and single numerical values within the range. For example, the range description of "1 to 6" or "1~6" covers all sub-ranges from 1 to 6 (such as 1 to 3, 2 to 5, etc.) and single numbers (such as 1, 2, 3, 4, 5, 6). Unless otherwise specified, the terms "including" and "including" used in this article mean "including but not limited to"; relational terms such as "first" and "second" are only used to distinguish different entities or operations, and do not imply an actual sequence or association relationship; "and / or" means that multiple situations can exist alone or simultaneously; expressions such as "at least one", "multiple", and "at least one" refer to any combination of corresponding objects, including a combination of single or multiple objects. The proportional relationships involved in the text, such as mass ratios, molar ratios, etc., should be understood as the corresponding relationship between the first and second terms of the proportional formula in the order of description. The raw materials, reagents, instruments and equipment used in this article can be purchased on the market or prepared by existing methods.

[0039] Figure 1 The following is a schematic flow chart of a method for preparing alumina powder with low radioactive element content provided in an embodiment of the present application;

[0040] like Figure 1 As shown, the embodiment of the present application provides a method for preparing alumina powder with low radioactive element content, wherein the alumina powder contains uranium and thorium, and the preparation method comprises:

[0041] S1. The metallurgical grade alumina is slurried and ground to obtain an alumina slurry raw material having a preset median particle size;

[0042] S2. Using a mixed gas containing carbon dioxide, the alumina slurry raw material is subjected to a neutralization reaction, so that the uranium forms uranyl ions and the thorium element is dispersed to form thorium ions, to obtain a mixed reaction slurry; wherein the pressure of the mixed gas is ≥0.5 MPa;

[0043] S3. The mixed reaction slurry is subjected to solid-liquid separation to obtain a first alumina solid phase containing uranyl ions and thorium ions;

[0044] S4. Using an extraction solvent containing a silane coupling agent, the first alumina solid phase is subjected to a replacement reaction to separate the uranyl ions and thorium ions to obtain a low-radioactive alumina slurry.

[0045] It should be noted that the average median particle size of the metallurgical grade alumina is 50 μm to 100 μm.

[0046] It should be noted that the slurry grinding process can use ultrapure water as a solvent for dissolution.

[0047] It should be noted that the flow rate of the mixed gas during the neutralization reaction is 0.5m 3 / min.

[0048] It should be noted that both the neutralization reaction and the replacement reaction can be carried out under stirring conditions.

[0049] It should be noted that the present invention provides a method for preparing alumina powder with low radioactive element content. This method can achieve the simultaneous removal of radioactive elements such as uranium and thorium from metallurgical-grade alumina. The specific principle is as follows:

[0050] 1. Raw material pretreatment and particle size control:

[0051] The slurry grinding process refines metallurgical-grade alumina to the micron level, increasing the specific surface area and improving subsequent reaction efficiency. Fine particle size allows uranium and thorium compounds to be more fully exposed to the reaction interface.

[0052] 2. High-pressure CO2 neutralization reaction mechanism:

[0053] Under the mixed gas pressure condition of ≥0.5MPa, CO2 forms a carbonic acid system (H2CO3 / HCO3 - ), whose acidic environment promotes the conversion of uranium to uranyl ions (UO2 2+ ) in the form of solution.

[0054] Thorium oxide / complex is physically dispersed by mixed gas in high pressure environment and forms soluble Th through carbonic acid coordination. 4+ -Carbonate complexes.

[0055] 3. Silane coupling agent replacement separation:

[0056] The extraction solvent containing silane coupling agent can absorb UO2 adsorbed in the pores of alumina through surface tension. 2+ and Th 4+ This step can reduce the uranium content to below 5 ppb, while simultaneously achieving the same purification level for thorium.

[0057] This preparation method achieves efficient separation of uranium and thorium ions from the alumina solid phase through the neutralization reaction of the mixed gas and the displacement reaction of the silane coupling agent, and is suitable for the production of semiconductor-grade low-radioactive alumina.

[0058] In some optional embodiments, the volume of the carbon dioxide is 35% to 40% of the volume of the mixed gas; and / or

[0059] The mass of the silane coupling agent is 1% to 5% of the mass of the extraction solvent.

[0060] In these embodiments, the volume of carbon dioxide is 35% to 40% of the volume of the mixed gas, which can form a large number of carbonate molecules during the neutralization reaction. These carbonate molecules react with uranium or uranium oxide, so that uranium dissolves in the liquid phase in the form of uranyl ions. At the same time, thorium compounds can coordinate with carbonate molecules under high pressure to form soluble Th 4+ -carbonate complex, which can also be dissolved in the liquid phase, ultimately achieving the separation of uranium and thorium compounds from the alumina solid phase. In addition, a silane coupling agent with a mass of 1% to 5% of the mass of the extraction solvent can effectively separate the UO2 adsorbed in the pores of alumina. 2+ and Th 4+ Replacement to the liquid phase to further reduce the content of uranium and thorium in the alumina solid phase.

[0061] The volume of the carbon dioxide may be 35%, 36%, 37%, 38%, 39% or 40% of the volume of the mixed gas.

[0062] The mass of the silane coupling agent may be 1%, 2%, 3%, 4% or 5% of the mass of the extraction solvent.

[0063] In some optional embodiments, the temperature of the neutralization reaction is 35° C. to 45° C., and the time of the neutralization reaction is ≥ 1 h; and / or

[0064] The replacement reaction time is 0.5h to 2h.

[0065] In these embodiments, the neutralization reaction at a temperature of 35°C to 45°C and a time of ≥1 hour can promote the carbon dioxide-containing mixed gas to fully react with the liquid phase of the alumina slurry raw material to form sufficient carbonic acid molecules. These carbonic acid molecules can form uranyl ions with uranium on the one hand, and can coordinate with thorium compounds under high pressure to form soluble Th 4+ -carbonate complex, and finally achieve the separation of uranium and thorium compounds from the alumina solid phase. In addition, the replacement reaction time of 0.5h to 2h can give the silane coupling agent enough time to remove the UO2 adsorbed in the alumina pores. 2+ and Th 4+Replacement to the liquid phase to further reduce the content of uranium and thorium in the alumina solid phase.

[0066] The temperature of the neutralization reaction can be 35°C, 36°C, 37°C, 38°C, 39°C, 40°C, 41°C, 42°C, 43°C, 44°C or 45°C.

[0067] The time of the displacement reaction can be 0.5 h, 0.6 h, 0.7 h, 0.8 h, 0.9 h, 1.0 h, 1.5 h or 2.0 h.

[0068] In some optional embodiments, the silane coupling agent includes hexamethyldisilazane and / or methyltrimethoxysilane.

[0069] In these embodiments, hexamethyldisilazane or methyltrimethoxysilane is used as a silane coupling agent to effectively bind UO2 adsorbed in the pores of alumina. 2+ and Th 4+ Replacement to the liquid phase to further reduce the content of uranium and thorium in the alumina solid phase.

[0070] In some optional embodiments, the neutralization reaction is carried out in a first stirring manner, and the speed of the first stirring is ≥180 r / min; and / or

[0071] The replacement reaction is carried out in a second stirring manner, and the rotation speed of the second stirring is ≥150 r / min.

[0072] In these embodiments, the first stirring at a speed of ≥180 r / min can break up the mixed gas in the neutralization reaction into small bubbles, thereby increasing the reaction efficiency between the liquid phase of the alumina slurry raw material and carbon dioxide, and ultimately obtaining a large number of carbonic acid molecules. In addition, the second stirring at a speed of ≥150 r / min can fully mix the first alumina solid phase and the extraction solvent, so that the UO2 adsorbed in the pores of the alumina can be removed by the silane coupling agent of the extraction solvent. 2+ and Th 4+ Replacement to the liquid phase to further reduce the content of uranium and thorium in the alumina solid phase.

[0073] Figure 2 The following is a schematic diagram showing a detailed process flow of a method for preparing alumina powder with low radioactive element content provided in an embodiment of the present application;

[0074] In some optional embodiments, such as Figure 2 As shown, the method of slurry-mixing and grinding metallurgical-grade alumina to obtain an alumina slurry raw material with a preset median particle size includes the following steps:

[0075] S101. The metallurgical grade alumina is first tempered to obtain a first alumina slurry;

[0076] S102. Grinding the first alumina slurry to a predetermined median particle size to obtain a second alumina slurry;

[0077] S103. Perform a second tempering on the second alumina slurry to obtain an alumina slurry raw material.

[0078] In these embodiments, the metallurgical-grade alumina is first subjected to a first tempering process, so that the alumina can form a first alumina slurry, which is convenient for subsequent wet grinding. The morphology of the alumina can be improved by grinding to obtain a second alumina slurry with a preset median particle size. At the same time, it is also convenient to finally obtain an alumina powder product with a uniform morphology distribution; finally, the second alumina slurry is diluted by a second tempering process to facilitate the subsequent neutralization reaction.

[0079] In some optional embodiments, the preset median particle size is 5 μm to 40 μm; and / or

[0080] The mass concentration of the first alumina slurry is 300 g / L to 400 g / L; and / or

[0081] The mass concentration of the alumina slurry raw material is ≤200g / L.

[0082] In these embodiments, a preset median particle size of 5 μm to 40 μm allows the particles of the alumina slurry raw material to be in the micron range. These micron-sized particles can increase the specific surface area of the alumina slurry raw material, thereby improving the efficiency of subsequent reactions. Furthermore, fine particle size allows the uranium and thorium compounds to be more fully exposed to the reaction interface. Furthermore, a first alumina slurry with a mass concentration of 300 g / L to 400 g / L facilitates subsequent grinding to ultimately obtain a second alumina slurry with a preset median particle size. Furthermore, a mass concentration of ≤200 g / L of the alumina slurry raw material facilitates the subsequent neutralization reaction, ultimately achieving the separation of the uranium and thorium compounds from the alumina solid phase.

[0083] The predetermined median particle size may be 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm or 40 μm.

[0084] The mass concentration of the first alumina slurry may be 300 g / L, 310 g / L, 320 g / L, 330 g / L, 340 g / L, 350 g / L, 360 g / L, 370 g / L, 380 g / L, 390 g / L, or 400 g / L.

[0085] The mass concentration of the alumina slurry raw material is 150g / L, 160g / L, 170g / L, 180g / L, 190g / L or 200g / L.

[0086] Figure 3 The following is a schematic diagram showing a detailed process of a method for preparing alumina powder with low radioactive element content provided in an embodiment of the present application;

[0087] In some optional embodiments, such as Figure 3 As shown, the extraction solvent containing a silane coupling agent is used to perform a replacement reaction on the first alumina solid phase to separate the uranyl ions and thorium ions to obtain a low-radioactive alumina slurry, which then includes the steps of:

[0088] S5. The low-radioactive alumina slurry is subjected to solid-liquid separation to obtain a second alumina solid phase;

[0089] S6. calcining the second alumina solid phase to obtain alumina powder with low radioactive element content.

[0090] In these embodiments, the obtained low-radioactive alumina slurry is subjected to solid-liquid separation, and the obtained second alumina solid phase is then calcined to remove moisture from the second alumina solid phase and transform the second alumina solid phase into an α phase, ultimately obtaining alumina powder with a low radioactive element content that meets the requirements.

[0091] In some optional embodiments, the calcination temperature is ≥1250° C., and the calcination time is 2 h to 2.5 h.

[0092] In these embodiments, calcination at a temperature of ≥1250° C. and for a time of 2 h to 2.5 h can promote sufficient phase transformation of the second alumina solid phase, so as to ultimately obtain an alumina powder product with uniform morphology.

[0093] The calcination temperature may be 1250°C, 1260°C, 1270°C, 1280°C, 1290°C or 1300°C.

[0094] The calcination time may be 2 h, 2.1 h, 2.2 h, 2.3 h, 2.4 h or 2.5 h.

[0095] The present application is further described below with reference to specific examples. Experimental methods in the following examples where specific conditions are not specified are generally measured in accordance with national / industry standards. If there are no corresponding national / industry standards, the methods are carried out in accordance with commonly used international standards, conventional conditions, or conditions recommended by the manufacturer.

[0096] Example 1

[0097] like Figure 2 and Figure 3 A method for preparing alumina powder with low radioactive element content, wherein the alumina powder contains uranium and thorium, comprises:

[0098] S101. Using deionized water, 500 g of metallurgical-grade alumina having an average median particle size of about 75 μm is first tempered to obtain a first alumina slurry;

[0099] S102. Grinding the first alumina slurry to a predetermined median particle size using a sand mill to obtain a second alumina slurry;

[0100] S103. The second alumina slurry is subjected to a second tempering process using deionized water to obtain an alumina slurry raw material;

[0101] S2. A mixed gas containing carbon dioxide is used to neutralize the alumina slurry raw material, so that uranium forms uranyl ions and thorium elements are dispersed to form thorium ions to obtain a mixed reaction slurry; wherein the pressure of the mixed gas is 0.5 MPa;

[0102] S3. The mixed reaction slurry is subjected to solid-liquid separation to obtain a first alumina solid phase containing uranyl ions and thorium ions;

[0103] S4. Using an extraction solvent containing a silane coupling agent, the first alumina solid phase is subjected to a replacement reaction to separate the uranyl ions and thorium ions to obtain a low-radioactive alumina slurry;

[0104] S5. The low-radioactive alumina slurry is subjected to solid-liquid separation to obtain a second alumina solid phase;

[0105] S6. calcining the second alumina solid phase to obtain alumina powder with low radioactive element content.

[0106] The volume of carbon dioxide is 35% of the volume of the mixed gas;

[0107] The mass of the silane coupling agent is 2% of the mass of the extraction solvent.

[0108] The temperature of the neutralization reaction is 40°C, and the neutralization reaction time is 1 h;

[0109] The replacement reaction time is 1.0 h.

[0110] The silane coupling agent is hexamethyldisilazane.

[0111] The neutralization reaction was carried out in a first stirring mode, and the speed of the first stirring was 180 r / min;

[0112] The replacement reaction was carried out in a second stirring mode, and the rotation speed of the second stirring was 150 r / min.

[0113] The preset median particle size is 40 μm;

[0114] The mass concentration of the first alumina slurry is 300 g / L;

[0115] The mass concentration of the alumina slurry raw material is 200 g / L.

[0116] The calcination temperature is 1250°C and the calcination time is 2 h.

[0117] Example 2

[0118] Compared with Example 1, this embodiment has the following differences, and the rest are the same:

[0119] The volume of carbon dioxide is 37% of the volume of the mixed gas;

[0120] The mass of the silane coupling agent is 3% of the mass of the extraction solvent.

[0121] The temperature of the neutralization reaction is 35°C, and the neutralization reaction time is 1 h;

[0122] The replacement reaction time is 0.5 h.

[0123] The preset median particle size is 20 μm.

[0124] Example 3

[0125] Compared with Example 1, this embodiment has the following differences, and the rest are the same:

[0126] The volume of carbon dioxide is 40% of the volume of the mixed gas;

[0127] The mass of the silane coupling agent is 5% of the mass of the extraction solvent.

[0128] The temperature of the neutralization reaction is 45°C, and the neutralization reaction time is 1 h;

[0129] The replacement reaction time is 2 h.

[0130] The preset median particle size is 5 μm.

[0131] Comparative Example 1

[0132] Compared with Example 1, the differences of this comparative example are as follows, and the rest are the same:

[0133] Low-radioactive alumina powder was prepared using the prior art (1) in the background technology. The specific process is as follows:

[0134] Step 1: calcining aluminum hydroxide with a surface uranium content of ≤30 ppb in a calcination device to obtain aluminum oxide powder.

[0135] Step 2: prepare an acidic solution with a pH value less than 4, then immerse the alumina powder in the acidic solution and perform a uniform dispersion treatment for 0.5 to 2 hours.

[0136] Step 3: Separate the dispersed powder from the acidic solution, then place it in a solvent containing a silane coupling agent and perform solvent replacement for 0.5 to 6 hours.

[0137] Step 4: Separate the powder after solvent replacement, and then dry the powder at 100-120° C. for 2-6 hours to obtain low-radioactive alumina powder with a surface uranium content of ≤5 ppb.

[0138] Comparative Example 2

[0139] Compared with Example 1, the differences of this comparative example are as follows, and the rest are the same:

[0140] The pressure of the mixed gas is 0.2 MPa.

[0141] Comparative Example 3

[0142] Compared with Example 1, the differences of this comparative example are as follows, and the rest are the same:

[0143] The volume of carbon dioxide is 30% of the volume of the mixed gas.

[0144] Comparative Example 4

[0145] Compared with Example 1, the differences of this comparative example are as follows, and the rest are the same:

[0146] The volume of carbon dioxide is 50% of the volume of the mixed gas.

[0147] Comparative Example 5

[0148] Compared with Example 1, the differences of this comparative example are as follows, and the rest are the same:

[0149] The mass of the silane coupling agent is 3% of the mass of the extraction solvent.

[0150] Comparative Example 6

[0151] Compared with Example 1, the differences of this comparative example are as follows, and the rest are the same:

[0152] The mass of the silane coupling agent is 5% of the mass of the extraction solvent.

[0153] Comparative Example 7

[0154] Compared with Example 1, the differences of this comparative example are as follows, and the rest are the same:

[0155] The temperature of the neutralization reaction was 30°C.

[0156] Comparative Example 8

[0157] Compared with Example 1, the differences of this comparative example are as follows, and the rest are the same:

[0158] The temperature of the neutralization reaction was 60°C.

[0159] Related experiments and effect data:

[0160] Alumina powder samples obtained in each embodiment and comparative example were collected, and then the uranium and thorium contents on the surface of these samples were tested using GD-MS glow discharge mass spectrometry. The specific testing method was as follows: the alumina powder samples were pressed into sheet samples of uniform thickness, and then these sheet samples were directly placed in a GD-MS glow discharge mass spectrometer for direct detection of uranium and thorium. The results are shown in Table 1.

[0161] Table 1 Distribution of uranium and thorium contents in the alumina powders obtained in the examples and comparative examples

[0162]

[0163]

[0164] As can be seen from Table 1, the embodiment of the present application provides a method for preparing alumina powder with a low content of radioactive elements. This preparation method achieves efficient separation of uranium and thorium ions from the alumina solid phase through a neutralization reaction of a mixed gas and a displacement reaction of a silane coupling agent, so that the content of radioactive elements such as uranium and thorium in the final alumina powder product is below 5 ppb.

[0165] Compared with Example 1, Comparative Example 1 uses traditional low-radioactive alumina preparation technology. Although its uranium content can be controlled below 5 ppb, the thorium content is as high as 124 ppb.

[0166] Compared with Example 1, Comparative Example 2 uses a mixed gas with a lower pressure, which makes it difficult for the mixed gas to break up the partially agglomerated alumina slurry raw materials, resulting in a large amount of residual radioactive elements such as uranium and thorium.

[0167] Compared to Example 1, Comparative Example 3 used less carbon dioxide gas, resulting in a lower content of carbonic acid molecules during the neutralization reaction, making it difficult to separate the uranium and thorium compounds from the alumina solid phase, resulting in a large amount of residual radioactive elements such as uranium and thorium. Comparative Example 4 used more carbon dioxide, resulting in an excessive content of carbonic acid molecules during the neutralization reaction, which consumed some alumina and affected the final alumina yield.

[0168] Compared with Example 1, Comparative Example 5 uses less silane coupling agent, which makes it difficult for the extraction solvent to remove the UO2 adsorbed in the pores of alumina. 2+ and Th 4+ The replacement to the liquid phase results in a large amount of radioactive elements such as uranium and thorium remaining in the alumina powder. Comparative Example 6 uses a large amount of silane coupling agent, which increases the cost of the replacement reaction and also affects the purity of the final alumina powder.

[0169] Compared to Example 1, Comparative Example 7 used a lower neutralization reaction temperature, which prevented the carbonic acid molecules from reacting fully with the uranium and thorium compounds, resulting in some residual radioactive elements such as uranium and thorium in the alumina. Comparative Example 8 used a higher neutralization reaction temperature, which caused the carbonic acid molecules to decompose due to the heat, resulting in a large amount of residual radioactive elements such as uranium and thorium.

[0170] In summary, the embodiments of the present application provide a method for preparing alumina powder with low radioactive element content, which can achieve the simultaneous removal of radioactive elements such as uranium and thorium in metallurgical-grade alumina, and the uranium and thorium contents of the final alumina powder are reduced to below 5 ppb.

[0171] In addition, an embodiment of the present application provides a method for preparing alumina powder with a low content of radioactive elements. The preparation method uses carbonate molecules formed by carbon dioxide to preliminarily remove uranium and thorium from alumina, which can reduce the consumption of strong acid or special weak acid to reduce production costs, and can also reduce the harm of these acids to the environment and personnel.

[0172] In addition, an embodiment of the present application provides a method for preparing alumina powder with low radioactive element content. The neutralization reaction and replacement reaction of this preparation method have little effect on the particle size and morphology of alumina, and can obtain an alumina powder product that meets usage requirements and has low radioactive elements. It is suitable for the production of semiconductor-grade low-radioactive alumina, and can also provide technical support for the alumina thermal conductive material industry.

[0173] The foregoing is merely a detailed description of the present invention, intended to enable those skilled in the art to understand or implement the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein, but rather is intended to conform to the broadest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for preparing alumina powder with low radioactive element content, wherein the alumina powder contains uranium and thorium, the preparation method comprising: Grinding the metallurgical grade alumina to obtain an alumina slurry raw material with a preset median particle size; Using a mixed gas containing carbon dioxide, neutralizing the alumina slurry raw material, so that the uranium forms uranyl ions and the thorium element disperses to form thorium ions, to obtain a mixed reaction slurry; wherein the pressure of the mixed gas is ≥0.5 MPa; performing solid-liquid separation on the mixed reaction slurry to obtain a first alumina solid phase containing uranyl ions and thorium ions; The first alumina solid phase is subjected to a replacement reaction using an extraction solvent containing a silane coupling agent to separate the uranyl ions and thorium ions, thereby obtaining a low-radioactive alumina slurry.

2. The preparation method according to claim 1, characterized in that The volume of the carbon dioxide is 35% to 40% of the volume of the mixed gas; and / or The mass of the silane coupling agent is 1% to 5% of the mass of the extraction solvent.

3. The preparation method according to claim 1, characterized in that The neutralization reaction temperature is 35°C to 45°C, and the neutralization reaction time is ≥ 1h; and / or The replacement reaction time is 0.5h to 2h.

4. The preparation method according to claim 1, characterized in that The silane coupling agent includes hexamethyldisilazane and / or methyltrimethoxysilane.

5. The preparation method according to claim 1, characterized in that The neutralization reaction is carried out in a first stirring manner, wherein the first stirring speed is ≥180 r / min; and / or The replacement reaction is carried out in a second stirring manner, and the rotation speed of the second stirring is ≥150 r / min.

6. The preparation method according to claim 1, characterized in that The method of slurry-mixing and grinding metallurgical-grade alumina to obtain an alumina slurry raw material having a preset median particle size comprises the following steps: Performing a first tempering on the metallurgical grade alumina to obtain a first alumina slurry; Grinding the first alumina slurry to a preset median particle size to obtain a second alumina slurry; The second alumina slurry is subjected to a second tempering to obtain an alumina slurry raw material.

7. The preparation method according to claim 6, characterized in that The preset median particle size is 5 μm to 40 μm; and / or The mass concentration of the first alumina slurry is 300 g / L to 400 g / L; and / or The mass concentration of the alumina slurry raw material is ≤200g / L.

8. The preparation method according to claim 6, characterized in that The method uses an extraction solvent containing a silane coupling agent to perform a replacement reaction on the first alumina solid phase to separate the uranyl ions and thorium ions to obtain a low-radioactive alumina slurry, and then includes the following steps: performing solid-liquid separation on the low-radioactive alumina slurry to obtain a second alumina solid phase; The second aluminum oxide solid phase is calcined to obtain aluminum oxide powder with low radioactive element content.

9. The preparation method according to claim 8, characterized in that The calcination temperature is ≥1250° C., and the calcination time is 2 h to 2.5 h.

10. A thermally conductive filler, comprising alumina powder obtained by the preparation method according to any one of claims 1 to 9.

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