Low-alpha-ray aluminum oxide and preparation method thereof

Abstract

The invention relates to low-alpha-ray aluminum oxide and a preparation method thereof, and belongs to the technical field of aluminum oxide powder preparation. Raw materials of the low-alpha-ray aluminum oxide comprise a sodium aluminate solution, the sodium aluminate solution contains thorium and uranium, and the method comprises the following steps: carrying out a first decomposition reaction on the sodium aluminate solution by using a first aluminum hydroxide seed crystal to obtain a first decomposition solution; carrying out solid-liquid separation on the first decomposition solution to obtain a liquid-phase substance; performing a second decomposition reaction on the liquid-phase substance by using a second aluminum hydroxide seed crystal to obtain aluminum hydroxide; dissolving aluminum hydroxide with sulfuric acid to obtain an aluminum sulfate solution; performing chemical reaction on the aluminum sulfate solution and ammonium sulfate to obtain aluminum ammonium sulfate; re-crystallizing the aluminum ammonium sulfate for multiple times to obtain high-purity aluminum ammonium sulfate; and roasting the high-purity aluminum ammonium sulfate to obtain the low-alpha-ray aluminum oxide. The purity of the low-alpha-ray aluminum oxide is greater than or equal to 99.99%, the thorium content is less than or equal to 5ppb, the uranium content is less than or equal to 5ppb, and the median particle size is adjustable in a range of 1-50 microns.

Description

Technical Field

[0001] The present application relates to the technical field of alumina powder preparation, and in particular to a low α-ray alumina and a preparation method thereof. Background Art

[0002] Low α-ray alumina is an aluminum oxide material containing low radioactive elements, and is often used as a raw material for thermally conductive packaging fillers. This thermally conductive packaging filler has the advantages of low radioactive elements uranium (U) and thorium (Th), high thermal conductivity, excellent insulation, and adjustable particle size distribution. It is widely used in high-storage, high-performance or special-purpose chip packaging fields, and is particularly effective in preventing memory device failures caused by α-rays.

[0003] At present, the method for preparing low α-ray alumina has problems such as high requirements for raw material purity, safety risks in the processing process, stringent requirements for equipment, and unstable control of impurity element content. Summary of the invention

[0004] The present application provides a low α-ray alumina and a preparation method thereof to solve the following technical problem: how to improve the purity of the low α-ray alumina.

[0005] In a first aspect, the present application provides a method for preparing low-alpha-ray alumina, wherein the raw material of the low-alpha-ray alumina comprises a sodium aluminate solution, wherein the sodium aluminate solution contains radioactive elements thorium and uranium, and the method comprises:

[0006] Using a first aluminum hydroxide seed crystal to perform a first decomposition reaction on the sodium aluminate solution to obtain a first decomposed solution;

[0007] Performing solid-liquid separation on the first decomposition solution to obtain a liquid phase substance;

[0008] Using a second aluminum hydroxide seed crystal to perform a second decomposition reaction on the liquid phase material to obtain aluminum hydroxide having a set thorium content and a set uranium content;

[0009] Dissolving the aluminum hydroxide having a set thorium content and a set uranium content using sulfuric acid to obtain an aluminum sulfate solution;

[0010] The aluminum sulfate solution is chemically reacted with ammonium sulfate to obtain ammonium aluminum sulfate;

[0011] Recrystallizing the ammonium aluminum sulfate multiple times to obtain high-purity ammonium aluminum sulfate;

[0012] The high-purity ammonium aluminum sulfate is roasted to obtain low-alpha-ray alumina.

[0013] Optionally, the thorium content is set to ≤20ppb; and / or,

[0014] The uranium content is set to be ≤20ppb.

[0015] Optionally, the temperature of the first decomposition reaction is 30° C. to 45° C.; and / or,

[0016] The weight of the first aluminum hydroxide seed crystals is 1.5% to 5% of the weight of aluminum oxide in the sodium aluminate solution.

[0017] Optionally, the temperature of the second decomposition reaction is 50° C. to 80° C.; and / or,

[0018] The weight of the second aluminum hydroxide seed crystals is 0.5% to 1.5% of the weight of aluminum oxide in the liquid phase material.

[0019] Optionally, the recrystallization temperature is 10°C to 40°C.

[0020] Optionally, the purity of the high-purity ammonium aluminum sulfate is >99.99%.

[0021] Optionally, the calcination temperature is 1200°C to 1350°C.

[0022] Optionally, the particle size of the first aluminum hydroxide seed crystal is 0.2 μm to 1.5 μm; and / or,

[0023] The particle size of the second aluminum hydroxide seed crystals is 1.5 μm to 4 μm.

[0024] Optionally, the low α-ray alumina meets the following indicators: purity ≥ 99.99%, thorium content ≤ 5 ppb, uranium content ≤ 5 ppb, and median particle size adjustable from 1 μm to 50 μm.

[0025] In a second aspect, the present application provides a low α-ray alumina, which is prepared by any method described in the first aspect.

[0026] The above technical solution provided by the embodiment of the present application has the following advantages compared with the prior art:

[0027] The preparation method of the low α-ray alumina provided in an embodiment of the present application comprises a raw material of the low α-ray alumina comprising a sodium aluminate solution, wherein the sodium aluminate solution contains radioactive elements thorium and uranium, and the method comprises: using a first aluminum hydroxide seed to perform a first decomposition reaction on the sodium aluminate solution to obtain a first decomposition solution; performing solid-liquid separation on the first decomposition solution to obtain a liquid phase substance; using a second aluminum hydroxide seed to perform a second decomposition reaction on the liquid phase substance to obtain aluminum hydroxide having a set thorium content and a set uranium content; using sulfuric acid to dissolve the aluminum hydroxide having a set thorium content and a set uranium content to obtain an aluminum sulfate solution; chemically reacting the aluminum sulfate solution with ammonium sulfate to obtain ammonium aluminum sulfate; recrystallizing the ammonium aluminum sulfate multiple times to obtain high-purity ammonium aluminum sulfate; and roasting the high-purity ammonium aluminum sulfate to obtain low α-ray alumina. The aluminum hydroxide seed promotes the decomposition of the sodium aluminate solution into aluminum hydroxide. The crystal structure and surface properties of the aluminum hydroxide seed will guide the newly generated aluminum hydroxide to grow in a specific direction and form. As the sodium aluminate solution is first decomposed, impurities such as Th and U are adsorbed in the precipitate during the process of generating nano-scale particle precipitation; the first decomposed solution is subjected to solid-liquid separation to separate the solid phase material containing more impurities; the second aluminum hydroxide seed causes the liquid phase material to undergo a second decomposition reaction to further reduce the content of impurities such as Th and U in the liquid phase material, and adjust the particle size distribution of the second decomposition reaction product, thereby obtaining aluminum hydroxide with a set thorium content and a set uranium content; sulfuric acid is used to dissolve the aluminum hydroxide with a set thorium content and a set uranium content, and the obtained aluminum sulfate solution reacts chemically with ammonium sulfate to generate ammonium aluminum sulfate; the ammonium aluminum sulfate is recrystallized multiple times to achieve a high degree of purification of the ammonium aluminum sulfate, thereby obtaining high-purity ammonium aluminum sulfate; finally, the high-purity ammonium aluminum sulfate is roasted to obtain low-α-ray alumina. Therefore, aluminum hydroxide seeds are used to promote the step-by-step decomposition of the sodium aluminate solution to preliminarily obtain aluminum hydroxide with low Th and U contents; multiple recrystallizations of ammonium aluminum sulfate are performed to further reduce Th, U and other impurities in the ammonium aluminum sulfate, and then high-purity low-α-ray alumina is obtained by roasting. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] 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.

[0029] 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 paying any creative labor.

[0030] Figure 1A schematic flow chart of a method for preparing low α-ray alumina provided in an embodiment of the present application;

[0031] Figure 2 A practical simplified process diagram of a method for preparing low α-ray alumina provided in an embodiment of the present application;

[0032] Figure 3 A particle size distribution diagram of low α-ray alumina provided in Example 1 of the present application;

[0033] Figure 4 A particle size distribution diagram of low α-ray alumina provided in Example 2 of the present application;

[0034] Figure 5 A particle size distribution diagram of low α-ray alumina provided in Example 3 of the present application;

[0035] Figure 6 A particle size distribution diagram of a low α-ray alumina provided in Comparative Example 1 of the present application;

[0036] Figure 7 A particle size distribution diagram of low α-ray alumina provided in Comparative Example 2 of the present application;

[0037] Figure 8 A particle size distribution diagram of low α-ray alumina provided for Comparative Example 3 of the present application. DETAILED DESCRIPTION

[0038] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0039] Various embodiments of the present application may be presented in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity, and should not be understood as a rigid limitation on the scope of the present application; therefore, the range description should be considered to have specifically disclosed all possible sub-ranges and single numerical values ​​within the range. For example, the range description from 1 to 6 should be considered to have specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers within the range, such as 1, 2, 3, 4, 5 and 6, which apply regardless of the range. In addition, whenever a numerical range is indicated herein, it is meant to include any cited number (fractional or integer) within the indicated range.

[0040] In the present application, unless otherwise stated, the directional words used, such as "upper" and "lower", refer specifically to the directions of the drawings in the accompanying drawings. In addition, in the description of the present specification, the terms "include", "comprise", etc., refer to "including but not limited to". In this article, relational terms such as "first" and "second", etc., are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. In this article, "and / or" describes the association relationship of associated objects, indicating that three relationships may exist, for example, A and / or B, which can represent: A exists alone, A and B exist at the same time, and B exists alone. Wherein A and B can be singular or plural. Unless otherwise specified, the various raw materials, reagents, instruments and equipment used in this application can be purchased on the market or prepared by existing methods.

[0041] In a first aspect, the present application provides a method for preparing low-alpha-ray alumina, wherein the raw material of the low-alpha-ray alumina comprises a sodium aluminate solution, wherein the sodium aluminate solution contains radioactive elements thorium and uranium, Figure 1 A schematic diagram of a process for preparing a low α-ray alumina provided in an embodiment of the present application; see Figure 1 , the method comprising:

[0042] S1, using a first aluminum hydroxide seed crystal to perform a first decomposition reaction on the sodium aluminate solution to obtain a first decomposed solution;

[0043] S2, performing solid-liquid separation on the first decomposition solution to obtain a liquid phase substance;

[0044] S3, using a second aluminum hydroxide seed crystal to perform a second decomposition reaction on the liquid phase material to obtain aluminum hydroxide having a set thorium content and a set uranium content;

[0045] In an embodiment of the present application, the two-step decomposition reaction (the first decomposition reaction and the second decomposition reaction) of the above-mentioned sodium aluminate solution is achieved by a seed separation method. The seed separation method (seed separation decomposition method) is a method of using seed crystals to induce the crystallization of solutes in a solution. The core is to add seed crystals to a supersaturated solution so that the solute crystallizes with the seed crystals as the core, thereby achieving the purpose of separating and purifying the solute. During the decomposition of the sodium aluminate solution, the aluminum hydroxide seed crystals provide the starting core for the crystallization process. The aluminum hydroxide seed crystals promote the decomposition of the sodium aluminate solution into aluminum hydroxide. The crystal structure and surface properties of the aluminum hydroxide seed crystals will guide the newly generated aluminum hydroxide to grow in a specific direction and morphology. As the sodium aluminate solution is first decomposed, impurities such as Th and U are adsorbed in the precipitate during the generation of nano-scale particle precipitation. The first decomposed solution is subjected to solid-liquid separation to separate the solid phase material containing more impurities to obtain a liquid phase material.

[0046] The use of the second aluminum hydroxide seed to carry out the second decomposition reaction on the liquid phase material has many effects. On the one hand, it further promotes the aluminate ions in the liquid phase to continue to be converted into aluminum hydroxide, thereby increasing the yield of the target product; on the other hand, more importantly, it can further reduce the content of impurities such as Th and U in the liquid phase material. Because with the new aluminum hydroxide generation and crystallization process, impurities will be redistributed between the solution and the crystals, and some impurities may remain in the solution without participating in the crystallization, thereby further reducing the impurity content. At the same time, this step can also adjust the particle size distribution of the second decomposition reaction product, so that the final aluminum hydroxide is more in line with the subsequent process requirements in terms of particle size.

[0047] In some embodiments, the temperature of the first decomposition reaction is 30°C to 45°C; and / or,

[0048] The weight of the first aluminum hydroxide seed crystals is 1.5% to 5% of the weight of aluminum oxide in the sodium aluminate solution.

[0049] In an embodiment of the present application, the temperature of the first decomposition reaction can be 30°C to 45°C, which can regulate the decomposition rate of the sodium aluminate solution, thereby ensuring that more impurities such as Th and U are attached or wrapped in the process of rapid crystallization of aluminum hydroxide, so as to precipitate out, thereby achieving effective impurity removal of the sodium aluminate solution. Exemplarily, the temperature of the first decomposition reaction can be 30°C, 31°C, 32°C, 33°C, 34°C, 35°C, 36°C, 37°C, 38°C, 39°C, 40°C, 41°C, 42°C, 43°C, 44°C, 45°C, etc. The weight of the first aluminum hydroxide seed can be 1.5% to 5% of the weight of aluminum oxide in the sodium aluminate solution. An appropriate amount of sodium aluminate solution seed can attach or wrap more impurities such as Th and U in the process of rapid crystallization growth of aluminum hydroxide, so as to precipitate out, thereby achieving effective impurity removal of the sodium aluminate solution. Illustratively, the weight of the first aluminum hydroxide seed crystals can be 1.5%, 2.0%, 2.3%, 2.5%, 2.8%, 3.0%, 3.3%, 3.5%, 3.8%, 4.0%, 4.3%, 4.5%, 4.8%, 5.0%, etc., of the weight of aluminum oxide in the sodium aluminate solution.

[0050] In some embodiments, the temperature of the second decomposition reaction is 50°C to 80°C; and / or,

[0051] The weight of the second aluminum hydroxide seed crystals is 0.5% to 1.5% of the weight of aluminum oxide in the liquid phase material.

[0052] In an embodiment of the present application, the temperature of the second decomposition reaction can be 50°C to 80°C, which can effectively regulate the decomposition rate of the second decomposition reaction, further reduce the content of impurities such as Th and U in the liquid phase material, and make the particle size of the second decomposition reaction product aluminum hydroxide uniformly distributed, and the crystal form and morphology are complete. Exemplarily, the temperature of the second decomposition reaction can be 50°C, 53°C, 55°C, 58°C, 60°C, 63°C, 65°C, 68°C, 70°C, 73°C, 75°C, 78°C, 80°C, etc. The weight of the second aluminum hydroxide seed can be 0.5% to 1.5% of the weight of aluminum oxide in the liquid phase material, which can effectively reduce the content of impurities such as Th and U in the liquid phase material, and make the particle size of the second decomposition reaction product aluminum hydroxide uniformly distributed, and the crystal form and morphology are complete, which has a synergistic effect with the second decomposition temperature. Exemplarily, the weight of the second aluminum hydroxide seed crystals can be 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, etc. of the weight of aluminum oxide in the liquid phase. Generally speaking, the second decomposed solution obtained after the second decomposition reaction is subjected to solid-liquid separation to obtain aluminum hydroxide with a set thorium content and a set uranium content.

[0053] In some embodiments, the particle size of the first aluminum hydroxide seed crystal is 0.2 μm to 1.5 μm; and / or,

[0054] The particle size of the second aluminum hydroxide seed crystals is 1.5 μm to 4 μm.

[0055] In the embodiment of the present application, the particle size of the first aluminum hydroxide seed can be 0.2-1.5 μm, which can make the aluminum hydroxide seed highly active, make the efficiency of the first reaction decomposition reaction high, the crystal form and morphology complete, and the particle size distribution uniform. Exemplarily, the particle size of the first aluminum hydroxide seed can be 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1.0 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, etc. The particle size of the second aluminum hydroxide seed can be 1.5-4 μm, which can reduce the rate of the second decomposition reaction, accurately control the decomposition process, and improve the purity of the material. Illustratively, the particle size of the second aluminum hydroxide seed crystals can be 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, 2.0 μm, 2.1 μm, 2.2 μm, 2.3 μm, 2.4 μm, 2.5 μm, etc.

[0056] In addition, the above-mentioned sodium aluminate solution is obtained in the following manner: the aluminum hydroxide raw material is redissolved by ion membrane liquid alkali (NaOH content is 32±2%); the aluminum hydroxide raw material can be conventional aluminum hydroxide HP-999SP (purity greater than 99%, main impurity element content: Ca≤10ppm, Fe≤10ppm, Na≤1000ppm, Si≤10ppm, Th≤200ppb, U≤200ppb, etc.) produced by Chalco Shandong Co., Ltd. or aluminum hydroxide with a purity ≥99% sold on the market.

[0057] In some embodiments, the set thorium content is ≤20 ppb; and / or,

[0058] The uranium content is set to be ≤20ppb.

[0059] In an embodiment of the present application, after the above-mentioned second decomposition reaction, the thorium content in aluminum hydroxide can be 20ppb, 19ppb, 18ppb, 17ppb, 16ppb, 15ppb, 14ppb, etc.; the uranium content can be 20ppb, 19ppb, 18ppb, 17ppb, 16ppb, 15ppb, 14ppb, etc.

[0060] S4, using sulfuric acid to dissolve the aluminum hydroxide having a set thorium content and a set uranium content to obtain an aluminum sulfate solution;

[0061] S5, chemically reacting the aluminum sulfate solution with ammonium sulfate to obtain ammonium aluminum sulfate;

[0062] In some embodiments, the recrystallization temperature is 10°C to 40°C.

[0063] In some embodiments, the purity of the high-purity ammonium aluminum sulfate is >99.99%.

[0064] In the present application embodiment, aluminum hydroxide with a set thorium content and a set uranium content is dissolved using sulfuric acid, and the obtained aluminum sulfate solution reacts chemically with ammonium sulfate to generate ammonium aluminum sulfate. Recrystallization of ammonium aluminum sulfate multiple times is a key link in the depth purification of the entire process. The principle of recrystallization is based on the difference in solubility of impurities and ammonium aluminum sulfate at different temperatures. In each recrystallization process, operations such as heating for dissolution and cooling crystallization are performed to make ammonium aluminum sulfate preferentially crystallize out, while impurities are more retained in the mother liquor. With the increase of the number of recrystallizations, the content of impurities (including Th, U and other possible trace impurities) in the product ammonium aluminum sulfate will continue to decrease, and finally achieve a high degree of purification of ammonium aluminum sulfate to obtain high-purity ammonium aluminum sulfate. Exemplary, the purity of the high-purity ammonium aluminum sulfate can be 99.991%, 99.992%, 99.993%, 99.994%, etc., wherein Fe content ≤3ppm, Ca content ≤5ppm. The temperature of recrystallization can be 10°C to 40°C. The solubility of ammonium aluminum sulfate is relatively low, which is conducive to the slow and uniform growth of ammonium aluminum sulfate crystals and the removal of impurities such as Th and U. By recrystallizing ammonium aluminum sulfate multiple times, the high purity of ammonium aluminum sulfate is achieved. Exemplarily, the temperature of the recrystallization can be 10°C, 13°C, 15°C, 17°C, 20°C, 23°C, 25°C, 28°C, 30°C, 33°C, 35°C, 38°C, 40°C, etc.

[0065] S6, recrystallizing the ammonium aluminum sulfate multiple times to obtain high-purity ammonium aluminum sulfate;

[0066] S7, roasting the high-purity ammonium aluminum sulfate to obtain low-α-ray alumina.

[0067] In some embodiments, the calcination temperature is 1200°C to 1350°C.

[0068] In the embodiment of the present application, the calcination temperature can be 1200°C to 1350°C, so that the high-purity ammonium aluminum sulfate is fully converted into low-α-ray alumina, and the low-α-ray alumina has excellent performance and high purity. Exemplarily, the calcination temperature can be 1200°C, 1220°C, 1240°C, 1260°C, 1280°C, 1300°C, 1320°C, 1340°C, 1350°C, etc. The low-α-ray alumina obtained after calcination can be successively ground, crushed and classified, and sieved into low-α-ray alumina with three adjustable particle size ranges within D50=1μm~50μm, wherein the particle size distribution can be: D50=2μm~5μm, D90<10μm; D50=6μm~10μm, D90<20μm; D50=20μm~25μm, D90<45μm.

[0069] In some embodiments, the low α-ray alumina meets the following indicators: purity ≥ 99.99%, thorium content ≤ 5 ppb, uranium content ≤ 5 ppb, and median particle size adjustable from 1 μm to 50 μm.

[0070] In the embodiments of the present application, through the above-mentioned preparation method of low α-ray alumina, it is possible to achieve high purity, low radioactive elements and controllable particle size distribution of low α-ray alumina.

[0071] In summary, by promoting the step-by-step decomposition of sodium aluminate solution with aluminum hydroxide seeds, the goal of reducing the Th and U impurity content was initially achieved in the early stage, laying the foundation for subsequent purification. Then, with the help of multiple recrystallizations of ammonium aluminum sulfate, impurities, including Th, U and other trace impurities, were further deeply removed. After multiple steps of synergistic effects, high-purity low-α-ray alumina was finally obtained.

[0072] In a second aspect, the present application provides a low α-ray alumina, which is prepared by any method described in the first aspect.

[0073] The low-α-ray alumina is realized based on the preparation method of the low-α-ray alumina mentioned above. The specific steps of the preparation method of the low-α-ray alumina can refer to the above embodiment. Since the low-α-ray alumina adopts part or all of the technical solutions of the above embodiment, it at least has all the beneficial effects brought by the technical solutions of the above embodiment, which will not be described one by one here.

[0074] The present application will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are intended only to illustrate the present application and are not intended to limit the scope of the present application. The experimental methods for the unrecorded specific conditions in the following examples are usually measured according to national standards. If there is no corresponding national standard, then carry out according to general international standards, normal conditions or according to the conditions recommended by the manufacturer.

[0075] Example 1

[0076] A method for preparing low-α-ray alumina. The raw material of the low-α-ray alumina comprises a sodium aluminate solution, the sodium aluminate solution contains thorium and uranium, and the sodium aluminate solution is obtained by redissolving an aluminum hydroxide raw material through an ion membrane liquid alkali. The purity of the aluminum hydroxide raw material is 99.6%, and the contents of major impurity elements are as follows: Ca=10ppm, Fe=10ppm, Na=968ppm, Si=10ppm, Th=178ppb, U=187ppb). Figure 2 This is a practical simplified process diagram of a method for preparing low α-ray alumina provided in the embodiment of the present application; see Figure 2 , the method comprising:

[0077] Using a first aluminum hydroxide seed crystal to perform a first decomposition reaction on a sodium aluminate solution to obtain a first decomposed solution;

[0078] Performing solid-liquid separation on the first decomposed solution to obtain a liquid phase substance;

[0079] Using a second aluminum hydroxide seed crystal to perform a second decomposition reaction on the liquid phase material to obtain aluminum hydroxide having a set thorium content and a set uranium content;

[0080] Among them, conventional aluminum hydroxide HP-999SP of Chalco Shandong Co., Ltd. is used as the first aluminum hydroxide seed crystal and the second aluminum hydroxide seed crystal; in the first decomposition reaction: the decomposition temperature is 30° C., the seed particle size is 0.3 μm, and the weight of the first aluminum hydroxide seed crystal is 1.5% of the weight of aluminum oxide in the sodium aluminate solution; in the second decomposition reaction: the decomposition temperature is 60° C., the seed particle size is 1.5 μm, the weight of the second aluminum hydroxide seed crystal is 1.5% of the weight of aluminum oxide in the liquid phase, and the time is 16 hours; the thorium content is set to 14 ppb and the uranium content is set to 18 ppb;

[0081] Dissolving aluminum hydroxide having a set thorium content and a set uranium content using sulfuric acid to obtain an aluminum sulfate solution;

[0082] The aluminum sulfate solution is chemically reacted with ammonium sulfate to obtain ammonium aluminum sulfate;

[0083] The ammonium aluminum sulfate is recrystallized for multiple times to obtain high-purity ammonium aluminum sulfate; specifically, the ammonium aluminum sulfate is heated and concentrated, cooled to 20° C. (recrystallization temperature), and filtered to obtain a primary crystalline aluminum salt; the primary crystalline aluminum salt is dissolved in 95° C. water, cooled to 20° C. (recrystallization temperature) after being completely dissolved, filtered, and then dried at 80° C. to obtain high-purity ammonium aluminum sulfate, wherein the purity of the ammonium aluminum sulfate is 99.993%;

[0084] High-purity ammonium aluminum sulfate is roasted to obtain low-alpha-ray alumina, and the roasting temperature is 1300°C.

[0085] Example 2

[0086] A method for preparing low-α-ray alumina, wherein the raw material of the low-α-ray alumina comprises a sodium aluminate solution, wherein the sodium aluminate solution contains thorium and uranium, and the sodium aluminate solution is obtained by redissolving an aluminum hydroxide raw material through an ion membrane liquid alkali, wherein the purity of the aluminum hydroxide raw material is 99.6%, and the contents of the main impurity elements are as follows: Ca=9ppm, Fe=9ppm, Na=935ppm, Si=8ppm, Th=162ppb, and U=189ppb). The method comprises:

[0087] Using a first aluminum hydroxide seed crystal to perform a first decomposition reaction on a sodium aluminate solution to obtain a first decomposed solution;

[0088] Performing solid-liquid separation on the first decomposed solution to obtain a liquid phase substance;

[0089] Using a second aluminum hydroxide seed crystal to perform a second decomposition reaction on the liquid phase material to obtain aluminum hydroxide having a set thorium content and a set uranium content;

[0090] Among them, conventional aluminum hydroxide HP-999SP of Chalco Shandong Co., Ltd. is used as the first aluminum hydroxide seed and the second aluminum hydroxide seed; in the first decomposition reaction: the decomposition temperature is 35° C., the seed particle size is 1.0 μm, and the weight of the first aluminum hydroxide seed is 2.5% of the weight of aluminum oxide in the sodium aluminate solution; in the second decomposition reaction: the decomposition temperature is 70° C., the seed particle size is 2.5 μm, the weight of the second aluminum hydroxide seed is 1.0% of the weight of aluminum oxide in the liquid phase, and the time is 16 hours; the thorium content is set to 13 ppb and the uranium content is set to 17 ppb;

[0091] Dissolving aluminum hydroxide having a set thorium content and a set uranium content using sulfuric acid to obtain an aluminum sulfate solution;

[0092] The aluminum sulfate solution is chemically reacted with ammonium sulfate to obtain ammonium aluminum sulfate;

[0093] The ammonium aluminum sulfate is recrystallized for multiple times to obtain high-purity ammonium aluminum sulfate; specifically, the ammonium aluminum sulfate is heated and concentrated, cooled to 15° C. (recrystallization temperature), and filtered to obtain a primary crystalline aluminum salt; the primary crystalline aluminum salt is dissolved in 95° C. water, cooled to 15° C. (recrystallization temperature) after being completely dissolved, filtered, and then dried at 80° C. to obtain high-purity ammonium aluminum sulfate, wherein the purity of the ammonium aluminum sulfate is 99.992%;

[0094] High-purity ammonium aluminum sulfate is roasted to obtain low-α-ray alumina, and the roasting temperature is 1250°C.

[0095] Example 3

[0096] A method for preparing low-α-ray alumina, wherein the raw material of the low-α-ray alumina comprises a sodium aluminate solution, wherein the sodium aluminate solution contains thorium and uranium, and the sodium aluminate solution is obtained by redissolving an aluminum hydroxide raw material through an ion membrane liquid alkali, wherein the purity of the aluminum hydroxide raw material is .99.6%, and the contents of the main impurity elements are: Ca=10ppm, Fe=10ppm, Na=973ppm, Si=9ppm, Th=168ppb, and U=174ppb). The method comprises:

[0097] Using a first aluminum hydroxide seed crystal to perform a first decomposition reaction on a sodium aluminate solution to obtain a first decomposed solution;

[0098] Performing solid-liquid separation on the first decomposed solution to obtain a liquid phase substance;

[0099] Using a second aluminum hydroxide seed crystal to perform a second decomposition reaction on the liquid phase material to obtain aluminum hydroxide having a set thorium content and a set uranium content;

[0100] Among them, conventional aluminum hydroxide HP-999SP of Chalco Shandong Co., Ltd. is used as the first aluminum hydroxide seed crystal and the second aluminum hydroxide seed crystal; in the first decomposition reaction: the decomposition temperature is 40°C, the seed particle size is 1.5μm, and the weight of the first aluminum hydroxide seed crystal is 3% of the weight of the sodium aluminate solution; in the second decomposition reaction: the decomposition temperature is 80°C, the seed particle size is 3.5, the weight of the second aluminum hydroxide seed crystal is 0.5% of the weight of the liquid phase substance, and the time is 16h; the thorium content is set to 15ppb and the uranium content is set to 18ppb;

[0101] Dissolving aluminum hydroxide having a set thorium content and a set uranium content using sulfuric acid to obtain an aluminum sulfate solution;

[0102] The aluminum sulfate solution is chemically reacted with ammonium sulfate to obtain ammonium aluminum sulfate;

[0103] The ammonium aluminum sulfate is recrystallized for multiple times to obtain high-purity ammonium aluminum sulfate; specifically, the ammonium aluminum sulfate is heated and concentrated, cooled to 20° C. (recrystallization temperature), and filtered to obtain a primary crystalline aluminum salt; the primary crystalline aluminum salt is dissolved in 95° C. water, cooled to 20° C. (recrystallization temperature) after being completely dissolved, filtered, and then dried at 80° C. to obtain high-purity ammonium aluminum sulfate, wherein the purity of the ammonium aluminum sulfate is 99.992%;

[0104] High-purity ammonium aluminum sulfate is roasted to obtain low-alpha-ray alumina, and the roasting temperature is 1300°C.

[0105] Comparative Example 1

[0106] Comparative Example 1 is taken as a reference to Example 1. The difference between Comparative Example 1 and Example 1 is that the amount of seed crystal added in the second decomposition reaction process is 0.2%.

[0107] Comparative Example 2

[0108] Comparative Example 2 is taken as a reference for Example 2, and the difference between Comparative Example 2 and Example 2 is that the temperature of the second decomposition reaction is 40°C.

[0109] Comparative Example 3

[0110] Comparative Example 3 takes Example 3 as a reference, and the difference between Comparative Example 3 and Example 3 is that the calcination temperature is 1100°C.

[0111] The purity indexes of the low α-ray alumina prepared in Examples 1 to 3 and Comparative Examples 1 to 3 were tested. Please refer to Table 1 for the test results.

[0112] Table 1 Indicators of low α-ray alumina

[0113]

[0114] It can be seen from the data in Table 1 that the purity of the low α-ray alumina prepared in Examples 1-3 is greater than 99.99%, and the content of radioactive elements Th and U is less than 5 ppb. Figure 3 A particle size distribution diagram of low α-ray alumina provided in Example 1 of the present application;

[0115] Figure 4 A particle size distribution diagram of low α-ray alumina provided in Example 2 of the present application; Figure 5 A particle size distribution diagram of a low α-ray alumina provided in Example 3 of the present application; see Figure 3 to Figure 5 , indicating that the particle size distribution of the low α-ray alumina prepared in Examples 1 to 3 is uniform.

[0116] In Comparative Example 1, the amount of seed added in the second decomposition process is too low, which affects the stability and efficiency of the crystallization process. The impurity element content is high, the purity is 99.96%, the Th content is 47 ppb, the U content is 62 ppb, the particle size distribution is uneven, and the particles are coarse. Figure 6 A particle size distribution diagram of a low α-ray alumina provided for comparative example 1 of this application; see Figure 6 In Comparative Example 2, the second decomposition temperature is too low, resulting in a too fast decomposition rate, which affects the growth and crystallization quality of the seed crystal and reduces the product purity, with a purity of 99.97%, a Th content of 29 ppb, and a U content of 45 ppb. The particle size distribution is uneven, and the proportion of fine particles is high. Figure 7 shown. Figure 6 A particle size distribution diagram of a low α-ray alumina provided in Comparative Example 1 of the present application; Figure 7 A particle size distribution diagram of a low α-ray alumina provided for comparative example 2 of this application; see Figure 7 In Comparative Example 3, the calcination temperature is too low, resulting in a large amount of sulfate remaining in the alumina, with an S content of 18 ppm, which will affect the subsequent spheroidization process and cause uneven particle size distribution. Figure 8 A particle size distribution diagram of low α-ray alumina provided for comparative example 3 of this application; see Figure 8 .

[0117] One or more technical solutions in the embodiments of the present application also have at least the following technical effects or advantages:

[0118] (1) The seed production process is connected in series with the multi-process of ammonium aluminum sulfate recrystallization to remove uranium and thorium impurities in a targeted manner. The decomposition of sodium aluminate initially reduces the content of radioactive elements uranium and thorium to less than 20ppb; ammonium aluminum sulfate is recrystallized multiple times to obtain low-α-ray alumina with low impurity element content and high index stability;

[0119] (2) Adjustable particle size distribution: The calcined alumina can be ground, crushed and sieved to obtain three low-α-ray alumina products with different particle size distributions in the range of D50 = 1 to 50 μm.

[0120] The above description is only a specific implementation of the present application, so that those skilled in the art can understand or implement the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features applied for herein.

Claims

1. A method for preparing low-α-ray alumina, wherein the raw material of the low-α-ray alumina comprises a sodium aluminate solution, wherein the sodium aluminate solution contains radioactive elements thorium and uranium, and the method comprises: Using a first aluminum hydroxide seed crystal to perform a first decomposition reaction on the sodium aluminate solution to obtain a first decomposed solution; Performing solid-liquid separation on the first decomposition solution to obtain a liquid phase substance; Using a second aluminum hydroxide seed crystal to perform a second decomposition reaction on the liquid phase material to obtain aluminum hydroxide having a set thorium content and a set uranium content; Dissolving the aluminum hydroxide having a set thorium content and a set uranium content using sulfuric acid to obtain an aluminum sulfate solution; The aluminum sulfate solution is chemically reacted with ammonium sulfate to obtain ammonium aluminum sulfate; Recrystallizing the ammonium aluminum sulfate multiple times to obtain high-purity ammonium aluminum sulfate; The high-purity ammonium aluminum sulfate is roasted to obtain low-alpha-ray alumina.

2. The method according to claim 1, characterized in that: The thorium content is set to ≤20ppb; and / or, The uranium content is set to be ≤20ppb.

3. The method according to claim 1, characterized in that: The temperature of the first decomposition reaction is 30°C to 45°C; and / or, The weight of the first aluminum hydroxide seed crystals is 1.5% to 5% of the weight of aluminum oxide in the sodium aluminate solution.

4. The method according to claim 1, characterized in that: The temperature of the second decomposition reaction is 50°C to 80°C; and / or, The weight of the second aluminum hydroxide seed crystals is 0.5% to 1.5% of the weight of aluminum oxide in the liquid phase material.

5. The method according to claim 1, characterized in that The recrystallization temperature is 10°C to 40°C.

6. The method according to claim 1 or 5, characterized in that: The purity of the high-purity ammonium aluminum sulfate is >99.99%.

7. The method according to claim 1, characterized in that The calcination temperature is 1200°C to 1350°C.

8. The method according to claim 1, characterized in that The particle size of the first aluminum hydroxide seed crystal is 0.2 to 1.5 μm; and / or, The particle size of the second aluminum hydroxide seed crystals is 1.5 μm to 4 μm.

9. The method according to claim 1, characterized in that: The low α-ray alumina meets the following indicators: purity is ≥99.99%, thorium content is ≤5ppb, uranium content is ≤5ppb, and median particle size is adjustable from 1μm to 50μm.

10. A low-α-ray alumina, wherein the low-α-ray alumina is prepared by the method according to any one of claims 1 to 9.

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