Preparation method of low-radioactivity alumina powder

Abstract

The invention discloses a preparation method of low-radioactivity alumina powder, which comprises the following steps: carrying out acid washing by boron-10 acid to dissolve radioactive elements such as U in the boron-10 acid, dispersing uranium adsorbed on the surface of an alumina single crystal in a solution under an acidic condition to exist in a uranyl ion (UO2 < 2 + >) state, and improving the insoluble efficiency; the isotope B-10 has good neutron absorption capacity, so that the influence of cleaning waste liquid on the environment can be reduced; meanwhile, gaseous BF3 and UF6 are generated from the acid-washed aluminum oxide and ammonium fluoride at a high temperature, so that radioactive elements in the aluminum oxide are removed, the separation method can be used for treating the aluminum oxide with the uranium content of dozens to hundreds of ppb, uranium in the aluminum oxide raw material is converted into an easy-to-separate substance, the uranium content in the treated aluminum oxide is reduced to 5 ppb or below, and the uranium content in the treated aluminum oxide is reduced to 5 ppb or below. And the production requirements of the semiconductor industry are met.

Description

Technical Field

[0001] The invention belongs to the field of alumina, and in particular relates to a method for preparing low-radioactive alumina powder. Background Art

[0002] Alumina is an important industrial product with important applications in many fields. In particular, spherical alumina has good thermal conductivity and can be used in chips and other components with high heat generation in the current 5G communications, new energy and other industries to maintain the reliable performance of the components.

[0003] Alumina is used as a packaging filler for devices, and it is necessary to avoid errors in device signal transmission, so high requirements are placed on the quality of alumina. Common alumina powder contains a certain concentration of radioactive elements such as uranium (U) and thorium (Th). The uranium concentration of alumina prepared under normal conditions can reach several hundred ppm, which will affect the accuracy of device signal transmission.

[0004] In the prior art, for the radioactive treatment of alumina, Chinese patent CN102249276A discloses a method for preparing spherical alumina powder, wherein alumina is flame-sprayed to prepare powder, the spherical alumina is heated in a mixed aqueous solution of sulfuric acid and phosphoric acid to dissolve the powder to prepare an aqueous solution, the obtained aqueous solution is contacted with a cyclohexane solution containing tributyl phosphate, and used as a reagent for extracting uranium to extract the uranium contained in the aqueous solution, so as to provide spherical alumina powder with a small specific surface area and a low uranium content, and the uranium concentration reaches less than 10 ppb. This method is limited by whether the alumina can be completely burned at high temperature in a combustible gas, and the overall energy consumption is large. Although the uranium on the surface of the alumina can be removed, it is difficult to remove the uranium remaining inside the alumina.

[0005] Chinese patent CN 115947361 A discloses a low-radioactive alumina powder and a preparation method thereof. By dispersing alumina in an acidic solution, uranium adsorbed on the surface of alumina single crystals can be dispersed in the solution in the form of uranyl ions under acidic conditions, and then replaced by a solvent of a silane coupling agent. Under the action of surface tension, the acidic solution and the uranyl ions remaining in the gaps of the alumina are replaced outside the alumina powder. Finally, the alumina powder is dried at high temperature to reduce the uranium content contained therein, and the uranium content of the raw material is reduced from about 30 ppb to less than 5 ppb. However, the replacement reaction is time-consuming and consumes a lot of silane coupling agents. It is also necessary to perform subsequent separation treatment on the silane coupling agent that has replaced the inside and surface of the alumina, which is difficult. In addition, the radioactive uranyl ions present in the acidic solution will also have radioactivity and affect the human body and the environment during industrial production.

[0006] Based on this, how to provide a safer, simpler and more efficient method for preparing low-radioactive alumina powder is a difficult problem that needs to be solved urgently. Summary of the invention

[0007] In order to solve the above problems, the present application proposes a method for preparing low-radioactive alumina powder, and the specific technical solution is as follows:

[0008] A method for preparing low-radioactive alumina, comprising the following specific steps:

[0009] Step 1: Immerse the aluminum oxide powder in an acidic solution containing boric acid to dissolve the radioactive elements on the surface and inside of the aluminum oxide to form oxide ions;

[0010] Step 2: filtering and separating the product obtained in step 1, adding a fluorine ammonium salt solution to the solid obtained after filtration to react, so as to convert the oxidized radioactive element into a fluorinated radioactive element;

[0011] Step 3: Filter the product of step 2, and calcine the filtered solid alumina at high temperature to obtain low-radioactive alumina.

[0012] Preferably, the acidic solution in step 1 is boric acid 10 or a mixed acid solution containing B-10, wherein the mixed acid is boric acid 10 and one or more inorganic acids;

[0013] Preferably, the inorganic acid is phosphoric acid, nitric acid, sulfuric acid or hydrochloric acid.

[0014] Preferably, the pH of the acidic solution in step 1 is 2-5, and the immersion time is 1-3 hours.

[0015] Preferably, the ammonium fluoride salt solution in step 2 is a mixed solution of ammonium fluoride and ammonium bifluoride, and the mass fraction of the solution is 20-70%.

[0016] Preferably, the reaction time in step 2 is 1-2h.

[0017] Preferably, the abundance of isotope B-10 in boric acid in step 1 is greater than 80%, and more preferably, the abundance of isotope B-10 is greater than 90%.

[0018] Preferably, the alumina in step 1 is obtained by calcining aluminum hydroxide, and the calcination is carried out at 900-1050° C. for 4-8 hours.

[0019] Preferably, the calcination temperature in step three is 150-300° C., and the calcination time is 2-4 hours.

[0020] Technical Effects

[0021] In the present invention, the radioactive elements such as U are dissolved by pickling with boric acid, and the uranium adsorbed on the surface of the alumina single crystal can be dispersed in the solution under acidic conditions to form uranyl ions (UO2 2+ ) state, and because B-10 has good neutron absorption capacity, it can reduce the impact of radioactive elements in the cleaning waste liquid on the environment and workers; at the same time, the use of ammonium fluoride salt to treat the acid-washed alumina can cause the residual uranyl ions in the alumina to react with fluorine to replace oxygen, and generate gaseous uranium hexafluoride UF6 under a high temperature environment, and at the same time, the residual boric acid 10 is reacted to generate boron trifluoride gas, and the ammonium radical added later is also converted into ammonia gas under heating conditions and separated from the alumina, thereby separating the radioactive elements in the cleaning liquid and the gap from the alumina solid. This separation method does not require the uranium concentration of the alumina raw material, and can process alumina with a uranium content of hundreds of ppb. At the same time, the uranium in the alumina raw material is converted into easily separable substances, and uranium can be separated from the alumina by heating only, and the uranium content of the alumina can be reduced to less than 5 ppb. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a scanning electron microscope image of the surface morphology of the aluminum oxide powder in the embodiment. DETAILED DESCRIPTION

[0023] The implementation of the technical solution of the present invention and the beneficial effects thereof are described in detail below through specific embodiments, but they cannot be regarded as any limitation on the applicable scope of the present invention.

[0024] Example 1

[0025] Take specific surface area ≥ 60m 2 / g, aluminum hydroxide with an average particle size of 40um was calcined at 1000℃ for 5h, and then ground to obtain aluminum oxide powder (such as Figure 1 5 g of alumina powder was immersed in boric acid 10 at pH = 3, in which the abundance of isotope B10 was 86%, stirred for 2 h, and then filtered to collect the filtrate, the filtered alumina was added to a 30% by mass ammonium fluoride solution, ultrasonically reacted for 2 h, the reacted alumina was heated to 300 ° C and calcined for 2 h and the gas produced by the reaction was collected, and finally low-radioactive alumina powder was obtained.

[0026] Example 2

[0027] Take specific surface area ≥ 60m 2 / g, aluminum hydroxide with an average particle size of 40um is calcined at 900℃ for 4h, and then ground to obtain aluminum oxide powder; 5g of aluminum oxide powder is immersed in a mixed acid of boric acid 10 and hydrochloric acid (mass ratio of 2:1) with a pH of 5, wherein the abundance of the isotope B10 is 80%, stirred for 3h, and then filtered to collect the filtrate, the filtered aluminum oxide is added to a 20% by mass ammonium fluoride solution, ultrasonically reacted for 2h, the reacted aluminum oxide is heated to 200℃ and calcined for 3h and the gas produced by the reaction is collected, and finally low-radioactive aluminum oxide powder is obtained.

[0028] Example 3

[0029] Take specific surface area ≥ 60m 2 / g, aluminum hydroxide with an average particle size of 40um is calcined at 1050℃ for 7h, and then ground to obtain aluminum oxide powder; 5g of aluminum oxide powder is immersed in a mixed acid of boric acid 10 and nitric acid (mass ratio is 1:1) with a pH of 2, wherein the abundance of the isotope B10 is 90%, stirred for 1h, and then filtered to collect the filtrate, the filtered aluminum oxide is added to a mixed solution of ammonium fluoride and ammonium bifluoride with a mass fraction of 60%, ultrasonically reacted for 1h, the reacted aluminum oxide is heated to 150℃ and calcined for 4h, and the gas generated by the reaction is collected to finally obtain low-radioactive aluminum oxide powder.

[0030] Example 4

[0031] Take specific surface area ≥ 60m 2 / g, aluminum hydroxide with an average particle size of 40um was calcined at 1000℃ for 5h, and then ground to obtain aluminum oxide powder (such as Figure 1 5 g of alumina powder was immersed in ordinary boric acid at pH = 3, in which the abundance of isotope B10 was 19%, stirred for 2 h, and then filtered to collect the filtrate, the filtered alumina was added to a 30% by mass ammonium fluoride solution, ultrasonically reacted for 2 h, the reacted alumina was heated to 300 ° C and calcined for 2 h and the gas produced by the reaction was collected to finally obtain low-radioactive alumina powder.

[0032] Example 5

[0033] Take specific surface area ≥ 60m 2 / g, aluminum hydroxide with an average particle size of 40um was calcined at 1000℃ for 5h, and then ground to obtain aluminum oxide powder (such as Figure 1 5 g of alumina powder was immersed in boric acid 10 at pH = 3, in which the abundance of isotope B10 was 86%, stirred for 2 h, and then filtered to collect the filtrate, the filtered alumina was added to ultrapure water, ultrasonicated for 2 h, and then the alumina was heated to 300 ° C and calcined for 2 h to finally obtain low-radioactive alumina powder.

[0034] The low-radioactive alumina obtained by treating the alumina obtained in Examples 1-5 was subjected to uranium content measurement, and the acidic filtrate after acid treatment was gasified and then the radioactive substances were detected using a detector. The specific measurement method is as follows:

[0035] Uranium content measurement method: ICP-MS inductively coupled plasma mass spectrometry is used to test the uranium content on the sample surface: 0.1g of aluminum oxide sample is digested with sulfuric acid, nitric acid and phosphoric acid in a digestion tank for 30 minutes, and then dried at 180°C to remove the acid. After removing the acid, the volume is adjusted to 100ml with 1% nitric acid, and then the adjusted sample is detected by ICP-MS.

[0036] Radioactive material detection: An α / β counter, model MPC9604, was used to detect radioactive materials. The total α standard material was 241Am powder with a specific activity of 10.4Bq / g and a relative expanded uncertainty of 3.6% (k=2), CaSO4 matrix, and a particle size less than 119mm (100 mesh); the total β standard material was high-purity KCl with a specific activity of 16.3Bq / g and a relative expanded uncertainty of 1.8% (k=2).

[0037]

[0038] It can be seen from the above embodiments that the content of radioactive U in alumina treated with boric acid and fluorinated ammonium salt solution is reduced to less than 5 ppb, which can meet the requirements of semiconductor field for alumina; although ordinary boric acid treatment can also reduce radioactivity, the content of radioactive U in both acid waste liquid and alumina is high, which cannot meet the requirements of semiconductor field for alumina. It can be seen that alumina with low concentration of radioactive U can be obtained by treating with boric acid and fluorinated ammonium salt solution. If only acid treatment is used, the radioactive elements inside the alumina gap are not removed, so as not to meet the requirements of semiconductor packaging. However, the present application converts the radioactive elements inside into volatile substances through fluorinated ammonium salt treatment to reduce the overall radioactivity. In addition, since B-10 has neutron absorption capacity, the radioactive contamination of the filtrate after pickling is significantly reduced, which reduces the harm to the environment and operators in the industrial process and is more environmentally friendly.

Claims

1. A method for preparing low-radioactive alumina powder, characterized in that: The specific steps are: Step 1: Immerse the aluminum oxide powder in an acidic solution containing boric acid to dissolve the radioactive elements on the surface and inside of the aluminum oxide to form oxide ions; Step 2: filtering and separating the product obtained in step 1, adding a fluorine ammonium salt solution to the solid obtained after filtration to react, so as to convert the oxidized radioactive element into a fluorinated radioactive element; Step 3: Filter the product of step 2, and calcine the filtered solid alumina at high temperature to obtain low-radioactive alumina.

2. The method for preparing low-radioactive alumina powder according to claim 1, characterized in that: The acidic solution in step 1 is boric acid 10 or a mixed acid solution containing B-10, wherein the mixed acid is boric acid 10 and one or more inorganic acids.

3. The method for preparing low-radioactive alumina powder according to claim 2, characterized in that: The inorganic acid is phosphoric acid, nitric acid, sulfuric acid or hydrochloric acid.

4. The method for preparing low-radioactive alumina powder according to claim 1, characterized in that: The pH of the acidic solution in step 1 is 2-5, and the immersion time is 1-3 hours.

5. The method for preparing low-radioactive alumina powder according to claim 1, characterized in that: The ammonium fluoride salt solution in step 2 is a mixed solution of ammonium fluoride and ammonium bifluoride, and the mass fraction of the solution is 20-70%.

6. The method for preparing low-radioactive alumina powder according to claim 1, characterized in that: The reaction time in step 2 is 1-2h.

7. The method for preparing low-radioactive alumina powder according to claim 1, characterized in that: In step 1, the abundance of isotope B-10 in boric acid 10 is more than 80%.

8. The method for preparing low-radioactive alumina powder according to claim 7, characterized in that: In step 1, the abundance of isotope B-10 in boric acid 10 is more than 90%.

9. The method for preparing low-radioactive alumina powder according to claim 1, characterized in that: The alumina in step 1 is obtained by calcining aluminum hydroxide, and the calcination is carried out at 900-1050° C. for 4-8 hours.

10. The method for preparing low-radioactive alumina powder according to claim 1, characterized in that: The calcination temperature in step 3 is 150-300° C., and the calcination time is 2-4 hours.

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