Method for deep boron removal from silicon carbide powder, silicon carbide raw material

Abstract

The application discloses a method for deeply removing boron from silicon carbide powder and silicon carbide raw material, which comprises the following steps: mixing the silicon carbide raw material, a complexing agent and deionized water, adjusting the pH to 3-5, and performing wet complexation extraction pretreatment to obtain a suspension; mixing the suspension with an adsorbent and then performing adsorption treatment, and performing solid-liquid separation to obtain the silicon carbide powder, wherein the content of boron in the silicon carbide powder is less than or equal to 0.005 ppm; wherein the adsorbent comprises at least one of a boron removal resin and a porous material loaded with a hydroxylated metal oxide. The application combines the wet complexation extraction pretreatment and the adsorption treatment, realizes efficient synergy of mild desorption of boron and targeted capture of boron, reduces the cost and pollution, reduces the boron content of the silicon carbide raw material from 0.1 ppm-1 ppm to below 0.005 ppm, and meets the growth requirement of semi-insulating silicon carbide crystals.

Description

Technical Field

[0001] This application relates to the field of semiconductor material purification technology, specifically to a method for deep boron removal from silicon carbide powder and silicon carbide raw materials. Background Technology

[0002] Silicon carbide (SiC), as a third-generation wide-bandgap semiconductor material, is widely used in high-temperature, high-frequency, and high-power electronic devices due to its large bandgap, high thermal conductivity, and strong breakdown electric field. Semi-insulating silicon carbide crystal is the core substrate for fabricating high-frequency microwave devices, and its quality directly depends on the purity of the silicon carbide powder—especially boron (B) impurities. If the boron content exceeds 0.01 ppm, it will cause the crystal to yellow and its semi-insulating properties to deteriorate, failing to meet the requirements for device fabrication.

[0003] Conventional boron removal technologies for silicon carbide raw materials have significant drawbacks: traditional high-temperature volatilization methods require temperatures above 2200℃, resulting in extremely high energy consumption and a tendency for powder sintering; acid leaching methods rely on concentrated acids such as HF and aqua regia, causing severe pollution and making it difficult to penetrate encapsulated boron impurities, with a boron removal rate of only 80%-85%; and single-functional adsorption methods cannot effectively capture deep-seated boron due to the obstruction of the oxide layer on the surface of silicon carbide raw materials, ultimately making it difficult to reduce the boron content to below 0.005 ppm.

[0004] Therefore, developing a low-energy-consumption, low-pollution, low-cost process that can achieve deep boron removal has become the key to solving the purification problem of semi-insulating silicon carbide raw materials.

[0005] It should be noted that the above statements are only used to provide background information related to this application and do not necessarily constitute prior art. Summary of the Invention

[0006] In a first aspect, this application proposes a method for deep boron removal from silicon carbide powder, comprising: mixing silicon carbide raw material, a complexing agent, and deionized water, adjusting the pH to 3-5, and performing wet complexing extraction pretreatment to obtain a suspension; mixing the suspension with an adsorbent and performing adsorption treatment, followed by solid-liquid separation to obtain silicon carbide powder, wherein the boron content in the silicon carbide powder is less than or equal to 0.005 ppm; wherein the adsorbent includes at least one of boron removal resin and porous materials loaded with hydroxylated metal oxides. This application combines wet complexing extraction pretreatment with adsorption treatment. First, wet complexing extraction pretreatment breaks the hydrogen bonds and coordination forces between boron and the SiO2 oxide layer on the surface of the silicon carbide raw material, causing boron to desorb from the surface of the silicon carbide raw material into the liquid phase and react with the complexing agent to form a highly stable borate ester complex. Then, adsorption treatment deeply adsorbs boron, synergistically achieving efficient, low-consumption, and environmentally friendly boron removal. Furthermore, this method has low energy consumption, low pollution, and is easy to mass-produce.

[0007] In some embodiments, the mass fraction of the hydroxylated metal oxide in the porous material loaded with the hydroxylated metal oxide is 5%-20%. This allows the pores of the porous material to be prevented from being overly covered, thus fully exposing the adsorption sites.

[0008] In some embodiments, the boron content in the silicon carbide raw material is 0.1 ppm to 1 ppm, and / or the particle size of the silicon carbide raw material is 1 μm to 50 μm. Therefore, the silicon carbide raw material has a certain purity and high powder sintering activity.

[0009] In some embodiments, the mass ratio of the silicon carbide raw material to the deionized water is (1:10)-(1:20). This solid-liquid dispersion ensures sufficient contact between the surface of the silicon carbide raw material and the aqueous phase, providing a mass transfer channel for subsequent complexation reactions, reducing silicon carbide raw material agglomeration, and making it less likely for boron impurities to be encapsulated.

[0010] In some embodiments, the complexing agent includes at least one selected from mannitol, sorbitol, and glucose; and / or, the mass ratio of the complexing agent to the silicon carbide raw material is (1:5)-(1:15); and / or, the temperature of the wet complexation extraction pretreatment is 40℃-60℃, and the time is 1h-2h. This facilitates the complexation reaction and improves the desorption efficiency of boron from the silicon carbide raw material.

[0011] In some embodiments, the adsorption treatment is carried out at a temperature of 30°C-50°C for a time of 0.5h-1h. This balances adsorption kinetics and thermodynamics, improves the slow diffusion rate of complexed boron, shortens the adsorption equilibrium time, and increases adsorption efficiency, while not disrupting the coordinate bonds between the adsorbent and boron.

[0012] In some embodiments, the mass ratio of the adsorbent to the silicon carbide raw material is (1:20)-(1:30). This is beneficial for improving the adsorption efficiency of boron ions.

[0013] In some embodiments, the metal oxide includes at least one selected from TiO2, ZrO2, Al2O3, and CeO2; the porous material includes at least one selected from mesoporous silica gel, mesoporous silica microspheres, mesoporous molecular sieves, porous ceramics, mesoporous alumina, and mesoporous zirconium oxide; optionally, the porous material includes mesoporous silica gel. Thus, the raw materials are widely available, facilitating large-scale promotion.

[0014] In some embodiments, the pore size of the porous material is 5 nm-20 nm; and / or, the specific surface area of ​​the porous material is greater than or equal to 500 m². 2 / g. This provides ample adsorption sites.

[0015] In some embodiments, a method for preparing the porous material loaded with hydroxylated metal oxides includes: immersing the porous material in a metal salt ethanol solution, drying it, sintering it, cooling it, and then immersing it in a hydroxylation solution to obtain the porous material loaded with hydroxylated metal oxides. As a result, a large number of hydroxyl groups are generated on the surface of the porous material loaded with hydroxylated metal oxides. The O atoms in the hydroxyl groups have lone pairs of electrons, which can form coordinate bonds with the B atoms (empty orbitals) in the complexed boron, achieving selective trapping.

[0016] In some embodiments, the metal salt ethanol solution includes at least one selected from TiCl4 ethanol solution, ZrCl4 ethanol solution, AlCl3 ethanol solution, and Ce(NO3)3 ethanol solution; and / or, the concentration of the metal salt ethanol solution is 0.5 mol / L to 1 mol / L. Therefore, the raw materials are widely available and the cost is low, and the loading of metal oxides in the porous material can be controlled by adjusting the concentration of the metal salt ethanol solution.

[0017] In some embodiments, the sintering treatment is performed at a temperature of 500°C-600°C for 2-4 hours. This yields a highly active metal oxide crystal form and improves the hydroxylation efficiency.

[0018] In some embodiments, the hydroxylation solution includes at least one of sodium hydroxide solution, hydrogen peroxide solution, and dilute hydrochloric acid solution. This facilitates the formation of hydroxyl groups on the surface of the metal oxide.

[0019] In some embodiments, the boron-removing resin includes Tulsimer CH-99 resin or HP119 resin; and / or, the degree of crosslinking of the boron-removing resin is 8%-12%. Thus, the hydroxyl and amino groups in the functional groups (such as N-methylglucosamine groups) on the surface of the boron-removing resin can react with unreacted B(OH)4. - It forms bidentate or polydentate coordination bonds, and its binding force on boron ions is much stronger than that on other ions in solution (such as Si). 4+ Na + Cl - This enables the selective capture of boron ions.

[0020] In some embodiments, the method further includes: soaking the boron-adsorbent in an acid solution and washing it with deionized water until neutral to obtain the adsorbent; optionally, the acid solution includes at least one selected from sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, and citric acid. This allows for the desorption of adsorbed boron ions, thereby regenerating the adsorbent.

[0021] In some embodiments, the method further includes: adding an alkaline earth metal hydroxide to the solution after adsorption treatment, adjusting the pH to 8-9, and concentrating the filtered supernatant by vacuum distillation to recover the complexing agent; wherein the alkaline earth metal hydroxide includes at least one of Ca(OH)2, Mg(OH)2, and Ba(OH)2. This allows for the recovery of the complexing agent and its recycling.

[0022] In a second aspect of this application, a silicon carbide powder is provided, prepared using the method described in the first aspect of this application, wherein the boron content of the silicon carbide powder is less than or equal to 0.005 ppm. Therefore, the silicon carbide powder has high purity. Attached Figure Description

[0023] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, wherein, Figure 1 This is a process flow diagram of one embodiment of this application. Detailed Implementation

[0024] The embodiments of this application are described in detail below, with examples of these embodiments shown in the accompanying drawings. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0025] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used in this application is for the purpose of describing particular embodiments only and is not intended to limit this application; unless otherwise stated, the values ​​of the parameters mentioned in this application can be measured using various measurement methods commonly used in the art (e.g., they can be tested according to the methods given in the embodiments of this application).

[0026] The terms “comprising” and “having”, and any variations thereof, in the specification and claims of this application are open-ended expressions, meaning they include what is specified in this application but do not exclude other aspects.

[0027] In the description of this application, all figures disclosed herein, whether or not the words "approximately" or "about" are used, are approximate values. Each figure may vary by less than 10% or by a difference that is considered reasonable by one of the art, such as 1%, 2%, 3%, 4%, or 5%.

[0028] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0029] In the description of this application, "A and / or B" can include any of the cases of A alone, B alone, or A and B, where A and B are merely examples and can be any technical feature connected by "and / or" in this application.

[0030] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0031] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0032] This application combines wet complexation extraction pretreatment with adsorption treatment. First, wet complexation extraction pretreatment breaks the hydrogen bonds and coordination forces between boron and the SiO2 oxide layer on the surface of silicon carbide raw material, allowing boron to desorb from the surface of silicon carbide raw material and enter the liquid phase. There, boron reacts with a complexing agent to form a borate ester complex with high stability. Then, adsorption treatment deeply adsorbs boron, achieving a synergistic effect of efficient, low-consumption, and environmentally friendly boron removal. Moreover, this method has low energy consumption, low pollution, and is easy to mass-produce.

[0033] In the first aspect of this application, a method for deep boron removal from silicon carbide powder is proposed, referring to... Figure 1 The method includes: S1: Mix silicon carbide raw material, complexing agent and deionized water, adjust pH to 3-5, and perform wet complexing extraction pretreatment to obtain suspension.

[0034] In some embodiments, the boron content in the silicon carbide raw material is 0.1ppm-1ppm, for example, 0.1ppm, 0.2ppm, 0.4ppm, 0.6ppm, 0.8ppm, or 1ppm. Therefore, the silicon carbide raw material has a certain purity.

[0035] In some embodiments, the particle size of the silicon carbide raw material is 1μm-50μm, for example, it can be 1μm, 2μm, 5μm, 8μm, 10μm, 15μm, 20μm, 25μm, 30μm, 35μm, 40μm, 45μm, or 50μm. Therefore, the silicon carbide raw material has high powder sintering activity.

[0036] In some embodiments, the mass ratio of the silicon carbide raw material to the deionized water is (1:10)-(1:20), for example, 1:10, 1:12, 1:14, 1:16, 1:18, or 1:20. This solid-liquid dispersion ensures sufficient contact between the surface of the silicon carbide raw material and the aqueous phase, providing a mass transfer channel for subsequent complexation reactions, reducing silicon carbide agglomeration, and making it less likely for boron impurities to be encapsulated.

[0037] In some embodiments, the complexing agent includes at least one of mannitol, sorbitol, and glucose (purity ≥ 99%).

[0038] Taking mannitol as an example, the physicochemical reaction that occurs during the wet complex extraction pretreatment is: C6H 14 O6+B(OH)4 - →[C6H 12 O5·B(OH)3] - +H₂O+OH - .

[0039] In some embodiments, the mass ratio of the complexing agent to the silicon carbide raw material is (1:5)-(1:15), for example, it can be 1:5, 1:7, 1:9, 1:11, 1:13 or 1:15.

[0040] In some embodiments, the temperature of the wet complexation extraction pretreatment is 40℃-60℃ (e.g., 40℃, 45℃, 50℃, 55℃, or 60℃), and the time is 1h-2h (e.g., 1h, 1.5h, or 2h). This facilitates the complexation reaction and improves the desorption efficiency of boron in the silicon carbide raw material.

[0041] In some embodiments, the reagents used to adjust the pH include 0.1 mol / L to 1 mol / L HCl solution or NaOH solution. When the pH is in the range of 3-5, boron on the surface of the silicon carbide raw material mainly exists as B(OH)4. - Form exists (H3BO3) H + + B(OH)4 - This pH range promotes dissociation; the polyhydroxyl groups (-OH) in complexing agents (such as mannitol) molecules can react with B(OH)4. - A stable six-membered ring complex is formed, which disrupts the hydrogen bonding / coordination forces between boron and the SiO2 oxide layer on the surface of silicon carbide raw material, causing boron to desorb from the surface of silicon carbide raw material and enter the liquid phase.

[0042] S2: The suspension is mixed with an adsorbent and then subjected to adsorption treatment. After solid-liquid separation, silicon carbide powder is obtained. The boron content in the silicon carbide powder is less than or equal to 0.005 ppm. The adsorbent includes at least one of boron removal resin and porous material loaded with hydroxylated metal oxides.

[0043] In some embodiments, the mass fraction of the hydroxylated metal oxide in the porous material loaded with the hydroxylated metal oxide is 5%-20%, for example, 5%, 10%, 15%, or 20%. This prevents the pores of the porous material from being overly covered, thus fully exposing the adsorption sites.

[0044] In some embodiments, the adsorption treatment temperature is 30℃-50℃ (e.g., 30℃, 35℃, 40℃, 45℃, or 50℃), and the time is 0.5h-1h (e.g., 0.5h, 0.8h, or 1h). This balances adsorption kinetics and thermodynamics, increases the diffusion rate of complexed boron, shortens the adsorption equilibrium time, and improves adsorption efficiency, while not disrupting the coordinate bonds between the adsorbent and boron.

[0045] In some embodiments, the mass ratio of the adsorbent to the silicon carbide raw material is (1:20)-(1:30), for example, it can be 1:20, 1:22, 1:24, 1:26, 1:28 or 1:30. This is beneficial to improving the adsorption efficiency of boron ions.

[0046] In some embodiments, the metal oxide includes at least one selected from TiO2, ZrO2, Al2O3, and CeO2; the porous material includes at least one selected from mesoporous silica gel, mesoporous silica microspheres, mesoporous molecular sieves, porous ceramics, mesoporous alumina, and mesoporous zirconium oxide; optionally, the porous material includes mesoporous silica gel. Thus, the raw materials are widely available, facilitating large-scale promotion.

[0047] In some embodiments, the adsorbent includes at least one of the following: mesoporous silica gel loaded with hydroxylated TiO2, mesoporous silica microspheres loaded with hydroxylated ZrO2, mesoporous molecular sieves loaded with hydroxylated Al2O3, and mesoporous zirconium oxide loaded with hydroxylated CeO2.

[0048] Taking mesoporous silica gel loaded with hydroxylated TiO2 as an example, the physicochemical reaction that occurs during the adsorption process is: TiO2 (surface)-OH+[C6H 12 O5·B(OH)3] - →TiO2(surface)-OB(OH)2·C6H 12 O5+OH - .

[0049] In some embodiments, the pore size of the porous material is 5nm-20nm, for example, it can be 5nm, 10nm, 15nm or 20nm; and / or, the specific surface area of ​​the porous material is greater than or equal to 500m². 2 / g, for example, can be 500m 2 / g、520m 2 / g、550m 2 / g、580m 2 / g、600m 2 / g、650m 2 / g or 700m 2 / g, etc. This helps to provide sufficient adsorption sites.

[0050] In some embodiments, a method for preparing the porous material loaded with hydroxylated metal oxides includes: immersing the porous material in a metal salt ethanol solution, drying it, sintering it, cooling it, and then immersing it in a hydroxylation solution to obtain the porous material loaded with hydroxylated metal oxides. As a result, a large number of hydroxyl groups are generated on the surface of the porous material loaded with hydroxylated metal oxides. The O atoms in the hydroxyl groups have lone pairs of electrons, which can form coordinate bonds with the B atoms (empty orbitals) in the complexed boron, achieving selective trapping.

[0051] In some embodiments, the metal salt ethanol solution includes at least one selected from TiCl4 ethanol solution, ZrCl4 ethanol solution, AlCl3 ethanol solution, and Ce(NO3)3 ethanol solution; and / or, the concentration of the metal salt ethanol solution is 0.5 mol / L to 1 mol / L, for example, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, or 1 mol / L. Therefore, the raw materials are widely available and the cost is low, and the loading of metal oxides in the porous material can be controlled by adjusting the concentration of the metal salt ethanol solution.

[0052] Specifically, when the corresponding metal oxide is TiO2, the concentration of TiCl4 ethanol solution is 0.5 mol / L-1 mol / L; when the corresponding metal oxide is ZrO2, the concentration of ZrCl4 ethanol solution is 0.5 mol / L-1 mol / L; when the corresponding metal oxide is Al2O3, the concentration of AlCl3 ethanol solution is 0.3 mol / L-0.8 mol / L; and when the corresponding metal oxide is CeO2, the concentration of Ce(NO3)3 ethanol solution is 0.4 mol / L-0.9 mol / L.

[0053] In some embodiments, the sintering treatment is performed at a temperature of 500℃-600℃ (e.g., 500℃, 520℃, 540℃, 560℃, 580℃, or 600℃) for a time of 2h-4h (e.g., 2h, 3h, or 4h). This allows for the acquisition of highly active metal oxide crystal forms and improves hydroxylation efficiency.

[0054] In some embodiments, the hydroxylation solution includes at least one of sodium hydroxide solution, hydrogen peroxide solution, and dilute hydrochloric acid solution. This facilitates the formation of hydroxyl groups on the surface of the metal oxide.

[0055] As an example, a method for preparing mesoporous silica gel loaded with hydroxylated TiO2 includes: immersing the mesoporous silica gel in a 0.5 mol / L-1 mol / L TiCl4 ethanol solution and sonicating it for 30-45 minutes (ultrasonic frequency 20 kHz-40 kHz, to promote TiO2 loading). 4+ Uniform loading), drying at 100℃-120℃ for 2-3 hours (to remove ethanol solvent and avoid residual organic matter affecting adsorption), followed by sintering at 500℃-600℃ for 2 hours (to convert TiCl4 to TiO2, i.e., TiCl4 + 2H2O → TiO2 + 4HCl↑), cooling, and then soaking in 0.1mol / L-0.3mol / L NaOH solution for 1-1.5 hours (NaOH reacts with TiO2 to generate surface hydroxyl groups: TiO2 + NaOH + H2O → Na[Ti(OH)3O] + H2O, and washing with water to remove Na). + Hydroxylated TiO2 was obtained, and the target adsorbent was obtained by washing with deionized water until neutral.

[0056] In some embodiments, the boron-removing resin includes Tulsimer CH-99 resin or HP119 resin. Thus, the hydroxyl and amino groups in the functional groups (such as N-methylglucosamine groups) on the surface of the boron-removing resin can react with unreacted B(OH)4. - It forms bidentate or polydentate coordination bonds, and its binding force on boron ions is much stronger than that on other ions in solution (such as Si). 4+ Na + Cl - This enables the selective capture of boron ions.

[0057] In some embodiments, the degree of crosslinking of the boron-removing resin is 8%-12%, for example, it can be 8%, 9%, 10%, 11% or 12%. This helps to form a loose and stable resin network that is not prone to swelling and collapse, or site encapsulation. At the same time, the pores are not excessively dense, resulting in low mass transfer resistance, high mechanical strength, and resistance to cracking. Furthermore, the particles are uniform and easy to separate, and are not prone to clogging the equipment.

[0058] In some embodiments, the mixed system after adsorption in step S2 is filtered to remove the adsorbent and liquid phase, resulting in a silicon carbide powder filter cake. The cake is washed 2-3 times with deionized water (each time the amount of water is 5-10 times the mass of the powder) to remove the complexing agent and adsorbent remaining on the surface of the silicon carbide powder. The cake is then vacuum dried at 80℃-100℃ for 4-5 hours (vacuum degree ≤100Pa, to avoid high-temperature oxidation, and at the same time to accelerate water evaporation and reduce powder agglomeration) to obtain low-boron silicon carbide powder with a boron content ≤0.005ppm. In some embodiments, the method further includes step S3, adsorbent regeneration: soaking the boron-adsorbent in an acid solution and washing with deionized water until neutral to obtain the adsorbent; optionally, the acid solution includes at least one selected from sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, and citric acid. This allows for the desorption of adsorbed boron ions, thus regenerating the adsorbent.

[0059] In some embodiments, the concentration of the acid solution is 0.5 mol / L to 0.8 mol / L, for example, it can be 0.5 mol / L, 0.6 mol / L, 0.7 mol / L or 0.8 mol / L.

[0060] In some embodiments, the soaking time is 1-2 hours, for example, 1 hour, 1.5 hours, or 2 hours.

[0061] As an example, the filtered adsorbent is soaked in a 0.5 mol / L-0.8 mol / L H2SO4 solution for 1-2 hours to desorb the adsorbed boron ions. After washing with deionized water until neutral, it can be reused in step S2, with a regeneration count of ≥30 times. The regeneration principle is that H2SO4 provides a high concentration of H+. + H + It combines with O atoms on the surface of the adsorbent, breaking the TiO2-OB coordination bond, and causing boron to desorb in the form of H3BO3.

[0062] The physicochemical reactions that occur during the desorption of the adsorbent are as follows: TiO2(surface)-OB(OH)2·C6H 12 O5 + H2SO4 → TiO2 (surface) -OH + C6H 12 O5+H3BO3+HSO4 -(Desorption rate ≥95%, hydroxyl groups on the surface of the adsorbent are restored after regeneration, and the adsorption efficiency remains above 85% of the initial value).

[0063] In some embodiments, the physicochemical reaction occurring during the desorption of boron-removing resin is: R-NH-CH2-(CHOH)4-CH2O-B(OH)3+H2SO4→R-NH-CH2-(CHOH)4-CH2OH+H3BO3+HSO4 - (During acid desorption, dilute sulfuric acid provides H₂) + The oxygen atom of the resin-boron coordination bond is attacked, breaking the OB bond; the adsorbed boron species are converted into free boric acid (H3BO3) and enter the desorption solution, while sulfuric acid is converted into HSO4. - Form exists within the system.

[0064] In some embodiments, the method further includes step S3, recovery of the complexing agent: adding an alkaline earth metal hydroxide to the solution after adsorption treatment, adjusting the pH to 8-9, and concentrating the filtered supernatant by vacuum distillation to recover the complexing agent; wherein the alkaline earth metal hydroxide includes at least one of Ca(OH)2, Mg(OH)2, and Ba(OH)2. Thus, the complexing agent can be recovered and recycled.

[0065] As an example, the washing liquid from step S2 and the desorption liquid from step S3 are collected, and Ca(OH)2 powder is added to adjust the pH to 8-9 to generate Ca3(BO3)2 precipitate. After filtration, the supernatant is concentrated by vacuum distillation (temperature 60℃-70℃, vacuum degree 5kPa-10kPa, to avoid high temperature decomposition of complexing agent) to recover the complexing agent (recovery rate ≥80%), which can be recycled for step S1.

[0066] The principle of recovering the complexing agent is as follows: When pH=8-9, B(OH)3 reacts with Ca(OH)2 to generate insoluble Ca3(BO3)2 (solubility ≤0.01 g / L). The physicochemical reaction that occurs is: 2H3BO3+3Ca(OH)2→Ca3(BO3)2↓+6H2O, which realizes the separation of boron and complexing agent. Vacuum distillation concentration can reduce the boiling point of the complexing agent (e.g., the boiling point of mannitol is reduced from 290℃ to 60℃-70℃), reducing energy consumption and complexing agent loss.

[0067] The method for deep boron removal from silicon carbide raw materials described in this application has at least the following beneficial effects: (1) High boron removal efficiency: Through the synergistic effect of “complexation desorption + targeted adsorption”, the boron content of silicon carbide powder is reduced from 0.1ppm-1ppm to below 0.005ppm, with a boron removal rate of ≥99.5%, which meets the stringent requirements of low boron silicon carbide powder for the growth of semi-insulating silicon carbide crystals; (2) Low cost: No high temperature or high energy equipment is required; the complexing agent and adsorbent can be recycled and regenerated, and the cost of consumables is low; (3) Green and environmentally friendly: The entire process adopts an aqueous system, with no toxic reagents such as HF and HCl, and no corrosive waste gas emissions; the wastewater discharge is only 10% of that of the traditional acid leaching method, and can be recovered through complexing agents to achieve near-zero discharge; the solid waste is only a small amount of waste adsorbent (which can be treated as ordinary solid waste). (4) Easy to mass-produce: The process parameters are stable and controllable. The mixing, filtering and other equipment can be directly connected to the existing powder production line. The processing capacity can reach 50kg / h-100kg / h, which is suitable for large-scale industrial production.

[0068] In a second aspect of this application, a silicon carbide powder is provided, prepared using the method described in the first aspect of this application. The boron content in the silicon carbide powder is less than or equal to 0.005 ppm, for example, it can be 0.001 ppm, 0.002 ppm, 0.003 ppm, 0.004 ppm, or 0.005 ppm, etc. Therefore, the silicon carbide powder has high purity.

[0069] The description of the various embodiments above tends to emphasize the differences between the various embodiments. The similarities or similarities between them can be referred to, and for the sake of brevity, they will not be repeated here.

[0070] The following specific embodiments illustrate the solution of this application. It should be noted that these embodiments are for illustrative purposes only and should not be considered as limiting the scope of this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0071] Example 1 Step 1: Take 1 kg of silicon carbide raw material with an initial boron content of 0.5 ppm and a particle size of 20 μm, add 15 L of deionized water, and stir to form a suspension with a solid-liquid ratio of 1:15; add 200 g of mannitol (the mass ratio of complexing agent to silicon carbide source is 1:5, and the purity is 99.5%), adjust the pH to 4 with 0.5 mol / L HCl, and stir the reaction at 50℃ for 1.5 hours; Step 2: Add 50 g of mesoporous silica gel loaded with hydroxylated TiO2 (prepared by the aforementioned method, the mass fraction of hydroxylated TiO2 in the mesoporous silica gel loaded with hydroxylated TiO2 is 10%), stir at 40°C for 1 hour for adsorption. Step 3: Filter and separate the powder, wash three times with 10 L of deionized water, and vacuum dry at 80℃ for 4 hours. The boron content in the silicon carbide powder is 0.003 ppm, and the boron removal rate is 99.4%. The adsorbent is regenerated by soaking in 0.6 mol / L H2SO4 for 1.5 hours. After 30 regenerations, the adsorption efficiency still remains above 85% of the initial value. After mixing the washing liquid and the desorption liquid, Ca(OH)2 is added to adjust the pH to 8.5. Filter to remove Ca3(BO3)2 precipitate, and concentrate the supernatant by vacuum distillation to recover mannitol with a recovery rate of 82%.

[0072] Example 2 Step 1: Take 2 kg of silicon carbide raw material with an initial boron content of 1 ppm and a particle size of 5 μm, add 30 L of deionized water, and stir to form a suspension with a solid-liquid ratio of 1:15; add 200 g of sorbitol (the mass ratio of complexing agent to silicon carbide raw material is 1:10, and the purity is 99.2%), adjust the pH to 3.5 with 0.3 mol / L HCl, and stir the reaction at 55℃ for 1.2 hours; Step 2: Add 80 g of mesoporous silica gel loaded with hydroxylated TiO2 (the mass fraction of hydroxylated TiO2 in the mesoporous silica gel loaded with hydroxylated TiO2 is 10%) and stir at 45°C for 0.8 hours for adsorption. Step 3: Filter and separate the powder, wash it three times with 10 L of deionized water, and vacuum dry it at 80℃ for 4 hours. The boron content in the silicon carbide powder was found to be 0.002 ppm, and the boron removal rate was 99.8%. After 25 regenerations of the adsorbent, the efficiency did not decrease significantly, and the sorbitol recovery rate was 85%.

[0073] Example 3 The difference from Example 1 is as follows: Step 2: Replace the mesoporous silica gel loaded with hydroxylated TiO2 with Tulsimer CH-99 resin.

[0074] Results: The boron content in the silicon carbide powder was 0.0025 ppm, and the boron removal rate was 99.75%.

[0075] Example 4 The difference from Example 1 is as follows: Step 2: Replace the mesoporous silica gel loaded with hydroxylated TiO2 with mesoporous molecular sieve loaded with hydroxylated Al2O3.

[0076] Results: The boron content in the silicon carbide powder was 0.0032 ppm, and the boron removal rate was 99.68%.

[0077] Comparative Example 1 Process: Only step 1 of Example 1 is performed, without step 2 adsorption, and subsequent filtration and drying are performed directly.

[0078] Results: The final boron content in the silicon carbide powder was 0.04 ppm, and the boron removal rate was 92% (which could not meet the requirement of ≤0.01 ppm). The underlying reason is that complexation can only desorb boron from the surface of silicon carbide raw materials into the liquid phase, but it cannot capture trace amounts of boron ions in the liquid phase, resulting in boron remaining on the surface of the powder along with the liquid phase.

[0079] Comparative Example 2 Process: Without performing the complexation step 1, 1 kg of silicon carbide raw material with an initial boron content of 0.5 ppm was directly added to 15 L of deionized water, and 50 g of adsorbent was added for adsorption according to step 2 of Example 1. Results: The boron content in the final silicon carbide powder was 0.06 ppm, and the boron removal rate was 88% (not meeting the requirements). The underlying reason is that the SiO2 oxide layer (2nm-5nm thick) on the surface of the powder hinders the adsorbent from contacting the deep boron layer, and can only adsorb a small amount of surface boron. Furthermore, the uncomplexed boron has a strong binding force with the powder, making it difficult for the adsorbent to capture it.

[0080] Comparative Example 3 Process: Soak 1 kg of silicon carbide raw material with an initial boron content of 0.5 ppm in a mixed acid of 10% HF and 20% HNO3 (liquid-solid ratio 15:1), stir at 80℃ for 2 hours, filter, wash and dry; Results: The final boron content in the silicon carbide powder was 0.08 ppm, the boron removal rate was 84%, and the COD value of the wastewater was 6200 mg / L (12 times that of this application). The underlying reason is that although HF can dissolve the SiO2 oxide layer (SiO2 + 4HF = SiF4↑ + 2H2O), boron readily forms BF4 in concentrated acid systems. - (H3BO3+4HF=HBF4+3H2O), BF4 - With silicon carbide surface Si 4+ It has strong binding force and is difficult to remove by washing; moreover, the mixed acid is highly corrosive, producing a large amount of fluoride- and nitrogen-containing wastewater.

[0081] The specific processing data for the above embodiments and comparative examples are shown in Table 1.

[0082] Table 1

[0083] As shown in Table 1, the final boron content of Examples 1-4 is far below the ≤0.01 ppm standard required for the growth of semi-insulating silicon carbide crystals, with a boron removal rate of over 99% and a low cost per treatment. In contrast, Comparative Examples 1-3 (single complexation, single adsorption, and traditional acid leaching) have lower costs, but their boron removal rates of 84%-92% do not meet industry requirements. In summary, this application achieves a significant cost reduction compared to existing high-efficiency boron removal processes while ensuring deep boron removal, and is far superior to traditional / single-process methods that fail to meet the required results, thus realizing the dual advantages of "high efficiency + economy."

[0084] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A method for deep boron removal from silicon carbide raw materials, characterized in that, include: Silicon carbide raw material, complexing agent and deionized water are mixed, pH is adjusted to 3-5, and wet complexing extraction pretreatment is carried out to obtain suspension; The suspension is mixed with an adsorbent and then subjected to adsorption treatment. After solid-liquid separation, silicon carbide powder is obtained, wherein the boron content in the silicon carbide powder is less than or equal to 0.005 ppm. The adsorbent includes at least one of boron-removing resin and porous materials loaded with hydroxylated metal oxides.

2. The method according to claim 1, characterized in that, The mass fraction of the hydroxylated metal oxide in the porous material loaded with hydroxylated metal oxide is 5%-20%.

3. The method according to claim 1, characterized in that, The boron content in the silicon carbide raw material is 0.1ppm-1ppm, and / or the particle size of the silicon carbide raw material is 1μm-50μm.

4. The method according to claim 1, characterized in that, The mass ratio of the silicon carbide raw material to the deionized water is (1:10)-(1:20); and / or, The complexing agent includes at least one of mannitol, sorbitol, and glucose; and / or, The mass ratio of the complexing agent to the silicon carbide raw material is (1:5)-(1:15); and / or, The wet complex extraction pretreatment is performed at a temperature of 40℃-60℃ for 1-2 hours.

5. The method according to claim 4, characterized in that, The adsorption treatment is performed at a temperature of 30℃-50℃ for a time of 0.5h-1h; and / or, The mass ratio of the adsorbent to the silicon carbide raw material is (1:20)-(1:30).

6. The method according to claim 1, characterized in that, The metal oxide includes at least one of TiO2, ZrO2, Al2O3, and CeO2; The porous material includes at least one of mesoporous silica gel, mesoporous silica microspheres, mesoporous molecular sieves, porous ceramics, mesoporous alumina, and mesoporous zirconium oxide; optionally, the porous material includes mesoporous silica gel.

7. The method according to claim 6, characterized in that, The porous material has a pore size of 5nm-20nm; and / or, The specific surface area of ​​the porous material is greater than or equal to 500 m². 2 / g.

8. The method according to claim 6, characterized in that, The method for preparing the porous material loaded with hydroxylated metal oxides includes: The porous material is immersed in a metal salt ethanol solution, dried, sintered, cooled, and then immersed in a hydroxylation solution to obtain the porous material loaded with hydroxylated metal oxides.

9. The method according to claim 8, characterized in that, The metal salt ethanol solution includes at least one selected from TiCl4 ethanol solution, ZrCl4 ethanol solution, AlCl3 ethanol solution, and Ce(NO3)3 ethanol solution; and / or, The concentration of the metal salt ethanol solution is 0.5 mol / L to 1 mol / L; and / or, The sintering treatment is performed at a temperature of 500℃-600℃ for 2-4 hours; and / or, The hydroxylation solution includes at least one of sodium hydroxide solution, hydrogen peroxide solution, and dilute hydrochloric acid solution.

10. The method according to claim 1, characterized in that, The boron-removing resin includes Tulsimer CH-99 resin or HP119 resin; and / or, The degree of crosslinking of the boron-removing resin is 8%-12%.

11. The method according to claim 1, characterized in that, Also includes: The adsorbent containing boron is soaked in an acid solution and washed with deionized water until neutral to obtain the adsorbent. Optionally, the acid solution includes at least one of sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, and citric acid.

12. The method according to claim 11, characterized in that, Also includes: Alkaline earth metal hydroxides were added to the solution after adsorption treatment to adjust the pH to 8-9. The supernatant after filtration was concentrated by vacuum distillation to recover the complexing agent. The alkaline earth metal hydroxide includes at least one of Ca(OH)2, Mg(OH)2, and Ba(OH)2.

13. A silicon carbide powder, characterized in that, The silicon carbide powder is prepared by the method according to any one of claims 1-12, wherein the boron content in the silicon carbide powder is less than or equal to 0.005 ppm.

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