A method for recovering diamonds from silicon carbide wafer polishing waste

Abstract

The application discloses a method for recovering diamond from silicon carbide wafer grinding waste liquid, which comprises the following steps: adding a dispersing agent into the silicon carbide wafer grinding waste liquid, and then performing spray drying to obtain solid A; adding the solid A into an alkali solution, and performing ultrasonic and stirring treatment for a set time; after solid-liquid separation, solid B is obtained; adding the solid B into a strong acid solution, and performing ultrasonic and stirring treatment for a set time; after solid-liquid separation, solid C is obtained; adding the solid C into a surfactant solution, and heating and stirring for a set time; finally, adding a dispersing agent into the mixed system, removing wafer debris through flotation, and drying the remaining solid to obtain diamond; the dispersing agent is one of sodium hexametaphosphate, sodium tripolyphosphate or polyacrylic alcohol or a combination thereof. The method can effectively improve the recovery rate and purity of diamond abrasive grains.

Description

Technical Field

[0001] This invention relates to the field of silicon carbide wafer processing technology, and more specifically, to a method for recovering diamond from silicon carbide wafer grinding waste liquid. This invention is applicable to the recovery process of silicon carbide wafer grinding waste liquid in semiconductor manufacturing and chemical mechanical polishing processes, particularly addressing the problem of diamond abrasive grain recovery involved in grinding silicon carbide wafers. Background Technology

[0002] The statements herein provide only background information in relation to this invention and do not necessarily constitute prior art.

[0003] Silicon carbide (SiC), a widely used wide-bandgap semiconductor material, is extensively used in the manufacturing of high-power devices and high-frequency electronic equipment due to its excellent physical, chemical, and electronic properties. The processing of silicon carbide wafers typically includes chemical mechanical polishing (CMP) to achieve high-precision surface flatness and low surface roughness.

[0004] In this process, diamond abrasive grains are widely used in the grinding of silicon carbide wafers due to their extremely high hardness. However, the large amount of grinding waste liquid generated during the grinding process still contains large diamond abrasive grains. Direct discharge of this waste liquid not only wastes valuable diamond resources but also causes serious environmental pollution. Therefore, how to efficiently recover diamond abrasive grains from silicon carbide wafer grinding waste liquid has become one of the urgent problems to be solved in the current technological field. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the purpose of this invention is to provide a method for recovering diamond from silicon carbide wafer grinding waste liquid.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0007] This invention provides a method for recovering diamond from silicon carbide wafer grinding waste liquid, comprising the following steps:

[0008] A dispersant was added to the silicon carbide wafer grinding waste liquid, and then spray-dried to obtain solid A;

[0009] Solid A is added to an alkaline solution, and the mixture is ultrasonicated and stirred for a set time. After solid-liquid separation, solid B is obtained.

[0010] Solid B was added to a strong acid solution, and the mixture was sonicated and stirred for a set time. After solid-liquid separation, solid C was obtained.

[0011] Solid C is added to the surfactant solution, and the mixture is heated and stirred for a set time.

[0012] Finally, a dispersant is added to the mixed system to remove wafer debris by flotation, and the remaining solid is dried to obtain diamond;

[0013] The dispersant is one of sodium hexametaphosphate, sodium tripolyphosphate or polyvinyl alcohol, or a combination thereof.

[0014] The main components of the silicon carbide wafer grinding waste liquid include suspended particles, chemical reagents (such as oxidizing agents, complexing agents, etc.) and grinding liquid components, wherein the concentration of the suspended particles is high, and the particle size is small, which is easy to agglomerate and adhere to the diamond abrasive particles through complex chemical components.

[0015] However, in the prior art, the solid mixture is generally separated from the grinding waste liquid by filtration, and then steps of removing metal impurities, residual oily substances, etc. are performed.

[0016] However, the inventors found that due to the complex chemical components in the grinding waste liquid, especially the residual oily substances, which have certain adhesion properties, there is not only agglomeration between the suspended particles themselves, but also adhesion between the solid particles, especially between the fine solid particles and the diamond abrasive particles.

[0017] When the solid particles in the grinding waste liquid are simply separated and dried, the dispersion between the obtained solid substances is poor, and even if subsequent pickling and alkaline washing are performed, the chemical components adhered between the solid particles are difficult to clean, and thus the solid particles are difficult to uniformly disperse. In this case, on the one hand, the surface of the recovered diamond abrasive particles is adhered with a large amount of solid particle impurities, which is difficult to recycle and reuse; on the other hand, the agglomerated solid particles are difficult to completely remove by flotation due to their large weight, which affects the purity of the recovered diamond abrasive particles.

[0018] To solve the above problems, the inventors first perform spray drying treatment on the grinding waste liquid to obtain a solid mixture of diamond powder, wafer debris, metal debris and other additives. Compared with oven drying or centrifugal treatment, the solid obtained by spray drying is usually small and uniform in powder form, and the dispersant suitable for the grinding waste liquid is added during operation, so that the obtained solid has good dispersibility and is suitable for further impurity removal treatment.

[0019] Then, the solid mixture is added to the lye to remove the residual grease in the waste liquid through saponification reaction, so as to avoid adhesion between the impurity particles and the diamond; the addition of ethanol can increase the solubility of the grease and the rate of the saponification reaction; and then acidification treatment is performed to remove the metal impurities introduced during the wafer grinding process.

[0020] Then the surfactant solution is added, heated and stirred for a set time to break the adsorption between the particles and modify the surface of the particles to effectively dissociate them;

[0021] Finally, a dispersant is added to the mixed system, and fine wafer debris is removed by flotation. The surfactant acts as a flotation agent (collector) in this process, and the wafer debris is selectively attached to the bubbles and floated to the surface by virtue of the difference in affinity between the surfactant and the diamond particles and wafer debris. In this process, a suitable dispersant can prevent agglomeration between particles and ensure uniform dispersion of particles.

[0022] Finally, the lower solid is washed several times with deionized water and dried at high temperature to separate and recover the diamond abrasive. The method in the present application has the advantages of simple process, low cost, suitability for mass production, and high recovery rate.

[0023] In some embodiments, the concentration of the dispersant in the silicon carbide wafer grinding waste liquid is 0.5wt%-10wt%. The dispersant helps to prevent agglomeration between particles and ensures uniform dispersion of particles, facilitating subsequent impurity removal and separation.

[0024] In some embodiments, the process conditions for spray drying are as follows: the inlet air temperature of the drying tower is 100-250℃, the outlet air temperature is 80-150℃, the slurry feed rate is 10-500mL / min, the hot air flow rate is 1-5m / s, and the protective atmosphere is one or more of nitrogen, argon or air. Appropriate process parameters can improve work efficiency and recovery rate, resulting in better recovery effect.

[0025] In some embodiments, the alkaline substance in the lye is one or a combination of sodium hydroxide, ammonia, potassium hydroxide, sodium bicarbonate, and potassium bicarbonate.

[0026] Preferably, the concentration of the lye is 0.5-5mol / L. A too low concentration of the strong alkali solution makes it difficult to completely remove oily substances in the waste liquid, and a too high concentration of the strong alkali solution causes material waste and increases cost.

[0027] Preferably, the lye also includes ethanol, and the mass percentage of ethanol is 5%-50%. The addition of an appropriate amount of ethanol can increase the compatibility of oil and water in the reaction system, reduce the interfacial tension between them, and facilitate better mixing and reaction of the two. In addition, ethanol can act as a solvent in the reaction system to dilute the reaction mixture, making it easier to stir and handle, which helps to improve the reaction efficiency.

[0028] Preferably, the solid A is ultrasonically treated and stirred in the alkaline solution for 10-240 min at a temperature of 20-70℃. Ultrasonic treatment can reduce the surface adsorption capacity by vibration, but cannot achieve the effect of effective separation; stirring can provide effective shear stress to increase the distance between molecules, thus achieving the effect of separation, and therefore, ultrasonic treatment and stirring can achieve better results. Too low ultrasonic treatment and stirring time or temperature can result in incomplete removal of oil stains, thus affecting the separation effect.

[0029] In some embodiments, the strong acid is one or a combination of sulfuric acid, nitric acid or hydrochloric acid, and the concentration of the strong acid solution is 0.1-3 mol / L. To ensure complete cleaning of metal impurities in the waste liquid, the concentration of the strong acid solution should not be too low; to save costs, the concentration of the strong acid should not be too high.

[0030] Preferably, the solid B is ultrasonically treated and stirred in the strong acid solution for 10-240 min at a temperature of 20-70℃. To ensure complete pickling cleaning, the ultrasonic treatment and stirring time and temperature should not be too low.

[0031] In some embodiments, the surfactant is one or a combination of sodium silicate, polyethylene glycol or sodium silicate.

[0032] Preferably, in the surfactant solution, the concentration of the surfactant solution is 0.01-5 wt%. Suitable types and concentrations can selectively make the wafer debris adhere to the bubbles by taking advantage of the difference in affinity between the diamond particles and the impurities, thus obtaining better flotation effect.

[0033] Preferably, after the solid C is mixed with the surfactant solution, the solid C is ultrasonically treated and stirred for 30-240 min at a temperature of 20-60℃. Too short heating and stirring time or too low temperature is not conducive to the dissolution of the surfactant, and too long heating and stirring time or too high temperature can cause the decomposition of the surfactant, thus affecting the separation effect.

[0034] In some embodiments, the concentration of the dispersant added during flotation is 1 wt%-5 wt%. The dispersant helps to prevent agglomeration between particles and ensures uniform dispersion of particles.

[0035] Preferably, during flotation, the aeration rate of the micro-nano bubble generator is 0.2-0.5 L / min, and the aeration time is 10 min-60 min. Suitable aeration rate and time can improve the flotation separation effect and improve the recovery rate of diamond particles.

[0036] The beneficial effects achieved by one or more embodiments of the present application are as follows:

[0037] The present application first obtains a solid mixture of diamond powder, wafer debris, metal debris and other additives by spray drying. Compared with oven drying or centrifugal treatment, the solid obtained by spray drying is usually small and uniform powder. When adding a dispersant suitable for the grinding waste liquid, the obtained solid has good dispersibility and is suitable for further impurity removal treatment.

[0038] Then a strong alkali solution is added. The basic substances in the strong alkali solution can undergo saponification reaction with components such as fatty acids in the oil. At a higher temperature, the viscosity of the oil is reduced, which makes the oil more easily mixed with the basic solution, thereby accelerating the reaction rate. The addition of ethanol not only improves the solubility of the oil molecules, but also further accelerates the saponification reaction.

[0039] Then, by acidification treatment, the metal impurities, especially iron elements, in the waste slurry can be removed. The addition of strong acid solution helps to remove the metal impurities introduced during the processing. Finally, a surfactant solution is added to remove the fine wafer debris by flotation.

[0040] The surfactant acts as a flotation agent (collector) here, and selectively makes the wafer debris adhere to the bubbles and float to the surface by using the difference in affinity between the surfactant and the diamond particles and wafer debris. In this process, a suitable dispersant can prevent agglomeration between particles and ensure uniform dispersion of particles.

[0041] Finally, the lower solid is washed several times with deionized water and dried at high temperature to realize the separation and recovery of diamond abrasive. The method in the present application has the advantages of simple process, low cost, high recovery rate and suitability for batch production. BRIEF DESCRIPTION OF DRAWINGS

[0042] The accompanying drawings, which form a part of the present application, are used to provide further understanding of the present application, and the illustrative embodiments of the present application and their description serve the purpose of explaining the present application, and do not constitute an improper limitation of the present application.

[0043] Figure 1 is a scanning electron microscope (SEM) image of solid A obtained by spray drying of the grinding waste liquid in Example 1;

[0044] Figure 2 is a scanning electron microscope (SEM) image of solid D (diamond) recovered in Example 1;

[0045] Figure 3 is a scanning electron microscope (SEM) image of solid D (diamond) recovered in Comparative Example 1;

[0046] Figure 4 is a process flow diagram of the present application. DETAILED DESCRIPTION

[0047] It should be noted that the following detailed description is illustrative only and is intended to provide further description of the application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

[0048] The technical solutions of the present application will be further described below in combination with specific examples.

[0049] Example 1

[0050] Step 1: Add 10 mL of 5% sodium hexametaphosphate solution to 2 kg of grinding waste liquid, stir evenly, dry tower inlet air temperature 150℃, outlet air temperature 100℃, atmosphere argon, flow rate 4 m / s, slurry feeding speed 100 mL / min, spray drying to collect solid A.

[0051] Step 2: Mix solid A with 2000 mL of 1 mol / L potassium hydroxide solution, with 10% ethanol, ultrasonic at 50℃ and stir for 30 min, natural sedimentation to obtain solid B.

[0052] Step 3: Mix solid B with 2000 mL of 0.5 mol / L hydrochloric acid, ultrasonic at 40℃ and stir for 60 min, natural sedimentation to obtain solid C.

[0053] Step 4: Mix solid C with 4000 mL of 0.1 wt% sodium metasilicate solution, stir at 40℃ for 30 min, add 10 mL of 5% sodium hexametaphosphate solution, micro-nano bubble generator aeration rate 0.2 L / min, aeration time 30 min, scrape off the scum, get the lower solid and dry, finally get powder solid D (diamond).

[0054] Figure 2 The SEM image of the solid D (diamond) recovered in Example 1 is shown in Figure 3 The SEM image of the diamond recovered in Comparative Example 1 is shown in Figure 3 In the above-mentioned comparative example 1, a large number of silicon carbide particles are adsorbed on the surface of the solid, which is due to the poor separation effect caused by not adding a dispersing agent during flotation.

[0055] After cleaning, there is almost no silicon carbide debris on the surface of the diamond, which shows that a suitable flotation process is necessary for the recovery of diamond powder from the grinding waste liquid.

[0056] The ICP-AES results of the diamond abrasive particles recovered in Example 1 are shown in Table 1 below:

[0057] Table 1

[0058]

[0059]

[0060] The element analysis of the diamond particles before and after recovery by ICP-AES shows that the mass fraction of main metal impurities such as Na, Al, V, Cr, Mn and Fe is greatly reduced, which proves the effectiveness of the recovery process in efficiently removing metal contaminants and provides data support for the recycling of waste diamond cutting fluid in high-end wafer cutting.

[0061] The particle size index of the diamond abrasive particles recovered in Example 1 is shown in the following table:

[0062] Table 2

[0063]

[0064] The particle size test of the recovered diamond shows that the D50 of the cleaned recovered material is 2.93 μm, the D90 / D10 is 2.8, the particle size distribution range is narrow, and the D100 is 5.87 μm, which shows that the recovery process can ensure the particle size consistency of the cutting abrasive particles and avoid scratching the wafer by large particles.

[0065] The multiple recovery rate statistics of the diamond abrasive particles recovered in Example 1 are shown in the following table 3:

[0066] Table 3

[0067]

[0068] Through the quality statistics of the diamond before and after cleaning, the recovery rate is at least 80%, and the recovery rate is higher when the single batch processing capacity is higher. The recovery rate result shows that the recovery process of the present application can realize efficient recovery and reduce the waste of diamond abrasive.

[0069] Example 2

[0070] Step 1: Add 4 kg of grinding waste liquid to 10 mL of 3% sodium tripolyphosphate solution, stir uniformly, dry tower inlet air temperature 180℃, outlet air temperature 120℃, atmosphere nitrogen, flow rate 3m / s, slurry feeding speed 200mL / min, spray drying to collect solid A.

[0071] Step 2: Mix solid A with 5000 mL of 0.5 mol / L sodium hydroxide solution, with an ethanol ratio of 25%, ultrasonic and stir at 40℃ for 60 min, and naturally settle to obtain solid B.

[0072] Step 3: Mix solid B with 5000 mL of 1 mol / L sulfuric acid, ultrasonic and stir at 45℃ for 120 min, and naturally settle to obtain solid C.

[0073] Step 4: Mix solid C with 8000 mL of 0.5wt% polyethylene glycol solution, stir at 45℃ for 40 min, add 10 mL of 3% sodium tripolyphosphate solution, the micro-nano bubble generator is ventilated at a rate of 0.3 L / min, and the ventilation time is 30 min. Scrape off the floating froth to obtain the lower solid and dry it to obtain powder solid D (diamond).

[0074] Example 3

[0075] Step 1: Add 5 kg of grinding waste liquid to 20 mL of 5% polyvinyl alcohol solution, stir evenly, dry tower inlet air temperature 250℃, outlet air temperature 150℃, atmosphere nitrogen, flow rate 5 m / s, slurry feeding speed 250 mL / min, spray drying to collect solid A.

[0076] Step 2: Mix solid A with 6000 mL of 1.5 mol / L ammonia water, with ethanol accounting for 30%, ultrasonic and stir at 45℃ for 120 min, and naturally settle to obtain solid B.

[0077] Step 3: Mix solid B with 6000 mL of 1.5 mol / L nitric acid, ultrasonic and stir at 50℃ for 120 min, and naturally settle to obtain solid C.

[0078] Step 4: Mix solid C with 10000 mL of 1wt% sodium silicate solution, stir at 40℃ for 60 min, add 20 mL of 5% sodium hexametaphosphate solution, the micro-nano bubble generator is ventilated at a rate of 0.2 L / min, and the ventilation time is 20 min. Scrape off the floating froth to obtain the lower solid and dry it to obtain powder solid D (diamond).

[0079] Comparative Example 1

[0080] The difference from Example 1 is that no sodium hexametaphosphate solution is added in Step 4, and the others are the same as Example 1.

[0081] Step 1: Add 5 kg of grinding waste liquid to 20 mL of 5% polyvinyl alcohol solution, stir evenly, dry tower inlet air temperature 250℃, outlet air temperature 150℃, atmosphere nitrogen, flow rate 5 m / s, slurry feeding speed 250 mL / min, spray drying to collect solid A.

[0082] Step 2: Mix solid A with 2000 mL of 1 mol / L potassium hydroxide solution, with ethanol accounting for 10%, ultrasonic and stir at 50℃ for 30 min, and naturally settle to obtain solid B.

[0083] Step 3: Mix solid B with 2000 mL of 0.5 mol / L hydrochloric acid, ultrasonic and stir at 40℃ for 60 min, and naturally settle to obtain solid C.

[0084] Step 4: Mix solid C with 4000 mL of 0.1wt% sodium metasilicate solution, stir for 30 min at 40℃, do not add sodium hexametaphosphate solution, the micro-nano bubble generator is ventilated at a rate of 0.2 L / min, the ventilation time is 30 min, scrape off the foam, get the lower solid and dry, finally get powder solid D (diamond).

[0085] The ICP-AES results of the recovered diamond abrasive particles of Comparative Example 1 are shown in Table 4 below:

[0086] Table 4

[0087]

[0088]

[0089] The particle size index of the recovered diamond abrasive particles of Comparative Example 1 is shown in Table 5 below. It can be seen that when no sodium hexametaphosphate solution is added in Step 4, the particle size distribution of the recovered diamond becomes wider, it is difficult to ensure the consistency of the particle size of the cutting abrasive particles, and it is easy to cause the wafer to be scratched by large particles.

[0090] Table 5

[0091]

[0092] The multiple recovery rate statistics of the diamond abrasive particles recovered in Comparative Example 1 are shown in Table 6 below:

[0093] Table 6

[0094]

[0095] Comparative Example 2

[0096] The difference from Example 1 is that in Step 1, sodium hexametaphosphate is omitted, and the others are the same as Example 1.

[0097] Step 1: Stir 2 kg of grinding waste liquid uniformly, the inlet air temperature of the drying tower is 150℃, the outlet air temperature is 100℃, the atmosphere is argon, the flow rate is 4 m / s, the slurry feeding speed is 100 mL / min, and the spray drying is collected to obtain solid A.

[0098] Step 2: Mix solid A with 2000 mL of 1 mol / L potassium hydroxide solution, the ethanol content is 10%, ultrasonic and stir for 30 min at 50℃, and naturally settle to obtain solid B.

[0099] Step 3: Mix solid B with 2000 mL of 0.5 mol / L hydrochloric acid, ultrasonic and stir for 60 min at 40℃, and naturally settle to obtain solid C.

[0100] Step 4: solid C was mixed with 4000 mL of 0.1 wt% sodium metasilicate solution, stirred at 40°C for 30 min, 10 mL of 5% sodium hexametaphosphate solution was added, the micro-nano bubble generator was ventilated at a rate of 0.2 L / min, the ventilation time was 30 min, the floating scum was scraped off, the lower solid was obtained and dried, and finally powder solid D (diamond) was obtained.

[0101] The ICP-AES results of the recovered diamond abrasive particles of Comparative Example 2 are shown in Table 7 below:

[0102] Table 7

[0103]

[0104] The particle size index of the recovered diamond abrasive particles of Comparative Example 2 is shown in Table 8 below:

[0105] Table 8

[0106]

[0107] The multiple recovery rate statistics of the recovered diamond abrasive particles of Comparative Example 2 are shown in Table 9 below:

[0108] Table 9

[0109]

[0110] Comparative Example 3

[0111] The difference from Example 1 is that in Step 2, ethanol is omitted, and the others are the same as Example 1.

[0112] Step 1: 10 mL of 5% sodium hexametaphosphate solution was added to 2 kg of grinding waste liquid, stirred uniformly, the inlet air temperature of the drying tower was 150°C, the outlet air temperature was 100°C, the atmosphere was argon, the flow rate was 4 m / s, the slurry feeding speed was 100 mL / min, and the solid A was collected by spray drying.

[0113] Step 2: solid A was mixed with 2000 mL of 1 mol / L potassium hydroxide solution, without adding ethanol, ultrasonic and stirring at 50°C for 30 min, and natural sedimentation to obtain solid B.

[0114] Step 3: solid B was mixed with 2000 mL of 0.5 mol / L hydrochloric acid, ultrasonic and stirring at 40°C for 60 min, and natural sedimentation to obtain solid C.

[0115] Step 4: solid C was mixed with 4000 mL of 0.1 wt% sodium silicate solution, stirred at 40°C for 30 min, 10 mL of 5% sodium hexametaphosphate solution was added, the micro-nano bubble generator was ventilated at a rate of 0.2 L / min, the ventilation time was 30 min, the floating scum was scraped off, the lower solid was obtained and dried, and finally powder solid D (diamond) was obtained.

[0116] The ICP-AES results of the recovered diamond abrasive particles of Comparative Example 3 are shown in Table 10 below:

[0117] Table 10

[0118]

[0119] The particle size index of the recovered diamond abrasive particles of Comparative Example 3 is shown in Table 11 below:

[0120] Table 11

[0121]

[0122] The multiple recovery rate statistics of the recovered diamond abrasive particles of Comparative Example 3 are shown in Table 12 below:

[0123] Table 12

[0124]

[0125]

[0126] Comparative Example 4

[0127] The difference from Example 1 is that in Step 1, sodium hexametaphosphate is replaced by sodium dodecyl sulfate (SDS), and the others are the same as Example 1.

[0128] Step 1: 10 mL of 5% sodium dodecyl sulfate (SDS) solution was added to 2 kg of grinding waste liquid, stirred uniformly, the inlet air temperature of the drying tower was 150°C, the outlet air temperature was 100°C, the atmosphere was argon, the flow rate was 4 m / s, the slurry feeding speed was 100 mL / min, and the solid A was collected by spray drying.

[0129] Step 2: solid A was mixed with 2000 mL of 1 mol / L potassium hydroxide solution, the ethanol accounted for 10%, ultrasonic and stirred at 50°C for 30 min, and the solid B was obtained by natural sedimentation.

[0130] Step 3: solid B was mixed with 2000 mL of 0.5 mol / L hydrochloric acid, ultrasonic and stirred at 40°C for 60 min, and the solid C was obtained by natural sedimentation.

[0131] Step 4: solid C was mixed with 4000 mL of 0.1wt% sodium metasilicate solution, stirred at 40℃ for 30 min, 10 mL of 5% sodium hexametaphosphate solution was added, the micro-nano bubble generator was ventilated at a rate of 0.2 L / min, the ventilation time was 30 min, the floating scum was scraped off, the lower solid was obtained and dried, and finally powder solid D (diamond) was obtained.

[0132] The ICP-AES results of the recovered diamond abrasive particles of Comparative Example 4 are shown in Table 13 below:

[0133] Table 13

[0134]

[0135]

[0136] The particle size index of the recovered diamond abrasive particles of Comparative Example 4 is shown in Table 14 below:

[0137] Table 14

[0138]

[0139] The multiple recovery rate statistics of the recovered diamond abrasive particles of Comparative Example 4 are shown in Table 15 below:

[0140] Table 15

[0141]

[0142] The above descriptions are only preferred embodiments of the present application and are not intended to limit the present application. The present application can have various modifications and changes for those skilled in the art. Any modification, equivalent replacement, improvement, etc. within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A method for recovering diamonds from a silicon carbide wafer polishing waste solution, comprising: The method comprises the following steps: ​ adding a dispersant to the silicon carbide wafer polishing waste liquid, and then performing spray drying to obtain solid A; adding the solid A to an alkali solution, and performing ultrasonic and stirring treatment for a set time, and then performing solid-liquid separation to obtain solid B; adding the solid B to a strong acid solution, and performing ultrasonic and stirring treatment for a set time, and then performing solid-liquid separation to obtain solid C; adding the solid C to a surfactant solution, and performing heating and stirring for a set time; finally adding a dispersant to the mixed system, removing wafer debris through flotation, and drying the remaining solid to obtain diamond; the dispersant is one or a combination of sodium hexametaphosphate, sodium tripolyphosphate or polyvinyl alcohol; the alkali solution further comprises ethanol, and the mass percentage of the ethanol is 5%-50%.

2. The method of recovering diamonds from silicon carbide wafer polishing waste according to claim 1, wherein: During spray drying, the concentration of the dispersant in the silicon carbide wafer polishing waste liquid is 0.5wt%-10wt%.

3. The method of recovering diamonds from silicon carbide wafer polishing waste according to claim 1, wherein: The process conditions for spray drying are as follows: the inlet air temperature of the drying tower is 100-250℃, the outlet air temperature is 80-150℃, the slurry feeding speed is 10-500mL / min, the hot air flow rate is 1-5m / s, and the protective atmosphere is one or a combination of nitrogen, argon or air.

4. The method of recovering diamonds from silicon carbide wafer polishing waste according to claim 1, wherein: The alkaline substance in the alkali solution is one or a combination of sodium hydroxide, ammonia, potassium hydroxide, sodium bicarbonate or potassium bicarbonate.

5. The method of recovering diamonds from silicon carbide wafer polishing waste fluid of claim 1, wherein The concentration of the alkali solution is 0.5-5 mol / L.

6. The method of recovering diamonds from silicon carbide wafer polishing waste fluid of claim 1, wherein, The ultrasonic and stirring time of the solid A in the alkali solution is 10-240min, and the temperature is 20-70℃.

7. The method of recovering diamonds from silicon carbide wafer polishing waste fluid of claim 1, wherein: The strong acid is one or a combination of sulfuric acid, nitric acid or hydrochloric acid, and the concentration of the strong acid solution is 0.1-3 mol / L.

8. The method of recovering diamonds from silicon carbide wafer polishing waste fluid of claim 1, wherein, The ultrasonic and stirring time of the solid B after being mixed with the strong acid solution is 10-240min, and the temperature is 20-70℃.

9. The method of recovering diamonds from silicon carbide wafer polishing waste fluid of claim 1, wherein: The surfactant is one or a combination of sodium silicate, polyethylene glycol or sodium silicate.

10. The method of recovering diamonds from silicon carbide wafer polishing waste fluid of claim 9, wherein: The concentration of the surfactant solution is 0.01-5wt%.

11. The method of recovering diamonds from silicon carbide wafer polishing waste fluid of claim 1, wherein: The ultrasonic and stirring time of the solid C after being mixed with the surfactant solution is 30-240min, and the temperature is 20-60℃.

12. The method of recovering diamonds from silicon carbide wafer polishing waste fluid of claim 1, wherein: The concentration of the dispersant added during flotation is 1wt%-5wt%.

13. The method of recovering diamonds from silicon carbide wafer polishing waste fluid of claim 1, wherein: During flotation, the aeration rate of the micro-nano bubble generator is 0.2-0.5L / min, and the aeration time is 10min-60min.

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