Method for recovering diamond from silicon carbide wafer grinding waste liquid

Abstract

The invention 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 carrying out spray drying to obtain a solid A; adding the solid A into alkali liquor, carrying out ultrasonic treatment and stirring treatment for set time, and carrying out solid-liquid separation to obtain a solid B; adding the solid B into a strong acid solution, carrying out ultrasonic treatment and stirring treatment for a set time, and carrying out solid-liquid separation to obtain a solid C; adding the solid C into the surfactant solution, heating and stirring for a set time; and finally, a dispersing agent is added into the mixed system, wafer chippings are removed through flotation, and the diamond is obtained after remaining solids are dried. The dispersing agent is one or a combination of sodium hexametaphosphate, sodium tripolyphosphate or polypropylene glycol. The method can effectively improve the recovery rate and purity of the diamond abrasive particles.

Description

Technical Field

[0001] The present invention relates to the technical field of silicon carbide wafer processing, and more specifically, to a method for recovering diamond from silicon carbide wafer grinding waste liquid. The present invention is applicable to the recovery process of silicon carbide wafer grinding waste liquid in semiconductor manufacturing and chemical mechanical polishing processes, especially the problem of recovering diamond abrasive grains involved in the grinding of silicon carbide wafers. Background Art

[0002] The statements herein only provide background art related to the present invention and do not necessarily constitute prior art.

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

[0004] In this process, diamond abrasive grains are widely used in the grinding process of silicon carbide wafers due to their extremely high hardness. However, a large amount of grinding waste liquid generated during the grinding process still contains relatively large diamond abrasive grains. The 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 technical field. Summary of the Invention

[0005] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide a method for recovering diamond from silicon carbide wafer grinding waste liquid.

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

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

[0008] Adding a dispersant to the silicon carbide wafer grinding waste liquid, and then performing spray drying to obtain solid A;

[0009] Adding solid A to an alkali solution, performing ultrasonic and stirring treatment for a set time, and after solid-liquid separation, obtaining solid B;

[0010] Adding solid B to a strong acid solution, performing ultrasonic and stirring treatment for a set time, and after solid-liquid separation, obtaining solid C;

[0011] Adding solid C to a surfactant solution, heating and stirring for a set time;

[0012] Finally, a dispersant is added to the mixed system, and the wafer debris is removed by flotation. After drying the remaining solid, diamond is obtained.

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

[0014] The main components of the silicon carbide wafer grinding waste liquid include suspended particles, chemical reagents (such as oxidants, complexing agents, etc.) and grinding fluid components. Among them, the concentration of suspended particles is relatively high, and the particle size is small, which is easy to agglomerate and is easily adhered to diamond abrasives through complex chemical components. If the diamond abrasives are to be recycled and reused, the impurity particles attached to the surface of the diamond abrasives need to be cleaned.

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

[0016] However, the inventor found that due to the complex chemical components in the grinding waste liquid, especially the residual oily substances, which have a certain adhesion property, it leads to not only the agglomeration of the suspended particles themselves, but also the adhesion between solid particles, especially the adhesion between fine solid particles and diamond abrasives.

[0017] When the solid particles in the grinding waste liquid are simply separated and dried, the dispersibility of the obtained solid substances is poor. Even if subsequent pickling and alkali washing are carried out, it is difficult to clean the chemical components adhered between the solid particles, and thus it is difficult to make the solid particles disperse evenly. In this case, on the one hand, a large amount of solid particle impurities adhere to the surface of the recycled diamond abrasives, making it difficult to recycle and reuse; on the other hand, the agglomerated solid particles are heavier and difficult to be completely removed by flotation, affecting the purity of the recycled diamond abrasives.

[0018] To solve the above problems, first, the grinding waste liquid is subjected to spray drying treatment to obtain a solid mixture of diamond powder, wafer debris, metal debris and other additives. Compared with oven drying or centrifugation, the solids obtained by spray drying are usually small and uniform powders. When operating, a dispersant suitable for the grinding waste liquid is added, and the obtained solids have better dispersibility, which is suitable for further impurity removal treatment;

[0019] Then the solid mixture is added to the alkali solution, and the residual grease in the waste liquid is removed through saponification reaction to avoid adhesion between impurity particles and diamond. The addition of ethanol can increase the solubility of grease and the rate of saponification reaction; subsequently, acidification treatment is carried out to remove the metal impurities introduced during wafer grinding;

[0020] Then add the surfactant solution, heat and stir for a set time to break the adsorption between particles and modify the surface of the particles to achieve effective dissociation;

[0021] Finally, add a dispersant to the mixed system and remove the fine wafer debris by flotation. The surfactant acts as a flotation agent (collector) here. By utilizing the difference in affinity between the surfactant and diamond particles and wafer debris, the wafer debris is selectively attached to the bubbles and floats to the liquid surface. During this process, a suitable dispersant can prevent the agglomeration between particles and ensure uniform dispersion of the particles.

[0022] Finally, wash the lower-layer solid with deionized water multiple times and dry it at high temperature to achieve the separation and recovery of diamond abrasives. The method in the present invention 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 0.5 wt%-10 wt%. The dispersant helps prevent the agglomeration between particles, ensures uniform dispersion of the particles, and facilitates 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 °C, the outlet air temperature is 80-150 °C, the slurry feeding rate is 10-500 mL / min, the hot air flow rate is 1-5 m / s, and the protective atmosphere is one or more of nitrogen, argon, or air. Appropriate process parameters can improve work efficiency and recovery rate, and produce better recovery effects.

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

[0026] Preferably, the concentration of the alkali solution is 0.5-5 mol / L. If the concentration of the strong alkali solution is too low, it is difficult to completely remove the oily substances in the waste liquid. If the concentration of the strong alkali solution is too high, it will cause waste of materials and increase costs.

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

[0028] Preferably, solid A is ultrasonically treated and stirred in an alkaline solution for 10 - 240 min at a temperature of 20 - 70 °C. Ultrasonication can reduce the surface adsorption capacity through vibration, but it cannot achieve the effect of effective separation; stirring can provide effective shear stress, increasing the intermolecular distance to achieve the separation effect. Therefore, ultrasonication and stirring simultaneously can achieve better results. Too low ultrasonication and stirring time or temperature will result in incomplete removal of oil stains, thereby 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 thorough cleaning of metal impurities in the waste liquid, the concentration of the strong acid solution should not be too low; to save costs, the strong acid concentration should not be too high.

[0030] Preferably, after solid B is mixed with the strong acid solution, the ultrasonication and stirring time is 10 - 240 min at a temperature of 20 - 70 °C. To ensure thorough pickling cleaning, the time and temperature of the ultrasonication and stirring treatment should not be too low.

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

[0032] Preferably, in the surfactant solution, the concentration of the surfactant solution is 0.01 - 5 wt%. The appropriate type and concentration can utilize the affinity difference between diamond particles and impurities to selectively attach wafer debris to bubbles, obtaining a better flotation effect.

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

[0034] In some embodiments, the concentration of the dispersant added during flotation is 1 wt% - 5 wt%. The dispersant helps prevent agglomeration between particles and ensures uniform dispersion of the 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. The appropriate aeration rate and time can improve the flotation separation effect and increase the recovery rate of diamond particles.

[0036] The beneficial effects obtained by one or more of the above embodiments of the present invention are as follows:

[0037] The present invention first obtains a solid mixture of diamond powder, wafer chips, metal chips, and other additives through spray drying. Compared with oven drying or centrifugation, the solids obtained by spray drying are usually small and uniform powders. When operating, a dispersant suitable for the grinding waste liquid is added, and the resulting solids have good dispersibility, which is suitable for further impurity removal treatment;

[0038] After that, a strong alkali solution is added. The alkaline substances in the strong alkali solution can undergo a saponification reaction with components such as fatty acids in the grease. At a relatively high temperature, the viscosity of the grease will decrease, which makes it easier for the grease to mix with the alkaline solution, thereby accelerating the reaction rate. The addition of ethanol can not only increase the solubility of grease molecules but also further accelerate the saponification reaction.

[0039] After that, through acidification treatment, metal impurities in the waste mortar can be removed, especially iron elements. The addition of a strong acid solution helps to remove the metal impurities introduced during the processing; finally, a surfactant solution is added, and the fine wafer chips are removed by flotation.

[0040] The surfactant acts as a flotation agent (collector) here. By utilizing the difference in affinity between the surfactant and diamond particles and wafer chips, the wafer chips are selectively attached to the bubbles and float to the liquid surface. During this process, a suitable dispersant can prevent agglomeration between particles and ensure uniform particle dispersion.

[0041] Finally, the lower-layer solid is washed multiple times with deionized water and dried at a high temperature to achieve the separation and recovery of diamond abrasives. The method in the present invention has the advantages of simple process, low cost, high recovery rate, and suitability for batch production. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] The specification drawings forming a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention.

[0043] Figure 1 is a scanning electron microscope (SEM) image of solid A obtained by spray drying 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 chart of the embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0047] It should be noted that the following detailed description is illustrative and aims to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention pertains.

[0048] The technical solution of the present invention will be further elaborated below in conjunction with specific embodiments.

[0049] Example 1

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

[0051] Step 2: Mix solid A with 2000 mL of 1 mol / L potassium hydroxide solution, where the proportion of ethanol is 10%, ultrasonically stir at 50 °C for 30 min, and naturally settle to obtain solid B.

[0052] Step 3: Mix solid B with 2000 mL of 0.5 mol / L hydrochloric acid, ultrasonically stir at 40 °C for 60 min, and naturally settle to obtain solid C.

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

[0054] Figure 2 is the SEM image of solid D (diamond) recovered in Example 1, Figure 3 is the SEM image of the diamond recovered in Comparative Example 1. It can be seen that Figure 3 a large number of silicon carbide particles are adsorbed on the surface of the solid in, which is due to the poor separation effect caused by the lack of a dispersant during flotation.

[0055] Almost no silicon carbide debris can be seen on the surface of the diamond after cleaning, indicating that a suitable flotation process is necessary for recovering diamond powder from grinding waste liquid.

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

[0057] Table 1

[0058]

[0059]

[0060] Elemental analysis was carried out on the diamond particles before and after recycling by ICP-AES. The results showed that the mass fractions of the main metal impurities such as Na, Al, V, Cr, Mn, and Fe were significantly reduced. This result confirmed the effectiveness of the recycling process in efficiently removing metal pollutants and provided data support for the recycling and reuse of waste diamond cutting fluid in high-end wafer cutting.

[0061] The particle size indexes of the recycled diamond abrasives in Example 1 are shown in the following table:

[0062] Table 2

[0063]

[0064] By testing the particle size of the recycled diamonds, the D50 of the cleaned recycled material was 2.93 μm, D90 / D10 = 2.8, the particle size distribution range was narrow, and D100 = 5.87 μm. The results showed that the recycling process could ensure the particle size consistency of the cutting abrasives and avoid scratching the wafer with large particles.

[0065] The statistical results of the multiple recovery rates of the recycled diamond abrasives in Example 1 are shown in Table 3 below:

[0066] Table 3

[0067]

[0068] By statistically analyzing the mass of the diamonds before and after cleaning multiple times, the recovery rate was at least 80%, and when the single-batch processing volume was larger, the recovery rate was higher. The recovery rate results showed that the recycling process of the present invention could achieve efficient recovery and reduce the waste of diamond abrasives.

[0069] Example 2

[0070] Step 1: Add 4 kg of grinding waste liquid to 10 mL of 3% sodium tripolyphosphate solution, stir evenly, the inlet air temperature of the drying tower is 180 °C, the outlet air temperature is 120 °C, the atmosphere is nitrogen, the flow rate is 3 m / s, and the slurry feeding rate is 200 mL / min. Spray drying is carried out to collect solid A.

[0071] Step 2: Mix solid A with 5000 mL of 0.5 mol / L sodium hydroxide solution, where the proportion of ethanol is 25%. Ultrasonic and stir at 40 °C for 60 min, and let it settle naturally to obtain solid B.

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

[0073] Step 4: Mix solid C with 8000 mL of 0.5 wt% polyethylene glycol solution, stir at 45 °C for 40 min, add 10 mL of 3% sodium tripolyphosphate solution, the aeration rate of the micro-nano bubble generator is 0.3 L / min, the aeration time is 30 min, scrape off the foam, obtain the lower-layer solid and dry it, and finally 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, the inlet air temperature of the drying tower is 250 °C, the outlet air temperature is 150 °C, the atmosphere is nitrogen, the flow rate is 5 m / s, the slurry feeding rate is 250 mL / min, and collect the solid A by spray drying.

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

[0078] Step 4: Mix solid C with 10000 mL of 1 wt% sodium silicate solution, stir at 40 °C for 60 min, add 20 mL of 5% sodium hexametaphosphate solution, the aeration rate of the micro-nano bubble generator is 0.2 L / min, the aeration time is 20 min, scrape off the foam, obtain the lower-layer solid and dry it, and finally obtain powder solid D (diamond).

[0079] Comparative Example 1

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

[0081] Step 1: Add 2 kg of grinding waste liquid to 10 mL of 5% sodium hexametaphosphate solution, stir evenly, the inlet air temperature of the drying tower is 150 °C, the outlet air temperature is 100 °C, the atmosphere is argon, the flow rate is 4 m / s, the slurry feeding rate is 100 mL / min, and collect the solid A by spray drying.

[0082] Step 2: Mix solid A with 2000 mL of 1 mol / L potassium hydroxide solution, where the proportion of ethanol is 10%, ultrasonic and stir at 50 °C 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 °C for 60 min, and naturally settle to obtain solid C.

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

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

[0086] Table 4

[0087]

[0088]

[0089] The particle size index of the diamond abrasives recovered in Comparative Example 1 is shown in Table 5 below. It can be seen that when sodium hexametaphosphate solution is not added in Step 4, the particle size distribution of the recovered diamond becomes wider, it is difficult to ensure the particle size consistency of the cutting abrasives, and large particles are likely to scratch the wafer.

[0090] Table 5

[0091]

[0092] The statistical results of the multiple recovery rates of the diamond abrasives 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 in Example 1.

[0097] Step 1: Stir 2 kg of grinding waste liquid evenly, the inlet air temperature of the drying tower is 150 °C, the outlet air temperature is 100 °C, the atmosphere is argon, the flow rate is 4 m / s, the slurry feeding rate is 100 mL / min, and spray drying is carried out to collect solid A.

[0098] Step 2: Mix solid A with 2000 mL of 1 mol / L potassium hydroxide solution, where the proportion of ethanol is 10%, ultrasonic and stir at 50 °C for 30 min, 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 at 40 °C for 60 min, and naturally settle to obtain solid C.

[0100] Step 4: Mix solid C with 4000 mL of 0.1 wt% sodium metasilicate solution, stir at 40 °C for 30 min, add 10 mL of 5% sodium hexametaphosphate solution, the aeration rate of the micro-nano bubble generator is 0.2 L / min, the aeration time is 30 min, scrape off the foam, obtain the lower-layer solid and dry it to finally obtain powder solid D (diamond).

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

[0102] Table 7

[0103]

[0104] The particle size indexes of the diamond abrasives recovered in Comparative Example 2 are shown in Table 8 below:

[0105] Table 8

[0106]

[0107] The statistical results of the multiple recovery rates of the diamond abrasives recovered in 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 in Example 1.

[0112] Step 1: Add 10 mL of 5% sodium hexametaphosphate solution to 2 kg of grinding waste liquid, stir evenly, the inlet air temperature of the drying tower is 150 °C, the outlet air temperature is 100 °C, the atmosphere is argon, the flow rate is 4 m / s, and the slurry feeding rate is 100 mL / min. Spray dry and collect to obtain solid A.

[0113] Step 2: Mix solid A with 2000 mL of 1 mol / L potassium hydroxide solution, do not add ethanol, ultrasonic and stir at 50 °C for 30 min, and naturally settle to obtain solid B.

[0114] Step 3: Mix solid B with 2000 mL of 0.5 mol / L hydrochloric acid, ultrasonic and stir at 40 °C for 60 min, and naturally settle to obtain solid C.

[0115] Step 4: Mix solid C with 4000 mL of 0.1 wt% sodium metasilicate solution, stir at 40 °C for 30 min, add 10 mL of 5% sodium hexametaphosphate solution, the aeration rate of the micro-nano bubble generator is 0.2 L / min, the aeration time is 30 min, scrape off the foam, obtain the lower-layer solid and dry it to finally obtain powder solid D (diamond).

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

[0117] Table 10

[0118]

[0119] The particle size indexes of the diamond abrasives recovered in Comparative Example 3 are shown in Table 11 below:

[0120] Table 11

[0121]

[0122] The statistics of the multiple recovery rates of the diamond abrasives recovered in 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 in Example 1.

[0128] Step 1: Add 10 mL of 5% sodium dodecyl sulfate (SDS) solution to 2 kg of grinding waste liquid, stir evenly, the inlet air temperature of the drying tower is 150 °C, the outlet air temperature is 100 °C, the atmosphere is argon, the flow rate is 4 m / s, and the slurry feeding rate is 100 mL / min. Spray dry and collect to obtain solid A.

[0129] Step 2: Mix solid A with 2000 mL of 1 mol / L potassium hydroxide solution, where the proportion of ethanol is 10%, ultrasonically stir at 50 °C for 30 min, and naturally settle to obtain solid B.

[0130] Step 3: Mix solid B with 2000 mL of 0.5 mol / L hydrochloric acid, ultrasonically stir at 40 °C for 60 min, and naturally settle to obtain solid C.

[0131] Step 4: Mix solid C with 4000 mL of 0.1 wt% sodium metasilicate solution, stir at 40 °C for 30 min, add 10 mL of 5% sodium hexametaphosphate solution, the ventilation rate of the micro-nano bubble generator is 0.2 L / min, the ventilation time is 30 min, scrape off the foam, obtain the lower-layer solid and dry it to finally obtain powder solid D (diamond).

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

[0133] Table 13

[0134]

[0135]

[0136] The particle size indexes of the diamond abrasives recovered in Comparative Example 4 are shown in Table 14 below:

[0137] Table 14

[0138]

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

[0140] Table 15

[0141]

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

Claims

1. A method for recovering diamond from silicon carbide wafer grinding waste liquid, characterized in that: It includes the following steps: Adding a dispersant to the waste liquid from the grinding of silicon carbide wafers, and then performing spray drying to obtain solid A; Adding solid A to an alkaline solution, performing ultrasonic and stirring treatment for a set time, and after solid-liquid separation, obtaining solid B; Adding solid B to a strong acid solution, performing ultrasonic and stirring treatment for a set time, and after solid-liquid separation, obtaining solid C; Adding solid C to a surfactant solution, heating and stirring for a set time; Finally, adding a dispersant to the mixed system, removing wafer debris by flotation, and drying the remaining solid to obtain diamond; The dispersant is one or a combination of sodium hexametaphosphate, sodium tripolyphosphate, or polyvinyl alcohol.

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

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

4. The method for recovering diamond from the silicon carbide wafer grinding waste liquid according to claim 1, characterized in that: The alkaline substance in the alkaline solution is one or a combination of sodium hydroxide, ammonia water, potassium hydroxide, sodium bicarbonate, or potassium bicarbonate; Preferably, the concentration of the alkaline solution is 0.5-5 mol / L; Preferably, the alkaline solution further includes ethanol, and the mass percentage of ethanol is 5%-50%; Preferably, the time for ultrasonic and stirring of solid A in the alkaline solution is 10-240 min, and the temperature is 20-70°C.

5. The method for recovering diamond from silicon carbide wafer grinding waste liquid according to claim 1, characterized in that: 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; Preferably, the time for ultrasonic and stirring after mixing solid B with the strong acid solution is 10-240 min, and the temperature is 20-70°C.

6. The method for recovering diamond from the silicon carbide wafer grinding waste liquid according to claim 1, characterized in that: The surfactant is one or a combination of sodium metasilicate, polyethylene glycol, or sodium silicate.

7. The method for recovering diamond from the silicon carbide wafer grinding waste liquid according to claim 6, wherein: In the surfactant solution, the concentration of the surfactant solution is 0.01-5wt%.

8. The method for recovering diamond from the silicon carbide wafer grinding waste liquid according to claim 1, wherein: After mixing solid C with the surfactant solution, the time for ultrasonic and stirring is 30-240 min, and the temperature is 20-60°C.

9. The method for recovering diamond from the silicon carbide wafer grinding waste liquid according to claim 1, wherein: The concentration of the dispersant added during flotation is 1wt%-5wt%.

10. The method for recovering diamond from the waste liquid of silicon carbide wafer grinding according to claim 1, characterized in that: 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.

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