Method for recycling BOE waste liquid

Abstract

The invention discloses a BOE waste liquid resource reutilization method, which comprises: 1, converting silicon ions in a BOE waste liquid into SiO2 precipitate, removing the SiO2 precipitate, and converting fluorine ions in the BOE waste liquid into NH4F; 2, fluorine ions in the filtrate obtained in the step 1 are converted into CaF2, and ammonium ions in the filtrate obtained in the step 1 are converted into ammonia water; 3, ammonia gas in the filtrate obtained in the step 2 escapes, CaF2 is separated after the filtrate is cooled, the separated CaF2 is used for producing HF, and the HF is used for preparing BOE for recycling; 4, directly feeding the filtrate obtained in the step 3 to sewage treatment; 5, the ammonia gas obtained in the step 3 is used for silicon removal and BOE preparation in the step 1 for recycling. According to the method, high-purity CaF2 can be obtained with high yield, NH4 < + > in BOE can be recycled, and the whole process is high in resource utilization rate and high in fluorine ion recovery rate.

Description

Technical Field

[0001] The present application relates to the technical field of BOE waste liquid resource utilization, and specifically to a method for resource reuse of BOE waste liquid. Background Art

[0002] With the rapid development of electronic-grade semiconductor technology, wet etching to finely control the microscopic pattern of chips has become an important process in chip production. As an important wet etchant, BOE is widely used to etch silicon dioxide and silicon nitride films.

[0003] BOE stock solution mainly contains hydrofluoric acid and ammonium fluoride, but after BOE has finished etching the silicon dioxide film, a small amount of fluorosilicic acid will be added to the BOE waste liquid. If the BOE waste liquid is directly discharged as waste liquid, it will not only waste resources but also cause environmental pollution. Moreover, fluorite, as a scarce non-renewable resource, has been listed as a strategic key mineral, so it is of great significance to utilize BOE waste liquid as a resource and reduce the consumption of fluorite.

[0004] The traditional BOE waste liquid treatment process is to directly use quicklime and slaked lime to precipitate the fluoride ions in the BOE waste liquid. However, since the BOE waste liquid also contains fluorosilicic acid, the precipitated CaF2 also contains a lot of SiO2 impurities, which makes the purity of CaF2 low and cannot be directly used for HF production. Although the patent with application number CN2021114611532 can obtain high-purity CaF2, the method is complicated and a variety of chemical reagents are used in the process, which will form more salts. Therefore, in order to obtain high-purity CaF2, high-temperature firing is required in the process, resulting in a lot of energy consumption.

[0005] Patent application number CN2023102478553 discloses a method for recycling BOE waste liquid, which can determine whether to produce ammonium chloride products or ammonium sulfate products based on the content of impurities such as sulfate or chloride in the BOE waste liquid. The main components in the BOE waste liquid can be fully recycled, and sodium fluorosilicate, cryolite and agricultural ammonium salt products that meet the requirements of relevant national standards can be produced, realizing high-value utilization of resources. Although this patent also involves the recycling of BOE waste liquid, it cannot achieve the recycling of components, nor can it achieve the acquisition of CaF2.

[0006] Therefore, how to obtain high-purity CaF2 with high yield and recycle NH4 in BOE? + , which is a technical problem that needs to be solved urgently. Summary of the invention

[0007] The purpose of this application is to provide a method for resource recycling of BOE waste liquid to solve the problems in the above-mentioned background technology.

[0008] To achieve the above objectives, the present application provides the following technical solution: a method for recycling BOE waste liquid, comprising: Step 1: within a certain pH range and a certain reaction temperature, silicon ions in the BOE waste liquid are converted into SiO2 precipitation for removal, and fluoride ions in the BOE waste liquid are converted into NH4F; Step 2: converting the fluoride ions in the filtrate obtained in step 1 into CaF2, and converting the ammonium ions into ammonia water; Step 3: Within a certain reaction temperature, the ammonia in the reaction solution of step 2 is released, and the filtrate is cooled after filtering to separate CaF2. The separated CaF2 is used to produce HF, and HF is used for preparing BOE for recycling; Step 4: The filtrate obtained in step 3 contains substantially no F - and NH4 + , can be directly sent to sewage treatment; Step 5: The ammonia obtained in step 3 is used for desiliconization in step 1 and for preparing BOE for recycling.

[0009] After experimental testing, the purity of CaF2 obtained in this application can reach more than 95%, and the recovery rate of fluoride ions can reach 96%. Not only can high-purity CaF2 be obtained at a high yield, but NH4 in BOE can also be recovered and reused. + The resource utilization rate of the whole process is high and the recovery rate of fluoride ions is high.

[0010] Furthermore, in step 1, ammonia water is used to react with HF and H2SiF6 in the BOE waste liquid respectively, so as to convert silicon ions in the BOE waste liquid into SiO2 and convert fluoride ions into NH4F. The reaction formula is: , .

[0011] Furthermore, the reaction pH range of step 1 is 8.5-9.5, and the reaction temperature is 30-40°C.

[0012] Furthermore, when removing SiO2, a flocculant is added to the reaction solution to precipitate SiO2 and then filter it to complete the removal.

[0013] Furthermore, the filtrate obtained in step 1 contains NH4F. 1.0-1.05 reaction equivalents of calcium oxide are added to the filtrate. After sufficient reaction, calcium oxide and NH4F react to convert fluoride ions in the filtrate into CaF2 and ammonium ions into ammonia water. The reaction formula is: .

[0014] Furthermore, in step three: the ammonia in the reaction solution of step two is blown off by heating at 70-90°C, and the filtrate is cooled to 25-40°C after filtering to obtain a filter cake, which is then washed and separated to obtain high-purity fluorite powder, which can be directly used to produce HF and used for BOE recycling.

[0015] Furthermore, the ammonia gas obtained in step three is absorbed by water to form ammonia water for recycling, and is used to realize the conversion of silicon ions in the BOE waste liquid into SiO2 and the conversion of fluoride ions into NH4F in step one.

[0016] Furthermore, the ammonia obtained in step 3 is absorbed by water and used to prepare NH4F, and NH4F is used to prepare BOE for recycling.

[0017] Furthermore, the ammonia water reacts with HF and H2SiF6 in the BOE waste liquid to generate NH4F and SiO2.

[0018] Furthermore, the flocculant is at least one of polyacrylamide, starch derivatives and cellulose derivatives.

[0019] Compared with the prior art, the beneficial effects of this application are: The method for recycling BOE waste liquid in this application can not only obtain high-purity CaF2 with high yield, but also recycle and reuse NH4 in BOE. + The whole process has high resource utilization rate, and the use of quicklime as a precipitant can make full use of its exothermic effect, reduce the amount of steam used in the stripping of ammonia, and reduce the energy consumption of the recovery process. At the same time, after the stripping of ammonia, Ca(OH)2 can be more fully converted into CaF2 to obtain high-purity recovered fluorite powder. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Schematic diagram of the steps of Example 1. DETAILED DESCRIPTION

[0021] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0022] Example 1 A method for recycling BOE waste liquid, such as Figure 1 As shown, including: Step 1: adding ammonia water to the BOE waste liquid at a pH range of 8.5-9.5 and a temperature of 30-40°C, the ammonia water reacts with HF and H2SiF6 in the BOE waste liquid respectively, converting the silicon ions in the BOE waste liquid into SiO2, and converting the fluoride ions into NH4F. When removing SiO2, adding a flocculant to the reaction liquid to precipitate SiO2 and then filtering to complete the removal. The filtered filtrate mainly contains NH4F; Step 2: Add calcium oxide to the filtrate obtained in step 1, and after sufficient reaction, convert fluoride ions into CaF2 and ammonium ions into ammonia water; Step 3: The ammonia in the reaction solution obtained in step 2 is released at 70-90°C. After the ammonia is completely released, the reaction solution is cooled to 25-40°C and then filtered to separate CaF2. The separated CaF2 is high-purity fluorite powder, which can be directly used to produce HF, and HF is used to prepare BOE for recycling; Step 4: The filtrate obtained in step 3 contains substantially no F - and NH4 + , can be directly sent to sewage treatment; Step 5: The ammonia gas obtained in step 3 is absorbed by water to form ammonia water, which is used to convert fluoride ions into NH4F in step 1 and remove silicon ions in BOE waste liquid. On the other hand, it is used to prepare NH4F, which is used for preparing BOE for recycling.

[0023] Example 2 After analyzing the components of the recycled BOE waste liquid from the memory chip factory, the content is as follows: Ingredient name Content (w / w%) HF 17.4 <![CDATA[NH4F]]> 19.6 <![CDATA[H2SiF6]]> 3.1 .

[0024] The BOE waste liquid was recycled by referring to the method of Example 1. Specifically, 1 kg of the BOE waste liquid was put into a 5 L PFA cup, and ammonia water (15%) was added thereto to adjust the pH value of the solution to 8.8. The solution was stirred at 35°C for 15 min, and then a flocculant was added to flocculate and the solution was filtered to remove SiO2•H2O precipitation. The filtrate temperature was 32.4°C. The filtrate was transferred to a 5 L three-necked flask, and 432.2 g of quicklime was quickly added to the filtrate. - The equivalent of 1.01 was added, and then the ammonia absorption device was connected. After stirring, a large amount of ammonia escaped and was absorbed. The highest temperature of the system was 65.3℃. The ammonia evaporation temperature was maintained at 80℃ by water bath heating. After the ammonia evaporation was completed, the reaction liquid was cooled to 30℃ and filtered to obtain a CaF2 filter cake. The filter cake was washed and dried to obtain a high-purity CaF2 powder of 601.8g in total, and the theoretical recovery amount was 596.0g. The purity of the CaF2 powder was tested to be 95.6%, so the F of BOE - The recovery rate YF is: .

[0025] Example 3 H2SiF6 was added to the BOE waste liquid in Example 2 to adjust the composition of the BOE waste liquid. The composition of the BOE waste liquid after adjustment is shown in the following table: Ingredient name Content (w / w%) HF 16.5 <![CDATA[NH4F]]> 18.5 <![CDATA[H2SiF6]]> 8.3 .

[0026] The BOE waste liquid was recycled by referring to the method of Example 1. Specifically, 1 kg of the BOE waste liquid was put into a 5 L PFA cup, and ammonia water (15%) was added thereto to adjust the pH value of the solution to 8.7. The solution was stirred at 35°C for 15 min, and then a flocculant was added to flocculate and the solution was filtered to remove SiO2•H2O precipitation. The filtrate temperature was 32.5°C. The filtrate was transferred to a 5 L three-necked flask, and 472.5 g of quicklime was quickly added to the filtrate. - The equivalent of 1.01 was added, and then the ammonia absorption device was connected. After stirring, a large amount of ammonia escaped and was absorbed. The highest temperature of the system was 69.2°C. The ammonia evaporation temperature was maintained at 80°C by water bath heating. After the ammonia evaporation was completed, the reaction liquid was cooled to 30°C, and the CaF2 filter cake was filtered. After washing and drying, a total of 656.4g of high-purity CaF2 powder was obtained, and the theoretical recovery amount was 651.6g. The purity of the CaF2 powder was tested to be 95.5%, so the F of BOE - The recovery rate YF is: .

[0027] Example 4 This example continues to use the BOE waste liquid of Example 3, and also refers to the method of Example 1 to perform resource recycling of the BOE waste liquid. Specifically, 1 kg of the BOE waste liquid is put into a 5L PFA cup, and ammonia water (15%) is added thereto to adjust the pH of the solution to 8.7. The solution is stirred at 35°C for 15 minutes, and then a flocculant is added to flocculate and the solution is filtered to remove SiO2•H2O precipitation. The obtained filtrate temperature is 32.5°C. The filtrate is transferred to a 5L three-necked flask. Different from Example 3, the amount of quicklime added in this example is changed to 449.3g, and the amount of quicklime added is adjusted according to F - Add 1.05 times the equivalent, then connect the ammonia absorption device. After stirring, a large amount of ammonia escapes and is absorbed. The highest temperature of the system is 69.2℃. Heat in a water bath to maintain the ammonia evaporation temperature at 80℃. After the ammonia evaporation is completed, cool the reaction liquid to 30℃, filter to obtain CaF2 filter cake, wash and dry to obtain a total of 614.2g of CaF2 powder. The purity of CaF2 powder is 94.9% after testing, so the F of BOE - The recovery rate is: .

[0028] Example 5 This example continues to use the BOE waste liquid of Example 3, and refers to the method of Example 1 to perform resource recycling of the BOE waste liquid. Specifically, 1 kg of the BOE waste liquid is put into a 5L PFA cup. Unlike Example 3, the amount of ammonia water added is changed to (15%), and the pH of the solution is adjusted to 7.2. The reaction is stirred at 35°C for 15 minutes, and then a flocculant is added to flocculate and the solution is filtered to remove SiO2•H2O precipitation. The filtrate temperature is 31.3°C. The filtrate is transferred to a 5L three-necked flask. Unlike Example 3, the amount of quicklime added in this example is changed to 449.3g. According to F - Add 1.05 times the equivalent, then connect the ammonia absorption device. After stirring, a large amount of ammonia escapes and is absorbed. The highest temperature of the system is 69.2℃. Heat in a water bath to maintain the ammonia evaporation temperature at 80℃. After the ammonia evaporation is completed, cool the reaction liquid to 30℃, filter to obtain CaF2 filter cake, wash and dry to obtain a total of 662.7g of CaF2 powder. The purity of CaF2 powder is 94.3% after testing, so the F of BOE - The recovery rate is: .

[0029] Example 6 In this embodiment, based on the embodiment 2, the stirring temperature of the silicon removal step was controlled to 15°C and stirred for 15 minutes, and the CaF2 powder finally obtained was 574.7g. The purity of the CaF2 powder was 95.6%, so the F content of BOE was - The recovery rate is: .

[0030] Example 7 In this example, based on Example 2, the ammonia evaporation temperature was changed to 60°C, and the final CaF2 powder obtained was 598.9g. The purity of the CaF2 powder was 95.1%, so the F - The recovery rate is: .

[0031] In summary, from the comparison between Examples 2 and 3, it can be seen that the recovery scheme has a high tolerance for the content of H2SiF6 in BOE waste liquid, and the increase in H2SiF6 content does not affect the purity and F content of the recovered fluorite powder. - From the comparison of Examples 2 and 4, it can be seen that the increase in the amount of quicklime added will cause the recovered fluorite powder to be mixed with slaked lime impurities, thereby reducing the purity of the fluorite powder, but excessive quicklime will cause the F in the waste liquid - The precipitation is more complete, so F- The recovery rate will increase; from the comparison of Examples 2 and 6, it can be seen that when the stirring temperature during silicon removal is reduced, F - The recovery rate is reduced because the temperature is too low, causing some NH4F to precipitate and be removed and lost during silicon removal. By comparing Example 2 with Example 7, it can be seen that lowering the ammonia evaporation temperature will lead to a decrease in the purity of the recovered CaF2 powder. - The recovery rate is also reduced. This is because the ammonia evaporation temperature is not enough, resulting in incomplete volatilization of ammonia water. The remaining ammonia water will cause CaF2 to generate a small amount of Ca(OH)2, which will reduce the purity of fluorite powder and F - The recovery rate is reduced, and if the temperature is too high, a large amount of water will evaporate and the energy consumption will be too high. By comparing Examples 3 and 5, it can be seen that when the pH during silicon removal is too low, incomplete silicon removal will occur, which will cause the recovered fluorite powder to contain SiO2 impurities and reduce the purity. Therefore, the pH value of silicon removal should be controlled well.

Claims

1. A method for recycling BOE waste liquid, characterized in that: include: Step 1: within a certain pH range and a certain reaction temperature, silicon ions in the BOE waste liquid are converted into SiO2 precipitation for removal, and fluoride ions in the BOE waste liquid are converted into NH4F; Step 2: converting the fluoride ions in the filtrate obtained in step 1 into CaF2, and converting the ammonium ions into ammonia water; Step 3: Within a certain reaction temperature, the ammonia in the reaction solution of step 2 is released, and the filtrate is cooled after filtering to separate CaF2. The separated CaF2 is used to produce HF, and HF is used for preparing BOE for recycling; Step 4: directly send the filtrate obtained in step 3 to sewage treatment; Step 5: The ammonia obtained in step 3 is used for preparing BOE for recycling.

2. The method for recycling BOE waste liquid according to claim 1, characterized in that: In step 1, ammonia water is used to react with HF and H2SiF6 in the BOE waste liquid respectively, so as to convert silicon ions in the BOE waste liquid into SiO2 and convert fluoride ions into NH4F.

3. The method for recycling BOE waste liquid according to claim 2, characterized in that: The reaction pH range of step 1 is 8.5-9.5, and the reaction temperature is 30-40°C.

4. The method for recycling BOE waste liquid according to claim 1, characterized in that: When removing SiO2, a flocculant is added to the reaction solution to precipitate SiO2 and then filtered to complete the removal.

5. A method for recycling BOE waste liquid according to claim 1, 3 or 4, characterized in that: In step 2: calcium oxide or calcium hydroxide is added to the filtrate obtained in step 1, and the calcium oxide or calcium hydroxide reacts with NH4F to convert the fluoride ions in the filtrate into CaF2 and the ammonium ions into ammonia water.

6. The method for recycling BOE waste liquid according to claim 1 or 4, characterized in that: In step 3: heat and blow off at 70-90°C to remove ammonia in the reaction solution of step 2, filter and cool the filtrate to 25-40°C to obtain a filter cake, wash and separate CaF2.

7. The method for recycling BOE waste liquid according to claim 6, characterized in that: The ammonia gas obtained in step three is absorbed by water to form ammonia water for recycling, and is used to convert silicon ions in the BOE waste liquid into SiO2 and fluoride ions into NH4F in step one.

8. The method for recycling BOE waste liquid according to claim 6, characterized in that: The ammonia obtained in step 3 is absorbed by water and then recycled to prepare NH4F, and NH4F is used to prepare BOE and recycled.

9. The method for recycling BOE waste liquid according to claim 7, characterized in that: Ammonia water reacts with HF and H2SiF6 in BOE waste liquid to generate NH4F and SiO2.

10. The method for recycling BOE waste liquid according to claim 4, characterized in that: The flocculant is at least one of polyacrylamide, starch derivatives and cellulose derivatives.

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