A method and system for treating photovoltaic waste liquid

Abstract

This application relates to the field of industrial wastewater treatment technology, and discloses a method and system for treating photovoltaic waste liquid. The method for treating photovoltaic waste liquid provided by this application includes the following steps: adding calcium hydroxide and calcium chloride to a fluoride-containing acidic waste liquid, and controlling the pH value of the reaction solution to 6-8. The fluoride-containing acidic waste liquid includes dilute acid and concentrated acid. Fluorine in photovoltaic waste liquid exists only in dilute and concentrated acids, while dilute and concentrated alkalis contain almost no fluorine. This application mixes dilute and concentrated acids to form a fluoride-containing acidic waste liquid, and mixes dilute and concentrated alkalis to form a fluoride-free waste liquid. By adding calcium hydroxide and calcium chloride to the fluoride-containing acidic waste liquid, the pH value of the fluoride-containing acidic waste liquid is adjusted by calcium hydroxide and calcium chloride, while calcium fluoride precipitate is generated to fix the fluorine element. This not only effectively reduces the fluorine element in the fluoride-containing acidic waste liquid, but also saves the amount of reagents used, simplifies the treatment steps, and improves the reaction efficiency.

Description

Technical Field

[0001] This application relates to the field of industrial wastewater treatment technology, specifically to a method and system for treating photovoltaic waste liquid. Background Technology

[0002] In photovoltaic production processes (such as silicon wafer cutting, cleaning, texturing, and etching), a large amount of waste liquid is generated. This includes dilute acid containing low concentrations of mixed acids such as hydrofluoric acid, sulfuric acid, or hydrochloric acid; concentrated acid containing high concentrations of mixed acids such as hydrofluoric acid, hydrochloric acid, or sulfuric acid; dilute alkali containing low concentrations of sodium hydroxide or potassium hydroxide solution; and concentrated alkali containing high concentrations of sodium hydroxide or potassium hydroxide solution. The industry commonly uses a mixture of dilute acid, concentrated acid, dilute alkali, and concentrated alkali for treatment. However, because the amount of each type of waste liquid collected is not fixed, the resulting mixture... pH values ​​are random, so in actual treatment, it is usually necessary to test the pH value of the mixture. If the mixture is acidic, sodium hydroxide is added; if the mixture is alkaline, sulfuric acid is added to adjust the pH to 7-8. Then, a reagent is added to the mixture to adjust the pH value and precipitate fluoride. Finally, a flocculant is added to the mixture to reduce the concentration of fluoride ions in the waste liquid. After treatment, the pH value of the waste liquid is tested again and adjusted to meet the discharge standard.

[0003] Although the above methods can achieve the harmless treatment of photovoltaic waste liquid to a certain extent, at least two prominent problems have been exposed in actual operation: First, in the process of mixing and treating dilute acid, concentrated acid, dilute alkali, and concentrated alkali, the pH value of the mixed solution is highly uncertain because the amount of waste liquid of dilute acid, concentrated acid, dilute alkali, and concentrated alkali in the mixed solution is not fixed. On the one hand, it is necessary to repeatedly measure the pH value of the mixed solution during the treatment process and select appropriate reagents based on the measured pH value. However, the dosage is difficult to estimate accurately, often resulting in repeated cycles of "overdosing and adjustment," which wastes reagents. On the other hand, the fluctuation of the pH value of the mixed solution affects the defluorination efficiency. First, existing photovoltaic wastewater treatment methods are unstable, often requiring additional reagents, and involve cumbersome monitoring and complex operation. Second, fluoride in photovoltaic wastewater is only present in dilute and concentrated acids (derived from hydrofluoric acid), while dilute and concentrated alkalis contain almost no fluoride. Mixing alkaline and acidic wastewater may result in a neutralization reaction, but this neutralization itself does not remove fluoride. On the contrary, this method consumes hydrogen ions in the acidic wastewater, increasing the amount of reagent needed for subsequent calcium fluoride precipitation. Furthermore, the increased volume of alkaline solution dilutes the fluoride ion concentration, requiring not only sufficient reagents but also potentially prolonging sedimentation. Therefore, existing photovoltaic wastewater treatment methods are cumbersome to operate, require large amounts of reagents, and have low treatment efficiency. Summary of the Invention

[0004] This application provides a method for treating photovoltaic waste liquid, which solves the technical problems of complicated operation, large amount of reagents, and low treatment efficiency in photovoltaic waste liquid treatment methods.

[0005] In a first aspect, this application provides a method for treating photovoltaic waste liquid, comprising the following steps: adding calcium hydroxide and calcium chloride to a fluoride-containing acidic waste liquid, and controlling the pH value of the fluoride-containing acidic waste liquid at 6-8, wherein the fluoride-containing acidic waste liquid includes dilute acid and concentrated acid.

[0006] As an example, the pH value of the fluorinated acidic waste liquid is controlled at 6, 6.1, 6.2, 6.5, 6.7, 6.8, 7, 7.2, 7.3, 7.4, 7.5, 7.6, 7.7, 7.8, 7.9, or 8, or within any range of the above values.

[0007] In one optional embodiment, the pH value of the fluoride-containing acidic waste liquid is controlled at 6.8-7.5.

[0008] In one optional embodiment, the pH value of the fluoride-containing acidic waste liquid is controlled at 7.2-7.8.

[0009] In one optional embodiment, the concentration of calcium hydroxide is 5.5-8.5 g / L and the concentration of calcium chloride is 3.8-6 g / L, based on the volume of the fluoride-containing acidic waste liquid.

[0010] In one optional embodiment, the volume ratio of the dilute acid to the concentrated acid is 2-5:1.

[0011] In one optional embodiment, the method for treating photovoltaic waste liquid further includes the step of adding a flocculant to the fluoride-containing acidic waste liquid.

[0012] In one alternative embodiment, the method further includes a step of precipitating the fluorinated acidic wastewater after the addition of the flocculant.

[0013] In one alternative embodiment, the flocculant includes at least one of polyacrylamide and polyaluminum chloride.

[0014] In one alternative embodiment, the concentration of the flocculant is 3-5 mg / L, based on the volume of the fluorinated acidic waste liquid.

[0015] In one optional embodiment, the method further includes mixing dilute alkali and concentrated alkali to form an alkaline waste liquid, and then adding dilute sulfuric acid to the alkaline waste liquid to adjust the pH value of the alkaline waste liquid to 6.8-7.5.

[0016] In one optional embodiment, the method further includes the step of mixing the fluorinated wastewater after flocculant precipitation with an alkaline solution after pH adjustment.

[0017] Secondly, this application also provides a photovoltaic waste liquid treatment system, characterized in that it includes an acid treatment unit, the acid treatment unit including an acid conditioning tank and a first neutralization precipitation reaction tank, and the photovoltaic waste liquid treatment system is used to implement the above-mentioned photovoltaic waste liquid treatment method.

[0018] In one optional embodiment, an alkaline treatment unit is further included, the alkaline treatment unit comprising an alkaline conditioning tank and a second neutralization precipitation reaction tank.

[0019] In one alternative implementation, the treatment system further includes a sedimentation tank and a pH adjustment tank.

[0020] The technical solution of this application has the following advantages: The photovoltaic waste liquid treatment method provided in this application includes the following steps: adding calcium hydroxide and calcium chloride to a fluoride-containing acidic waste liquid, and controlling the pH value of the reaction solution to 6-8. The fluoride-containing acidic waste liquid includes dilute acid and concentrated acid. Fluorine in photovoltaic waste liquid exists only in dilute and concentrated acids, while dilute and concentrated alkalis contain almost no fluorine. This application mixes dilute and concentrated acids to form a fluoride-containing acidic waste liquid, and mixes dilute and concentrated alkalis to form a fluoride-free waste liquid. By adding calcium hydroxide and calcium chloride to the fluoride-containing acidic waste liquid, the pH value of the fluoride-containing acidic waste liquid is adjusted by calcium hydroxide and calcium chloride, while calcium fluoride precipitate is generated to fix the fluorine element. This not only effectively reduces the fluorine element in the fluoride-containing acidic waste liquid, but also saves on reagent usage, simplifies the treatment steps, and improves reaction efficiency.

[0021] The photovoltaic waste liquid treatment method provided in this application can reduce the fluoride ion concentration of the waste liquid to 8 mg / L and the pH value of the waste liquid to 6.5-7.5, thus meeting the discharge standards. Detailed Implementation

[0022] The following embodiments are provided to better understand this application. However, the following embodiments do not constitute a limitation on the content and scope of protection of this application. Any product that is the same as or similar to this application, derived by anyone under the guidance of this application or by combining the features of this application with other prior art, falls within the scope of protection of this application.

[0023] Unless otherwise specified, all experimental steps or conditions in the examples were performed according to conventional experimental procedures and conditions in the art. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0024] The photovoltaic waste liquids collected in the embodiments and comparative examples of this application are dilute acid (hydrofluoric acid concentration 5wt%), concentrated acid (hydrofluoric acid concentration 40wt%), dilute alkali (sodium hydroxide concentration 4wt%), and concentrated alkali (sodium hydroxide concentration 30wt%), respectively.

[0025] Example 1 This embodiment provides a method for treating photovoltaic waste liquid, and the specific steps and parameters are as follows: (1) According to the volume ratio of dilute acid to concentrated acid of 3:1, dilute acid and concentrated acid are mixed and pumped into the acid conditioning tank to form a fluoride-containing acidic waste liquid. The pH value of the fluoride-containing acidic waste liquid is 1.2 and the fluoride ion concentration is 8500mg / L. The fluoride-containing acidic waste liquid is then injected into the first neutralization and precipitation reaction tank. Calcium hydroxide and calcium chloride are added to the first neutralization and precipitation reaction tank so that the concentration of calcium hydroxide in the fluoride-containing acidic waste liquid is 6.2g / L and the concentration of calcium chloride is 4.5g / L. The mixture is stirred at 50rpm for 30min at 25℃ to obtain the first treatment liquid. The pH value of the first treatment liquid is 7.2 and the fluoride ion concentration is 6.5mg / L. Polyacrylamide flocculant is added to the first treatment liquid so that the concentration of polyacrylamide flocculant is 3mg / L. After stirring at 20rpm for 5min, the mixture is allowed to stand in the sedimentation tank for 20min. The supernatant is then separated and sent to the pH adjustment tank.

[0026] (2) According to the volume ratio of dilute alkali to concentrated alkali of 2:1, the dilute alkali and concentrated alkali are mixed and pumped into the alkaline adjustment tank to form alkaline waste liquid. The pH value of the alkaline waste liquid is 12.5. The alkaline waste liquid is injected into the sedimentation tank of the second neutralization tank. Under stirring conditions, 20wt% dilute sulfuric acid is added to it. The stirring speed is 10rpm and stirring is carried out for 15min until the pH value of the alkaline waste liquid is 7.0, and the second treatment liquid is obtained.

[0027] (3) The supernatant obtained in step (1) and the second treatment liquid obtained in step (2) are mixed in a pH adjustment tank. The pH value of the mixture is 7.1 and the fluoride ion concentration is 3.2 mg / L, which meets the emission standard.

[0028] Example 2 This embodiment provides a method for treating photovoltaic waste liquid, and the specific steps and parameters are as follows: (1) According to the volume ratio of dilute acid to concentrated acid of 2:1, dilute acid and concentrated acid are mixed and pumped into the acid conditioning tank to form a fluoride-containing acidic waste liquid. The pH value of the fluoride-containing acidic waste liquid is 1.0 and the fluoride ion concentration is 12000mg / L. Then, the fluoride-containing acidic waste liquid is injected into the first neutralization precipitation reaction tank. Calcium hydroxide and calcium chloride are added to the first neutralization precipitation reaction tank so that the concentration of calcium hydroxide in the fluoride-containing acidic waste liquid is 8.5g / L and the concentration of calcium chloride is 6g / L. Stir at 50rpm for 30min at 25℃ to obtain the first treatment liquid. The pH value of the first treatment liquid is 7.1 and the fluoride ion concentration is 5.8mg / L. Polyacrylamide flocculant is added to the first treatment liquid so that the concentration of polyacrylamide flocculant is 4mg / L. After stirring at 20rpm for 5min, it is put into the sedimentation tank and left to stand for 20min. The supernatant is separated and put into the pH adjustment tank.

[0029] (2) According to the volume ratio of dilute alkali to concentrated alkali of 2:1, the dilute alkali and concentrated alkali are mixed and pumped into the alkaline adjustment tank to form alkaline waste liquid. The pH value of the alkaline waste liquid is 12.5. The alkaline waste liquid is injected into the sedimentation tank of the second neutralization tank. Under stirring conditions, 20wt% dilute sulfuric acid is added to it. The stirring speed is 10rpm and stirring is carried out for 15min until the pH value of the alkaline waste liquid is 7.0, and the second treatment liquid is obtained.

[0030] (3) The supernatant obtained in step (1) and the second treatment liquid obtained in step (2) are mixed in a pH adjustment tank. The pH value of the mixture is 7 and the fluoride ion concentration is 2.9 mg / L, which meets the emission standard.

[0031] Example 3 This embodiment provides a method for treating photovoltaic waste liquid, and the specific steps and parameters are as follows: (1) According to the volume ratio of dilute acid to concentrated acid of 4:1, dilute acid and concentrated acid are mixed and pumped into the acid conditioning tank to form a fluoride-containing acidic waste liquid. The pH value of the fluoride-containing acidic waste liquid is 1.6 and the fluoride ion concentration is 7200mg / L. The fluoride-containing acidic waste liquid is then injected into the first neutralization and precipitation reaction tank. Calcium hydroxide and calcium chloride are added to the first neutralization and precipitation reaction tank so that the concentration of calcium hydroxide in the fluoride-containing acidic waste liquid is 5.5g / L and the concentration of calcium chloride is 3.8g / L. The mixture is stirred at 50rpm for 30min at 25℃ to obtain the first treatment liquid. The pH value of the first treatment liquid is 7.2 and the fluoride ion concentration is 7.2mg / L. Polyacrylamide flocculant is added to the first treatment liquid so that the concentration of polyacrylamide flocculant is 5mg / L. After stirring at 20rpm for 5min, the mixture is allowed to stand in the sedimentation tank for 20min. The supernatant is then separated and sent to the pH adjustment tank.

[0032] (2) According to the volume ratio of dilute alkali to concentrated alkali of 2:1, the dilute alkali and concentrated alkali are mixed and pumped into the alkaline adjustment tank to form alkaline waste liquid. The pH value of the alkaline waste liquid is 12.5. The alkaline waste liquid is injected into the sedimentation tank of the second neutralization tank. Under stirring conditions, 20wt% dilute sulfuric acid is added to it. The stirring speed is 10rpm and stirring is carried out for 15min until the pH value of the alkaline waste liquid is 7.0, and the second treatment liquid is obtained.

[0033] (3) The supernatant obtained in step (1) and the second treatment liquid obtained in step (2) are mixed in a pH adjustment tank. The pH value of the mixture is 7.2 and the fluoride ion concentration is 3 mg / L, which meets the emission standard.

[0034] Example 4 This embodiment provides a method for treating photovoltaic waste liquid, and the specific steps and parameters are as follows: (1) According to the volume ratio of dilute acid to concentrated acid of 2.5:1, dilute acid and concentrated acid are mixed and pumped into the acid conditioning tank to form a fluoride-containing acidic waste liquid. The pH value of the fluoride-containing acidic waste liquid is 1.1 and the fluoride ion concentration is 10500mg / L. The fluoride-containing acidic waste liquid is then injected into the first neutralization and precipitation reaction tank. Calcium hydroxide and calcium chloride are added to the first neutralization and precipitation reaction tank so that the concentration of calcium hydroxide in the fluoride-containing acidic waste liquid is 7.2g / L and the concentration of calcium chloride is 5.2g / L. The mixture is stirred at 50rpm for 30min at 25℃ to obtain the first treatment liquid. The pH value of the first treatment liquid is 6.9 and the fluoride ion concentration is 6.1mg / L. Polyacrylamide flocculant is added to the first treatment liquid so that the concentration of polyacrylamide flocculant is 3mg / L. After stirring at 20rpm for 5min, the mixture is allowed to stand in the sedimentation tank for 20min. The supernatant is then separated and sent to the pH adjustment tank.

[0035] (2) According to the volume ratio of dilute alkali to concentrated alkali of 2:1, the dilute alkali and concentrated alkali are mixed and pumped into the alkaline adjustment tank to form alkaline waste liquid. The pH value of the alkaline waste liquid is 12.5. The alkaline waste liquid is injected into the sedimentation tank of the second neutralization tank. Under stirring conditions, 20wt% dilute sulfuric acid is added to it. The stirring speed is 10rpm and stirring is carried out for 15min until the pH value of the alkaline waste liquid is 7.0, and the second treatment liquid is obtained.

[0036] (3) The supernatant obtained in step (1) and the second treatment liquid obtained in step (2) are mixed in a pH adjustment tank. The pH value of the mixture is 6.9 and the fluoride ion concentration is 3.08 mg / L, which meets the emission standard.

[0037] Example 5 This embodiment provides a method for treating photovoltaic waste liquid, and the specific steps and parameters are as follows: (1) According to the volume ratio of dilute acid to concentrated acid of 3:1, dilute acid and concentrated acid are mixed and pumped into the acid conditioning tank to form a fluoride-containing acidic waste liquid. The pH value of the fluoride-containing acidic waste liquid is 1.2 and the fluoride ion concentration is 8500mg / L. The fluoride-containing acidic waste liquid is then injected into the first neutralization and precipitation reaction tank. Calcium hydroxide and calcium chloride are added to the first neutralization and precipitation reaction tank so that the concentration of calcium hydroxide in the fluoride-containing acidic waste liquid is 6g / L and the concentration of calcium chloride is 4g / L. The mixture is stirred at 50rpm for 30min at 25℃ to obtain the first treatment liquid. The pH value of the first treatment liquid is 7.8 and the fluoride ion concentration is 6mg / L. Polyacrylamide flocculant is added to the first treatment liquid so that the concentration of polyacrylamide flocculant is 4mg / L. After stirring at 20rpm for 5min, the mixture is allowed to stand in the sedimentation tank for 20min. The supernatant is then separated and sent to the pH adjustment tank.

[0038] (2) According to the volume ratio of dilute alkali to concentrated alkali of 2:1, the dilute alkali and concentrated alkali are mixed and pumped into the alkaline adjustment tank to form alkaline waste liquid. The pH value of the alkaline waste liquid is 12.5. The alkaline waste liquid is injected into the sedimentation tank of the second neutralization tank. Under stirring conditions, 20wt% dilute sulfuric acid is added to it. The stirring speed is 10rpm and stirring is carried out for 15min until the pH value of the alkaline waste liquid is 7.0, and the second treatment liquid is obtained.

[0039] (3) The supernatant obtained in step (1) and the second treatment liquid obtained in step (2) are mixed in a pH adjustment tank. The pH value of the mixture is 7.3 and the fluoride ion concentration is 3.5 mg / L, which meets the emission standard.

[0040] Example 6 This embodiment provides a method for treating photovoltaic waste liquid. The specific steps and parameters are the same as in embodiment 1. The difference is that in step (1), calcium hydroxide and calcium chloride are added to the first neutralization and precipitation reaction tank so that the concentration of calcium hydroxide in the fluoride-containing acidic waste liquid is 6.1 g / L and the concentration of calcium chloride is 4.2 g / L. After treatment, the pH value of the first treatment liquid is 7.2 and the fluoride ion concentration is 6.9 mg / L. Polyacrylamide flocculant is added to the first treatment liquid so that the concentration of polyacrylamide flocculant is 4.5 mg / L.

[0041] (2) Same as in Example 1; (3) The supernatant obtained in step (1) and the second treatment liquid obtained in step (2) are mixed in a pH adjustment tank. The pH value of the mixture is 7.3 and the fluoride ion concentration is 3.6 mg / L, which meets the emission standard.

[0042] Example 7 This embodiment provides a method for treating photovoltaic waste liquid. The specific steps and parameters are the same as in embodiment 1. The difference is that in step (1), calcium hydroxide and calcium chloride are added to the first neutralization and precipitation reaction tank so that the concentration of calcium hydroxide in the fluoride-containing acidic waste liquid is 5.9 g / L and the concentration of calcium chloride is 4.5 g / L. After treatment, the pH value of the first treated liquid is 7 and the fluoride ion concentration is 6.4 mg / L. Polyacrylamide flocculant is added to the first treated liquid so that the concentration of polyacrylamide flocculant is 4.8 mg / L.

[0043] (2) Same as in Example 1; (3) The supernatant obtained in step (1) and the second treatment liquid obtained in step (2) are mixed in a pH adjustment tank. The pH value of the mixture is 6.9 and the fluoride ion concentration is 3.3 mg / L, which meets the emission standard.

[0044] Example 8 This embodiment provides a method for treating photovoltaic waste liquid. The specific steps and parameters are the same as in embodiment 1. The difference is that in step (1), calcium hydroxide and calcium chloride are added to the first neutralization and precipitation reaction tank so that the concentration of calcium hydroxide in the fluoride-containing acidic waste liquid is 4.9 g / L and the concentration of calcium chloride is 5.3 g / L. After treatment, the pH value of the first treated liquid is 6.5 and the fluoride ion concentration is 7.2 mg / L. Polyacrylamide flocculant is added to the first treated liquid so that the concentration of polyacrylamide flocculant is 5.6 mg / L.

[0045] (2) Same as in Example 1; (3) The supernatant obtained in step (1) and the second treatment liquid obtained in step (2) are mixed in a pH adjustment tank. The pH value of the mixture is 6.8 and the fluoride ion concentration is 4.1 mg / L, which meets the emission standard.

[0046] Example 9 This embodiment provides a method for treating photovoltaic waste liquid. The specific steps and parameters are the same as in embodiment 1. The difference is that in step (1), calcium hydroxide and calcium chloride are added to the first neutralization and precipitation reaction tank so that the concentration of calcium hydroxide in the fluoride-containing acidic waste liquid is 5.3 g / L and the concentration of calcium chloride is 5.1 g / L. After treatment, the pH value of the first treated liquid is 6.7 and the fluoride ion concentration is 6.9 mg / L. Polyacrylamide flocculant is added to the first treated liquid so that the concentration of polyacrylamide flocculant is 5 mg / L.

[0047] (2) Same as in Example 1; (3) The supernatant obtained in step (1) and the second treatment liquid obtained in step (2) are mixed in a pH adjustment tank. The pH value of the mixture is 6.8 and the fluoride ion concentration is 3.7 mg / L, which meets the emission standard.

[0048] Comparative Example 1 This comparative example provides a method for treating photovoltaic waste liquid, and the specific steps and parameters are as follows: The dilute acid, concentrated acid, dilute alkali, and concentrated alkali were mixed in a volume ratio of 3:1:2:1. The pH of the mixture was measured to be 5.1, and the fluoride ion concentration was 6500 mg / L. The mixture was then injected into a neutralization reaction tank, and 2.5 g / L of sodium hydroxide was added to adjust the pH to 7. Lime and calcium chloride were then added to the mixture to achieve a calcium carbonate concentration of 3.4 g / L and a calcium chloride concentration of 4.5 g / L in the fluoride-containing acidic wastewater. The mixture was then heated at 25°C at rpm. Stirring at a constant speed for 30 minutes yields a treated liquid with a pH of 9.4 and a fluoride ion concentration of 7.2 mg / L. Polyacrylamide flocculant is added to the treated liquid to achieve a concentration of 4.2 mg / L. The mixture is stirred at 20 rpm for 5 minutes and then allowed to settle in a sedimentation tank for 20 minutes. After settling, the pH of the supernatant is greater than 9. The supernatant is then returned to a pH adjustment tank, where chemicals are added to adjust the pH of the waste liquid to 6-8, meeting the discharge standards.

[0049] Comparative Example 2 This comparative example provides a method for treating photovoltaic waste liquid, and the specific steps and parameters are as follows: The dilute acid, concentrated acid, dilute alkali, and concentrated alkali were mixed in a volume ratio of 3:1:3:1. The pH of the mixture was measured to be 11, and the fluoride ion concentration was 7200 mg / L. The mixture was then injected into a neutralization reaction tank, and 1.5 g / L of sulfuric acid was added to the tank to bring the pH to 7.2. Calcium carbonate and calcium chloride were then added to the mixture, resulting in a calcium carbonate concentration of 3.1 g / L and a calcium chloride concentration of 4.8 g / L in the fluoride-containing acidic wastewater. The mixture was then heated at 25°C with a flow rate of 20 r / min. The solution was stirred at 10 rpm for 30 minutes to obtain a treated liquid with a pH of 9.1 and a fluoride ion concentration of 6.9 mg / L. Polyacrylamide flocculant was added to the treated liquid to bring the concentration to 4.5 mg / L. The solution was stirred at 10 rpm for 5 minutes and then allowed to settle in a sedimentation tank for 20 minutes. After settling, the pH of the supernatant was greater than 9. The supernatant was then returned to the pH adjustment tank, and a chemical solution was added to the pH adjustment tank to adjust the pH of the waste liquid to 6-8, meeting the discharge standards.

[0050] Comparative Example 3 This comparative example provides a method for treating photovoltaic waste liquid, and the specific steps and parameters are as follows: (1) According to the volume ratio of dilute acid to concentrated acid of 3:1, dilute acid and concentrated acid are mixed and pumped into the acid conditioning tank to form a fluoride-containing acidic waste liquid. The pH value of the fluoride-containing acidic waste liquid is 1.2 and the fluoride ion concentration is 8500mg / L. The fluoride-containing acidic waste liquid is then injected into the first neutralization and precipitation reaction tank. Calcium hydroxide and calcium chloride are added to the first neutralization and precipitation reaction tank so that the concentration of calcium hydroxide in the fluoride-containing acidic waste liquid is 2.3g / L and the concentration of calcium chloride is 5g / L. The mixture is stirred at 50rpm for 30min at 25℃ to obtain the first treatment liquid. The pH value of the first treatment liquid is 5.5 and the fluoride ion concentration is 9mg / L. Polyacrylamide flocculant is added to the first treatment liquid so that the concentration of polyacrylamide flocculant is 3mg / L. The mixture is stirred at 20rpm for 5min and then placed in the sedimentation tank for 20min. The supernatant is then separated and placed in the pH adjustment tank.

[0051] (2) According to the volume ratio of dilute alkali to concentrated alkali of 2:1, the dilute alkali and concentrated alkali are mixed and pumped into the alkaline adjustment tank to form alkaline waste liquid. The pH value of the alkaline waste liquid is 12.5. The alkaline waste liquid is injected into the sedimentation tank of the second neutralization tank. Under stirring conditions, 20wt% dilute sulfuric acid is added to it. The stirring speed is 10rpm and stirring is carried out for 15min until the pH value of the alkaline waste liquid is 7.0, and the second treatment liquid is obtained.

[0052] (3) The supernatant obtained in step (1) and the second treatment liquid obtained in step (2) are mixed in the pH adjustment tank. The pH value of the mixture is 5.9 and the fluoride ion concentration is 6 mg / L. The pH value cannot meet the discharge standard and the pH needs to be further adjusted in the adjustment tank.

[0053] Comparative Example 4 This comparative example provides a method for treating photovoltaic waste liquid, and the specific steps and parameters are as follows: (1) According to the volume ratio of dilute acid to concentrated acid of 3:1, dilute acid and concentrated acid are mixed and pumped into the acid conditioning tank to form a fluoride-containing acidic waste liquid. The pH value of the fluoride-containing acidic waste liquid is 1.2 and the fluoride ion concentration is 8500mg / L. The fluoride-containing acidic waste liquid is then injected into the first neutralization and precipitation reaction tank. Calcium hydroxide and calcium chloride are added to the first neutralization and precipitation reaction tank so that the concentration of calcium hydroxide in the fluoride-containing acidic waste liquid is 6.8g / L and the concentration of calcium chloride is 4.5g / L. The mixture is stirred at 50rpm for 30min at 25℃ to obtain the first treatment liquid. The pH value of the first treatment liquid is 8.5 and the fluoride ion concentration is 8.4mg / L. Polyacrylamide flocculant is added to the first treatment liquid so that the concentration of polyacrylamide flocculant is 3mg / L. The mixture is stirred at 20rpm for 5min and then placed in the sedimentation tank for 20min. The supernatant is then separated and placed in the pH adjustment tank.

[0054] (2) According to the volume ratio of dilute alkali to concentrated alkali of 2:1, the dilute alkali and concentrated alkali are mixed and pumped into the alkaline adjustment tank to form alkaline waste liquid. The pH value of the alkaline waste liquid is 12.5. The alkaline waste liquid is injected into the sedimentation tank of the second neutralization tank. Under stirring conditions, 20wt% dilute sulfuric acid is added to it. The stirring speed is 10rpm and stirring is carried out for 15min until the pH value of the alkaline waste liquid is 7.0, and the second treatment liquid is obtained.

[0055] (3) The supernatant obtained in step (1) and the second treatment liquid obtained in step (2) are mixed in the pH adjustment tank. The pH value of the mixture is 8.1 and the fluoride ion concentration is 5 mg / L. The pH value cannot meet the emission standard and the pH needs to be further adjusted in the pH adjustment tank.

[0056] Table 1 summarizes the parameters of the photovoltaic waste liquid treatment methods provided in Examples 1-9 and Comparative Examples 1-4 of this application.

[0057] Table 1. Treatment parameters and results of photovoltaic waste liquid

[0058] According to Table 1, in Comparative Example 1, a fluoride-containing solution was formed by mixing dilute acid, concentrated acid, dilute alkali, and concentrated alkali in photovoltaic wastewater. After adjusting the pH with sodium hydroxide and adding a flocculant, the pH of the photovoltaic wastewater was 9.4, and the fluoride content was 7.2 mg / L. In Comparative Example 2, a fluoride-containing solution was formed by mixing dilute acid, concentrated acid, dilute alkali, and concentrated alkali in photovoltaic wastewater. After adjusting the pH with sulfuric acid and adding a flocculant, the pH of the photovoltaic wastewater was 9.1, and the fluoride content was 6.9 mg / L. However, due to the increased volume of the fluoride-containing solution in Comparative Examples 1 and 2, the consumption of reagents, such as pH adjuster, lime, calcium carbonate, calcium chloride, and flocculant, needed to be doubled. Furthermore, the pH of the treated photovoltaic wastewater still did not meet the standards and could not be discharged. In Comparative Example 3, the pH of the fluoride-containing acidic wastewater was... The pH value was adjusted to 5.5. After treatment, the pH value of the photovoltaic waste liquid was 5.9, and the fluoride content was 6 mg / L. The pH value could not meet the emission standards. Comparative Example 4 adjusted the pH value of the fluoride-containing acidic waste liquid to 8.5. After treatment, the pH value of the photovoltaic waste liquid was 8.1, and the fluoride content was 5 mg / L. The pH value could not meet the emission standards, and it was necessary to add reagents to the pH adjustment tank to adjust the pH value to meet the emission standards. The technical solution provided in this application adjusts the pH value of the fluoride-containing acidic waste liquid to 6-8 by adding calcium hydroxide and calcium chloride. At the same time, calcium fluoride precipitate is generated to fix the fluoride element. This not only effectively reduces the fluoride element in the fluoride-containing acidic waste liquid, but also saves the amount of reagents, simplifies the treatment steps, and improves the reaction efficiency.

[0059] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this application.

Claims

1. A method for treating photovoltaic waste liquid, characterized in that, Includes the following steps, Calcium hydroxide and calcium chloride are added to the fluoride-containing acidic waste liquid to control the pH value of the fluoride-containing acidic waste liquid at 6-8. The fluoride-containing acidic waste liquid includes dilute acid and concentrated acid.

2. The method for treating photovoltaic waste liquid according to claim 1, characterized in that, The pH value of the fluoride-containing acidic waste liquid is controlled between 6.8 and 7.

5.

3. The method for treating photovoltaic waste liquid according to claim 1, characterized in that, Based on the volume of the fluoride-containing acidic waste liquid, the concentration of calcium hydroxide is 5.5-8.5 g / L, and the concentration of calcium chloride is 3.8-6 g / L.

4. The method for treating photovoltaic waste liquid according to claim 3, characterized in that, The volume ratio of the dilute acid to the concentrated acid is 2-5:

1.

5. The method for treating photovoltaic waste liquid according to claim 1, characterized in that, The method for treating photovoltaic waste liquid also includes the step of adding a flocculant to the fluoride-containing acidic waste liquid.

6. The method for treating photovoltaic waste liquid according to claim 5, characterized in that, It also includes the step of precipitating the fluoride-containing acidic wastewater after the addition of flocculants; The flocculant includes at least one of polyacrylamide and polyaluminum chloride; The concentration of the flocculant is 3-5 mg / L, based on the volume of the fluoride-containing acidic waste liquid.

7. The method for treating photovoltaic waste liquid according to claim 6, characterized in that, It also includes mixing dilute and concentrated alkali to form an alkaline waste liquid, and then adding dilute sulfuric acid to the alkaline waste liquid to adjust the pH value of the alkaline waste liquid to 6.8-7.

5.

8. The method for treating photovoltaic waste liquid according to claim 7, characterized in that, It also includes the step of mixing the fluorinated waste liquid after flocculant precipitation with an alkaline solution after pH adjustment.

9. A photovoltaic waste liquid treatment system, characterized in that, The system includes an acid treatment unit, which comprises an acid conditioning tank and a first neutralization and precipitation reaction tank. The photovoltaic waste liquid treatment system is used to implement the photovoltaic waste liquid treatment method according to any one of claims 1-8.

10. The photovoltaic waste liquid treatment system according to claim 9, characterized in that, It also includes an alkaline treatment unit, which comprises an alkaline conditioning tank and a second neutralization precipitation reaction tank; The treatment system also includes a sedimentation tank and a pH adjustment tank.

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