A method for treating wastewater from the production of pyrethroid insecticide.

Abstract

This invention discloses a method for treating wastewater from the production of pyrethroid insecticide, comprising: (1) adjusting the pH to 11-12 and adding sodium thiosulfate solution to react and obtain a reaction solution; (2) adding sulfur to the reaction solution and refluxing the reaction at 100-102°C for a set time to obtain a synthetic solution; (3) evaporating and concentrating the synthetic solution to obtain a concentrated solution, adding activated carbon and heating it to perform solid-liquid separation to obtain a filtrate; (4) cooling and crystallizing the filtrate, separating the crystals to obtain sodium thiosulfate pentahydrate. The wastewater treatment process for pyrethroid insecticide of this invention can directly produce high-value-added, high-quality sodium thiosulfate products, realizing the recycling of materials. No polluting gases are generated during the treatment process, the process is simple, and the treatment cost is low.

Description

Technical Field

[0001] This invention relates to the field of wastewater purification, treatment, and recycling technology, and in particular to a treatment method for cyanide-containing wastewater generated during the synthesis of pyrethroids, which can directly yield high-value-added products, is low-cost, and has a simple process. Background Technology

[0002] Mefenoxam is a highly effective, low-toxicity, broad-spectrum biomimetic insecticide belonging to the nereistoxin class of insecticides. After nearly 25 years of continuous improvement and optimization of its production process, it has now reached international standards in China. The current production process primarily involves reacting chlorpyrifos monophosphate or chlorpyrifos diphosphate with a 30% sodium cyanide aqueous solution under alkaline conditions, using haloalkanes as extractants to obtain a thiocyanate haloalkanes solution. This solution is then subjected to alcoholysis or hydrolysis, solvent removal, separation, and drying to obtain chlorpyrifos. This process results in high yield, good quality, and stable product.

[0003] The current cyanidation process inevitably generates a large amount of cyanide-containing wastewater with sodium sulfite. This wastewater is highly toxic and saline, making it difficult to treat directly. Pretreatment procedures such as cyanide destruction and evaporation are required. Currently, manufacturers typically employ a pretreatment and recovery process involving high-temperature cyanide destruction followed by evaporation to extract solid sodium sulfite. This solid is then either sold directly or used in the synthesis of thiosulfate. Patent applications are filed separately, such as Jiangsu Tianrong Group's patent ZL200810122513.4. However, this process still has certain shortcomings in terms of clean production, energy consumption, and yield / quality.

[0004] (1) The rate of high-quality sodium sulfite obtained by high-temperature cyanide decomposition followed by evaporation and salt precipitation is not high, and low-content sodium sulfite is difficult to process.

[0005] (2) Energy reuse leads to waste. The extraction of sodium nitrite from cyanide-containing wastewater by evaporation requires a large amount of steam (3.5 tons of steam per ton of wastewater). Then, the sodium nitrite is synthesized in the water system, and the product is obtained by concentration, decolorization and crystallization, which requires steam (2.0 tons of steam per ton of wastewater). The repeated evaporation significantly increases energy consumption.

[0006] (3) Complex processes increase processing costs. Summary of the Invention

[0007] This invention provides a method for treating wastewater from the production of methomyl that can directly yield high-value-added products, is low-cost, and has a simple process, thereby solving the technical problems of poor economic efficiency and complex processes in existing treatment processes.

[0008] To solve the above-mentioned technical problems, the technical solution proposed by this invention is as follows:

[0009] A method for treating wastewater from the production of pyrethroid insecticide includes the following steps:

[0010] (1) After adjusting the pH of the wastewater from the production of pyridaben to 11-12, sodium thiosulfate solution is added and the reaction is carried out for a set time to obtain the reaction solution;

[0011] (2) Add sulfur to the reaction solution and reflux at 100-102°C for a set time to obtain the synthesis solution;

[0012] (3) The synthesis liquid is evaporated and concentrated to obtain a concentrated liquid. Activated carbon is added to the concentrated liquid and the temperature is raised to 60-70°C. After keeping it at the temperature for a set time, solid-liquid separation is performed to obtain a filtrate.

[0013] (4) Cool the filtrate to crystallize it, and separate the crystals to obtain sodium thiosulfate pentahydrate, thus completing the treatment of the wastewater from the production of pyridaben.

[0014] The design concept of the above technical solution is that, compared with the existing high-temperature cyanide decomposition followed by evaporation and salting out method, this invention uses sodium thiosulfate for chemical cyanide decomposition, solving the problem of further collection and treatment of ammonia generated during existing high-temperature cyanide decomposition. Simultaneously, the sodium sulfite produced after cyanide decomposition in this invention is of high grade and high content, and can directly produce high-value-added sodium thiosulfate after reacting with sulfur. This solves the energy consumption problem of repeated heating and evaporation in the original high-temperature cyanide decomposition for sodium sulfite extraction and subsequent synthesis of sodium thiosulfate, simplifying the process and significantly reducing the standard coal consumption per ton and production costs. Furthermore, the produced sodium thiosulfate can be reused as a raw material in the cyanide decomposition process, achieving material recycling and further reducing the cost of wastewater treatment. The reaction equations involved in the treatment method of this invention are as follows:

[0015] NaCN+Na2S2O3→Na2SO3+NaSCN;

[0016] Na₂SO₃ + S → Na₂S₂O₃;

[0017] Na2S2O3+5H2O→Na2S2O3·5H2O.

[0018] In step (1), the pH adjustment range is based on the fact that the wastewater from the production of pyridaben contains sodium sulfite, and its optimal pH value under alkaline conditions is 11 to 12.

[0019] As a further preferred embodiment of the above technical solution, in step (1), before adjusting the pH of the wastewater from the production of pyridaben, the wastewater from the production of pyridaben is subjected to three stages of sedimentation to remove the organic phase and dynamic pressure filtration.

[0020] As a further preferred embodiment of the above technical solution, in step (1), the sodium thiosulfate solution contains sodium thiosulfate and CN in the wastewater from the production of fenitrothion. -The molar ratio is 1:(0.5 to 1.5), and more preferably 1:(0.8 to 1.2).

[0021] As a further preferred embodiment of the above technical solution, in step (1), the reaction time between the wastewater from the production of pyridaben and the sodium thiosulfate solution is 0.5 to 2 hours, and more preferably 0.5 to 1 hour; the CN- concentration in the reaction solution after the reaction is less than 0.5 ppm.

[0022] As a further preferred embodiment of the above technical solution, in step (2), the molar ratio of sodium sulfite to sulfur in the reaction solution is 1:(1-1.5), and more preferably 1:(1.1-1.2). Powdered sulfur is preferred, as this increases the specific surface area of ​​the sulfur, thereby reducing the influence of other impurities on the reaction effect.

[0023] As a further preferred embodiment of the above technical solution, in step (2), the reaction time of the residual sulfur in the reaction liquid is 5 to 12 hours, and more preferably 8 to 9 hours.

[0024] As a further preferred embodiment of the above technical solution, the reaction temperature of the reaction solution and sulfur in step (2) is 100-102℃.

[0025] As a further preferred embodiment of the above technical solution, in step (3), the synthesis solution is first concentrated by evaporation using an MVR evaporator until the sodium thiosulfate concentration in the synthesis solution is 30%–40% (more preferably 32%–36%); then it is transferred to a single-effect evaporator for further evaporation and concentration until the sodium thiosulfate concentration is 45%–55% (more preferably 48%–52%), thus obtaining the concentrated solution. The concentration range of sodium thiosulfate is taken into account that the system contains other impurities, rather than a pure sodium sulfite solution. Therefore, a reasonable concentration should be selected to avoid the generation of other solids during the concentration process and blockage of the heater pipes.

[0026] As a further preferred embodiment of the above technical solution, the mass ratio of activated carbon to sodium thiosulfate in step (3) is (15-50):1000, more preferably (20-30):1000; the heat preservation time is 0.5-2h, more preferably 1-1.5h. The function of activated carbon is, on the one hand, decolorization and on the other hand, removal of other impurities. The amount of activated carbon and the temperature are determined according to the total amount of impurities.

[0027] As a further preferred embodiment of the above technical solution, in step (3), a power filter press is used for solid-liquid separation, and the outlet temperature is controlled at 30-70°C, more preferably 45-55°C.

[0028] As a further preferred embodiment of the above technical solution, in step (4), when the filtrate is cooled and crystallized, the temperature is controlled using the ternary phase diagram of NaSCN-Na2S2O3-H2O. Due to the different concentrations of substances in the filtrate, NaSCN is prevented from crystallizing. The temperature is controlled at 25–35℃ (more preferably 28℃–32℃). After solid-liquid separation, sodium thiosulfate pentahydrate is obtained. The mother liquor is collected and recycled to a single-effect evaporator for decolorization and slag removal, thereby achieving the separation of sodium thiocyanate and sodium thiosulfate. The ternary phase diagram is drawn based on the different concentrations of substances in the system for crystallization separation. Removing the generated sodium thiocyanate improves the quality of sodium thiosulfate pentahydrate, while also increasing product yield and reducing production costs.

[0029] As a further preferred embodiment of the above technical solution, the sodium thiosulfate obtained in step (4) is recycled in step (1), and the mother liquor obtained by cooling and crystallization in step (4) is recycled to the evaporation and concentration step in step (3).

[0030] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0031] The wastewater treatment process for pyrethroid insecticide production of the present invention can directly produce high-value-added, high-quality sodium thiosulfate, realizing the recycling of materials. No polluting gases are generated during the treatment process, and the process is simple and has low treatment costs.

[0032] The present invention will now be described in further detail with reference to the accompanying drawings. Attached Figure Description

[0033] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0034] Figure 1 This is a schematic diagram of the process for treating wastewater from the production of methomyl in Example 1. Detailed Implementation

[0035] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings, but the present invention can be implemented in many different ways as defined and covered by the claims.

[0036] Example 1:

[0037] like Figure 1 The method for treating wastewater from the production of pyrethroid insecticide shown in this embodiment includes the following steps:

[0038] (1) Collect 8000 kg of cyanide-containing wastewater from the cyanidation process during the synthesis of fenitrothion technical and place it in a three-stage settling tank. Take samples for analysis of its CN content. -The content is 3225 ppm, and the sodium sulfite content is 11.25%.

[0039] (2) After the wastewater is allowed to stand to remove the lower organic phase, it is pumped into a cyanide remover (i.e., a synthesizer) and stirred. First, liquid alkali is added to adjust the pH to 11.8, then 250 kg of sodium thiosulfate (sodium thiosulfate hydrate) is added. After stirring at room temperature for 45 minutes, a reaction solution is obtained. A sample is taken for CN analysis. - The content, according to analytical data, was 0.25 ppm.

[0040] (3) Add 285 kg of sulfur (converted to 100%) to the reaction solution. After adding the sulfur, turn on the steam in the coil of the synthesizer to raise the temperature and stabilize it at 102°C. Maintain the reflux state for 9.0 hours. After the temperature is maintained, take a sample to analyze the sodium thiosulfate content (the sodium thiosulfate content in the reaction solution is 14.5%) and cool it down to 90°C to discharge the synthesis solution. Store the solution in an intermediate temporary storage tank for later use.

[0041] (4) Start the MVR evaporator and pass the synthesis liquid through it for evaporation and concentration to increase the sodium thiosulfate concentration. When the concentration reaches 35.5%, the evaporation is stopped and the liquid is discharged into a single-effect evaporator for further concentration. When the concentration reaches 50.5%, the single-effect evaporation is stopped and the liquid is discharged into the decolorizer. Add 40 kg of activated carbon to the decolorizer according to the formula, stir and heat to 65°C, keep it at that temperature for 1.5 hours, and then discharge the liquid into a plate and frame filter press for slag removal to obtain filtrate. The slag removal discharge temperature is maintained at 49°C.

[0042] (5) The filtrate was collected into a crystallizer, and the built-in coil cooling water was turned on for cooling and crystallization. The temperature was controlled at 31℃ based on the filtrate concentration and the phase diagram of the NaSCN-Na2S2O3-H2O ternary system. The filtrate was then discharged at a constant temperature into a horizontal screw discharge centrifuge for solid-liquid separation to obtain sodium thiosulfate pentahydrate. The mother liquor was collected and recycled to a single-effect evaporator for decolorization and slag removal to achieve the separation of sodium thiocyanate and sodium thiosulfate. The specific results were as follows: 1450 kg of sodium thiosulfate pentahydrate was obtained with a content of 98.25% and an initial recovery rate of 70.61%; 1245 kg of mother liquor was obtained with a sodium thiosulfate content of 27.25% and a total recovery rate of 97.00%.

[0043] Compared with the technical solution used in the patent ZL200810122513.4 mentioned in the background technology, the initial recovery rate of the technical solution is generally around 55%, the total recovery rate is around 83%, and the content of pentahydrate thiosulfate is around 96%. The recovery rate is somewhat different from that of this embodiment, and at the same time, a large amount of steam and electricity are consumed.

[0044] Conventional methods (first, high-temperature cyanide removal from cyanide-containing wastewater, then reaction of the resulting sodium sulfite-containing wastewater with sulfur, followed by decolorization and crystallization to obtain sodium thiosulfate pentahydrate) require temperatures exceeding 160°C within 8 hours to allow the CN (cyanide) to dissolve. - The concentration of sodium methoxide in the wastewater needs to be reduced to below 20 ppm, but this requires a large amount of steam. Furthermore, the sodium methoxide produced during high-temperature cyanide removal affects the reaction yield and product quality, and also oxidizes the sodium sulfite in the wastewater to some extent, reducing the overall yield. Compared to this embodiment, the power cost of this embodiment is reduced by approximately 50%, and the pretreatment cost accounts for about 20% of the total cost.

[0045] Example 2:

[0046] The method for treating wastewater from pyrethroid insecticide production in this embodiment includes the following steps:

[0047] (1) Collect 7980 kg of cyanide-containing wastewater from the cyanidation process during the synthesis of pyrethroid insecticide into a three-stage settling tank, and sample it for CN analysis. - The content is 3350 ppm, and the sodium sulfite content is 10.95%.

[0048] (2) After the wastewater is allowed to stand to remove the lower organic phase, it is pumped into a cyanide remover (i.e., a synthesizer) and stirred. First, liquid alkali is added to adjust the pH to 11.6, then 250 kg of sodium thiosulfate (sodium thiosulfate hydrate) is added. After stirring at room temperature for 45 minutes, a reaction solution is obtained. A sample is taken for CN analysis. - The content, according to analytical data, was 0.30 ppm.

[0049] (3) Add 270 kg of sulfur (converted to 100%) to the reaction solution. After adding the sulfur, turn on the steam in the coil of the synthesizer to raise the temperature and stabilize it at 102°C. Maintain the reflux state for 9.0 hours. After the temperature is maintained, take a sample to analyze the sodium thiosulfate content (analyzed sodium thiosulfate content in the reaction solution is 14.25%) and cool it down to 90°C to discharge the synthesis solution. Store the solution in an intermediate temporary storage tank for later use.

[0050] (4) Start the MVR evaporator and pass the synthesis liquid through it for evaporation and concentration to increase the sodium thiosulfate concentration. When the concentration reaches 35.2%, the evaporation is stopped and the liquid is discharged into a single-effect evaporator for further concentration. When the concentration reaches 51.3%, the single-effect evaporation is stopped and the liquid is discharged into the decolorizer. Add 35 kg of activated carbon to the decolorizer according to the formula, stir and heat to 68°C, keep it at that temperature for 1.5 hours, and then discharge the liquid into a plate and frame filter press for slag removal to obtain filtrate. The slag removal discharge temperature is maintained at 52°C.

[0051] (5) The filtrate was collected into a crystallizer, and the built-in coil cooling water was turned on for cooling and crystallization. The temperature was controlled at 30℃ based on the filtrate concentration and the phase diagram of the NaSCN-Na2S2O3-H2O ternary system. The filtrate was then discharged at a constant temperature into a horizontal screw discharge centrifuge for solid-liquid separation to obtain sodium thiosulfate pentahydrate. The mother liquor was collected and recycled to a single-effect evaporator for decolorization and slag removal to achieve the separation of sodium thiocyanate and sodium thiosulfate. The specific results were as follows: 1400 kg of sodium thiosulfate pentahydrate was obtained with a content of 97.92% and an initial recovery rate of 69.44%; 1325 kg of mother liquor was obtained with a sodium thiosulfate content of 25.64% and a total recovery rate of 96.46%.

[0052] Example 3:

[0053] The method for treating wastewater from the production of pyrethroid insecticide in this embodiment includes the following steps:

[0054] (1) Collect 80-10 kg of cyanide-containing wastewater from the cyanidation process during the synthesis of pyrethroid insecticide into a three-stage settling tank, and sample it for CN analysis. - The content is 3150 ppm, and the sodium sulfite content is 1082%.

[0055] (2) After the wastewater is allowed to stand to remove the lower organic phase, it is pumped into a cyanide separator (i.e., a synthesizer) and stirred. Liquid alkali is first added to adjust the pH to 11.9, then 1245 kg of the sodium thiosulfate mother liquor obtained in Example 1 (sodium thiosulfate concentration of 27.25%) is added. After stirring at room temperature for 45 minutes, a reaction solution is obtained. A sample is taken for CN analysis. - The content was 0.32 ppm according to the analysis.

[0056] (3) Add 265 kg of sulfur (converted to 100%) to the reaction solution. After adding the sulfur, turn on the steam in the coil of the synthesizer to raise the temperature and stabilize it at 102.5°C. Maintain the reflux state for 8.5 hours. After the temperature is maintained, take a sample to analyze the sodium thiosulfate content (analyzed sodium thiosulfate content in the reaction solution is 14.85%). Cool the solution to 90°C and discharge it to obtain the synthesis solution. Store it in an intermediate temporary storage tank for later use.

[0057] (4) Start the MVR evaporator and pass the synthesis liquid through it for evaporation and concentration to increase the sodium thiosulfate concentration. When the concentration reaches 34.6%, the evaporation is stopped and the liquid is discharged into a single-effect evaporator for further concentration. When the concentration reaches 49.5%, the single-effect evaporation is stopped and the liquid is discharged into the decolorizer. Add 42 kg of activated carbon to the decolorizer according to the formula, stir and heat to 68°C, keep it at that temperature for 80 minutes, and then discharge the liquid into a plate and frame filter press for slag removal to obtain filtrate. The slag removal discharge temperature is maintained at 48°C.

[0058] (5) The filtrate was collected into a crystallizer, and the built-in coil cooling water was turned on for cooling and crystallization. The temperature was controlled at 28℃ based on the filtrate concentration and the phase diagram of the NaSCN-Na2S2O3-H2O ternary system. The filtrate was then discharged at a constant temperature into a horizontal screw discharge centrifuge for solid-liquid separation to obtain sodium thiosulfate pentahydrate. The mother liquor was collected and recycled to a single-effect evaporator for decolorization and slag removal to achieve the separation of sodium thiocyanate and sodium thiosulfate. The specific results were as follows: 1550 kg of sodium thiosulfate pentahydrate was obtained with a content of 97.82% and an initial recovery rate of 67.73%; 1600 kg of mother liquor was obtained with a sodium thiosulfate content of 25.93% and a total recovery rate of 96.80%.

[0059] Example 4:

[0060] The method for treating wastewater from the production of pyrethroid insecticide in this embodiment includes the following steps:

[0061] (1) Collect 7950 kg of cyanide-containing wastewater from the cyanidation process during the synthesis of pyrethroid insecticide into a three-stage settling tank, and sample it for CN analysis. - The content was 3263 ppm, and the sodium sulfite content was 11.24%.

[0062] (2) After the wastewater is allowed to stand to remove the lower organic phase, it is pumped into a cyanide remover (i.e., a synthesizer) and stirred. Liquid alkali is first added to adjust the pH to 11.6, then 1325 kg of the sodium thiosulfate mother liquor obtained in Example 2 (sodium thiosulfate mass concentration is 25.64%) is added. After stirring at room temperature for 45 minutes, a reaction solution is obtained. A sample is taken for CN analysis. - The content was 0.28 ppm according to the analysis.

[0063] (3) Add 280 kg of sulfur (converted to 100%) to the reaction solution. After adding the sulfur, turn on the steam in the coil of the synthesizer to raise the temperature and stabilize it at 102°C. Maintain the reflux state for 9.0 hours. After the temperature is maintained, take a sample to analyze the sodium thiosulfate content (analyze the sodium thiosulfate content in the reaction solution to be 15.00%). Cool the solution to 90°C and discharge it to obtain the synthesis solution. Store it in an intermediate temporary storage tank for later use.

[0064] (4) Start the MVR evaporator and pass the synthesis liquid through it for evaporation and concentration to increase the sodium thiosulfate concentration. When the concentration reaches 34.9%, the evaporation is stopped and the liquid is discharged into a single-effect evaporator for further concentration. When the concentration reaches 50.2%, the single-effect evaporation is stopped and the liquid is discharged into the decolorizer. Add 40 kg of activated carbon to the decolorizer according to the formula, stir and heat to 65°C, keep it at that temperature for 80 minutes, and then discharge the liquid into a plate and frame filter press for slag removal to obtain filtrate. The slag removal discharge temperature is maintained at 51°C.

[0065] (5) The filtrate was collected into a crystallizer, and the built-in coil cooling water was turned on for cooling and crystallization. The temperature was controlled according to the filtrate concentration and the phase diagram of the NaSCN-Na2S2O3-H2O ternary system, and the controlled temperature was 31.5℃. Then, the material was discharged at a constant temperature into a horizontal screw discharge centrifuge for solid-liquid separation to obtain sodium thiosulfate pentahydrate. The mother liquor was collected and recycled to a single-effect evaporator for decolorization and slag removal to achieve the separation of sodium thiocyanate and sodium thiosulfate. The specific results were as follows: 1625 kg of sodium thiosulfate pentahydrate was obtained with a content of 98.17% and an initial recovery rate of 69.60%; 1465 kg of mother liquor was obtained with a sodium thiosulfate content of 27.10% and a total recovery rate of 96.79%.

[0066] Example 5:

[0067] The method for treating wastewater from pyrethroid insecticide production in this embodiment includes the following steps:

[0068] (1) Collect 1600 kg of sodium thiosulfate mother liquor obtained in Example 3 (sodium thiosulfate mass concentration of 25.93%) and 1465 kg of sodium thiosulfate mother liquor obtained in Example 4 (sodium thiosulfate mass concentration of 27.10%), stir evenly, and then enter a single-effect evaporator for evaporation and concentration. When the concentration reaches 48.5%, the single-effect evaporation ends and the material is discharged into a decolorizer. Add 25 kg of activated carbon to the decolorizer according to the formula, stir and heat to 65°C, keep warm for 1.5 hours, and then discharge the material into a plate and frame filter press for slag removal to obtain filtrate. The slag removal discharge temperature is maintained at 54°C.

[0069] (2) The filtrate was collected into a crystallizer, and the built-in coil cooling water was turned on for cooling and crystallization. The temperature was controlled at 32℃ based on the filtrate concentration and the phase diagram of the NaSCN-Na2S2O3-H2O ternary system. The filtrate was then discharged at a constant temperature into a horizontal screw discharge centrifuge for solid-liquid separation to obtain sodium thiosulfate pentahydrate. The mother liquor was collected and recycled to a single-effect evaporator for decolorization and slag removal to achieve the separation of sodium thiocyanate and sodium thiosulfate. The specific results were as follows: 900 kg of sodium thiosulfate pentahydrate was obtained with a content of 97.37% and an initial recovery rate of 69.00%; 735 kg of mother liquor was obtained with a sodium thiosulfate content of 28.25% and a total recovery rate of 94.67%.

[0070] The above are merely preferred embodiments of this application and are not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application. The above are merely preferred embodiments of the present invention, and the protection scope of the present invention is not limited to the above embodiments. For those skilled in the art, improvements and modifications obtained without departing from the technical concept of the present invention should also be considered within the protection scope of the present invention.

Claims

1. A method for treating wastewater from the production of methomyl, characterized in that, Includes the following steps: (1) After adjusting the pH of the wastewater from the production of pyridaben to 11-12, sodium thiosulfate solution is added and the reaction is carried out for a set time to obtain the reaction solution; (2) Add sulfur to the reaction solution and reflux at 95-105°C for a set time to obtain the synthesis solution; (3) The synthetic liquid is evaporated and concentrated to obtain a concentrated liquid. Activated carbon is added to the concentrated liquid and the temperature is raised to 50-80°C. After keeping it at the temperature for a set time, solid-liquid separation is performed to obtain a filtrate. (4) Cool the filtrate to crystallize it, and separate the crystals to obtain sodium thiosulfate pentahydrate, thus completing the treatment of the wastewater from the production of pyridaben.

2. The method for treating wastewater from the production of methomyl as described in claim 1, characterized in that, In step (1), before adjusting the pH of the wastewater from the production of pyridaben, the wastewater from the production of pyridaben is subjected to three stages of sedimentation to remove the organic phase and dynamic pressure filtration.

3. The method for treating wastewater from the production of pyrethroid insecticide according to claim 1, characterized in that, In step (1), the sodium thiosulfate solution contains sodium thiosulfate, which reacts with CN in the wastewater from the production of fenitrothion. - The molar ratio is 1:(0.5~1.5).

4. The method for treating wastewater from the production of pyrethroid insecticide according to claim 1, characterized in that, In step (1), the reaction time between the wastewater from the production of pyridaben and the sodium thiosulfate solution is 0.5 to 2 hours.

5. The method for treating wastewater from the production of methomyl according to any one of claims 1-4, characterized in that, In step (2), the molar ratio of sodium sulfite to sulfur in the reaction solution is 1:(1-1.5).

6. The method for treating wastewater from the production of pyrethroid insecticide according to any one of claims 1-4, characterized in that, In step (2), the reaction time of the residual sulfur in the reaction solution is 5 to 12 hours.

7. The method for treating wastewater from the production of pyrethroid insecticide according to any one of claims 1-4, characterized in that, In step (3), the synthesis solution is first concentrated by evaporation using an MVR evaporator until the sodium thiosulfate concentration in the synthesis solution is 30% to 40%; then it is transferred to a single-effect evaporator for further evaporation and concentration until the sodium thiosulfate concentration is 45% to 55%, thus obtaining the concentrated solution.

8. The method for treating wastewater from the production of pyrethroid insecticide according to any one of claims 1-4, characterized in that, The mass ratio of activated carbon to sodium thiosulfate in step (3) is (15-50):1000; the heat preservation time is 1-1.5h.

9. The method for treating wastewater from the production of methomyl according to any one of claims 1-4, characterized in that, In step (3), a power filter press is used for solid-liquid separation, and the outlet temperature is controlled at 30-70℃.

10. The method for treating wastewater from the production of pyrethroid insecticide according to any one of claims 1-4, characterized in that, In step (4), when the filtrate is cooled and crystallized, the temperature of the NaSCN-Na2S2O3-H2O ternary system phase diagram is controlled.

11. The method for treating wastewater from the production of pyrethroid insecticide according to any one of claims 1-4, characterized in that, The sodium thiosulfate obtained in step (4) is recycled in step (1), and the mother liquor obtained by cooling and crystallization in step (4) is recycled to the evaporation and concentration step in step (3).

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