Efficient green reagent and method for removing h2s in urban sewer pipe

Abstract

The present application relates to the field of sewage treatment, in particular to a kind of efficient green reagent and method for removing H2S in urban drainage pipeline.The present application utilizes iron-containing waste in the recycling process of waste power battery, obtains FeC2O4 reagent after purification treatment, as a new type of green reagent, applied to the efficient removal of H2S in urban drainage pipeline.Through experimental verification, FeC2O4 reagent shows effective removal ability to sulfide;The optimal reagent dosing strategy is Fe / S=1, and multiple pulse dosing mode is adopted, to ensure the best removal effect and economy.The present application simulates the real drainage pipeline environment through the laboratory scale pressure pipe reactor system, provides a continuous source of iron salt for the removal of H2S in urban drainage system, and provides an optimal dosing scheme.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment, specifically to a highly efficient and green reagent and method for removing H2S from urban drainage pipes. Background Technology

[0002] In urban drainage systems, hydrogen sulfide (H2S) emissions are a major contributor to sewage pipe network corrosion and odor problems. To address this issue, existing research has reported several reliable control methods, including nitrite addition, adequate aeration, and increasing sewage pH. Each method has its advantages and disadvantages. For example, while nitrite addition is highly effective at removing hydrogen sulfide, continuous dosing is required, leading to high chemical costs. Furthermore, nitrite can be harmful to human health and the environment at high concentrations or when used improperly. In contrast, adequate aeration by introducing oxygen into the sewage system has the fewest side effects on the entire system, but it is extremely expensive and requires sophisticated operating conditions and equipment. Therefore, considering the removal efficiency and economic benefits of various methods, the addition of iron salts has been widely used for sulfide control in sewage systems. The principle of this method is that iron salts remove dissolved sulfides (S2S). 2- and HS - The process converts ferric salts into insoluble FeS, thereby reducing the emission of gaseous hydrogen sulfide into the sewer atmosphere. However, in practical applications, the dosage ratio of ferric salts to sulfides is usually much higher than the stoichiometric requirement, thus reducing the economic viability of this method. Therefore, there is an urgent need to develop a sustainable and economical in-situ control method to effectively improve the odor problem in drainage networks.

[0003] The recycling process for new energy vehicle batteries primarily focuses on recovering valuable metals such as lithium, cobalt, and manganese, while iron is discarded during this process. It is worth noting that lithium iron phosphate (LFP) batteries, used in power batteries, contain approximately 75% iron in their cathode materials. Failure to properly recycle this iron will result in significant resource waste and adverse environmental impacts. Depending on the leaching method, iron-containing waste mainly includes Fe(OH)3, FePO4, and FeC2O4.

[0004] In modern urban drainage systems, soluble iron salts such as FeCl2, FeCl3, Fe2(SO4)3, and Fe(NO3)3 are commonly used to treat wastewater to promote the removal of harmful odors such as H2S. Insoluble iron salts, such as Fe(OH)3, are often used to treat sulfides in sewer sediments. Furthermore, some insoluble iron salts, such as FeC2O4 and FeCO3, are also used in biogas desulfurization.

[0005] However, research on the use of sparingly soluble iron salts in pressure pipelines of urban drainage networks, especially for H2S removal, is still rare. Furthermore, current sources of sparingly soluble iron salts on the market are mainly limited to chemical production, which is not economically viable and suffers from unstable and unsustainable supply. Therefore, the potential applications of sparingly soluble iron salts in urban drainage systems have not been fully explored. Future research should focus on developing sustainable and cost-effective sources of sparingly soluble iron salts to promote innovation and sustainable development of H2S removal technologies in urban drainage networks. Summary of the Invention

[0006] This invention aims to provide a novel, continuously available, highly efficient, and green reagent and method for removing H2S from urban drainage pipes, and to provide an optimal dosing strategy for this reagent based on control effects and economic benefits, thereby effectively improving the odor problem in drainage pipe networks.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows.

[0008] A first aspect of the present invention provides an efficient method for removing H2S from urban drainage pipes, comprising the following steps:

[0009] Step 1: Obtain ferrous oxalate solution from waste lithium iron phosphate battery cathode materials using a wet recycling process;

[0010] Step 2: Purify the ferrous oxalate solution to obtain FeC2O4 reagent;

[0011] Step 3: Add FeC2O4 reagent into the pressure pipe of the urban drainage network to remove H2S from the sewage.

[0012] Furthermore, the method for obtaining FeC2O4 reagent by purifying the ferrous oxalate solution in step 2 includes the following steps:

[0013] Step S1: React ferrous oxalate solution with a complexing agent to form complex precipitates with other metal ions, and remove metal impurities by filtration or precipitation separation.

[0014] Step S2: Extract the organic matter from the ferrous oxalate solution using an organic solvent, and then separate the organic phase to remove the organic matter;

[0015] Step S3: Use vacuum dehydration to remove water from the ferrous oxalate solution, thereby increasing the concentration and purity of the solution.

[0016] Step S4: Control the temperature and pH of the ferrous oxalate solution to promote the first crystallization and precipitation of ferrous oxalate. After the first crystallization and precipitation, heat the solution and adjust the pH value, and let it stand to crystallize. Remove other impurities by filtration and washing to obtain FeC2O4 reagent.

[0017] Furthermore, in step S1 of the method for obtaining the FeC2O4 reagent, the complexing agent is sodium cyanide.

[0018] Furthermore, in step S2 of the method for obtaining the FeC2O4 reagent, the organic solvent is diethyl ether or acetone.

[0019] Furthermore, in step S3 of the method for obtaining the FeC2O4 reagent, the water in the ferrous oxalate solution is removed by vacuum distillation or vacuum drying.

[0020] Furthermore, in step S4 of the method for obtaining the FeC2O4 reagent, the temperature of the ferrous oxalate solution is controlled at 25–40°C and the pH is controlled at 4.5–5.0 to promote the first crystallization and precipitation of ferrous oxalate.

[0021] Furthermore, in step S4 of the method for obtaining the FeC2O4 reagent, after the first crystallization precipitation, the solution is heated to 30-40°C and the pH value is adjusted to 4.5-5.0, and then allowed to stand for crystallization.

[0022] Furthermore, in step 3, the dosage of FeC2O4 reagent is Fe / S = 1.

[0023] In a second aspect, the present invention provides a highly efficient and green reagent for removing H2S from urban drainage pipes, wherein the highly efficient and green reagent is a FeC2O4 agent.

[0024] Furthermore, the FeC2O4 reagent is prepared by obtaining ferrous oxalate solution from waste lithium iron phosphate battery cathode materials using a wet recycling process, and then purifying the ferrous oxalate solution.

[0025] In this invention, experiments have verified that FeC2O4, an iron-containing waste material in the power battery recycling process, is effective in removing sulfides from wastewater. Therefore, the novel green agent developed in this invention uses FeC2O4 as a waste material from the recycling of waste lithium iron phosphate batteries.

[0026] Furthermore, FeC2O4, which has passed the effectiveness test and has been purified, was added to a parallel reactor system according to different dosing strategies (such as different Fe / S ratios and single / multiple pulse dosing) set in the experiment. By performing chemical reaction kinetic calculations on the experimental results, the optimal dosing strategy was explored and the dosing method was optimized.

[0027] Experiments have verified that the optimal dosage ratio for removing sulfides from wastewater using FeC2O4, an iron-containing waste material, in the power battery recycling process is 1:1. Furthermore, experiments have shown that, under equal dosage conditions, multiple pulse dosing is more effective at removing sulfides than a single dosing method.

[0028] Therefore, taking into full account the sulfide removal rate and the economic efficiency of the reagents, the dosing mode finally explored by this invention is as follows: reagent dosage: Fe / S = 1; under the premise of equal dosage, the reagent is added in three pulses within one sewage pump cycle.

[0029] Compared with the prior art, the beneficial effects of the present invention are:

[0030] 1. The precipitates formed by sparingly soluble iron salts in wastewater are more stable and can react with harmful substances such as hydrogen sulfide for a longer period, effectively removing malodorous gases. Furthermore, compared to soluble iron salts, sparingly soluble iron salts are less volatile and less soluble, reducing reagent loss and environmental risks during treatment.

[0031] 2. Using recycled waste from spent power batteries as a source of iron salts demonstrates the advantages of environmental protection and resource utilization. This method helps reduce the environmental impact of waste, improves resource reuse rates, and aligns with the concept of sustainable development.

[0032] 3. With the large-scale use of electric vehicle batteries, the number of used batteries is gradually increasing, providing a continuous guarantee for the supply of iron salts. Utilizing this continuous supply advantage can ensure the sustained use of this green agent in urban drainage systems, improving treatment efficiency and reducing operating costs, thereby achieving more environmentally friendly and economical drainage pipeline management.

[0033] 4. The optimal reagent dosing strategy explored in this invention can ensure a high sulfide removal rate while taking into account reagent costs and avoiding waste. This comprehensive consideration helps to improve treatment efficiency and reduce operating costs, making this invention more advantageous in terms of efficiency and economy. Through a carefully designed dosing strategy, the effective utilization of reagents is ensured, achieving efficient and environmentally friendly sewer wastewater treatment. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the reactor system simulating the pressure pipe of an urban drainage network in Embodiment 1 of the present invention.

[0035] Figure 2 This is a schematic diagram of the anaerobic bottle device used for testing the effectiveness of a reagent in Embodiment 2 of the present invention.

[0036] Figure 3 This is a schematic diagram of a typical wet process for recovering ferrous oxalate from waste lithium iron phosphate batteries in Embodiment 3 of the present invention.

[0037] Figure 4 This is a schematic diagram showing the concentration of sulfides in wastewater at different time points after adding different iron-containing recycled waste materials in Example 4 of the present invention.

[0038] Figure 5 This is a graph showing the change of sulfide concentration over time under different Fe / S ratios in Example 5 of the present invention.

[0039] Figure 6 This is the SRR-t curve obtained by fitting the equal area method in Embodiment 5 of the present invention.

[0040] Figure 7 In Embodiment 5 of the present invention Relationship diagram.

[0041] Figure 8 This is a graph showing the change of sulfide concentration over time under different dosing modes in Example 6 of the present invention.

[0042] Figure 9 This is a graph showing the change of sulfur reduction rate over time under different dosing modes in Example 6 of the present invention.

[0043] Figure 1 middle:

[0044] 1-Dosing port; 2-Wastewater storage chamber (4℃); 3-Water bath; 4-Peristaltic pump; 5-Water pipe; 6-Experimental system; 7-Control system; 8-Magnetic stirrer; 9-Reactor; 10-Biofilm; 11-Small container (for replenishing wastewater volume); 12-Sampling port; 13-Wastewater inlet; 14-Wastewater outlet.

[0045] Figure 2 middle:

[0046] 15-Anaerobic bottle; 16-Sealed rubber cap; 17-Needle; 18-Instrument; 19-Nitrogen bag. Detailed Implementation

[0047] The specific embodiments of the present invention will be further described below. It should be noted that these descriptions are for the purpose of aiding understanding the present invention, but do not constitute a limitation thereof. Furthermore, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0048] Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods, and the experimental materials used in the following embodiments are all available through conventional commercial channels.

[0049] Example 1: Construction and Operation of a Reactor System for Simulating Pressure Pipes in Urban Drainage Networks

[0050] Figure 1 This is a schematic diagram of a reactor system simulating the pressure pipes of an urban drainage network. (Example:) Figure 1 As shown, the reactor system utilizes two reactors connected in series with drainage pipes to simulate a pressure drainage pipe. The reactor system consists of two systems: an experimental system 6 and a control system 7. Each system comprises two completely enclosed reactors 9, each with a volume of 1.0 L and an inner diameter of 80 mm. Each reactor 9 has a small container 11 mounted on its upper part, filled with the same wastewater as the reactor 9, to prevent air from entering during wastewater replacement. Circular plastic carriers with a diameter of 1 cm are aggregated onto two stainless steel rods within each reactor 9 to provide additional growth area for the biofilm 10, allowing the biofilm 10 to be obtained without disturbing its structure.

[0051] In this invention, the wastewater used for experimental research comes from the Tangjia Pumping Station in Xiangzhou District, Zhuhai City. Fresh wastewater is collected weekly for experiments and stored in a 4°C cold room to minimize biotransformation during storage. Before being pumped into the reactor, the wastewater is preheated to 20±1°C in a water bath. Testing revealed that the wastewater typically contains sulfides at a concentration of 1–3 mgS / L and sulfates at a concentration of 15–22 mgS / L.

[0052] The operation method of the reactor system simulating the pressure pipe of an urban drainage network in this invention is as follows: Sewage is intermittently injected using a peristaltic pump 4. A total of four identical pumping events occur within 24 hours, and each day is divided into four identical 6-hour cycles. Each pumping operation lasts longer than 2 minutes, with a flow rate of 0.5 L / min. -1 This is to completely replace the residual wastewater in the reactor. During the pumping operation, the wastewater is mixed in each reactor by magnetic stirrers, with the stirrer speed set to 200 rpm.

[0053] Example 2: Construction of an anaerobic bottle apparatus for testing the effectiveness of reagents

[0054] Figure 2 This is a schematic diagram of an anaerobic bottle apparatus used to test the effectiveness of reagents. Figure 2 As shown, the anaerobic bottle used in this invention for testing the effectiveness of reagents utilizes a laboratory-scale anaerobic bottle apparatus. The anaerobic bottle 15 is made of glass. The assembly method for the anaerobic bottle apparatus is as follows: Several anaerobic bottle 15 apparatuses are prepared and constructed in parallel. The anaerobic bottle 15 apparatus is sealed with a matching blue sealing rubber cap 16 and an aluminum foil cap, and further sealed with a matching capping device to simulate the anaerobic conditions of a sewer pressure pipe. The bottom diameter of the anaerobic bottle 15 is 65 mm, its height is 114 mm, and its effective volume is 378 ml. An aluminum foil nitrogen bag 19 is connected to the top of the apparatus to balance the internal pressure and ensure smooth extraction of liquid samples.

[0055] In this invention, the anaerobic bottle 15 device uses a 15ml syringe 18 that passes through the bottle cap for sampling and reagent addition. A needle 17 is connected to an aluminum foil nitrogen bag 19 via a flexible tube, with the other end of the needle 17 passing through a blue sealing rubber cap 18 to balance the internal pressure of the bottle during sampling and reagent addition. Before the formal experiment, the gas in the syringe 18 is purged and the nitrogen bag 19 is filled. Squeezing the nitrogen bag 19 pumps nitrogen into the anaerobic bottle, causing the piston of the syringe 18 to move upwards. When the volume of nitrogen pumped in equals the volume of gas in the syringe 18, it indicates that the device has good airtightness.

[0056] Example 3: Recovery and purification of ferrous oxalate from wet waste of spent lithium iron phosphate batteries

[0057] This embodiment provides a highly efficient and green agent and method for removing H2S from pressure pipes in urban drainage networks according to the present invention. To simulate and test the effectiveness of FeC2O4 agent in removing H2S from sewers, a laboratory-scale pressure pipe reactor system as described in Example 1 was constructed and operated to simulate real drainage pipe conditions, and the system was periodically monitored for steady-state stability; once the system stabilized, experiments were conducted. In this embodiment, based on the above-mentioned pressure pipe reactor system, the highly efficient and green method for removing H2S from pressure pipes in urban drainage networks according to the present invention includes the following steps:

[0058] Step 1: Obtain ferrous oxalate solution from waste lithium iron phosphate battery cathode materials using a wet recycling process;

[0059] Step 2: Purify the ferrous oxalate solution to obtain FeC2O4 reagent;

[0060] Step 3: Add FeC2O4 reagent into the pressure pipe of the urban drainage network (in the following test experiments, FeC2O4 reagent will be added into the parallel reactor system) to remove sulfides from the sewage.

[0061] Figure 3 This is a schematic diagram of a typical wet process for recovering ferrous oxalate from spent lithium iron phosphate batteries. Figure 3As shown, iron-containing waste is mainly found in cathode materials. Ferrous oxalate recovered from spent power battery cathode materials may contain certain levels of impurities and impurities, primarily including the following categories: a. Metallic impurities: Cathode materials from spent power batteries may contain impurities of other metallic elements, such as manganese (Mn), nickel (Ni), and cobalt (Co). These metallic impurities may form impurity compounds with iron, affecting the purity of ferrous oxalate. b. Organic matter: Cathode materials from spent power batteries may contain residual organic matter, such as organic polymers and lubricants. These organic substances may remain during the ferrous oxalate recovery process, leading to impurities in the ferrous oxalate. c. Moisture: Since cathode materials from spent power batteries may contain a certain amount of moisture, the recovered ferrous oxalate solution may contain moisture, increasing the complexity and impurity of the solution. d. Other impurities: In addition to the main impurities listed above, other impurities such as oxides and carbonates may also be present, which may affect the properties and applications of ferrous oxalate. Therefore, during the recovery and purification of ferrous oxalate, it is necessary to effectively treat and remove the above-mentioned possible impurities and impurities in order to improve the purity and quality of ferrous oxalate and ensure its effectiveness and safety in subsequent applications.

[0062] Based on the above process flow, this invention uses a wet recycling process to obtain ferrous oxalate solution from waste lithium iron phosphate battery cathode materials, and then purifies the ferrous oxalate solution to obtain FeC2O4 reagent. The purification method of FeC2O4 reagent is as follows:

[0063] Step S1, Removal of metal impurities: Using the complex precipitation method, the ferrous oxalate solution recovered from the cathode material of the waste power battery reacts with a complexing agent (such as sodium cyanide) to form a complex precipitate with other metal ions. Then, the metal impurities are removed by filtration or precipitation separation steps.

[0064] Step S2, Removal of organic matter: Using an extraction method, organic matter is extracted from the ferrous oxalate solution using an organic solvent (such as ether, acetone, etc.), and then the organic phase is separated to remove the organic matter;

[0065] Step S3, Moisture Removal: Use vacuum dehydration method, such as vacuum distillation or vacuum drying, to remove moisture from the ferrous oxalate solution, thereby improving the concentration and purity of the solution.

[0066] Step S4, Removal of other impurities: Using a crystallization method, the temperature of the ferrous oxalate solution is controlled at 25-40℃ and the pH at 4.5-5.0 to promote the first crystallization and precipitation of ferrous oxalate; after the first crystallization and precipitation, the solution is heated to 30-40℃ and the pH is adjusted to 4.5-5.0, and allowed to stand for crystallization; other impurities are removed by filtration and washing to obtain FeC2O4 reagent.

[0067] By combining the above purification steps, metallic impurities, organic matter, sulfides, moisture and other impurities in ferrous oxalate solution can be effectively removed, thereby improving the purity and quality of ferrous oxalate and obtaining high-purity FeC2O4 reagent.

[0068] Example 4: Test of the effectiveness of FeC2O4 reagent in removing sulfides from wastewater in an anaerobic bottle device.

[0069] Using the anaerobic bottle apparatus described in Example 2, this example is used to investigate the effectiveness of FeC2O4 reagent in removing sulfides from wastewater.

[0070] Prepare a 300 mg / L Na₂S solution using deionized water that has been deoxygenated by nitrogen blowing. Take three 150 ml anaerobic flasks and number them 1 to 3. Add a certain amount of ferric hydroxide powder, 90 ml of deionized water, and 5 ml of phosphate buffer solution to anaerobic flask 1, cap it tightly, and blow away the air from the top of the flask with nitrogen. Add a certain amount of ferrous oxalate powder, 90 ml of deionized water, and 5 ml of phosphate buffer solution to anaerobic flask 2, cap it tightly, and blow away the air from the top of the flask with nitrogen. Add a certain amount of ferric phosphate powder, 90 ml of deionized water, and 5 ml of phosphate buffer solution to anaerobic flask 3, cap it tightly, and blow away the air from the top of the flask with nitrogen. Inject 5 ml of sodium sulfide solution into each anaerobic flask using a syringe, with the other end using a nitrogen bag to assist in the injection. Fix the anaerobic flasks on a shaker and gently mix at 60 rpm. After mixing for 30 min, 10 ml of sample was drawn from each of anaerobic bottles 1-3 using a syringe, with the other end removed using a nitrogen-filled gas sampling bag as an auxiliary solution. After mixing for 90 min, 10 ml of sample was drawn from each of anaerobic bottles 1-3 using a syringe. After mixing for 150 min, 10 ml of sample was drawn from each of anaerobic bottles 1-3 using a syringe, and the S content of the sample was detected using a modified methylene blue spectrophotometric method. 2- The concentration, the results are as follows Figure 4 As shown. Figure 4 This diagram illustrates the concentration of sulfides in wastewater at different time points after the addition of different iron-containing recycled waste materials.

[0071] like Figure 4 As shown, except for the group with FeC2O4, the sulfide concentration in the other groups did not change significantly over time. However, the group with FeC2O4 showed a significant increase in sulfide concentration over 2.5 hours.2- The concentration decreased from 15.36 mgS / L to 1.25 mgS / L, with a removal rate of 91.8%. Therefore, this result demonstrates that the FeC2O4 reagent of the present invention is effective in removing sulfides.

[0072] Example 5: Exploration of the optimal dosage strategy for FeC2O4 reagent in removing sulfides from wastewater

[0073] In this embodiment, some experiments were conducted in a simulated sewer pressure pipe reactor system that had reached steady-state conditions, in order to simulate the dosing of chemicals in the pressure pipes of a real urban drainage network.

[0074] After using FeC2O4 as an effective reagent for removing sulfides, to determine the optimal dosage, the method in the "Reagent Effectiveness Test Experiment in Anaerobic Bottle Apparatus" was repeated using different dosages of FeC2O4. The difference was that the amount of FeC2O4 added resulted in Fe / S ratios of 0.1, 1, 2, 4, and 8 in the system. Then, S was measured at different time points. 2- Concentration, results as follows Figure 5 As shown.

[0075] like Figure 5 As shown, when the iron-sulfur ratio was increased from 0.1 to 1, the sulfide concentration in the system decreased significantly at each time point, indicating that the Fe / S=1 ratio was more effective in removing sulfides. However, when the iron-sulfur ratio was increased from 1 to higher levels, the sulfide concentration in the system did not decrease significantly at each time point, indicating that there was a waste of reagents at this point.

[0076] In addition, the chemical reaction kinetics of the reaction between ferrous oxalate and sulfide were analyzed using the differential method, and the results are as follows: Figures 6-7 As shown. Among them, Figure 6 The graph shows the measured values ​​and fitted trend line of the sulfur reduction rate (SRR) over time when Fe / S = 1. Figure 7 for and Relationship diagram.

[0077] Figure 6 In it, its R 2 The value is 0.96, which indicates that the model can fit the measured values ​​well. Figure 7 Based on the slope, the reaction order n is 2.30, and the rate constant k = 0.0289. The calculation results show that Fe / S has a relatively small effect on the value of n. When Fe / S = 1, the value of k is significantly higher than the other two groups. Therefore, the optimal dosage of FeC2O4 can be determined to be Fe / S = 1.

[0078] Example 6: Investigation on the effect of single / multiple pulse dosing of FeC2O4 reagent on the removal of sulfides from wastewater

[0079] After confirming the optimal dosage of FeC2O4, in order to determine the effect of the dosing mode on sulfide removal, the method in the "Anaerobic Bottle Device Reagent Effectiveness Test Experiment" was repeated using both single-dose and three-pulse-dose dosing modes, while ensuring that the total dosage of the reagent was Fe / S = 1. Then, S was measured at different time points. 2- Concentration. Results as follows Figure 8 As shown. The sulfur reduction rate was then calculated based on the experimental results, and the results are as follows. Figure 9 As shown. Among them, Figure 8 This is a graph showing the change in sulfide concentration over time. Figure 9 This is a graph showing the change in sulfur reduction rate over time.

[0080] like Figure 8 As shown, at the end of a pumping cycle, the sulfide concentration was lower in the three-stage dosing mode, indicating a higher removal rate. Furthermore, as... Figure 9 As shown, except for the initial 2 hours, the sulfur reduction rate of the three-stage addition was significantly higher than that of the single-stage addition group. Therefore, it can be determined that under the same dosage conditions, multiple pulse additions are more effective than single-stage additions in removing sulfides.

[0081] In summary, the following conclusions can be drawn:

[0082] 1. FeC2O4 for removing S 2- Effective, while FePO4 and Fe(OH)3 are effective in removing S. 2- The effect was not obvious, so the novel green agent of the present invention is FeC2O4, which is a waste product of recycled lithium iron phosphate batteries.

[0083] 2. When Fe / S = 1, FeC₂O₄ removes S. 2- The optimal effect is achieved by adding small amounts of reagent multiple times, which is more effective than a single addition, provided that the same amount of reagent is added. Therefore, taking into full account the sulfide removal rate and the economics of the reagent, the final dosing mode explored is as follows: reagent dosage: Fe / S = 1; under the premise of equal dosage, the reagent is added in three pulses within one sewage pump cycle.

[0084] Therefore, this invention utilizes iron-containing waste from the recycling process of spent power batteries, and after purification, obtains FeC2O4 reagent as a novel green reagent for the efficient removal of H2S in urban drainage pipes. Experimental verification shows that the FeC2O4 reagent exhibits effective removal capabilities for sulfides. The optimal reagent dosing strategy is Fe / S = 1, employing a multiple pulse dosing mode to ensure optimal removal efficiency and cost-effectiveness. This technical solution simulates the real drainage pipe environment using a laboratory-scale pressure tube reactor system, providing a continuous source of iron salts for H2S removal in urban drainage systems and offering an optimal dosing scheme.

[0085] The embodiments of the present invention have been described in detail above, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and these variations still fall within the protection scope of the present invention.

Claims

1. A highly efficient method for removing H2S from urban drainage pipes, characterized in that, Includes the following steps: Step 1: Obtain ferrous oxalate solution from waste lithium iron phosphate battery cathode materials using a wet recycling process; Step 2: Purify the ferrous oxalate solution to obtain the FeC2O4 reagent, including the following steps: Step S21: React ferrous oxalate solution with sodium cyanide complexing agent to form complex precipitates with other metal ions and complexing agent, and remove metal impurities by filtration or precipitation separation method; Step S22: Extract the organic matter from the ferrous oxalate solution using the organic solvent diethyl ether or acetone, and then separate the organic phase to remove the organic matter; Step S23: Use vacuum dehydration to remove water from the ferrous oxalate solution, thereby increasing the concentration and purity of the solution; Step S24: Control the temperature and pH of the ferrous oxalate solution to promote the first crystallization and precipitation of ferrous oxalate. After the first crystallization and precipitation, heat the solution and adjust the pH value, and let it stand to crystallize. Remove other impurities by filtration and washing to obtain FeC2O4 reagent. Step 3: Add FeC2O4 reagent into the pressure pipe of the urban drainage network to remove H2S from the sewage.

2. The efficient method for removing H2S from urban drainage pipes according to claim 1, characterized in that, In step S23, water in the ferrous oxalate solution is removed by vacuum distillation or vacuum drying.

3. The efficient method for removing H2S from urban drainage pipes according to claim 1, characterized in that, In step S24, the temperature of the ferrous oxalate solution is controlled at 25–40 °C and the pH is controlled at 4.5–5.0 to promote the first crystallization and precipitation of ferrous oxalate.

4. The efficient method for removing H2S from urban drainage pipes according to claim 1, characterized in that, In step S24, after the first crystallization precipitation, the solution is heated to 30-40 °C and the pH value is adjusted to 4.5-5.0, and then allowed to stand for crystallization.

5. The efficient method for removing H2S from urban drainage pipes according to claim 1, characterized in that, In step 3, the dosage of FeC2O4 reagent is Fe / S=1.

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