Efficient green reagent and method for removing H2S in urban drainage pipeline

Abstract

The invention relates to the field of sewage treatment, in particular to an efficient green reagent and method for removing H2S in urban drainage pipelines. According to the method, the FeC2O4 medicament is obtained by purifying the iron-containing waste in the waste power battery recycling process, and the FeC2O4 medicament is used as a novel green medicament and is applied to efficient removal of H2S in urban drainage pipelines. Through experimental verification, the FeC2O4 medicament shows the effective removal capability on sulfides; the optimal medicament adding strategy is Fe / S = 1, and a multi-pulse medicament adding mode is adopted, so that the optimal removal effect and economical efficiency are ensured. A real drainage pipeline environment is simulated through a laboratory-scale pressure pipe reactor system, a continuous ferric salt source is provided for removal of H2S in an urban drainage system, and an optimal dosing scheme is provided.

Description

Technical Field

[0001] The present invention relates to the field of sewage treatment, and particularly to an efficient and green reagent and method for removing H 2 S from urban drainage pipes. Background Art

[0002] In the urban drainage system, the emission of hydrogen sulfide (H 2 S) is one of the main factors causing corrosion and malodor problems in sewage pipe networks. To address this issue, several reliable control methods have been reported in existing research, including adding nitrite, sufficient aeration, and increasing the pH value of sewage. Each method has its advantages and disadvantages. For example, although adding nitrite has the ability to efficiently remove hydrogen sulfide, the control of hydrogen sulfide requires continuous dosing, resulting in a high chemical cost. In addition, under high concentrations or improper use, nitrite may pose hazards to humans and the environment. In contrast, the method of fully aerating the sewage in the sewer by introducing oxygen has the least side effects on the entire sewer system, but its cost is extremely high and it has high requirements for operating conditions and equipment. Therefore, considering the removal effect and economic benefits of each method, the method of adding iron salts has been widely used for sulfide control in the sewer system. The principle of this method is that iron salts convert dissolved sulfides (S 2- and HS - ) into insoluble FeS, thereby reducing the emission of gaseous hydrogen sulfide into the sewer atmosphere. However, in actual applications, the dosing ratio of iron salts to sulfides is usually much higher than the stoichiometric requirement, thus reducing the economy of this method. Therefore, there is an urgent need to develop a continuous supply and economical in-situ control method to efficiently improve the malodor problem of drainage pipe networks.

[0003] The battery recycling process of new energy vehicles mainly focuses on the recovery of valuable metals such as lithium, cobalt, and manganese, while iron elements are discarded in this process. It should be noted that in lithium iron phosphate (LFP) batteries for power batteries, the iron element content in the cathode material reaches about 75%. If the iron element is not properly recycled, it will cause serious resource waste and adverse environmental impacts. According to different leaching methods, iron-containing waste mainly includes Fe(OH) 3 , FePO 4 , FeC 2 O 4 , etc.

[0004] In today's urban drainage system, soluble iron salts such as FeCl 2 , FeCl 3 , Fe 2 (SO 4 ) 3 and Fe(NO 3 )3 to treat sewage to promote the removal of harmful odors such as H 2 S. Insoluble iron salts, such as Fe(OH) 3 , are commonly used to treat sulfides in sewer sediments. In addition, some insoluble iron salts are also applied to biogas desulfurization, such as FeC 2 O 4 and FeCO 3 .

[0005] However, for pressure pipes in urban drainage networks, especially in terms of H 2 S removal, the use of insoluble iron salts has been rarely studied. Moreover, the current sources of insoluble iron salts in the market are mainly limited to chemical production, with low economic efficiency and unstable supply, lacking sustainability. Therefore, the potential application of insoluble iron salts in urban drainage systems has not been fully explored. Future research should focus on developing sustainable and economically efficient sources of insoluble iron salts to promote the innovation and sustainable development of H 2 S removal technologies in urban drainage networks. Summary of the Invention

[0006] The present invention aims to provide a new type of efficient green reagent and method for continuously removing H 2 S in urban drainage pipes, and to provide the optimal dosing strategy for this reagent based on control effects and economic benefits, so as to effectively improve the odor problem in drainage networks.

[0007] To achieve the above object, the technical solutions adopted by the present invention are as follows.

[0008] In the first aspect of the present invention, an efficient method for removing H 2 S in urban drainage pipes is provided, including the following steps:

[0009] Step 1: Obtain an iron oxalate solution from the cathode material of waste lithium iron phosphate batteries using a wet recycling process;

[0010] Step 2: Purify the iron oxalate solution to obtain FeC 2 O 4 reagent;

[0011] Step 3: Put the FeC 2 O 4 reagent into the pressure pipes of urban drainage networks to remove H 2 S in sewage.

[0012] Furthermore, the method for purifying the iron oxalate solution to obtain FeC 2 O 4 reagent in Step 2 includes the following steps:

[0013] Step S1: React the ferrous oxalate solution with a complexing agent to form a complex precipitate of other metal ions with the complexing agent, and remove metal impurities through filtration or precipitation separation methods;

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

[0015] Step S3: Use vacuum dehydration to remove the water in the ferrous oxalate solution, and improve 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 precipitation of ferrous oxalate. After the first crystallization precipitation, heat the solution and adjust the pH value, and let it stand for crystallization; remove other impurities through filtration and washing methods to obtain FeC 2 O 4 agent.

[0017] Furthermore, in step S1 of the method for obtaining the FeC 2 O 4 agent, the complexing agent is sodium cyanide.

[0018] Furthermore, in step S2 of the method for obtaining the FeC 2 O 4 agent, the organic solvent is ether or acetone.

[0019] Furthermore, in step S3 of the method for obtaining the FeC 2 O 4 agent, remove the water in the ferrous oxalate solution by vacuum distillation or vacuum drying.

[0020] Furthermore, in step S4 of the method for obtaining the FeC 2 O 4 agent, control the temperature of the ferrous oxalate solution at 25 - 40 °C and the pH at 4.5 - 5.0 to promote the first crystallization precipitation of ferrous oxalate.

[0021] Furthermore, in step S4 of the method for obtaining the FeC 2 O 4 agent, after the first crystallization precipitation, heat the solution to 30 - 40 °C, and adjust the pH value to 4.5 - 5.0, and let it stand for crystallization.

[0022] Further, in step 3, the dosage of the FeC 2 O 4 agent is Fe / S = 1.

[0023] In the second aspect of the present invention, there is provided a method for removing H in urban drainage pipes 2Highly efficient green reagent for S, and the highly efficient green reagent is FeC 2 O 4 agent.

[0024] Furthermore, the FeC 2 O 4 agent is prepared by using a wet recovery process from the cathode material of waste lithium iron phosphate batteries to obtain an iron oxalate solution, and then purifying the iron oxalate solution.

[0025] In the present invention, through experimental verification, the iron-containing waste in the power battery recycling process flow - FeC 2 O 4 is effective in removing sulfides in sewage. Therefore, the novel green agent developed in the present invention is an agent with FeC 2 O 4 as the waste from the recycling of waste lithium iron phosphate batteries.

[0026] Furthermore, the FeC 2 O 4 after passing the effectiveness test and purification treatment is put into the reactor system set in parallel according to different dosing strategies set in the experiment (such as different Fe / S, single / multiple pulse dosing). By performing chemical reaction kinetics calculations on the experimental results, the optimal dosing strategy is explored to optimize the dosing method.

[0027] Through experimental verification, the iron-containing waste in the power battery recycling process flow - FeC 2 O 4 The optimal dosing ratio of the agent for removing sulfides in sewage is 1:1. In addition, through experimental verification, under the condition of equal dosing, the mode of using multiple pulse dosing has a better effect on removing sulfides than the mode of single dosing.

[0028] Therefore, fully considering the sulfide removal rate and the economy of the agent, the dosing mode finally explored in the present invention is: dosing amount of the agent: Fe / S = 1; under the premise of equal dosing, it is pulsed three times in one sewage pump delivery cycle.

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

[0030] 1. The precipitate formed by the insoluble iron salt in the wastewater is more stable, can react with harmful substances such as hydrogen sulfide persistently, and effectively removes malodorous gases. In addition, compared with soluble iron salts, insoluble iron salts are not easily volatilized and dissolved, reducing the loss of the agent and environmental risks during the treatment process.

[0031] 2. Using waste from recycled spent power batteries as the source of iron salts demonstrates the advantages of environmental protection and resource utilization. This method helps reduce the environmental impact of waste, improves the recycling rate of resources, and conforms to the concept of sustainable development.

[0032] 3. With the large-scale use of electric vehicle batteries, the number of spent batteries is gradually increasing, providing a continuous guarantee for the supply of iron salts. By leveraging this continuous supply advantage, the continuous use of this green reagent in the urban drainage system can be ensured, improving the treatment efficiency and reducing the operating costs, thus 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 the reagent cost and avoiding waste. This comprehensive consideration helps improve the treatment efficiency and reduce the operating costs, making this invention more advantageous in terms of efficiency and economy. Through the carefully designed dosing strategy, the effective utilization of the reagent is ensured, achieving efficient and environmentally friendly sewer sewage treatment. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

[0036] Figure 3 It is a schematic process flow diagram of typically recovering ferrous oxalate from spent lithium iron phosphate batteries by wet method in Embodiment 3 of the present invention.

[0037] Figure 4 It is a schematic diagram of the sulfide concentration in sewage at different time points after adding different iron-containing recycled wastes in Embodiment 4 of the present invention.

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

[0039] Figure 6 It is a SRR-t curve graph fitted by 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 It is a graph showing the change of sulfide concentration over time under different dosing modes in Embodiment 6 of the present invention.

[0042] Figure 9This 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 In which:

[0044] 1 - Chemical dosing port; 2 - Sewage storage chamber (4°C); 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 supplementing sewage volume); 12 - Sampling port; 13 - Sewage inlet; 14 - Sewage outlet.

[0045] Figure 2 In which:

[0046] 15 - Anaerobic bottle; 16 - Sealing rubber cap; 17 - Needle; 18 - Syringe; 19 - Nitrogen bag. Specific embodiments

[0047] The following further describes the specific embodiments of the present invention. It should be noted here that the description of these embodiments is for helping to understand the present invention, but does not constitute a limitation to the present invention. In addition, the technical features involved in the following various embodiments of the present invention can be combined with each other as long as they do not conflict with each other.

[0048] The experimental methods in the following embodiments are all conventional methods unless otherwise specified, and the test materials used in the following embodiments are all commercially available through conventional channels unless otherwise specified.

[0049] Example 1: Construction and operation of a reactor system for simulating a pressure pipe in an urban drainage network

[0050] Figure 1 It is a schematic structural diagram of a reactor system for simulating a pressure pipe in an urban drainage network. As Figure 1 shown, the reactor system uses two drainage pipe reactors in series to simulate a pressure drainage pipe. The reactor system consists of two systems, one is an experimental system 6, and the other is a control system 7; among them, each system consists of two completely enclosed reactors 9, and the volume of each reactor 9 is 1.0 L, and the inner diameter is 80 mm. A small container 11 is installed on the upper part of each reactor 9, which is filled with the same wastewater as that in the reactor 9 to prevent air from entering during wastewater replacement. Circular plastic carriers with a diameter of 1 cm are aggregated on two stainless steel rods in each reactor 9 to provide an additional growth area for the biofilm 10, and the biofilm 10 can also be obtained without disturbing the biofilm structure.

[0051] In the present invention, the wastewater for experimental research is from the Tangjia Pumping Station in Xiangzhou District, Zhuhai City. Fresh sewage is taken for experiments every week and stored in a cold room at 4 °C to minimize biological transformation during storage. Before being pumped into the reactor, the sewage is preheated to 20 ± 1 °C in a water bath. After detection, the sewage usually contains sulfide at a concentration of 1 - 3 mgS / L and sulfate at a concentration of 15 - 22 mgS / L.

[0052] The operation method of the reactor system simulating the pressure pipe of the urban drainage network in the present invention is as follows: A peristaltic pump 4 is used to intermittently inject sewage. Among them, a total of 4 identical pumping events occur within 24 hours, and each day is divided into 4 identical 6-hour cycles. Each pumping operation lasts for more than 2 minutes, and the flow rate is 0.5 L·min -1 , so as to completely replace the residual sewage in the reactor. During the pumping operation, the wastewater is mixed in each reactor by a magnetic stirrer, and the rotation speed of the magnetic stirrer 8 is set at 200 rpm.

[0053] Example 2: Construction of an anaerobic bottle device for testing the effectiveness of pharmaceuticals

[0054] Figure 2 It is a schematic structural diagram of an anaerobic bottle device for testing the effectiveness of pharmaceuticals. As Figure 2 shown, the anaerobic bottle for testing the effectiveness of pharmaceuticals in the present invention uses a laboratory-scale anaerobic bottle device, and the anaerobic bottle 15 is made of glass. The construction method of the anaerobic bottle device is as follows: Prepare several anaerobic bottle 15 devices and establish them in parallel. The anaerobic bottle 15 device is sealed with a supporting blue sealing rubber cap 16 and an aluminum foil cap, and sealed with a supporting capping device to simulate the anaerobic conditions of the sewer pressure pipe. The bottom diameter of the anaerobic bottle 15 is 65 mm, its height is 114 mm, and the effective volume is 378 ml. The top of the device is connected to an aluminum foil nitrogen bag 19 to balance the internal air pressure of the device and ensure the smooth extraction of liquid samples.

[0055] In the present invention, a 15-ml syringe 18 is used in the anaerobic bottle 15 device to penetrate the bottle cap for sampling and adding pharmaceuticals. The needle 17 is connected to the aluminum foil nitrogen bag 19 through a hose, and the other end of the needle 17 penetrates the blue sealing rubber cap 18 to balance the internal air pressure of the bottle during sampling and adding pharmaceuticals. Before the formal experiment, the gas in the syringe 18 is emptied and the nitrogen bag 19 is filled. Squeeze the nitrogen bag 19 to pump nitrogen into the anaerobic bottle. At this time, the piston of the syringe 18 will move upward. When the volume of the pumped nitrogen gas is equal to the volume of the gas in the syringe 18, it indicates that the airtightness of this device is good.

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

[0057] This example is used to provide the removal of H in the pressure pipe of the urban drainage network in the present invention2 Efficient green agents and methods for S. To simulate the test of FeC 2 O 4 The effect of the agent in removing H in the sewer 2 S, a laboratory-scale pressure tube reactor system described in Example 1 was built and operated to simulate the actual drainage pipeline situation, and the system was monitored regularly and in a steady state; once the system was stable, experiments were carried out. In this embodiment, based on the above pressure tube reactor system, the efficient green method for removing H 2 S in the pressure tube of the urban drainage pipe network of the present invention includes the following steps:

[0058] Step 1: Obtain ferrous oxalate solution from the cathode material of waste lithium iron phosphate batteries using a wet recycling process;

[0059] Step 2: Purify the ferrous oxalate solution to obtain FeC 2 O 4 agent;

[0060] Step 3: Put the FeC 2 O 4 agent into the pressure tube of the urban drainage pipe network (in the following test experiments, the FeC 2 O 4 agent was put into the reactor system arranged in parallel) to remove sulfide in the sewage.

[0061] Figure 3 It is a schematic process flow diagram of typically recycling ferrous oxalate from waste lithium iron phosphate batteries by wet method. As Figure 3 shown, iron-containing recycling waste mainly exists in the cathode material. Ferrous oxalate recovered from the cathode material of waste power batteries may contain a certain degree of impurities and impure substances, mainly including the following categories: a. Metal impurities: The cathode material in waste power batteries may contain impurities of other metal elements, such as manganese (Mn), nickel (Ni), cobalt (Co), etc. These metal impurities may form impurity compounds with iron, affecting the purity of ferrous oxalate. b. Organic substances: The cathode material in waste power batteries may contain residues of organic substances, such as organic polymers, lubricants, etc. These organic substances may remain during the recovery process of ferrous oxalate, resulting in the impurity of ferrous oxalate. c. Moisture: Since the cathode material in waste 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, there may also be other impurities such as oxides, carbonates, etc. These impurities may affect the properties and applications of ferrous oxalate. Therefore, in the process of recovering and purifying ferrous oxalate, it is necessary to effectively treat and remove the above possible impurities and impure substances 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, in the present invention, an iron oxalate solution is obtained from the cathode material of waste lithium iron phosphate batteries using a wet recovery process, and then the iron oxalate solution is purified to obtain FeC 2 O 4 agent. The purification method of the FeC 2 O 4 agent is as follows:

[0063] Step S1, removal of metal impurities: Using the complex precipitation method, the iron oxalate solution obtained from the cathode material of waste power batteries reacts with a complexing agent (such as sodium cyanide), and other metal ions form complex precipitates with the complexing agent, and then the metal impurities are removed through filtration or precipitation separation steps;

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

[0065] Step S3, removal of moisture: Using the vacuum dehydration method, the moisture in the iron oxalate solution is removed by vacuum distillation or vacuum drying to improve the concentration and purity of the solution;

[0066] Step S4, removal of other impurities: Using the crystallization method, the temperature of the iron oxalate solution is controlled at 25 - 40 °C and the pH is 4.5 - 5.0 to promote the first crystallization precipitation of iron oxalate; 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; other impurities are removed by filtration and washing methods to obtain FeC 2 O 4 agent.

[0067] By comprehensively applying the above purification steps, metal impurities, organic substances, sulfides, moisture and other impurities in the iron oxalate solution can be effectively removed, thereby improving the purity and quality of iron oxalate and obtaining high-purity FeC 2 O 4 agent.

[0068] Example 4, effectiveness test of FeC 2 O 4 agent in removing sulfides from sewage

[0069] Using the anaerobic bottle device described in Example 2, this example is used to explore the effectiveness of FeC 2 O 4 agent in removing sulfides from sewage.

[0070] Prepare a Na₂S solution with a concentration of 300 mgS / L using deionized water deoxygenated by nitrogen blowing. 2 Take 3 anaerobic bottles with a volume of 150 ml, numbered from 1 to 3. Add a certain amount of ferric hydroxide powder, 90 ml of deionized water, and 5 ml of phosphate buffer solution to the No. 1 anaerobic bottle in sequence. Cover the bottle cap and press it tightly, and use nitrogen blowing to remove the air above the bottle. Add a certain amount of ferrous oxalate powder, 90 ml of deionized water, and 5 ml of phosphate buffer solution to the No. 2 anaerobic bottle in sequence. Cover the bottle cap and press it tightly, and use nitrogen blowing to remove the air above the bottle. Add a certain amount of ferric phosphate powder, 90 ml of deionized water, and 5 ml of phosphate buffer solution to the No. 3 anaerobic bottle in sequence. Cover the bottle cap and press it tightly, and use nitrogen blowing to remove the air above the bottle. Use a syringe to aspirate 5 ml of sodium sulfide solution and inject it into each anaerobic bottle respectively, and use a nitrogen bag to assist the injection of the solution at the other end. Fix the anaerobic bottles on a shaker and mix gently at 60 rpm. After mixing for 30 min, use a syringe to aspirate 10 ml of sample from each of the anaerobic bottles 1 - 3 respectively, and use a gas sampling bag filled with nitrogen to assist the extraction of the solution at the other end; after mixing for 90 min, use a syringe to aspirate 10 ml of sample from each of the anaerobic bottles 1 - 3 respectively; after mixing for 150 min, use a syringe to aspirate 10 ml of sample from each of the anaerobic bottles 1 - 3 respectively, and use the modified methylene blue spectrophotometry to detect the concentration of S 2- in the sample, and the results are as Figure 4 shown. Figure 4 It is a schematic diagram of the sulfide concentration in sewage at different time points after adding different iron-containing recovery waste materials.

[0071] As Figure 4 shown, except for the group adding FeC 2 O 4 , the change of sulfide concentration in other groups with time is not obvious. While in the group adding FeC 2 O 4 , the S 2- concentration decreases from 15.36 mgS / L to 1.25 mgS / L within 2.5 h, and the removal rate reaches 91.8%. Therefore, this result shows that the FeC 2 O 4 agent of the present invention is effective in removing sulfide.

[0072] Example 5. Exploration of the optimal agent dosage strategy for FeC 2 O 4 agent to remove sulfide in sewage

[0073] Part of the experiments in this example were carried out in a simulated sewer pressure pipe reactor system that has reached steady-state conditions to simulate the dosing in the pressure pipes of the real urban drainage network.

[0074] When adding FeC 2 O 4After using it as an effective reagent for removing sulfides, in order to obtain the optimal dosage of the reagent, different dosages of FeC 2 O 4 Repeat the method in the "Experiment on the Effectiveness of Reagents in Anaerobic Bottle Device", except that the amount of FeC 2 O 4 added is such that Fe / S in the system is 0.1, 1, 2, 4, and 8 respectively. Then, the S 2- concentration is measured at different time points, and the results are as Figure 5 shown.

[0075] As Figure 5 shown, when the iron-sulfur ratio is increased from 0.1 to 1, the sulfide concentration in the system at each time point decreases significantly, indicating that the group with Fe / S = 1 has a better effect on removing sulfides. However, when the iron-sulfur ratio is increased from 1 to higher values, the sulfide concentration in the system at each time point does not decrease significantly, indicating that there is a situation of reagent waste at this time.

[0076] In addition, the chemical reaction kinetics of the reaction between ferrous oxalate and sulfide was analyzed using the differential method, and the results are as Figures 6 - 7 shown. Among them, Figure 6 is the measured value and the fitted trend line graph of the sulfur reduction rate (SRR) over time when Fe / S = 1, Figure 7 is versus relationship graph.

[0077] Figure 6 In 2 , its R Figure 7 is 0.96, indicating that the model can fit the measured values well. 2 O 4 In , according to its slope, the reaction order n is 2.30, and the rate constant k = 0.0289. The calculation results show that the influence of Fe / S on the n value is small. When Fe / S = 1, the k value is significantly higher than the other two groups. Therefore, it can be determined that the optimal dosage of FeC

[0078] Example 6. Investigation on the effect of single - time / multiple - pulse dosing of FeC 2 O 4 reagent on removing sulfides from sewage

[0079] After confirming the optimal dosage of FeC 2 O 4 in order to obtain the influence of the dosing mode on the removal of sulfides, on the premise of ensuring that the total dosage of the reagent is Fe / S = 1, the methods in the "Experiment on the Effectiveness of Reagents in Anaerobic Bottle Device" are repeated using single - time dosing and three - pulse dosing modes respectively. Then, the S​2- Concentration. The results are as Figure 8 shown. Then, calculate the sulfur reduction rate based on the experimental results. The results are as Figure 9 shown. Among them, Figure 8 is the graph of sulfide concentration changing with time, Figure 9 is the graph of sulfur reduction rate changing with time.

[0080] As Figure 8 shown, at the end of one pumping cycle, the sulfide concentration in the three - dosing mode is lower, that is, the removal rate is higher. In addition, as Figure 9 shown, except for the initial 2 h, the sulfur reduction rate of the three - dosing mode is significantly higher than that of the one - time dosing group. Therefore, it can be determined that under the condition of equal dosage, multiple - pulse dosing is better than one - time dosing in removing sulfide.

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

[0082] 1. FeC 2 O 4 is effective in removing S 2- , while FePO 4 and Fe(OH) 3 are not obvious in removing S 2- . Therefore, the new green agent of the present invention is the waste from the recycling of waste lithium iron phosphate batteries: FeC 2 O 4 .

[0083] 2. When Fe / S = 1, the effect of FeC 2 O 4 in removing S 2- is the best; under the premise of adding the same amount of agent, adding in small amounts and multiple times is better than adding once. Therefore, fully considering the sulfide removal rate and the economy of the agent, the finally explored dosing mode is: agent dosage: Fe / S = 1; under the premise of equal dosage, pulse dosing three times within one sewage pump delivery cycle.

[0084] Therefore, the present invention uses the iron - containing waste in the recycling process of waste power batteries, and obtains the FeC 2 O 4 agent through purification treatment. As a new green agent, it is applied to the efficient removal of H2S in urban drainage pipes. Through experimental verification, the FeC 2 O 4 agent shows an effective ability to remove sulfide. The optimal agent dosing strategy is Fe / S = 1, and a multiple - pulse dosing mode is adopted to ensure the best removal effect and economy. This technical solution simulates the real drainage pipe environment through a laboratory - scale pressure pipe reactor system, for H 2The removal of S provides a continuous source of iron salt and an optimal chemical dosing scheme.

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

Claims

1. An efficient method for removing H2S from urban drainage pipes, characterized in that: The following steps are involved: Step 1, using a wet recovery process to obtain a ferrous oxalate solution from waste lithium iron phosphate battery cathode materials; Step 2, purifying the ferrous oxalate solution to obtain FeC2O4 reagent; Step 3: Put FeC2O4 reagent into the pressure pipe of the urban drainage network to remove H2S in the sewage.

2. The efficient method for removing H2S from urban drainage pipes according to claim 1, characterized in that: The method for obtaining FeC2O4 agent by purifying the ferrous oxalate solution in step 2 comprises the following steps: Step S1, reacting the ferrous oxalate solution with a complexing agent, forming a complex precipitate with other metal ions and the complexing agent, and removing metal impurities by filtering or precipitation separation method; Step S2, extracting the organic matter from the ferrous oxalate solution using an organic solvent, and then separating the organic phase to remove the organic matter; Step S3, using a vacuum dehydration method to remove water from the ferrous oxalate solution to increase the concentration and purity of the solution; Step S4, controlling the temperature and pH of the ferrous oxalate solution to promote the first crystallization precipitation of ferrous oxalate. After the first crystallization precipitation, heating the solution and adjusting the pH value, and standing for crystallization; removing other impurities by filtering and washing methods to obtain FeC2O4 agent.

3. The efficient method for removing H2S from urban drainage pipes according to claim 2, characterized in that: In step S1 of the method for obtaining FeC2O4 reagent, the complexing agent is sodium cyanide.

4. The efficient method for removing H2S from urban drainage pipes according to claim 2, characterized in that: In step S2 of the method for obtaining FeC2O4 reagent, the organic solvent is ether or acetone.

5. The efficient method for removing H2S from urban drainage pipes according to claim 2, characterized in that: In step S3 of the method for obtaining the FeC2O4 agent, water in the ferrous oxalate solution is removed by vacuum distillation or vacuum drying.

6. The efficient method for removing H2S from urban drainage pipes according to claim 2, characterized in that: In step S4 of the method for obtaining the FeC2O4 agent, the temperature of the ferrous oxalate solution is controlled at 25-40°C, and the pH is controlled at 4.5-5.0, so as to promote the first crystallization precipitation of ferrous oxalate.

7. The efficient method for removing H2S from urban drainage pipes according to claim 2, characterized in that: In step S4 of the method for obtaining 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.

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

9. An efficient green reagent for removing H2S from urban drainage pipes, characterized in that: The high-efficiency green reagent is FeC2O4 reagent.

10. A highly efficient green reagent for removing H2S from urban drainage pipes according to claim 9, characterized in that: The FeC2O4 agent is prepared by obtaining a ferrous oxalate solution from waste lithium iron phosphate battery cathode materials using a wet recovery process and then purifying the ferrous oxalate solution.

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