Multi-element electro-catalysis treatment method and system for high-nitrogen wastewater in lead storage battery recovery converter process

Abstract

The invention belongs to the technical field of industrial wastewater treatment, discloses a multi-element electro-catalysis treatment method for high-nitrogen wastewater in a lead storage battery recovery converter process and a modular equipment system, and realizes internal circulation of process water. According to the matched equipment, standardized electro-catalysis modules capable of being connected in series and in parallel serve as the core, detachable electrode assemblies, a precise dosing mechanism and an intelligent monitoring unit are integrated, the single-module treatment capacity is 8-25 m < 3 > / d, and the installation period is smaller than or equal to 3 days. According to the method, the defects of poor electrode activity, insufficient additive adaptability and difficulty in equipment amplification in the prior art are overcome, the total nitrogen removal rate is greater than or equal to 90%, the use amount of liquid caustic soda is reduced by 30-50%, and the method is suitable for high-nitrogen wastewater of different processes and dynamic adjustment requirements of productivity, and has remarkable environmental protection and economic values.

Description

Technical Field

[0001] This invention belongs to the field of industrial wastewater treatment technology, and particularly relates to a multi-element electrocatalytic treatment method and modular equipment system for high-nitrogen wastewater from lead-acid battery recycling converter process. Background Technology

[0002] Lead-acid battery recycling involves multiple processes, including dismantling, pretreatment, smelting, acid production, and refining. The generation of high-nitrogen wastewater permeates several core processes and is deeply intertwined with environmental governance. Specifically, the sources can be categorized into four types: First, alkaline absorption products from converter smelting flue gas. When waste lead paste and lead grids are crushed and fed into a converter for high-temperature (1200–1500℃) smelting, on the one hand, nitrogen-containing organic additives in the raw materials (such as nitrogen-containing polymers generated from the degradation of battery separators) react with ammonium salt desulfurizers (such as (NH4)2CO3) to generate nitrogen oxides (NOx) such as NO and NO2; on the other hand, nitrogen in the air generates thermal NOx under high temperature and heavy metal catalysis, with NOx concentrations in the flue gas reaching 800–1500 mg / m³. 3 To meet the NOx emission requirement of ≤200 mg / m³ in the "Emission Standard of Pollutants for Battery Industry" (GB30484-2013), 3 According to regulations, enterprises must use 20%–30% liquid alkali (NaOH) for spray absorption, resulting in the reactions NO + NO₂ + 2NaOH = 2NaNO₂ + H₂O and 2NO₂ + 2NaOH = NaNO₃ + NaNO₂ + H₂O, directly generating highly alkaline wastewater (pH 11–13) containing NaNO₂ and NaNO₃. Treating one ton of flue gas requires 0.8–1.2 kg of liquid alkali, and the annual treatment cost accounts for more than 20% of the total environmental protection investment. Secondly, there are byproducts of the wet desulfurization conversion process. Pretreatment of waste lead paste often uses ammonia desulfurization, converting PbSO₄ into soluble Pb(NH₃)₄ through NH₃·H₂O or (NH₄)₂SO₄. 2+ The ammonium sulfate produced in the reaction is discharged with the washing water, causing the nitrogen content of the wastewater to rise to >2000 mg / L, and the wastewater is weakly alkaline (pH 8.5–9.5) due to the presence of excess ammonia. A wet process workshop of a lead recycling company with an annual production capacity of 50,000 tons can generate 30–50 m³ of this high-ammonium wastewater daily. 3Direct discharge incurs high pollution discharge fees, while storage and treatment require corrosion-resistant tanks, increasing equipment investment by 2-3 million yuan. Thirdly, the acid production process generates nitrogen-containing wastewater. In the acid production process of lead-acid battery recycling, to enhance the purification efficiency of waste electrolyte (dilute sulfuric acid) or pre-treat lead paste, some companies add dilute nitric acid (HNO3) as an oxidant to oxidize impurities such as low-valence lead (Pb) and iron (Fe2+), reacting to produce soluble lead nitrate (Pb(NO3)2) and other products. Simultaneously, if ammonia is used to treat tail gas or neutralize waste acid during acid production, excess ammonia nitrogen will be discharged with washing water and condensate, forming mixed high-nitrogen wastewater containing nitrate and ammonia nitrogen, with a total nitrogen concentration reaching 1600-2200 mg / L, and accompanied by high salt (ammonium sulfate, sodium sulfate) characteristics, with a salinity of 8%-12%. A certain acid production workshop discharges 15-25 m³ of such wastewater daily. 3 Direct treatment is difficult and consumes a lot of reagents. Fourth, there is the wastewater from plate cleaning and electrolyte neutralization. The sulfuric acid electrolyte (concentration 30% to 40%) leaked during dismantling needs to be neutralized to pH 6 to 9 with liquid alkali. Although the Na2SO4 generated by the neutralization reaction is nitrogen-free, when mixed with the nitrogen-containing wastewater from the converter, acid production, and wet desulfurization processes mentioned above, the total salinity will rise to 8% to 15%, further increasing the difficulty of treatment.

[0003] High-nitrogen wastewater from the entire process has become an "environmental deadlock" for lead-acid battery recycling companies. Its treatment faces a triple dilemma of "high cost, great difficulty, and poor stability." In terms of cost, alkaline absorption and subsequent neutralization form a vicious cycle—flue gas absorption requires a large amount of liquid alkali to maintain a high pH to ensure NOx absorption rate (≥90%), and nitrogen-containing wastewater in the acid production and desulfurization stages requires the addition of acid to adjust the pH, with the cost of acid and alkali reagents per ton of wastewater reaching 200-400 yuan. If traditional biological denitrification is used, the nitrification process requires 7.14 kg of CaCO3 to replenish alkalinity for every 1 kg of ammonia nitrogen oxidized, and denitrification requires the addition of sodium acetate as a carbon source, which increases the operating cost by another 50-80 yuan / ton, with the annual treatment cost exceeding 10 million yuan. In terms of treatment difficulty, the wastewater's complex characteristics of "high nitrogen, high alkalinity, high salinity, and heavy metals" are superimposed: ① Nitrogen forms are complex; converter wastewater is mainly nitrate nitrogen, acid production wastewater contains nitrate nitrogen and ammonia nitrogen, and wet desulfurization wastewater is mainly ammonium nitrogen, all containing trace amounts of organic nitrogen, which cannot be removed simultaneously by a single process; ② High salinity (8%–15% ammonium sulfate, sodium sulfate) leads to osmotic pressure imbalance in biological processes, reducing microbial activity by more than 50%, or even causing complete inactivation; ③ Under highly alkaline conditions, Pb... 2+ It readily forms soluble Pb(OH)4 2- Traditional chemical precipitation methods have a removal rate of only 60% to 70%, and the precipitates are prone to back-dissolution, causing secondary pollution; ④NO 3- NH 4+ In high-salt systems, mass transfer efficiency is low, and electrodes of traditional electrochemical methods are easily poisoned by heavy metals, resulting in a total nitrogen removal rate of less than 75%.

[0004] Existing technologies struggle to overcome the aforementioned bottlenecks: biological denitrification processes have reaction cycles of 24–72 hours and require large sedimentation tanks and aeration systems, occupying 3–5 times the space of this invention, and are unsuitable for high-salt wastewater such as acid production; chemical precipitation methods (such as the MAP method) require the addition of magnesium salts and phosphates, with reagent costs exceeding 200 yuan / ton, and the resulting sludge contains heavy metals, with hazardous waste disposal costs reaching 3000 yuan / ton; traditional electrochemical methods use binary alloy electrodes (such as Ti-Ru) and a single NaCl additive, which only improves conductivity but cannot solve the problems of electrode poisoning and the selectivity of nitrogen conversion in different forms, with energy consumption as high as 5–8 kWh / m³. 3 Therefore, developing treatment technologies that are compatible with the complex pollution characteristics of the entire process and are both economical and efficient has become the key to achieving "environmental compliance and cost control" in the lead-acid battery recycling industry.

[0005] Based on the above analysis, the problems and shortcomings of the existing technology are as follows:

[0006] (1) The biological denitrification method has a reaction cycle of 24 to 72 hours and requires a large sedimentation tank and aeration system, which takes up 3 to 5 times the area of ​​the present invention. It is also unsuitable for high-salt wastewater such as acid production. Chemical precipitation methods (such as MAP method) require the addition of magnesium salts and phosphates, with a reagent cost of over 200 yuan / ton. In addition, the sludge produced contains heavy metals, and the hazardous waste disposal cost reaches 3,000 yuan / ton.

[0007] (2) Traditional electrochemical methods use binary alloy electrodes (such as Ti-Ru) and a single NaCl additive, which can only improve conductivity but cannot solve the problems of electrode poisoning and the selectivity of nitrogen conversion in different forms. The energy consumption is as high as 5-8 kWh / m 3 . Summary of the Invention

[0008] To address the problems existing in the prior art, this invention provides a multi-element electrocatalytic treatment method and modular equipment system for high-nitrogen wastewater from lead-acid battery recycling converter processes.

[0009] This invention is implemented as follows: a multi-element electrocatalytic treatment method for high-nitrogen wastewater from a lead-acid battery recycling converter process, comprising:

[0010] Step 1, Pretreatment: Adjust the pH of the wastewater, and remove suspended solids and heavy metals through sedimentation and filtration (removal rate ≥95%).

[0011] Step 2, Electrocatalytic Degradation: The pretreated wastewater is introduced into a multi-element electrocatalytic reactor, and a composite additive of "sodium succinate-potassium citrate-NaCl-(NH4)2SO4-EDTA disodium" is added. The reactor is operated at a voltage of 1.8–3.2V and an A / cm² voltage of 25–55mA. 2 Under current density, nitrogen pollutants are directionally converted into nitrogen gas.

[0012] Step 3, solid-liquid separation: separation and recovery of nitrate crystals;

[0013] Step 4, Recycling and reuse: When the total nitrogen in the effluent is ≤100mg / L, it is circulated within the workshop.

[0014] Another objective of this invention is to provide a modular equipment system for the multi-element electrocatalytic treatment of high-nitrogen wastewater from lead-acid battery recycling converter processes, comprising:

[0015] The pretreatment module is used to adjust the pH of wastewater and remove suspended solids and heavy metals through sedimentation and filtration (removal rate ≥95%).

[0016] The electrocatalytic degradation module is used to introduce pretreated wastewater into a multi-element electrocatalytic reactor, adding a composite additive of "sodium succinate-potassium citrate-NaCl-(NH4)2SO4-disodium EDTA" at a voltage of 1.8–3.2V and an A / cm² voltage of 25–55mA. 2 Under current density, nitrogen pollutants are directionally converted into nitrogen gas.

[0017] Solid-liquid separation module, used to separate and recover nitrate crystals;

[0018] The recycling module is used for internal circulation in the workshop when the total nitrogen in the effluent is ≤100mg / L.

[0019] Based on the above technical solutions and the technical problems solved, the advantages and positive effects of the technical solution to be protected by this invention are as follows:

[0020] This invention discloses a multi-element electrocatalytic treatment method and modular equipment system for high-nitrogen wastewater from the entire lead-acid battery recycling process, belonging to the field of industrial wastewater deep treatment and equipment technology. The method targets high-nitrogen wastewater generated in each process stage of lead-acid battery recycling. Suspended solids and heavy metals are removed through pH adjustment and "precipitation-ceramic membrane filtration" (removal rate ≥95%). The core electrocatalytic degradation stage uses a Ti-based Ru-Ir-Sn-Mn quaternary oxide anode and a Ni-Co-Fe-Cu multi-element alloy cathode, with the addition of a "sodium succinate-potassium citrate-NaCl-(NH4)2SO4-EDTA disodium" composite additive, operating at a voltage of 1.8–3.2V and an A / cm² voltage of 25–55mA. 2 At a specific current density, nitrogen pollutants are directionally converted into nitrogen gas, resulting in a total nitrogen concentration ≤150 mg / L after treatment, enabling internal recycling of process water. The supporting equipment is centered around a standardized electrocatalytic module that can be connected in series and parallel, integrating detachable electrode components, a precise dosing mechanism, and an intelligent monitoring unit. A single module has a processing capacity of 8–25 m³ / h. 3 / d, installation cycle ≤3 days. This invention solves the shortcomings of traditional technologies such as poor electrode activity, insufficient additive compatibility, and difficulty in equipment scale-up. The total nitrogen removal rate is ≥90%, the liquid alkali consumption is reduced by 30% to 50%, and it is suitable for high-nitrogen wastewater from different processes and dynamic adjustment of production capacity, thus possessing significant environmental and economic value. Attached Figure Description

[0021] Figure 1 This is a flowchart of a multi-element electrocatalytic treatment method for high-nitrogen wastewater from a lead-acid battery recycling converter process, provided in an embodiment of the present invention.

[0022] Figure 2 This is a structural block diagram of a modular equipment system for the multi-element electrocatalytic treatment of high-nitrogen wastewater from a lead-acid battery recycling converter process, provided in an embodiment of the present invention.

[0023] Figure 3 This is a color comparison image of converter high-nitrogen wastewater before and after electrochemical treatment, provided in an embodiment of the present invention. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0025] In the lead-acid battery recycling converter process, wastewater often contains extremely high concentrations of nitrogen pollutants, along with accompanying heavy metal ions and suspended solids. If this wastewater is discharged directly without treatment, it will not only disrupt the nitrogen cycle and cause eutrophication, but also exacerbate heavy metal toxicity, making traditional biological treatment methods difficult and resulting in poor operational stability. Existing technologies mostly rely on chemical precipitation or single electrocatalytic degradation, which suffers from low nitrogen removal efficiency, high energy consumption, and difficulty in recovering byproducts. Therefore, the industry urgently needs a treatment method that can simultaneously achieve efficient removal of nitrogen pollutants, resource utilization, and modular engineering.

[0026] The proposed multi-element electrocatalytic method first employs a pretreatment stage to adjust the pH of the wastewater and then uses precipitation and filtration to effectively remove suspended solids and heavy metals. Due to the complexity of heavy metals involved in lead-acid battery recycling, a multi-step precipitation-filtration approach is used to ensure a removal rate of over 95%, thus providing stable influent conditions for the subsequent electrocatalytic reaction, preventing metal ion deposition on the electrode surface, and improving the long-term stability of the electrodes. This stage achieves an organic combination of physical and chemical actions, laying the foundation for the continuous operation of the electrocatalytic reactor.

[0027] In the electrocatalytic degradation process, wastewater is introduced into a multi-element electrocatalytic reactor, and a composite additive consisting of sodium succinate, potassium citrate, NaCl, (NH4)2SO4, and disodium EDTA is added. This composite system produces a synergistic effect at the electrode interface: the organic complexing agent can regulate the stability of metal ions, chloride ions promote the generation of active chloride species, and organic acid salts enhance the electron transfer rate, thereby achieving a voltage of 1.8–3.2 V and an A / cm² of 25–55 mA. 2 It achieves efficient and targeted transformation of nitrogen pollutants at low current densities. Its core mechanism lies in reducing or oxidizing nitrates and ammonia nitrogen via an electrochemical pathway, ultimately generating harmless nitrogen molecules and significantly reducing the total nitrogen concentration.

[0028] After the reaction is complete, the system is introduced into a solid-liquid separation unit. During the electrocatalytic process, some nitrates form stable crystals under specific reaction conditions and are recovered through physical separation. This not only avoids secondary pollution but also realizes the resource utilization of by-products. This step differs from the traditional "simple removal" process in that it emphasizes the closed-loop value of the industrial chain, converting high-nitrogen wastewater into recyclable salt resources, which has strong economic added value.

[0029] After solid-liquid separation and deep electrocatalysis, the total nitrogen concentration of the effluent can be stably controlled below 100 mg / L. By incorporating a recycling module, this compliant effluent can be directly reused in the cooling or rinsing processes within the workshop production system, avoiding excessive consumption of fresh water resources and achieving water resource recycling within the factory. Compared to traditional external discharge compliance solutions, this design possesses significant industrial competitiveness in the context of energy conservation, emission reduction, and green manufacturing.

[0030] This multi-element electrocatalytic method solves the problems of insufficient nitrogen pollutant removal efficiency, severe heavy metal interference, lack of value utilization of by-products, and high operating costs in traditional processes. Its working principle is based on a multi-dimensional integration of electrochemical reaction kinetics regulation, additive synergistic catalysis, resource recovery, and modular system integration. Through refined process path design, it not only ensures the complete removal of nitrogen pollutants but also achieves the dual goals of resource recovery and recycling, demonstrating the industrial advantages of combining environmental engineering with clean production.

[0031] like Figure 1 As shown in the figure, the multi-element electrocatalytic treatment method for high-nitrogen wastewater from the lead-acid battery recycling converter process provided in this embodiment of the invention includes the following steps:

[0032] S101, Pretreatment: Adjust the pH of the wastewater, and remove suspended solids and heavy metals through sedimentation and filtration (removal rate ≥95%).

[0033] S102, Electrocatalytic Degradation: Pretreated wastewater is introduced into a multi-element electrocatalytic reactor, and a composite additive of "sodium succinate-potassium citrate-NaCl-(NH4)2SO4-EDTA disodium" is added. The reactor operates at a voltage of 1.8–3.2V and an A / cm² voltage of 25–55mA. 2 Under current density, nitrogen pollutants are directionally converted into nitrogen gas.

[0034] S103, Solid-liquid separation: Separation and recovery of nitrate crystals;

[0035] S104, Recycling: Internal circulation within the workshop when the total nitrogen in the effluent is ≤100mg / L.

[0036] like Figure 2 As shown in the figure, the modular equipment system for multi-element electrocatalytic treatment of high-nitrogen wastewater from lead-acid battery recycling converter process provided in this embodiment of the invention includes:

[0037] The pretreatment module is used to adjust the pH of wastewater and remove suspended solids and heavy metals through sedimentation and filtration (removal rate ≥95%).

[0038] The electrocatalytic degradation module is used to introduce pretreated wastewater into a multi-element electrocatalytic reactor, adding a composite additive of "sodium succinate-potassium citrate-NaCl-(NH4)2SO4-disodium EDTA" at a voltage of 1.8–3.2V and an A / cm² voltage of 25–55mA. 2 Under current density, nitrogen pollutants are directionally converted into nitrogen gas.

[0039] Solid-liquid separation module, used to separate and recover nitrate crystals;

[0040] The recycling module is used for internal circulation in the workshop when the total nitrogen in the effluent is ≤100mg / L.

[0041] Wastewater from lead-acid battery recycling converter processes often contains high concentrations of heavy metal ions and suspended particles. The core mechanism of the pretreatment module is to adjust the pH value so that metal ions react with hydroxide or carbonate ions to form insoluble precipitates, while the solid particles formed are removed through sedimentation and filtration. This process effectively reduces the concentration of heavy metals such as lead, cadmium, and copper in the wastewater, achieving a removal rate of over 95%, thereby reducing the risk of poisoning and clogging of the active sites on the subsequent electrode surfaces and providing stable feed water for the electrocatalytic degradation module.

[0042] In the electrocatalytic degradation module, wastewater enters a multi-component electrocatalytic reactor, where a constant voltage and current density are applied. Oxidation occurs at the anode, generating active chloride species and hydroxyl radicals, while at the cathode, the reduction of nitrogen oxides is promoted. Sodium succinate and potassium citrate act as electron mediators within the reaction zone, enhancing mass transfer rates and regulating the reaction kinetics at the electrode interface. NaCl provides chloride ions to form hypochlorous acid, which then oxidizes ammonia nitrogen. (NH4)2SO4 provides an ammonia source to balance the reaction system. Disodium EDTA complexes residual heavy metals, preventing their deposition on the electrode surface. Through the synergistic effect of these multiple components, nitrogen pollutants are efficiently and directionally converted into nitrogen gas.

[0043] In the reactor, ammonia nitrogen, nitrate, and nitrite are removed via electrochemical pathways: ammonia nitrogen is oxidized to nitrogen gas by active chlorine species at the anode; nitrate is gradually deoxygenated to nitrogen gas during electrochemical reduction at the cathode; and nitrite is further converted as an intermediate product. The entire process maintains a dynamic balance between reduction and oxidation reactions through electrode potential regulation, ultimately achieving the harmless release of nitrogen species. Compared to traditional biochemical methods, this pathway does not rely on microbial activity, thus exhibiting higher resistance to shock loads and more stable operational performance.

[0044] During the electrocatalytic reaction, some nitrate ions accumulate and form stable crystals under specific reaction conditions. The solid-liquid separation module separates and collects the crystal particles from the liquid phase through centrifugation or filtration, achieving resource recovery of nitrates. This not only reduces the residual dissolved nitrogen content in wastewater but also provides a byproduct for industrial production, achieving the dual effect of waste reduction and resource utilization. The high efficiency of the solid-liquid separation process ensures further purification of downstream water quality.

[0045] When the final effluent, after testing confirms a total nitrogen concentration of less than or equal to 100 mg / L, is recycled back to production processes such as cooling and rinsing in the workshop via a recycling module. This module is equipped with online monitoring devices and automatic valves to control the water flow in real time, ensuring the safety of the recycled water. When the water quality fails to meet standards, the effluent is directed to subsequent advanced treatment or safe discharge units. Through this closed-loop circulation, the system not only reduces nitrogen emission load but also reduces fresh water consumption, achieving the goals of industrial water conservation and green production.

[0046] Example 1 (Converter flue gas absorption for high-nitrate nitrogen wastewater treatment)

[0047] (1) Wastewater source and characteristics: The wastewater was taken from the converter flue gas absorption system of a lead recycling company with an annual output of 500,000 tons. The wastewater contained 1800 mg / L NaNO3, 300 mg / L NaNO2, 2100 mg / L total nitrogen, pH 12.5, salinity 10% (calculated as Na2SO4), and Pb 2+ Concentration 1.8 mg / L, daily emission 15 m³3 .

[0048] (2) Pretreatment: The wastewater was introduced into an automatic pH adjustment tank, and 10% dilute sulfuric acid was added to adjust the pH to 7.0; it was then sent to an inclined tube sedimentation tank and allowed to stand for 1.5 hours. The supernatant was filtered through a 0.8μm precision ceramic membrane to obtain pretreated wastewater (suspended solids content 4mg / L, Pb content 4mg / L, Pb content 4mg / L). 2+ 0.4 mg / L).

[0049] (3) Electrode preparation: ① Anode: Ti substrate was pretreated by blasting with 80-mesh corundum sand and boiling with 5% oxalic acid for 30 min. A mixed sol of RuCl3·xH2O-IrCl3·3H2O-SnCl4·5H2O-MnCl2·4H2O (molar ratio 2:3:4:1, solvent ethanol-hydrochloric acid = 4:1) was prepared, coated 5 times (per side), dried at 120℃ for 10 min / time, and calcined at 500℃ for 2 h to form a 12 μm active layer; ② Cathode: Ni-Co-Fe-Cu powder (molar ratio 6:2:1:1) was mixed with 0.5% stearic acid, pressed at 5 MPa, degreased at 300℃ for 2 h, and sintered at 800℃ for 4 h to form a porous cathode (pore size 30 μm, specific surface area 18 m²). 2 / g).

[0050] (4) Electrochemical degradation: Two parallel electrocatalytic modules were activated (each module has a processing capacity of 8m³). 3 / d), pretreated wastewater is pumped in, and a compound additive (sodium succinate 2.0 g / L, potassium citrate 1.2 g / L, NaCl 3.5 g / L, (NH4)2SO4 2.0 g / L, disodium EDTA 0.4 g / L) is added; the electrode spacing is set to 12 mm, a DC voltage of 2.4 V is applied, and the current density is 40 mA / cm². 2 The water bath temperature is controlled at 35℃, and the reaction is carried out for 70 minutes. Nitrogen gas is collected and discharged through the exhaust port.

[0051] (5) Solid-liquid separation: The reaction solution was centrifuged at 8000 r / min for 20 min, the precipitate was washed three times with anhydrous ethanol, and dried at 75℃ for 5 h to obtain nitrate crystals (purity 68%) 32 kg / d.

[0052] (6) Treatment results: Total nitrogen in the effluent was 130 mg / L, total nitrogen removal rate was 93.9%, and decolorization efficiency was >95% (e.g., Figure 3 As shown), Pb 2+ <0.1mg / L, energy consumption 3.3kWh / m 3 Directly recycled for flue gas scrubbing, the monthly liquid alkali consumption decreased by 42%, dilution water was saved by 310 tons, and the cost of the reagents was reduced to 65 yuan / ton.

[0053] Example 2 (Treatment of High-Nitrogen Mixed Wastewater from Acid Production Process)

[0054] (1) Wastewater source and characteristics: The wastewater was taken from the acid production workshop of a certain enterprise. It was a mixture of nitric acid pretreatment wastewater and concentrated condensate, containing 1200 mg / L NaNO3, 800 mg / L (NH4)2SO4, 1600 mg / L total nitrogen, pH 9.2, salinity 12%, and Pb. 2+ 0.9 mg / L, daily emissions 20 m³ 3 .

[0055] (2) Pretreatment: Add dilute sulfuric acid to adjust the pH to 7.2, let it stand in an inclined tube sedimentation tank for 1 hour, filter with a 0.45μm precision filter, and pretreated wastewater with suspended solids of 3mg / L and Pb. 2+ 0.3 mg / L.

[0056] (3) Electrochemical degradation: Three electrocatalytic modules (2 in parallel and 1 in series) were activated, and composite additives (sodium succinate 1.9 g / L, potassium citrate 1.1 g / L, NaCl 3.2 g / L, (NH4)2SO4 1.8 g / L, disodium EDTA 0.3 g / L) were added; the electrode parameters were the same as in Example 1, with a voltage of 2.3 V and a current density of 38 mA / cm². 2 The reaction time is 65 minutes.

[0057] (4) Solid-liquid separation: Centrifuge at 7500 r / min for 15 min to obtain 30 kg / d of nitrate crystals.

[0058] (5) Treatment results: Total nitrogen in effluent was 110 mg / L, total nitrogen removal rate was 93.1%, and energy consumption was 3.2 kWh / m³. 3 It can be reused in the acid production process washing steps, reducing acid consumption by 30% and saving 150,000 yuan per year.

[0059] Example 3 (Treatment of High Ammonium Nitrogen Wastewater from Wet Desulfurization)

[0060] (1) Wastewater source and characteristics: Taken from a wet desulfurization workshop of a certain enterprise, containing (NH4)2SO4 1600mg / L, total nitrogen 1500mg / L, pH 9.0, salinity 8%, Pb 2+ 0.9 mg / L, daily emissions 25 m³ 3 .

[0061] (2) Pretreatment: Add sodium bicarbonate to adjust the pH to 7.5, let it stand in the inclined tube sedimentation tank for 1 hour, filter with a 0.45μm precision filter, and pretreat the wastewater with suspended solids of 3mg / L.

[0062] (3) Electrochemical degradation: Three electrocatalytic modules (2 in parallel and 1 in series) were activated, and composite additives (sodium succinate 1.8 g / L, potassium citrate 1.0 g / L, NaCl 3.0 g / L, (NH4)2SO4 1.5 g / L, disodium EDTA 0.3 g / L) were added; the electrode parameters were the same as in Example 1, with a voltage of 2.2 V and a current density of 35 mA / cm². 2 The reaction time is 60 minutes.

[0063] (4) Solid-liquid separation: Centrifuge at 7500 r / min for 15 min to obtain 28 kg / d of nitrate crystals.

[0064] (5) Treatment results: Total nitrogen in effluent was 95 mg / L, total nitrogen removal rate was 90.3%, and energy consumption was 3.1 kWh / m³. 3 The ammonia is recycled back into the desulfurization washing process, reducing ammonia consumption by 35% and saving 180,000 yuan per year.

[0065] Example 4 (Treatment of mixed high-salt and high-heavy-metal wastewater throughout the entire process)

[0066] (1) Wastewater source and characteristics: A mixture of converter absorption wastewater, acid production wastewater, and wet desulfurization wastewater, with a total nitrogen content of 1900 mg / L (NO3-1200 mg / L, NH4+). + 600 mg / L, organic nitrogen 100 mg / L), pH 11.8, salinity 15%, Pb 2+ 2.5 mg / L, daily emissions 30 m³ 3 .

[0067] (2) Pretreatment: Adjust pH to 6.8 with dilute sulfuric acid, let stand in inclined tube sedimentation tank for 2 hours, filter with 1.0μm ceramic membrane, Pb 2+ It decreased to 0.5 mg / L.

[0068] (3) Electrochemical degradation: Four parallel electrocatalytic modules were activated, and composite additives (sodium succinate 2.5 g / L, potassium citrate 1.8 g / L, NaCl 5.0 g / L, (NH4)2SO4 3.0 g / L, disodium EDTA 0.6 g / L) were added; a voltage of 2.8 V and a current density of 50 mA / cm² were applied. 2 Temperature controlled at 40℃, reaction time 90 min.

[0069] (4) Solid-liquid separation: Centrifuge at 9000 r / min for 25 min to obtain 45 kg / d of nitrate crystals.

[0070] (5) Treatment results: Total nitrogen in effluent 80 mg / L, Pb 2+ <0.1mg / L, energy consumption 3.8kWh / m 3After 30 days of continuous operation, the electrode impedance remained stable at 10–13Ω with no significant poisoning attenuation. After wastewater was recycled and reused, the load on the wastewater treatment plant decreased by 60%, with no instances of exceeding discharge standards.

[0071] In the lead-acid battery recycling converter process, the nitrogen content and heavy metal ion concentration in the wastewater are generally high, making it difficult for traditional biological denitrification or single physicochemical methods to meet effluent standards. Furthermore, these methods suffer from long treatment cycles and low resource recovery rates. Direct discharge of this high-nitrogen wastewater will exacerbate nitrogen pollution in receiving water bodies and lead to eutrophication risks. The presence of high concentrations of lead and cadmium ions poses serious threats to the environment and human health. Therefore, achieving efficient nitrogen removal and resource recovery has become a critical issue that the industry urgently needs to address. The multi-element electrocatalytic treatment method proposed in this invention is specifically designed to address the unique challenges of this type of high-nitrogen wastewater treatment, overcoming the bottlenecks of traditional processes in terms of removal efficiency, resource utilization, and effluent recycling.

[0072] This method primarily relies on chemical precipitation and filtration in the pretreatment stage. By adding calcium carbonate or sodium hydroxide to the wastewater, dissolved heavy metal ions such as lead, cadmium, and zinc can be precipitated as insoluble carbonates or hydroxides. After filtration, the heavy metal load can be significantly reduced, with a removal rate exceeding 95%. This step not only improves the operating environment of the subsequent electrocatalytic reaction and avoids electrode poisoning, but also ensures that the wastewater has controllable water quality conditions before entering the electrocatalytic module. This step has the dual effect of water quality stabilization and pollutant reduction, laying the foundation for subsequent advanced treatment.

[0073] Upon entering the electrocatalytic module, the wastewater forms a strong redox environment on the surface of the titanium-based platinum-iridium coated electrode. Combined with a composite additive of sodium succinate, potassium citrate, sodium chloride, ammonium sulfate, and disodium EDTA, a multi-element catalytic system is constructed. Under applied voltages of 1.8 to 3.2 volts and current densities of 25 to 55 mA / cm², nitrates, nitrites, and ammonium ions in the wastewater are gradually converted into nitrogen gas, achieving the gas-phase release of nitrogen. Compared to single electrocatalysis, this composite system utilizes the additives to synergistically generate free radicals or complex intermediates during the reaction, effectively improving electron transfer efficiency and pollutant conversion rates, thereby significantly enhancing the total nitrogen removal rate.

[0074] During the reaction, some nitrogen precipitates as nitrate crystals. These crystals are separated and collected using a solid-liquid separation module, enabling the resource recovery of this byproduct. This crystalline product has value in the chemical or fertilizer industries, avoiding the generation of secondary waste. This model, combining pollutant conversion with crystallization recovery, ensures that the effluent meets standards while creating additional economic benefits, aligning with the principles of a circular economy and green manufacturing. The design of this stage reflects the closed-loop nature of the process and the sustainability of its industrial applications.

[0075] The system also includes a buffer tank and a recycling module for engineering applications. The buffer tank ensures the stability of the influent flow and quality under different operating conditions, avoiding fluctuations in the electrocatalytic reaction. The recycling module achieves real-time reuse of the effluent through online monitoring of total nitrogen and automatic valve switching. When the total nitrogen concentration is below 100 mg / L, the effluent is directly returned to the workshop production process. This internal circulation mode effectively reduces the amount of fresh water used and the amount of wastewater discharged, achieving clean production and cascade utilization of water resources.

[0076] The industrial application value of this technology is reflected in three aspects. First, it solves the problems of low treatment efficiency and high nitrogen residue in high-nitrogen wastewater from the lead-acid battery recycling industry, achieving complete nitrogen removal. Second, it balances environmental and economic benefits through the efficient removal of heavy metal ions and the resource-based recovery of nitrate crystals. Finally, through integrated system design and intelligent circulation control, it ensures operational stability and sustainability, providing a new, scalable wastewater treatment model for highly polluting industries such as lead-acid battery recycling. This method and system not only comply with environmental regulations but also provide technical support for the industry's transformation towards green and low-carbon development.

[0077] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications, equivalent substitutions, and improvements made by those skilled in the art within the scope of the technology disclosed in the present invention, and within the spirit and principles of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A multi-element electrocatalytic treatment method for high-nitrogen wastewater from a lead-acid battery recycling converter process, characterized in that, Includes the following steps: S1, adjusts the pH value of wastewater, removes suspended solids and heavy metals through sedimentation and filtration, with a removal rate of not less than 95%; S2 involves introducing pretreated wastewater into a multi-element electrocatalytic reactor, adding a composite additive composed of sodium succinate, potassium citrate, sodium chloride, ammonium sulfate, and disodium ethylenediaminetetraacetate, and reacting under conditions of 1.8 to 3.2 volts and a current density of 25 to 55 mA per square centimeter to convert nitrogen pollutants in the wastewater into nitrogen gas. S3, nitrate crystals are separated and recovered through a solid-liquid separation process; S4. When the total nitrogen concentration in the effluent is less than or equal to 100 mg / L, the effluent will be recycled back to the workshop.

2. The method according to claim 1, characterized in that, In step S1, calcium carbonate or sodium hydroxide is used as a precipitant to remove heavy metal ions.

3. The method according to claim 1, characterized in that, The electrode for the electrocatalytic reaction in step S2 is a titanium-based platinum-iridium coated electrode.

4. A multi-element electrocatalytic treatment system for high-nitrogen wastewater from a lead-acid battery recycling converter process used in implementing the method of claim 1, characterized in that, include: The pretreatment module is used to adjust the pH of wastewater and remove suspended solids and heavy metals through sedimentation and filtration; An electrocatalytic degradation module is used to add composite additives and apply voltage and current density conditions in a multi-element electrocatalytic reactor to achieve the conversion of nitrogen pollutants; Solid-liquid separation module, used to separate and recover nitrate crystals; The recycling module is used to reuse effluent with total nitrogen less than or equal to 100 mg / L in the workshop.

5. The system according to claim 4, characterized in that, A buffer tank is provided between the pretreatment module and the electrocatalytic degradation module to stabilize the quality and quantity of the influent water.

6. The system according to claim 4, characterized in that, The recycling module includes a return pipeline and a control valve, which are used to automatically switch the direction of the effluent flow based on the real-time monitored total nitrogen concentration.

7. A multi-element electrocatalytic reactor for use in the method of claim 1, characterized in that, include: The anode and cathode have an active coating on their surface to promote the oxidation reaction, while the cathode is used for the reduction reaction of nitrogen oxides. Power control unit for providing constant voltage or constant current conditions from 1.8 to 3.2 volts; An additive dosing device is used to uniformly inject a solution of sodium succinate, potassium citrate, sodium chloride, ammonium sulfate, and disodium ethylenediaminetetraacetate into the reaction zone.

8. The reactor according to claim 7, characterized in that, The anode material is titanium-based iridium-plated platinum, and the cathode material is graphite felt.

9. A modular multi-element electrocatalytic treatment equipment for high-nitrogen wastewater from a lead-acid battery recycling converter process, characterized in that, The equipment consists of multiple independent functional modules, each connected to valves via pipelines. The modules include: The system includes a pretreatment module, an electrocatalytic reaction module, a solid-liquid separation module, and a recycling module, all of which can be started and stopped independently based on the wastewater quality.

10. The modular equipment according to claim 9, characterized in that, The connections between the modules employ a replaceable quick-connect piping structure to facilitate module disassembly and assembly.

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