A method for targeted recovery of heavy metals from municipal sludge

Abstract

This invention relates to the interdisciplinary fields of environmental engineering, solid waste resource utilization, and advanced functional materials technology, specifically to a method for targeted recovery of heavy metals from municipal sewage sludge. The method discloses a method for targeted recovery of heavy metals from municipal sewage sludge. First, a magnetic nanomaterial with a hydrophilic brush layer and a surface ion-imprinted layer is prepared. Then, the sludge is acid-dissolved to obtain a leachate, and the material is added to selectively adsorb the target heavy metals. After magnetic separation, desorption is performed using a low-voltage pulsed electric field. Finally, the desorbate is purified by iron removal, and high-purity copper is recovered by constant-potential electrodeposition. This invention achieves highly selective capture and recovery of heavy metals in complex systems, and the material is recyclable, possessing good industrial application prospects.

Description

Technical Field

[0001] This invention relates to the interdisciplinary fields of environmental engineering, solid waste resource utilization and advanced functional materials technology, and specifically to a method for targeted recovery of heavy metals from municipal sludge. Background Technology

[0002] Municipal sludge is a complex heterogeneous byproduct generated during wastewater treatment. It is rich in nitrogen, phosphorus, and organic matter, but also highly enriched with heavy metals such as copper, zinc, lead, cadmium, chromium, and nickel. These heavy metals are biotoxic, non-degradable, and bioaccumulate in the food chain. Currently, pretreatment methods for heavy metal extraction mainly include high-temperature heat treatment, bioleaching, and chemical leaching. However, these methods suffer from high energy consumption, long cycles, and severe equipment corrosion. In particular, the large amounts of extracellular polymeric substances (EPS) and calcium and magnesium ions present in the sludge leachate lead to bottlenecks in subsequent separation processes, such as severe organic pollution, resin poisoning, and poor selectivity. Traditional chemical precipitation, solvent extraction, and ion exchange resins are all insufficient for achieving efficient and selective recovery of heavy metals.

[0003] Existing technologies attempt to use ion-imprinted polymer technology to achieve precise and highly selective separation of specific target heavy metals. For example, CN121372353A discloses an adsorbent material targeting chromium, its preparation method, and its application. The preparation method of the chromium-targeting adsorbent material includes the following steps: S1, crushing, sieving, and pyrolyzing the stems of potassium-rich plants to obtain biomass carbon; S2, dispersing the biomass carbon in a solvent and adding Cr... 6+ Template ions, Cr 3+ Template ions, functional monomers, crosslinking agents, and initiators react, followed by washing and drying to obtain an ion-imprinted polymer; S3, a reducing barrier agent is first dissolved in a solvent, then the ion-imprinted polymer is added, and the reaction is carried out at room temperature to obtain the targeted chromium adsorbent material; the potassium-rich plant is a plant with a total potassium content of 5%~8%. The prepared material is used to target and repair heavy metal Cr. 6+ / Cr 3+ Long-lasting adsorption materials for reducing the volume of polluted soil and groundwater possess extremely strong specificity and high adsorption efficiency, showing significant advantages in heavy metal treatment efficiency, sustainability, and resistance to acid interference. However, ion-imprinted polymers, as smart materials capable of specifically recognizing target metal ions, have not yet been applied to the selective separation and recovery of heavy metals from municipal sludge leachate.

[0004] In summary, how to innovate a new method to effectively resist the interference of EPS and calcium and magnesium ions in complex sludge leachate systems, achieve highly selective targeted capture, mild desorption and high-purity recovery of heavy metals, and at the same time have good recycling performance has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for targeted recovery of heavy metals from municipal sludge, so as to solve the technical problems of insufficient selectivity caused by non-specific adsorption and the aggregation and deactivation of nanomaterials in complex media in the prior art.

[0006] The specific technical solution is as follows:

[0007] This invention provides a method for targeted recovery of heavy metals from municipal sewage sludge, comprising the following steps: S1: Dehydrated sludge was placed in an ultrasonic-electrochemical reactor, sulfuric acid solution was added, and the ultrasonic generator was turned on for treatment. Then, the reactor was switched to pulsed electrochemical mode, with a graphite plate as the anode and a stainless steel plate as the cathode. A pulsed electric field was applied for further treatment for 6 hours. After the reaction, the mixture was transferred to a centrifuge for centrifugation. The supernatant was vacuum filtered through a 0.45μm mixed cellulose ester microfiltration membrane to obtain a clear leaching solution. 1mol / L sodium hydroxide was added to the leaching solution to adjust the pH to 5.0. Then, the surface ion-imprinted magnetic nanomaterials were added to the pH-adjusted leaching solution and placed in a constant temperature shaking incubator for specific oscillation and adsorption. An external permanent magnet was placed near the bottom of the reaction vessel for magnetic separation. Solid-liquid separation was completed within 3 minutes to obtain a magnetic material loaded with copper ions.

[0008] S2: The copper-loaded magnetic material was transferred to a pulsed electrochemical desorption cell, placed in a titanium mesh basket as the cathode, and a platinum sheet as the anode with a 5cm electrode spacing. Nitric acid solution was added as the desorption solution, and a pulsed electric field was applied. After desorption, the regenerated material was separated by an external magnet, yielding the regenerated magnetic material and the copper-containing desorption solution. 30% hydrogen peroxide solution was added to the desorption solution, and the mixture was stirred at room temperature for 15 minutes. Then, sodium hydroxide solution was added dropwise to adjust the pH. The mixture was allowed to stand for 30 minutes, then transferred to a 70℃ water bath and aged with continuous stirring for 40 minutes. The precipitate was removed by filtration through a 0.45μm membrane, yielding a solution after iron removal. The pH of the solution was adjusted to 2.8 for later use.

[0009] S3: The iron-removed solution is placed in an electrolytic cell with a stainless steel plate as the cathode and titanium-based ruthenium dioxide as the anode, with an electrode distance of 8 cm. An Ag / AgCl (3M KCl) electrode is used as the reference electrode. Copper is recovered by electrodeposition under stirring at room temperature after controlling the cathode potential. Purple-red metallic copper is deposited on the cathode surface. It is periodically scraped and collected, washed with deionized water, dehydrated with anhydrous ethanol, and vacuum dried to obtain the copper product.

[0010] Further, the sulfuric acid solution in S1 has a concentration of 0.1~0.5 mol / L; the centrifugation is set to a rotation speed of 3000~5000 rpm and a time of 5~15 minutes; the oscillation adsorption is set to a temperature of 20~30℃, a rotation speed of 120~180 rpm, and a time of 45~75 minutes.

[0011] Further, the nitric acid solution in S2 has a concentration of 0.2~0.6 mol / L; the pulsed electric field treatment lasts for 30~90 minutes.

[0012] Furthermore, copper is recovered by electrodeposition under room temperature stirring after controlling the cathode potential as described in S3, with the potential controlled in the range of -0.50 to -0.35 (vs. Ag / AgCl) and the electrodeposition time controlled in the range of 3 to 5 hours.

[0013] This invention also provides a method for preparing surface ion-imprinted magnetic nanomaterials, specifically: magnetic nanoparticles are dispersed in anhydrous ethanol, ultrasonically dispersed for 30 minutes, then tetraethyl orthosilicate and ammonia are added, and the reaction is carried out with mechanical stirring in a water bath. After magnetic separation by an external permanent magnet, washing three times with anhydrous ethanol, and vacuum drying, Fe3O4@SiO2 core-shell material is obtained; the core-shell material is dispersed in 80 mL of anhydrous toluene, and 3-aminopropyltriethoxysilane is slowly added dropwise. The mixture is heated to 80 °C and refluxed for 12 hours under nitrogen protection. After magnetic separation, washing three times with anhydrous toluene and three times with anhydrous ethanol, and vacuum drying at 60 °C for 6 hours, an amino-modified magnetic carrier is obtained; the amino-modified magnetic carrier is dispersed in anhydrous xylene, α-bromoisobutyryl bromide and triethylamine are added, and the mixture is reacted in an ice bath for 4 hours, then heated to 60 °C and reacted for 12 hours. After magnetic separation and washing... The magnetic carrier modified with a surface initiator was obtained by drying. The carrier was then dispersed in a mixed solvent of methanol and water, and hydroxyethyl methacrylate monomer, cuprous bromide catalyst, and pentamethyldiethylenetriamine ligand were added. After three cycles of liquid nitrogen freezing-vacuuming-thawing to remove oxygen, surface-initiated atom transfer radical polymerization was carried out in a 60°C oil bath with magnetic stirring for 8 hours. After the reaction, the product was separated by an external magnet, washed three times with methanol, and vacuum dried to obtain a magnetic material modified with a poly(hydroxyethyl methacrylate) brush layer. The brush-modified magnetic material was dispersed in a mixed solution of acetic acid and water, and functional monomers for the metal ion imprinted polymer layer and anhydrous copper sulfate were added. The mixture was stirred at room temperature for 2 hours to ensure sufficient coordination. Glutaraldehyde crosslinking agent was then added, and the reaction was carried out at 60°C for 4 hours to complete the imprint layer fixation. The product was separated by an external magnet, and the template Cu was removed by shaking and washing with a template eluent. 2+ The material was washed with deionized water until neutral, then vacuum dried to obtain surface ion-imprinted magnetic nanomaterials.

[0014] Furthermore, the surface ion-imprinted magnetic nanomaterial, based on 10 parts by mass of magnetic nanoparticles, comprises the following raw materials: 3-8 parts tetraethyl orthosilicate, 1-3 parts ammonia, 1-3 parts 3-aminopropyltriethoxysilane, 0.5-1.2 parts α-bromoisobutyryl bromide, 0.8-1.5 parts triethylamine, 10-20 parts hydroxyethyl methacrylate, 0.2-0.4 parts cuprous bromide, 0.3-0.8 parts pentamethyldiethylenetriamine ligand, 1.5-2.5 parts functional monomers of the metal ion-imprinted polymer layer, 0.5-1.5 parts anhydrous copper sulfate, and 1.0-2.0 parts glutaraldehyde.

[0015] Furthermore, the magnetic nanoparticles are Fe3O4 or γ-Fe2O3; the functional monomers of the metal ion imprinted polymer layer are chitosan or polyethyleneimine; the metal ion imprinted polymer layer uses the target heavy metal ion as a template, and the template eluent is ethylenediaminetetraacetic acid or citric acid.

[0016] Compared with the prior art, the present invention has the following beneficial effects: (1) High selectivity: The hydrophilic brush layer of poly(hydroxyethyl methacrylate) effectively inhibits the non-specific adsorption of organic matter and calcium and magnesium ions through the dual mechanisms of steric hindrance and hydration repulsion, protecting the surface imprint layer from contamination. Combined with surface ion imprinting technology, it achieves high selective recognition of target heavy metals.

[0017] (2) Mild desorption conditions: Low-voltage pulsed electric field assisted desorption, achieving efficient desorption under mild conditions, avoiding damage to the imprint structure caused by long-term immersion in strong acid, the material can be recycled for a long time, and the processing capacity can be maintained by adding a small amount, significantly reducing costs.

[0018] (3) High recovery efficiency: The selective iron removal step efficiently removes interfering ions, and the constant potential electrodeposition precisely controls the cathode potential, avoiding co-deposition of impurities, and obtaining high-purity heavy metal products, thus achieving high-quality recovery from complex systems.

[0019] (4) Complete process integration: The unit operations such as leaching, capture, separation, desorption, purification, electrodeposition and material regeneration are organically integrated to form a closed-loop process, providing a feasible technical path for the resource utilization of heavy metals in municipal sludge.

[0020] Obviously, based on the above description of the present invention, and according to common technical knowledge and conventional methods in the field, various other modifications, substitutions or alterations can be made without departing from the basic technical concept of the present invention.

[0021] The following detailed embodiments further illustrate the above-described content of the present invention. However, this should not be construed as limiting the scope of the present invention to the following examples. All technologies implemented based on the above-described content of the present invention fall within the scope of the present invention. Attached Figure Description

[0022] Figure 1 This is a flowchart of a method for targeted recovery of heavy metals from municipal sludge according to the present invention.

[0023] Figure 2 The infrared spectra of Fe3O4 nanoparticles, Fe3O4@SiO2 core-shell materials, and surface ion-imprinted magnetic nanomaterials in Example 1 of this invention are shown. Detailed Implementation

[0024] This invention proposes a method for targeted recovery of heavy metals from municipal sewage sludge, such as... Figure 1 The diagram shows a flowchart of a method for targeted recovery of heavy metals from municipal sludge according to the present invention. The detailed preparation steps are as follows: 1. Preparation of magnetic materials First, surface-imprinted magnetic nanomaterials with a three-layer core-shell structure were prepared. Fe3O4 nanoparticles were used as the magnetic core, and a SiO2 shell was coated onto their surface via a sol-gel method to form a Fe3O4@SiO2 core-shell structure. The SiO2 shell protects the magnetic core and provides chemical stability. The Fe3O4@SiO2 core-shell material was collected by magnetic separation, washed three times with anhydrous ethanol to remove unreacted substances, vacuum dried, and dispersed in anhydrous toluene. 3-Aminopropyltriethoxysilane was slowly added dropwise, and the mixture was heated under reflux under nitrogen protection to obtain an amino-modified magnetic precursor support. This amino-modified support was transferred and dispersed in anhydrous xylene, and an interfacial amidation reaction was carried out using dropwise α-bromoisobutyryl bromide and triethylamine to obtain a high-density surface initiator-modified magnetic support. Subsequently, a hydrophilic brush layer of poly(hydroxyethyl methacrylate) was grafted onto the SiO2 surface using surface-initiated atom transfer radical polymerization. This brush layer forms a dense hydration layer through a strong hydration effect, effectively inhibiting the non-specific adsorption of extracellular polymers, proteins, and other organic matter in the sludge leachate through a dual mechanism of steric hindrance and hydration repulsion. Finally, chitosan was used as the functional monomer, and Cu... 2+ Using template ions, a coordination crosslinking reaction is carried out on the surface of the hydrophilic brush layer to form a surface ion-imprinted layer with a thickness of 2-5 nm. After the template is washed off with ethylenediaminetetraacetic acid solution, a residue of Cu is left on the outermost layer of the material. 2+ Recognition holes with highly matched shape, size, and coordination orientation enable highly selective capture of target heavy metal ions.

[0025] 2. Separation of dissolution and adsorption Municipal dewatered sludge was mixed with 0.3 mol / L sulfuric acid solution at a specific liquid-to-solid ratio and placed in an ultrasonic-electrochemical reactor. First, the ultrasonic generator was activated to utilize cavitation to disrupt the sludge floc structure. Then, the reactor was switched to pulsed electrochemical mode, and a pulsed electric field was applied for further treatment for 6 hours. The pulsed electric field, through periodic switching on and off, reduced concentration polarization and side reactions, and synergistically with ultrasound to drive the directional migration of heavy metal ions from the sludge solid phase into the liquid phase. After the reaction, the solution was centrifuged and filtered through a microfiltration membrane to obtain a clear leachate. Sodium hydroxide was added dropwise to the leachate to adjust the pH to 5.0. Then, surface-imprinted magnetic nanomaterials were added to the leachate at a dosage of 0.36 g / L, and the mixture was shaken and adsorbed at 25°C and 150 rpm for 60 minutes. The imprinted holes on the material surface selectively recognized and captured Cu. 2+ And for Zn 2+ Fe 3+ The adsorption of coexisting ions is relatively weak. After adsorption is complete, an external permanent magnet is applied near the bottom of the reaction vessel, and magnetic separation is completed within 3 minutes, yielding a magnetic material loaded with copper ions and the residual liquid after adsorption.

[0026] 3. Desorption and iron removal purification A magnetic material loaded with copper ions was transferred to a pulsed electrochemical desorption cell and placed inside a titanium mesh basket as the cathode. An external magnetic field was applied to ensure the material adhered tightly to the inner wall of the basket, forming good electrical contact. A platinum sheet was used as the anode, and 0.4 mol / L nitric acid solution was added as the desorption solution. A low-voltage pulsed electric field was applied for 60 minutes to enhance interfacial mass transfer, allowing the Cu ions to be desorbed under mild conditions. 2+ Efficient desorption from imprint cavities is achieved while avoiding damage to the imprint structure caused by prolonged immersion in strong acid. After desorption, the regenerated material is separated by an external magnet, yielding regenerated magnetic material and a copper-containing desorption solution. Hydrogen peroxide solution is added to the desorption solution to remove Fe. 2+ Oxidized to Fe 3+ Then, sodium hydroxide solution was added dropwise to adjust the pH to 3.2, Fe 3+ Under these pH conditions, selective hydrolysis produces ferric hydroxide precipitate, while Cu... 2+ Keep the solution dissolved. Transfer the solution to a 70°C water bath and stir continuously for 40 minutes to allow the ferric hydroxide flocs to grow and coarsen. Remove the flocs via membrane filtration, while Cu... 2+ The copper-containing desorption solution was kept dissolved in the solution to obtain the purified copper-containing desorption solution.

[0027] 4. Electrodeposition recovery The copper-containing desorbate, purified after iron removal, was placed in an electrolytic cell. A stainless steel plate was used as the cathode, titanium-based ruthenium dioxide as the anode, and an Ag / AgCl (3M KCl) electrode as the reference electrode. The cathode potential was precisely controlled to -0.45 (vs. Ag / AgCl) using a potentiostat. Electrodeposition was performed at room temperature for 4 hours. This potentiostat mode avoids the influence of Cu... 2+The potential drift caused by concentration change effectively inhibits the co-deposition of impurities such as Fe and Zn. Purple-red metallic copper is precipitated on the cathode surface. After collection, washing and drying, a high-purity copper product is obtained with a copper purity of more than 90% and a zinc content of less than 1%.

[0028] The technical solution designed by this invention to solve the existing problems includes the following key points: 1. Anti-fouling surface ion-imprinted magnetic nanomaterials In complex systems such as municipal sludge leachate, traditional magnetic adsorption materials are prone to non-specific adsorption of extracellular polymers, proteins and other organic matter on their surface due to the lack of anti-pollution design. This results in physical shielding of imprinted sites, a significant decrease in selectivity, and the bulk imprinted structure is difficult to achieve rapid and efficient identification due to the deep embedding of sites and high mass transfer resistance. To address the aforementioned issues, this invention constructs a three-layer core-shell magnetic nanomaterial consisting of a Fe3O4 magnetic core, a SiO2 isolation layer, a PHEMA hydrophilic brush layer, and a surface ion-imprinted layer. The principle is as follows: the Fe3O4 core provides superparamagnetism for rapid magnetic separation; the SiO2 intermediate layer protects the magnetic core and facilitates surface modification; the PHEMA hydrophilic brush layer forms a dense hydration layer on the material surface through its strong hydration effect, effectively suppressing the non-specific adhesion of organic matter and impurity ions using both steric hindrance and hydration repulsion mechanisms; the surface ion-imprinted layer uses target heavy metal ions as templates to construct recognition holes with a thickness of 2-5 nm on the outermost layer of the material, with fully exposed imprinted sites. These holes are highly matched to the template ions in shape, size, and coordination orientation, thereby achieving highly selective capture of target heavy metal ions.

[0029] To verify whether the three-layer core-shell structure of the surface ion-imprinted magnetic nanomaterials prepared in this invention has been successfully constructed. Figure 2 Infrared spectra of Fe3O4 nanoparticles, Fe3O4@SiO2 core-shell materials, and surface ion-imprinted magnetic nanomaterials from Example 1 are given. Figure 2 As shown, the infrared spectrum of Fe3O4 nanoparticles is at approximately 570 cm⁻¹. -1 The characteristic absorption peak of the Fe-O bond appears at approximately 1100 cm⁻¹, corresponding to the stretching vibration of the Fe₃O₄ magnetic core; the infrared spectrum of the Fe₃O₄@SiO₂ core-shell material retains the characteristic peak of Fe₃O₄, and also shows a peak at approximately 1100 cm⁻¹. -1 800cm -1 and 470cm -1 Three new characteristic absorption peaks appeared at approximately 1730 cm⁻¹, corresponding to the antisymmetric stretching vibration, symmetric stretching vibration, and skeletal bending vibration of Si-O-Si, respectively, indicating that the SiO₂ shell was successfully coated on the surface of Fe₃O₄ nanoparticles; in addition to retaining the characteristic peaks of Fe₃O₄ and SiO₂, the infrared spectrum of the surface ion-imprinted magnetic nanomaterials showed a new peak at approximately 1730 cm⁻¹. -1A strong characteristic absorption peak appears at the C=O carbonyl group, corresponding to the stretching vibration of the ester group in the hydrophilic brush layer of PHEMA; at approximately 1655 cm⁻¹ -1 and 1595cm -1 The absorption peaks appearing at [location missing] correspond to the superposition of the amide I band (C=O stretching vibration) and the C=N imine bond formed by glutaraldehyde crosslinking in the chitosan imprinted layer, and the superposition of the amide II band and the NH bending vibration of the free primary amine (-NH2); at approximately 1080 cm⁻¹... -1 and 1030cm -1 The enhanced absorption peak appearing at 1655 cm⁻¹ corresponds to the CO stretching vibration of the chitosan glycocycle. Specifically, the peak at 1655 cm⁻¹... -1 The broadening and enhancement of the peaks also include contributions from the C=N imine bonds formed by glutaraldehyde crosslinking, indicating that the chitosan imprinted layer has been successfully crosslinked and fixed on the surface of the PHEMA brush layer. The appearance of the above characteristic peaks confirms that the PHEMA hydrophilic brush layer and the chitosan ion-imprinted layer have been successfully grafted onto the surface of the magnetic material.

[0030] 2. Pulsed electric field enhancement-selective purification-potential constant electrodeposition coupling process In traditional sludge heavy metal recovery processes, acid dissolution methods suffer from long dissolution times and high energy consumption. Furthermore, strong acid desorption can easily damage the structure of the imprinted material, particularly Fe. 3+ Coexisting ions interfere with electrodeposition, resulting in low product purity. Furthermore, in constant current electrodeposition mode, potential drift with ion concentration easily leads to impurity co-deposition. Although municipal sludge is enriched with multiple heavy metals such as copper, zinc, chromium, and nickel, the recovery value and separation difficulty of different heavy metals vary significantly. While zinc content is high, its recovery value is low, and it is easily interfered with by coexisting ions such as calcium and magnesium during electrodeposition, making it difficult to achieve economically viable product purity, with recovery costs far exceeding benefits. In contrast, copper has high recovery value and good electrodeposition selectivity, and high-purity recovery can be achieved through ion imprinting technology. Therefore, this invention focuses on the targeted recovery of copper. Small amounts of zinc ions in the electrodeposition tail liquid can be returned to the leaching section for recycling or treated to meet discharge standards and are not included in the recovery scope of this invention.

[0031] To address the aforementioned issues, this invention proposes a coupled process of pulsed electrochemical dissolution-pulse electrochemical desorption-selective iron removal-potential constant electrodeposition. The principle is as follows: In the dissolution stage, the pulsed electric field reduces concentration polarization and side reactions through periodic switching, synergistically disrupting the sludge floc structure with ultrasonic cavitation, driving heavy metal ions to migrate directionally into the liquid phase. In the desorption stage, a low-voltage pulsed electric field assists desorption, enhancing interfacial mass transfer and achieving efficient desorption under mild conditions while avoiding damage to the imprinted structure from prolonged immersion in strong acid. In the purification stage, the selective hydrolysis of iron ions within a specific pH range to form ferric hydroxide precipitate is utilized; precise pH control enables selective removal of iron ions, while copper ions remain dissolved under these pH conditions. In the electrodeposition stage, a constant potential mode controls the cathode potential, utilizing the difference in copper ion reduction potential to achieve distributed deposition. Constant potential control avoids potential drift caused by ion concentration changes, effectively suppressing the co-deposition of impurity ions, thereby obtaining a high-purity copper product.

[0032] Example 1 Table 1 Raw Material Information Table

[0033] A method for targeted recovery of heavy metals from municipal sewage sludge includes the following steps: S1: 10 parts of Fe3O4 nanoparticles were dispersed in 100 mL of anhydrous ethanol and ultrasonically dispersed for 30 minutes. Then, 8 parts of tetraethyl orthosilicate and 3 parts of ammonia were added. The mixture was mechanically stirred in a 40°C water bath for 12 hours. After magnetic separation with an external permanent magnet, washing with anhydrous ethanol three times, and vacuum drying at 60°C for 6 hours, Fe3O4@SiO2 core-shell material was obtained. The core-shell material was dispersed in 80 mL of anhydrous toluene, and 2 parts of 3-aminopropyltriethoxysilane were slowly added. The mixture was heated to 80°C and refluxed for 12 hours under nitrogen protection. After magnetic separation, washing with anhydrous toluene three times, washing with anhydrous ethanol three times, and vacuum drying at 60°C for 6 hours, an amino-modified magnetic carrier was obtained. The amino-modified magnetic carrier was dispersed in 80 mL of anhydrous xylene, and 0.8 parts of α-bromoisobutyryl bromide and 1.2 parts of triethylamine were added. After reacting in an ice bath for 4 hours, the temperature was raised to 60°C and reacted for 12 hours. After magnetic separation, washing, and drying, a surface initiator-modified magnetic carrier was obtained. A magnetic carrier modified with poly(hydroxyethyl methacrylate) was prepared. The carrier was then dispersed in 100 mL of a 1:1 mixture of methanol and water. 15 parts of hydroxyethyl methacrylate monomer, 0.3 parts of cuprous bromide catalyst, and 0.5 parts of pentamethyldiethylenetriamine ligand were added. After three cycles of liquid nitrogen freezing-vacuuming-thawing to remove oxygen, surface-initiated atom transfer radical polymerization was carried out in a 60°C oil bath with magnetic stirring for 8 hours. After the reaction, the product was separated by an external magnet, washed three times with methanol, and vacuum dried at 60°C to obtain a magnetic material modified with a hydroxyethyl methacrylate brush layer. Ten parts of the brush-modified magnetic material were dispersed in 50 mL of a mixed solution of acetic acid and water. 2 parts of chitosan and 1 part of anhydrous copper sulfate were added, and the mixture was stirred at room temperature for 2 hours to ensure sufficient coordination. Then, 1.5 parts of glutaraldehyde crosslinking agent were added, and the reaction was carried out at 60°C for 4 hours to complete the imprint layer fixation. The product was separated by an external magnet, and the template Cu was removed by shaking and washing with 0.5 mol / L ethylenediaminetetraacetic acid solution for 4 hours. 2+ The material was washed with deionized water until neutral, and then vacuum dried at 60°C for 12 hours to finally obtain surface ion-imprinted magnetic nanomaterials.

[0034] S2: Take 1000 portions of dewatered sludge and place them in an ultrasonic-electrochemical reactor. Add 5000 mL of 0.3 mol / L sulfuric acid solution and turn on the ultrasonic generator for 25 minutes. Then switch to pulsed electrochemical mode, using a graphite plate as the anode and a stainless steel plate as the cathode, and apply a pulsed electric field to continue treatment for 6 hours. After the reaction, transfer the mixture to a centrifuge and centrifuge at 4000 rpm for 10 minutes. Vacuum filter the supernatant through a 0.45 μm mixed cellulose ester microfiltration membrane to obtain a clear leaching solution. Add 1 mol / L sodium hydroxide to the leaching solution to adjust the pH to 5.0. Then take 1.5 portions of surface ion-imprinted magnetic nanomaterials and add them to the pH-adjusted leaching solution. Place the solution in a constant temperature shaking incubator and perform specific shaking adsorption at 25℃ and 150 rpm for 60 minutes. Use an external permanent magnet to perform magnetic separation near the bottom of the reaction vessel. Solid-liquid separation is completed within 3 minutes to obtain a magnetic material loaded with copper ions.

[0035] S3: The copper-loaded magnetic material was transferred to a pulsed electrochemical desorption cell, placed in a titanium mesh basket as the cathode, and a platinum sheet as the anode, with an electrode spacing of 5 cm. 80 mL of 0.4 mol / L nitric acid solution was added as the desorption solution. A pulsed electric field was applied for 60 minutes. After desorption, the regenerated material was separated by an external magnet, yielding the regenerated magnetic material and the copper-containing desorption solution. 0.6 parts of 30% hydrogen peroxide solution were added to the desorption solution, and the mixture was stirred at room temperature for 15 minutes to allow Fe... 2+ Oxidized to Fe 3+ Then, 1 mol / L sodium hydroxide solution was added dropwise to adjust the pH to 3.2, and the mixture was allowed to stand for 30 minutes to allow Fe to precipitate. 3+ Hydrolysis produces ferric hydroxide precipitate, while Cu 2+ Keep the solution in a dissolved state. Transfer the solution to a 70°C water bath and stir continuously for 40 minutes to allow the ferric hydroxide flocs to grow and coarsen. Filter through a 0.45μm membrane to remove the precipitate, obtaining the iron-removed solution. Adjust the pH of the solution to 2.8 for later use.

[0036] S4: The iron-removed solution is placed in an electrolytic cell with a stainless steel plate as the cathode and titanium-based ruthenium dioxide as the anode, with an electrode distance of 8 cm. An Ag / AgCl electrode is used as the reference electrode, and the cathode potential is controlled at -0.45 (vs. Ag / AgCl). Copper is recovered by electrodeposition for 4 hours under stirring at room temperature. Purple-red metallic copper is deposited on the cathode surface. It is collected periodically by scraping, washing with deionized water, dehydrating with anhydrous ethanol, and vacuum drying at 60°C. The copper product is obtained.

[0037] Example 2 The preparation method is the same as in Example 1, except that: S1: 3 parts tetraethyl orthosilicate and 1 part ammonia; 1 part 3-aminopropyltriethoxysilane; 0.5 parts α-bromoisobutyryl bromide and 0.8 parts triethylamine; 10 parts hydroxyethyl methacrylate monomer, 0.2 parts cuprous bromide catalyst, 0.3 parts pentamethyldiethylenetriamine ligand; 1.5 parts chitosan and 0.5 parts anhydrous copper sulfate; 1.0 part glutaraldehyde crosslinking agent; All other steps are the same.

[0038] Example 3 The preparation method is the same as in Example 1, except that: S1: 8 parts tetraethyl orthosilicate and 3 parts ammonia; 3 parts 3-aminopropyltriethoxysilane; 1.2 parts α-bromoisobutyryl bromide and 1.5 parts triethylamine; 20 parts hydroxyethyl methacrylate monomer, 0.4 parts cuprous bromide catalyst, 0.8 parts pentamethyldiethylenetriamine ligand; 2.5 parts chitosan and 1.5 parts anhydrous copper sulfate; 2.0 parts glutaraldehyde crosslinking agent; All other steps are the same.

[0039] Example 4 The preparation method is the same as in Example 1, except that: S2: 0.1 mol / L sulfuric acid solution; centrifuge at 3000 rpm for 5 minutes; adsorb at 20℃ and 120 rpm for 45 minutes; S3: 0.2 mol / L nitric acid solution was used as the desorption solution, and a pulsed electric field was applied for treatment for 30 minutes; S4: Control the cathode potential to -0.50 (vs. Ag / AgCl), and recover copper by electrodeposition for 3 hours with stirring at room temperature; All other steps are the same.

[0040] Example 5 The preparation method is the same as in Example 1, except that: S2: 0.5 mol / L sulfuric acid solution; centrifuge at 5000 rpm for 15 minutes; adsorption by shaking at 30℃ and 180 rpm for 75 minutes; S3: 0.6 mol / L nitric acid solution was used as the desorption solution, and a pulsed electric field was applied for treatment for 90 minutes; S4: Control the cathode potential to -0.35 (vs. Ag / AgCl), and recover copper by electrodeposition for 5 hours with stirring at room temperature; All other steps are the same.

[0041] Example 6 The preparation method is the same as in Example 1, except that: S1: Replacing Fe3O4 nanoparticles with γ-Fe2O3 nanoparticles can both provide magnetic responsiveness and achieve rapid magnetic separation. All other steps are the same.

[0042] Example 7 The preparation method is the same as in Example 1, except that: S1: Replacing chitosan with polyethyleneimine (PEI) can provide coordination sites for Cu. 2+ Forming reversible complexes and constructing imprinted cavities; All other steps are the same.

[0043] Example 8 The preparation method is the same as in Example 1, except that: S1: Replace the ethylenediaminetetraacetic acid solution with citric acid; All other steps are the same.

[0044] Comparative Example 1 A traditional chemical precipitation method was used to treat heavy metals in municipal sewage sludge. The preparation method was as follows: 1000 parts of dewatered sludge were taken and added to 5000 mL of 0.3 mol / L sulfuric acid solution. The mixture was mechanically stirred for 6 hours, centrifuged, and filtered to obtain a leachate. A 1 mol / L sodium hydroxide solution was added dropwise to the leachate to adjust the pH to 9.0, so that Cu... 2+ Zn 2+ Fe 3+ Metal ions are co-precipitated as hydroxides, and centrifugation is used to obtain mixed metal hydroxide precipitates. The precipitates are washed and dried to obtain mixed metal hydroxide solids.

[0045] Comparative Example 2 The preparation method is the same as in Example 1, except that: S1: The step of grafting the PHEMA hydrophilic brush layer is omitted, and the chitosan imprinted layer is directly coated on the surface of the Fe3O4@SiO2 core-shell material; All other steps are the same.

[0046] Comparative Example 3 The preparation method is the same as in Example 1, except that: S1: The surface imprinting method is omitted and replaced by directly mixing Fe3O4@SiO2, chitosan, CuSO4, and glutaraldehyde for bulk polymerization to obtain a magnetic material with imprinted sites randomly distributed inside the material. All other steps are the same.

[0047] Comparative Example 4 The preparation method is the same as in Example 1, except that: S2: The step of applying a pulsed electric field is omitted, and only ultrasonic and acid dissolution treatment is used; All other steps are the same.

[0048] Comparative Example 5 The preparation method is the same as in Example 1, except that: S3: The step of adjusting pH to remove iron is omitted, and the desorption solution directly enters the electrodeposition process; All other steps are the same.

[0049] Experimental Example 1 The copper and zinc products prepared in Examples 1-8 and Comparative Examples 1-5 were measured: (1) Purity of copper products: Referring to GB / T 5121.28-2021 "Chemical Analysis Methods for Copper and Copper Alloys—Part 28: Determination of Chromium, Iron, Manganese, Cobalt, Nickel, Zinc, Arsenic, Selenium, Silver, Cadmium, Tin, Antimony, Tellurium, Lead and Bismuth Content—Inductively Coupled Plasma Mass Spectrometry", an appropriate amount of copper product sample was weighed, digested by acid dissolution, and after being brought to a fixed volume, the mass concentration of copper in the solution was determined by inductively coupled plasma mass spectrometry (ICP-MS). The mass fraction of copper in the copper product was calculated by mass balance. Impurity elements were determined simultaneously, and the copper purity was calculated by difference method or direct method. Each group of valid samples should have no less than 5 samples, and the final result is the average.

[0050] (2) Zinc content in copper products: Referring to GB / T 5121.28-2021 "Chemical Analysis Methods for Copper and Copper Alloys—Part 28: Determination of the Content of Chromium, Iron, Manganese, Cobalt, Nickel, Zinc, Arsenic, Selenium, Silver, Cadmium, Tin, Antimony, Tellurium, Lead and Bismuth—Inductively Coupled Plasma Mass Spectrometry", the mass concentration of zinc was determined using ICP-MS in the same digestion solution used to determine the purity of the copper products. The mass fraction of zinc in the copper products was calculated based on the sample mass and the fixed volume. Characteristic spectral lines of zinc were selected for quantitative analysis, and the content was calculated using the standard curve method. At least 5 parallel samples were tested in each group, and the average value of the results was taken.

[0051] (3) Copper recovery rate: Referring to GB / T 3884.21-2018 "Chemical Analysis Methods for Copper Concentrates—Part 21: Determination of Copper, Sulfur, Lead, Zinc, Iron, Aluminum, Calcium, Magnesium and Manganese—Wavelength Dispersive X-ray Fluorescence Spectrometry", the copper recovery rate is the overall recovery efficiency, calculated using the following formula: Copper recovery rate (%) = (Copper product mass × Copper product purity) / (Leachate volume × Copper ion concentration in leaching solution) × 100%. The copper ion concentration in the leaching solution was determined using ICP-OES. To obtain reliable data, at least three parallel samples were tested for each group, and the average value was taken.

[0052] Table 2 Comparison of experimental results of Examples 1-8 and Comparative Examples 1-5

[0053] The experimental results of Examples 1-8 and Comparative Examples 1-5 are shown in Table 2. The copper product obtained by the present invention has a purity of 95.83%, a zinc content of only 0.97%, and a copper recovery rate of 91.52%. All indicators are at a high level and have small fluctuations. While ensuring high purity recovery, good recovery efficiency is achieved. The material ratio and process parameters have reached the optimal balance. Therefore, this is the best implementation method of the present invention.

[0054] Example 2: Insufficient material usage resulted in inadequate functional layer thickness and cross-linking density, causing copper purity to drop to 93.26%, zinc content to rise to 1.82%, and copper recovery rate to drop to 86.43%, demonstrating that an excessively low material ratio weakens the material's anti-fouling ability and selective recognition performance. Example 3: Excessively high material usage resulted in denser functional layers, increasing copper purity to 96.24% and recovery rate to 93.54%, demonstrating that appropriately increasing the material ratio is beneficial for optimizing material performance, but the cost increases accordingly with limited improvement. Example 4: The use of low-intensity process parameters led to reduced leaching and adsorption efficiencies, with copper recovery rate significantly decreasing to 78.27%, demonstrating that excessively low process intensity severely affects overall recovery efficiency, and that coordinated matching of each unit operation is necessary. Example 5: The use of high-intensity process parameters improved the efficiency of leaching, adsorption, desorption, and electrodeposition. All units achieved optimal performance, with copper purity reaching 96.56% and recovery rate reaching 94.83%, demonstrating that improving process intensity is beneficial to the overall improvement of various indicators. In Example 6, after replacing Fe3O4 with γ-Fe2O3, the magnetic response performance of both was similar, and the various indicators were slightly lower than those in Example 1, proving that γ-Fe2O3 can be used as an effective alternative magnetic core material to Fe3O4. In Example 7, after replacing chitosan with PEI, the greater flexibility of the PEI molecular chain led to a decrease in the accuracy of imprinted hole recognition, and the zinc content in copper increased to 1.63%, proving that chitosan is superior to PEI in constructing highly selective imprinted layers. In Example 8, after replacing EDTA with citric acid, the weaker complexing ability of citric acid led to incomplete template elution, and the copper purity dropped to 93.56%, proving that the template elution efficiency of EDTA is superior to that of citric acid.

[0055] Comparative Examples 1-5, lacking key technologies, showed varying degrees of reduced overall performance compared to the examples. Comparative Example 1 employed a traditional chemical precipitation method without using surface ion-imprinted magnetic materials, failing to achieve selective separation. All metal ions in the leachate co-precipitated, resulting in a copper product purity of only 38.66% and a zinc content as high as 22.47%. The product was a mixed metal hydroxide with no single zinc product. Although the copper recovery rate reached 85.57%, the product had no economic value, demonstrating that traditional methods cannot achieve targeted recovery of heavy metals. Comparative Example 2 omitted the PHEMA hydrophilic brush layer, resulting in a material surface lacking anti-fouling capabilities. Large amounts of extracellular polymers, proteins, and other organic matter in the sludge leachate were non-specifically adsorbed onto the material surface, physically shielding the imprinted sites and significantly reducing selectivity. Copper purity decreased to 78.65%, while zinc content increased to 9.87%, demonstrating that the PHEMA hydrophilic brush layer plays a crucial role in inhibiting organic pollution and protecting the activity of the imprinted sites. Comparative Example 3 used bulk imprinting instead of surface imprinting. The imprinted sites were randomly distributed inside the material rather than exposed on the surface. Most sites were buried too deeply, resulting in high mass transfer resistance, poor accessibility, incomplete template ion elution, and a small number of effectively identified holes. Copper purity decreased to 68.47%, zinc content increased to 14.56%, and copper recovery was only 58.37%, demonstrating the necessity of surface imprinting technology for ensuring complete exposure of imprinted sites and reducing mass transfer resistance. Comparative Example 4 omitted the pulsed electric field dissolution step, using only ultrasonic and acid dissolution treatments. Lacking the concentration polarization reduction effect and ion directional migration driving effect of the pulsed electric field, the heavy metal dissolution efficiency was significantly reduced, the total amount of copper entering the liquid phase decreased, the copper recovery rate dropped to 72.58%, and the copper purity also decreased to 89.67%, demonstrating the important role of the pulsed electric field in enhancing heavy metal dissolution and improving recovery efficiency. Comparative Example 5 omitted the iron removal purification step, resulting in high concentrations of Fe in the desorbate. 3+ Remove directly from the electrodeposition process, due to Fe 3+ original potential and Cu 2+ Similar to Cu during electrodeposition. 2+ Severe co-deposition resulted in a significant increase in iron content in the copper product and a substantial decrease in copper purity to 55.28%, demonstrating the effectiveness of selective iron removal in eliminating Fe. 3+ Ensuring the high purity of copper products is of paramount importance.

[0056] In summary, this invention constructs a surface ion-imprinted magnetic nanomaterial with a Fe3O4@SiO2@PHEMA three-layer core-shell structure, and combines it with pulsed electric field-enhanced dissolution, low-voltage pulsed electric field-based gentle desorption, selective iron removal and purification, and constant potential electrodeposition coupling process to achieve highly selective targeted capture and high-purity recovery of copper ions in municipal sludge leachate, which has good prospects for industrial application.

Claims

1. A method for targeted recovery of heavy metals from municipal sewage sludge, characterized in that, Includes the following steps: S1: Take dehydrated sludge and add it to sulfuric acid solution for ultrasonic treatment. Then apply a pulsed electric field to continue the treatment for 6 hours. After the treatment is completed, centrifuge the mixture and filter the supernatant under vacuum to obtain a clear dissolution solution. 1 mol / L sodium hydroxide was added dropwise to the dissolution solution to adjust the pH to 5.

0. Then, the surface ion-imprinted magnetic nanomaterial was added to the pH-adjusted dissolution solution for specific oscillation adsorption. The external permanent magnet was used for magnetic separation. Solid-liquid separation was completed within 3 minutes to obtain a magnetic material loaded with copper ions. S2: The magnetic material loaded with copper ions is transferred to a nitric acid solution, and a pulsed electric field is applied for desorption treatment. After desorption, the regenerated material is separated by an external magnet to obtain the regenerated magnetic material and the copper-containing desorption solution. 30% hydrogen peroxide solution is added to the desorption solution and stirred at room temperature for 15 minutes. Then, sodium hydroxide solution is added dropwise to adjust the pH. The solution is allowed to stand for 30 minutes and then transferred to a 70°C water bath. It is continuously stirred and aged for 40 minutes. Then, the precipitate is removed by filtration to obtain the iron-removed solution. The pH of the solution is adjusted to 2.8 for later use. S3: The iron-removed solution is subjected to electrodeposition treatment. Copper is recovered by electrodeposition under stirring at room temperature after controlling the cathode potential. The precipitated purplish-red metallic copper is periodically scraped and collected, washed with deionized water, dehydrated with anhydrous ethanol, and vacuum dried to obtain the copper product.

2. The method for targeted recovery of heavy metals from municipal sewage sludge as described in claim 1, characterized in that, The preparation method of the surface ion-imprinted magnetic nanomaterial is as follows: Magnetic nanoparticles are dispersed in anhydrous ethanol and ultrasonically dispersed for 30 minutes. Then, tetraethyl orthosilicate and ammonia are added, and the reaction is carried out with mechanical stirring in a water bath. After magnetic separation by an external permanent magnet, washing three times with anhydrous ethanol, and vacuum drying, Fe3O4@SiO2 core-shell material is obtained. The core-shell material is dispersed in anhydrous toluene, and 3-aminopropyltriethoxysilane is added dropwise. The mixture is heated to 80°C and refluxed for 12 hours under nitrogen protection. After magnetic separation, washing three times with anhydrous toluene and three times with anhydrous ethanol, and vacuum drying at 60°C for 6 hours, an amino-modified magnetic carrier is obtained. The amino-modified magnetic carrier is dispersed in anhydrous xylene, and α-bromoisobutyryl bromide and triethylamine are added. After reacting in an ice bath for 4 hours, the temperature is raised to 60°C and reacted for 12 hours. After magnetic separation, washing, and drying, the surface ion-imprinted magnetic carrier is obtained. A magnetic carrier modified with a surface initiator was prepared. The carrier was then dispersed in a mixed solvent of methanol and water, and hydroxyethyl methacrylate monomer, cuprous bromide catalyst, and pentamethyldiethylenetriamine ligand were added. After three cycles of liquid nitrogen freezing-vacuuming-thawing to remove oxygen, surface-initiated atom transfer radical polymerization was carried out in a 60°C oil bath with magnetic stirring for 8 hours. After the reaction, the product was separated by an external magnet, washed three times with methanol, and vacuum dried to obtain a magnetic material modified with a hydroxyethyl methacrylate brush layer. The brush-modified magnetic material was dispersed in a mixed solution of acetic acid and water, and a functional monomer for the metal ion imprinted polymer layer and anhydrous copper sulfate were added. The mixture was stirred at room temperature for 2 hours to ensure sufficient coordination. Glutaraldehyde crosslinking agent was then added, and the reaction was carried out at 60°C for 4 hours to complete the imprint layer fixation. The product was separated by an external magnet, and the template Cu was removed by shaking and washing with a template eluent. 2+ The material was washed with deionized water until neutral, then vacuum dried to obtain surface ion-imprinted magnetic nanomaterials.

3. The method for targeted recovery of heavy metals from municipal sewage sludge as described in claim 1, characterized in that, The sulfuric acid solution described in S1 has a concentration of 0.1~0.5 mol / L.

4. The method for targeted recovery of heavy metals from municipal sewage sludge as described in claim 1, characterized in that, The centrifugation described in S1 is performed under the following conditions: rotation speed 3000~5000 rpm, time 5~15 minutes.

5. The method for targeted recovery of heavy metals from municipal sewage sludge as described in claim 1, characterized in that, The oscillating adsorption described in S1 is performed under the following conditions: temperature 20-30℃, rotation speed 120-180rpm, and time 45-75 minutes.

6. The method for targeted recovery of heavy metals from municipal sewage sludge as described in claim 1, characterized in that, The nitric acid solution described in S2 has a concentration of 0.2~0.6 mol / L.

7. The method for targeted recovery of heavy metals from municipal sewage sludge as described in claim 1, characterized in that, The pulsed electric field applied in S2 has a processing time of 30 to 90 minutes.

8. The method for targeted recovery of heavy metals from municipal sewage sludge as described in claim 1, characterized in that, S3 describes the control of the cathode potential followed by electrodeposition and recovery of copper at room temperature with stirring. The potential is controlled within the range of -0.50 to -0.35 (vs. Ag / AgCl), and the electrodeposition time is controlled within 3 to 5 hours.

9. The method for targeted recovery of heavy metals from municipal sewage sludge as described in claim 2, characterized in that, The surface ion-imprinted magnetic nanomaterial, based on 10 parts by weight of the magnetic nanoparticles, comprises the following raw materials: 3-8 parts tetraethyl orthosilicate, 1-3 parts ammonia, 1-3 parts 3-aminopropyltriethoxysilane, 0.5-1.2 parts α-bromoisobutyryl bromide, 0.8-1.5 parts triethylamine, 10-20 parts hydroxyethyl methacrylate, 0.2-0.4 parts cuprous bromide, 0.3-0.8 parts pentamethyldiethylenetriamine ligand, 1.5-2.5 parts functional monomers of the metal ion-imprinted polymer layer, 0.5-1.5 parts anhydrous copper sulfate, and 1.0-2.0 parts glutaraldehyde.

10. The method for targeted recovery of heavy metals from municipal sewage sludge as described in claim 2, characterized in that, The magnetic nanoparticles are Fe3O4 or γ-Fe2O3; the functional monomers of the metal ion imprinted polymer layer are chitosan or polyethyleneimine; the metal ion imprinted polymer layer uses the target heavy metal ion as a template, and the template eluent is ethylenediaminetetraacetic acid or citric acid.

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