Chitosan bipyridine group acid-resistant adsorbent as well as preparation method and application thereof

Abstract

The invention discloses a chitosan bipyridine group acid-resistant adsorbent as well as a preparation method and application thereof, and belongs to the technical field of electroplating sludge treatment. According to the invention, chitosan is selected as a matrix, and grafting of amido and pyridyl is carried out on the basis of the matrix, so that the adsorbent containing amido and pyridyl is prepared, and the problems that hydroxyl and amido on a chitosan body are protonated in an acid solution, so that the ability of chelating metal cations is poor, and the adsorption effect is poor are solved. The heavy metal in the acid solution cannot be effectively separated. In addition, amido and a reagent 2-chloromethylpyridine hydrochloric acid (2-CPD) with lower price are used for substitution reaction, and compared with existing M4195 commercial resin, the production cost is reduced, and the preparation method is suitable for large-scale popularization and application.

Description

Technical Field

[0001] The present invention belongs to the technical field of electroplating sludge treatment, and more specifically relates to a chitosan bipyridine group acid-resistant adsorbent, its preparation method and application. Background Art

[0002] With the rapid development of the economy and industrialization, the electroplating industry has also developed rapidly. Electroplating sludge (ES) is a metal-containing waste generated in the electroplating and surface treatment industries. Since the sludge contains various complex and highly toxic components, it is listed as a hazardous waste worldwide. As a hazardous waste, ES is landfilled or solidified to stabilize toxic and harmful substances. In the past, improper disposal of hazardous solid waste has led to serious problems. For example, potential toxic metals are released and infiltrate into the soil and groundwater, affecting the health of animals, plants, especially humans, through the chemical cycle and food. In addition, due to the higher content of certain precious metals in ES than in natural minerals and concentrates, resources are wasted. In order to achieve the goals of environmental protection and metal resource recovery, it is urgent to explore effective ways for sludge resource recovery and detoxification.

[0003] Compared with other methods for recovering metals from ES, hydrometallurgical processes are considered promising because they show effectiveness in extracting metals. Metal dissolution is the first step in hydrometallurgy, involving chemical leaching and bioleaching. Commonly used chemical leaching includes acid leaching and alkali leaching. Yi et al. used sulfuric acid leaching to treat copper-containing electroplating sludge. Under the conditions of sulfuric acid concentration of 1M and liquid-solid ratio of 15:1, the copper leaching rate can reach 90%. In addition, copper in electroplating sludge is recovered by ammonia leaching and hydrogen reduction under high pressure. At an ammonia concentration of 6.5M, the leaching efficiency of copper can reach over 77.42%. Both acid leaching and alkali leaching can extract metals from electroplating sludge well, but they also have disadvantages such as lack of selective leaching, secondary pollution and equipment corrosion. Bioleaching can overcome the above disadvantages, but has disadvantages such as slow dynamic speed and difficult subsequent recovery. Therefore, it is urgent to develop an efficient and environmentally friendly method for recovering valuable metals from electroplating sludge.

[0004] Therefore, the selective recovery of metals after hydrometallurgy has always been a research hotspot. In this regard, adsorption is considered the most promising method because of the great flexibility in designing functional groups, which helps to create a variety of adsorbents with different selective absorption properties. However, so far, the research on the recovery of heavy metal ions (HMCs) by adsorption has mainly focused on neutral or weakly acidic wastewater, and there has been little research on strongly acidic wastewater. This is mainly because the functional groups of most adsorbents are inhibited by high-concentration protons in a strongly acidic environment and cannot capture HMCs. Therefore, if acid-resistant adsorbents for one or several HMCs in strongly acidic leachates can be developed, not only can the recovery of HMCs be made simpler and more environmentally friendly, but the purified low-toxic acidic wastewater can also be further utilized, such as neutralizing other alkaline wastewater. Summary of the Invention

[0005] The object of the present invention is to provide a chitosan bipyridine group acid-resistant adsorbent, its preparation method and application, so as to solve the problems existing in the above-mentioned prior art and realize the preparation of an adsorbent that can efficiently and highly selectively adsorb heavy metals (copper and nickel) in strongly acidic wastewater.

[0006] To achieve the above object, the present invention provides the following solutions:

[0007] One of the technical solutions of the present invention: provides a preparation method of a chitosan bipyridine group acid-resistant adsorbent, including the following steps:

[0008] Using spherical chitosan as the raw material, after amino protection, it reacts with epichlorohydrin in the first reaction to obtain the first product;

[0009] Mix the first product, ethylenediamine and a solvent and then carry out the second reaction to obtain the second product;

[0010] Mix the second product, 2-chloromethylpyridine hydrochloride, a deacidifying agent and a solvent and then carry out the third reaction to obtain the chitosan bipyridine group acid-resistant adsorbent.

[0011] Preferably, the preparation of the spherical chitosan includes: adding a chitosan solution to a sodium hydroxide solution to form spherical chitosan; the solvent in the chitosan solution is a mixed solution of acetic acid and water, and the mass fraction of chitosan in the chitosan solution is 2-5 wt%; the mass fraction of sodium hydroxide in the sodium hydroxide solution is 2 wt%.

[0012] Furthermore, the present invention does not specifically limit the way of adding the chitosan solution to the sodium hydroxide solution, and ensuring uniform addition is sufficient to ensure the formation of uniform spherical chitosan.

[0013] Preferably, the amino protection includes: mixing the spherical chitosan and benzaldehyde and then standing still to obtain the spherical chitosan with protected amino groups; the dosage ratio of benzaldehyde to chitosan in the chitosan solution is 50-100 mL: 3-10 g; the standing time is 12-24 h.

[0014] Preferably, the dosage ratio of epichlorohydrin to chitosan in the chitosan solution is 6-10 mL: 3-10 g; the reaction conditions for the first reaction are: pH value is 9-14, temperature is 50-65 °C, and time is 6-10 h.

[0015] Preferably, in the second reaction and the third reaction, the solvent is ethanol and water with a volume ratio of 1:1.

[0016] Preferably, the volume ratio of the first product, ethylenediamine, and the solvent is 3-10: 8-12: 150-200; the temperature of the second reaction is 50-70 °C, and the time is 6-10 h.

[0017] Furthermore, the second product needs to be stored in water for standby.

[0018] Preferably, the acid-binding agent includes one or more of sodium carbonate, potassium carbonate, and sodium hydroxide; the dosage ratio of the second product, 2-chloromethylpyridine hydrochloride, the acid-binding agent, and the solvent is 3-10 mL: 1-5 g: 1-3 g: 150-200 mL; the temperature of the third reaction is 80-100 °C, and the time is 12-36 h.

[0019] Preferably, the step of mixing the second product, 2-chloromethylpyridine hydrochloride, sodium carbonate, and the solvent includes: first adding 2-chloromethylpyridine hydrochloride and sodium carbonate to water, then adding ethanol thereto, and finally adding the second product.

[0020] Technical solution two of the present invention: providing a chitosan double-pyridine group acid-resistant adsorbent prepared by the above preparation method.

[0021] Technical solution three of the present invention: providing the application of the above chitosan double-pyridine group acid-resistant adsorbent in treating electroplating sludge.

[0022] Furthermore, providing the application of the above chitosan double-pyridine group acid-resistant adsorbent in the strongly acidic leaching solution of electroplating sludge.

[0023] Furthermore, the pH value of the strongly acidic leaching solution is 1-5.

[0024] Technical solution four of the present invention: providing a method for synergistically and selectively recovering copper and nickel in electroplating sludge by leaching-adsorption, including the following steps:

[0025] First, mix electroplating sludge and nitric acid for leaching reaction, then take the supernatant, and use the above-mentioned chitosan bipyridine group acid-resistant adsorbent to achieve the leaching of copper and nickel in the supernatant;

[0026] The dosage ratio of the electroplating sludge to the nitric acid is 1 - 10 g: 10 - 100 mL;

[0027] The pH value of the supernatant is 1 - 5;

[0028] The dosage ratio of the chitosan bipyridine group acid-resistant adsorbent to the supernatant is 0.029 g: 30 mL.

[0029] The technical principle of the present invention is as follows:

[0030] Chitosan has the advantages of low price, non-toxicity, good biocompatibility, etc., so it is widely used as an adsorbent. Chitosan-based adsorbents have good hydrophilicity, flexible structure, rich functional groups, good reaction activity and chelating ability. In the present invention, chitosan is selected as the matrix, and amino groups and pyridyl groups are grafted on it to prepare an adsorbent containing amino groups and pyridyl groups, which solves the problem that the hydroxyl groups and amino groups on the chitosan body are protonated in acidic solutions and have poor ability to chelate metal cations, and cannot effectively separate heavy metals in acidic solutions. Moreover, in the present invention, the amino group is used for substitution reaction with the cheaper reagent 2-chloromethylpyridine hydrochloride (2-CPD). Compared with the existing M4195 commercial resin, the production cost is reduced, which is suitable for large-scale popularization and application.

[0031] The present invention discloses the following technical effects:

[0032] The present invention utilizes leaching-adsorption to synergistically recover nickel and copper from electroplating sludge. First, nitric acid is used to leach the metals in the electroplating sludge. Since the leaching solution is strongly acidic and there is an obvious protonation phenomenon in a strongly acidic medium (pH < 2.5), it is somewhat challenging to effectively separate heavy metal cations (HMCs) using conventional adsorption methods. On this basis, the present invention provides an acid-resistant chitosan bipyridine group adsorbent (APCS-CPD), which can adsorb copper and nickel in a strong acid solution. The results show that this adsorbent has excellent adsorption effects. APCS-CPD has good adsorption performance for Cu(II) and Ni(II) under acidic conditions (PH = 1.5), and the maximum adsorption capacities are 69.303 mg / g and 59.217 mg / g respectively. This adsorbent has high adsorption selectivity and good resistance to coexisting inorganic salts under acidic conditions. At the same time, the adsorption processes of other coexisting metal ions (Zn(Ⅱ), Fe(Ⅱ), Cr(Ⅲ)) on its adsorption of Cu(Ⅱ) and Ni(Ⅱ) can be ignored. In addition, repeated experiments show that APCS-CPD has good recovery performance, and dynamic column experiments further prove that APCS-CPD has great potential for recovering Cu(Ⅱ) and Ni(Ⅱ) in industrial acidic solutions, and can directly achieve the recovery and secondary utilization of metals. Description of the Drawings

[0033] Figure 1 is the XPS diagram of the electroplating sludge, where (a) is the XPS energy spectrum diagram of Ni2p, and (b) is the XPS energy spectrum diagram of Cu2p;

[0034] Figure 2 is the physical diagram of APCS-CPD, APCS-ED after freeze-drying and APCS-CPD after freeze-drying. Among them, (a) and (b) are the physical diagrams of APCS-CPD, (c) is the physical diagram of APCS-ED after freeze-drying, and (d) is the physical diagram of APCS-CPD after freeze-drying;

[0035] Figure 3 is the characterization result diagram of APCS, APCS-ED and APCS-CPD. Among them, (a) and (b) are the SEM diagrams of APCS-CPD at different magnification multiples, (c) is the XPS full spectrum diagram of APCS-CPD, (d) is the high-resolution XPS N1s spectrum diagram of APCS-CPD, (e) is the FTIR spectrum diagrams of APCS, APCS-ED and APCS-CPD, and (f) is the TGA result diagram of APCS, APCS-ED and APCS-CPD;

[0036] Figure 4Adsorption effects of APCS, APCS-ED, and APCS-CPD on Cu(II) and Ni(II) at different acidities, where (a) corresponds to Cu(II) and (b) corresponds to Ni(II);

[0037] Figure 5 Test results of the adsorption selectivity of APCS-CPD for Cu(II) and Ni(II). Among them, (a) are the test results of the adsorption selectivity in binary systems composed of Mn with Cu and Ni respectively, (b) are the test results of the adsorption selectivity in binary systems composed of Zn with Cu and Ni respectively, (c) are the test results of the adsorption selectivity in binary systems composed of Cr with Cu and Ni respectively, and (d) are the test results of the adsorption selectivity in binary systems composed of Fe with Cu and Ni respectively;

[0038] Figure 6 Test results of the adsorption affinity of APCS-CPD for different heavy metal ions;

[0039] Figure 7 Adsorption kinetic process curves of APCS-ED and APCS-CPD for Cu(II) and Ni(II). Among them, (a) is the adsorption kinetic process curve for Cu(II), and (b) is the adsorption kinetic process curve for Ni(II);

[0040] Figure 8 Adsorption isotherm process curves of APCS-ED and APCS-CPD for Cu(II) and Ni(II). Among them, (a) is the adsorption isotherm process curve for Cu(II), and (b) is the adsorption isotherm process curve for Ni(II);

[0041] Figure 9 Results of the influence of different inorganic salts on the adsorption performance of APCS-CPD;

[0042] Figure 10 Test results of the adsorption stability of APCS-CPD;

[0043] Figure 11 Diagram of the structural stability results after the adsorption of APCS-CPD;

[0044] Figure 12 Diagram of the device for the dynamic column test;

[0045] Figure 13 Adsorption performance of APCS-CPD for Cu(II) and Ni(II) during the dynamic column test;

[0046] Figure 14 Diagram of the adsorption effect of APCS-CPD on heavy metal ions when treating electroplating sludge;

[0047] Figure 15 FTIR spectra of APCS-CPD before and after adsorbing heavy metal ions;

[0048] Figure 16 Full spectrum and high-resolution XPS N1s spectra of APCS-CPD before and after adsorbing heavy metal ions, where (a) is the full spectrum and (b) is the high-resolution XPS N1s spectrum;

[0049] Figure 17 Mechanism of APCS-CPD for adsorbing Cu(II) and Ni(II) under strong acidic condition (pH = 1.5). Detailed implementation manners

[0050] Now, various exemplary implementation manners of the present invention will be described in detail. This detailed description should not be considered as a limitation to the present invention, but should be understood as a more detailed description of certain aspects, characteristics and implementation schemes of the present invention.

[0051] It should be understood that the terms described in the present invention are only for describing specific implementation manners and are not used to limit the present invention. In addition, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded from the range.

[0052] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention pertains. Although the present invention only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein can also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the documents. In case of conflict with any incorporated document, the content of this specification shall prevail.

[0053] Without departing from the scope or spirit of the present invention, various improvements and changes can be made to the specific implementation manners of the specification of the present invention, which are obvious to those skilled in the art. Other implementation manners obtained from the specification of the present invention are obvious to those skilled in the art. The specification and embodiments of the present invention are only exemplary.

[0054] Regarding the terms "comprising", "including", "having", "containing", etc. used herein, they are all open-ended terms, that is, they are meant to include but not limited to.

[0055] It should be noted that the parts not described in detail in the present invention are all conventional operation means in the art and are not the focus of the present invention.

[0056] The sources of the chemical drugs and reagents used in the following examples, characterization and performance testing processes of the present invention are as follows:

[0057] The electroplating sludge was provided by an electroplating factory in Jiangxi Province. The electroplating sludge was first dried to a constant weight at 60 °C and ground into fine particles of about 100 mesh with a mortar for standby. After digestion with a mixed acid of HCl / HNO 3 , the contents of the main metals (Ni, Cu, Fe, Zn, Cr, Ca) in the sludge were determined using an inductively coupled plasma optical emission spectrometer (ICP-MS). The composition of the electroplating sludge is shown in Table 1, and the metal forms in the electroplating sludge were further analyzed by XPS. As Figure 1 shown, the iron in the electroplating sludge mainly exists in the form of FeO and Fe 2 O 3 , and the copper mainly exists in the form of Cu(OH) 2 and CuO.

[0058] Table 1 Composition of electroplating sludge

[0059] Element type Ni (mg / g) Cu (mg / g) Fe (mg / g) Zn (mg / g) Content 156.862 44.107 15.775 19.564

[0060] CS (degree of deacetylation: 90%), benzaldehyde (C 7 H 6 O, 99%), epichlorohydrin (C 3 H 5 ClO, 99.7%), acetic acid (C 2 H 4 O 2 , 99.5%) were all purchased from Shanghai Aladdin Industrial Co., Ltd. Ethylenediamine (C 2 H 8 N 2 , 99%) was purchased from Tianjin Damao Chemical Reagent Factory. 2-Chloromethylpyridine hydrochloride (C 6 H 7 Cl 2 N, 98%) was purchased from Shanghai Merck Chemical Technology Co., Ltd. Sulfuric acid (H 2 SO 4 , 98%), hydrochloric acid (HCl, 37%), methanol (MeOH), ethanol (EtOH), sodium carbonate (Na 2 CO 3 ), sodium hydroxide (NaOH, 99%) were purchased from Sinopharm Chemical Reagent Co., Ltd. All chemical reagents were pure analytical reagents or more pure reagents, and all ultrapure water was 18.20 MΩ ultrapure water.

[0061] In the following examples of the present invention and the performance test process, the room temperature involved is calculated as 25±5°C unless otherwise specified.

[0062] Example 1

[0063] Preparation of APCS: Take 3 g of chitosan powder and dissolve it in 80 mL of 3 vol% acetic acid solution. Stir magnetically for 30 min to form a 3.75 wt% chitosan solution. Then, defoam by ultrasonic for 10 min. Aspirate the chitosan solution with a 10 mL syringe and use an electrospinning machine to uniformly drop this solvent into 200 mL of 2 wt% NaOH solution to form uniform spherical chitosan. After the ball formation is completed, let it stand for 1 h, collect the spherical chitosan and wash it 3 times with ultrapure water. Add the prepared spherical chitosan into 80 mL of benzaldehyde solution, let it stand at room temperature for 12 h, and then wash it 3 times with methanol and ultrapure water respectively to remove the excess benzaldehyde solution on the spherical chitosan, obtaining spherical chitosan with benzaldehyde-protected amino groups. Then add the spherical chitosan into 200 mL of ultrapure water, adjust the pH value to 13, add 8 mL of epichlorohydrin, heat it in a water bath at 55°C. After washing the obtained spherical chitosan, soak it in 200 mL of 2.5 vol% hydrochloric acid solution for 12 h and then wash it 3 times with ultrapure water to obtain APCS.

[0064] Preparation of APCS-ED: Add the above-prepared APCS into a solution of 150 mL of ethanol and ultrapure water with a volume ratio of 1:1, then add 10 mL of ethylenediamine, and react under the condition of a water bath at 60°C for 6 h. Wash the product 3 times with ultrapure water to obtain APCS-ED, and store it in ultrapure water for standby.

[0065] Preparation of APCS-CPD: Add 2.5 g of anhydrous sodium carbonate and 3.75 g of 2-chloromethylpyridine hydrochloride (2-CPD) into 75 mL of ultrapure water in sequence, then add 75 mL of ethanol, and ultrasonicate for 10 min. Add the above-prepared APCD-ED into this solution and transfer it to a three-necked flask, heat and reflux at 90°C for 24 h, and wash it thoroughly with ultrapure water to obtain a chitosan bipyridine group acid-resistant adsorbent, denoted as APCS-CPD.

[0066] Characterize and test the performance of APCS, APCS-ED, and APCS-CPD described in Example 1:

[0067] All samples used for characterization and testing (APCS, APCS-ED, and APCS-CPD) were freeze-dried under vacuum at -60 °C before characterization and testing. The microscopic morphology of the samples was characterized by scanning electron microscopy (SEM, Nova Nano SEM450). The surface elemental state of the samples was measured by X-ray photoelectron spectroscopy (XPS, Axis Ultra DLD). The C, H, and N contents of the samples were measured by an organic elemental analyzer (EA, Lementar Unicube). The thermal stability of the materials was determined using a thermogravimetric differential thermal analyzer (TGA, HT1600) under a nitrogen atmosphere (30 - 800 °C) at a heating rate of 10 °C / min. Fourier transform infrared spectroscopy (FTIR) was obtained using VERTEX70. The concentration of metal ions was determined by inductively coupled plasma optical emission spectrometer (ICP-MS, iCAP Q).

[0068] 1. Structure and morphology characterization of APCS, APCS-ED, and APCS-CPD:

[0069] Characterization results: Figure 2 Figures show the physical pictures of freeze-dried APCS-CPD, APCS-ED, and APCS-CPD. Among them, (a) and (b) are the physical pictures of APCS-CPD, (c) is the physical picture of freeze-dried APCS-ED, (d) is the physical picture of freeze-dried APCS-CPD, and (e) is the adsorption performance test result of the small balls of the color shown in (a) and the small balls of the color shown in (b). It can be Figure 2 seen that APCS-ED and APCS-CPD present a uniform slightly red spherical shape with a diameter of 0.8 - 1 mm. At the same time, separating the small balls with relatively different colors in the obtained product APCS-CPD (as shown in (a) and (b) of Figure 2 ) shows that the prepared APCS-CPD contains the vast majority of slightly red small balls and a very small part of yellow small balls. It was found that the color of APCS-CPD is affected by the grafting amount of 2-CPD and the washing process, and its color is mostly between yellow and slightly red, as shown in (a) and (b) of Figure 2 . The small balls with less grafting amount in (a) show yellow, and the small balls with relatively more grafting amount in (b) show red.

[0070] Due to the deviation in the grafting amount during the reaction process, the grafting amount of each small ball in the product will be different and cannot be completely consistent. The difference in the grafting amount will lead to the difference in the adsorption amount of the small balls. Therefore, the grafting amount and the difference in relative color of each small ball in the obtained product are determined by comparing the adsorption performance. The specific test process for the adsorption amount is as follows: Prepare single-component metal ion solutions of Cu(II) and Ni(II) with an initial concentration of 200 mg / L and pH = 1.5, and add 0.3 g of adsorbents with a small grafting amount (APCS-CPD-a, Figure 2 the small balls of the color shown in (a)) and a relatively large grafting amount (APCS-CPD-b, Figure 2 the small balls of the color shown in (b)) respectively, and oscillate at a constant temperature of 25 °C for 24 h. Then, measure the adsorption performance of the two, and the results are as Figure 2 shown in (e).

[0071] In addition, the content of APCS-CPD-a in the synthesized product is extremely small and will not affect the overall adsorption effect of APCS-CPD.

[0072] The structure and morphology characterization results of APCS, APCS-ED, and APCS-CPD are as Figure 3 shown. Figure 3 Figures for the characterization results of APCS, APCS-ED, and APCS-CPD. Among them, (a) and (b) are SEM images of APCS-CPD at different magnifications, (c) is the XPS full spectrum of APCS-CPD, (d) is the high-resolution XPS N1s spectrum of APCS-CPD, (e) is the FTIR spectrum of APCS, APCS-ED, and APCS-CPD, and (f) is the TGA result graph of APCS, APCS-ED, and APCS-CPD.

[0073] The SEM images of APCS-CPD are as Figure 3 shown in (a) and (b). From Figure 3 the (a) and (b), it can be seen that the surface of APCS-CPD has a porous structure, and its interior is a network structure. These structures increase the specific surface area of the material and are more conducive to the mass transfer between the adsorbent material and metal ions. The results of EA (Table 2) show that the nitrogen content of APCS-CPD increases from 6.39% to 9.17% compared with APCS-ED. The change in nitrogen content indicates the successful introduction of pyridine groups, and the XPS results (as Figure 3 shown in (c) and (d)) also confirm this inference. The peaks at 398.67 eV, 399.14 eV, and 401.24 eV should correspond to pyridine nitrogen, amino group, and protonated amino group respectively, indicating the successful preparation of the APCS-CPD adsorbent material. The FTIR results are as Figure 3 shown in (e), 3425 cm-1 The broadband appearing at this position is the stretching vibration of -OH / -NH. In APCS-ED, at 1380 cm -1 it comes from the primary amine of chitosan, and at 1078 cm -1 it is C-O-C in the chitosan backbone, and at 1026 cm -1 it is the stretching vibration of -CO. And as shown in the elemental analysis data of EA (Table 2) and the functional group density, the nitrogen content in APCS-ED is higher than that in APCS. These results indicate that the introduction of ethylenediamine and the increase of amino groups can be achieved through chemical modification. In APCS-CPD, at 1590 cm -1 it comes from the vibration of the aromatic ring skeleton, and at 765 cm -1 the characteristic absorption peak at this position is attributed to the out-of-plane bending vibration of C-H from the aromatic ring, indicating the successful introduction of the pyridine group. Analyzing the TGA curves of APCS, APCS-ED, and APCS-CPD (as shown in (f) of Figure 3 ), it is found that the mass reduction of the three materials is roughly divided into three stages. The first stage occurs at 30°C - 180°C, and the reason for the mass loss may be the evaporation of physically adsorbed water. The second stage occurs at 180°C - 550°C, and the reason is the loss of the chitosan backbone due to heating. In the third stage, the three materials go through the molecular carbonization stage and then enter the final stage. By comparison, it is found that the mass loss trends of the three materials are similar, but the overall weight loss of the material APCS-CPD after introducing the pyridine group is the least among the three, so APCS-CPD has better thermal stability.

[0074] Table 2 EA results of APCS, APCS-ED, and APCS-CPD

[0075] Adsorbent type C(％) H(％) N(％) APCS 29.48 6.12 4.11 APCS-ED 31.67 7.06 6.39 APCS-CPD 46.03 6.06 9.17

[0076] 2. Performance tests of APCS, APCS-ED, and APCS-CPD:

[0077] During the performance test, except for the specified acidity, the pH value of the metal ion solution used was adjusted to 1.5 with hydrochloric acid or nitric acid. 30 mL of the metal ion solution and 0.3 g of the wet (dry weight of 0.029 g) adsorbent samples (APCS, APCS-ED, and APCS-CPD) were placed in a 50 mL conical flask, and then placed in a constant temperature oscillator and shaken at room temperature and 180 r / min for 24 h to reach the adsorption equilibrium. The equilibrium adsorption capacity Qe (mg / g) of the adsorbent sample for the metal ion was calculated by Equation (1):

[0078]

[0079] In the formula, C 0(mg / L) is the initial Cu(II) and Ni(II) concentrations of the metal ion solution; C e (mg / L) is the equilibrium Cu(II) and Ni(II) concentrations of the solution after adsorption; V (L) is the volume of the Cu(II) and Ni(II) solutions; m (g) is the mass of the adsorbent sample; Q e (mg / g) is the equilibrium adsorption capacity.

[0080] 2.1. Effect of solution acidity on the adsorption performance of APCS, APCS-ED, and APCS-CPD:

[0081] Prepare a metal ion solution with a concentration of 200 mg / L and an initial pH value ranging from 1.0 to 5.0 containing Cu(II) and Ni(II), and conduct a 24-hour adsorption experiment to reach adsorption equilibrium. Take the supernatant for metal ion concentration determination to explore the effect of solution acidity on the adsorption performance of APCS, APCS-ED, and APCS-CPD. The test conditions are as follows: room temperature. The equilibrium adsorption amount Qe (mg / g) of the adsorbent sample for metal ions is calculated by Equation (1).

[0082] Test results: Generally, ordinary functional groups such as amino and hydroxyl groups have unsatisfactory adsorption effects under acidic conditions due to protonation. Therefore, to verify the acid resistance of the introduced pyridine groups, the effect of the initial acidity of the metal ion solution on the adsorption effects of the three adsorbents was explored, and the results are as Figure 4 shown, Figure 4 is the adsorption effects of APCS, APCS-ED, and APCS-CPD on Cu(II) and Ni(II) at different acidities (pH values ranging from 1.0 to 5.0), where (a) corresponds to Cu(II) and (b) corresponds to Ni(II). As Figure 4 can be seen, as the pH value of the metal ion solution increases, the adsorption amount of APCS-CPD for these two HMCs first increases and then basically remains unchanged, which is mainly due to the deprotonation of protonated functional groups (especially pyridine nitrogen); in addition, as Figure 4 can be seen, whether it is Cu(II) or Ni(II), the adsorption amount of APCS-CPD far exceeds that of APCS and APCS-ED, which also shows that the adsorption performance of APCS-CPD for Cu(II) and Ni(II) is superior to the other two materials. This is because the content of the dipyridylamine group in APCS-CPD is relatively high. At pH = 1.5, the adsorption amounts of APCS-CPD for Cu(II) and Ni(II) are 68.74 mg / g and 59.45 mg / g, respectively, which are much higher than those of other ordinary adsorbents (the types and properties of the adsorbents are shown in Table 3). Therefore, APCS-CPD is a promising adsorbent for recovering HMCs from acidic leachates and acidic wastewater.

[0083] Table 3 Performance of the adsorbents

[0084]

[0085] 2.2. Adsorption selectivity of APCS-CPD:

[0086] Under normal circumstances, the components in the acidic leaching solution of electroplating sludge and acidic wastewater are complex and contain various HMCs. Adsorbents with certain selective adsorption for the HMCs to be recovered are more popular. To evaluate the adsorption selectivity of APCS-CPD, the effects of APCS-CPD on the adsorption of Cu(II) and Ni(II) in two-component systems coexisting with Zn(II), Fe(II), Cr(III), and Mn(II) at equal concentrations were studied. The test conditions were: room temperature, 24 h. The specific two-component systems set were: solutions containing Cu(II) and Zn(II) with a concentration of 200 mg / L each; solutions containing Cu(II) and Fe(II) with a concentration of 200 mg / L each; solutions containing Cu(II) and Cr(III) with a concentration of 200 mg / L each; solutions containing Cu(II) and Mn(II) with a concentration of 200 mg / L each; solutions containing Ni(II) and Zn(II) with a concentration of 200 mg / L each; solutions containing Ni(II) and Fe(II) with a concentration of 200 mg / L each; solutions containing Ni(II) and Cr(III) with a concentration of 200 mg / L each; solutions containing Ni(II) and Mn(II) with a concentration of 200 mg / L each. The normalized selectivity coefficient ε was used as an index for the adsorption selectivity of APCS-CPD in the above two-component systems (pH value = 1.0) and was calculated using Equation (2). The higher the ε value, the stronger the adsorption capacity of APCS-CPD for it and the greater the relative adsorption advantage.

[0087]

[0088] In the formula, M 1 and M 2 respectively represent the two heavy metal ions coexisting in the two-component system, that is, represents the equilibrium adsorption capacity for one of the heavy metal ions in the two-component system, while

[0089] represents the equilibrium adsorption capacity for the other heavy metal ion. Figure 5As shown in the figure, among several coexisting components, both εNi and εCu are between 0.846 and 0.954, much greater than εZn, εFe, εCr, and εMn. Moreover, the interference of Zn(II) and Fe(II) is relatively small, while the interference of Cr(III) and Mn(II) is almost negligible. The results indicate that the adsorbent has good selectivity for Cu(II) and Ni(II) in acidic leaching solutions. This is because the nitrogen atoms in the pyridine ring can act as ligands to donate electrons to metal ions, thereby forming complexes. Copper and nickel can form stable complexes with nitrogen-containing ligands, while the complex oxidation states of iron, manganese, and chromium reduce their binding ability to pyridine. Additionally, Figure 6 The results of the affinity test in

[0090] also confirm the selectivity of the adsorbent, fully demonstrating that APCS-CPD is an acid-resistant adsorbent with great application potential.

[0091] Test method: Solutions containing Cu(II), Ni(II), Zn(II), Fe(II), Cr(III), and Mn(II) with an initial metal ion concentration of 200 mg / L and pH = 1.5 were respectively prepared as metal ion solutions, and an adsorption experiment was conducted for 24 h to reach adsorption equilibrium. The supernatant was taken to measure the metal ion concentration to explore the isothermal adsorption law of the adsorbent. The test conditions were: room temperature. The equilibrium adsorption capacity Qe (mg / g) of the adsorbent sample for metal ions was calculated by Equation (1).

[0092] The results are as Figure 6 shown. Figure 6 Figure shows the test results of the adsorption affinity of APCS-CPD for different heavy metal ions.

[0093] It can be seen from Figure 6 that the adsorption affinity of APCS-CPD for Cu(II) and Ni(II) is much higher than that of other heavy metal ions (Zn(II), Fe(II), Cr(III), and Mn(II)), indicating that APCS-CPD has high selectivity and can efficiently remove Cu(II) and Ni(II).

[0094] 2.4. Investigation of the adsorption kinetics of APCS-ED and APCS-CPD:

[0095] The adsorption rate is an important criterion for the industrial application of adsorbents. A slow adsorption rate results in low economic efficiency and is difficult to promote in industry. Therefore, it is of great significance to explore the influence of adsorption time on the material properties. At the same time, adsorption kinetics can also preliminarily judge the adsorption properties of adsorbents and provide ideas for subsequent mechanism exploration. Therefore, the adsorption kinetics of APCS-CPD and APCS-ED were investigated using metal ion solutions containing Cu(II) and Ni(II) with an initial concentration of 250 mg / L, respectively.

[0096] Test method: 0.3 g of wet adsorbent samples (APCS-ED and APCS-CPD, with a dry weight of 0.029 g) were added to 50 mL of acidic metal ion solutions with pH = 1.5, and 0.1 mL of the supernatant was taken at specified intervals (0.1 h, 0.5 h, 1 h, 2 h, 3 h, 5 h, 8 h, 18 h, 19 h, 20 h, 21 h, 22 h, and 24 h) to measure the concentration of metal ions (denoted as C t ), and the adsorption capacity Q t (mg / g) of the adsorbent samples for metal ions was calculated by Equation (3):

[0097]

[0098] In the formula, C 0 (mg / L) is the initial concentration of Cu(II) and Ni(II) in the metal ion solution; C t (mg / L) is the equilibrium concentration of Cu(II) and Ni(II) in the solution after adsorption; V (L) is the volume of the Cu(II) and Ni(II) solutions; m (g) is the mass of the adsorbent sample; Q t (mg / g) is the adsorption capacity at different times.

[0099] The test conditions were: room temperature. The results are as Figure 7 shown. Figure 7 Figures (a) and (b) are the adsorption process curves of APCS-CPD and APCS-ED for the adsorption of Cu(II) and Ni(II) investigated using the pseudo-first-order kinetic model and the pseudo-second-order kinetic model at pH = 1.5. These two kinetic parameters were obtained by fitting the equations. Figure 7 In it, the dashed line represents the pseudo-first-order kinetics, and the solid line represents the pseudo-second-order kinetics. Test conditions: room temperature.

[0100] Test results: First, within the first 150 min, both materials rapidly adsorbed Cu(II) and Ni(II), and reached the adsorption equilibrium at 300 min. The relatively fast adsorption rate was due to the large specific surface area and pore volume of both materials, which exposed more functional sites. By comparing the two adsorption kinetic models and the kinetic fitting parameters, it was found that the correlation coefficients (R 2 = 0.929, 0.925, 0.920, 0.905) of the pseudo-second-order kinetic model for the adsorption of Cu(II) and Ni(II) by both adsorbents were higher than those (R 2 = 0.814, 0.826, 0.758, 0.692) of the pseudo-first-order kinetic model (as shown in Table 4). This indicates that the adsorption process of the two metal ions, Cu(II) and Ni(II), by both adsorbents is suitable to be explained by the pseudo-second-order kinetic model and belongs to the chemisorption process governed by chemical bonds and electron transfer.

[0101] Table 4 Parameters of the pseudo-first-order kinetic model and the pseudo-second-order kinetic model

[0102]

[0103]

[0104] 2.5. Adsorption isotherms of APCS-ED and APCS-CPD:

[0105] Test method: Prepare a metal ion solution containing Cu(II) and Ni(II) with an initial metal ion concentration of 100 - 500 mg / L and pH = 1.5, and conduct a 24-hour adsorption experiment to reach the adsorption equilibrium. Take the supernatant to measure the metal ion concentration and explore the isothermal adsorption law of the adsorbent. The test conditions are: room temperature. The equilibrium adsorption capacity Qe (mg / g) of the adsorbent sample for metal ions is calculated by Equation (1).

[0106] The adsorption isotherm process curves of APCS-ED and APCS-CPD for Cu(II) and Ni(II) shown in (a) and (b) are obtained by fitting the parameters (as shown in Table 5) using the Langmuir model and the Freundlich model. Figure 8 In it, the dashed line represents the Freundlich model, and the solid line represents the Langmuir model. Figure 8 As can be seen from

[0107] From Figure 8 it can be seen that the R obtained by fitting the Langmuir model 2The values are significantly higher than those of the Freundlich model, indicating monolayer adsorption of Cu(II) and Ni(II) on APCS-CPD. At pH = 1.5, the maximum adsorption capacities of APCS-CPD for Cu(II) and Ni(II) are 69.303 mg / g and 59.217 mg / g respectively, both higher than those of the APCS-ED adsorbent. This shows that APCS-CPD has excellent ability to capture Cu(II) and Ni(II) under acidic (pH = 1.5) conditions and has great potential for industrial applications.

[0108] Table 5 Parameters obtained by fitting the Langmuir model and the Freundlich model

[0109]

[0110]

[0111] 2.6. Investigation of the effect of inorganic salts on the adsorption performance of APCS-CPD:

[0112] Since electroplating sludge leachate and acidic industrial wastewater often contain various inorganic salts, it is necessary to investigate the effect of these inorganic salts on the adsorption of Cu(II) and Ni(II) by this material.

[0113] Test method: Prepare a solution containing Cu(II) and Ni(II) with a concentration of 200 mg / L and pH = 1.5 as the metal ion solution. Add NaCl, CaCl 2 , MgCl 2 , NaNO 3 and Na 2 SO 4 with concentrations of 10 mmol / L and 100 mmol / L respectively to the solution containing Cu(II) and Ni(II), and conduct a 24-hour adsorption experiment to reach adsorption equilibrium. Take the supernatant for determination of metal ion concentration to investigate the effect of inorganic salts on the adsorption performance of APCS-CPD. The test conditions are: room temperature. The equilibrium adsorption capacity Qe (mg / g) of the adsorbent sample for metal ions is calculated by Equation (1).

[0114] The results are as Figure 9 shown. Figure 9 Figure shows the effect of different inorganic salts on the adsorption performance of APCS-CPD.

[0115] From Figure 9It can be seen that inorganic salts of different concentrations and different types all promote the adsorption of the two metal ions, and the higher the concentration, the more significant the promoting effect. This is because the large amount of anions can reduce the positive charge on the surface of the adsorbent under acidic conditions. Anions can act as non-coordinating outer layer ions of heavy metal cations, reducing the apparent charge of some heavy metal cations. Moreover, the promoting effect of Ca(Ⅱ) and Mg(Ⅱ) on the adsorption of the two ions is significantly lower than that of Na(Ⅰ). This is because divalent alkaline earth metals have a stronger competitive effect with Cu(Ⅱ) and Ni(Ⅱ) at the binding sites of the adsorbent during the adsorption process than monovalent alkaline earth metals.

[0116] 2.7. Adsorption stability test of APCS-CPD:

[0117] The reusability and stability of APCS-CPD were evaluated through adsorption-desorption experiments.

[0118] Test method: Prepare a solution containing Cu(Ⅱ) and Ni(Ⅱ) with a concentration of 200 mg / L and pH = 1.5 as the metal ion solution, and conduct a 24-hour adsorption experiment to reach adsorption equilibrium. Take the supernatant for metal ion concentration determination, and record the equilibrium adsorption capacity measured at this time as Q 1 (mg / g). After adsorption, recover the adsorbent, desorb the recovered adsorbent in 10 mL of 20 wt% hydrochloric acid, and repeat the adsorption-desorption experiment four times. Record the equilibrium adsorption capacity measured each time during the repeated test as Q n (mg / g), and calculate the value of Q n / Q 1 . The test conditions are: room temperature. The equilibrium adsorption capacity Qe (mg / g) of the adsorbent sample for metal ions is calculated by Equation (1).

[0119] The results are as Figure 10 shown. Figure 10 It is the adsorption stability test result of APCS-CPD.

[0120] From Figure 10 it can be seen that the adsorption capacity of the adsorbent for the two ions in the second adsorption is more than 90% of that in the first adsorption. In the third adsorption, the adsorption capacity of the adsorbent for Ni(Ⅱ) is 80.88% of that in the first adsorption, and the adsorption capacity for Cu(Ⅱ) reaches 82.32% of that in the first adsorption. In the fourth adsorption, the adsorption capacity for the two ions can still reach more than 72% of that in the first adsorption, indicating that the adsorbent has a certain regeneration ability; and after four adsorptions, the adsorbent can still maintain a complete spherical structure (as Figure 11 shown), which also indicates that the adsorbent has good stability. Figure 11Among them, the left side is the physical picture of APCS-CPD after the fourth adsorption of Cu, and the right side is the physical picture of APCS-CPD after the fourth adsorption of Ni.

[0121] 2.8. Test the adsorption performance of APCS-CPD during actual application:

[0122] Due to its advantages such as simple operation and continuous control, fixed-bed columns are widely used in large-scale industrial wastewater treatment. The device for the dynamic column test is as Figure 12 shown. The wet adsorbent of APCS-CPD is filled into a glass column to form an adsorption column (Φ16×100 mm). A solution with an initial pH = 1.5 containing Cu(II) and Ni(II) is configured as the metal ion solution, where the initial concentrations (C 0 ) of the two metal ions, Cu(II) and Ni(II), are 482.47 mg / L and 506.76 mg / L respectively. The metal ion solution is passed through the adsorption column at a flow rate of 0.34 mL / min by a peristaltic pump, and the effluent is collected at regular intervals to measure the concentration (C) of each metal ion in the effluent solution. The test conditions are: room temperature.

[0123] The results are as Figure 13 shown. Figure 13 It is the adsorption performance of APCS-CPD for Cu(II) and Ni(II) during the dynamic column test.

[0124] As can be Figure 13 seen, during the continuous adsorption process, before the breakthrough point (concentration < 1 mg / L) of the fixed bed for the adsorption of Cu(II), the effective operation time of the fixed bed system is 8.5 h, and for Ni(II) it is 6.5 h. The APCS-CPD adsorption column adsorbs a total of 60.208 mg of Cu(II) and 51.300 mg of Ni(II). After calculation, the adsorption amounts are 72.25 mg / g and 61.56 mg / g respectively. It is close to the maximum adsorption amounts of 61.301 - 69.303 mg / g and 50.23 - 59.217 mg / g in the static adsorption test, and even higher than the maximum adsorption amounts in the static adsorption test. This further confirms the great potential of the APCS-CPD material in actual industrial recovery.

[0125] 2.9. Test the adsorption of heavy metal ions by APCS-CPD when treating electroplating sludge:

[0126] Add 10 g of electroplating sludge to 100 mL of 1 mol / L nitric acid, and stir with a magnetic stirrer at room temperature for 2 h. After leaching, collect the supernatant by centrifugation, and measure the leaching rate of each metal ion in the leachate with an atomic absorption spectrophotometer. The test conditions are: room temperature. The equilibrium adsorption capacity Qe (mg / g) of the adsorbent sample for metal ions is calculated by Equation (1).

[0127] The results are as Figure 14 shown. Figure 14 The adsorption effect of APCS-CPD on heavy metal ions when treating electroplating sludge.

[0128] It can be seen from Figure 14 that the APCS-CPD obtained in the present invention can achieve efficient adsorption of heavy metal ions (Ni, Cu) when treating electroplating sludge. Note: Since the metal content in electroplating sludge is relatively high, the metal ion concentration in the leachate is also relatively high. Therefore, the equilibrium adsorption capacity is used here to express the practicability of the adsorbent sample instead of the removal rate.

[0129] 2.10. Solid-phase characterization and mechanism analysis of APCS-CPD before and after adsorbing heavy metal ions:

[0130] Prepare a solution containing Cu(II) and Ni(II) with an initial pH of 1.5 and a concentration of 200 mg / L as the metal ion solution, and conduct a 24-h adsorption experiment to reach adsorption equilibrium, and recover the adsorbent. Obtain the Fourier transform infrared spectrum (FTIR) of the adsorbent before and after adsorption with VERTEX70. And obtain the energy spectrum of the adsorbent before and after adsorption through an X-ray photoelectron spectrometer (XPS, Axis Ultra DLD). The test conditions are: room temperature.

[0131] The results are as Figure 15 and Figure 16 shown.

[0132] Figure 15 The FTIR diagrams of APCS-CPD before and after adsorbing heavy metal ions.

[0133] Test results: First, it can be seen from Figure 4 that the adsorption capacity of APCS and APCS-ED for the two metal ions at pH = 1.5 is lower than 25 mg / g, and is significantly lower than the adsorption capacity of APCS-CPD. Therefore, it can be determined that the main function is the grafted pyridine group. And since no metal ions appear during the synthesis of APCS-CPD, this material cannot rely on cation exchange for adsorption, but captures metal ions through chelation. To verify the above inference, the above test was carried out and Figure 15 was obtained. It can be seen from Figure 15 that after adsorbing metal ions, -NH2 The bending vibration of -1 shifts from 1611.4 cm -1 to 1615.5 cm -1 and 1619.8 cm -1 . The stretching vibration peak of C-OH decreases from 1062 cm -1 to 1058.6 cm -1 and 1054.5 cm -1 respectively. The 765.8 cm -1 of the pyridine ring shifts to 763.1 cm -1 and 763.8 cm, indicating that the pyridine ring interacts with heavy metal ions, i.e., pyridine nitrogen coordinates.

[0134] Figure 16 Figures (a) and (b) are the full-spectrum and high-resolution XPS N1s spectra of APCS-CPD before and after adsorbing heavy metal ions, where (a) is the full-spectrum and (b) is the high-resolution XPS N1s spectrum. Figure 16 In (a) of

[0135] , APCS-CPD-Ni represents the adsorbent after adsorbing nickel ions, and APCS-CPD-Cu represents the adsorbent after adsorbing copper ions. Figure 16 As can be seen from

[0136] , in the full-spectrum, the peaks of Cu 2p and Ni 2p can be clearly observed. In the fine spectrum of N1s, after adsorbing metal ions, the peak of pyridine nitrogen on the adsorbent at 398.4 eV shifts to 399.51 - 399.53 eV, and the peak of amino nitrogen also shifts from 401.53 eV to 401.65 - 401.66 eV, indicating that the adsorbent adsorbs metal ions through the coordination of amino nitrogen and pyridine nitrogen with metal ions. Figure 17 shown in

[0137] 2.11. Cost comparison:

[0138] The comparison results of the costs of the reagents used in the technical solution of the present invention in the actual production process and the costs of the reagents used in the existing M4195 commercial resin in the actual production process are shown in Table 6.

[0139] Table 6 Cost comparison

[0140]

[0141] As can be seen from Table 6, the cost required for preparing the materials of the present invention is significantly lower than that for preparing the conventional M4195.

[0142] In this specification, the various embodiments are described in a progressive manner. Each embodiment focuses on the differences from other embodiments. For the same or similar parts among the various embodiments, reference may be made to each other.

[0143] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art. The general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a chitosan bipyridine group acid-resistant adsorbent, characterized in that: The steps include: Spherical chitosan is used as a raw material, and after amino protection, it is reacted with epichlorohydrin to obtain a first product; The first product, ethylenediamine and a solvent are mixed and then subjected to a second reaction to obtain a second product; The second product, 2-chloromethylpyridine hydrochloride, an acid-binding agent and a solvent are mixed and then subjected to a third reaction to obtain the chitosan bipyridine group acid-resistant adsorbent.

2. The preparation method according to claim 1, characterized in that: The preparation of the spherical chitosan comprises: adding a chitosan solution into a sodium hydroxide solution to form spherical chitosan; the solvent in the chitosan solution is a mixture of acetic acid and water, the mass fraction of chitosan in the chitosan solution is 2-5wt%; the mass fraction of sodium hydroxide in the sodium hydroxide solution is 2wt%; And / or, the amino protection comprises: mixing the spherical chitosan and benzaldehyde and then standing to obtain spherical chitosan with protected amino groups; the amount ratio of benzaldehyde to chitosan in the chitosan solution is 50-100 mL: 3-10 g; and the standing time is 12-24 h.

3. The preparation method according to claim 1, characterized in that: The dosage ratio of epichlorohydrin to chitosan in the chitosan solution is 6-10 mL: 3-10 g; and / or, the reaction conditions of the first reaction are: pH value is 9-14, temperature is 50-65° C., and time is 6-10 h.

4. The preparation method according to claim 1, characterized in that: The solvent in the second reaction and the third reaction is ethanol and water in a volume ratio of 1:

1.

5. The preparation method according to claim 1, characterized in that: The volume ratio of the first product, ethylenediamine and solvent is 3-10:8-12:150-200; and / or, the temperature of the second reaction is 50-70° C., and the time is 6-10 hours.

6. The preparation method according to claim 1, characterized in that: The acid binding agent includes one or more of sodium carbonate, potassium carbonate and sodium hydroxide; and / or, the dosage ratio of the second product, 2-chloromethylpyridine hydrochloride, acid binding agent and solvent is 3-10 mL: 1-5 g: 1-3 g: 150-200 mL; and / or, the temperature of the third reaction is 80-100° C., and the time is 12-36 h.

7. The preparation method according to claim 4, characterized in that: The step of mixing the second product, 2-chloromethylpyridine hydrochloride, sodium carbonate and solvent comprises: firstly adding 2-chloromethylpyridine hydrochloride and sodium carbonate into water, then adding ethanol thereto, and finally adding the second product.

8. The acid-resistant adsorbent containing bipyridine groups of chitosan prepared by the preparation method according to any one of claims 1 to 7.

9. Use of the chitosan bipyridine group acid-resistant adsorbent according to claim 8 in treating electroplating sludge.

10. A method for selectively recovering copper and nickel from electroplating sludge by leaching-adsorption synergistically, characterized in that: The steps include: First, the electroplating sludge and nitric acid are mixed to carry out a leaching reaction, and then the supernatant is taken, and the copper and nickel in the supernatant are leached using the chitosan bipyridine group acid-resistant adsorbent according to claim 8; The usage ratio of the electroplating sludge and nitric acid is 1-10 g:10-100 mL; The pH value of the supernatant is 1 to 5; The dosage ratio of the chitosan bipyridine group acid-resistant adsorbent to the supernatant is 0.029 g:30 mL.

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