A nitrogen-containing polyionic liquid, a preparation method and application thereof

Abstract

This invention belongs to the field of materials technology for precious metal recovery, and relates to a nitrogen-containing polyionic liquid, its preparation method, and its applications. The polyionic liquid adsorbs precious metal ions through electrostatic attraction and redox reactions, achieving an adsorption efficiency higher than 99.99%. Furthermore, the polyionic liquid possesses good acid resistance and chemical stability. By selecting a suitable back-extraction agent, stepwise back-extraction is achieved, enabling the recycling and reuse of the polyionic liquid.

Description

Technical Field

[0001] This invention belongs to the field of materials technology for precious metal recycling, and relates to a nitrogen-containing polyionic liquid, its preparation method, and its application. Background Technology

[0002] In industrial production and daily life, the discharge of wastewater, waste residue, and exhaust gases containing precious metals and other heavy metals has become a significant source of environmental pollution. Once these heavy metals enter the environment, they accumulate in aquatic organisms and crops, and enter the human body through drinking water and the food chain, seriously threatening human health. Therefore, how to efficiently and cost-effectively remove heavy metal ions, especially precious metal ions, from water has become a crucial issue in the field of environmental protection. Traditional heavy metal ion removal technologies include chemical precipitation, membrane separation, and ion exchange, but these methods often suffer from high costs, complex operations, and secondary pollution. Adsorption technology, due to its high efficiency, simplicity, low cost, and ease of treatment, has become a research hotspot in heavy metal wastewater treatment. Currently, commonly used adsorbents include minerals, activated carbon and its fibers, liquid extracts, ion exchangers, lactic acid bacteria, and chelates. Among these, activated carbon fibers have good adsorption effects, but their preparation cost is high, and they mainly rely on physical adsorption, resulting in insufficient adsorption capacity and difficulties in recycling. Therefore, developing new, low-cost, and efficient adsorption materials is particularly important. Polyionic liquids, as a novel type of functional material, have attracted widespread attention due to their unique structure and excellent adsorption properties. Polyionic liquids possess good chemical and thermal stability, high ionic conductivity, and tunable structural characteristics. In particular, nitrogen-containing polyionic liquids exhibit excellent adsorption performance due to their strong affinity for noble metal ions. However, research on polyionic liquid materials for the efficient adsorption of noble metal ions is currently lacking.

[0003] This invention provides a nitrogen-containing polyionic liquid that can efficiently adsorb noble metal ions such as chloroaurate, chloroplatinate, and chloropalladate ions, solving the problems of insufficient adsorption capacity, high preparation cost, and difficulty in recycling in the prior art, and has broad application prospects. Summary of the Invention

[0004] To address the above technical problems, this invention provides a nitrogen-containing polyionic liquid, its preparation method, and its application. The nitrogen-containing polyionic liquid adsorbs noble metal ions through electrostatic attraction and redox reactions, using only a trace amount of polyionic liquid, exhibiting high adsorption and recovery efficiency, good chemical stability, and excellent recycling performance.

[0005] This invention provides a nitrogen-containing polyionic liquid, its preparation method, and its applications. The polyionic liquid adsorbs noble metal ions through electrostatic attraction and redox reactions, achieving an adsorption efficiency higher than 99.99%. Furthermore, the polyionic liquid exhibits good acid resistance and chemical stability. Stepwise back-extraction is achieved by selecting a suitable back-extraction agent, enabling the recycling and reuse of the polyionic liquid.

[0006] This invention is achieved through the following technical solution:

[0007] A nitrogen-containing polyionic liquid has the following structural formula:

[0008] .

[0009] A second objective of this invention is to provide a method for preparing the nitrogen-containing polyionic liquid, comprising the following steps:

[0010] (1) Synthesis of nitrogen-containing ionic liquid monomers;

[0011] In an acetonitrile solution, N,N,N,N'-tetramethyl-1,6-hexanediamine and 4-vinylbenzylchlorobenzene were added and reacted to produce a white solid, which was then washed with ethyl acetate and dried for later use.

[0012] The reaction equation is as follows:

[0013]

[0014] (2) Preparation of polyionic liquids

[0015] In a mixed solution of ethyl acetate, ethanol and water, the product 1-(4-vinylbenzyl)-N,N,N',N'-tetramethylhexammonium chloride obtained in step (1) was added, and then the initiator azobisisobutyronitrile was added to carry out the reaction. After the reaction was completed, the product was washed with ethanol and then with deionized water, and then freeze-dried to obtain the target product.

[0016] The reaction equation is as follows:

[0017] .

[0018] Furthermore, in step (1), the molar ratio of N,N,N,N' tetramethyl-1,6-hexanediamine to 4-vinylbenzyl chloride is 1:1.

[0019] Furthermore, the reaction conditions for step (1) are: heating to 70-85°C under nitrogen gas and controlling the reaction time to 5-10 h.

[0020] Furthermore, in the mixed solution of step (2), the volume ratio of ethyl acetate, ethanol and water is 5:1:1.

[0021] Furthermore, in the mixed solution of step (2), the mass ratio of 1-(4-vinylbenzyl)-N,N,N',N'-tetramethylhexammonium chloride to azobisisobutyronitrile is 20:1.

[0022] Furthermore, the reaction conditions for step (2) are as follows: first, nitrogen gas is passed through for 15 minutes without heating, then the temperature is adjusted to 70-80℃, and the heating time is controlled for 6-18 hours.

[0023] The present invention also provides the application of the nitrogen-containing ionic liquid in the adsorption of noble metal ions.

[0024] Furthermore, the nitrogen-containing ionic liquid selectively adsorbs Au(III), Pd(II), and Pt(IV), and can be recycled.

[0025] Compared with the prior art, the beneficial technical effects of the present invention are as follows: The present invention first synthesizes nitrogen-containing ionic liquid monomers, and then uses azobisisobutyronitrile (AIBN) to achieve free radical polymerization of the ionic liquid monomers in a nitrogen atmosphere, finally forming a nitrogen-containing polyionic liquid with a carbon skeleton single-chain polymer structure.

[0026] The nitrogen-containing polyionic liquid contains nitrogen positive ion centers, which adsorb noble metal ions through electrostatic attraction and redox reactions, achieving an adsorption rate greater than 99.99%. This characteristic enables significant recovery of noble metal ions from nickel-containing anode sludge wastewater. The residual gold concentration after adsorption is less than 0.01 mg / L, palladium content is less than 0.01 mg / L, and platinum content is also less than 0.01 mg / L. Furthermore, the polyionic liquid is a non-toxic and odorless molecular polymer, which will not harm the natural environment. Compared with fluorine-containing ionic liquids, this noble metal adsorbent has significant advantages.

[0027] By employing the technical solution of this invention, this novel nitrogen-containing polymer material exhibits excellent adsorption capacity for precious metals, demonstrating significant economic and technological advantages in the field of wastewater treatment. As a highly efficient adsorbent separation technology, it possesses characteristics such as high efficiency and low energy consumption. This not only provides an effective purification method for addressing the current challenges of wastewater from secondary resources in anode sludge, but also opens up new avenues for the recycling of precious metals, achieving the goal of turning waste into treasure. Attached Figure Description

[0028] Figure 1 The 1H NMR spectrum of the polyionic liquid monomer;

[0029] Figure 2 This is the nitrogen adsorption-desorption isotherm.

[0030] Figure 3 A pore size distribution diagram of the BET test material;

[0031] Figure 4 The results of infrared characterization of the acid and salt resistance of polyionic liquids are shown in the figure.

[0032] Figure 5 Scanning electron microscopy (SEM) images of the untreated polyionic liquid (a, b) and the polyionic liquid treated with 6 mol / L HCl (c, d);

[0033] Figure 6 This is a selective extraction diagram;

[0034] Figure 7 This is a flowchart of the recycling process. Detailed Implementation

[0035] The present invention will be further described below with reference to the embodiments, but the present invention is not limited to the following embodiments.

[0036] Example 1

[0037]

[0038] S1. Add N,N,N,N'-tetramethyl-1,6-hexanediamine (0.01 mol) and 4-vinylbenzyl chloride (0.01 mol) dropwise to a three-necked flask containing 30 ml of acetonitrile solution. Then, under nitrogen purging, heat to 78°C and control the reaction time to 8 h to form a white precipitate. Wash the precipitate three times with ethyl acetate and place it in a vacuum drying oven for later use.

[0039]

[0040] S2. Weigh 2.0 g of 1-(4-vinylbenzyl)-N,N,N',N'-tetramethylhexammonium chloride into a mixed solution (ethyl acetate:ethanol:water volume ratio of 5:1:1). Then weigh 0.1 g of azobisisobutyronitrile (AIBN) and add it to the three-necked flask. First, purge the flask with nitrogen for 15 minutes without heating to purge oxygen from the flask and eliminate the influence of oxygen on free radical polymerization. Then adjust the temperature to 75°C and heat for 12 hours. After the reaction is complete, wash the mixture three times with ethanol and three times with deionized water, then freeze-dry for later use.

[0041] Example 2

[0042] S1. Add N,N,N,N'-tetramethyl-1,6-hexanediamine (0.01 mol) and 4-vinylbenzyl chloride (0.01 mol) dropwise to a three-necked flask containing 30 ml of acetonitrile solution. Then, under nitrogen purging, heat to 70°C and control the reaction time to 10 h to form a white precipitate. Wash the precipitate three times with ethyl acetate and place it in a vacuum drying oven for later use.

[0043] S2. Weigh 2.0 g of 1-(4-vinylbenzyl)-N,N,N',N'-tetramethylhexammonium chloride into a mixed solution (ethyl acetate:ethanol:water volume ratio of 5:1:1). Then weigh 0.1 g of azobisisobutyronitrile (AIBN) and add it to the three-necked flask. First, purge the flask with nitrogen for 15 minutes without heating to purge oxygen from the flask and eliminate the influence of oxygen on free radical polymerization. Then adjust the temperature to 70°C and heat for 18 hours. After the reaction is complete, wash the mixture three times with ethanol and three times with deionized water, then freeze-dry for later use.

[0044] Example 3

[0045] S1. Add N,N,N,N'-tetramethyl-1,6-hexanediamine (0.01 mol) and 4-vinylbenzyl chloride (0.01 mol) dropwise to a three-necked flask containing 30 ml of acetonitrile solution. Then, under nitrogen purging, heat to 85°C and control the reaction time to 5 h to form a white precipitate. Wash the precipitate three times with ethyl acetate and place it in a vacuum drying oven for later use.

[0046] S2. Weigh 2.0 g of 1-(4-vinylbenzyl)-N,N,N',N'-tetramethylhexammonium chloride into a mixed solution (ethyl acetate:ethanol:water volume ratio of 5:1:1). Then weigh 0.1 g of azobisisobutyronitrile (AIBN) and add it to the three-necked flask. First, purge the flask with nitrogen for 15 minutes without heating to purge oxygen from the flask and eliminate the influence of oxygen on free radical polymerization. Then adjust the temperature to 80℃ and heat for 6 hours. After the reaction is complete, wash the mixture three times with ethanol and three times with deionized water, then freeze-dry for later use.

[0047] The 1-(4-vinylbenzyl)-N,N,N',N'-tetramethylhexammonium chloride obtained in step S1 of Example 1 was characterized by NMR, as follows: Figure 1 As shown, the 1H NMR spectrum (400 MHz, CD3OD, δ / ppm) shows peaks at the following positions: 1.52 (m, 4H, 2CH2), 2.00 (m, 4H, 2CH2), 3.08 (m, 12H, 4CH3), 3.40 (m, 4H, 2CH2), 4.59 (s, 4H, 4CH2), 5.38 (q, 2H, 2CH), 5.93 (q, 2H, 2CH), 6.84 (q, 2H, 4CH), and 7.61 (m, 8H, 4CH), confirming the synthesis of the dication-centered ionic liquid.

[0048] The nitrogen-containing polyionic liquid obtained in Example 1 was characterized by nitrogen adsorption, and the nitrogen adsorption isotherms of the nitrogen-containing polyionic liquid were tested under the conditions of P / P0=1 and 150 K. Figure 2 As can be seen from the data, the maximum nitrogen adsorption capacity of this ionic liquid is 26.755 m. 2 / g, the specific surface area calculated based on nitrogen adsorption data is 26.755 m². 2 / g, pore size distribution is mainly 2.77nm (see Figure 3 ).

[0049] To investigate the stability of the polyionic liquid structure, 10 mg of the polyionic liquid was weighed into 7 mL centrifuge tubes, and then 1 mL of 6 mol / L HCl, 12 mol / L HCl, and 5 mol / L NaCl solutions were added respectively. The tubes were shaken at room temperature for 1 h, centrifuged, washed with deionized water, and dried in a vacuum drying oven. The polyionic liquid was then analyzed using Fourier transform infrared spectroscopy. Figure 4 As shown, the characteristic functional groups of the polyionic liquid remained unchanged after treatment with various solutions. Scanning electron microscopy (SEM) characterization of the untreated polyionic liquid and the polyionic liquid treated with 6 mol / L HCl yielded the following results: Figure 5 As shown, it was found that the morphology of the polyionic liquid after acid treatment was not changed compared with that of the untreated polyionic liquid, which means that it has good acid resistance and its morphology will not be destroyed by hydrochloric acid.

[0050] Example 4

[0051] Extraction experiments were conducted in 7 mL plastic centrifuge tubes. First, 3 mL of 5 mmol / L Au(III) solution was added to the tubes. Then, 3 mg, 4 mg, 5 mg, 6 mg, 7 mg, and 8 mg of the polyionic liquid prepared in Example 1 were added, respectively. The centrifuge tubes were then shaken in a shaker at room temperature for half an hour. The supernatant was then collected, and the Au(III) content in the solution was determined using inductively coupled plasma optical emission spectrometry (ICP-OES).

[0052] The formulas used to calculate the extraction efficiency (E%) and back-extraction efficiency (S%) are as follows:

[0053]

[0054] in, c in and c eq These represent the concentrations of Au(Ⅲ), Pd(Ⅱ), and Pt(Ⅳ) in the solution before and after extraction, respectively. c av represents the concentrations of Au(III), Pd(II), and Pt(IV) in the solution after back-extraction equilibrium. a This represents the volume of the stripping agent added. v in This represents the volume of Au(Ⅲ), Pd(Ⅱ), and Pt(Ⅳ) solutions added.

[0055] Table 1 Extraction rates of Au(III) by ionic liquids of different masses.

[0056]

[0057] Example 5

[0058] Extraction of palladium(II) and Pt(IV) was carried out in 7 mL plastic centrifuge tubes. First, 2 mL of 5 mmol / L palladium(IV) and platinum(IV) solution was added, followed by 4 mg, 6 mg, 8 mg, 10 mg, 12 mg, and 14 mg of the polyionic liquid prepared in Example 1, respectively. The centrifuge tubes were then shaken at room temperature for half an hour. The supernatant was then collected, and the remaining Pd(II) and Pt(IV) content in the solution was determined using inductively coupled plasma optical emission spectrometry (ICP-OES).

[0059] Table 2 Extraction rates of Pd(II) and Pt(IV) by ionic liquids at different masses

[0060]

[0061] As shown in Tables 1 and 2, by fixing the volume of the precious metal solution and increasing the mass of the polyionic liquid, it was determined that with a volume of 3 ml of gold solution, the optimal extraction amount of 6 mg could achieve an extraction rate of 98%; with a volume of 2 ml of palladium-platinum solution, the optimal extraction agent amount of 8 mg also achieved an extraction efficiency of over 98%.

[0062] Example 6

[0063] 1. Effect of acidic conditions on polyionic liquid extraction of gold

[0064] Extraction was performed in 7 mL plastic centrifuge tubes with a fixed Au(III) concentration of 5 mmol / L and a hydrochloric acid concentration gradient of 0.1–1.6 mol / L. To further investigate the effects of hydrogen and chloride ion concentrations in the hydrochloric acid, the hydrogen ion concentration was fixed at 0.1 mol / L with chloride ion concentrations increased by 0.1–1.6 mol / L, and the chloride ion concentration was fixed at 1.6 mol / L with hydrogen ion concentrations increased by 0.1–1.6 mol / L, respectively. Then, 6 mg of polyionic liquid was added to 7 mL centrifuge tubes with different hydrochloric acid, hydrogen ion, and chloride ion concentrations, and the solutions were shaken at room temperature for half an hour. After centrifugation, the supernatant was collected, and the concentration of remaining Au(III) ions in the solution was determined using inductively coupled plasma optical emission spectrometry (ICP-OES). Tables 3, 4, and 5 show that the polyionic liquid maintained high extraction efficiency under different chemical environments, with overall extraction efficiencies reaching 98% or higher.

[0065] Table 3 Extraction rates of Au(III) by ionic liquids with different hydrochloric acid concentrations

[0066]

[0067] Table 4 Extraction rates of Au(III) by ionic liquids with different hydrogen ion concentrations

[0068]

[0069] Table 5 Extraction rates of Au(III) by ionic liquids with different chloride ion concentrations

[0070]

[0071] 2. Effect of acidic conditions on polyionic liquid extraction of Pd(II) and Pt(IV)

[0072] Extraction was performed in 7 mL plastic centrifuge tubes. A fixed concentration of Pd(II) and Pt(IV) was designed at 5 mmol / L, with a hydrochloric acid concentration gradient of 0.1–1.6 mol / L. To further investigate the effects of hydrogen and chloride ion concentrations in the hydrochloric acid, the hydrogen ion concentration was fixed at 0.1 mol / L, with chloride ion concentrations increased by 0.1–1.6 mol / L; and the chloride ion concentration was fixed at 1.6 mol / L, with hydrogen ion concentrations increased by 0.1–1.6 mol / L. Then, 8 mg of polyionic liquid was added to each of the different series of hydrochloric acid, hydrogen ion, and chloride ion concentrations, and the solution volume was 2 mL in each 7 mL centrifuge tube. After shaking in a shaker at room temperature for half an hour, the supernatant was centrifuged, and the concentrations of unextracted Pd(II) and Pt(IV) ions were determined.

[0073] Table 6 Extraction rates of Pd(II) and Pt(IV) by ionic liquids with different hydrochloric acid concentrations

[0074]

[0075] Table 7 Extraction rates of Pd(II) and Pt(IV) by ionic liquids with different hydrogen ion concentrations

[0076]

[0077] Table 8 Extraction rates of ionic liquids Pd(II) and Pt(IV) with different chloride ion concentrations

[0078]

[0079] Example 7: Selective adsorption of various metal ions in nickel-containing anode mud leachate wastewater by polyionic liquids

[0080] Industrial wastewater was collected and adsorbed into 7 mL plastic centrifuge tubes. The pH of the solution was adjusted to 0.1 mol / L using sodium hydroxide solution. 1 mL of wastewater was taken, and 8 mg of polyionic liquid was added. The mixture was shaken in a shaker at room temperature for half an hour. After centrifugation, the supernatant was collected, and the metal ion concentration in the supernatant was determined using ICP. In the presence of copper, nickel, lead, and arsenic ions, the polyionic liquid showed excellent adsorption effects only on gold, palladium, and platinum ions, with an adsorption efficiency of 99.99%.

[0081] Experimental Example 8: Recycling of the Nitrogen-Containing Polyionic Liquid via Stepwise Back-Extraction

[0082] The nitrogen-containing polyionic liquid prepared in Example 1 can remove noble metal ions from water via adsorption, and then remove them via stepwise back-extraction, as shown in Example 1. Figure 7The flowchart separates the adsorbed noble metal ions. Gold is back-extracted from the metal-loaded polyionic liquid using a 0.1 mol / L Na₂S₂O₃ solution, followed by palladium back-extraction using an NH₄Cl / H₂O₂ solution, and then platinum back-extraction using a 0.1 mol / L CS(NH₂)₂ / HCl mixed solution (HCl concentration 0.1 mol / L). This cycle is repeated, and the extraction rate for each round is calculated. During the back-extraction process, because the redox potentials of gold, palladium, and platinum are different in the first step of gold extraction, different chemical reagents are used in stages to recover gold, palladium, and platinum separately. Firstly, a sodium sulfite solution of a certain concentration is used to treat the gold-adsorbed polyionic liquid, converting the adsorbed trivalent gold to monovalent gold, which is then returned to the solution, achieving the purpose of gold desorption. The target desorption of palladium can be achieved by forming a black precipitate of (NH4)2PdCl6 in the presence of NH4Cl / H2O2. This precipitate is then heated and decomposed to release the palladium into the solution. Palladium is then back-extracted out. Finally, the addition of acidic thiourea can back-extract divalent platinum, thus achieving effective elution of platinum.

[0083] Table 9. Cyclic efficiency of nitrogen-containing polyionic liquids

[0084]

Claims

1. A method for preparing a nitrogen-containing polyionic liquid, characterized in that: Includes the following steps: (1) Synthesis of nitrogen-containing ionic liquid monomers; In an acetonitrile solution, N,N,N,N'-tetramethyl-1,6-hexanediamine and 4-vinylbenzyl chloride were added and reacted to produce a white solid, which was then washed with ethyl acetate and dried for later use. The reaction equation is as follows: (2) Preparation of polyionic liquids In a mixed solution of ethyl acetate, ethanol and water, the product 1-(4-vinylbenzyl)-N,N,N',N'-tetramethylhexammonium chloride obtained in step (1) was added, and then the initiator azobisisobutyronitrile was added to carry out the reaction. After the reaction was completed, the product was washed with ethanol and then with deionized water, and then freeze-dried to obtain the target product. The reaction equation is as follows: 。 2. The method for preparing nitrogen-containing polyionic liquid according to claim 1, characterized in that: In step (1), the molar ratio of N,N,N,N' tetramethyl-1,6-hexanediamine to 4-vinylbenzyl chloride is 1:

1.

3. The method for preparing nitrogen-containing polyionic liquid according to claim 1, characterized in that: The reaction conditions for step (1) are: heating to 70-85℃ under nitrogen gas and controlling the reaction time to 5-10h.

4. The method for preparing nitrogen-containing polyionic liquid according to claim 1, characterized in that: In the mixed solution of step (2), the volume ratio of ethyl acetate, ethanol and water is 5:1:

1.

5. The method for preparing nitrogen-containing polyionic liquid according to claim 1, characterized in that: In the mixed solution of step (2), the mass ratio of 1-(4-vinylbenzyl)-N,N,N',N'-tetramethylhexammonium chloride to azobisisobutyronitrile is 20:

1.

6. The method for preparing nitrogen-containing polyionic liquid according to claim 1, characterized in that: The reaction conditions for step (2) are as follows: first, nitrogen gas is passed through for 15 minutes without heating, then the temperature is adjusted to 70-80℃, and the heating time is controlled for 6-18 hours.

7. The application of a nitrogen-containing polyionic liquid prepared by any one of claims 1-6 in the selective adsorption of noble metal ions.

8. The application of the nitrogen-containing polyionic liquid according to claim 7 in the selective adsorption of noble metal ions, characterized in that: The noble metal ions are Au(Ⅲ), Pd(Ⅱ), and Pt(Ⅳ), and the nitrogen-containing polyionic liquid can be recycled.

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