Magnetic lignin-based composite adsorbent as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of lignin-based composite materials, and particularly relates to a magnetic lignin-based composite adsorbent, a preparation method thereof and application of the magnetic lignin-based composite adsorbent in removal of As (III) in wastewater. According to the method, the magnetic Fe-PEI / SLS adsorbent is prepared by adopting a chemical coprecipitation method. The method is simple in step and low in energy consumption, and the prepared adsorbent has excellent adsorption performance on As (III). The invention further discloses the characterization of the Fe-PEI / SLS and the As (III) adsorption performance of the Fe-PEI / SLS. The adsorbent prepared by the invention has an excellent removal effect on As (III) in wastewater, and meets the actual wastewater treatment requirements. The adsorbent is prepared on the basis of lignin, and solid waste is recycled and efficiently utilized.

Description

Technical Field

[0001] This invention belongs to the field of lignin-based composite material technology, and in particular relates to a magnetic lignin-based composite adsorbent, its preparation method, and its application in removing As(III) from wastewater. Background Technology

[0002] Water sources in water supply systems often contain contaminants such as silt and suspended particles. To ensure the cleanliness and safety of the water supply, water plants perform sludge removal treatment. The sludge removal process aims to remove impurities from the water, but it may also lead to the accumulation and release of some harmful substances, such as arsenic.

[0003] Arsenic (As(III)) is a common pollutant in industrial wastewater, affecting not only water quality but also threatening human health and safety. Furthermore, the International Agency for Research on Cancer (IARC) has classified arsenic and arsenic compounds as Group 1 carcinogens for humans. Therefore, the removal of As(III) from wastewater is urgently needed. Many methods for removing As(III) from water have been proposed, such as electrodialysis, membrane filtration, and adsorption technologies. However, most of these technologies are costly (coagulation, flocculation, filtration, oxidation, and nanofiltration), produce high levels of sludge (coagulation / flocculation), suffer from membrane fouling (nanofiltration), and require continuous monitoring of ions. Therefore, the use of these technologies is limited. Conversely, adsorption technology, due to its low cost, has been adopted as one of the effective strategies for As(III) removal.

[0004] Lignin is one of the three major components of wood and the second most abundant biopolymer on Earth. However, as a byproduct of biorefining and papermaking, its primary use is for energy production through combustion, with less than 5% of lignin being utilized for high-value purposes, resulting in resource waste. Therefore, it is essential to provide a method for modifying and utilizing lignin. Summary of the Invention

[0005] The main objective of this invention is to provide a magnetic lignin-based composite adsorbent, its preparation method, and its application. Using renewable biomass (lignin) as raw material, a magnetic lignin-based composite adsorbent for removing As(III) from aqueous solutions was prepared, and its performance was investigated. To increase the number of active sites on the lignin surface, amine functional groups were introduced onto the surface of lignin sulfonate, which was then cross-linked with magnetic materials to synthesize a magnetic Fe-PEI / SLS adsorbent with high magnetic strength, enabling the recycling and efficient utilization of industrial waste. This adsorbent exhibits rapid adsorption capacity (adsorption equilibrium time approximately 5 h) and high removal capacity for As(III) at room temperature.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] This invention provides a method for preparing a magnetic lignin-based composite adsorbent. The method includes: crosslinking lignin with polyethyleneimine at room temperature for 1-2 hours to obtain polyethyleneimine / lignin; wherein, polyethyleneimine is denoted as PEI; preparing a magnetic solution and adjusting the pH of the magnetic solution to alkaline; adding the polyethyleneimine / lignin to the magnetic solution and stirring for 1-2 hours until black particles are generated; separating the obtained particles from the solution, washing with deionized water, and freeze-drying to obtain the magnetic lignin-based composite adsorbent.

[0008] Furthermore, the preparation method specifically includes the following steps: (1) adding PEI to a lignin solution and stirring for 1-2 hours to carry out a cross-linking reaction to obtain polyethyleneimine / lignin; (2) taking Fe... 2+ Compounds and compounds containing Fe 3+ The compound is dissolved in deionized water, and the pH of the solution is adjusted to 8-10 to obtain a magnetic solution; (3) The polyethyleneimine / lignin is slowly added to the magnetic solution, stirred at 50℃-70℃ for 1-2 hours, washed with deionized water, and freeze-dried to obtain the magnetic lignin-based composite adsorbent.

[0009] Furthermore, the lignin is lignin sulfonate; wherein, lignin sulfonate is denoted as SLS.

[0010] Furthermore, in step (1), the concentration of SLS is 1 to 3 g / L.

[0011] Furthermore, in step (1), the mass of the PEI is 0.5 to 1% of the mass of the SLS.

[0012] Furthermore, in step (1), the crosslinking agent used in the crosslinking reaction is glutaraldehyde, and the amount added is 0.1 to 0.5% of the mass of the SLS.

[0013] Furthermore, containing Fe 2+ Fe in compounds 2+ With Fe 3+ Fe in compounds 3+ The mass ratio is 1:2; the substance containing Fe 2+ The compound is ferrous sulfate heptahydrate, which contains Fe 3+ The compound is ferric chloride hexahydrate.

[0014] The present invention also provides a magnetic lignin-based composite adsorbent prepared by the above-described method for preparing magnetic lignin-based composite adsorbent.

[0015] The present invention also provides the application of the above-mentioned magnetic lignin-based composite adsorbent as a wastewater treatment material.

[0016] Furthermore, the method includes using the magnetic lignin-based composite adsorbent to adsorb trivalent arsenic from wastewater; the method includes: adding the magnetic lignin-based composite adsorbent to wastewater containing trivalent arsenic; wherein the concentration of trivalent arsenic in the wastewater containing trivalent arsenic is greater than 0 and less than or equal to 500 mg / L, the pH value is 2 to 8, the concentration of the magnetic lignin-based composite adsorbent is 0.5 to 1 g / L, and the adsorption temperature is 25°C.

[0017] Furthermore, the adsorption time of As(III) wastewater was 0–12 h, and the As(III) concentration was tested by ICP-OES instrument after filtration.

[0018] Furthermore, the pH value of As(III) wastewater is 2-8, and the pH of the wastewater can be adjusted using HCl and NaOH.

[0019] Compared with the prior art, the beneficial effects of the present invention are:

[0020] (1) The present invention provides a method for preparing magnetic lignin-based composite adsorbents by modifying lignin from solid waste, thereby realizing a circular economy of “treating waste with waste”.

[0021] (2) The magnetic lignin-based composite adsorbent prepared by the technical solution of the present invention achieves deep arsenic removal at room temperature with zero energy consumption through the dual action of coordination bond-complexation. The adsorption capacity of As(III) can reach 54.98 mg / g, and the adsorption equilibrium can be reached in 5 hours. It is an ideal new As(III) adsorbent material.

[0022] (3) The technical solution of the present invention, by magnetically modifying lignin, endows it with excellent magnetism, and the adsorbent is easy to recover to avoid secondary pollution; the cross-linking of PEI gives it a large specific surface area and abundant active centers, which greatly improves the performance of wastewater treatment. Attached Figure Description

[0023] Figure 1 Fourier transform infrared spectra of the magnetic Fe-PEI / SLS adsorbent before and after modification provided in Example 1 of this invention;

[0024] Figure 2 This is a schematic diagram of the magnetic Fe-PEI / SLS adsorbent recovery using a magnet provided in Embodiment 1 of the present invention;

[0025] Figure 3 This is a schematic diagram of the adsorption capacities of SLS, PEI / SLS, and Fe-PEI / SLS provided in Example 2 of the present invention;

[0026] Figure 4 This is a graph showing the effect of time on the capacity of the magnetic Fe-PEI / SLS adsorbent provided in Example 3 of the present invention;

[0027] Figure 5 This is a graph showing the effect of the initial As(Ⅲ) concentration on the capacity of the magnetic Fe-PEI / SLS adsorbent provided in Example 4 of the present invention.

[0028] Figure 6 This is a graph showing the effect of pH on the capacity of the magnetic Fe-PEI / SLS adsorbent provided in Example 5 of the present invention. Detailed Implementation

[0029] The inventors discovered that lignin, due to its high porosity and the presence of oxygen-containing groups such as hydroxyl, carbonyl, and methoxy groups, can absorb some heavy metal ions through ion exchange and chelation. However, effectively separating lignin from the aqueous solution after adsorption to ensure the recycling of the adsorbent remains a major challenge. To address this issue, the technique of combining non-magnetic polymers with magnetic materials to prepare absorbents has attracted attention. On the other hand, lignin has a negatively charged surface and lacks anion exchange capacity. Polyethyleneimine (PEI), a polyamine containing multiple amine groups, is widely used for adsorbent modification due to its strong chelating ability for heavy metal ions. Surface modification with iron or manganese oxides can increase the positive potential and impart magnetism to lignin-based adsorbents, facilitating adsorbent recovery and regeneration. Studies have shown that arsenic migration is mainly controlled by iron oxide, and Fe-O has a high affinity for arsenic. The preparation of lignin-based adsorbents using lignin as a raw material has advantages such as low cost, ease of preparation, and easy controllability of modification, and has potential application as a heavy metal ion adsorbent. Therefore, a novel environmentally friendly magnetic Fe-PEI / SLS adsorbent was designed to improve its adsorption capacity for arsenic.

[0030] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0031] In the following embodiments, unless otherwise specified, the raw materials or processing techniques are conventional commercially available raw materials or conventional processing techniques in the art.

[0032] Example 1

[0033] 1) First, dissolve 200 mg of lignin sulfonate in 100 mL of water, then add 2 mg of PEI and 1 mg of glutaraldehyde, stir at room temperature for 1 h, and wash with deionized water to obtain PEI / SLS particles.

[0034] 2) Take a certain amount of ferrous sulfate heptahydrate (Fe) in a mass ratio of 1:2. 2+ ): Ferric chloride hexahydrate (Fe 3+ Dissolve the substance in 100 mL of deionized water, adjust the pH of the solution to 9 with NaOH, and prepare a magnetic solution.

[0035] 3) The PEI / SLS particles prepared in 1) are slowly added to the magnetic solution prepared in 2), stirred at 60°C for 1 h, washed, and freeze-dried under vacuum to obtain a magnetic lignin-based composite adsorbent, denoted as Fe-PEI / SLS adsorbent.

[0036] The prepared Fe-PEI / SLS adsorbent is shown in infrared spectroscopy. Figure 1 As shown, the results indicate that at 3400cm -1 2935cm -1 1600cm -1 1511cm -1 and 1460cm -1 1232cm -1 The characteristic peak of SLS appears at 1125 cm⁻¹. PEI-SLS shows a peak at 1125 cm⁻¹. -1 The presence of CN-bond stretching vibrations at 3400 cm⁻¹ indicates that the PEI chain has been successfully grafted onto the SLS. For Fe-PEI / SL, at 3400 cm⁻¹... -1 2935cm -1 and 2941cm -1 The characteristic peaks attenuated further at 617 cm⁻¹. -1 The appearance of a new peak is attributed to the Fe–O stretching vibration. This indicates the successful synthesis of the magnetic Fe-PEI / SLS adsorbent. Figure 2 It can be seen that the prepared Fe-PEI / SLS is easily collected by a magnet, which is beneficial for the recycling of the adsorbent.

[0037] Example 2

[0038] 1) First, dissolve 200 mg of lignin sulfonate in 100 mL of water, then add 2 mg of PEI and 1 mg of glutaraldehyde, stir at room temperature for 1 h, and wash with deionized water to obtain PEI / SLS particles.

[0039] 2) Take a certain amount of ferrous sulfate heptahydrate (Fe) in a mass ratio of 1:2. 2+ ): Ferric chloride (Fe) 3+ Dissolve the substance in 100 mL of deionized water, adjust the pH of the solution to 9 with NaOH, and prepare a magnetic solution.

[0040] 3) Slowly add the PEI / SLS particles prepared in 1) to the magnetic solution prepared in 2), stir at 60°C for 1 h, wash, and freeze dry under vacuum to obtain Fe-PEI / SLS adsorbent.

[0041] 4) Add 0.03g of SLS, PEI / SLS and Fe-PEI / SLS to 25mL of wastewater containing arsenic (200mg / L) and pH 6, respectively, stir, and adsorb for 12h.

[0042] 5) After adsorption, filter the solution with a 45μm filter membrane and then test the As(III) concentration using an ICP-OES instrument (Thermo Fisher iCPPRO(OES)).

[0043] 6) The adsorption capacity q of the adsorbent e (mg / g) is calculated as follows:

[0044]

[0045] Where, q e (mg / g) represents the amount of substance adsorbed per unit mass of adsorbent at adsorption equilibrium; C0 (mg / L) and C e (mg / L) represents the initial concentration of As(III) and the concentration at adsorption equilibrium, respectively.

[0046] For As(III) adsorption, loading with magnetic materials can significantly improve absorption compared to PEI / SLS, such as... Figure 3 As shown, PEI / SLS has a limited adsorption capacity for As(III), with a maximum adsorption capacity of 2.73 mg / g, while the Fe-PEI / SLS-1 adsorbent significantly improves the absorption capacity of As(III), with a maximum capacity of 54.98 mg / g. The experimental results demonstrate that the prepared Fe-PEI / SLS adsorbent exhibits a significant adsorption effect on As(III), indicating the feasibility of using iron-modified PEI / SLS composite adsorbents to adsorb As(III).

[0047] Example 3

[0048] 1) First, dissolve 200 mg of lignin sulfonate in 100 mL of water, then add 2 mg of PEI and 1 mg of glutaraldehyde, stir at room temperature for 1 h, and wash with deionized water to obtain PEI / SLS particles.

[0049] 2) Take a certain amount of ferrous sulfate heptahydrate (Fe) in a mass ratio of 1:2. 2+ ): Ferric chloride (Fe) 3+ Dissolve the substance in 100 mL of deionized water, adjust the pH of the solution to 9 with NaOH, and prepare a magnetic solution.

[0050] 3) Slowly add the PEI / SLS particles prepared in 1) to the magnetic solution prepared in 2), stir at 60°C for 1 h, wash, and freeze dry under vacuum to obtain Fe-PEI / SLS adsorbent.

[0051] 4) Add 0.15g of Fe-PEI / SLS to 150mL of wastewater containing arsenic (200mg / L) and with a pH of 6, and stir.

[0052] 5) To investigate the adsorption equilibrium time, the water sample from step 4) was filtered at 0, 5 min, 10 min, 30 min, 1 h, 2 h, 4 h, 9 h, 10 h and 24 h respectively. The As(III) concentration was then measured using an ICP-OES instrument.

[0053] 6) The adsorption capacity q of the adsorbent e (mg / g) is calculated as follows:

[0054]

[0055] Where, q e (mg / g) represents the amount of substance adsorbed per unit mass of adsorbent at adsorption equilibrium; C0 (mg / L) and C e (mg / L) represents the initial concentration of As(III) and the concentration at adsorption equilibrium, respectively.

[0056] Figure 4 This is a trend graph showing the adsorption capacity of Fe-PEI / SLS for As(III) at different time points. The graph shows that the adsorption process is rapid before approximately 2 hours. At this time, the Fe-PEI / SLS adsorbent surface has a large number of active sites, providing a relatively large concentration gradient that drives the adsorption of a large amount of As(III) in a short period. Then, from 2 to 4 hours, the adsorption capacity increases slowly as the active sites are occupied and decrease, leading to a gradual slowdown in the increase in adsorption capacity, and the adsorption begins to tend towards equilibrium. Finally, after 5 hours, the adsorption remains constant, reaching equilibrium, with the Fe-PEI / SLS adsorption capacity at 65 mg / g.

[0057] Example 4

[0058] 1) First, dissolve 200 mg of lignin sulfonate in 100 mL of water, then add 2 mg of PEI and 1 mg of glutaraldehyde, stir at room temperature for 1 h, and wash with deionized water to obtain PEI / SLS particles.

[0059] 2) Take a certain amount of ferrous sulfate heptahydrate (Fe) in a mass ratio of 1:2. 2+ ): Ferric chloride (Fe) 3+ Dissolve the substance in 100 mL of deionized water, adjust the pH of the solution to 9 with NaOH, and prepare a magnetic solution.

[0060] 3) Slowly add the PEI / SLS particles prepared in 1) to the magnetic solution prepared in 2), stir at 60°C for 1 h, wash, and freeze dry under vacuum to obtain Fe-PEI / SLS adsorbent.

[0061] 4) Add 0.03g of SLS, PEI / SLS and Fe-PEI / SLS to 25mL of wastewater containing arsenic (0-500mg / L) with a pH of 6, respectively, stir, and adsorb for 12h.

[0062] 5) After adsorption, filter with a 45μm filter membrane and test the As(Ⅲ) concentration with an ICP-OES instrument.

[0063] 6) The adsorption capacity q of the adsorbent e (mg / g) is calculated as follows:

[0064]

[0065] Where, q e (mg / g) represents the amount of substance adsorbed per unit mass of adsorbent at adsorption equilibrium; C0 (mg / L) and C e (mg / L) represents the initial concentration of As(III) and the concentration at adsorption equilibrium, respectively.

[0066] The adsorption capacity of Fe-PEI / SLS in As(III) solutions with different initial concentrations is as follows: Figure 5 As shown, the adsorption capacity of the Fe-PEI / SLS adsorbent gradually increases with the gradual increase of As(III) concentration. When the As(III) solution concentration is low, the ratio of As(III) to Fe-PEI / SLS adsorbent is low, resulting in a low adsorption capacity. When the As(III) solution concentration is high, a large amount of As(III) can interact more fully with the adsorption sites on the Fe-PEI / SLS surface, thus increasing the adsorption capacity.

[0067] Example 5

[0068] 1) First, dissolve 200 mg of lignin sulfonate in 100 mL of water, then add 2 mg of PEI and 1 mg of glutaraldehyde, stir at room temperature for 1 h, and wash with deionized water to obtain PEI / SLS particles.

[0069] 2) Take a certain amount of ferrous sulfate heptahydrate (Fe) in a mass ratio of 1:2. 2+ ): Ferric chloride (Fe) 3+ Dissolve the substance in 100 mL of deionized water, adjust the pH of the solution to 9 with NaOH, and prepare a magnetic solution.

[0070] 3) Slowly add the PEI / SLS particles prepared in 1) to the magnetic solution prepared in 2), stir at 60°C for 1 h, wash, and freeze dry under vacuum to obtain Fe-PEI / SLS adsorbent.

[0071] 4) Add 0.03g of SLS, PEI / SLS and Fe-PEI / SLS to 25mL of arsenic-containing solution (200mg / L) respectively, adjust the pH of the simulated wastewater to 2, 4, 6, 7 and 8, stir and adsorb for 12h.

[0072] 5) After adsorption, filter with a 45μm filter membrane and test the As(Ⅲ) concentration with an ICP-OES instrument.

[0073] 6) The adsorption capacity q of the adsorbent e (mg / g) is calculated as follows:

[0074]

[0075] Where, q e (mg / g) represents the amount of substance adsorbed per unit mass of adsorbent at adsorption equilibrium; C0 (mg / L) and C e (mg / L) represents the initial concentration of As(III) and the concentration at adsorption equilibrium, respectively.

[0076] Figure 6 The graph shows the effect of Fe-PEI / SLS on the adsorption capacity of As(III) under different pH conditions. It can be seen that the adsorption capacity gradually decreases with increasing pH. Under otherwise constant conditions, the maximum adsorption capacity of 116 mg / L is reached at pH 2. Actual wastewater is generally neutral or weakly acidic, and even at pH 6-7, it still exhibits a relatively high adsorption capacity. Therefore, Fe-PEI / SLS adsorbent has a certain removal capacity for As(III) in wastewater.

[0077] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A method for preparing a magnetic lignin-based composite adsorbent, characterized in that, The preparation method includes: Lignin was crosslinked with polyethyleneimine at room temperature for 1–2 h to obtain polyethyleneimine / lignin; wherein, polyethyleneimine is denoted as PEI; Prepare a magnetic solution and adjust the pH of the magnetic solution to alkaline. The polyethyleneimine / lignin was added to the magnetic solution and stirred for 1-2 hours until black particles were generated. The resulting particles were separated from the solution, washed with deionized water, and freeze-dried to obtain the magnetic lignin-based composite adsorbent.

2. The preparation method of the magnetic lignin-based composite adsorbent according to claim 1, characterized in that, The preparation method specifically includes the following steps: (1) Add PEI to lignin solution and stir for 1-2 hours to carry out cross-linking reaction to obtain polyethyleneimine / lignin; (2) Take a sample containing Fe 2+ Compounds and compounds containing Fe 3+ The compound is dissolved in deionized water, and the pH of the solution is adjusted to 8-10 to obtain a magnetic solution; (3) The polyethyleneimine / lignin is slowly added to the magnetic solution, stirred at 50℃~70℃ for 1~2h, washed with deionized water, and freeze-dried to obtain the magnetic lignin-based composite adsorbent.

3. The preparation method of the magnetic lignin-based composite adsorbent according to claim 2, characterized in that, The lignin is lignin sulfonate; wherein, lignin sulfonate is denoted as SLS.

4. The preparation method of the magnetic lignin-based composite adsorbent according to claim 3, characterized in that, In step (1), the concentration of SLS is 1 to 3 g / L.

5. The preparation method of the magnetic lignin-based composite adsorbent according to claim 3, characterized in that, In step (1), the mass of the PEI is 0.5 to 1% of the mass of the SLS.

6. The method for preparing the magnetic lignin-based composite adsorbent according to claim 3, characterized in that, In step (1), the crosslinking agent used in the crosslinking reaction is glutaraldehyde, and the amount added is 0.1 to 0.5% of the mass of the SLS.

7. The method for preparing the magnetic lignin-based composite adsorbent according to claim 2, characterized in that, Contains Fe 2+ Fe in compounds 2+ With Fe 3+ Fe in compounds 3+ The mass ratio is 1:2; The containing Fe 2+ The compound is ferrous sulfate heptahydrate, which contains Fe 3+ The compound is ferric chloride hexahydrate.

8. A magnetic lignin-based composite adsorbent prepared by the method of preparing a magnetic lignin-based composite adsorbent according to any one of claims 1 to 7.

9. The application of the magnetic lignin-based composite adsorbent according to claim 8 as a wastewater treatment material.

10. The application according to claim 9, characterized in that, This includes a method for using the magnetic lignin-based composite adsorbent to adsorb trivalent arsenic from wastewater; The method includes: adding the magnetic lignin-based composite adsorbent to wastewater containing trivalent arsenic; wherein the concentration of trivalent arsenic in the wastewater is greater than 0 and less than or equal to 500 mg / L, the pH value is 2 to 8, the concentration of the magnetic lignin-based composite adsorbent is 0.5 to 1 g / L, and the adsorption temperature is 25°C.

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