A heavy metal ion adsorbent, its preparation method and application

Abstract

This invention belongs to the field of adsorption material technology, and relates to a heavy metal ion adsorbent, its preparation method, and its application. The invention provides a method for preparing a heavy metal ion adsorbent, comprising: crushing banana peels into a first banana peel powder and a second banana peel powder; impregnating the first banana peel powder sequentially with a sulfonate solution and an iron-containing solution to obtain a first modified banana peel powder; impregnating the second banana peel powder sequentially with an ammonium formate solution and an ethyl tetrasilicate ethanol solution, hydrolyzing it under alkaline conditions, drying it, and washing the surface with water until neutral to obtain a second modified banana peel powder; and pyrolyzing the first and second modified banana peel powders to obtain a heavy metal ion adsorbent. This invention unexpectedly found that this heavy metal ion adsorbent performs excellently in removing heavy metal ions from water containing low concentrations of heavy metal ions in a flowing state, thus solving the problem of purifying flowing water containing low concentrations of heavy metal ions.

Description

Technical Field

[0001] This invention belongs to the field of adsorption materials technology, and relates to a heavy metal ion adsorbent, its preparation method and application. Background Technology

[0002] Heavy metal ions exhibit significant biotoxicity, with a large portion adsorbing onto particulate matter or colloids in water, eventually accumulating as precipitates at the bottom of water bodies. These precipitates are difficult for aquatic microorganisms to degrade, posing a threat to human health. Therefore, removing heavy metal ions from water is crucial for ecological and environmental protection. Adsorption methods for removing heavy metal ions from water primarily rely on adsorbents with high surface energy and large specific surface areas, utilizing their adsorption properties to separate and remove heavy metal ions. Fruit peels, as a type of agricultural and forestry waste, contain abundant lignin, cellulose, hemicellulose, and polysaccharides. The rich porous structure of fruit peels, exhibiting lamellar, honeycomb, and irregularly wrinkled forms, ensures sufficient interaction area between the material and the adsorbate, thus endowing them with excellent adsorption properties. Fruit peels also contain a large amount of phenols, lipids, and amino acids; their abundant functional groups can interact with metal ions through ion exchange and chelation.

[0003] Biochar is a highly aromatic, highly resistant carbonaceous solid material produced by the pyrolysis and carbonization of plant or animal waste biomass under completely or partially anoxic conditions. It is an organic continuum rich in carbon. Biochar has a large specific surface area, is porous, and contains active functional groups such as phenolic hydroxyl groups, carboxyl groups, and carbonyl groups. It has adsorption and fixation effects on various heavy metal ions and can be used to remove toxic and harmful heavy metal ions from water bodies. Directly using fruit peel materials to make biochar as an adsorbent to remove heavy metal ions from wastewater has disadvantages such as small exchange capacity, poor stability, and difficulty in long-term storage. Moreover, some soluble organic substances in the fruit peel, such as lignin, tannic acid, and pectin, may increase the chemical oxygen demand in the water and affect the adsorption effect when dissolved. Therefore, optimization treatment of fruit peels can be considered. Currently, the optimization and modification of fruit peel materials usually involves introducing functional groups to improve the exchange capacity. For example, by derivatizing the numerous hydroxyl groups in the cellulose structure, anionic groups such as sulfonic acid groups and phosphate groups, which have strong adsorption capacity for heavy metal cations, can be introduced to improve the adsorption performance of the fruit peel material. Alternatively, cellulose can be used as the basic framework to graft other chelating groups containing elements such as S, N, and P, which can then bind to heavy metal ions through ionic or coordinate bonds, thereby enhancing their adsorption performance. Although the above methods have achieved good results in removing heavy metal ions from water, they are not effective in removing heavy metal ions from water containing low concentrations of heavy metal ions in a flowing state. Summary of the Invention

[0004] The purpose of this invention is to solve at least one of the above-mentioned technical problems, and to modify biochar made from banana peels in a simple and low-cost manner so that it can effectively remove heavy metal ions from water containing low concentrations of heavy metal ions in a flowing state. To this end, this invention provides a heavy metal ion adsorbent, its preparation method and application.

[0005] On one hand, the present invention relates to a method for preparing a heavy metal ion adsorbent, comprising: crushing banana peels into a first banana peel powder and a second banana peel powder respectively; impregnating the first banana peel powder sequentially with a sulfonate solution and an iron-containing solution to obtain a first modified banana peel powder; impregnating the second banana peel powder sequentially with an ammonium formate solution and an ethyl orthosilicate ethanol solution, hydrolyzing it under alkaline conditions, drying it, washing the surface with water until neutral to obtain a second modified banana peel powder; mixing the first modified banana peel powder and the second modified banana peel powder in a mass ratio of 1:1 to 3 and impregnating them in an alkaline ethanol solution to obtain a precursor, wherein the precursor is first pyrolyzed at 350 to 400°C for 1 to 2 hours, then pyrolyzed at 650 to 700°C for 20 to 40 minutes, and finally pyrolyzed at 500 to 550°C for 1 to 2 hours.

[0006] Furthermore, in the preparation method of the heavy metal ion adsorbent provided by the present invention, the particle size of the first banana peel powder is 50-100 mesh, and the particle size of the second banana peel powder is 400-600 mesh.

[0007] Furthermore, in the preparation method of the heavy metal ion adsorbent provided by the present invention, the sulfonate is selected from at least one of sodium dodecylbenzenesulfonate, sodium dodecylnaphthalenesulfonate, and sodium dihexyl sulfosuccinate.

[0008] The iron-containing solution includes at least one of ferric chloride, ferric sulfate, ferric nitrate, ferric acetate, ferrous chloride, ferrous sulfate, ferrous nitrate, and ferrous acetate; the alkali in the ethanol solution of the alkali is one of sodium hydroxide, potassium hydroxide, and ammonia.

[0009] Furthermore, in the preparation method of the heavy metal ion adsorbent provided by the present invention, the concentration of the sulfonate solution is 1-3 wt%; the concentration of the iron-containing solution is 0.5-1 mol / L; the mass ratio of tetraethyl orthosilicate, ethanol, and water in the tetraethyl orthosilicate ethanol solution is 20-30:50-60:20-30; the concentration of the alkali in the alkali ethanol solution is 0.01-0.05 mol / L; and the concentration of the ammonium formate solution is 30-40 wt%.

[0010] Furthermore, in the preparation method of the heavy metal ion adsorbent provided by the present invention, the alkaline condition is pH = 9 to 10.

[0011] Furthermore, in the preparation method of the heavy metal ion adsorbent provided by the present invention, the hydrolysis treatment is carried out by stirring at 200-400 r / min for 30-60 min at 40-50℃.

[0012] Furthermore, in the preparation method of the heavy metal ion adsorbent provided by the present invention, the ethanol solution impregnated with alkali is stirred at 200-400 r / min for 10-15 min at room temperature and then dried at 105-120°C.

[0013] On the other hand, the present invention relates to a heavy metal ion adsorbent, which is prepared by the aforementioned method for preparing heavy metal ion adsorbents.

[0014] On the other hand, the present invention relates to the application of the aforementioned heavy metal ion adsorbent in the adsorption of heavy metal ions in water.

[0015] Furthermore, in the application provided by the present invention, the flow rate of the water is 0.5 to 1.5 m / s.

[0016] Compared with the prior art, the technical solution provided by the present invention has the following beneficial effects or advantages:

[0017] Due to its high stability, biochar has been modified in many studies, specifically by impregnating biomass in a solution containing various ions or functional groups followed by pyrolysis. The primary aim of these methods is to increase specific surface area and adsorption capacity. However, the loading of different ions onto the biomass in the impregnation solution is difficult to control, and may even lead to a relative decrease in specific surface area and adsorption capacity. This invention uses banana peel powder as a biomass raw material and modifies it by sulfonation and loading it with iron ions and silicon-containing groups. Unexpectedly, the resulting heavy metal ion adsorbent showed excellent performance in removing heavy metal ions from water containing low concentrations of heavy metal ions in a flowing state.

[0018] According to the preparation method of the heavy metal ion adsorbent provided by the present invention, banana peel powder is treated with a sulfonate solution and then impregnated in an iron-containing solution for pyrolysis. On the one hand, banana peel powder contains abundant lignin, polysaccharide, cellulose, pectin and other groups. After treatment with sulfonate solution, it can better combine with iron ions and embed itself in the pores, acting as an electron donor to facilitate complexation and adsorption, thereby facilitating the adsorption of heavy metal ions in water. On the other hand, due to the porous structure and high specific surface area of ​​banana peel powder, iron ions and / or ferrous ions in the iron-containing solution will embed into the pores of the banana peel powder, and some iron ions and / or ferrous ions will undergo hydrolysis to generate ferric hydroxide and / or ferrous hydroxide. Thus, through multiple processes such as reduction, complexation and precipitation, the adsorption of heavy metal ions in water is achieved.

[0019] According to the preparation method of the heavy metal ion adsorbent provided by the present invention, banana peel powder is impregnated with tetraethyl orthosilicate ethanol solution and then hydrolyzed under alkaline conditions. This process results in banana peel powder exhibiting hydrophobic and oleophilic characteristics and a dense porous structure, thus enriching the internal framework of the banana peel powder. On one hand, the number and types of surface functional groups in the banana peel powder are enriched after impregnation; on the other hand, the silicon-containing functional groups and sulfonation in the first and second modified banana peel powders act as binders, resulting in a composite microporous network structure containing abundant functional groups and a disordered microporous structure. This also effectively increases the reusability of the heavy metal ion adsorbent.

[0020] To effectively remove heavy metal ions from water containing low concentrations of heavy metal ions in a flowing state, biochar typically increases its specific surface area and the number of surface functional groups. In contrast, the preparation method of the heavy metal ion adsorbent provided by this invention differs from constructing a more ordered and uniform pore structure; instead, it constructs a more disordered and irregular pore structure. On one hand, this invention modifies the surface with different types of functional groups, such as iron-containing functional groups, sulfonation, and silicon-containing functional groups, and then links them together in the final preparation process. On the other hand, this invention uses short-term high-temperature treatment and alkaline treatment to prepare varying degrees of fragmentation and circular collapse on the surface. Longer high-temperature treatment or higher concentration alkaline treatment would further damage the structure, hindering the removal of heavy metal ions. Furthermore, the invention employs a combination of biomass with different particle sizes to increase the complexity of the internal pores. This preparation method allows water in a flowing state to be better retained inside the heavy metal ion adsorbent, and it can fix more heavy metal ions in a shorter time and has a shorter adsorption equilibrium time, making it more effective in removing heavy metal ions from water containing low concentrations of heavy metal ions in a flowing state. Attached Figure Description

[0021] To more clearly illustrate the technical solution of the present invention, the accompanying drawings involved in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings in the description are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 The desorption effect of thallium-containing wastewater at different concentrations is shown.

[0023] Figure 2 The desorption effect of low-concentration thallium-containing wastewater at different flow rates was studied.

[0024] Where C / C0 represents the ratio of the final concentration of thallium in the thallium-containing wastewater to the initial concentration. Detailed Implementation

[0025] The technical solution of the present invention will be described below with reference to embodiments. However, the present invention is not limited to the following embodiments. Unless otherwise specified, the experimental methods and detection methods described in each embodiment are conventional methods; unless otherwise specified, the reagents and materials are all commercially available. Unless otherwise specified, "%" represents mass percentage.

[0026] The banana peels obtained after removing the flesh from the bananas are washed with distilled water, transferred to an oven, dried at 100°C, pulverized using a universal grinder, and sieved to obtain banana peel powder with a distribution of 50-100 mesh, thus obtaining the first banana peel powder; following the same method, banana peel powder with a distribution of 400-600 mesh is obtained, thus obtaining the second banana peel powder.

[0027] Example 1

[0028] This embodiment provides a preparation process for a heavy metal ion adsorbent.

[0029] Step 1: The first banana peel powder was impregnated at a solid-liquid ratio of 20 g / L, ultrasonicated in a 1% sodium dihexyl sulfosuccinate solution for 30 min and then filtered. The mixture was then impregnated in a 0.5 mol / L ferric chloride solution, ultrasonicated for 30 min and then filtered to obtain the first modified banana peel powder.

[0030] Step 2: The second banana peel powder is impregnated at a solid-liquid ratio of 20 g / L, ultrasonicated in a 30% ammonium formate solution for 30 min, filtered, and then impregnated in an ethyl orthosilicate ethanol solution (the mass ratio of ethyl orthosilicate, ethanol, and water is 20:50:20). The mixture is stirred at 200 r / min for 30 min in a 40℃ water bath, filtered, and washed with water until neutral to obtain the second modified banana peel powder.

[0031] Step 3: Mix the first modified banana peel powder and the second modified banana peel powder in a 1:1 mass ratio by shaking until homogeneous. Then, impregnate the mixture in an ethanol solution of 0.01 mol / L sodium hydroxide at a solid-liquid ratio of 20 g / L. Stir at 200 r / min for 10 min and dry in an oven at 105 °C to obtain the precursor.

[0032] Step 4: First, heat the precursor to 350℃ at a rate of 5℃ / min and pyrolyze it at a constant temperature for 1 hour. Then, heat it to 650℃ at a rate of 5℃ / min and pyrolyze it at a constant temperature for 20 minutes. Finally, cool it down to 500℃ and pyrolyze it for 1 hour to obtain the heavy metal ion adsorbent.

[0033] Example 2

[0034] This embodiment provides a preparation process for a heavy metal ion adsorbent.

[0035] Step 1: The first banana peel powder was impregnated at a solid-liquid ratio of 20 g / L, ultrasonicated in a 2% sodium dodecyl naphthalene sulfonate solution for 30 min and then filtered. The powder was then impregnated in a 0.8 mol / L ferric sulfate solution, ultrasonicated for 30 min and then filtered to obtain the first modified banana peel powder.

[0036] Step 2: The second banana peel powder is impregnated at a solid-liquid ratio of 20 g / L, sonicated in a 35% ammonium formate solution for 30 min, filtered, and then impregnated in an ethyl orthosilicate ethanol solution (the mass ratio of ethyl orthosilicate, ethanol, and water is 25:55:25). The mixture is stirred at 300 r / min for 45 min in a 45℃ water bath, filtered, and washed with water until neutral to obtain the second modified banana peel powder.

[0037] Step 3: Mix the first modified banana peel powder and the second modified banana peel powder in a mass ratio of 1:2 by shaking until homogeneous. Then, impregnate the mixture in an ethanol solution of 0.03 mol / L potassium hydroxide at a solid-liquid ratio of 20 g / L. Stir at 300 r / min for 12 min and then dry in an oven at 110 °C to obtain the precursor.

[0038] Step 4: First, heat the precursor to 400℃ at a rate of 5℃ / min and pyrolyze it at a constant temperature for 1.5h. Then, heat it to 700℃ at a rate of 5℃ / min and pyrolyze it at a constant temperature for 30min. Finally, cool it down to 550℃ and pyrolyze it for 1.5h to obtain the heavy metal ion adsorbent.

[0039] Example 3

[0040] This embodiment provides a preparation process for a heavy metal ion adsorbent.

[0041] Step 1: The first banana peel powder was impregnated at a solid-liquid ratio of 20 g / L, ultrasonicated in a 3% sodium dodecylbenzenesulfonate solution for 30 min and then filtered. The mixture was then impregnated in a 1 mol / L ferric nitrate solution, ultrasonicated for 30 min and then filtered to obtain the first modified banana peel powder.

[0042] Step 2: The second banana peel powder is impregnated at a solid-liquid ratio of 20 g / L, ultrasonicated in a 40% ammonium formate solution for 30 min, filtered, and then impregnated in an ethyl orthosilicate ethanol solution (the mass ratio of ethyl orthosilicate, ethanol, and water is 30:60:30). The mixture is stirred at 400 r / min for 60 min in a 50℃ water bath, filtered, and washed with water until neutral to obtain the second modified banana peel powder.

[0043] Step 3: Mix the first modified banana peel powder and the second modified banana peel powder in a mass ratio of 1:3 by shaking until homogeneous. Then, impregnate the mixture in an ethanol solution of 0.05 mol / L ammonia water at a solid-liquid ratio of 20 g / L. Stir at 400 r / min for 15 min and dry in an oven at 120℃ to obtain the precursor.

[0044] Step 4: First, heat the precursor to 400℃ at a rate of 5℃ / min and pyrolyze it at a constant temperature for 2 hours. Then, heat it to 700℃ at a rate of 5℃ / min and pyrolyze it at a constant temperature for 40 minutes. Finally, cool it down to 550℃ and pyrolyze it for 2 hours to obtain the heavy metal ion adsorbent.

[0045] Comparative Example 1

[0046] This comparative example is the same as Example 1, except that in step 2, the second banana peel powder is replaced with the first banana peel powder.

[0047] Comparative Example 2

[0048] This comparative example is the same as Example 1, except that in step 3, the first modified banana peel powder and the second modified banana peel powder are taken in a 1:1 mass ratio, and then impregnated in an ethanol solution of 0.01 mol / L sodium hydroxide at a solid-liquid ratio of 20 g / L. After stirring at 200 r / min for 10 min, they are dried in an oven at 105 °C and finally mixed to obtain the precursor.

[0049] Comparative Example 3

[0050] This comparative example is the same as Example 1, except that in step 4, the precursor is first heated to 400°C at a rate of 5°C / min and kept at a constant temperature for 1.5h, then heated to 700°C at a rate of 5°C / min and kept at a constant temperature for 1h, and then cooled to 550°C and kept at a constant temperature for 1.5h to obtain a heavy metal ion adsorbent.

[0051] Example 4

[0052] This embodiment provides the adsorption performance of the heavy metal ion adsorbents prepared in Examples 1-3 and Comparative Examples 1-3.

[0053] Take 20 mL of thallium-containing wastewater with pH 7 and concentrations of 5, 10, and 100 ppm respectively into 50 mL centrifuge tubes; weigh 0.03 g of the heavy metal ion adsorbents prepared in Examples 1-3 and Comparative Examples 1-3 respectively and add them to the solutions. React in a shaker at 25°C and a constant speed of 150 rpm for 30 min. After 30 min of adsorption reaction, use a disposable syringe to take 9.5 mL of the supernatant of the reaction solution, filter it through a 0.45 μm filter, and place it in a 10 mL centrifuge tube. Add 200 μL of 1:1 nitric acid for storage. Perform three parallel experiments for each material or concentration. Determine the concentration of thallium in the solution using ICP. The experimental results are as follows: Figure 1 As shown.

[0054] Take 45cm respectively 3The heavy metal ion adsorbents prepared in Examples 1-3 and Comparative Examples 1-3 were fixed in glass tubes with a diameter of 30 mm and secured with metal mesh at both ends. They were circulated three times at flow rates of 0.5 m / s, 1 m / s, and 1.5 m / s into 500 mL of thallium-containing wastewater with a pH of 7 and a concentration of 10 ppm. The concentration of thallium in the final solution was measured, and the experimental results are as follows: Figure 2 As shown.

[0055] Depend on Figure 1 It can be seen that when used for the removal of heavy metal ions from low-concentration thallium-containing wastewater (5 ppm or 10 ppm), the heavy metal ion adsorbents prepared in Examples 1-3 have significantly higher heavy metal ion removal effects than those prepared in Comparative Examples 1-3 (p < 0.01); when used for the removal of heavy metal ions from high-concentration thallium-containing wastewater (100 ppm), the heavy metal ion removal effects of the heavy metal ion adsorbents prepared in Examples 1-3 are similar to those prepared in Comparative Examples 1-2 (p > 0.05), and better than those prepared in Comparative Example 3 (p < 0.05).

[0056] Depend on Figure 2 It can be seen that, when used for the removal of heavy metal ions from water containing low concentrations of heavy metal ions at low flow rates (0.5 m / s), the heavy metal ion adsorbents prepared in Examples 1-3 showed significantly higher heavy metal ion removal efficiency than those prepared in Comparative Examples 1-3 (p < 0.05); when used for the removal of heavy metal ions from water containing low concentrations of heavy metal ions at high flow rates (1.0 m / s or 1.5 m / s), the heavy metal ion adsorbents prepared in Examples 1-3 showed significantly higher heavy metal ion removal efficiency than those prepared in Comparative Examples 1-3 (p < 0.01).

[0057] As described above, the basic principles, main features, and advantages of the present invention have been well described. The above embodiments and specifications are merely descriptions of preferred embodiments of the present invention, and the present invention is not limited to the above embodiments. Various changes and improvements made to the technical solutions of the present invention by those skilled in the art without departing from the spirit and scope of the present invention should fall within the protection scope defined by the present invention.

Claims

1. A method for preparing a heavy metal ion adsorbent, characterized in that, include: The banana peels were crushed into first banana peel powder and second banana peel powder respectively; The first banana peel powder was successively impregnated with a sulfonate solution and an iron-containing solution to obtain the first modified banana peel powder; The second banana peel powder was successively impregnated with ammonium formate solution and ethyl orthosilicate ethanol solution, hydrolyzed under alkaline conditions, dried, and washed with water until neutral to obtain the second modified banana peel powder. By mass ratio, the first modified banana peel powder and the second modified banana peel powder are mixed in a ratio of 1:1 to 3 and impregnated in an alkaline ethanol solution to obtain a precursor. The precursor is first pyrolyzed at 350 to 400°C for 1 to 2 hours, then pyrolyzed at 650 to 700°C for 20 to 40 minutes, and finally pyrolyzed at 500 to 550°C for 1 to 2 hours.

2. The method for preparing the heavy metal ion adsorbent according to claim 1, characterized in that, The first banana peel powder has a particle size of 50-100 mesh, and the second banana peel powder has a particle size of 400-600 mesh.

3. The method for preparing the heavy metal ion adsorbent according to claim 1, characterized in that, The sulfonate is selected from at least one of sodium dodecylbenzenesulfonate, sodium dodecylnaphthalenesulfonate, and sodium dihexyl sulfosuccinate; The iron-containing solution includes at least one of ferric chloride, ferric sulfate, ferric nitrate, ferric acetate, ferrous chloride, ferrous sulfate, ferrous nitrate, and ferrous acetate. The alkali in the ethanol solution of the alkali is one of sodium hydroxide, potassium hydroxide, or ammonia.

4. The method for preparing the heavy metal ion adsorbent according to claim 3, characterized in that, The concentration of the sulfonate solution is 1–3 wt%. The concentration of the iron-containing solution is 0.5–1 mol / L; The mass ratio of tetraethyl orthosilicate, ethanol and water in the tetraethyl orthosilicate ethanol solution is 20-30:50-60:20-30. The concentration of the alkali in the ethanol solution is 0.01–0.05 mol / L; The concentration of the ammonium formate solution is 30–40 wt%.

5. The method for preparing the heavy metal ion adsorbent according to claim 1, characterized in that, The alkaline conditions are pH = 9 to 10.

6. The method for preparing the heavy metal ion adsorbent according to claim 1, characterized in that, The hydrolysis process involves stirring at 200–400 r / min for 30–60 min at 40–50 °C.

7. The method for preparing the heavy metal ion adsorbent according to claim 1, characterized in that, The ethanol solution impregnated with alkali is stirred at 200-400 r / min for 10-15 min at room temperature and then dried at 105-120℃.

8. A heavy metal ion adsorbent, characterized in that, It is prepared by the method of any one of claims 1 to 7 for the preparation of heavy metal ion adsorbent.

9. The application of the heavy metal ion adsorbent according to claim 8 in the adsorption of heavy metal ions in water.

10. The application according to claim 9, characterized in that, The water flow velocity is 0.5 to 1.5 m / s.

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