A modified kaolinite-based composite adsorbent and a preparation method and application thereof

Abstract

The application discloses a kind of composite adsorbent based on modified kaolinite and its preparation method and application, belong to resource utilization coal-based kaolinite technical field;It is after mixing kaolinite, DMSO aqueous solution is heated and stirred, then join MeOH is hydrothermally reacted, then join CTAC / MeOH solution is hydrothermally reacted and prepared tubular CK-CTAC, then chitosan is added and N, N-methylene bisacrylamide is reacted together under nitrogen environment, and composite adsorbent is obtained;The microstructure of kaolinite modification of the application is tubular, relative area and the number of functional groups are improved, after grafting chitosan, compared with traditional kaolinite and chitosan, the adsorption capacity of composite adsorbent to Pb (II) in water has been significantly improved.

Description

Technical Field

[0001] This invention belongs to the field of coal-based kaolinite technology for resource utilization, and relates to a tubular modified kaolinite grafted with chitosan composite material adsorbent, its preparation method and application. Background Technology

[0002] Large quantities of wastewater contain lead ions, and direct discharge can lead to lead pollution of water sources. Lead ions are persistent and bioaccumulative; once they enter the environment, their strong chemical stability makes them difficult to biodegrade, leading to bioaccumulation in organisms, further impacting the food chain and endangering human health. Adsorption technology, as a highly efficient and economical water treatment method, is widely used for the removal of heavy metal ions from wastewater due to its simple design, convenient operation, and low cost. Utilizing inexpensive coal-based kaolinite as an adsorbent can not only reduce solid waste problems during coal mining and achieve comprehensive resource utilization and environmental pollution reduction, but also significantly reduce adsorbent costs, possessing significant economic and environmental value. However, the insufficient adsorption capacity of natural coal-based kaolinite means that its performance in adsorbing heavy metal ions cannot meet industrial needs. Summary of the Invention

[0003] This invention overcomes the shortcomings of existing technologies by proposing a composite adsorbent based on modified kaolinite, its preparation method, and its application. It addresses the problems of land degradation caused by the low utilization rate and stockpiling of coal-based kaolinite, as well as the insufficient adsorption capacity of natural coal-based kaolinite and its inability to meet industrial demands for heavy metal ion adsorption.

[0004] To achieve the above objectives, the present invention is implemented through the following technical solution.

[0005] A method for preparing a composite adsorbent based on modified kaolinite includes the following steps:

[0006] 1) Preparation of CK-D: Kaolinite was added to a dimethyl sulfoxide aqueous solution and stirred at 60-90℃ to obtain the kaolinite / DMSO intercalation compound CK-D;

[0007] 2) Preparation of CK-M: The prepared CK-D was mixed with AlCl3 and methanol, and then hydrochloric acid was added dropwise. After hydrothermal reaction, the kaolinite / MeOH intercalation compound CK-M was obtained.

[0008] 3) Preparation of CK-CTAC: The CK-M and hexadecyltrimethylammonium chloride methanol solution were mixed and stirred and then subjected to hydrothermal reaction to obtain the kaolinite / CTAC intercalation compound CK-CTAC.

[0009] 4) Preparation of CK-CTAC / CTS: Take the CK-CTAC and chitosan, add water and stir, then add N,N-methylenebisacrylamide and potassium persulfate and stir together for 5-10 hours to obtain the composite adsorbent.

[0010] Preferably, the kaolinite is high-purity kaolinite, which is obtained by grinding coal-based kaolinite, adding hydrochloric acid, washing with water to remove impurities, sieving, filtering, drying, and then grinding.

[0011] Preferably, in step 1), after stirring, the mixture is cooled, washed, centrifuged, dried, and ground to obtain the kaolinite / DMSO intercalation compound CK-D.

[0012] Preferably, the temperature of the hydrothermal reaction in step 2) is 120°C, and the temperature of the hydrothermal reaction in step 3) is 100°C.

[0013] Preferably, in step 2), after the hydrothermal reaction, the mixture is cooled, washed, centrifuged, dried, and ground to obtain the kaolinite / MeOH intercalation compound CK-M.

[0014] Preferably, in step 3), after the hydrothermal reaction, the kaolinite / CTAC intercalation compound CK-CTAC is obtained through multiple alternating shaking and stirring operations.

[0015] Even better, after repeated alternating shaking and stirring, the kaolinite / CTAC intercalation compound CK-CTAC is obtained through washing, centrifugation, drying, and grinding.

[0016] Preferably, in step 4), the 5-10h holding period is carried out in an N2 atmosphere at 60°C.

[0017] A composite adsorbent prepared using the aforementioned method for preparing a composite adsorbent based on modified kaolinite.

[0018] The application of the composite adsorbent in adsorbing Pb(II) in water.

[0019] The beneficial effects of this invention compared to the prior art are as follows:

[0020] 1. Natural clay minerals and biopolymer materials possess advantages such as biocompatibility, non-toxicity, antimicrobial activity, and low cost. Kaolinite consists of tetrahedral silica sheets and octahedral alumina sheets linked by hydrogen bonds, forming a sheet-like structure. The biopolymer chitosan contains a large number of amino and hydroxyl groups, making it an excellent material for removing Pb(II) from wastewater. Modifying kaolinite into a tubular shape increases pore size and specific surface area, while also exposing the hydroxyl groups on the inner surface of the kaolinite, providing more sites for Pb(II) adsorption. The modified kaolinite-chitosan composite material contains a large number of hydroxyl and amino groups, exhibiting stronger adsorption capacity compared to the single material.

[0021] 2. The coal-based kaolinite in the CK-CTAC / CTS composite adsorbent proposed in this invention comes from coal-based solid waste generated during coal mining, and is inexpensive and widely available.

[0022] 3. This invention uses coal-series kaolinite as raw material, which is modified into a tubular structure through three intercalation processes. Chitosan is then grafted onto the tubular structure using N,N-methylenebisacrylamide as a crosslinking agent to obtain a composite adsorbent, overcoming the insufficient adsorption performance of natural coal-series kaolinite. The advantage of this invention lies in the fact that when the modified kaolinite is peeled and rolled into a tubular structure, the inner surface between the original kaolinite flakes becomes the tubular outer surface, exposing the hydroxyl groups on the inner surface. This increases the number of atoms on the particle surface, and the lack of atomic coordination and high surface energy give these atoms high activity, making them easily combine with other atoms, significantly improving the adsorption of heavy metals. Chitosan is abundant in nature and contains a large number of amino and hydroxyl groups, which can effectively chelate heavy metals. The synergistic adsorption effect of the two materials greatly improves the adsorption performance of the composite material for Pb(II) in water, promoting the development of water purification and comprehensive utilization of coal-based solid waste.

[0023] 4. The present invention has been verified in the adsorption of Pb(II) under different conditions. It has a significant effect compared with kaolinite and chitosan alone. At 25°C and pH 6, the adsorption rate is 94.99% and the equilibrium maximum adsorption capacity is 195.37 mg / g.

[0024] 5. Based on the characteristics, microstructure and the mechanism of hydroxyl outward turning of the inner surface of coal-based kaolinite, this invention proposes a method for preparing modified kaolinite-chitosan composite adsorbent by changing the microstructure of kaolinite and combining it with chitosan. The advantages are: (1) Coal-based kaolinite is used to prepare composite adsorbent, which achieves high-value utilization and waste treatment; (2) Modified kaolinite / chitosan composite adsorbent has a higher adsorption effect on Pb(II) in wastewater; (3) The process of modifying kaolinite uses a hydrothermal reactor and ultrasonic vibration, which accelerates the preparation of composite materials and improves the success rate of modification into tubular structure. Attached Figure Description

[0025] Figure 1 This represents the particle size distribution of coal-series kaolinite after pretreatment.

[0026] Figure 2 The image shows the XRD pattern of coal-bearing kaolinite after pretreatment.

[0027] Figure 3 for Figure 2 Enlarged view of the area within the dashed box.

[0028] Figure 4 The XRD patterns of the various intercalation products of the prepared tubular modified kaolinite are shown.

[0029] Figure 5 for Figure 4 An enlarged view of the area between the two dashed line segments.

[0030] Figure 6 SEM images of the various intercalation products of the prepared tubular modified kaolinite are shown, where (a) is kaolinite after coal-series kaolinite pretreatment, (b) is CK-D, (c) is CK-M, and (d) is CK-CTAC.

[0031] Figure 7 The images show SEM images of chitosan and the composite adsorbent, where (a) is chitosan and (b) is the composite adsorbent.

[0032] Figure 8 The performance curves of the CK-CTAC / CTS composite adsorbent, the best sample prepared, adsorbed Pb(II) under different pH conditions are shown.

[0033] Figure 9 The adsorption performance curves of the optimal sample CK-CTAC / CTS composite adsorbent for Pb(II) under different temperature conditions are shown. Detailed Implementation

[0034] To make the technical problems to be solved, the technical solutions, and the beneficial effects of this invention clearer, the invention will be further described in detail with reference to the embodiments and accompanying drawings. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. The technical solutions of this invention are described in detail below with reference to the embodiments and accompanying drawings, but the scope of protection is not limited thereto.

[0035] Example 1

[0036] S1: Coal-based kaolinite pretreatment: After grinding the coal-based kaolinite, a small amount of hydrochloric acid is added, and the impurities are removed by washing with water. The kaolinite is then sieved using a 325-mesh sieve, filtered, dried, and ground to obtain high-purity kaolinite (CK).

[0037] S2: Preparation of CK-D: 300 mL of DMSO (dimethyl sulfoxide) and 30 mL of ultrapure water were stirred at room temperature for 10 min, then 30 g of CK was added and stirring was continued for 20 min. The mixture was placed in an 80℃ water bath and stirred for 3 h. After cooling to room temperature, it was washed with water, centrifuged, dried in a 50℃ vacuum drying oven, and then ground to obtain the kaolinite / DMSO intercalation compound CK-D.

[0038] S3: Preparation of CK-M: 4 g CK-D, 50 mL MeOH (methanol), and 0.5 g AlCl3 were mixed and stirred. Then, 5 mL of hydrochloric acid was added dropwise. The mixture was poured into a hydrothermal reactor at 120 ℃ and stirred for 1 h. After cooling to room temperature, the mixture was washed several times with 50 mL of MeOH solution, centrifuged, vacuum dried, and ground to obtain the kaolinite / MeOH intercalation compound CK-M.

[0039] S4: Preparation of CK-CTAC: 3 g of CK-M and 50 ml of 1 mol / L CTAC (hexadecyltrimethylammonium chloride) / MeOH solution were mixed and stirred for 20 min, then transferred to a hydrothermal reactor at 100 ℃ and stirred for 30 h. After cooling to room temperature, the mixture was placed in an Erlenmeyer flask and ultrasonically vibrated for 1 h. After stirring for 30 min, the mixture was vibrated for another 1 h. This cycle was repeated 3 times. After washing, centrifugation, vacuum drying, and grinding, the kaolinite / CTAC intercalation compound CK-CTAC was obtained.

[0040] S5: Preparation of CK-CTAC / CTS: 2 g of CK-CTAC and CTS (chitosan) in different mass ratios were placed in a three-necked flask, water was added and stirred for 30 min, followed by the addition of 1 g of N,N-methylenebisacrylamide and 0.5 g of potassium persulfate, and stirred for 5 min. The mixture was kept at 60 ℃ in a N2 atmosphere for 8 h. After cooling to room temperature, the mixture was washed, filtered, vacuum dried and ground to obtain composite adsorbents with different proportions.

[0041] Example 2

[0042] S1: Perform coal-series kaolinite pretreatment according to Example 1.

[0043] S2: Preparation of CK-D: 300 mL of DMSO and 30 mL of ultrapure water were stirred at room temperature for 10 min, then 30 g of CK was added and stirring was continued for 20 min. After stirring the mixture for 3 h, it was washed with water, centrifuged, dried in a vacuum drying oven at 50 ℃, and then ground to obtain the kaolinite / DMSO intercalation compound CK-D.

[0044] S3: Preparation of CK-M: 4 g CK-D, 50 mL MeOH, and 0.5 g AlCl3 were mixed and stirred. Then, 5 mL hydrochloric acid was added dropwise. The mixture was poured into a hydrothermal reactor at 120 ℃ and stirred for 1 h. After cooling to room temperature, the mixture was washed several times with 50 mL MeOH solution, centrifuged, vacuum dried, and ground to obtain the kaolinite / MeOH intercalation compound CK-M.

[0045] S4: Preparation of CK-CTAC: 3 g of CK-M and 50 ml of 1 mol / L CTAC / MeOH solution were mixed and stirred for 20 min, then transferred to a hydrothermal reactor at 100 ℃ and stirred for 30 h. After cooling to room temperature, the mixture was placed in an Erlenmeyer flask and shaken in an ultrasonic oscillator for 1 h. After stirring for 30 min, the shaking was continued for 1 h. This cycle was repeated 3 times. After washing, centrifugation, vacuum drying, and grinding, the kaolinite / CTAC intercalation compound CK-CTAC was obtained.

[0046] S5: Preparation of CK-CTAC / CTS: 2 g of CK-CTAC and CTS in different mass ratios were placed in a three-necked flask, water was added and the mixture was stirred for 30 min. Then, 1 g of N,N-methylenebisacrylamide and 0.5 g of potassium persulfate were added and stirred for 5 min. The mixture was kept in a N2 atmosphere at 60 ℃ for 8 h. After cooling to room temperature, the mixture was washed, filtered, vacuum dried and ground to obtain composite adsorbents with different proportions.

[0047] Example 3

[0048] S1~S2: Coal-based kaolinite pretreatment and CK-D preparation were carried out according to Example 1.

[0049] S3: Preparation of CK-M. 4 g of CK-D, 50 mL of MeOH and 0.5 g of AlCl3 were mixed and stirred. Then, 5 mL of hydrochloric acid was added dropwise. After stirring the mixture for 1 h, it was washed several times with 50 mL of MeOH solution, centrifuged, vacuum dried and ground to obtain the kaolinite / MeOH intercalation compound CK-M.

[0050] S4: Preparation of CK-CTAC. 3 g of CK-M and 50 ml of 1 mol / L CTAC / MeOH solution were mixed and stirred for 20 min, then transferred to a hydrothermal reactor at 100 ℃ and stirred for 30 h. After cooling to room temperature, the mixture was placed in an Erlenmeyer flask and ultrasonically vibrated for 1 h. After stirring for 30 min, the mixture was vibrated for another 1 h. This cycle was repeated 3 times. After washing, centrifugation, vacuum drying, and grinding, the kaolinite / CTAC intercalation compound CK-CTAC was obtained.

[0051] S5: Preparation of CK-CTAC / CTS. 2 g of CK-CTAC and CTS in different mass ratios were placed in a three-necked flask, water was added, and the mixture was stirred for 30 min. Then, 1 g of N,N-methylenebisacrylamide and 0.5 g of potassium persulfate were added, and the mixture was stirred for 5 min. The mixture was kept at 60 ℃ under a N2 atmosphere for 8 h. After cooling to room temperature, the mixture was washed, filtered, vacuum dried, and ground to obtain composite adsorbents with different proportions.

[0052] Example 4

[0053] S1~S3: Coal-based kaolinite pretreatment, CK-D and CK-M preparation were carried out according to Example 1.

[0054] S4: Preparation of CK-CTAC. 3 g of CK-M and 50 ml of 1 mol / L CTAC / MeOH solution were mixed and stirred for 30 h, then placed in an Erlenmeyer flask and ultrasonically vibrated for 1 h. After stirring for 30 min, the mixture was vibrated for another 1 h. This cycle was repeated 3 times. After washing, centrifugation, vacuum drying, and grinding, the kaolinite / CTAC intercalation compound CK-CTAC was obtained.

[0055] S5: Preparation of CK-CTAC / CTS. 2 g of CK-CTAC and CTS in different mass ratios were placed in a three-necked flask, water was added, and the mixture was stirred for 30 min. Then, 1 g of N,N-methylenebisacrylamide and 0.5 g of potassium persulfate were added, and the mixture was stirred for 5 min. The mixture was kept at 60 ℃ under a N2 atmosphere for 8 h. After cooling to room temperature, the mixture was washed, filtered, vacuum dried, and ground to obtain composite adsorbents with different proportions.

[0056] Example 5

[0057] S1~S3: Coal-based kaolinite pretreatment, CK-D and CK-M preparation were carried out according to Example 1.

[0058] S4: Preparation of CK-CTAC. 3 g of CK-M and 50 ml of 1 mol / L CTAC / MeOH solution were mixed and stirred for 20 min, then transferred to a hydrothermal reactor at 100 ℃ and stirred for 30 h. After cooling to room temperature, the mixture was washed, centrifuged, vacuum dried, and ground to obtain the kaolinite / CTAC intercalation compound CK-CTAC.

[0059] S5: Preparation of CK-CTAC / CTS. 2 g of CK-CTAC and CTS in different mass ratios were placed in a three-necked flask, water was added, and the mixture was stirred for 30 min. Then, 1 g of N,N-methylenebisacrylamide and 0.5 g of potassium persulfate were added, and the mixture was stirred for 5 min. The mixture was kept at 60 ℃ under a N2 atmosphere for 8 h. After cooling to room temperature, the mixture was washed, filtered, vacuum dried, and ground to obtain composite adsorbents with different proportions.

[0060] Example 6

[0061] S1~S4: Prepare coal-series kaolinite pretreatment, CK-D, CK-M and CK-CTAC according to Example 1.

[0062] S5: Preparation of CK-CTAC / CTS. 2 g of CK-CTAC and CTS in different mass ratios were placed in a three-necked flask, water was added and the mixture was stirred for 30 min. The mixture was then kept at 60 ℃ under a N2 atmosphere for 8 h. After cooling to room temperature, the flasks were washed, filtered, vacuum dried, and ground to obtain composite adsorbents with different proportions.

[0063] The above are merely comparative embodiments of the present invention and are not limited to the scope of the present invention. All equivalent changes and modifications made within the scope of the present invention should be considered within the technical scope of the present invention.

[0064] Figure 1 The particle size distribution of coal-series kaolinite after pretreatment is 2-5 μm, which meets the test requirements.

[0065] Figure 2 The image shows the XRD pattern of coal-bearing kaolinite after pretreatment. Figure 3 for Figure 2 The magnified view within the dashed box shows the characteristic peaks d(001) 7.14 Å and d(002) 3.57 Å, along with five distinct split diffraction peaks between d(001) and d(002), indicating that it fully conforms to the characteristics of kaolinite crystals. The Hinckley index (HI) calculates the crystallinity of CK to be 1.40, reaching a high crystallinity level.

[0066] Figure 4 The XRD patterns of the various intercalation products of the prepared tubular modified kaolinite are shown. Figure 5 for Figure 4 The enlarged view between the two dashed lines shows that the interlayer spacing of kaolinite continuously changes during the three-step intercalation process. The initial interlayer spacing d used in the experiment was 7.14 Å. When DMSO molecules were intercalated into the kaolinite interlayer, the original peaks almost disappeared, and a new sharp diffraction peak with a d value of 11.16 Å appeared at 7.86 °, indicating successful preparation of CK-D. After MeOH intercalation, MeOH molecules replaced DMSO molecules and were inserted into the kaolinite interlayer, reducing the d value from 11.16 Å to 8.53 Å. The original diffraction peaks disappeared, and a new diffraction peak appeared at 10.36 °. The intensity of the diffraction peak at 12.38 ° increased, suggesting that some CK-D reverted to CK. After CTAC intercalation, a new diffraction peak with a d value of 39.42 Å appeared at 2.42 °, indicating successful preparation of CK-CTAC.

[0067] Figure 6SEM images of the various intercalation products of the prepared tubular modified kaolinite are shown. After intercalation with DMSO and MeOH, the intermediate intercalators CK-D(b) and CK-M(c) show the same morphology as CK, except for changes in interlayer spacing; both exhibit a hexagonal lamellar stacked structure. CK-CTAC(d) shows a significant morphological change after the experiment, with the lamellar structure detaching and curling, some completely curling to form a tubular shape, thus completing the preparation of the tubular modified kaolinite.

[0068] Figure 7 The images show SEM images of chitosan and the composite adsorbent. Chitosan exhibits an irregular, large, flat morphology with a relatively smooth surface. In the composite adsorbent, chitosan is fragmented and adheres to the surface of the tubular CK-CTAC, resulting in an overall irregular, three-dimensional spatial structure.

[0069] Figure 8 The adsorption performance curves of the best sample CK-CTAC / CTS composite adsorbent for Pb(II) under different pH conditions show that the adsorption performance is optimal at pH 6.

[0070] Figure 9 The adsorption performance curves of the best sample CK-CTAC / CTS composite adsorbent for Pb(II) under different temperature conditions show that the adsorption performance is basically at its maximum at 25℃.

[0071] The above description is a further detailed explanation of the present invention in conjunction with specific preferred embodiments. It should not be considered that the specific embodiments of the present invention are limited to this. For those skilled in the art, several simple deductions or substitutions can be made without departing from the present invention, and all of these should be considered to fall within the scope of patent protection determined by the submitted claims.

Claims

1. Use of a modified kaolinite-based composite adsorbent for adsorbing Pb(II) in water, characterized in that, The composite adsorbent is used for adsorbing Pb(II) in water at pH 6 and temperature 25℃. The preparation method of the modified kaolinite-based composite adsorbent comprises the following steps: 1) preparation of CK-D: kaolinite is added into dimethyl sulfoxide aqueous solution and treated by stirring at 60-90℃ to obtain a kaolinite / DMSO intercalation compound CK-D; 2) preparation of CK-M: the prepared CK-D is mixed with AlCl3 and methanol, and then hydrochloric acid is added dropwise, and then hydrothermal reaction is carried out to obtain a kaolinite / MeOH intercalation compound CK-M; 3) preparation of CK-CTAC: the CK-M and a methanol solution of cetyltrimethylammonium chloride are mixed and stirred, and then hydrothermal reaction is carried out, and then multiple alternating operations of oscillation and stirring are carried out, and then washing, centrifugation, drying and grinding are carried out to obtain a tubular kaolinite / CTAC intercalation compound CK-CTAC; 4) preparation of CK-CTAC / CTS: the CK-CTAC and chitosan are mixed and stirred with water, and then N,N-methylenebisacrylamide and potassium persulfate are added and stirred together for 5-10h to obtain the modified kaolinite-based composite adsorbent.

2. Use according to claim 1, characterized in that, The kaolinite is high-purity kaolinite, which is prepared by grinding coal-based kaolinite, adding hydrochloric acid, removing impurities by water washing, screening, vacuum filtration and drying, and then grinding.

3. Use according to claim 1, characterized in that, In step 1), after stirring, cooling, water washing, centrifugation, drying and grinding, the kaolinite / DMSO intercalation compound CK-D is obtained.

4. Use according to claim 1, characterized in that, In step 2), the temperature of the hydrothermal reaction is 120℃, and in step 3), the temperature of the hydrothermal reaction is 100℃.

5. The use according to claim 1, characterized in that, In step 2), after hydrothermal reaction, cooling, water washing, centrifugation, drying and grinding, the kaolinite / MeOH intercalation compound CK-M is obtained.

6. Use according to claim 1, characterized in that, In step 4), the 5-10h of keeping is carried out in an N2 atmosphere at 60℃.

Images