A halloysite-based adsorbent and its preparation method and application

Abstract

The application discloses a kind of halloysite-based adsorbents and its preparation method and application, belong to fluoride removal agent material technical field, soluble Al 3+ Salt solution is dropped into 50~95 ℃ halloysite and alkali metal Cl ‑ In the suspension formed by salt solution, pH value is controlled to be 8~11, co-precipitation reaction, Al 3+ And Cl ‑ Form [AlCl4] ‑ Coordination, hydrolysis boehmite type alumina and load in halloysite, obtain composite product;The composite product is calcined at 400~700 ℃, and halloysite-based adsorbent is obtained.The crystal form of the alumina loaded under the condition of pH=8~11 synthesized in the application is boehmite, and it can be converted into active alumina with relatively large adsorption activity to fluoride ion by calcining at 400~700 ℃, and the active alumina is mainly loaded in the inner / outer tube of halloysite, which is a wormhole porous structure, and the loading of active alumina improves the micropore ratio of the adsorbent, thereby improving the adsorption performance.

Description

Technical Field

[0001] The present invention relates to the technical field of fluorine removal agent materials, and in particular to a halloysite-based adsorbent and a preparation method and application thereof. Background Art

[0002] With the rapid development of emerging industries such as semiconductors in my country, fluoride-containing wastewater has gradually become an important source of environmental fluoride pollution, which poses a serious challenge to human survival and safety. The high-concentration fluoride ion removal technology currently in practical use is mainly the pharmaceutical method, but it can usually only treat fluoride ions to about 10 mg / L, which is much higher than the 1.5 mg / L drinking water standard stipulated by the World Health Organization. In order to obtain low-fluoride water, the water pre-treated by the pharmaceutical method needs to be further deeply defluorinated. Among various methods, the adsorption method has a simple process, easy operation and low cost, and has attracted much attention. Among them, the development of efficient fluoride ion adsorption materials is the key to achieving deep defluorination.

[0003] Activated alumina, with its high specific surface area and excellent fluoride removal performance, is often considered an ideal material for deep defluorination. However, its high synthesis cost, narrow adsorption pH range, and tendency to agglomerate limit its practical defluoridation effectiveness. Morphology manipulation, pore creation, and composite methods can enhance alumina's fluoride removal performance.

[0004] Clay minerals such as kaolinite, illite, attapulgite, and halloysite are abundant, cost-effective, and environmentally friendly. Halloysite, with its unique tubular morphology, has attracted widespread attention and is often used in chemical catalysis, antibacterial and anti-inflammatory treatment, drug delivery, and wastewater treatment. However, its fluoride removal capacity is relatively low. Summary of the Invention

[0005] The present invention provides a halloysite-based adsorbent, a preparation method and application thereof, which effectively solves the technical problems of high defluorination cost and low defluorination efficiency when using single activated alumina or halloysite as a defluorination agent. The present invention uses natural tubular halloysite mineral as a carrier, first loads boehmite-type alumina on the halloysite surface through a simple co-precipitation method, and then further calcines and activates it to prepare a composite adsorbent with activated alumina loaded on the inner and outer tube walls of the halloysite.

[0006] The first object of the present invention is to provide a method for preparing a halloysite-based adsorbent, comprising the following steps:

[0007] The soluble Al 3+ The salt solution is dropped into 50℃~95℃ halloysite and alkali metal Cl - In the suspension formed by the salt solution, the pH value is controlled at 8-11, and the coprecipitation reaction is carried out. 3+ With Cl - Formation of [AlCl4] -The ligand is then hydrolyzed to obtain boehmite-type alumina, which is then loaded on halloysite to obtain a composite product;

[0008] The composite product is calcined at 400-700° C. to obtain a halloysite-based adsorbent.

[0009] As a preferred embodiment, the alkali metal Cl - Cl in salt solution - The concentration of the soluble Al 3+ Al in salt solution 3+ The concentration of the alkali metal Cl is 10 to 100 mol / mL. - Salt solution and soluble Al 3+ The volume ratio of the salt solution is 1-5:1-5.

[0010] As a preferred embodiment, the halloysite and the alkali metal Cl - The dosage ratio of the saline solution is 0.2-5g:30ml.

[0011] As a preferred embodiment, the coprecipitation reaction time is 10 minutes to 24 hours.

[0012] As a preferred embodiment, the calcination time is 1 to 6 hours.

[0013] As a preferred embodiment, the soluble Al 3+ The salt is one or more of aluminum sulfate, aluminum nitrate, aluminum chloride and alum.

[0014] As a preferred embodiment, after the coprecipitation reaction is completed, centrifugation is performed to obtain a primary product, and the primary product is washed and dried at 50° C. to 60° C. overnight to obtain a composite product.

[0015] The second object of the present invention is to provide a halloysite-based adsorbent prepared by the above preparation method.

[0016] The third object of the present invention is to provide a use of the above-mentioned halloysite-based adsorbent in removing fluoride ions in water.

[0017] As a preferred embodiment, the concentration of fluoride ions in the water body is ≤10 mg / L.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] (1) The present invention firstly combines halloysite with alkali metal Cl - Mix the salt solution to obtain a suspension; at 50℃~95℃, soluble Al 3+The salt solution is dripped into the suspension, the pH value is controlled to 8-11, a coprecipitation reaction occurs, and the alkali metal Cl is added - Salt, on the one hand, is beneficial to the chloride ion and Al 3+ [AlCl4] is preferentially generated - The ligand slowly hydrolyzes to form boehmite, which facilitates migration to the halloysite surface to form a load, thereby obtaining a composite product. Furthermore, it can increase the solution viscosity and reduce the continuity of the boehmite, facilitating the subsequent formation of an activated alumina nanostructure. The composite product is heated to 400°C to 700°C and calcined to obtain a halloysite-based adsorbent. The loaded alumina synthesized under pH conditions of 8 to 11 has a boehmite crystalline form, and calcination at 400°C to 700°C converts it into activated alumina with greater fluoride ion adsorption activity. The activated alumina is primarily loaded in the inner and outer tubes of the halloysite, forming a wormhole porous structure. The loaded activated alumina increases the micropore ratio of the adsorbent material, thereby improving adsorption performance.

[0020] (2) The present invention only uses conventional soluble aluminum salts, alkali metal chlorides and natural halloysite minerals as reaction reagents and raw materials, instead of expensive metal salts and artificial synthetic carriers. The synthesis method is simple, does not require special equipment, and effectively reduces production costs. The present invention uses tubular halloysite as a carrier, which effectively improves the dispersibility of activated alumina nanoparticles and reduces their agglomeration; the loaded alumina has porous wormhole characteristics and exists simultaneously in the inner and outer tubes of the halloysite, and the crystal form is the γ type that is most favorable for fluoride ion adsorption, so the adsorption efficiency is high and the adsorption capacity is large, and it can deeply defluorinate fluoride-containing wastewater with a fluoride ion concentration of less than 10 mg / L to less than 1 mg / L. In addition, compared with pure alumina, the amount of alumina used in the halloysite-based composite defluoridant is reduced, so the price of the defluoridant per unit mass is significantly reduced.

[0021] (3) The halloysite-based adsorbent prepared by the present invention has excellent fluoride removal performance. It can effectively remove fluoride ions in water bodies in both acidic and alkaline environments. In a solution environment with a pH of 3, it can still maintain a fluoride ion removal rate of more than 98% under a lower dosage of 0.125 g / L. In the defluoridation process, it is not interfered by other coexisting anions such as nitrate, carbonate, bicarbonate and sulfate, and can specifically remove fluoride ions in water bodies. Under low-dose usage, the fluoride removal efficiency of the halloysite-based adsorbent prepared by the present invention is also greater than that of commercial activated alumina balls, and has obvious cost advantages.

[0022] (4) In the process of removing fluoride ions from water, the adsorption of fluoride ions does not change the physical structure of the halloysite-based adsorbent material. Fluoride ions are first adsorbed on the inner and outer tube surfaces and edge parts of the adsorbent material through physical action, and then the Al-coordinated OH in the halloysite-based adsorbent material and F -Exchange is carried out, so as to firmly combine fluoride ions, and the effect of removing fluoride ions in water bodies is achieved. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 Transmission electron micrographs of halloysite-based adsorbent HA8-600 prepared in Example 1 of the present application and raw halloysite H; wherein, a figure is a partial morphology of halloysite H with tubular morphology; b figure and c figure are partial morphologies of halloysite-based adsorbent HA8-600 loaded with alumina inside and outside the tube; d figure is active alumina with porous wormhole morphology in halloysite-based adsorbent HA8-600; e figure is a crystal lattice fringe pattern of alumina in halloysite-based adsorbent HA8-600.

[0024] Figure 2 XRD spectra of halloysite (H), composite product (HA8) and halloysite-based adsorbent (HA8-600) in Example 1 of the present application.

[0025] Figure 3 Infrared spectra of halloysite (H), composite product (HA8) and halloysite-based adsorbent (HA8-600) in Example 1 of the present application.

[0026] Figure 4 Nitrogen adsorption isotherm curves of halloysite (H), composite product (HA8) and halloysite-based adsorbent (HA8-600) in Example 1 of the present application.

[0027] Figure 5 Pore size distribution diagrams of halloysite (H), composite product (HA8) and halloysite-based adsorbent (HA8-600) in Example 1 of the present application.

[0028] Figure 6 Fluoride removal rate comparison diagram of halloysite (H), composite product (HA8) and halloysite-based adsorbent (HA8-600) in Example 1 of the present application under the conditions of dosage of 0.5 g / L, fluoride removal time of 6 h, temperature of 30℃, initial concentration C0 of fluoride ion solution of 10 mg / L and pH of 4.

[0029] Figure 7 Fluoride removal rate comparison diagram of halloysite-based adsorbent (HA8-600) prepared in Example 1 of the present application in different pH water bodies under the conditions of dosage of 0.5 g / L, fluoride removal time of 6 h, temperature of 30℃ and initial concentration C0 of fluoride ion solution of 10 mg / L.

[0030] Figure 8 Fluoride removal rate (Removal) and equilibrium adsorption capacity (q) of halloysite-based adsorbent prepared in Example 1 of the present application at different dosages under the conditions of pH value of 4, fluoride removal time of 6 h, temperature of 30℃ and initial concentration C0 of fluoride ion solution of 10 mg / L.e ) comparison chart.

[0031] Figure 9 This figure shows the influence of coexisting anions in water on the fluoride removal performance of the halloysite-based adsorbent prepared in Example 1 of the present invention under the conditions of a dosage of 0.5 g / L, a pH value of 4, a fluoride removal time of 6 h, a temperature of 30°C, and an initial concentration C0 of the fluoride ion solution of 10 mg / L.

[0032] Figure 10 This is a comparison chart of the fluoride removal performance of the halloysite-based adsorbent HA8-600 prepared in Example 1 of the present invention and a commercial activated alumina defluoridator under more optimal pH conditions (pH = 3); wherein, the fluoride removal time is 6 hours, the temperature is 30°C, and the initial concentration C0 of the fluoride ion solution is 10 mg / L. DETAILED DESCRIPTION

[0033] To enable those skilled in the art to better understand and implement the technical solutions of the present invention, the present invention is further described below with reference to specific examples and accompanying drawings. However, the examples are not intended to limit the present invention. The following experimental and detection methods are conventional methods unless otherwise specified; the reagents and raw materials are commercially available unless otherwise specified.

[0034] In response to the technical problems mentioned in the background technology of the present invention: when activated alumina is used as a defluoridating agent, its synthesis cost is high, the adsorption pH range is narrow, and it is easy to agglomerate, resulting in poor defluoridation effect; when halloysite is used as a defluoridating agent, its defluoridation capacity is low, the present invention provides a halloysite-based adsorbent and its preparation method and application.

[0035] The technical solution of the present invention is now analyzed and explained in detail.

[0036] The present invention first provides a method for preparing a halloysite-based adsorbent, comprising the following steps:

[0037] The soluble Al 3+ The salt solution is dropped into 50℃~95℃ halloysite and alkali metal Cl - In the suspension formed by the salt solution, the pH value is controlled at 8-11, and the coprecipitation reaction is carried out. 3+ With Cl - Formation of [AlCl4] - The ligand is then hydrolyzed to obtain boehmite-type alumina, which is then loaded onto halloysite and centrifuged to obtain a primary product. The primary product is washed and dried overnight at 50°C to 60°C to obtain a composite product. The suspension temperature is 50°C to 95°C. If the reaction temperature is too high, such as above 100°C, the water will evaporate quickly due to the open reaction system. Otherwise, a high-pressure reactor is required, which increases production costs. If the temperature is too low, the reaction time is longer, which reduces production efficiency.

[0038] The composite product is calcined at 400-700°C to obtain the halloysite-based adsorbent.

[0039] In the above technical solution, the crystal form of the alumina-loaded adsorbent synthesized under the condition of pH=8-11 is boehmite, and the calcination at 400°C-700°C can convert it into active alumina with high adsorption activity for fluoride ions. The active alumina is mainly loaded in the inner / outer tube of halloysite, forming a wormhole porous structure, and the loading of active alumina increases the micropore proportion of the adsorbent material, thereby improving the adsorption performance.

[0040] It is emphasized that the concentration of Cl - in the alkali metal Cl - salt solution is 0.01-0.2 g / mL, the concentration of Al 3+ in the soluble Al 3+ salt solution is 10-100 mol / mL, and the volume ratio of the alkali metal Cl - salt solution to the soluble Al 3+ salt solution is 1-5:1-5. If the concentration of Cl - is too low, it is not conducive to the formation of nano-loading on the surface of halloysite through the "first ligand formation and then slow hydrolysis" mode; if the concentration of Cl - is too high, the preparation time is increased and the production cost is increased. Similarly, if the concentration of Al 3+ is too low, the amount of active alumina finally loaded on the surface of halloysite is too small, resulting in low overall adsorption efficiency; and if the concentration of Al 3+ is too high, the active alumina formed is prone to agglomeration on the surface of halloysite, reducing the surface active sites.

[0041] It is emphasized that the usage ratio of halloysite to the alkali metal Cl - salt solution is 0.2-5 g:30 mL. If the usage of halloysite is less than 0.2 g, it will cause waste of alkali metal chloride salt and aluminum salt; and if the usage of halloysite is greater than 5 g, it will inevitably cause waste of halloysite.

[0042] As a preferred embodiment, the time of the coprecipitation reaction is 10 min-24 h. If the time is too short, the amount of boehmite loaded on the surface of halloysite is too small, and when the reaction time is greater than 24 h, the coprecipitation reaction has already ended, and increasing the time is not beneficial to the production of alumina.

[0043] As a preferred embodiment, the calcination time is 1-6 h. If the calcination time is less than 1 h, it will cause incomplete conversion of boehmite to active alumina; and if the calcination time is longer than 6 h, the conversion has already been completed, and increasing the calcination time is not beneficial to the conversion rate.

[0044] It should be noted that the soluble Al 3+ The salt is one or more of aluminum sulfate, aluminum nitrate, aluminum chloride and alum.

[0045] The technical effects of the present invention are described below with reference to specific embodiments and comparative examples.

[0046] Example 1

[0047] A method for preparing a halloysite-based adsorbent comprises the following steps:

[0048] 5 g of halloysite (denoted as H) was mixed with 150 mL of a 0.02 g / mL sodium chloride aqueous solution to obtain a suspension; 150 mL of a 20 mmol / L aluminum nitrate solution was dropwise added to the suspension at 80° C. while controlling the pH value to 8. A coprecipitation reaction was performed for 2 h. The mixture was centrifuged, washed, and dried to obtain a composite product of boehmite supported on halloysite, denoted as HA8; the composite product was calcined at 600° C. for 3 h to obtain a halloysite-based adsorbent, denoted as HA8-600.

[0049] Example 2

[0050] A method for preparing a halloysite-based adsorbent comprises the following steps:

[0051] 5 g of halloysite was mixed with 150 mL of a 0.01 g / mL sodium chloride aqueous solution to obtain a suspension; 150 mL of a 20 mmol / L aluminum nitrate solution was dropwise added to the suspension at 80° C. while controlling the pH value to 8, and a coprecipitation reaction was performed for 2 hours. The mixture was centrifuged, washed, and dried to obtain a composite product in which boehmite was loaded on halloysite; the composite product was calcined at 600° C. for 3 hours to obtain a halloysite-based adsorbent.

[0052] Example 3

[0053] A method for preparing a halloysite-based adsorbent comprises the following steps:

[0054] 5 g of halloysite was mixed with 150 mL of a 0.2 g / mL sodium chloride aqueous solution to obtain a suspension; 150 mL of a 20 mmol / L aluminum nitrate solution was dropped into the suspension at 80° C. while controlling the pH value to 8, and a coprecipitation reaction was performed for 2 hours. The mixture was centrifuged, washed, and dried to obtain a composite product in which boehmite was loaded on halloysite; the composite product was calcined at 600° C. for 3 hours to obtain a halloysite-based adsorbent.

[0055] Example 4

[0056] A method for preparing a halloysite-based adsorbent comprises the following steps:

[0057] Mixing 5 g of halloysite with 150 mL of 0.02 g / mL sodium chloride aqueous solution to obtain a suspension; dropping 150 mL of 10 mmol / L aluminum nitrate solution into the suspension at 80°C while controlling the pH value to be 8, and performing a coprecipitation reaction for 2 h, centrifuging, washing, and drying to obtain a composite product of boehmite loaded on halloysite; calcining the composite product at 600°C for 3 h to obtain a halloysite-based adsorbent.

[0058] Example 5

[0059] A method for preparing a halloysite-based adsorbent, comprising the following steps:

[0060] Mixing 5 g of halloysite with 150 mL of 0.02 g / mL sodium chloride aqueous solution to obtain a suspension; dropping 150 mL of 10 mmol / L aluminum nitrate solution into the suspension at 80°C while controlling the pH value to be 8, and performing a coprecipitation reaction for 2 h, centrifuging, washing, and drying to obtain a composite product of boehmite loaded on halloysite; calcining the composite product at 600°C for 3 h to obtain a halloysite-based adsorbent.

[0061] Example 6

[0062] A method for preparing a halloysite-based adsorbent, comprising the following steps:

[0063] Mixing 5 g of halloysite with 150 mL of 0.02 g / mL sodium chloride aqueous solution to obtain a suspension; dropping 150 mL of 10 mmol / L aluminum nitrate solution into the suspension at 80°C while controlling the pH value to be 8, and performing a coprecipitation reaction for 2 h, centrifuging, washing, and drying to obtain a composite product of boehmite loaded on halloysite; calcining the composite product at 600°C for 3 h to obtain a halloysite-based adsorbent.

[0064] Example 7

[0065] A method for preparing a halloysite-based adsorbent, comprising the following steps:

[0066] Mixing 5 g of halloysite with 150 mL of 0.02 g / mL sodium chloride aqueous solution to obtain a suspension; dropping 150 mL of 10 mmol / L aluminum nitrate solution into the suspension at 80°C while controlling the pH value to be 8, and performing a coprecipitation reaction for 2 h, centrifuging, washing, and drying to obtain a composite product of boehmite loaded on halloysite; calcining the composite product at 600°C for 3 h to obtain a halloysite-based adsorbent.

[0067] Example 8

[0068] A method for preparing a halloysite-based adsorbent, comprising the following steps:

[0069] 5g of halloysite was mixed with 50mL of 0.02g / mL sodium chloride aqueous solution to obtain a suspension; 250mL of 20mmol / L aluminum nitrate solution was dropped into the suspension at 80℃ while controlling the pH value to be 8, and a coprecipitation reaction was carried out for 2h, and then centrifugation, washing and drying were performed to obtain a composite product of boehmite loaded on halloysite; and the composite product was calcined at 600℃ for 3h to obtain a halloysite-based adsorbent.

[0070] Example 9

[0071] A method for preparing a halloysite-based adsorbent, comprising the following steps:

[0072] 5g of halloysite was mixed with 250mL of 0.02g / mL sodium chloride aqueous solution to obtain a suspension; 50mL of 20mmol / L aluminum nitrate solution was dropped into the suspension at 80℃ while controlling the pH value to be 8, and a coprecipitation reaction was carried out for 2h, and then centrifugation, washing and drying were performed to obtain a composite product of boehmite loaded on halloysite; and the composite product was calcined at 600℃ for 3h to obtain a halloysite-based adsorbent.

[0073] Example 10

[0074] A method for preparing a halloysite-based adsorbent, comprising the following steps:

[0075] 5g of halloysite was mixed with 150mL of 0.02g / mL sodium chloride aqueous solution to obtain a suspension; 150mL of 20mmol / L aluminum nitrate solution was dropped into the suspension at 95℃ while controlling the pH value to be 8, and a coprecipitation reaction was carried out for 10min, and then centrifugation, washing and drying were performed to obtain a composite product of boehmite loaded on halloysite; and the composite product was calcined at 600℃ for 3h to obtain a halloysite-based adsorbent.

[0076] Example 11

[0077] A method for preparing a halloysite-based adsorbent, comprising the following steps:

[0078] 5g of halloysite was mixed with 150mL of 0.02g / mL sodium chloride aqueous solution to obtain a suspension; 150mL of 20mmol / L aluminum nitrate solution was dropped into the suspension at 50℃ while controlling the pH value to be 8, and a coprecipitation reaction was carried out for 24h, and then centrifugation, washing and drying were performed to obtain a composite product of boehmite loaded on halloysite; and the composite product was calcined at 600℃ for 3h to obtain a halloysite-based adsorbent.

[0079] Example 12

[0080] A method for preparing a halloysite-based adsorbent, comprising the following steps:

[0081] 5g of halloysite was mixed with 150mL of 0.02g / mL sodium chloride aqueous solution to obtain a suspension; 150mL of 20mmol / L aluminum nitrate solution was dropped into the suspension at 80℃ while controlling the pH value to be 11, and a coprecipitation reaction was carried out for 2h; after centrifugation, washing and drying, a composite product of boehmite loaded on halloysite was obtained; the composite product was calcined at 600℃ for 3h to obtain a halloysite-based adsorbent.

[0082] Example 13

[0083] A method for preparing a halloysite-based adsorbent comprises the following steps:

[0084] 5g of halloysite was mixed with 150mL of 0.02g / mL sodium chloride aqueous solution to obtain a suspension; 150mL of 20mmol / L aluminum nitrate solution was dropped into the suspension at 80℃ while controlling the pH value to be 8, and a coprecipitation reaction was carried out for 2h; after centrifugation, washing and drying, a composite product of boehmite loaded on halloysite was obtained; the composite product was calcined at 400℃ for 6h to obtain a halloysite-based adsorbent.

[0085] Example 14

[0086] A method for preparing a halloysite-based adsorbent comprises the following steps:

[0087] 5g of halloysite was mixed with 150mL of 0.02g / mL sodium chloride aqueous solution to obtain a suspension; 150mL of 20mmol / L aluminum nitrate solution was dropped into the suspension at 80℃ while controlling the pH value to be 8, and a coprecipitation reaction was carried out for 2h; after centrifugation, washing and drying, a composite product of boehmite loaded on halloysite was obtained; the composite product was calcined at 700℃ for 1h to obtain a halloysite-based adsorbent.

[0088] In order to further illustrate the technical effects of the present application, the present application also provides a comparative example, as follows:

[0089] Comparative Example 1

[0090] Compared with Example 1, the difference lies in that only 5g of halloysite is used.

[0091] The morphology and performance of the halloysite-based adsorbent prepared by the present application were characterized and analyzed, and the specific results are shown in Table 1 and Figures 1 to 10

[0092] Table 1 is a comparison of the adsorption rate, residual fluoride ion concentration and content of loaded aluminum oxide in the sample of the halloysite-based adsorbent HA8-600 prepared in Example 1 and a commercial active alumina under more optimal pH conditions (pH=3) (other conditions: defluorination time is 6h, temperature is 30℃, initial concentration of fluoride ion solution Co is 10mg / L).​

[0093] Table 1 Comparison of fluoride removal performance of the halloysite-based adsorbent of the present application and commercial activated alumina

[0094]

[0095] As can be seen from Table 1, although the fluoride removal rate of HA8-600 is only slightly higher than that of commercial activated alumina, only about 8.4% of alumina is loaded on halloysite, thus having obvious cost advantage; at the same time, the concentration of fluoride ions in the solution after removal of fluoride by HA8-600 is only 0.02 mg / L, far lower than 1 mg / L.

[0096] Figure 1 Figure 1 is a transmission electron micrograph of the halloysite-based adsorbent HA8-600 prepared in Example 1 of the present application and the raw material halloysite H; wherein, Figure a is the local morphology of halloysite H having a tubular morphology; Figures b and c are the local morphologies of the halloysite-based adsorbent HA8-600 loaded with alumina inside and outside the tube; Figure d is the active alumina having a porous hole morphology in the halloysite-based adsorbent HA8-600; Figure e is the crystal lattice fringe pattern of alumina in the halloysite-based adsorbent HA8-600, which proves that the loaded porous material is active alumina (γ-Al2O3).

[0097] Figure 2 Figure 2 is an XRD spectrum of the halloysite-based adsorbent HA8-600 prepared in Example 1 of the present application, the halloysite raw material H and the composite product HA8. Since the amount of boehmite loaded is small, the change of HA8 relative to pure halloysite H is not obvious; after calcination, the halloysite is in an amorphous state, and the active alumina also has weak diffraction peaks due to the small amount.

[0098] Figure 3 Figure 3 is an FTIR spectrum of the halloysite-based adsorbent HA8-600 prepared in Example 1 of the present application, the halloysite raw material H and the composite product HA8. After loading boehmite on halloysite, the stretching vibration peak of Si-O-Si at 1034 cm -1 and 1095 cm -1 is enhanced due to the hydrogen bonds generated between the surface-loaded boehmite and the silicon-oxygen tetrahedron on the surface of halloysite; after further calcination, dehydration occurs in both halloysite and boehmite, so some peaks in HA8-600 disappear.

[0099] Figure 4Nitrogen adsorption isotherms of the halloysite-based adsorbent HA8-600 prepared in Example 1 of the present application and halloysite raw material H, composite product HA8. The nitrogen adsorption results correspond to the IUPAC classification type IVa, corresponding to the mesoporous characteristics of halloysite. In the higher relative pressure stage, the adsorption amount gradually increases; while in these stages, the desorption is also gradually reduced, forming a hysteresis loop, which is related to capillary condensation and mesoporous adsorption and desorption, and thus is a typical feature of mesoporous adsorption.

[0100] Figure 5 Pore size distribution diagrams of the halloysite-based adsorbent HA8-600 prepared in Example 1 of the present application and halloysite raw material H, composite product HA8. When halloysite is loaded with boehmite and calcined, the proportion of pores at 10 nm decreases and the proportion of pores at 4 nm increases, mainly due to the occupation of part of the cavities of halloysite by porous wormhole-like alumina.

[0101] Figure 6 The defluorination rate comparison diagram of the halloysite-based adsorbent HA8-600 prepared in Example 1 of the present application, halloysite raw material H and composite product HA8 under the conditions of dosage of 0.5 g / L, defluorination time of 6 h, temperature of 30℃, initial concentration C0 of fluoride ion solution of 10 mg / L and pH of 4, wherein Figure 6 It can be seen that HA8-600 has obviously improved defluorination efficiency.

[0102] Figure 7 The defluorination rate comparison diagram of the halloysite-based adsorbent HA8-600 prepared in Example 1 of the present application in different pH water bodies under the conditions of dosage of 0.5 g / L, defluorination time of 6 h, temperature of 30℃ and initial concentration C0 of fluoride ion solution of 10 mg / L. From the diagram Figure 7 It can be seen that the halloysite-based adsorbent prepared in Example 1 of the present application has good defluorination rate in a wider pH range, but is better in acidic conditions. Because too high adsorption rate is not conducive to the study of the influence of various factors on the adsorption performance of the sample, pH = 4 is selected when studying the influence of other factors, and pH = 3 is selected when studying the optimal adsorption performance.

[0103] Figure 8 The defluorination rate (Removal) and equilibrium adsorption capacity (q e ) comparison diagram of the halloysite-based adsorbent prepared in Example 1 of the present application under different dosages under the conditions of pH value of 4, defluorination time of 6 h, temperature of 30℃ and initial concentration C0 of fluoride ion solution of 10 mg / L. From the diagram Figure 8It can be seen that the defluorination efficiency of the halloysite-based adsorbent is the lowest at the lowest dosage of 0.125 g / L, and the defluorination efficiency increases as the dosage increases to 1 g / L, mainly because the adsorption active sites increase as the dosage of the adsorbent increases; and the adsorption efficiency gradually decreases as the dosage further increases to 3 g / L, which is probably caused by the intensified particle overlapping phenomenon due to excessive defluorination agent. The equilibrium adsorption capacity q e decreases gradually, mainly because the active sites increase as the defluorination agent increases, but the concentration of fluoride ions in the solution is certain, so the equilibrium adsorption capacity gradually decreases. In the study of the influence of other factors, the dosage of 0.5 mg / L is selected to simultaneously consider the fluoride ion removal rate and the equilibrium adsorption capacity; and a higher dosage can be selected when the optimal adsorption rate is studied.

[0104] Figure 9 The influence of coexisting anions in water on the defluorination performance of the halloysite-based adsorbent prepared in Example 1 of the present application is shown in the figure under the conditions of the dosage of 0.5 g / L, the pH value of 4, the defluorination time of 6 h, the temperature of 30℃, and the initial concentration of fluoride ions C0 of 10 mg / L. Figure 9 It can be seen that the influence of the several anions studied on the performance of the coal gangue-based defluorination agent is not obvious, which indicates that the adsorption selectivity of the halloysite-based adsorbent is good.

[0105] Figure 10 The defluorination performance comparison between the halloysite-based adsorbent HA8-600 prepared in Example 1 of the present application and the commercial active alumina defluorination agent under the more optimal pH condition (pH = 3) is shown in the figure (other conditions: defluorination time of 6 h, temperature of 30℃, and initial concentration of fluoride ions C0 of 10 mg / L). Figure 10 It can be seen that the defluorination efficiency of the commercial active alumina decreases significantly as the dosage of the adsorbent decreases from 3 g / L to 0.5 g / L, but the defluorination efficiency of HA8-600 almost does not change, which indicates that a small amount of HA8-600 can achieve good defluorination effect, and the cost advantage is obvious.

[0106] Obviously, those skilled in the art can make various modifications and variations to the present application without departing from the spirit and scope of the present application. Thus, if these modifications and variations of the present application belong to the scope of the claims of the present application and the equivalent technologies thereof, the present application also intends to include these modifications and variations.

Claims

1. A method for preparing a halloysite-based adsorbent, characterized in that: The following steps are involved: The soluble Al 3+ Salt solution is added to 50℃~95℃ halloysite and alkali metal Cl - In the suspension formed by the salt solution, the pH value is controlled at 8~11, and the coprecipitation reaction is carried out. 3+ With Cl - Formation of [AlCl4] - The ligand is then hydrolyzed to obtain boehmite-type alumina, which is then loaded on halloysite to obtain a composite product; The composite product is calcined at 600-700° C. to obtain a halloysite-based adsorbent.

2. The preparation method according to claim 1, characterized in that The alkali metal Cl - Cl in salt solution - The concentration of the soluble Al 3+ Al in salt solution 3+ The concentration of the alkali metal Cl is 10~100mol / mL. - Salt solution and soluble Al 3+ The volume ratio of the salt solution is 1~5:1~5.

3. The preparation method according to claim 2, characterized in that The halloysite and the alkali metal Cl - The dosage ratio of saline solution is 0.2~5g:30ml.

4. The preparation method according to claim 1, characterized in that The coprecipitation reaction time is 10 min to 24 h.

5. The preparation method according to claim 1, characterized in that The calcination time is 1 to 6 hours.

6. The preparation method according to claim 1, characterized in that The soluble Al 3+ The salt is one or more of aluminum sulfate, aluminum nitrate, aluminum chloride and alum.

7. The preparation method according to claim 1, characterized in that After the coprecipitation reaction is completed, centrifugation is performed to obtain a primary product, which is then washed and dried at 50° C. to 60° C. overnight to obtain a composite product.

8. A halloysite-based adsorbent prepared by the preparation method according to any one of claims 1 to 7.

9. Use of the halloysite-based adsorbent according to claim 8 in removing fluoride ions from water.

10. The use according to claim 9, characterized in that The concentration of fluoride ions in the water body is ≤10 mg / L.

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