Preparation method and application of a La-magnetic montmorillonite hydrogel adsorbent

Abstract

The present invention relates to a preparation method and application of a La-magnetic montmorillonite hydrogel adsorbent. In this preparation method, montmorillonite is successively subjected to alkali activation, magnetization, crosslinking, and lanthanum modification to prepare the La-magnetic montmorillonite hydrogel adsorbent; by introducing iron elements and using rare earth element lanthanum for modification, it has a larger adsorption capacity, enhances the selectivity of the adsorbent for fluoride ions, and reduces the adsorption of other ions or pollutants; the whole process steps are simple and easy to operate; the obtained adsorbent can effectively remove fluoride from low-concentration fluoride-containing wastewater or fluoride-containing wastewater requiring in-depth treatment, and the treatment effect meets the requirements of the fluoride concentration in the effluent for drinking water.

Description

Technical Field

[0001] The present invention relates to a preparation method and application of a La-magnetic montmorillonite hydrogel adsorbent, belonging to the technical field of water treatment. Background Art

[0002] Fluoride pollution is one of the serious environmental problems faced globally. Excessive intake of fluoride can cause various harms to the human body, mainly manifested as skeletal fluorosis, dental fluorosis and damage to the central nervous system. With the development of high-tech industries, the fluorochemical industry in China has developed vigorously, and fluorine-containing substances are widely used in high-tech industries such as semiconductors and new materials, which has led to an increasing annual discharge of fluoride-containing wastewater in China. As the total discharge of sewage fluoride increases day by day, the water environment capacity in some areas has approached the limit. Therefore, some provinces and cities have successively issued new local water pollutant discharge standards in the past two years, and the discharge standard of fluoride has been significantly improved. There are already local policies requiring the concentration of fluoride in the effluent of sewage treatment plants to be reduced to 1.0 mg / L. However, in most of the previous studies on fluoride removal from wastewater, the main focus was on how to treat high-concentration fluoride-containing wastewater (fluoride concentration 30000-100 mg / L) to about 10 mg / L; due to the improvement of fluoride discharge standards in various regions, it is necessary to further deeply treat relatively low-concentration fluoride (20-10 mg / L) in wastewater so that the fluoride concentration in the tail water can be reduced to 1.5-1.0 mg / L.

[0003] Traditional fluoride-containing wastewater treatment technologies include chemical precipitation method, ion exchange method and adsorption method. The chemical precipitation method is to add an appropriate precipitant to react with fluoride ions to form an insoluble fluoride precipitate to achieve the removal of fluoride ions; this method has the advantages of convenient operation, simple process and low treatment cost, and is widely used in the treatment of high-concentration fluoride-containing wastewater, and generally can only reduce the fluoride ion concentration in the effluent to 20-30 mg / L.

[0004] The ion exchange method is to adsorb fluoride ions onto the exchanger and then remove fluoride in water through ion exchange. Commonly used fluoride-removing ion exchange resins include anion exchange resins and polyamide resins; the ion exchange method is simple in operation and stable in effect, but traditional ion exchange resins have poor selective adsorption for fluoride and small adsorption capacity, and due to the high price of the resins, large amounts of regenerated acid and alkali are used, resulting in high costs.

[0005] Adsorption method is one of the most widely applicable wastewater treatment technologies at present. In terms of deep fluoride removal, by exchanging fluoride ions in the wastewater with other ions or groups on the adsorbent, the fluoride ions are retained on the adsorbent, thus achieving the removal of fluoride ions. It has certain advantages in terms of cost, adsorption performance, selectivity, etc., and has good treatment effects and strong operability. The adsorption method is mainly used to treat wastewater with low fluoride content, deeply treat wastewater with fluoride concentration reduced to 15 - 30 mg / L after treatment, and deeply treat drinking water. Commonly used adsorbents include activated alumina, modified montmorillonite, polyferric sulfate, and rare earth adsorbents, etc. Natural mineral adsorbent materials cannot effectively treat high-concentration fluoride-containing wastewater, and the adsorption rate is too slow; traditional adsorbents are expensive. Montmorillonite is a cheap, new, and green adsorbent material, showing unique properties in removing fluoride ions from water. Montmorillonite ore has a wide source, good adsorption performance, and contains various trace elements beneficial to the human body, and will not introduce harmful substances, so it is a potential green adsorption raw material. Modified montmorillonite is a new type of porous adsorbent material formed by introducing some metal cations into the interlayer of montmorillonite or adsorbing them on its surface. Rare earth elements have unique physical and chemical properties. Their hydrated oxides and salts can adsorb anions and cations. Due to their unique fluorine affinity, rare earth substances can not only effectively remove excessive fluoride in water, but also improve the surface structure of conventional filter materials and increase the adsorption sites on the filter material surface; adding rare earth elements to traditional adsorbents can alleviate the problem of subsequent regeneration of saturated adsorbents due to limited adsorption capacity.

[0006] In view of the certain limitations of the existing adsorption method technical means in treating low-concentration fluoride-containing wastewater, it is urgent to prepare a new adsorbent to solve the above problems existing in the traditional low-concentration fluoride-containing wastewater or fluoride-containing wastewater deep treatment technology, and improve its treatment efficiency and safety. Summary of the Invention

[0007] The main purpose of the present invention is: to overcome the problems existing in the prior art, and propose a preparation method of La-magnetic montmorillonite hydrogel adsorbent. The obtained La-magnetic montmorillonite hydrogel adsorbent can effectively remove fluoride from low-concentration fluoride-containing wastewater or fluoride-containing wastewater that needs to be deeply treated, and the treatment effect meets the requirement of the fluoride concentration in the effluent of drinking water (≤1.0 mg / L). At the same time, the corresponding application is also proposed.

[0008] The technical solution for the present invention to solve its technical problems is as follows:

[0009] A preparation method of La-magnetic montmorillonite hydrogel adsorbent, comprising the following steps:

[0010] First step: Activate montmorillonite in sodium hydroxide solution; dissolve FeCl3·6H2O (i.e., ferric chloride hexahydrate) and FeSO4·7H2O (i.e., ferrous sulfate heptahydrate) in water to obtain a magnetic solution.

[0011] Second step: Thoroughly mix the activated montmorillonite obtained in the first step with the magnetic solution, perform ultrasonic treatment, stir, let it stand for aging, wash the obtained montmorillonite, dry it under vacuum, grind it and sieve it to obtain magnetic montmorillonite.

[0012] Third step: Dissolve HPMC (i.e., hydroxypropyl methylcellulose) in water, heat and stir at a constant temperature to dissolve it, cool it to room temperature to obtain an HPMC solution; dissolve the magnetic montmorillonite obtained in the second step in water to obtain a magnetic montmorillonite solution; add the magnetic montmorillonite solution to the HPMC solution, continuously stir and mix, and then add glutaraldehyde solution for crosslinking to obtain a crosslinked material.

[0013] Fourth step: Inject the crosslinked material obtained in the third step into lanthanum nitrate solution for modification and static settlement, wash and dry the obtained product to prepare a La-magnetic montmorillonite hydrogel adsorbent.

[0014] This method makes a La-magnetic montmorillonite hydrogel adsorbent by successively performing alkali activation, magnetization, crosslinking, and lanthanum modification on montmorillonite. The whole technological process is simple and easy to operate; the obtained adsorbent can effectively remove fluorine from low-concentration fluorine-containing wastewater or fluorine-containing wastewater that needs in-depth treatment, and the treatment effect meets the requirement of the fluorine concentration in the effluent of drinking water (≤1.0 mg / L).

[0015] In the La-magnetic montmorillonite hydrogel adsorbent prepared by this method, by introducing iron elements, the adsorbent has a large specific surface area and pore structure, so as to have a larger adsorption capacity, overcoming the deficiency of the small adsorption capacity of traditional adsorbents; using rare earth element lanthanum for modification can not only enhance the selectivity of the adsorbent for fluoride ions, reduce the adsorption of other ions or pollutants, thereby improving the treatment effect, but also increase the adsorption capacity of the adsorbent, improve the treatment efficiency and service life, and overcome the deficiency of the poor adsorption selectivity of traditional adsorbents for fluoride ions.

[0016] Preferably, in the first step, the activation conditions are: using a sodium hydroxide solution with a concentration of 1 ± 0.05 mol / L, activating for at least 4 h at a rotation speed of 300 ± 50 rpm, and the mass-volume ratio of montmorillonite to sodium hydroxide solution is 1 g:40 ± 5 mL; the mass-volume ratio of FeCl3·6H2O, FeSO4·7H2O, and water used for preparing the magnetic solution is 3 ± 0.3 g:2 ± 0.2 g:7.5 ± 1 mL; the mass-volume ratio of montmorillonite to the magnetic solution is 1 g:3 ± 0.5 mL.

[0017] By adopting the above preferred solutions, the specific parameters of the first-step alkali activation treatment and the preparation of the magnetic solution can be further optimized.

[0018] Preferably, in the second step, the ultrasonic treatment time is at least 30 min, the stirring time is at least 1 h, the static aging time is at least 24 h, the washing times are at least 6 times, the temperature of vacuum drying is 60°C ± 5°C and the time is at least 12 h, and the mesh number of the sieve used for sieving is 100 ± 20 meshes.

[0019] By adopting the above preferred solutions, the specific parameters of the second-step magnetization treatment can be further optimized.

[0020] Preferably, in the third step, the mass-volume ratio of HPMC to water for preparing the HPMC solution is 1 g: 20 ± 5 mL, and the temperature during heating and constant stirring for dissolution is 70°C ± 5°C; the mass-volume ratio of magnetic montmorillonite to water for preparing the magnetic montmorillonite solution is 1 g: 20 ± 5 mL; the mass concentration ratio of the magnetic montmorillonite solution to the HPMC solution is 1 ± 0.1: 1; the volume ratio of the magnetic montmorillonite solution to the HPMC solution is 1: 2 ± 0.2; the mass concentration of the glutaraldehyde solution is 2.5 ± 0.1%.

[0021] By adopting the above preferred solutions, the specific parameters of the third-step crosslinking treatment can be further optimized.

[0022] Preferably, in the fourth step, when injecting, a syringe is used to inject the crosslinking material in a strip shape or a dripping shape; the modified static time is at least 24 h, distilled water is used for washing, and the drying temperature is 60°C ± 5°C and the time is at least 12 h.

[0023] By adopting the above preferred solutions, the specific parameters of the fourth-step lanthanum modification treatment can be further optimized.

[0024] The present invention also proposes:

[0025] A La-magnetic montmorillonite hydrogel adsorbent prepared by the preparation method described above.

[0026] The application of the above-mentioned La-magnetic montmorillonite hydrogel adsorbent for removing fluoride ions in water bodies.

[0027] The present invention also proposes:

[0028] A method for treating fluoride-containing wastewater, comprising the following steps:

[0029] The first step, mixing the above-mentioned La-magnetic montmorillonite hydrogel adsorbent with fluoride-containing wastewater to form a mixed solution.

[0030] The second step, subjecting the mixed solution obtained in the first step to a constant-temperature oscillation reaction, standing, and filtering, and the obtained filtrate is the treated water sample.

[0031] Preferably, in the first step, the initial fluoride ion concentration of the fluoride-containing wastewater is ≤ 80 mg / L; the initial pH value of the fluoride-containing wastewater is 3 - 9; the dosage of the La-magnetic montmorillonite hydrogel adsorbent is 1 - 5 g / L; in the second step, the temperature of the constant-temperature shaking reaction is 25°C ± 5°C and the shaking rate is 150 - 180 r / min.

[0032] More preferably, in the first step, the initial fluoride ion concentration of the fluoride-containing wastewater is ≤ 40 mg / L; the dosage of the La-magnetic montmorillonite hydrogel adsorbent is 4 - 5 g / L.

[0033] This method can effectively remove fluoride from low-concentration fluoride-containing wastewater or fluoride-containing wastewater that needs to be deeply treated, and the treatment effect meets the requirements for the fluoride concentration in the effluent of drinking water (≤ 1.0 mg / L).

[0034] Compared with the prior art, the La-magnetic montmorillonite hydrogel adsorbent of the present invention is modified by introducing iron elements and using rare earth element lanthanum, has a larger adsorption capacity, enhances the selectivity of the adsorbent for fluoride ions, reduces the adsorption of other ions or pollutants, and thus can effectively remove fluoride from low-concentration fluoride-containing wastewater or fluoride-containing wastewater that needs to be deeply treated, and the treatment effect meets the requirements for the fluoride concentration in the effluent of drinking water. Description of the Drawings

[0035] Figure 1 It is a bar chart showing the influence of different montmorillonite-based adsorbents on the fluoride removal effect in water body in Example 2 of the present invention, and the results at adsorption time T = 5 h and adsorption time T = 1 h are shown in the figure.

[0036] Figure 2 It is an example diagram showing that the alkali-activated montmorillonite hydrogel (CH-OH-MMT-La) in Example 2 of the present invention is extremely easy to produce flocs under alkaline conditions with pH = 11.

[0037] Figure 3 It is a multi-group line chart showing the influence of the dosage of La-magnetic montmorillonite hydrogel on the fluoride removal effect in water body in Example 3 of the present invention.

[0038] Figure 4 It is a line chart showing the influence of different initial fluoride ion concentrations on the fluoride removal effect in water body in Example 4 of the present invention.

[0039] Figure 5 It is a line chart showing the influence of different initial pH values on the fluoride removal effect in water body in Example 5 of the present invention.

[0040] Figure 6This is the scanning electron microscope image of the La-magnetic montmorillonite hydrogel adsorbent in Example 6 of the present invention. This scanning electron microscope image provides information on the microscopic structure such as the morphology and particle distribution of the La-magnetic montmorillonite hydrogel. In the figure, the working distance WD = 9.7 mm, the magnification Mag = 50000, and the landing voltage HV = 20.00 kV.

[0041] Figure 7 This is the scanning electron microscope image of the La-magnetic montmorillonite hydrogel adsorbent in Example 6 of the present invention. This scanning electron microscope image provides information on the microscopic structure such as the morphology and particle distribution of the La-magnetic montmorillonite hydrogel. In the figure, the working distance WD = 9.7 mm, the magnification Mag = 160000, and the landing voltage HV = 20.00 kV. Detailed implementation manners

[0042] A preparation method of a La-magnetic montmorillonite hydrogel adsorbent specifically implemented in the present invention includes the following steps:

[0043] First step: Activate montmorillonite in a sodium hydroxide solution; dissolve FeCl3·6H2O and FeSO4·7H2O in water to obtain a magnetic solution.

[0044] Among them, the activation conditions are: using a 1 ± 0.05 mol / L sodium hydroxide solution, activating for at least 4 h at a rotation speed of 300 ± 50 rpm, and the mass-volume ratio of montmorillonite to the sodium hydroxide solution is 1 g:40 ± 5 mL; the mass-volume ratio of FeCl3·6H2O, FeSO4·7H2O, and water used to prepare the magnetic solution is 3 ± 0.3 g:2 ± 0.2 g:7.5 ± 1 mL; the mass-volume ratio of montmorillonite to the magnetic solution is 1 g:3 ± 0.5 mL.

[0045] Second step: Thoroughly mix the activated montmorillonite obtained in the first step with the magnetic solution, perform ultrasonic treatment, stir, stand for aging, wash the obtained montmorillonite, vacuum dry, grind and sieve to obtain magnetic montmorillonite.

[0046] Among them, the ultrasonic treatment time is at least 30 min, the stirring time is at least 1 h, the standing aging time is at least 24 h, the washing times are at least 6 times, the vacuum drying temperature is 60°C ± 5°C and the time is at least 12 h, and the mesh number of the sieve used for sieving is 100 ± 20 meshes.

[0047] Third step: Dissolve HPMC in water, heat and stir at a constant temperature to dissolve, cool to room temperature to obtain an HPMC solution; dissolve the magnetic montmorillonite obtained in the second step in water to obtain a magnetic montmorillonite solution; add the magnetic montmorillonite solution to the HPMC solution, continuously stir and mix, and then add a glutaraldehyde solution for crosslinking to obtain a crosslinked material.

[0048] Among them, the mass-volume ratio of HPMC to water for preparing the HPMC solution is 1 g: 20 ± 5 mL, and the temperature during heating, constant temperature stirring and dissolution is 70°C ± 5°C; the mass-volume ratio of magnetic montmorillonite to water for preparing the magnetic montmorillonite solution is 1 g: 20 ± 5 mL; the mass concentration ratio of the magnetic montmorillonite solution to the HPMC solution is 1 ± 0.1:1; the volume ratio of the magnetic montmorillonite solution to the HPMC solution is 1:2 ± 0.2; the mass concentration of the glutaraldehyde solution is 2.5 ± 0.1%.

[0049] Example of mass concentration: For example, a solution mass concentration of 10% means that each milliliter of the solution contains 0.1 g of solute, and so on.

[0050] Step 4: Inject the cross-linked material obtained in the third step into the lanthanum nitrate solution for modification and standing. After washing and drying the obtained product, the La-magnetic montmorillonite hydrogel adsorbent is prepared.

[0051] Among them, when injecting, a syringe is used to inject the cross-linked material in a long strip shape or in a dripping shape; the modification and standing time is at least 24 h, distilled water is used for washing, and the drying temperature is 60°C ± 5°C and the time is at least 12 h.

[0052] A La-magnetic montmorillonite hydrogel adsorbent prepared by the above preparation method is specifically implemented in the present invention.

[0053] The application of the above La-magnetic montmorillonite hydrogel adsorbent specifically implemented in the present invention for removing fluoride ions in water.

[0054] A method for treating fluoride-containing wastewater specifically implemented in the present invention includes the following steps:

[0055] Step 1: Mix the above La-magnetic montmorillonite hydrogel adsorbent with the fluoride-containing wastewater to form a mixed solution. Among them, the initial fluoride ion concentration of the fluoride-containing wastewater is ≤ 80 mg / L (or ≤ 40 mg / L); the initial pH value of the fluoride-containing wastewater is 3-9; the dosage of the La-magnetic montmorillonite hydrogel adsorbent is 1-5 g / L (or 4-5 g / L).

[0056] Step 2: Perform a constant temperature shaking reaction on the mixed solution obtained in the first step, stand, filter, and the obtained filtrate is the treated water sample. Among them, the temperature of the constant temperature shaking reaction is 25°C ± 5°C and the shaking rate is 150-180 r / min.

[0057] The present invention will be further described in detail below with reference to embodiments. However, the present invention is not limited to the given examples.

[0058] Example 1

[0059] This example is for preparing the La-magnetic montmorillonite hydrogel adsorbent.

[0060] The specific preparation process of this example is as follows:

[0061] First step: Place 5.0 g of montmorillonite in 200 mL of sodium hydroxide solution for activation. The activation conditions are as follows: Use a 1 mol / L sodium hydroxide solution, activate at a rotation speed of 300 rpm for 4 h.

[0062] Dissolve FeCl3·6H2O and FeSO4·7H2O in water according to a mass ratio of 3:2 to obtain a magnetic solution. Specifically in this example: Dissolve 6.0 g of FeCl3·6H2O (0.022 mol) and 4.0 g of FeSO4·7H2O (0.0144 mol) in 15 mL of water.

[0063] Second step: Thoroughly mix the activated montmorillonite obtained in the first step with the magnetic solution; perform ultrasonic treatment for 30 min; stir for 1 h; let it stand and age for 24 h; wash the obtained montmorillonite 6 times, then vacuum dry it at 60 °C for 12 h; grind and sieve it. The mesh number of the sieve used for sieving is 100 meshes to obtain magnetic montmorillonite.

[0064] Third step: Dissolve 5.0 g of HPMC in 100 mL of water, stir and dissolve it at a constant temperature of 70 °C, and cool it to room temperature to obtain an HPMC solution; place 2.5 g of the magnetic montmorillonite obtained in the second step in 50 mL of water and dissolve it to obtain a magnetic montmorillonite solution; add the magnetic montmorillonite solution to the HPMC solution. The mass concentration ratio of the magnetic montmorillonite solution to the HPMC solution is 1:1. After continuously stirring and mixing, add a glutaraldehyde solution with a mass concentration of 2.5% for crosslinking to obtain a crosslinked material.

[0065] Fourth step: Use a syringe to inject the crosslinked material obtained in the third step into a lanthanum nitrate solution with a mass concentration of 7.0% in the form of a long strip or droplets for modification and let it stand for 24 h. After washing the obtained product with distilled water and drying it at 60 °C for 12 h, the La-magnetic montmorillonite hydrogel adsorbent is prepared.

[0066] Example 2

[0067] This example is to verify the influence of the adsorbent on the removal effect of fluorine in water.

[0068] This example uses the La-magnetic montmorillonite hydrogel adsorbent prepared according to Example 1, also known as alkali-activated magnetic montmorillonite hydrogel, denoted as CH-OH-MMT-Fe3O4-La.

[0069] This example also uses the following adsorbents for comparison.

[0070] (1) Montmorillonite (denoted as MMT), using commercially available products.

[0071] (2) The alkali-activated montmorillonite (denoted as OH-MMT) was prepared by the following process:

[0072] 5.0 g of montmorillonite was placed in 200 mL of sodium hydroxide solution (1 mol / L), and activated at a rotation speed of 300 rpm for 4 h to obtain the alkali-activated montmorillonite.

[0073] (3) The alkali-activated magnetic montmorillonite (denoted as OH-MMT-Fe3O4) was prepared by the following process:

[0074] i) 5.0 g of montmorillonite was placed in 200 mL of sodium hydroxide solution (1 mol / L), and activated at a rotation speed of 300 rpm for 4 h to obtain the alkali-activated montmorillonite;

[0075] ii) 6.0 g of FeCl3·6H2O (0.022 mol) and 4.0 g of FeSO4·7H2O (0.0144 mol) were dissolved in 15 mL of water to prepare a magnetic solution;

[0076] iii) The above alkali-activated montmorillonite was mixed with the magnetic solution, and ultrasonic treatment was carried out for half an hour to prevent agglomeration (the pH of the mixed solution was 10 - 12), stirred for 1 h, allowed to stand and age for 24 h, washed 6 times, vacuum dried at 60 °C for 12 h, ground through a 100-mesh sieve to obtain the alkali-activated magnetic montmorillonite.

[0077] (4) The alkali-activated montmorillonite hydrogel (denoted as CH-OH-MMT-La) was prepared by the following process:

[0078] i) 5.0 g of montmorillonite was placed in 200 mL of sodium hydroxide solution (1 mol / L), and activated at a rotation speed of 300 rpm for 4 h to obtain the alkali-activated montmorillonite;

[0079] ii) 5.0 g of HPMC was dissolved in 100 mL of water, and stirred and dissolved at a constant temperature of 70 °C, cooled to room temperature to obtain an HPMC solution; 2.5 g of the above alkali-activated montmorillonite was dissolved in 50 mL of water to obtain an alkali-activated montmorillonite solution; the alkali-activated montmorillonite solution was added to the HPMC solution, continuously stirred and mixed, and crosslinked with a glutaraldehyde solution with a mass concentration of 2.5% to obtain a crosslinked material;

[0080] iii) The above crosslinked material was injected into a lanthanum nitrate solution with a mass concentration of 7.0% in the form of a long strip or drops with a syringe for modification and allowed to stand for 24 h. The obtained product was washed with distilled water and dried at 60 °C for 12 h to obtain the alkali-activated montmorillonite hydrogel.

[0081] The specific experimental process of this example is as follows.

[0082] Comparative experiment: In a constant-temperature shaker, with a shaking rate of 150 r / min, a reaction temperature of 25°C ± 5°C, an initial fluorine concentration C (F-)0 = 10 mg / L, a reaction solution volume V = 50 mL, and an adsorbent dosage of m = 0.2 g, the above-mentioned various adsorbents were added, namely: montmorillonite (MMT), alkali-activated montmorillonite (OH-MMT), alkali-activated magnetic montmorillonite (OH-MMT-Fe3O4), alkali-activated montmorillonite hydrogel (CH-OH-MMT-La), alkali-activated magnetic montmorillonite hydrogel (CH-OH-MMT-Fe3O4-La). After the constant-temperature shaking reaction, it was left to stand, filtered through a filter membrane with a pore size of 0.45 μm, and the filtrate was taken to measure the residual fluoride ion concentration in the water.

[0083] At adsorption times T = 1 h and T = 5 h, the influence results of each montmorillonite-based adsorbent on the removal effect of fluorine in water are as Figure 1 shown.

[0084] From the experimental result data: When the adsorption time T = 1 h, among the various montmorillonite-based adsorbents, the CH-OH-MMT-Fe3O4-La adsorbent reduced the effluent fluoride ion concentration to 0.95 mg / L, and its removal rate of fluoride ions in water was 90.50%; the removal rate of fluoride ions in water by the OH-MMT-Fe3O4 adsorbent was 9.00%; the defluorination ability of the CH-OH-MMT-Fe3O4-La adsorbent was 10.56 times that of OH-MMT-Fe3O4.

[0085] When the adsorption time T = 5 h, among the various montmorillonite-based adsorbents, the CH-OH-MMT-Fe3O4-La adsorbent reduced the effluent fluoride ion concentration to 0.7 mg / L, and its removal rate of fluoride ions in water was 93.00%; the removal rate of fluoride ions in water by the OH-MMT-Fe3O4 adsorbent was 10.00%; the defluorination ability of the CH-OH-MMT-Fe3O4-La adsorbent was 9.30 times that of OH-MMT-Fe3O4.

[0086] Thus, it can be seen that the CH-OH-MMT-Fe3O4-La adsorbent (i.e., the La-magnetic montmorillonite hydrogel adsorbent) has a good defluorination effect within a short adsorption time, and the adsorption effect is stable, and the treatment effect can meet the requirements for the effluent fluoride concentration in drinking water (≤1.0 mg / L).

[0087] In addition, although the treatment effect of the alkali-activated montmorillonite hydrogel (CH-OH-MMT-La) is also good, under alkaline conditions with pH = 11, the CH-OH-MMT-La adsorbent is extremely prone to forming flocs (such as Figure 2As shown; while the CH-OH-MMT-Fe3O4-La adsorbent (i.e., La-magnetic montmorillonite hydrogel adsorbent) produces relatively fewer flocs under alkaline conditions at pH = 11. Therefore, the La-magnetic montmorillonite hydrogel adsorbent was used for further experiments subsequently.

[0088] Example 3

[0089] This example was to verify the effect of the dosage of La-magnetic montmorillonite hydrogel on the removal of fluorine from water.

[0090] This example used the La-magnetic montmorillonite hydrogel adsorbent prepared according to Example 1.

[0091] The specific experimental process of this example is as follows.

[0092] Comparative experiment: In a constant-temperature shaking incubator, with a shaking rate of 150 r / min, a reaction temperature of 25°C ± 5°C, an initial fluorine concentration C (F-)0 = 10 mg / L, a reaction solution volume V = 50 mL, and a reaction time of 60 min, the dosages of La-magnetic montmorillonite hydrogel were 1 g / L, 2 g / L, 3 g / L, 4 g / L, and 5 g / L. After constant-temperature shaking reaction, let it stand, filter with a filter membrane with a pore size of 0.45 μm, and take the filtrate to measure the residual fluoride ion concentration in the water.

[0093] The influence results of the dosage of La-magnetic montmorillonite hydrogel on the removal of fluorine from water are as Figure 3 shown.

[0094] From the experimental result data: When the adsorption time T = 1 h, when the dosage of La-magnetic montmorillonite hydrogel was 4 g / L, the highest removal rate of fluoride ions in water was 93.00%; as the adsorption time increased, the adsorption effect of the adsorbent with each dosage on fluorine in water improved. When the adsorption time T = 4 h, the adsorbent with each dosage could control the effluent fluoride ion concentration below 1 mg / L. Among them, for the La-magnetic montmorillonite hydrogel with a dosage of 1 g / L, when the adsorption time was T = 4 h, the effluent fluoride ion concentration could be controlled below 1 mg / L.

[0095] It can be seen from this that when the dosage of La-magnetic montmorillonite hydrogel is 4 g / L, its adsorption effect is the best and it is the least affected by the adsorption time.

[0096] Example 4

[0097] This example was to verify the effect of different initial fluoride ion concentrations on the removal of fluorine from water.

[0098] This example used the La-magnetic montmorillonite hydrogel adsorbent prepared according to Example 1.

[0099] The specific experimental process of this embodiment is as follows.

[0100] Comparative experiment: In a constant temperature shaker, the shaking rate is 150 r / min, the reaction temperature is 25°C ± 5°C, the dosage of La-magnetic montmorillonite hydrogel adsorbent is m = 0.2 g, the volume of the reaction solution is V = 50 mL, the reaction time is 60 min, and different initial fluoride ion concentrations C (F-)0 = 10 mg / L, 40 mg / L, 80 mg / L, 100 mg / L are used. After the constant temperature shaking reaction, let it stand, filter with a filter membrane with a pore size of 0.45 μm, and take the filtrate to measure the residual fluoride ion concentration in the water.

[0101] The influence results of different initial fluoride ion concentrations on the fluoride removal effect in water are as Figure 4 shown.

[0102] From the experimental result data: Due to the addition of a fixed amount of adsorbent, as the initial fluoride concentration increases, the removal rate of fluoride in water decreases significantly.

[0103] At an initial fluoride concentration C (F-)0 = 80 mg / L, the adsorption capacity of the adsorbent is 7.55 mg / g, and the removal rate of fluoride ions in water is 37.75%; at an initial fluoride concentration C (F-)0 = 100 mg / L, the adsorption capacity of the adsorbent is still 7.55 mg / g, but the removal rate of fluoride ions in water drops to the lowest of 30.20%, and the adsorption capacity of the adsorbent tends to be stable; at an initial fluoride concentration C (F-)0 = 10 mg / L, the adsorption capacity of the adsorbent is 2.42 mg / g, and the removal rate of fluoride ions in water is 96.60%.

[0104] It can be seen that when the fluoride ion concentration in water is low, the adsorption capacity of the La-magnetic montmorillonite hydrogel adsorbent is not fully exerted; when the fluoride ion concentration in water gradually increases, the adsorption capacity of the La-magnetic montmorillonite hydrogel adsorbent will increase, but there is a certain limit.

[0105] Example 5

[0106] This example is to verify the influence of different initial pH values on the fluoride removal effect in water.

[0107] This example uses the La-magnetic montmorillonite hydrogel adsorbent prepared according to Example 1.

[0108] The specific experimental process of this example is as follows.

[0109] Comparative experiment: In a constant temperature shaker, the shaking rate is 150 r / min, the reaction temperature is 25°C ± 5°C, the initial fluoride concentration C (F-)0= 10 mg / L, the dosage of La-magnetic montmorillonite hydrogel adsorbent is m = 0.15 g, the volume of the reaction solution is V = 50 mL, and the reaction time is 60 min. Under the condition of different initial pH values of 3, 5, 7, 9, and 11. After constant temperature shaking reaction, let it stand, filter with a filter membrane with a pore size of 0.45 μm, and take the filtrate to measure the residual fluoride ion concentration in the water.

[0110] The influence results of different initial pH values on the fluoride removal effect in water are as Figure 5 shown.

[0111] From the experimental result data: when the initial pH is 3 - 9, the fluoride ion concentration in the effluent is less than 1 mg / L, and the removal rate of fluoride ions in water by the adsorbent is higher than 91%; among them, when the initial pH = 5, the fluoride ion concentration in the effluent is the lowest and is 0.37 mg / L, and the removal rate of fluoride ions in water by the adsorbent is the highest and is 96.30%.

[0112] However, when the initial pH = 11, the fluoride ion concentration in the effluent is the highest and is 8.85 mg / L, and the removal rate of fluoride ions in water is the lowest and is 11.50%.

[0113] Thus, it can be seen that the La-magnetic montmorillonite hydrogel adsorbent has poor alkali resistance, and its adsorption capacity decreases by 2.83 mg / g in a strong alkaline environment. The optimal adsorption pH range of the La-magnetic montmorillonite hydrogel adsorbent is 3 - 9.

[0114] Example 6

[0115] This example is to study the material microstructure of the La-magnetic montmorillonite hydrogel adsorbent.

[0116] The La-magnetic montmorillonite hydrogel adsorbent prepared according to Example 1 is used in this example.

[0117] As Figure 6 shown, this is a high-resolution scanning electron microscope image with a magnification of Mag = 50000. It can be seen that the surface of the La-magnetic montmorillonite hydrogel adsorbent material is composed of numerous laminations and folds, and these structures present an irregular and dynamic appearance. This morphologically complex surface provides a large amount of microscopic space and irregular edges, increasing the effective surface area of the material. These folds and pores at the microscopic level can provide more active sites, which helps to improve the adsorption capacity and rate. Small clusters can also be seen in the figure, which may be formed due to the uneven distribution of La element or other components in the hydrogel matrix.

[0118] As Figure 7As shown, this is a high-resolution scanning electron microscope image with a magnification of Mag = 160,000. The figure shows a three-dimensional network structure inside the La-magnetic montmorillonite hydrogel adsorbent, which is composed of units with different shapes and sizes. This structure is manifested as intricate textures, similar to randomly stacked leaves or flaky debris, revealing its highly porous characteristics. These characteristics constitute the microarchitecture of the material, providing it with a significantly increased surface area. In addition, the porous nature of the material ensures the presence of a large number of active adsorption sites in its microstructure. Due to the diversity and complexity of its morphology, the material provides enhanced channels and paths during the adsorption process, thus promoting the adsorption kinetics and achieving more efficient adsorption efficiency and capacity. This unique microarchitecture, combined with the specific chemical activity of lanthanum and the magnetic recovery ability of the material, enhances its adsorption efficacy.

[0119] Through the above embodiments, the present invention explores the efficacy of La-magnetic montmorillonite hydrogel in treating low-concentration fluoride-containing wastewater, which has important academic research and application value in the application and development of montmorillonite in water treatment and the advanced treatment of fluoride-containing wastewater.

[0120] In the La-magnetic montmorillonite hydrogel adsorbent of the present invention, by introducing iron elements, the adsorbent has a large specific surface area and pore structure, thus having a larger adsorption capacity and overcoming the deficiency of small adsorption capacity of traditional adsorbents; the use of rare earth element lanthanum for modification can not only enhance the selectivity of the adsorbent for fluoride ions, reduce the adsorption of other ions or pollutants, thereby improving the treatment effect, but also increase the adsorption capacity of the adsorbent, improve the treatment efficiency and service life, and overcome the deficiency of poor adsorption selectivity of traditional adsorbents for fluoride ions.

[0121] In addition to the above embodiments, the present invention may have other implementation manners. Any technical solutions formed by equivalent replacement or equivalent transformation fall within the protection scope required by the present invention.

Claims

1. A preparation method of a La-magnetic montmorillonite hydrogel adsorbent, characterized in that It includes the following steps: First step: Activate montmorillonite in a sodium hydroxide solution; dissolve FeCl3·6H2O and FeSO4·7H2O in water to obtain a magnetic solution. Among them, the conditions for activation are: use a 1±0.05mol / L sodium hydroxide solution, activate at a rotation speed of 300±50rpm for at least 4h, and the mass-volume ratio of montmorillonite to the sodium hydroxide solution is 1g:40±5mL; the mass-volume ratio of FeCl3·6H2O, FeSO4·7H2O and water used to prepare the magnetic solution is 3±0.3g:2±0.2g:7.5±1mL; the mass-volume ratio of montmorillonite to the magnetic solution is 1g:3±0.5mL. Second step: Fully mix the activated montmorillonite obtained in the first step with the magnetic solution, after ultrasonic treatment, stir, let it stand and age, wash the obtained montmorillonite, dry it under vacuum, grind and sieve it to obtain magnetic montmorillonite. Among them, the ultrasonic treatment time is at least 30min, the stirring time is at least 1h, the standing and aging time is at least 24h, the number of washing times is at least 6 times, the temperature of vacuum drying is 60℃±5℃ and the time is at least 12h, and the mesh number of the sieve used for sieving is 100±20 mesh. Third step: Dissolve HPMC in water, heat and stir at a constant temperature to dissolve, cool to room temperature to obtain an HPMC solution; dissolve the magnetic montmorillonite obtained in the second step in water to obtain a magnetic montmorillonite solution; add the magnetic montmorillonite solution to the HPMC solution, continuously stir and mix, and then add a glutaraldehyde solution for crosslinking to obtain a crosslinked material. Among them, the mass-volume ratio of HPMC to water used to prepare the HPMC solution is 1g:20±5mL, and the temperature during heating and stirring at a constant temperature for dissolution is 70℃±5℃; the mass-volume ratio of magnetic montmorillonite to water used to prepare the magnetic montmorillonite solution is 1g:20±5mL; the mass concentration ratio of the magnetic montmorillonite solution to the HPMC solution is 1±0.1:1; the volume ratio of the magnetic montmorillonite solution to the HPMC solution is 1:2±0.2; the mass concentration of the glutaraldehyde solution is 2.5±0.1%. Fourth step: Inject the crosslinked material obtained in the third step into a lanthanum nitrate solution for modification and standing, wash and dry the obtained product to obtain a La-magnetic montmorillonite hydrogel adsorbent; when injecting, use a syringe to inject the crosslinked material in a long strip or drop shape; the modification and standing time is at least 24h, use distilled water for washing, and the drying temperature is 60℃±5℃ and the time is at least 12h.

2. A La-magnetic montmorillonite hydrogel adsorbent prepared by the preparation method according to claim 1.

3. Application of the La-magnetic montmorillonite hydrogel adsorbent according to claim 2 for removing fluoride ions in water.

4. A method for treating fluorine-containing wastewater, characterized in that, It includes the following steps: Step 1: Mix the La-magnetic montmorillonite hydrogel adsorbent described in Claim 2 with the fluorine-containing wastewater to form a mixed solution; wherein, the initial fluoride ion concentration of the fluorine-containing wastewater is ≤ 40 mg / L; the initial pH value of the fluorine-containing wastewater is 3-9; the dosage of the La-magnetic montmorillonite hydrogel adsorbent is 4-5 g / L; Step 2: Subject the mixed solution obtained in Step 1 to a constant-temperature shaking reaction, let it stand, and filter. The obtained filtrate is the treated water sample; wherein, the temperature of the constant-temperature shaking reaction is 25°C ± 5°C and the shaking rate is 150-180 r / min.

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