Preparation method of talc with high specific surface area and application of talc in fluorine removal

Abstract

The invention discloses a preparation method of hydrotalcite with a high specific surface area and an application of the hydrotalcite in fluorine removal, the preparation method is simple to operate, and the specific surface area of the hydrotalcite can be increased by several times or even dozens of times so as to obtain excellent fluorine ion removal performance; belongs to the technical field of inorganic non-metallic material synthesis and fluorine ion removal, and can effectively solve the problem of agglomeration of hydrotalcite, the specific surface area of the hydrotalcite is greatly increased to 743 m < 2 > / g to the maximum while the dispersity of the hydrotalcite is improved, and the preparation process is simple and low in energy consumption. In the invention, the specific surface area of the prepared hydrotalcite is several times to dozens of times of that of hydrotalcite prepared by a conventional method, and the hydrotalcite has more exposed adsorption sites and pore structures, so that the adsorption capacity of the hydrotalcite on fluorine ions in water can be greatly improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of synthesis of inorganic non-metallic materials and fluoride ion removal, and specifically relates to a preparation method of high specific surface area hydrotalcite and its application in fluoride removal. Background Art

[0002] With the rapid development of industry, the discharge of fluoride-containing wastewater is increasing continuously, and the pollution problem of fluoride ions in the water environment is becoming increasingly serious. High-concentration fluoride ion wastewater not only pollutes water sources and destroys the stability of the aquatic ecosystem, but also excessive intake of fluoride ions will cause many harms to human health, such as causing diseases like dental fluorosis and skeletal fluorosis. Therefore, developing efficient methods for fluoride ion removal has important practical significance. Currently, the methods for removing fluoride ions in the water environment mainly include chemical precipitation method, flocculation method, electrochemistry method, membrane separation and adsorption method, etc. Among them, the adsorption method has the advantages of simple operation, wide application range, high removal efficiency and low cost, and has become the most promising defluorination method at present. Hydrotalcite is an anionic layered compound with a layered structure, which is assembled by a positively charged main layer board composed of divalent metal ions and trivalent metal ions and interlayer anions and water molecules through non-covalent interactions. Its interlayer exchangeable anion characteristics make it show good application prospects in removing fluoride ions in water.

[0003] In the preparation process of traditional hydrotalcite, agglomeration is likely to occur, resulting in a smaller specific surface area and insufficient exposure of active sites, thus affecting its adsorption capacity for fluoride ions. The invention patent CN201710982643.4 prepares high specific surface area calcined hydrotalcite-like material by introducing the polymer surfactant polyvinylpyrrolidone into the synthesis system, hydrothermally treating at 110 °C for 3 hours, and calcining the obtained product at 400 °C for 3 h in a nitrogen atmosphere. The specific surface area of the product is 180 - 300 m 2 / g. The invention patent CN106865677A introduces a method for removing fluoride ions from pickling wastewater of stainless steel using magnesium-aluminum hydrotalcite, but its use requires prior calcination of the hydrotalcite at 550 °C for 3 hours. The literature "Study on the preparation of Mg-Al hydrotalcite and its adsorption effect on fluoride ions in water, Functional Materials, 2024, 4(55), 04179-04184" prepared magnesium-aluminum hydrotalcite by the coprecipitation method and studied its adsorption effect on fluoride ions in water. 0.2 g of hydrotalcite was added to 50 ml of 100 mg / L NaF solution, and the adsorption equilibrium was reached in 80 minutes. The maximum adsorption capacity and the fluoride ion removal rate reached 74.7% - 90.5%. In order to improve the specific surface area and adsorption performance of hydrotalcite, researchers have conducted a lot of exploration. The invention patent CN102642853A discloses a preparation method of a high specific surface area hydrotalcite-like compound. By adding polyethylene glycol during the synthesis process to inhibit the interlayer thickness, a sheet-like hydrotalcite-like compound with a thin thickness, a large specific surface area, and a narrow particle size distribution was prepared, and the highest specific surface area was 150 m 2 / g.

[0004] However, so far, there are very few non-calcined hydrotalcites with a specific surface area exceeding 200 m 2 / g, and hydrotalcite-like compounds with a specific surface area exceeding 400 m 2 / g have not been reported.

[0005] The purpose of the present invention is to disclose a simple method that can greatly improve the specific surface area of hydrotalcite to meet its application requirements in the fields of catalysis and adsorption, especially in the field of removing fluoride ions from wastewater. Summary of the Invention

[0006] The purpose of the present invention is: to solve the above-mentioned problems, and to provide a preparation method of high specific surface area hydrotalcite and its application in removing fluorine.

[0007] The technical solution adopted by the present invention is as follows: A preparation method of high specific surface area magnesium-aluminum hydrotalcite, which includes the following steps:

[0008] S1: Weigh a certain amount of magnesium compound and aluminum compound, add them to deionized water and dissolve and mix evenly to prepare a metal mixed solution. The molar ratio of Mg 2+ and Al 3+ in the metal mixed solution is 1:(2 - 3);

[0009] S2: Weigh a certain amount of sodium hydroxide and sodium carbonate, add them to deionized water and dissolve and mix evenly to prepare two kinds of alkali solutions;

[0010] S3: Drop the metal mixed solution in step S1 into the sodium carbonate solution in step S2, and at the same time use the sodium hydroxide solution in step S2 to maintain the pH value of the obtained mixture at 8 - 9. Keep magnetic stirring during the dropping process, continue to stir the obtained mixture, after crystallization for a certain time, centrifuge the mixture to obtain a precipitate, wash it with deionized water until pH = 7, and then wash and centrifuge it with an organic solvent to obtain a precipitate;

[0011] S4: Add the precipitate obtained in step S3 into the same organic solvent as in step S3, after mixing evenly, continue magnetic stirring for a certain time, then filter and vacuum dry the mixture to obtain a high specific surface area hydrotalcite product;

[0012] S5: Collect, store and package the prepared product to end the entire preparation process.

[0013] In a preferred embodiment, in step S1, the magnesium compound is MgCl 2 、MgNO 3 、MgSO 4 any one or a plurality of any ratios.

[0014] In a preferred embodiment, in step S1, the aluminum compound is AlCl 3 、Al(NO 3 ) 3 、Al 2 (SO 4 ) 3 any one or a plurality of any ratios.

[0015] In a preferred embodiment, in step S2, the concentration of the sodium hydroxide solution is 1 - 2 mol / L.

[0016] In a preferred embodiment, in step S2, the molar ratio of sodium carbonate to Al 3+ is (2 - 4):1.

[0017] In a preferred embodiment, in step S3, the crystallization time is 2 - 3 h.

[0018] In a preferred embodiment, in step S3, the organic solvent used is any one or a mixture of any several of tetrahydrofuran, isopropanol and dimethyl sulfoxide;

[0019] In step S4, the organic solvent used is any one or a mixture of any several of tetrahydrofuran, isopropanol and dimethyl sulfoxide.

[0020] In a preferred embodiment, in step S3, the organic solvent used is dimethyl sulfoxide.

[0021] In step S4, the organic solvent used is dimethyl sulfoxide.

[0022] In a preferred embodiment, in step S4, the stirring time is 8 - 24 h.

[0023] In a preferred embodiment, the hydrotalcite is applied to the defluorination of fluoride - containing wastewater.

[0024] In summary, due to the adoption of the above - mentioned technical solutions, the beneficial effects of the present invention are as follows:

[0025] 1. In the present invention, the agglomeration problem of hydrotalcite can be effectively solved. While improving the dispersibility of hydrotalcite, the specific surface area of hydrotalcite is greatly increased, up to 743 m2 / g at most, and the preparation process is simple and the energy consumption is low.

[0026] 2. In the present invention, the specific surface area of the prepared hydrotalcite is several to more than ten times that of the hydrotalcite prepared by the conventional method, with more exposed adsorption sites and pore structures, which can greatly improve its adsorption capacity for fluoride ions in water. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is the flow chart of the preparation method of the present invention.

[0028] Figure 2 is the schematic diagram of the nitrogen adsorption - desorption isotherm of the high - specific - surface - area hydrotalcite prepared in Examples 1, 2, and 3 of the present invention at liquid nitrogen temperature.

[0029] Figure 3 is the XRD pattern of the high - specific - surface - area hydrotalcite prepared in Examples 1, 2, and 3 of the present invention.

[0030] Figure 4 is the comparison chart of the removal rate at different times of adsorbing F− in Application Examples 1, 2, and 3 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0031] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0032] Refer to Figures 1-4 ,

[0033] Example 1

[0034] Weigh 4.066 g of magnesium chloride hexahydrate (0.02 mol) and 2.414 g of aluminum chloride hexahydrate (0.01 mol), dissolve them in 25 ml of deionized water, stir evenly to prepare a metal mixed solution; weigh 2 g of sodium hydroxide (0.05 mol), dissolve it in 50 ml of deionized water to prepare a 1 mol / L sodium hydroxide solution; weigh 2.12 g of sodium carbonate (0.02 mol), dissolve it in 50 ml of deionized water to prepare a sodium carbonate solution; drop the metal mixed solution into the sodium carbonate solution under stirring, and use the sodium hydroxide solution to keep the pH value of the mixture at 8 - 9 during the dropping process. After the dropping is completed, continue to stir and crystallize for 2 hours, centrifuge the mixture, wash the precipitate with deionized water until the pH = 7, then wash the precipitate with dimethyl sulfoxide and centrifuge and separate; add the precipitate to 50 ml of dimethyl sulfoxide, mix evenly and continue to stir for 10 h, filter the mixture, and obtain a high specific surface area hydrotalcite after vacuum drying.

[0035] The N 2 adsorption - desorption curve of the high specific surface area hydrotalcite prepared in this example is as Figure 2 shown, and its specific surface area is as high as 750.0 m 2 / g; Figure 3 is the XRD pattern of the high specific surface area hydrotalcite. It can be seen that the crystallinity of this hydrotalcite is relatively low, but it can expose more adsorption sites, greatly improving its specific surface area.

[0036] Example 2

[0037] Weigh 4.066 g of magnesium chloride hexahydrate (0.02 mol) and 2.414 g of aluminum chloride hexahydrate (0.01 mol), dissolve them in 25 ml of deionized water, stir evenly to prepare a metal mixed solution; weigh 2 g of sodium hydroxide (0.05 mol), dissolve it in 50 ml of deionized water to prepare a 1 mol / L sodium hydroxide solution; weigh 2.12 g of sodium carbonate (0.02 mol), dissolve it in 50 ml of deionized water to prepare a sodium carbonate solution; drop the metal mixed solution into the sodium carbonate solution under stirring, and use the sodium hydroxide solution to keep the pH value of the mixture at 8 - 9 during the dropping process. After the dropping is completed, continue to stir and crystallize for 2 hours, centrifuge the mixture, wash the precipitate with deionized water until the pH = 7, then wash the precipitate with isopropanol and centrifuge and separate; add the precipitate to 50 ml of isopropanol, mix evenly and continue to stir for 10 h, filter the mixture, and obtain a high specific surface area hydrotalcite after vacuum drying.

[0038] The N 2 adsorption - desorption curve of the high specific surface area hydrotalcite prepared in this example is as Figure 2 shown, and its specific surface area is 388.7 m 2 / g; Figure 3XRD pattern of the hydrotalcite with high specific surface area shows that the crystallinity of this hydrotalcite is higher than that of the hydrotalcite prepared in Example 1, but still at a relatively low level, which can expose relatively more adsorption sites and increase its specific surface area by several times compared with ordinary hydrotalcite.

[0039] Example 3

[0040] Weigh 4.066 g of magnesium chloride hexahydrate (0.02 mol) and 2.414 g of aluminum chloride hexahydrate (0.01 mol), dissolve them in 25 ml of deionized water, stir evenly to prepare a metal mixed solution; weigh 2 g of sodium hydroxide (0.05 mol), dissolve it in 50 ml of deionized water to prepare a 1 mol / L sodium hydroxide solution; weigh 2.12 g of sodium carbonate (0.02 mol), dissolve it in 50 ml of deionized water to prepare a sodium carbonate solution; drop the metal mixed solution into the sodium carbonate solution under stirring, and use the sodium hydroxide solution to keep the pH value of the mixture at 8 - 9 during the dropping process. After the dropping is completed, continue to stir and crystallize for 2 hours. Centrifuge the mixture, wash the precipitate with deionized water until the pH = 7, then wash the precipitate with tetrahydrofuran and centrifuge for separation; add the precipitate to 50 ml of tetrahydrofuran, mix evenly and continue to stir for 10 h, filter the mixture, and obtain the hydrotalcite with high specific surface area after vacuum drying.

[0041] The N 2 adsorption - desorption curve of the hydrotalcite with high specific surface area prepared in this example is as Figure 2 shown, and its specific surface area is 206.7 m 2 / g; Figure 3 XRD pattern of the hydrotalcite with high specific surface area shows that the crystallinity of this hydrotalcite is the highest, its layered structure is the most intact, but the increase in specific surface area is the smallest.

[0042] Application Example 1:

[0043] Take 0.02 g of the hydrotalcite prepared in Example 1 in a conical flask, add 50 ml of sodium fluoride solution, where the concentration of F - is 100 mg / L. After oscillating at 200 rpm for 8 h at 25 °C, take the solution and filter it through a 0.22 - μm filter, and use a fluoride - ion selective electrode to measure the remaining F - concentration.

[0044] The removal efficiency of F - in this application example is as Figure 4 shown. The removal rate of F - can reach more than 99%, and the adsorption equilibrium can be reached in 30 min, showing extremely high F - removal ability. The corresponding F - adsorption capacity reaches 247.5 mg / g.

[0045] Application Example 2:

[0046] Take 0.02 g of the hydrotalcite prepared in Example 2 in a conical flask, add 50 ml of sodium fluoride solution, where the concentration of F - is 100 mg / L. After oscillating at 200 rpm for 8 h at 25 °C, take the solution and filter it through a 0.22-μm filter, and use a fluoride ion selective electrode to measure the remaining F - concentration.

[0047] In this application example, the removal efficiency of F - is as Figure 4 shown. The removal rate of F - can reach over 95%, and the corresponding adsorption capacity of F - reaches 237.5 mg / g. However, the time to reach adsorption equilibrium is increased to 2 h, and it still shows a high F - removal ability.

[0048] Application Example 3:

[0049] Take 0.02 g of the hydrotalcite prepared in Example 3 in a conical flask, add 50 ml of sodium fluoride solution, where the concentration of F - is 100 mg / L. After oscillating at 200 rpm for 8 h at 25 °C, take the solution and filter it through a 0.22-μm filter, and use a fluoride ion selective electrode to measure the remaining F - concentration.

[0050] In this application example, the removal efficiency of F - is as Figure 4 shown. The removal rate of F - can reach over 90%, and the corresponding adsorption capacity of F - reaches 225.0 mg / g. However, the time to reach adsorption equilibrium is relatively long, requiring 3 - 4 hours. Its F - removal ability is lower than that of Application Examples 1 and 2, but it also exceeds other reported adsorbents of the same type.

[0051] It can be seen from the above that:

[0052] In the present invention, the agglomeration problem of hydrotalcite can be effectively solved. While improving the dispersibility of hydrotalcite, the specific surface area of hydrotalcite is greatly increased, up to 743 m2 / g at most, and the preparation process is simple and the energy consumption is low.

[0053] In the present invention, the specific surface area of the prepared hydrotalcite is several times to more than ten times that of the hydrotalcite prepared by the conventional method, with more exposed adsorption sites and pore structures, which can greatly improve its adsorption capacity for fluoride ions in water.

[0054] It should be noted that in this text, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising" or any other variant thereof is intended to cover non-exclusive inclusion, such that a process, method, article, or device comprising a series of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or device. Without further limitation, an element defined by the statement "comprising an..." does not exclude the presence of additional identical elements in the process, method, article, or device comprising the said element.

[0055] The foregoing description enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a high specific surface area magnesium aluminum hydrotalcite, characterized in that: The steps include: S1: Weigh a certain amount of magnesium compound and aluminum compound, add them into deionized water, dissolve and mix them evenly, and prepare a metal mixed solution. The Mg in the metal mixed solution 2+ and Al 3+ The molar ratio is 1:(2-3); S2: Weigh a certain amount of sodium hydroxide and sodium carbonate, add them into deionized water, dissolve and mix them evenly, and prepare two alkali solutions; S3: dripping the metal mixed solution in step S1 into the sodium carbonate solution in step S2, and simultaneously maintaining the pH value of the obtained mixture at 8-9 using the sodium hydroxide solution in step S2, maintaining magnetic stirring during the dripping process, and continuously stirring the obtained mixture. After crystallization for a certain period of time, centrifuging the mixture to obtain a precipitate, washing with deionized water until the pH value is 7, and then washing with an organic solvent and centrifuging to obtain a precipitate; S4: adding the precipitate obtained in step S3 to the same organic solvent as in step S3, mixing evenly and continuing magnetic stirring for a certain period of time, filtering the mixture, and vacuum drying to obtain a high specific surface area hydrotalcite product; S5: Collect, preserve and package the prepared products, and the entire preparation process is completed.

2. The method for preparing a high specific surface area magnesium aluminum hydrotalcite according to claim 1, characterized in that: In the step S1, the magnesium compound is any one of MgCl2, MgNO3, and MgSO4, or multiple compounds in any proportion.

3. The method for preparing a high specific surface area magnesium aluminum hydrotalcite according to claim 1, characterized in that: In the step S1, the aluminum compound is any one of AlCl3, Al(NO3)3, Al2(SO4)3 or multiple compounds in any proportion.

4. The method for preparing a high specific surface area magnesium aluminum hydrotalcite according to claim 1, characterized in that: In step S2, the concentration of the sodium hydroxide solution is 1-2 mol / L.

5. The method for preparing a high specific surface area magnesium aluminum hydrotalcite according to claim 1, characterized in that: In step S2, sodium carbonate and Al 3+ The molar ratio is (2~4):

1.

6. The method for preparing a high specific surface area magnesium aluminum hydrotalcite according to claim 1, characterized in that: In the step S3, the crystallization time is 2 to 3 hours.

7. The method for preparing a high specific surface area magnesium aluminum hydrotalcite according to claim 1, characterized in that: In step S3, the organic solvent used is any one of tetrahydrofuran, isopropanol and dimethyl sulfoxide or a mixture of any two of them; In step S4, the organic solvent used is any one of tetrahydrofuran, isopropanol and dimethyl sulfoxide or a mixture of any two of them.

8. The method for preparing a high specific surface area magnesium aluminum hydrotalcite according to claim 1, characterized in that: In step S3, the organic solvent used is dimethyl sulfoxide; In the step S4, the organic solvent used is dimethyl sulfoxide (DMSO).

9. The method for preparing a high specific surface area magnesium aluminum hydrotalcite according to claim 1, characterized in that: In step S4, the stirring time is 8 to 24 hours.

10. The use of a high specific surface area magnesium aluminum hydrotalcite according to claim 1, characterized in that: The hydrotalcite is used for defluorination of fluoride-containing wastewater.

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