Preparation method of hydroxyapatite and application thereof in fluorine removal of mine water

Abstract

The application relates to the field of fluorine pollution treatment, in particular to a preparation method of hydroxyapatite and application of the hydroxyapatite in fluorine removal of mine water, and solves the problem that the adsorption effect of the existing fluorine removal agent is still poor, thereby limiting the wide application of the fluorine removal agent in fluorine wastewater. In the preparation process of the fluorine removal agent, the hydroxyapatite is loaded on lanthanum-doped porous nanofibers, the adsorption active sites on the surface of the hydroxyapatite are increased through the electrostatic attraction or ion exchange of metal ions or metal oxides on the electrically negative pollutants, the adsorption effect on fluorine ions is improved, the cetyltrimethylammonium bromide changes the surface charge by embedding into the hydroxyapatite crystal lattice, the surface of the hydroxyapatite shows positive charge, the electrostatic action between the hydroxyapatite and F ‑ is strengthened, a large number of amino functional groups are contained on the chitosan, the fluorine ions can be reacted with the fluorine ions, the fluorine ions in water can be adsorbed on the surface through adsorption, and the fluorine removal purpose is achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of fluorine pollution treatment, and particularly relates to a preparation method of hydroxyapatite. BACKGROUND

[0002] It is reported that drinking water with a fluorine ion concentration of 0.5-1 mg / L has a positive effect on teeth and bones, because it can reduce the occurrence of dental caries through mineralization, but when the fluorine ion concentration in drinking water exceeds 1.5 mg / L, the excessive fluorine ion in the teeth will reduce the activity of protease, thus causing abnormality of the structure of tooth enamel, and long-term intake of water with a fluorine ion concentration exceeding 4 mg / L will cause an increase in bone density, i.e., skeletal fluorosis, resulting in osteoporosis, paralysis and nervous system diseases, and severe fluorosis shows diseases of other organs, such as kidney, liver and neuronal diseases. Therefore, it is urgent to solve the fluorine pollution problem, which is also an important problem for guaranteeing the safety of drinking water for the public.

[0003] Existing methods for reducing the F - concentration in water include several main treatment methods: chemical precipitation, coagulation, ion exchange resin, membrane, electrochemistry and adsorption. The chemical precipitation method is relatively popular in the treatment of water with excessive fluorine due to its simple operation and low cost, but the industrial equipment is large, the amount of reagent is large, the sedimentation speed is slow, and the effluent is difficult to meet the discharge standard; compared with the chemical precipitation method, the coagulation method has a smaller amount of reagent, can handle a large amount of wastewater, but cannot guarantee the effluent quality, and the use cost is high, and the coagulant generally cannot be regenerated; the electrochemistry method has high fluorine removal efficiency and no pollution, but has the disadvantages of high energy consumption and large investment cost, and is not suitable for industrial production; the membrane process technology is clean and efficient in the fluorine removal process, can work in a wide pH value range, but has relatively high cost and maintenance cost, the reverse osmosis membrane is easily polluted, and is not suitable for the treatment of high-concentration fluorine solution; the ion exchange resin method has a high fluorine removal rate (90-95%), but the adsorption amount is easily affected by the fluorine concentration and competitive ions, and the cost is very high; the adsorption method refers to the ion exchange or chemical reaction of fluorine ions with adsorbents with large specific surface area or pores, most studies show that the adsorption method has low cost, convenient operation, high use efficiency and recycling, but the adsorption effect of the adsorption method is related to the adsorption characteristics of the defluorination agent, and the adsorption effect of the current defluorination agent is still not good, which limits its wide application in fluorine wastewater. SUMMARY

[0004] In order to overcome the above technical problems, the purpose of the present application is to provide a preparation method of hydroxyapatite: first, polyacrylonitrile and polyvinylpyrrolidone are used as raw materials for electrospinning to obtain nanofibers, then the nanofibers are fully immersed in a lanthanum nitrate solution to incorporate lanthanum ions, and then calcination is performed to form lanthanum ion-doped porous carbon nanofibers to obtain lanthanum-doped porous nanofibers, then calcium nitrate tetrahydrate and diammonium hydrogen phosphate are used as raw materials to prepare hydroxyapatite, then the lanthanum-doped porous nanofibers and the hydroxyapatite are fully immersed in a ferric nitrate and aluminum nitrate solution, then co-precipitation is performed, and the iron ions and aluminum ions are doped into the lanthanum-doped porous nanofibers and the hydroxyapatite, and at the same time, the lanthanum-doped porous nanofibers and the hydroxyapatite are tightly combined, the hydroxyapatite is loaded on the lanthanum-doped porous nanofibers to obtain fiber-loaded hydroxyapatite, then the fiber-loaded hydroxyapatite is modified by using cetyltrimethylammonium bromide to obtain modified composite hydroxyapatite, and finally the modified composite hydroxyapatite is modified by chitosan to obtain a defluorination agent, which solves the problem of poor adsorption effect of the existing defluorination agent, thereby limiting its wide application in fluorine wastewater.

[0005] The purpose of the present application can be achieved by the following technical solutions:

[0006] A preparation method of hydroxyapatite, comprising the following steps:

[0007] Step one: polyacrylonitrile, polyvinylpyrrolidone and N,N-dimethylformamide are added to a three-necked flask equipped with a stirrer and a thermometer, and stirred at a temperature of 25-30 DEG C and a stirring rate of 400-500 r / min for 20-30 h, then electrospun, and then placed in a vacuum drying oven and dried at a temperature of 80-85 DEG C for 8-10 h to obtain nanofibers;

[0008] Step two: the nanofibers and a lanthanum nitrate solution are added to a three-necked flask equipped with a stirrer and a thermometer, and stirred at a temperature of 25-30 DEG C and a stirring rate of 400-500 r / min for 3-5 h, then heated to 110-115 DEG C and continued to stir for 8-10 h, then cooled to room temperature after the reaction, vacuum filtered, and then placed the filter cake in a vacuum drying oven and dried at a temperature of 80-85 DEG C for 2-3 h, then added to a tube furnace, heated to 220-230 DEG C at a heating rate of 2-3 DEG C / min, calcined for 2-3 h, then protected by argon, heated to 900-920 DEG C at a heating rate of 3-5 DEG C / min, calcined for 2-3 h, then cooled with the furnace to obtain lanthanum-doped porous nanofibers;

[0009] Step three: calcium nitrate tetrahydrate, deionized water were added into a three-necked flask equipped with a stirrer, a thermometer and a constant pressure dropping funnel, and stirred at a temperature of 40-45℃ and a stirring rate of 400-500 r / min for 20-30 min, then diammonium hydrogen phosphate solution was added drop by drop while stirring, the dropping rate was controlled at 1-2 drops / s, after the addition was completed, ammonia water was added to adjust the pH to 9-11, then the reaction was continued to stir for 3-5 h, after the reaction was completed, the reaction product was cooled to room temperature, then aged for 30-40 h, then vacuum filtration, the filter cake was washed with distilled water for 3-5 times, then placed in a vacuum drying oven, dried at a temperature of 100-110℃ for 8-10 h, then ground through a 200 mesh sieve, to obtain hydroxyapatite;

[0010] Step four: lanthanum-doped porous nanofiber, hydroxyapatite, iron nitrate nonahydrate, aluminum nitrate nonahydrate and deionized water were added into a three-necked flask equipped with a stirrer, a thermometer and a constant pressure dropping funnel, and ultrasonic dispersed at an ultrasonic power of 250-300 W for 1.5-2 h, then sodium hydroxide solution was added drop by drop while stirring at a temperature of 60-65℃ and a stirring rate of 400-500 r / min until the pH was 7.5-8, the dropping rate was controlled at 1-2 drops / s, after the addition was completed, the reaction was continued to stir for 1-2 h, after the reaction was completed, the reaction product was cooled to room temperature, then aged for 10-15 h, then vacuum filtration, the filter cake was washed with distilled water for 3-5 times, then placed in a vacuum drying oven, dried at a temperature of 95-100℃ for 2-3 h, to obtain fiber-loaded hydroxyapatite;

[0011] Step five: fiber-loaded hydroxyapatite, cetyltrimethylammonium bromide and deionized water were added into a three-necked flask equipped with a stirrer and a thermometer, and stirred at a temperature of 35-40℃ and a stirring rate of 400-500 r / min for 5-6 h, after the reaction was completed, the reaction product was cooled to room temperature, then vacuum filtration, the filter cake was washed with distilled water for 3-5 times, then placed in a vacuum drying oven, dried at a temperature of 70-75℃ for 3-5 h, to obtain modified composite hydroxyapatite;

[0012] Step six: chitosan, acetic acid solution were added into a three-necked flask equipped with a stirrer and a thermometer, and stirred at a temperature of 35-40℃ and a stirring rate of 400-500 r / min for 30-40 min, then modified composite hydroxyapatite was added and the reaction was continued to stir for 5-6 h, after the reaction was completed, the reaction product was cooled to room temperature, then vacuum filtration, the filter cake was placed in a vacuum drying oven, dried at a temperature of 70-75℃ for 3-5 h, to obtain a defluorination agent.

[0013] As a further aspect of the present invention: the ratio of polyacrylonitrile, polyvinylpyrrolidone and N,N-dimethylformamide used in step one is 1g:1g:15-20g.

[0014] As a further aspect of the present invention: the ratio of the amount of nanofibers and lanthanum nitrate solution used in step two is 1g:45-50mL, and the molar concentration of the lanthanum nitrate solution is 0.1-0.2mol / L.

[0015] As a further aspect of the present invention: the ratio of the amount of calcium nitrate tetrahydrate, deionized water, and diammonium hydrogen phosphate solution in step three is 10 mmol: 50 mL: 50-55 mL, wherein the diammonium hydrogen phosphate solution is a solution formed by dissolving 1.2-1.3 mmol of diammonium hydrogen phosphate in 10 mL of deionized water, and the mass fraction of the ammonia water is 20-22%.

[0016] As a further aspect of the present invention: the ratio of the amount of lanthanum-doped porous nanofibers, hydroxyapatite, ferric nitrate nonahydrate, aluminum nitrate nonahydrate, and deionized water in step four is 5-10g:10g:10-15mmol:10-15mmol:80-100mL, and the molar concentration of the sodium hydroxide solution is 1-1.5mol / L.

[0017] As a further aspect of the present invention: the ratio of fiber-loaded hydroxyapatite, hexadecyltrimethylammonium bromide and deionized water in step five is 10g: 0.1-0.3g: 60-70mL.

[0018] As a further aspect of the present invention: the ratio of chitosan, acetic acid solution and modified composite hydroxyapatite in step six is ​​2-5g: 50-60mL: 5g, and the mass fraction of the acetic acid solution is 2-3%.

[0019] The present invention also provides an application of hydroxyapatite prepared by the above preparation method in the defluorination of mine water.

[0020] The beneficial effects of this invention are:

[0021] This invention discloses a method for preparing hydroxyapatite. First, nanofibers are obtained by electrospinning polyacrylonitrile and polyvinylpyrrolidone as raw materials. Then, the nanofibers are fully immersed in a lanthanum nitrate solution to incorporate lanthanum ions. After calcination, lanthanum-doped porous carbon nanofibers are formed, yielding lanthanum-doped porous nanofibers. Next, hydroxyapatite is prepared using calcium nitrate tetrahydrate and diammonium hydrogen phosphate as raw materials. Then, the lanthanum-doped porous nanofibers and hydroxyapatite are fully immersed in a solution of iron nitrate and aluminum nitrate, followed by co-precipitation to dope lanthanum with iron and aluminum ions. Lanthanum-doped porous nanofibers and hydroxyapatite are simultaneously bonded together. Hydroxyapatite is loaded onto lanthanum-doped porous nanofibers to obtain fiber-loaded hydroxyapatite. Subsequently, the fiber-loaded hydroxyapatite is modified with hexadecyltrimethylammonium bromide to obtain modified composite hydroxyapatite. Finally, the modified composite hydroxyapatite is further modified with chitosan to obtain a defluorinating agent. During the preparation of this defluorinating agent, a type of hydroxyapatite is prepared, with each unit cell containing 10 Ca atoms. 2+ 6 PO4 3- and 2 OH - Metal ions can substitute Ca through isomorphic substitution. 2+ Hydroxyapatite is thus incorporated into water treatment, making it suitable for treating heavy metal ion contamination. Similarly, anions like PO42- can also be incorporated. 3- and OH - It can also be F - Therefore, hydroxyapatite can also be used to treat F-related diseases. - When polluted water with high fluoride levels comes into contact with hydroxyapatite, a dual reaction occurs on the surface of the hydroxyapatite: adsorption and ion exchange. Fluoride ions in the water are adsorbed onto the filter media, and fluoride ions also react with PO4 on the surface of the filter media. 3- and OH - A fluoride removal process is achieved through a dual-effect physicochemical reaction involving exchange. A porous nanofiber with numerous micropores, high specific surface area, and good adsorption capacity was also prepared. After doping the porous nanofiber with lanthanum, high-valence metal ions or metal oxides were loaded onto the surface. The adsorption performance of the porous nanofiber was improved through electrostatic attraction or ion exchange between the metal ions and metal oxides and electronegative pollutants. Combining these two methods further enhanced the adsorption of fluoride ions. Subsequently, the composite material was doped with iron and aluminum ions, which were incorporated into the hydroxyapatite lattice, partially removing Ca2+. 2+The substitution process and the formation of amorphous oxides contribute to the increase of the specific surface area and pore volume of hydroxyapatite, further enhancing its electrostatic attraction to electronegative pollutants and increasing the number of adsorption active sites on the hydroxyapatite surface. Hexadecyltrimethylammonium bromide, a cationic surfactant and a quaternary ammonium salt, possesses excellent surface activity and high acid-base stability. By embedding itself into the hydroxyapatite lattice, it alters the surface charge, causing the hydroxyapatite surface to exhibit a positive charge. This enhances the adsorption of F... - The electrostatic interaction between them will F - Adsorbed onto the crystal surface, chitosan contains a large number of amino functional groups, which can react with fluoride ions to form fluorinated chitosan. In addition, chitosan itself has excellent adsorption properties, and can adsorb fluoride ions in water onto its surface through adsorption, thereby achieving the purpose of fluoride removal. In summary, by loading hydroxyapatite onto porous nanofibers and performing multiple modifications on it, the defluorinating agent can be endowed with excellent defluorination effect. Detailed Implementation

[0022] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0023] Example 1:

[0024] This embodiment describes a method for preparing hydroxyapatite, comprising the following steps:

[0025] Step 1: Add 1g of polyacrylonitrile, 1g of polyvinylpyrrolidone and 15g of N,N-dimethylformamide to a three-necked flask equipped with a stirrer and thermometer. Stir and react for 20h at 25℃ and 400r / min. Then electrospin the mixture and place it in a vacuum drying oven to dry for 8h at 80℃ to obtain nanofibers.

[0026] Step 2: 1g of nanofibers and 45mL of lanthanum nitrate solution with a molar concentration of 0.1mol / L were added to a three-necked flask equipped with a stirrer and a thermometer. The mixture was stirred at 25℃ and a stirring rate of 400r / min for 3h. Then, the temperature was raised to 110℃ and the stirring was continued for 8h. After the reaction was completed, the reaction product was cooled to room temperature and then vacuum filtered. The filter cake was placed in a vacuum drying oven and dried at 80℃ for 2h. Then, it was added to a tube furnace and calcined at 220℃ at a heating rate of 2℃ / min for 2h. Then, argon gas was introduced for protection and the temperature was raised to 900℃ at a heating rate of 3℃ / min for 2h. Finally, the furnace was cooled to obtain lanthanum-doped porous nanofibers.

[0027] Step 3: Add 10 mmol of calcium nitrate tetrahydrate and 50 mL of deionized water to a three-necked flask equipped with a stirrer, thermometer, and constant pressure dropping funnel. Stir the reaction at 40°C and 400 r / min for 20 min. Then, while stirring, add 50 mL of a diammonium hydrogen phosphate solution (1.2 mmol: 10 mL dissolved in deionized water) dropwise, controlling the dropping rate to 1 drop / s. After the addition is complete, adjust the pH to 9 with 20% ammonia water. Continue stirring for 3 h. After the reaction is complete, cool the reaction product to room temperature and then age it for 30 h. Then, vacuum filter the product and wash the filter cake three times with distilled water. Place it in a vacuum drying oven and dry it at 100°C for 8 h. Finally, grind it through a 200-mesh sieve to obtain hydroxyapatite.

[0028] Step 4: Add 5g of lanthanum-doped porous nanofibers, 10g of hydroxyapatite, 10 mmol of ferric nitrate nonahydrate, 10 mmol of aluminum nitrate nonahydrate, and 80mL of deionized water to a three-necked flask equipped with a stirrer, thermometer, and constant-pressure dropping funnel. Sonicate the mixture for 1.5h under ultrasonic power of 250W. Then, add 1mol / L sodium hydroxide solution dropwise while stirring at 60℃ and a stirring rate of 400r / min until the pH reaches 7.5. Control the dropping rate to 1 drop / s. After the addition is complete, continue stirring for 1h. After the reaction is complete, cool the reaction product to room temperature and then age it for 10h. Then, vacuum filter the product and wash the filter cake three times with distilled water. Place it in a vacuum drying oven and dry it at 95℃ for 2h to obtain fiber-supported hydroxyapatite.

[0029] Step 5: Add 10g of fiber-supported hydroxyapatite, 0.1g of hexadecyltrimethylammonium bromide and 60mL of deionized water to a three-necked flask equipped with a stirrer and thermometer. Stir the mixture at 35℃ and a stirring rate of 400r / min for 5h. After the reaction is complete, cool the reaction product to room temperature, then filter it under vacuum. Wash the filter cake three times with distilled water, and then place it in a vacuum drying oven and dry it at 70℃ for 3h to obtain modified composite hydroxyapatite.

[0030] Step 6: Add 2g of chitosan and 50mL of 2% acetic acid solution to a three-necked flask equipped with a stirrer and thermometer. Stir the mixture at 35℃ and a stirring rate of 400r / min for 30min. Then add 5g of modified composite hydroxyapatite and continue stirring for 5h. After the reaction is complete, cool the reaction product to room temperature, then vacuum filter it. Place the filter cake in a vacuum drying oven and dry it at 70℃ for 3h to obtain the defluorinating agent.

[0031] Example 2:

[0032] This embodiment describes a method for preparing hydroxyapatite, comprising the following steps:

[0033] Step 1: Add 1g of polyacrylonitrile, 1g of polyvinylpyrrolidone and 18g of N,N-dimethylformamide to a three-necked flask equipped with a stirrer and thermometer. Stir and react for 25h at 28℃ and 450r / min. Then electrospin the mixture and place it in a vacuum drying oven to dry for 9h at 82℃ to obtain nanofibers.

[0034] Step 2: 1g of nanofibers and 48mL of lanthanum nitrate solution with a molar concentration of 0.15mol / L were added to a three-necked flask equipped with a stirrer and a thermometer. The mixture was stirred at 28℃ and a stirring rate of 450r / min for 4h. After that, the temperature was raised to 112℃ and the stirring was continued for 9h. After the reaction was completed, the reaction product was cooled to room temperature and then vacuum filtered. The filter cake was placed in a vacuum drying oven and dried at 82℃ for 2.5h. Then it was added to a tube furnace and calcined at 225℃ for 2.5h at a heating rate of 2℃ / min. Then argon gas was introduced for protection and the temperature was raised to 910℃ for 2.5h at a heating rate of 4℃ / min. After that, the furnace was cooled to obtain lanthanum-doped porous nanofibers.

[0035] Step 3: Add 10 mmol of calcium nitrate tetrahydrate and 50 mL of deionized water to a three-necked flask equipped with a stirrer, thermometer, and constant pressure dropping funnel. Stir the reaction at 42°C and 450 r / min for 25 min. Then, while stirring, add 52 mL of a diammonium hydrogen phosphate solution (1.2 mmol: 10 mL dissolved in deionized water) dropwise, controlling the dropping rate to 2 drops / s. After the addition is complete, adjust the pH to 10 with 21% ammonia water. Continue stirring for 4 h. After the reaction is complete, cool the reaction product to room temperature and then age it for 35 h. Then, vacuum filter the product and wash the filter cake four times with distilled water. Place it in a vacuum drying oven and dry it at 105°C for 9 h. Finally, grind it through a 200-mesh sieve to obtain hydroxyapatite.

[0036] Step 4: Add 8g of lanthanum-doped porous nanofibers, 10g of hydroxyapatite, 12 mmol of ferric nitrate nonahydrate, 12 mmol of aluminum nitrate nonahydrate, and 90mL of deionized water to a three-necked flask equipped with a stirrer, thermometer, and constant-pressure dropping funnel. Sonicate the mixture for 1.8h under ultrasonic power of 275W. Then, add 1.2mol / L sodium hydroxide solution dropwise while stirring at 62℃ and a stirring rate of 450r / min until the pH reaches 7.8. Control the dropping rate to 2 drops / s. After the addition is complete, continue stirring for 1.5h. After the reaction is complete, cool the reaction product to room temperature and then age it for 12h. Then, vacuum filter the product and wash the filter cake four times with distilled water. Place it in a vacuum drying oven and dry it at 98℃ for 2.5h to obtain fiber-supported hydroxyapatite.

[0037] Step 5: Add 10g of fiber-supported hydroxyapatite, 0.2g of hexadecyltrimethylammonium bromide and 65mL of deionized water to a three-necked flask equipped with a stirrer and thermometer. Stir the reaction at 38℃ and 450r / min for 5.5h. After the reaction is complete, cool the reaction product to room temperature, then filter it under vacuum. Wash the filter cake four times with distilled water and then place it in a vacuum drying oven and dry it at 72℃ for 4h to obtain modified composite hydroxyapatite.

[0038] Step 6: Add 3.5g of chitosan and 55mL of 2.5% acetic acid solution to a three-necked flask equipped with a stirrer and thermometer. Stir the mixture at 38℃ and a stirring rate of 450r / min for 35min. Then add 5g of modified composite hydroxyapatite and continue stirring for 5.5h. After the reaction is complete, cool the reaction product to room temperature, then vacuum filter it. Place the filter cake in a vacuum drying oven and dry it at 72℃ for 4h to obtain the defluorinating agent.

[0039] Example 3:

[0040] This embodiment describes a method for preparing hydroxyapatite, comprising the following steps:

[0041] Step 1: Add 1g of polyacrylonitrile, 1g of polyvinylpyrrolidone and 20g of N,N-dimethylformamide to a three-necked flask equipped with a stirrer and thermometer. Stir and react for 30h at 30℃ and a stirring rate of 500r / min. Then electrospin the mixture and place it in a vacuum drying oven to dry for 10h at 85℃ to obtain nanofibers.

[0042] Step 2: 1g of nanofibers and 50mL of lanthanum nitrate solution with a molar concentration of 0.2mol / L were added to a three-necked flask equipped with a stirrer and a thermometer. The mixture was stirred at 30℃ and a stirring rate of 500r / min for 5h. Then, the temperature was raised to 115℃ and the stirring was continued for 10h. After the reaction was completed, the reaction product was cooled to room temperature and then vacuum filtered. The filter cake was placed in a vacuum drying oven and dried at 85℃ for 3h. Then, it was added to a tube furnace and calcined at 230℃ at a heating rate of 3℃ / min for 3h. Then, argon gas was introduced for protection and the temperature was raised to 920℃ at a heating rate of 5℃ / min for 3h. Finally, the furnace was cooled to obtain lanthanum-doped porous nanofibers.

[0043] Step 3: Add 10 mmol of calcium nitrate tetrahydrate and 50 mL of deionized water to a three-necked flask equipped with a stirrer, thermometer, and constant pressure dropping funnel. Stir the reaction at 45°C and a stirring rate of 500 r / min for 30 min. Then, while stirring, add 55 mL of a diammonium hydrogen phosphate solution (1.3 mmol: 10 mL dissolved in deionized water) dropwise, controlling the dropping rate to 2 drops / s. After the addition is complete, adjust the pH to 11 with 22% ammonia water. Continue stirring for 5 h. After the reaction is complete, cool the reaction product to room temperature and then age it for 40 h. Then, vacuum filter the product and wash the filter cake 5 times with distilled water. Place it in a vacuum drying oven and dry it at 110°C for 10 h. Finally, grind it through a 200-mesh sieve to obtain hydroxyapatite.

[0044] Step 4: Add 10g of lanthanum-doped porous nanofibers, 10g of hydroxyapatite, 15mmol of ferric nitrate nonahydrate, 15mmol of aluminum nitrate nonahydrate, and 100mL of deionized water to a three-necked flask equipped with a stirrer, thermometer, and constant-pressure dropping funnel. Sonicate the mixture for 2 hours at an ultrasonic power of 300W. Then, add 1.5mol / L sodium hydroxide solution dropwise while stirring at 65℃ and a stirring rate of 500r / min until the pH reaches 8. Control the dropping rate to 2 drops / s. After the addition is complete, continue stirring for 2 hours. After the reaction is complete, cool the reaction product to room temperature and then age it for 15 hours. Then, vacuum filter the product and wash the filter cake 5 times with distilled water. Then, place it in a vacuum drying oven and dry it at 100℃ for 3 hours to obtain fiber-supported hydroxyapatite.

[0045] Step 5: Add 10g of fiber-supported hydroxyapatite, 0.3g of cetyltrimethylammonium bromide and 70mL of deionized water to a three-necked flask equipped with a stirrer and thermometer. Stir the mixture at 40℃ and a stirring rate of 500r / min for 6h. After the reaction is complete, cool the reaction product to room temperature, then filter it under vacuum. Wash the filter cake five times with distilled water, and then place it in a vacuum drying oven and dry it at 75℃ for 5h to obtain modified composite hydroxyapatite.

[0046] Step 6: Add 5g of chitosan and 60mL of 3% acetic acid solution to a three-necked flask equipped with a stirrer and thermometer. Stir the mixture at 40℃ and a stirring rate of 500r / min for 40min. Then add 5g of modified composite hydroxyapatite and continue stirring for 6h. After the reaction is complete, cool the reaction product to room temperature, then vacuum filter it. Place the filter cake in a vacuum drying oven and dry it at 75℃ for 5h to obtain the defluorinating agent.

[0047] Example 4:

[0048] This embodiment describes a method for preparing hydroxyapatite, comprising the following steps:

[0049] Step 1: Add 1g of polyacrylonitrile, 1g of polyvinylpyrrolidone and 20g of N,N-dimethylformamide to a three-necked flask equipped with a stirrer and thermometer. Stir and react for 30h at 30℃ and a stirring rate of 500r / min. Then electrospin the mixture and place it in a vacuum drying oven to dry for 10h at 85℃ to obtain nanofibers.

[0050] Step 2: 1g of nanofibers and 50mL of lanthanum nitrate solution with a molar concentration of 0.2mol / L were added to a three-necked flask equipped with a stirrer and a thermometer. The mixture was stirred at 30℃ and a stirring rate of 500r / min for 5h. Then, the temperature was raised to 115℃ and the stirring was continued for 10h. After the reaction was completed, the reaction product was cooled to room temperature and then vacuum filtered. The filter cake was placed in a vacuum drying oven and dried at 85℃ for 3h. Then, it was added to a tube furnace and calcined at 230℃ at a heating rate of 3℃ / min for 3h. Then, argon gas was introduced for protection and the temperature was raised to 920℃ at a heating rate of 5℃ / min for 3h. Finally, the furnace was cooled to obtain lanthanum-doped porous nanofibers.

[0051] Step 3: Add 10 mmol of calcium nitrate tetrahydrate and 50 mL of deionized water to a three-necked flask equipped with a stirrer, thermometer, and constant pressure dropping funnel. Stir the reaction at 45°C and a stirring rate of 500 r / min for 30 min. Then, while stirring, add 55 mL of a diammonium hydrogen phosphate solution (1.3 mmol: 10 mL dissolved in deionized water) dropwise, controlling the dropping rate to 2 drops / s. After the addition is complete, adjust the pH to 11 with 22% ammonia water. Continue stirring for 5 h. After the reaction is complete, cool the reaction product to room temperature and then age it for 40 h. Then, vacuum filter the product and wash the filter cake 5 times with distilled water. Place it in a vacuum drying oven and dry it at 110°C for 10 h. Finally, grind it through a 200-mesh sieve to obtain hydroxyapatite.

[0052] Step 4: Add 10g of lanthanum-doped porous nanofibers, 10g of hydroxyapatite, and 100mL of deionized water to a three-necked flask equipped with a stirrer, thermometer, and constant-pressure dropping funnel. Disperse the mixture ultrasonically at a power of 300W for 2 hours. Then, stir the mixture at 65℃ and a stirring rate of 500r / min for 2 hours. After the reaction is complete, cool the reaction product to room temperature, then filter it under vacuum. Wash the filter cake five times with distilled water, and then place it in a vacuum drying oven and dry it at 100℃ for 3 hours to obtain the defluorinating agent.

[0053] Example 5:

[0054] This embodiment describes a method for preparing hydroxyapatite, comprising the following steps:

[0055] Step 1: Add 1g of polyacrylonitrile, 1g of polyvinylpyrrolidone and 20g of N,N-dimethylformamide to a three-necked flask equipped with a stirrer and thermometer. Stir and react for 30h at 30℃ and a stirring rate of 500r / min. Then electrospin the mixture and place it in a vacuum drying oven to dry for 10h at 85℃ to obtain nanofibers.

[0056] Step 2: 1g of nanofibers and 50mL of lanthanum nitrate solution with a molar concentration of 0.2mol / L were added to a three-necked flask equipped with a stirrer and a thermometer. The mixture was stirred at 30℃ and a stirring rate of 500r / min for 5h. Then, the temperature was raised to 115℃ and the stirring was continued for 10h. After the reaction was completed, the reaction product was cooled to room temperature and then vacuum filtered. The filter cake was placed in a vacuum drying oven and dried at 85℃ for 3h. Then, it was added to a tube furnace and calcined at 230℃ at a heating rate of 3℃ / min for 3h. Then, argon gas was introduced for protection and the temperature was raised to 920℃ at a heating rate of 5℃ / min for 3h. Finally, the furnace was cooled to obtain lanthanum-doped porous nanofibers.

[0057] Step 3: Add 10 mmol of calcium nitrate tetrahydrate and 50 mL of deionized water to a three-necked flask equipped with a stirrer, thermometer, and constant pressure dropping funnel. Stir the reaction at 45°C and a stirring rate of 500 r / min for 30 min. Then, while stirring, add 55 mL of a diammonium hydrogen phosphate solution (1.3 mmol: 10 mL dissolved in deionized water) dropwise, controlling the dropping rate to 2 drops / s. After the addition is complete, adjust the pH to 11 with 22% ammonia water. Continue stirring for 5 h. After the reaction is complete, cool the reaction product to room temperature and then age it for 40 h. Then, vacuum filter the product and wash the filter cake 5 times with distilled water. Place it in a vacuum drying oven and dry it at 110°C for 10 h. Finally, grind it through a 200-mesh sieve to obtain hydroxyapatite.

[0058] Step 4: Add 10g of lanthanum-doped porous nanofibers, 10g of hydroxyapatite, 15mmol of ferric nitrate nonahydrate, 15mmol of aluminum nitrate nonahydrate, and 100mL of deionized water to a three-necked flask equipped with a stirrer, thermometer, and constant-pressure dropping funnel. Sonicate the mixture for 2 hours at an ultrasonic power of 300W. Then, while stirring at 65℃ and a stirring rate of 500r / min, add 1.5mol / L sodium hydroxide solution dropwise until the pH reaches 8, controlling the dropping rate to 2 drops / s. After the addition is complete, continue stirring for 2 hours. After the reaction is complete, cool the reaction product to room temperature and then age it for 15 hours. Then, vacuum filter the product, wash the filter cake five times with distilled water, and then place it in a vacuum drying oven and dry it at 100℃ for 3 hours to obtain the defluorinating agent.

[0059] Example 6:

[0060] This embodiment describes a method for preparing hydroxyapatite, comprising the following steps:

[0061] Step 1: Add 1g of polyacrylonitrile, 1g of polyvinylpyrrolidone and 20g of N,N-dimethylformamide to a three-necked flask equipped with a stirrer and thermometer. Stir and react for 30h at 30℃ and a stirring rate of 500r / min. Then electrospin the mixture and place it in a vacuum drying oven to dry for 10h at 85℃ to obtain nanofibers.

[0062] Step 2: Place 1g of nanofibers in a vacuum drying oven and dry at 85℃ for 3h. Then add them to a tube furnace and calcine at 230℃ for 3h at a heating rate of 3℃ / min. Then purge with argon gas and calcine at 920℃ for 3h at a heating rate of 5℃ / min. Then cool with the furnace to obtain porous nanofibers.

[0063] Step 3: Add 10 mmol of calcium nitrate tetrahydrate and 50 mL of deionized water to a three-necked flask equipped with a stirrer, thermometer, and constant pressure dropping funnel. Stir the reaction at 45°C and a stirring rate of 500 r / min for 30 min. Then, while stirring, add 55 mL of a diammonium hydrogen phosphate solution (1.3 mmol: 10 mL dissolved in deionized water) dropwise, controlling the dropping rate to 2 drops / s. After the addition is complete, adjust the pH to 11 with 22% ammonia water. Continue stirring for 5 h. After the reaction is complete, cool the reaction product to room temperature and then age it for 40 h. Then, vacuum filter the product and wash the filter cake 5 times with distilled water. Place it in a vacuum drying oven and dry it at 110°C for 10 h. Finally, grind it through a 200-mesh sieve to obtain hydroxyapatite.

[0064] Step 4: Add 10g of porous nanofibers, 10g of hydroxyapatite, 15mmol of ferric nitrate nonahydrate, 15mmol of aluminum nitrate nonahydrate, and 100mL of deionized water to a three-necked flask equipped with a stirrer, thermometer, and constant-pressure dropping funnel. Sonicate the mixture for 2 hours at an ultrasonic power of 300W. Then, while stirring at 65℃ and a stirring rate of 500r / min, add 1.5mol / L sodium hydroxide solution dropwise until the pH reaches 8, controlling the dropping rate to 2 drops / s. After the addition is complete, continue stirring for 2 hours. After the reaction is complete, cool the reaction product to room temperature and then age it for 15 hours. After that, vacuum filter the product, wash the filter cake 5 times with distilled water, and then place it in a vacuum drying oven and dry it at 100℃ for 3 hours to obtain the defluorinating agent.

[0065] Blank example:

[0066] This blank example uses hydroxyapatite from Example 6 as a defluorinating agent.

[0067] Using sodium fluoride as the fluoride concentration (F), a 10 mg / L fluoride-containing solution was prepared. 0.5 g of the defluorinating agent from Examples 1-6 and the blank example was added to 100 mL of the fluoride-containing solution. The solution was then shaken in a shaker at room temperature for 60 min at a shaking speed of 200 r / min. The defluorination rate η was measured, and the results are shown in the table below.

[0068] Sample Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Blank C O , mg / L 10 10 10 10 10 10 10 [C1, mg / L] 0.411 0.332 0.245 1.476 0.854 0.923 3.632 η, % 95.89 96.68 97.55 85.24 91.46 90.77 63.68

[0069] in, C O C1 is the initial concentration, C2 is the concentration after defluorination, and η is the defluorination rate.

[0070] Referring to the data in the table above, and based on the comparison between Examples 1-6 and the blank example, it can be seen that loading with porous nanofibers, doping with iron and aluminum ions, and modifying with hexadecyltrimethylammonium bromide and chitosan can significantly improve the defluorination effect of hydroxyapatite. Moreover, the defluorination effect of the porous nanofiber-loaded hydroxyapatite of the present invention can reach more than 95%.

[0071] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0072] The above description is merely an example and illustration of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described, or use similar methods to replace them, as long as they do not deviate from the invention or exceed the scope defined in the claims, they should all fall within the protection scope of the present invention.

Claims

1. A method for preparing hydroxyapatite, characterized in that, Includes the following steps: Step 1: Polyacrylonitrile, polyvinylpyrrolidone and N,N-dimethylformamide are added to a three-necked flask and stirred to react. Then, the mixture is electrospun and dried to obtain nanofibers. Step 2: Add nanofibers and lanthanum nitrate solution to a three-necked flask and stir to react. After the reaction is complete, cool the reaction product, then vacuum filter it, dry the filter cake, and then put it into a tube furnace. Calcine it at 220-230℃ for 2-3 hours at a heating rate of 2-3℃ / min. Then, purge with argon gas and calcine it at 900-920℃ for 2-3 hours at a heating rate of 3-5℃ / min. Then, cool it with the furnace to obtain lanthanum-doped porous nanofibers. Step 3: Add calcium nitrate tetrahydrate and deionized water to a three-necked flask and stir to react. Then, while stirring, add diammonium hydrogen phosphate solution dropwise. After the addition is complete, adjust the pH and continue stirring to react. After the reaction is complete, cool the reaction product, then age it, then filter it under vacuum. Wash and dry the filter cake, then grind and sieve it to obtain hydroxyapatite. Step 4: Lanthanum-doped porous nanofibers, hydroxyapatite, ferric nitrate nonahydrate, aluminum nitrate nonahydrate, and deionized water were added to a three-necked flask and ultrasonically dispersed. The pH was then adjusted. After the reaction was completed, the reaction product was cooled, aged, and then vacuum filtered. The filter cake was washed and dried to obtain fiber-loaded hydroxyapatite. Step 5: Add fiber-supported hydroxyapatite, hexadecyltrimethylammonium bromide and deionized water to a three-necked flask and stir to react. After the reaction is completed, cool the reaction product, then filter under vacuum. Wash and dry the filter cake to obtain modified composite hydroxyapatite. Step 6: Add chitosan and acetic acid solution to a three-necked flask and stir to react. Then add modified composite hydroxyapatite and continue stirring to react. After the reaction is completed, cool the reaction product, then filter under vacuum and dry the filter cake to obtain the defluorinating agent.

2. The method for preparing hydroxyapatite according to claim 1, characterized in that, The ratio of polyacrylonitrile, polyvinylpyrrolidone, and N,N-dimethylformamide used in step one is 1g:1g:15-20g.

3. The method for preparing hydroxyapatite according to claim 1, characterized in that, In step two, the ratio of nanofibers to lanthanum nitrate solution is 1g:45-50mL, and the molar concentration of the lanthanum nitrate solution is 0.1-0.2mol / L.

4. The method for preparing hydroxyapatite according to claim 1, characterized in that, In step three, the ratio of the amount of calcium nitrate tetrahydrate, deionized water, and diammonium hydrogen phosphate solution is 10 mmol: 50 mL: 50-55 mL. The diammonium hydrogen phosphate solution is a solution formed by dissolving 1.2-1.3 mmol of diammonium hydrogen phosphate in 10 mL of deionized water.

5. The method for preparing hydroxyapatite according to claim 1, characterized in that, In step four, the ratio of lanthanum-doped porous nanofibers, hydroxyapatite, ferric nitrate nonahydrate, aluminum nitrate nonahydrate, and deionized water is 5-10g:10g:10-15mmol:10-15mmol:80-100mL.

6. The method for preparing hydroxyapatite according to claim 1, characterized in that, In step five, the ratio of fiber-loaded hydroxyapatite, hexadecyltrimethylammonium bromide, and deionized water is 10g:0.1-0.3g:60-70mL.

7. The method for preparing hydroxyapatite according to claim 1, characterized in that, In step six, the ratio of chitosan, acetic acid solution, and modified composite hydroxyapatite is 2-5g: 50-60mL: 5g, and the mass fraction of the acetic acid solution is 2-3%.

8. The application of hydroxyapatite prepared by the method of any one of claims 1 to 7 in the defluorination of mine water.