Double-tooth chelating fluorine removal agent as well as preparation method and application thereof

Abstract

The invention provides a preparation method of a bidentate chelating fluorine removal agent, which comprises the following steps: step 1, dropwise adding an inorganic alkali solution into an AlCl3 solution or an FeCl3 solution, and carrying out pre-hydrolysis reaction to obtain a pre-hydrolyzed aluminum solution or iron solution; 2, mixing silanetriol with the pre-hydrolyzed aluminum solution or iron solution obtained in the step 1 to obtain a mixed stock solution, 3, dropwise adding an inorganic alkali solution into the mixed stock solution obtained in the step 2, and carrying out an alkalization reaction to obtain an alkalized solution; and 4, aging the alkalized solution obtained in the step 3 to obtain the bidentate chelating fluorine removal agent. The prepared double-tooth chelating fluorine removal agent can effectively solve the problems that in the prior art, a fluorine removal agent is poor in selective removal capacity for fluoride in fluorine-containing sewage, poor in floc settling performance, large in dosage, residual in fluorine removal agent and the like.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, and in particular to a bidentate chelating defluorinating agent, its preparation method and uses. Background Technology

[0002] Fluoride is one of the most common anions in groundwater and surface water worldwide. Except for lanthanide fluorides and alkaline earth metal fluorides, most other fluorides are stable and readily soluble in nature. The primary source of fluoride is industrial production, characterized by its wide range of pollution and high concentrations. Specifically, large amounts of fluoride-containing wastewater are discharged from various industries, including coal mine water, coal chemical industry, deep well water industry, photovoltaic industry, fluorochemical industry, metal smelting industry, electroplating industry, and fluoride-containing mineral mining. Fluoride pollution in drinking water poses a serious threat to public health. Fluoride gradually accumulates in the human body, causing severe damage to human tissues. First, excessive fluoride in water damages bone cells, osteoclasts, and odontoblasts. Second, fluoride inhibits the growth and development of human tissues and affects normal physiological metabolism. Third, fluoride mineralizes some severely damaged tissues. It is estimated that over 200 million people worldwide have consumed water contaminated with fluoride, with fluoride concentrations exceeding 1.5 ppm (the standard concentration for fluoride is set by the World Health Organization). Therefore, how to effectively remove fluoride ions has become an increasingly important issue.

[0003] Existing defluorinating agents mainly rely on the synergistic effects of electrostatic attraction, chemical adsorption, and net-like sweeping of the hydrolysis and polymerization products of aluminum and iron salts, as well as the electrostatic attraction, hydrogen bonding, and complexation forces on the surface of metal adsorbents. These form monodentate bonds under ligand exchange or ion exchange, resulting in low selectivity for fluoride capture and separation processes based on monodentate bonds. Current technologies either directly mix the active ingredients or fail to adjust their morphology, thus failing to optimize the molecular structure for selective defluorination.

[0004] Existing defluoridating agents such as CN115636493B, CN113772762B, CN113087040B, CN113213607B, CN114853109B, and CN111302465B all employ a direct mixing and compounding method for the active ingredients. This results in incomplete and uniform mixing of the active ingredients, leading to a homogeneous mixture with weak bonds between components, making it difficult for them to exert a synergistic effect at the microscopic level. CN101298347B and CN104445553B proposed covalently bonded organic-inorganic composite defluoridating agents, but these failed to achieve selective defluorination based on the fluoride content characteristics of fluoride-containing wastewater.

[0005] Therefore, there is an urgent need to research and develop a defluoridating agent to effectively solve the problems of poor selective removal capacity of defluoridating agents for fluoride-containing wastewater, poor floc settling performance, large dosage, and defluoridating agent residue in existing technologies. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a method for preparing a bidentate chelating defluoridating agent. The prepared bidentate chelating defluoridating agent is intended to solve the problems of poor selective removal capacity of defluoridating agents (flocculators) for fluoride-containing wastewater, poor floc settling performance, large dosage, and defluoridating agent residue in existing technologies.

[0007] To achieve the above objectives and technical effects, the present invention adopts the following technical solution:

[0008] A method for preparing a bidentate chelating defluorinating agent includes the following steps:

[0009] Step 1: Add an inorganic alkali solution dropwise to an AlCl3 solution or FeCl3 solution and carry out a pre-hydrolysis reaction at a temperature of 60℃-110℃ to obtain a pre-hydrolyzed aluminum solution or iron solution. The pre-hydrolyzed aluminum solution exists in the form of aluminum-oxygen tetrahedra, and the pre-hydrolyzed iron solution exists in the form of iron-oxygen tetrahedra.

[0010] Step 2: Mix silanetriol with the pre-hydrolyzed aluminum or iron solution obtained in Step 1 to obtain a mixed stock solution. The structural formula of silanetriol is C1. n H 2n+1 N(CH3)2Cl(CH2)3Si(OH)3, wherein n is 0-30, preferably 0-20, more preferably 8-20, for example, n is 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 or 20;

[0011] Step 3: Add an inorganic alkali solution dropwise to the mixed stock solution obtained in Step 2, and carry out an alkalization reaction at a temperature of 80℃-100℃ to obtain an alkalized solution;

[0012] Step 4: Aging the alkalized solution obtained in Step 3 to obtain the bidentate chelate defluorinating agent.

[0013] According to the preparation method of the present invention, in step 1, the concentration of the AlCl3 solution or FeCl3 solution is 0.01 to 5 mol / L, preferably 0.1 to 3 mol / L, for example, 0.1 mol / L, 0.3 mol / L, 0.5 mol / L, 0.7 mol / L, 1 mol / L, 1.2 mol / L, 1.5 mol / L, 1.8 mol / L, 2 mol / L, 2.2 mol / L, 2.5 mol / L, 2.8 mol / L or 3 mol / L.

[0014] According to the preparation method of the present invention, in step 1, the inorganic alkali solution is a NaOH solution, a Na2CO3 solution, or a NaHCO3 solution, and the concentration of the inorganic alkali solution is 0.005–1 mol / L, preferably 0.01–0.8 mol / L, for example, 0.01 mol / L, 0.05 mol / L, 0.1 mol / L, 0.15 mol / L, 0.2 mol / L, 0.25 mol / L, 0.3 mol / L, 0.35 mol / L, 0.4 mol / L, 0.45 mol / L, 0.5 mol / L, 0.55 mol / L, 0.6 mol / L, 0.65 mol / L, 0.7 mol / L, 0.75 mol / L, or 0.8 mol / L.

[0015] According to the preparation method of the present invention, in step 1, the pH of the pre-hydrolyzed aluminum solution is 10-12, preferably 10-11.5, and the pH of the pre-hydrolyzed iron solution is 2-5, preferably 3-4.

[0016] According to the preparation method of the present invention, in step 2, the silanetriol is dodecylsilanetriol, tetradecylsilanetriol, octadecylsilanetriol, etc.

[0017] According to the preparation method of the present invention, in step 2, the molar ratio of Al / Si or Fe / Si in the obtained mixed stock solution is 10-35:1, for example 10:1, 15:1, 20:1, 25:1, 30:1 or 35:1.

[0018] According to the preparation method of the present invention, in step 3, the inorganic alkaline solution is a NaOH solution, a Na2CO3 solution, or a NaHCO3 solution, and the concentration of the inorganic alkaline solution is 0.005-1 mol / L, preferably 0.01-0.2 mol / L, for example 0.01 mol / L, 0.02 mol / L, 0.03 mol / L, 0.04 mol / L, 0.05 mol / L, 0.1 mol / L, 0.15 mol / L, or 0.2 mol / L.

[0019] According to the preparation method of the present invention, in step 3, the amount of inorganic alkali solution added is controlled by the endpoint alkalinity (B) of the alkali solution, which is 2.0-2.8, for example, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7 or 2.8. The alkalinity is the molar ratio of the amount of alkali added to the solution to the total amount of aluminum or iron in the solution.

[0020] According to the preparation method of the present invention, in step 4, the alkalization solution obtained in step 3 is aged for 24-72 hours, for example, 24 hours, 30 hours, 36 hours, 42 hours, 48 ​​hours, 54 hours, 60 hours, 66 hours or 72 hours.

[0021] According to the preparation method of the present invention, when the inorganic alkaline solution is NaOH solution, the preparation method of the bidentate chelating defluorinating agent includes the following reaction formula:

[0022]

[0023]

[0024]

[0025]

[0026] When the inorganic alkaline solution is Na2CO3 or NaHCO3, the preparation method of the bidentate chelating defluorinating agent also includes the following reaction formula:

[0027]

[0028]

[0029] Where M is Al or Fe;

[0030] in,

[0031] Reaction (1) corresponds to step 1;

[0032] Reaction formulas (2), (3) and (4) correspond to steps 3 and 4, where reaction formulas (3) and (4) represent the generation of two types of defluorinating agents, and reaction formula (3) is the dominant reaction.

[0033] The present invention also provides a bidentate chelating defluorinating agent, which is prepared by the method described above.

[0034] This invention also provides a method for defluoridating fluoride-containing wastewater, comprising the following steps:

[0035] Add the bidentate chelating defluorinating agent prepared according to the method described above to the fluoride-containing wastewater, stir, form a precipitate, separate the solid and liquid, and obtain defluorinated water.

[0036] According to the defluorination method of the present invention, a bidentate chelating defluorinating agent prepared according to the method described above is added to the fluoride-containing wastewater in one step.

[0037] According to the defluorination method of the present invention, the addition process is accompanied by rapid stirring followed by slow stirring to form flocculent precipitate (e.g., alum flocculent precipitate), followed by solid-liquid separation, and the resulting supernatant is defluorinated water.

[0038] According to the defluorination method of the present invention, the dosage of the bidentate chelating defluorinating agent is as follows: the molar ratio of total aluminum or total iron in the bidentate chelating defluorinating agent to total fluoride in fluoride-containing wastewater is 1:1 to 7:1, preferably 1:1 to 5:1, for example, 1:1, 2:1, 3:1, 4:1 or 5:1.

[0039] According to the defluorination method of the present invention, the rapid stirring speed is 120-300 rpm and the stirring time is 0.5-4 min; the slow stirring speed is 10-50 rpm and the stirring time is 5-20 min.

[0040] According to the defluorination method of the present invention, the fluoride-containing wastewater is fluoride-containing mine water, fluoride-containing industrial wastewater, fluoride-containing groundwater, etc.

[0041] The present invention also provides the use of the above-mentioned bidentate chelating defluorinating agent in the defluorination of fluoride-containing wastewater.

[0042] Beneficial effects

[0043] This invention provides a method for preparing a bidentate chelating defluoridating agent. The prepared bidentate chelating defluoridating agent can solve the problems of poor selective removal capacity of defluoridating agents for fluoride-containing wastewater, poor floc settling performance, large dosage, and defluoridating agent residue in the prior art. Attached Figure Description

[0044] Figure 1 The NMR spectrum of the bidentate chelating defluorinating agent prepared according to Example 1 of the present invention is shown.

[0045] Figure 2 The mass spectrum of the bidentate chelating defluorinating agent prepared according to Example 2 of the present invention is shown.

[0046] Figure 3 The diagram shows the iron speciation analysis of the bidentate chelating defluorinating agent prepared according to Example 3 of the present invention.

[0047] Figure 4 The diagram shows the iron speciation analysis of the bidentate chelating defluorinating agent prepared according to Example 4 of the present invention.

[0048] Figure 5 The diagram shows the iron speciation analysis of the bidentate chelating defluorinating agent prepared according to Example 5 of the present invention. Detailed Implementation

[0049] Preferred embodiments of the invention will now be described in more detail. While preferred embodiments of the invention are described below, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein.

[0050] The described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention are within the scope of protection of the present invention.

[0051] The main raw material information is as follows:

[0052] AlCl3, CAS No. 7446-70-0, analytical grade, molecular weight 133.34, purchased from Sinopharm Group.

[0053] FeCl3, CAS No. 7705-08-0, analytical grade, molecular weight 162.2, purchased from Sinopharm Group.

[0054] Tetradecylsilanetriol, with the structural formula C 14 H 29 N(CH3)2Cl(CH2)3Si(OH)3, analytical grade, molecular weight 398.1, purchased from Shanghai Shiyang Chemical Co., Ltd.

[0055] Octadecylsilanetriol, with the structural formula C 18 H 37 N(CH3)2Cl(CH2)3Si(OH)3, molecular weight 454.2, purchased from Shanghai Shiyang Chemical Co., Ltd.

[0056] Polyaluminum chloride (PAC) reagent, white powder, alkalinity greater than 60%, active ingredient content greater than 32%, purchased from Guangdong Zhongke Water Purification Materials Co., Ltd.

[0057] Polyacrylamide (PAM) agent, white powder, anionic, molecular weight 12 million, purchased from Guangdong Zhongke Water Purification Materials Co., Ltd.

[0058] Polyferric sulfate (PFS) reagent, yellow powder, with a total iron content greater than 30%, purchased from Guangdong Zhongke Water Purification Materials Co., Ltd.

[0059] Example

[0060] Example 1: Preparation method of bidentate chelating defluorinating agent

[0061] Add 0.1 mol / L Na2CO3 solution dropwise to 0.3 mol / L AlCl3 solution. The reaction is carried out in a constant temperature water bath at 60℃ with stirring. The solution is added dropwise until the pH of the reaction solution is 11, and a pre-hydrolyzed aluminum solution in the form of aluminum-oxygen tetrahedra is obtained.

[0062] Octadecylsilanetriol was mixed with the above aluminum solution, and the Al / Si molar ratio was controlled to be 20:1.

[0063] Add 0.01 mol / L sodium hydroxide solution dropwise to the above mixed stock solution to allow the precursor in the mixed stock solution to undergo slow alkalization simultaneously. The reaction is carried out in a constant temperature water bath at 80℃, and the final alkalinity of the solution is controlled to be 2.0.

[0064] The solution was aged for 24 hours to obtain a bidentate chelating defluorinating agent.

[0065] Defluorination reagent prepared using liquid aluminum NMR analysis 27 Al MAS NMR was performed on a Bruker Avance III 400 (9.4T) instrument. The test conditions were: resonant frequency 104 MHz, repetition delay 1 s, 128 scans, rotation speed 13 kHz, and sweep width 104166 Hz. The results are as follows: Figure 1 As shown, the peak at 63 ppm is the Al(O)4 tetrahedral peak, which is Al 13 The unique structure of the molecule, with the peak at 0 ppm representing aluminum in the form of monomers, indicates that under the experimental conditions described above, a large proportion of aluminum polymerized and hydrolyzed to form the polymer Al. 13 The morphology is that of the main form of bidentate chelate fluoride removal (indicating that the above reaction formula (3) is the dominant reaction).

[0066] Example 2

[0067] Add 0.5 mol / L NaOH solution dropwise to a 3 mol / L AlCl3 solution. The reaction is carried out in a constant temperature water bath at 100℃ with stirring. The solution is added dropwise until the pH of the reaction solution is 11.5, and a pre-hydrolyzed aluminum solution in the form of aluminum-oxygen tetrahedra is obtained.

[0068] Octadecylsilanetriol was mixed with the above aluminum solution, and the Al / Si molar ratio was controlled to be 10:1.

[0069] Add 0.1 mol / L sodium bicarbonate solution dropwise to the above mixed stock solution to allow the precursor in the mixed stock solution to undergo slow alkalization simultaneously. The reaction is carried out in a constant temperature water bath at 100℃, and the final alkalinity of the solution is controlled to be 2.2.

[0070] The solution was aged for 30 hours to obtain a bidentate chelating defluorinating agent.

[0071] The prepared defluorinating agent was analyzed using an electrospray ionization source and quadrupole-time-of-flight mass spectrometry (ESI-TOF-MS, 2695XE micro, Waters, USA). ESI-TOF-MS was scanned in positive ion mode. The detection conditions were as follows: spray voltage 3500.0 V, sample cone voltages 40 V, 60 V, 70 V, and 150 V, cone extraction voltage 5 V, source temperature 120 °C, desolvation temperature 150 °C, N2 flow rate 300 L / h, solution entry flow rate into the mass spectrometer 10 μL / min, and mass spectrometry scan range m / z 80–1000. Results are as follows: Figure 2 As shown, m / z at 243, 237, 231, 225, 219, and 213 represent AlO4Al 12 O 7+n (OH) 14-2n 3+ (n = 0-5, [Al) 13 ] 3+ Another set of m / z values ​​at 391, 382, ​​373, 364, 355, 346, 337, and 328 represent AlO4Al. 12 O 7+n (OH) 15-2n 2+ (n = 0 - 7, [Al) 13 ] 2+ In addition, there are a few peaks representing aluminum monomers at m / z 79 and 97, which are Al(OH)2(H2O). 1-2 + Under the above experimental conditions, a large proportion of aluminum polymerized and hydrolyzed to produce high-molecular-weight Al. 13 The morphology is that of the main form of bidentate chelate fluoride removal (indicating that the above reaction formula (3) is the dominant reaction).

[0072] Example 3

[0073] Add 0.5 mol / L NaHCO3 solution dropwise to 0.6 mol / L FeCl3 solution. The reaction is carried out in a constant temperature water bath at 110℃ with stirring. The solution is added dropwise until the pH of the reaction solution is 4, and a pre-hydrolyzed iron solution in the form of iron-oxygen tetrahedra is obtained.

[0074] Tetradecylsilanetriol was mixed with the above iron solution, and the Fe / Si molar ratio was controlled to be 35:1.

[0075] Add 0.2 mol / L Na2CO3 solution dropwise to the above mixed stock solution to allow the precursor in the mixed stock solution to undergo slow alkalization simultaneously. The reaction is carried out in a constant temperature water bath at 80℃, and the final alkalinity of the solution is controlled to be 2.5.

[0076] The solution was aged for 30 hours to obtain a bidentate chelating defluorinating agent.

[0077] The speciation of iron in the prepared defluorinating agent was analyzed using the Ferron time-wise complexometric colorimetric method. The total iron concentration in the solution was measured using a Perkin-Elmer Optima inductively coupled plasma optical emission spectrometer 2000 (ICP-OES, USA). For Ferron analysis, the defluorinating agent solution was first serially diluted 1000-fold. Ferron reagent (7-iodo-8-hydroxyquinoline-5-sulfonic acid) was then used to react with the iron in the solution. The iron that reacted with Ferron within 1 minute was Fe. a The shape and curve reach equilibrium at the point where Fe... b Fe c The remaining portion that could not be determined, Fe T =Fe a +Fe b +Fe c .

[0078] Iron morphology test results are as follows Figure 3 As shown. The total iron concentration of the defluorinating agent is 0.55 mol / L, derived from... Figure 3 It can be known that Fe a The monomeric iron content is approximately 0.1 mol / L, Fe b Medium-polymer iron and Fe c The polymer iron concentration was 0.45 mol / L, which is the main form of bidentate chelate fluoride removal (indicating that the above reaction formula (3) is the dominant reaction).

[0079] Example 4: Preparation method of bidentate chelating defluorinating agent

[0080] Add 0.01 mol / L NaOH solution dropwise to 0.1 mol / L AlCl3 solution. The reaction is carried out in a constant temperature water bath at 60℃ with stirring. The solution is added dropwise until the pH of the reaction solution is 10, and a pre-hydrolyzed aluminum solution in the form of aluminum-oxygen tetrahedra is obtained.

[0081] Octadecylsilanetriol was mixed with the above aluminum solution, and the Al / Si molar ratio was controlled to be 20:1.

[0082] Add 0.02 mol / L sodium hydroxide solution dropwise to the above mixed stock solution to allow the precursor in the mixed stock solution to undergo slow alkalization simultaneously. The reaction is carried out in a constant temperature water bath at 80℃, and the final alkalinity of the solution is controlled to be 2.0.

[0083] The solution was aged for 24 hours to obtain a bidentate chelating defluorinating agent.

[0084] The speciation of aluminum in the prepared defluorinating agent was analyzed using the Ferron time-wise complexometric colorimetric method. The total aluminum concentration in the solution was measured using a Perkin-Elmer Optima inductively coupled plasma optical emission spectrometer 2000 (ICP-OES, USA). For Ferron analysis, the defluorinating agent solution was first serially diluted 1000-fold. Ferron reagent (7-iodo-8-hydroxyquinoline-5-sulfonic acid) was then used to react with the aluminum in the solution. The aluminum that reacted with Ferron within 1 minute was Al. a The shape and curve reach equilibrium at point Al. b Al c The remaining portion that could not be measured, Al T =Al a +Al b +Al c .

[0085] Aluminum morphology test results are as follows Figure 4 As shown. The total aluminum concentration of the defluorinating agent is 0.055 mol / L, derived from... Figure 4 It can be seen that Al a The monomer aluminum content is approximately 0.01 mol / L, Al b The medium-polymer aluminum content is approximately 0.037 mol / L, Al c The polymer contains approximately 0.008 mol / L of aluminum. b And Al c This is the main form of bidentate chelate fluoride removal (indicating that reaction (3) above is the dominant reaction).

[0086] Example 5

[0087] Add 0.8 mol / L NaHCO3 solution dropwise to 0.1 mol / L FeCl3 solution. The reaction is carried out in a constant temperature water bath at 60℃ with stirring. The solution is added dropwise until the pH of the reaction solution is 3, and a pre-hydrolyzed iron solution in the form of iron-oxygen tetrahedra is obtained.

[0088] Tetradecylsilanetriol was mixed with the above iron solution, and the Fe / Si molar ratio was controlled to be 10:1.

[0089] Add 0.2 mol / L NaHCO3 solution dropwise to the above mixed stock solution to allow the precursor in the mixed stock solution to undergo slow alkalization simultaneously. The reaction is carried out in a constant temperature water bath at 100℃, and the final alkalinity of the solution is controlled to be 2.8.

[0090] The solution was aged for 72 hours to obtain a bidentate chelating defluorinating agent.

[0091] The speciation of iron in the prepared defluorinating agent was analyzed using the Ferron time-wise complexometric colorimetric method. The total iron concentration in the solution was measured using a Perkin-Elmer Optima inductively coupled plasma optical emission spectrometer 2000 (ICP-OES, USA). For Ferron analysis, the defluorinating agent solution was first serially diluted 1000-fold. Ferron reagent (7-iodo-8-hydroxyquinoline-5-sulfonic acid) was then used to react with the iron in the solution. The iron that reacted with Ferron within 1 minute was Fe. a The shape and curve reach equilibrium at the point where Fe... b Fe c The remaining portion that could not be determined, Fe T =Fe a +Fe b +Fe c .

[0092] Iron morphology test results are as follows Figure 5 As shown. The total iron concentration of the defluorinating agent is 0.65 mol / L, derived from... Figure 5 It can be known that Fe a The monomeric iron content is approximately 0.12 mol / L, Fe b Medium-polymer iron and Fe c The polymer iron concentration was 0.53 mol / L, which is the main form of bidentate chelate fluoride removal (indicating that the above reaction formula (3) is the dominant reaction).

[0093] Test Example 1

[0094] The bidentate chelating defluoridating agent prepared in Example 1 was added to the water from a typical fluoride-containing mine in western China, with a total aluminum to total fluoride molar ratio of 3:1. As a comparison, commercially available polyaluminum chloride (PAC) and polyacrylamide (PAM) (precipitating aids) were added to treat the fluoride-containing mine water, respectively. The PAC dosage was 5:1 aluminum to fluoride ratio, and the PAM dosage was 0.5 mg / L. The agent in Example 1 was added once, while the commercially available agent was added twice, and treatment was carried out using conventional coagulation and sedimentation methods. Both solutions were rapidly stirred at 150 rpm for 2 min, followed by slow stirring at 10 rpm for 10 min, and then allowed to settle naturally for 20 min after flocculation. The main water quality indicators of the original fluoride-containing mine water before the reaction and the supernatant after the reaction are shown in Table 1.

[0095] Table 1

[0096]

[0097]

[0098] Test Example 2

[0099] The bidentate chelating defluorinating agent prepared in Example 2 was added to the water from a typical fluoride-containing mine in western China, with a total aluminum to total fluoride molar ratio of 2:1. The solution was rapidly stirred at 200 rpm for 1.5 min, followed by slow stirring at 20 rpm for 10 min, and then allowed to settle naturally for 20 min after flocculation. The main water quality indicators of the original fluoride-containing mine water before the reaction and the supernatant after the reaction are shown in Table 2.

[0100] Table 2

[0101]

[0102] Test Example 3

[0103] The bidentate chelating defluoridating agent prepared in Example 3 was added to a typical fluoride-containing mine water in western China, with a total aluminum to total fluoride molar ratio of 3:1. Commercially available polyferric sulfate (PFS) and polyacrylamide (PAM) (precipitating aids) were also added as controls to treat the fluoride-containing mine water. The PFS dosage was 6:1 (ferric to fluoride ratio), and the PAM dosage was 0.5 mg / L. The agent in Example 3 was added once, while the commercially available agent was added twice, and treatment was carried out using conventional coagulation and sedimentation methods. Both solutions were rapidly stirred at 300 rpm for 2 min, followed by slow stirring at 30 rpm for 5 min, and then allowed to settle naturally for 20 min after flocculation. The main water quality indicators of the original fluoride-containing mine water before the reaction and the supernatant after the reaction are shown in Table 3.

[0104] Table 3

[0105]

[0106] Test Example 4

[0107] The bidentate chelating defluorinating agent prepared in Example 4 was added to the water from a typical fluoride-containing mine in western China, with a total aluminum to total fluoride molar ratio of 1:1. The solution was rapidly stirred at 200 rpm for 0.5 min, followed by slow stirring at 20 rpm for 5 min, and then allowed to settle naturally for 30 min after flocculation. The main water quality indicators of the original fluoride-containing mine water before the reaction and the supernatant after the reaction are shown in Table 4.

[0108] Table 4

[0109]

[0110]

[0111] Test Example 5

[0112] The bidentate chelating defluoridating agent prepared in Example 5 was added to a typical fluoride-containing mine water in western China, with a total aluminum to total fluoride molar ratio of 1:1. Commercially available polyferric sulfate (PFS) and polyacrylamide (PAM) (precipitating aids) were also added as controls to treat the fluoride-containing mine water. The PFS dosage was 6:1 (ferric to fluoride ratio), and the PAM dosage was 0.5 mg / L. The agent in Example 5 was added once, while the commercially available agent was added twice, treated using conventional coagulation and sedimentation methods. Both solutions were rapidly stirred at 120 rpm for 1 min, followed by slow stirring at 50 rpm for 20 min, and then allowed to settle naturally for 20 min after flocculation. The main water quality indicators of the original fluoride-containing mine water before the reaction and the supernatant after the reaction are shown in Table 5. The results of the supernatant after treatment with the commercially available agent (PFS+PAM) are shown in Table 3.

[0113] Table 5

[0114]

Claims

1. A method for preparing a bidentate chelating defluorinating agent, comprising the following steps: Step 1: Add an inorganic alkali solution dropwise to an AlCl3 solution or FeCl3 solution and carry out a pre-hydrolysis reaction at a temperature of 60℃-110℃ to obtain a pre-hydrolyzed aluminum solution or iron solution; Step 2: Mix silanetriol with the pre-hydrolyzed aluminum or iron solution obtained in Step 1 to obtain a mixed stock solution. The structural formula of silanetriol is C1. n H 2n+1 N(CH3)2Cl(CH2)3Si(OH)3, where n is 0-30; Step 3: Add an inorganic alkali solution dropwise to the mixed stock solution obtained in Step 2, and carry out an alkalization reaction at a temperature of 80℃-100℃ to obtain an alkalized solution; Step 4: Aging the alkalized solution obtained in Step 3 to obtain the bidentate chelate defluorinating agent.

2. The preparation method according to claim 1, wherein, In step 1, The concentration of AlCl3 solution or FeCl3 solution is 0.01–5 mol / L, preferably 0.1–3 mol / L; Preferably, the inorganic alkaline solution is a NaOH solution, a Na2CO3 solution, or a NaHCO3 solution, and the concentration of the inorganic alkaline solution is 0.005–1 mol / L, preferably 0.01–0.8 mol / L; Preferably, the pH of the pre-hydrolyzed aluminum solution is 10-12, and the pH of the pre-hydrolyzed iron solution is 2-5.

3. The preparation method according to claim 1 or 2, wherein, In step 2, The silanetriol is a dodecylsilanetriol, tetradecylsilanetriol, or octadecylsilanetriol; Preferably, the molar ratio of Al / Si or Fe / Si in the obtained mixed stock solution is 10-35:

1.

4. The preparation method according to claim 1 or 2, wherein, In step 3, The inorganic alkaline solution is a NaOH solution, a Na2CO3 solution, or a NaHCO3 solution, and the concentration of the inorganic alkaline solution is 0.005–1 mol / L, preferably 0.01–0.2 mol / L; Preferably, the amount of inorganic alkaline solution added is controlled by the final alkalinity of the alkaline solution, and the final alkalinity of the alkaline solution is 2.0-2.

8.

5. The preparation method according to claim 1 or 2, wherein, In step 4, the alkalized solution obtained in step 3 is aged for 24-72 hours.

6. A bidentate chelating defluorinating agent, wherein the bidentate chelating defluorinating agent is prepared by the preparation method according to any one of claims 1-5.

7. A method for defluoridating fluoride-containing wastewater, comprising the following steps: Add the bidentate chelating defluorinating agent prepared according to any one of claims 1-5 to the fluoride-containing wastewater, stir, form a precipitate, separate the solid and liquid, and obtain defluorinated water; Preferably, the bidentate chelating defluorinating agent prepared according to any one of claims 1-5 is added to the fluoride-containing wastewater in one step.

8. The defluorination method according to claim 7, wherein, The addition process involves rapid stirring followed by slow stirring. After the formation of flocculent precipitate, solid-liquid separation is performed, and the resulting supernatant is the defluorinated water. Preferably, the dosage of the bidentate chelating defluorinating agent is as follows: the molar ratio of total aluminum or total iron in the bidentate chelating defluorinating agent to total fluoride in the fluoride-containing wastewater is 1:1 to 7:1, preferably 1:1 to 5:1; Preferably, the fluoride-containing wastewater is fluoride-containing mine water, fluoride-containing industrial wastewater, or fluoride-containing groundwater.

9. The defluorination method according to claim 8, wherein, For rapid stirring, the speed is 120–300 rpm and the stirring time is 0.5–4 min; for slow stirring, the speed is 10–50 rpm and the stirring time is 5–20 min.

10. The use of the bidentate chelating defluorinating agent prepared by any one of claims 1-5 for defluorination of fluoride-containing wastewater.

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