Deep fluorine removal agent and preparation method thereof

Abstract

The application discloses a deep fluorine removal agent and a preparation method thereof. The preparation method comprises the following steps: adding ferric chloride and aluminum chloride into an acetic acid solution of chitosan to obtain a mixed solution; stirring the mixed solution after adjusting the pH of the mixed solution to 4.5-5.0 by using ammonia water for a set time to obtain a first dispersion solution; dispersing polyacrylamide in a water dispersion solution of nano calcium carbonate to obtain a second dispersion solution; adding the second dispersion solution into the first dispersion solution to obtain a third dispersion solution; and obtaining the fluorine removal agent by using ammonia water to adjust the pH of the third dispersion solution to 7-7.5 and then standing the precipitate. The application effectively solves the problem that the fluorine removal effect of the fluorine removal agent is good but the cost is high, or the cost is low but the fluorine removal effect is not ideal.

Description

Technical Field

[0001] This invention relates to the field of fluoride-containing wastewater treatment technology, and in particular to a deep defluorination process and defluorinating agent for fluoride-containing wastewater. Background Technology

[0002] Currently, fluoride ion removal processes generally include various technologies such as membrane separation, ion exchange, adsorption, and coagulation precipitation. Each of these methods has its applicable scope and advantages and disadvantages. For example, ion exchange and membrane separation are costly but require certain maintenance conditions; adsorption has a low treatment capacity and requires repeated regeneration, resulting in high operating costs, while its fluoride removal capacity gradually decreases; currently, defluorinating agents are often used to treat high-fluoride wastewater, such as a compound defluorinating agent disclosed in CN 113526639A, which includes a trivalent metal source, a calcium source, a magnesium source, and a hydrogen phosphate, wherein the trivalent metal source includes an aluminum source and / or an iron source. Under the combined action of the aluminum and / or iron source, calcium source, magnesium source, and hydrogen phosphate, the fluoride generated from fluoride ions in fluoride-containing wastewater can be rapidly precipitated in the form of precipitate flocs, effectively shortening the precipitation time of fluoride ions, and achieving a fluoride ion removal rate of >99%. However, this method simply mixes different defluorinating agents, lacking synergistic effects between the components. CN 113274968A discloses a method for preparing a calcium-iron-magnesium ternary nanocomposite defluorinating agent. A certain amount of calcium salt, iron salt, and magnesium salt are sequentially added to an appropriate amount of water, placed in a reaction vessel, and an alkaline solution is added dropwise to generate a nanoscale precipitate, thus obtaining the calcium-iron-magnesium ternary nanocomposite defluorinating agent. However, its defluorination method is relatively simple, and the defluorination effect is difficult to meet emission standards. CN 113651407A discloses a composite defluorinating agent comprising polyaspartic acid-sulfonated styrene copolymer, zinc salt, iron salt, and cationic starch ether quaternary ammonium salt. It mainly utilizes the strong coagulation and flocculation function of the cationic starch ether quaternary ammonium salt, combined with the adsorption and complexation ability of zinc and iron salts for fluoride ions. The polyaspartic acid copolymer is used to control the scaling of calcium salts. CN 114853109 A discloses a deep defluoridation agent, comprising yttrium oxide or yttrium carbonate, aluminum oxide or aluminum hydroxide, cerium oxide or cerium carbonate, iron oxide or ferric sulfate, samarium oxide or samarium carbonate, calcium oxide or calcium hydroxide, and sulfuric acid. This defluoridation agent has good treatment effect, but it uses rare earth metals, resulting in relatively high cost. Furthermore, most defluoridation agents achieve defluoridation through double-calcium coagulation and sedimentation, which is characterized by low cost and simple process, but it suffers from problems such as large sludge production, high fluoride ion content in the effluent, and significantly increased salinity in the effluent. Summary of the Invention

[0003] In view of this, the present invention provides a deep defluorination agent, which solves the problem that current defluorination agents have high cost for good defluorination effect and unsatisfactory defluorination effect for low cost.

[0004] In addition, this disclosure provides a method for preparing the aforementioned defluorination agent.

[0005] Firstly, the method for preparing the deep defluorination agent includes:

[0006] Ferric chloride and aluminum chloride are added to the acetic acid or citric acid solution of chitosan to obtain a mixture. The pH of the mixture is adjusted to 4.5-5.0 with ammonia water and then stirred for a set time to obtain a first dispersion.

[0007] A second dispersion was obtained by dispersing polyacrylamide in an aqueous dispersion of nano-calcium carbonate.

[0008] The second dispersion is added to the first dispersion to obtain a third dispersion. The pH of the third dispersion is adjusted to 7-7.5 with ammonia water, and the precipitate after standing is the defluorination agent.

[0009] In this disclosure and possible embodiments, the chitosan is 100 parts by weight, the ferric chloride is 540 to 648 parts by weight, the aluminum chloride is 145 to 241 parts by weight, the nano-calcium carbonate is 5 to 10 parts by weight, and the polyacrylamide is 0.0004 to 0.008 parts by weight.

[0010] In this disclosure and possible embodiments, the ferric chloride is ferric chloride hexahydrate, and the aluminum chloride is aluminum chloride hexahydrate.

[0011] In this disclosure and possible embodiments, the ferric chloride hexahydrate and the aluminum chloride hexahydrate are respectively prepared into 1.0-2.0 mol / L solutions. The ferric chloride hexahydrate solution and the aluminum chloride hexahydrate solution are added to the acetic acid or citric acid solution of chitosan and stirred for 20-30 minutes to obtain the mixture.

[0012] In this disclosure and possible embodiments, the set time is 50 min to 70 min.

[0013] In this disclosure and possible embodiments, the polyacrylamide is prepared into an aqueous solution with a mass concentration of 0.1% to 0.5%, and then added to the aqueous dispersion of nano-calcium carbonate and stirred for 2 to 5 minutes. After the stirring is completed, the mixture is allowed to stand for 20 to 60 minutes, and the lower precipitate is removed by filtration to obtain the second dispersion.

[0014] In this disclosure and possible embodiments, the third dispersion is allowed to stand for 50 to 70 minutes.

[0015] In this disclosure and possible embodiments, the precipitate is filtered out and then dried at a temperature of 70°C to 80°C for 10 to 20 hours. The dried precipitate is then pulverized to 100 to 200 mesh to obtain the defluorination agent.

[0016] In this disclosure and possible embodiments, the nano-calcium carbonate particles have a diameter of 10–100 nm.

[0017] Secondly, the deep defluorination agent is prepared using the preparation method described in the first aspect.

[0018] The beneficial effects of this invention are:

[0019] The deep defluorination agent of this invention removes fluoride by firstly by utilizing the adsorption of fluoride ions in water by the hydroxyl groups of chitosan and the complexation of fluoride with coordinated metal cations by the amino groups; secondly, by further enhancing the defluorination effect through the adsorption of nano-calcium carbonate by cationic polyacrylamide. The adsorption of nano-calcium carbonate by polyacrylamide couples the defluorination effects of nano-calcium carbonate and modified chitosan, achieving deep defluorination and stabilizing the fluoride ion concentration to below 1 mg / L, meeting emission standards. Therefore, this invention provides a defluorination agent that is simple to administer, has a high defluorination rate, low treatment cost, and a wide range of applications. Detailed Implementation

[0020] The present disclosure is described below based on embodiments; however, it is worth noting that the present disclosure is not limited to these embodiments. In the detailed description of the present disclosure below, certain specific details are described in detail. However, those skilled in the art will fully understand the present disclosure for the parts not described in detail.

[0021] Furthermore, those skilled in the art should understand that the descriptions of "first," "second," etc., in this disclosure are only used to distinguish the objects described and have no sequential or technical meaning.

[0022] The deep defluorination agent of this invention is designed to include chitosan, ferric chloride hexahydrate, aluminum chloride hexahydrate, nano-calcium carbonate, and cationic polyacrylamide, a high-molecular flocculant, the functions of which are as follows:

[0023] 1. Cationic polyacrylamide is a linear polymer containing a large number of active groups. The long molecular chain extends outward with many chemically active groups such as amide groups and carboxyl groups, which can adsorb nano-calcium carbonate or calcium ions after the reaction of nano-calcium carbonate onto the active groups. The positively charged cationic polyacrylamide has a stronger adsorption capacity for negatively charged ions, and the fluoride ions in the calcium fluoride generated by the reaction with calcium are not dissolved into the solution, thereby reducing the fluoride content in the solution.

[0024] 2. Nano-calcium carbonate is a hydrophilic material with a particle size of 10-100 nm. It can form calcium fluoride precipitate with fluoride ions in water and be adsorbed onto the active groups of cationic polyacrylamide to further remove fluoride ions.

[0025] 3. The hydroxyl groups in chitosan adsorb fluoride ions in water, the amino groups complex fluoride with coordinated iron ions, and the adsorption and trapping effect of Al(OH)3 colloids from aluminum hydrolysis remove fluoride. At the same time, the calcium carbonate or calcium ions adsorbed on the cationic polyacrylamide extending from the chitosan are bound to the polyacrylamide, and the fluoride ions in the calcium fluoride no longer dissolve into the solution, further reducing the fluoride content in the solution.

[0026] 4. The adsorption of fluoride ions by metal-modified chitosan is coupled with the chemical precipitation of nano-calcium carbonate bound by polyacrylamide, which improves the defluorination effect of the defluorinating agent.

[0027] Examples 1-3 of this disclosure employ the following method for preparing deep defluorination agents, with the specific steps as follows:

[0028] (1) Weigh 100g of chitosan and add it to 5-6L of acetic acid or citric acid with a concentration of 4%-6%, and stir until completely dissolved;

[0029] (2) Add 1.0-1.2L of 2mol / L ferric chloride hexahydrate solution to the chitosan acetic acid solution in step (1), with the amount of ferric chloride hexahydrate added being 540-648g, and stir until homogeneous; then add 0.3-0.5L of 2mol / L aluminum chloride hexahydrate solution, with the amount of aluminum chloride hexahydrate added being 145-241g, and stir for 20-30 minutes to obtain a mixed solution;

[0030] (3) Add 3% to 5% ammonia water to the mixture, adjust the pH of the mixture to 4.5 to 5.0, and stir for 50 to 70 minutes to obtain the first dispersion. The reason for choosing ammonia water is that ammonia water can make the pH reach the target value more accurately. Of course, other alkaline solutions can also be used for pH adjustment.

[0031] (4) Add 5-10g of nano-calcium carbonate to 1L of water and stir rapidly for 5-10min until no precipitate is found. Add 0.1%-0.5% cationic polyacrylamide (0.4mg-0.8mg by mass), stir rapidly for 2-5min, and let stand for 20-60min. Filter the lower precipitate after standing to obtain the second dispersion. Add the second dispersion to the first dispersion in step (3) and stir evenly to obtain the third dispersion.

[0032] (5) Adjust the pH of the third dispersion to 7 to 7.5 with ammonia water with a mass concentration of 3% to 5%, and let it stand for 50 to 70 minutes;

[0033] (6) The precipitate after standing is filtered, dried at 70-80℃ for 10-20h, and pulverized to 100-200 mesh to obtain the deep defluorination agent of the embodiment.

[0034] Example 1:

[0035] (1) Weigh 100g of chitosan and add it to 5L of 6% acetic acid, and stir until completely dissolved;

[0036] (2) Add 1.0L of ferric chloride hexahydrate solution with a concentration of 2mol / L and stir until homogeneous; then add 0.3L of aluminum chloride hexahydrate solution with a concentration of 2mol / L and stir for 20 minutes to obtain a mixed solution;

[0037] (3) Add 3% ammonia water to the mixture, adjust its pH to 4.5, and stir for 50 min to obtain the first dispersion;

[0038] (4) Add 5g of nano calcium carbonate to 1L of water and stir rapidly for 5min until there is no precipitate. Add 0.4mg of cationic polyacrylamide with a mass concentration of 0.5%. Stir rapidly for 2min and let stand for 20min. Filter the lower precipitate to obtain the second dispersion. Add the second dispersion to the first dispersion in step (3) and stir evenly to obtain the third dispersion.

[0039] (5) Adjust the pH of the third dispersion to 7 with 3% ammonia water and let it stand for 50 minutes.

[0040] (6) After filtering out the precipitate from the third dispersion, dry it at 80°C for 10 hours and pulverize it to 100-200 mesh to obtain the deep defluorination agent of Example 1.

[0041] Take 1L of pretreated coking wastewater with a fluoride ion concentration of 5mg / L, add 6g of the deep defluoridation agent of this embodiment, stir rapidly (250r / min) for 2min, then stir slowly (30r / min) for 3h, let it stand and settle for 30min, take the supernatant and measure the residual fluoride ion concentration in the water, which is 0.98mg / L (the "Standards for Drinking Water Quality" (GB5749-2006) stipulates that the concentration of fluoride ions in drinking water shall not exceed 1mg / L).

[0042] Example 2:

[0043] (1) Weigh 100g of chitosan and add it to 5.5L of 5% acetic acid, and stir until completely dissolved;

[0044] (2) Add 1.1L of ferric chloride hexahydrate solution with a concentration of 2mol / L and stir until homogeneous; then add 0.4L of aluminum chloride hexahydrate solution with a concentration of 2mol / L and stir for 25 minutes to obtain a mixed solution;

[0045] (3) Add 4% ammonia water to the mixture, adjust the pH of the mixture to 5.0, and stir for 60 min to obtain the first dispersion.

[0046] (4) Add 8g of nano calcium carbonate to 1L of water and stir rapidly for 8min until there is no precipitate. Add 0.6mg of cationic polyacrylamide with a mass concentration of 0.3%. Stir rapidly for 4min and let stand for 40min. Filter the lower precipitate to obtain the second dispersion. Add the second dispersion to the first dispersion in step (3) and stir evenly to obtain the third dispersion.

[0047] (5) Adjust the pH of the third dispersion to 7.5 with 4% ammonia water and let it stand for 60 minutes;

[0048] (6) After filtering out the precipitate from the third dispersion, dry it at 75°C for 15 hours and pulverize it to 100-200 mesh to obtain the deep defluorination agent of Example 2.

[0049] Take 1L of pretreated coking wastewater with a fluoride ion concentration of 5mg / L, add 6g of the deep defluorination agent of this embodiment, stir rapidly (250r / min) for 2min, then stir slowly (30r / min) for 3h, let stand and settle for 30min, take the supernatant and measure the residual fluoride ion concentration in the water, which is 0.90mg / L.

[0050] Example 3:

[0051] (1) Weigh 100g of chitosan and add it to 6L of 6% acetic acid, and stir until completely dissolved;

[0052] (2) Add 1.2L of ferric chloride hexahydrate solution with a concentration of 2mol / L and stir until homogeneous; then add 0.5L of aluminum chloride hexahydrate solution with a concentration of 2mol / L and stir for 20-30 minutes to obtain a mixed solution;

[0053] (3) Add 5% ammonia water to the mixture, adjust the pH of the mixture to 5.0, and stir for 70 minutes to obtain the first dispersion.

[0054] (4) Add 10g of nano calcium carbonate to 1L of water and stir rapidly for 10min until there is no precipitate. Add cationic polyacrylamide with a mass concentration of 0.1% to 0.5% and the amount of cationic polyacrylamide added is 0.8mg. Stir rapidly for 5min and let stand for 60min. Filter the lower precipitate to obtain the second dispersion. Add the second dispersion to the first dispersion in step (3) and stir evenly to obtain the third dispersion.

[0055] (5) Adjust the pH of the third dispersion to 7.5 with 5% ammonia solution and let it stand for 70 minutes;

[0056] (6) After filtering out the precipitate from the third dispersion, dry it at 70°C for 20 hours and pulverize it to 100-200 mesh to obtain the deep defluorination agent of Example 3.

[0057] Take 1L of pretreated coking wastewater with a fluoride ion concentration of 5mg / L, add 7g of the deep defluorination agent of this embodiment, stir rapidly (250r / min) for 2min, then stir slowly (30r / min) for 3h, let it stand and settle for 30min, take the supernatant and measure the residual fluoride ion concentration in the water, which is 0.83mg / L.

[0058] The embodiments described above are merely illustrative of implementation methods of this disclosure, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of this patent disclosure. It should be noted that those skilled in the art can make various modifications, equivalent substitutions, and improvements without departing from the concept of this disclosure, and these all fall within the protection scope of this disclosure. Therefore, the protection scope of this patent disclosure should be determined by the appended claims.

Claims

1. A method for preparing a deep fluorine-removing agent, characterized by, include: Ferric chloride and aluminum chloride are added to the acetic acid or citric acid solution of chitosan to obtain a mixture. The pH of the mixture is adjusted to 4.5-5.0 with ammonia water and then stirred for a set time to obtain a first dispersion. A second dispersion was obtained by dispersing polyacrylamide in an aqueous dispersion of nano-calcium carbonate. The second dispersion is added to the first dispersion to obtain a third dispersion. The pH of the third dispersion is adjusted to 7-7.5 with ammonia water, and the precipitate after standing is the defluorination agent.

2. The method for preparing the deep defluorination agent according to claim 1, characterized in that: Calculated by weight, the chitosan is 100 parts, the ferric chloride is 540 to 648 parts, the aluminum chloride is 145 to 241 parts, the nano-calcium carbonate is 5 to 10 parts, and the polyacrylamide is 0.0004 to 0.008 parts.

3. The method for preparing the deep defluorination agent according to claim 2, characterized in that: The ferric chloride is ferric chloride hexahydrate, and the aluminum chloride is aluminum chloride hexahydrate.

4. The method for preparing the deep defluorination agent according to claim 3, characterized in that: The ferric chloride hexahydrate and the aluminum chloride hexahydrate are each prepared into a 1.0-2.0 mol / L solution. The ferric chloride hexahydrate solution and the aluminum chloride hexahydrate solution are added to the acetic acid or citric acid solution of chitosan and stirred for 20-30 minutes to obtain the mixture.

5. The method for preparing the deep defluorination agent according to any one of claims 1-4, characterized in that: The set time is 50 minutes to 70 minutes.

6. The method for preparing the deep defluorination agent according to claim 5, characterized in that: The polyacrylamide was prepared into an aqueous solution with a mass concentration of 0.1% to 0.5%, and then added to the aqueous dispersion of nano-calcium carbonate and stirred for 2 to 5 minutes. After stirring, the mixture was allowed to stand for 20 to 60 minutes, and the lower precipitate was removed by filtration to obtain the second dispersion.

7. The method for preparing the deep defluorination agent according to any one of claims 1-4 or 6, characterized in that: The third dispersion should be allowed to stand for 50–70 minutes.

8. The method for preparing the deep defluorination agent according to claim 7, characterized in that: The precipitate is filtered out and then dried at a temperature of 70℃ to 80℃ for 10 to 20 hours. The dried precipitate is then pulverized to 100 to 200 mesh to obtain the defluorination agent.

9. The method for preparing the deep defluorination agent according to any one of claims 1-4, 6, or 8, characterized in that: The nano-calcium carbonate particles have a diameter of 10–100 nm.

10. A deep defluorination agent, characterized in that: It is prepared by any one of the preparation methods described in claims 1-9.