Compound deep defluoridation agent and preparation method thereof

Abstract

The present application belongs to the technical field of fluorine-containing wastewater treatment, and particularly relates to a compounded deep fluorine removal agent and a preparation method thereof. The present application provides a compounded deep fluorine removal agent, which comprises the following raw materials in parts by weight: Ca(NO3)2.4H2O 200-300 parts, (NH4)2HPO4 60-100 parts, sodium silicate 1000 parts, polyacrylamide 0.0049-0.007 parts, aluminum chloride hexahydrate 1932-2898 parts, and magnesium chloride hexahydrate 406-609 parts. ‑ The fluorine removal agent forms Si-F, Al-F, Mg-F and other chemical bonds to remove fluorine, and at the same time, the nanoscale solid-phase hydroxyapatite crystallized on the long chain of polyacrylamide synergistically adsorbs fluorine ions to further remove fluorine, and the two-phase coupling effect is used to jointly strengthen the removal of fluorine ions.

Description

Technical Field

[0001] This invention belongs to the field of fluoride-containing wastewater treatment technology, and particularly relates to a compound-type deep fluoride removal agent and its preparation method. Background Technology

[0002] Fluoride is one of the most common anions in groundwater and surface water worldwide due to its high solubility. However, because it can cause serious damage to human tissues, my country has established strict control standards for the concentration of fluoride ions in water. The "Standards for Drinking Water Quality" (GB5749-2006) stipulates that the concentration of fluoride ions in drinking water must not exceed 1 mg / L. The "Water Quality Standard for Wastewater Discharge into Urban Sewerage Systems" (GB / T31962-2015) Class A standard stipulates that the concentration of fluoride ions in discharged fluoride-containing wastewater must not exceed 10 mg / L. If untreated wastewater is directly discharged into natural water bodies, it will cause serious pollution to the ecological environment and threaten people's lives.

[0003] Currently, fluoride ion removal processes generally include various technologies such as membrane separation, ion exchange, adsorption, and coagulation sedimentation. 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; many wastewater treatments now use defluoridating agents to treat high-fluoride wastewater, and most defluoridating agents achieve their defluorination effect through coagulation sedimentation. This method has the advantages of low cost and simple process, but it also produces a large amount of sludge and high fluoride ion content in the effluent.

[0004] Patent CN113274968A discloses a method for synthesizing 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 nano-scale precipitate. After aging, the precipitate is dried and pulverized to obtain the calcium-iron-magnesium ternary nanocomposite defluorinating agent. The advantages are that the preparation process is simple and easy to operate at room temperature and pressure, and it can be produced and applied on a large scale. However, this defluorination method is relatively singular, and the defluorination effect is difficult to meet emission standards.

[0005] Patent CN114853109A discloses a deep defluoridation agent and its preparation and application methods, comprising 1%–5% yttrium oxide or yttrium carbonate, 1%–5% alumina or aluminum hydroxide, 1%–5% cerium oxide or cerium carbonate, 1%–5% ferric oxide or ferric sulfate, 1%–5% samarium oxide or samarium carbonate, 0.5%–2% calcium oxide or calcium hydroxide, 1%–3% sulfuric acid, and deionized water at a preset percentage. This invention provides a deep defluoridation agent that can treat influent fluoride ions from <300 mg / L to achieve an effluent fluoride ion concentration of <5 mg / L; it has a wide pH range; and it settles rapidly after the reaction, requiring no additional flocculant. Under the same influent and effluent concentrations, this novel defluoridation agent offers advantages such as simple dosing, high defluoridation rate, low sludge production, low treatment cost, and wide applicability. However, this method uses rare earth metals, resulting in relatively high costs.

[0006] Patent CN114735781A discloses a method for removing fluoride from neutral or weakly acidic solutions. The specific method involves first adding zirconium oxychloride and titanium dioxide to a concentrated sulfuric acid solution to dissolve them. Then, ammonia is added to adjust the pH of the mixed solution to 10-11, resulting in a titanium-zirconium composite precipitate. The precipitate is washed with deionized water and then calcined at 400-700℃. The calcined product is then ground to below 325 mesh for later use. This completes the preparation of the titanium-zirconium composite defluorinating agent. The ground titanium-zirconium composite is added to a solution, and the pH is adjusted to neutral or weakly acidic. The solution is then heated to approximately 30℃, allowing the titanium-zirconium composite to remove oil and fluoride from the solution. However, this method uses titanium and zirconium, which are difficult to obtain, resulting in relatively high costs.

[0007] Overall, the development of a fast, efficient, economical, and environmentally friendly defluorination agent is of practical significance. Summary of the Invention

[0008] The purpose of this invention is to provide a fluoride removal agent that is simple to administer, has a high fluoride removal rate, low treatment cost, wide range of applications, and does not significantly increase the salinity of the effluent. It can stably reduce fluoride ions to below 1 mg / L to meet emission standards.

[0009] To achieve the above objectives, the technical solution of the present invention is as follows:

[0010] The present invention provides a compound deep defluorination agent, which comprises the following raw materials in parts by weight: 200-300 parts of Ca(NO3)2·4H2O, 60-100 parts of (NH4)2HPO4, 1000 parts of sodium silicate, 0.0049-0.007 parts of polyacrylamide, 1932-2898 parts of aluminum chloride hexahydrate, and 406-609 parts of magnesium chloride hexahydrate.

[0011] Another aspect of the present invention provides a method for preparing the above-mentioned compound deep defluorination agent, the method comprising the following steps:

[0012] 1) Dissolve Ca(NO3)2·4H2O in water and stir at a constant temperature of 30-45℃ until clear to obtain Ca(NO3)2·4H2O solution;

[0013] 2) Dissolve (NH4)2HPO4 in water and add it to Ca(NO3)2·4H2O solution. Stir until clear, and adjust the pH of the mixture to 9-11. Continue stirring at a constant temperature.

[0014] 3) Add polyacrylamide diluted to a concentration of 0.1wt% to 0.5wt%, stir, and age at room temperature to uniformly grow and adsorb nano-hydroxyapatite onto the polyacrylamide. Pour off the supernatant and keep the lower precipitate for later use.

[0015] 4) Add a 10wt% to 20wt% hydrochloric acid solution to the sodium silicate solution, stir, adjust the pH to 3 to 5, let stand to activate, and prepare a polymeric silicate solution;

[0016] 5) Adjust the pH of the polysilicic acid solution to 4-6, add aluminum chloride hexahydrate solution, stir evenly, then add magnesium chloride hexahydrate solution, and stir for 20-35 minutes;

[0017] 6) Add the precipitate from the lower part of step 3) to the polymerized magnesium aluminum silicate solution obtained in step 5), stir, and let stand to obtain the defluorination agent.

[0018] In the above technical solution, further, in step 2), ammonia water is used to adjust the pH of the mixture; the constant temperature stirring time is 2-3 hours.

[0019] In the above technical solution, further, in step 3), the stirring time is 2 to 5 minutes; the aging time is 10 to 20 hours, in order to control the growth of crystal grain size and avoid it being too large.

[0020] In the above technical solution, further, in step 4), the static activation time is 2 to 20 hours.

[0021] In the above technical solution, further, in step 5), the pH of the polymeric silica solution is adjusted using hydrochloric acid with a concentration of 10wt% to 20wt%.

[0022] In the above technical solution, further, in step 6), the stirring time is 10-15 min; the standing time is 3-5 h.

[0023] The beneficial effects of this invention are as follows:

[0024] 1. The high-molecular organic flocculant polyacrylamide in this invention is a linear polymer containing a large number of active groups. The long molecular chains extend outwards many chemically active groups such as amide groups and carboxyl groups, which adsorb the hydroxyapatite generated in the reaction onto the active groups. While reducing the crystallinity of hydroxyapatite, it increases the number of crystals, forming a large number of nano-sized hydroxyapatite. The roughness of the crystal structure increases, the specific surface area increases, and the space for the substitution reaction with fluoride ions increases, thereby improving the adsorption capacity for fluoride ions.

[0025] 2. This invention utilizes polymerized magnesium aluminum silicate and F - While forming chemical bonds such as Si-F, Al-F, and Mg-F to defluorinate, it also interacts with the long chains of polyacrylamide to form chain-like, cyclic, and network structures, increasing the specific surface area of ​​the reagent and thus improving its adsorption and complexation of F in water. - This enhances the ability to remove fluoride and improves the defluorination effect.

[0026] 3. This invention couples polymerized magnesium aluminum silicate with F in the liquid phase. - The adsorption and complexation capabilities, as well as the adsorption capacity of nano-sized hydroxyapatite for fluoride ions in the solid phase, further enhance the defluorination effect of the defluorination agent.

[0027] In summary, this invention utilizes a defluorination agent in the liquid-phase polymerization of magnesium aluminum silicate with F - The process involves the formation of chemical bonds such as Si-F, Al-F, and Mg-F to remove fluoride. Simultaneously, the adsorption of fluoride ions by nanoscale solid-phase hydroxyapatite crystallized on the long chain of polyacrylamide further enhances the removal of fluoride ions through the coupling effect of the two phases. In addition, the solid phase and liquid phase are organically combined using the high-molecular-weight organic flocculant polyacrylamide, which strengthens the trapping or sweeping effect of polyaluminum silicate magnesium and polyacrylamide on fluoride ions, thus coupling the defluorination effects of the two phases and further improving the defluorination effect. This can stably reduce fluoride ions to below 1 mg / L, meeting emission standards. Detailed Implementation

[0028] The following examples are intended to enable those skilled in the art to more fully understand the present invention, but do not limit the invention in any way.

[0029] Unless otherwise specified, the materials used in the embodiments of the present invention can be obtained commercially or prepared according to conventional methods known to those skilled in the art.

[0030] Example 1

[0031] 1) Weigh 200g of Ca(NO3)2·4H2O, dissolve it in 5L of water, and stir at a constant temperature of 45℃ until clear;

[0032] 2) Dissolve 60g of (NH4)2HPO4 in 2L of water, then slowly add it to the Ca(NO3)2·4H2O solution and stir until clear. At the same time, adjust the pH of the mixture to 9 by adding 20wt% ammonia. After the addition is complete, continue stirring at a constant temperature for 2h.

[0033] 3) Add 0.7 mg / L of polyacrylamide diluted to 0.1 wt%, stir rapidly for 2 minutes, and age at room temperature for 20 hours to uniformly grow and adsorb nano-hydroxyapatite onto the polyacrylamide. Pour off the supernatant and keep the lower precipitate for later use.

[0034] 4) Prepare a 0.3 mol / L sodium silicate solution by dissolving 1 kg of sodium silicate in water, slowly add a 10 wt% hydrochloric acid solution while stirring continuously, adjust the pH to 3, and let it stand for 20 hours to activate the solution and obtain a polymeric silicate solution.

[0035] 5) Add 10wt% hydrochloric acid solution to adjust the pH of the polymeric silica solution to 4, add 2L of 4mol / L aluminum chloride hexahydrate solution, stir well, then add 0.5L of 4mol / L magnesium chloride hexahydrate solution and stir for 30min.

[0036] 6) Slowly add the precipitate from the lower part of step 3) into the polyaluminum magnesium silicate solution, stir for 10 minutes, and let stand for 3 hours to obtain the defluorination agent.

[0037] Take 1 L of coking wastewater with a fluoride ion concentration of 10 mg / L, add 2.6 mmol / L of the defluoridation agent prepared in Example 1, stir rapidly (280 r / min) for 2 min, then stir slowly (40 r / min) for 10 min, let stand and settle for 30 min, and take the supernatant to measure the residual fluoride in the water. - The concentration is 0.96 mg / L.

[0038] Example 2

[0039] 1) Weigh 250g of Ca(NO3)2·4H2O, dissolve it in 5L of water, and stir at a constant temperature of 40℃ until clear;

[0040] 2) Dissolve 80g of (NH4)2HPO4 in 2L of water, then slowly add it to the Ca(NO3)2·4H2O solution and stir until clear. At the same time, adjust the pH of the mixture to between 10 by adding 20% ​​ammonia water. After the addition is complete, continue stirring at a constant temperature for 2.5h.

[0041] 3) Add 0.9 mg / L of polyacrylamide diluted to 0.3 wt%, stir rapidly for 3 minutes, and age at room temperature for 15 hours to uniformly grow and adsorb nano-hydroxyapatite onto the polyacrylamide. Pour off the supernatant and keep the lower precipitate for later use.

[0042] 4) Prepare a 0.35 mol / L sodium silicate solution by dissolving 1 kg of sodium silicate in water, slowly add a 15 wt% hydrochloric acid solution, stir continuously, adjust the pH to 4, let stand for 10 h to activate, and prepare a polymeric silicate solution.

[0043] 5) Add 15wt% hydrochloric acid solution to adjust the pH of the polymeric silica solution to 5, add 2.5L of 4mol / L aluminum chloride hexahydrate solution, stir well, then add 0.6L of 4mol / L magnesium chloride hexahydrate solution and stir for 30min.

[0044] 6) Slowly add the precipitate from the lower part of step 3) into the polyaluminum magnesium silicate solution, stir for 13 minutes, and let stand for 4 hours to obtain the defluorination agent.

[0045] Take 1 L of coking wastewater with a fluoride ion concentration of 10 mg / L, add 2.4 mmol / L of the fluoride removal agent prepared in Example 2, stir rapidly (280 r / min) for 2 min, then stir slowly (40 r / min) for 10 min, let stand and settle for 30 min, and take the supernatant to measure the residual fluoride in the water. - The concentration is 0.91 mg / L.

[0046] Example 3

[0047] 1) Weigh 300g of Ca(NO3)2·4H2O, dissolve it in 5L of water, and stir at a constant temperature of 30℃ until clear;

[0048] 2) Dissolve 100g of (NH4)2HPO4 in 2L of water, then slowly add it to the Ca(NO3)2·4H2O solution and stir until clear. At the same time, adjust the pH of the mixture to between 1 and 11 by adding 20% ​​ammonia water. After the addition is complete, continue stirring at a constant temperature for 3 hours.

[0049] 3) Add 1.0 mg / L of polyacrylamide diluted to 0.5 wt%, stir rapidly for 5 minutes, and age at room temperature for 10 hours to uniformly grow and adsorb nano-hydroxyapatite onto the polyacrylamide. Pour off the supernatant and keep the lower precipitate for later use.

[0050] 4) Prepare a 0.4 mol / L sodium silicate solution by dissolving 1 kg of sodium silicate in water, slowly add a 20 wt% hydrochloric acid solution while stirring continuously, adjust the pH to 5, let stand for 2 hours to activate, and prepare a polymeric silicate solution.

[0051] 5) Add 20wt% hydrochloric acid solution to adjust the pH of the polymeric silica solution to 6, add 3L of 4mol / L aluminum chloride hexahydrate solution, stir well, then add 0.75L of 4mol / L magnesium chloride hexahydrate solution and stir for 30min.

[0052] 6) Slowly add the precipitate from the lower part of step 3) into the polyaluminum magnesium silicate solution, stir for 15 minutes, and let stand for 5 hours to obtain the defluorination agent.

[0053] Take 1 L of coking wastewater with a fluoride ion concentration of 10 mg / L, add 2.4 mmol / L of the defluoridation agent prepared in Example 3, stir rapidly (280 r / min) for 2 min, then stir slowly (40 r / min) for 10 min, let stand and settle for 30 min, and take the supernatant to measure the residual fluoride in the water. - The concentration is 0.85 mg / L.

[0054] Comparative Example 1

[0055] Preparation method of hydroxyapatite:

[0056] Prepare 200 mL of a mixed solution of 0.167 mol / L Ca(NO3)2·4H2O and 0.1 mol / L HNO3, add it to a three-necked flask, and stir. Prepare 200 mL of a mixed solution of 0.1 mol / L (NH4)2HPO4 and 0.5 mol / L urea [(NH2)2CO], and stir at 6 cm⁻¹ under reflux conditions in an oil bath at 50 °C. 3 The solution was slowly added dropwise at a rate of 1 / min to a stirred three-necked flask. After the addition was complete, the oil bath temperature was adjusted to 80°C and the reaction was carried out under reflux for 72 hours. Then the temperature was adjusted to 90°C and the reaction was carried out for 24 hours. After the reaction was completed, the solution was filtered, washed with deionized water, and placed in an oven to dry at 80°C for 12 hours.

[0057] Take 1 L of coking wastewater with a fluoride ion concentration of 10 mg / L, add 1.0 g / L of hydroxyapatite prepared in Comparative Example 1, stir rapidly (280 r / min) for 2 min, then stir slowly (40 r / min) for 10 min, let stand and settle for 30 min, and take the supernatant to measure the residual fluoride in the water. - The concentration is 1.64 mg / L.

[0058] Comparative Example 2

[0059] Preparation method of polyaluminum magnesium silicate:

[0060] Prepare a 0.3 mol / L sodium silicate solution. On a magnetic stirrer, slowly add the sodium silicate solution to a (1+1) hydrochloric acid solution, stir rapidly, adjust the pH to 3.0, and let it stand for 2 hours to activate and obtain a polymeric silicate solution. Prepare aluminum chloride solution and magnesium chloride solution according to the ratio of n(Si) / n(Al+Mg)=1:4 and n(Al) / n(Mg)=4:1. Add the aluminum chloride solution and magnesium chloride solution to the activated polymeric silicate solution, stir thoroughly and let it stand to obtain a colorless and transparent polymeric aluminum magnesium silicate solution.

[0061] Take 1L of coking wastewater with a fluoride ion concentration of 10mg / L, add 2.4mmol / L of the polyaluminum magnesium silicate prepared in Comparative Example 2, stir rapidly (280r / min) for 2min, then stir slowly (40r / min) for 10min, let stand and settle for 30min, take the supernatant and measure the residual F- concentration in the water, which is 2.38mg / L.

[0062] Comparative Example 3

[0063] Take 1 L of coking wastewater with a fluoride ion concentration of 10 mg / L, add 1.0 g / L hydroxyapatite prepared in Comparative Example 1 and 2.4 mmol / L polyaluminum magnesium silicate prepared in Comparative Example 2, stir rapidly (280 r / min) for 2 min, then stir slowly (40 r / min) for 10 min, let stand and settle for 30 min, take the supernatant and measure the residual fluoride in the water. - The concentration is 1.53 mg / L.

[0064] The results show that the defluorination agent of the present invention has a significantly improved defluorination effect compared with traditional defluorination agents.

[0065] The above embodiments are merely preferred embodiments of the present invention and are not intended to limit the implementation. The scope of protection of the present invention should be determined by the scope defined in the claims. Other variations or modifications can be made based on the above description. Obvious variations or modifications derived therefrom are still within the scope of protection of the present invention.

Claims

1. A method for preparing a complex deep defluoridation agent, characterized in that, The fluoride removing agent comprises the following raw materials by weight: Ca(NO3)2 4H2O 200~300 parts, (NH4)2HPO4 60~100 parts, sodium silicate 1000 parts, polyacrylamide 0.0049~0.007 parts, aluminum chloride hexahydrate 1932~2898 parts, magnesium chloride hexahydrate 406~609 parts; The method comprises the following steps: 1) Ca(NO3)2 4H2O is dissolved in water, and stirred at constant temperature of 30-45°C until clear, to obtain a Ca(NO3)2 4H2O solution; 2) After dissolving (NH4)2HPO4 in water, add to Ca(NO3)2 4H2O solution, stir until clear, and adjust the pH of the mixture to 9-11, continue constant temperature stirring; 3) adding polyacrylamide with a dilution concentration of 0.1wt%-0.5wt%, stirring, aging at room temperature, and uniformly growing and adsorbing the nano-hydroxyapatite on the polyacrylamide, pouring away the supernatant, and reserving the lower precipitate; 4) adding a hydrochloric acid solution with a concentration of 10wt%-20wt% to the sodium silicate solution, stirring, adjusting the pH to 3-5, and standing for activation to prepare a polymeric silicic acid solution; 5) adjusting the pH of the polymeric silicic acid solution to 4-6, adding an aluminum chloride hexahydrate solution, stirring uniformly, then adding a magnesium chloride hexahydrate solution, and stirring for 20-35 min; 6) adding the lower precipitate in step 3) to the polymeric magnesium aluminum silicate solution obtained in step 5), stirring, and standing to obtain the defluorination agent.

2. The production method according to claim 1, characterized by, In step 2), ammonia is used to adjust the pH of the mixed solution; the constant-temperature stirring time is 2-3 h.

3. The production method according to claim 1, characterized by, In step 3), the stirring time is 2-5 min; and the aging time is 10-20 h.

4. The method of claim 1, wherein, In step 4), the standing time for activation is 2-20 h.

5. The preparation method according to claim 1, characterized in that, In step 5), a hydrochloric acid solution with a concentration of 10wt%-20wt% is used to adjust the pH of the polymeric silicic acid solution.

6. The production method according to claim 1, characterized by, In step 6), the stirring time is 10-15 min; and the standing time is 3-5 h.