Self-buffering composite defluorination preparation prepared by resource utilization of chemical sludge

Abstract

The invention discloses a self-buffering type composite defluorination preparation prepared by resource utilization of chemical sludge, and belongs to the field of sewage treatment preparations. The novel self-buffering type composite defluorination preparation provided by the invention has the capabilities of deeply removing fluorine ions and adjusting pH by utilizing the adsorption, net capturing and other effects of Si-Al-OH colloid generated after phosphorus polysilicate aluminum iron is hydrolyzed, phosphate radical vacancy and Ca < 2 + > and buffering property of calcium carbonate in chalk; the self-buffering type composite defluorination preparation is put into photovoltaic wastewater with the inlet water fluorine concentration of 14.2 mg / L and the pH value of 7.8, and after static settlement is conducted for 30 min, the outlet water fluorine concentration is lower than 1.5 mg / L, and the pH value is still kept to be 6.5 or above.

Description

Technical Field

[0001] This invention relates to a self-buffered composite defluorination agent prepared by resource utilization of chemical sludge, belonging to the field of wastewater treatment agents. Background Technology

[0002] In recent years, my country's photovoltaic, semiconductor manufacturing, and electronic information industries have developed rapidly. Processes such as wet texturing, silicon wafer cleaning, and metal etching utilize large amounts of hydrofluoric acid solutions, leading to a continuous expansion of high-concentration fluoride-containing wastewater discharge. my country has established strict discharge standards for fluoride-containing wastewater. The "Emission Standard of Water Pollutants for Electronic Industry" (GB39731-2020) stipulates that fluorides (with F...) must be discharged within a certain limit. - The direct emission limit for fluoride (calculated) is 10 mg / L, and the indirect emission limit is 20 mg / L; the Class III fluoride emission standard in the "Surface Water Environmental Quality Standard" (GB 3838—2002) shall not exceed 1.0 mg / L; the emission limit for fluoride in the "Urban Wastewater Treatment Plant Pollutant Discharge Standard" (DB32 / 4440—2022) issued by Jiangsu Province is 1.5 mg / L. The implementation of these standards has placed higher demands on industrial fluoride-containing wastewater treatment technologies. How to achieve economical, green, and efficient deep fluoride removal is a significant technological bottleneck in the current national industrial green manufacturing system.

[0003] Calcium salt precipitation has advantages such as simple operation, low treatment cost, and suitability for treating high-concentration fluoride wastewater. However, after calcium salt precipitation, the residual fluoride concentration remains high, typically 15-30 mg / L, which fails to meet the Class I discharge standard (10 mg / L) of the "Integrated Wastewater Discharge Standard" (GB8978-1996). Therefore, advanced fluoride removal units require the addition of a defluorinating agent to the fluoride-containing wastewater, adjusting the pH to an appropriate level, and then using chemical or physical reactions to combine with fluoride ions in the water to form flocs, which are eventually precipitated and discharged. - The concentration is reduced to below 1.0 mg / L. Common defluorinating agents are mainly aluminum salts, such as alumina, aluminum sulfate, polyaluminum chloride, and polyaluminum silicate. These defluorinating agents are acidic, and the pH will drop significantly after addition. However, the defluorination reaction has strict pH requirements, with an optimal pH of 6.5-7, requiring the addition of a large amount of alkali. In addition, the flocs generated by the defluorinating agents are loose and have poor settling performance, requiring the addition of coagulants such as PAM. The combination of "defluorinating agent + alkali + PAM" used for deep defluorination is not only expensive in terms of reagents, but also requires three reagent dosing pumps, making operation complex and control cumbersome.

[0004] Therefore, the ability to simultaneously adjust pH and enhance flocculation has become a new direction in the development of defluorination agents. There is an urgent need to develop a novel self-buffered composite defluorination agent that can simultaneously adjust pH and enhance flocculation to effectively solve the problems of difficult deep defluorination, complex acidic pH adjustment, and poor flocculation effect. Summary of the Invention

[0005] To effectively address the challenges of deep fluoride removal, complex acidic pH adjustments, and poor flocculation, this invention provides a self-buffered composite fluoride removal agent prepared from resource-utilized chemical sludge. This novel self-buffered composite fluoride removal agent utilizes the adsorption and trapping effects of Si-Al-OH colloids generated after the hydrolysis of aluminum-iron phosphate polysilicate, as well as phosphate vacancies and the CaO in chalk. 2+ It has buffering properties and the ability to deeply remove fluoride ions and regulate pH. When the self-buffered compound defluoridation agent is added to photovoltaic wastewater with an influent fluoride concentration of 14.2 mg / L and pH=7.8, after standing for 30 min, the effluent fluoride concentration is lower than 1.5 mg / L, and the pH remains above 6.5.

[0006] The first objective of this invention is to provide a method for preparing a self-buffered composite defluorination agent, comprising the following steps: A self-buffered composite fluoride removal agent was obtained by mixing and grinding chalk powder with phosphorus-polymerized aluminum iron silicate powder at a ratio of 1~2 g: 5~10 g. The preparation method of phosphorus-polymerized aluminum-iron silicate powder is as follows: sludge powder is added to the polymerized silica solution, and after standing and activating for 1-2 hours, it is filtered, dried, and ground to obtain phosphorus-polymerized aluminum-iron silicate powder.

[0007] In one embodiment, the concentration of sodium silicate in the polymeric silicate solution is 25~50 g / L.

[0008] In one embodiment, the mass ratio of sludge powder to sodium silicate is 4~6:1~2.

[0009] In one embodiment, the drying is performed at 60-100°C for 6-10 hours.

[0010] In one embodiment, the grinding is performed to a particle size of 100-200 mesh.

[0011] In one embodiment, the sludge powder is prepared by filtering the sludge, washing it with clean water, drying it at 60-100°C for 6-10 hours, and grinding it to a particle size of 100-200 mesh to obtain sludge powder.

[0012] In one embodiment, the sludge is sludge from the air flotation chemical phosphorus removal unit of a municipal wastewater treatment plant.

[0013] In one embodiment, the sludge contains P, Al, and Fe.

[0014] In one embodiment, the preparation method of the polymeric silica solution is as follows: 50-100 mL of hydrochloric acid solution with a concentration of 250-500 g / L is added dropwise to a 25-50 g / L sodium silicate aqueous solution, and the solution is allowed to stand for 1-2 h to activate before obtaining the polymeric silica solution.

[0015] A second objective of this invention is to provide a self-buffered composite defluorination agent prepared by any of the methods described above.

[0016] The third objective of this invention is to provide a method for removing fluoride ions from wastewater, using the self-buffered composite defluorinating agent described above, with the following steps: Add the self-buffered compound defluoridation agent to the wastewater at a dosage of 100~2000 mg / L, stir, and let it settle.

[0017] In one embodiment, the stirring and settling process involves stirring for 1-5 minutes followed by settling for 30-60 minutes.

[0018] The fourth objective of this invention is to provide a method for simultaneously improving the removal efficiency of fluoride ions in wastewater and adjusting the pH of the wastewater, using the self-buffered composite defluoridation agent described above, with the following steps: Add the self-buffered compound defluoridation agent to the wastewater at a dosage of 100~2000 mg / L, stir, and let it settle.

[0019] In one embodiment, the stirring and settling process involves stirring for 1-5 minutes followed by settling for 30-60 minutes.

[0020] A fifth objective of this invention is to provide the application of any of the methods described above and the self-buffered composite defluorination agents described above in the environmental field.

[0021] In one embodiment, the application includes reducing fluoride ions, adjusting pH, reducing the amount of alkali used, and reducing the amount of PAM used.

[0022] Beneficial effects (1) It simultaneously solves the problems of difficult deep fluoride removal and acidic pH adjustment: The novel self-buffered composite defluorination agent provided by this invention utilizes the Si-Al-OH colloid generated after the hydrolysis of ferric aluminum phosphate, which binds to fluoride ions through adsorption, charge neutralization, trapping, and sweeping. The Ca produced by the dissolution of chalk... 2+ The phosphate vacancies in polyaluminum ferric silicate can combine with fluoride ions to form a fluorinated hydroxyapatite structure, thereby achieving deep removal of fluorides.

[0023] The novel self-buffered composite fluoride removal agent provided by this invention adjusts pH by: utilizing the acid generated from the hydrolysis of calcium carbonate in chalk with aluminum ferric phosphate polysilicate to produce Ca 2+ It can regulate pH by adding CO2 and water to achieve self-buffering capacity; when the self-buffering compound defluoridation agent is added to photovoltaic wastewater with an influent fluoride concentration of 14.2 mg / L and pH=7.8, after standing for 30 min, the effluent fluoride concentration is lower than 1.5 mg / L, and the pH remains at around 6.7.

[0024] (2) The operation process is simple: The novel self-buffered composite defluorination agent used in this invention can simultaneously regulate pH and aid coagulation. The hydroxyl groups on the surface of algal remains in chalk can form hydrogen bonds with Al(OH)3 colloids, which helps in the formation of flocs. Undissolved calcium carbonate and Fe(OH)3 in aluminum ferric phosphate... x Furthermore, the fluorinated hydroxyapatite component produced during defluorination has a high density, which can accelerate the precipitation of flocs, eliminating the need to add alkali and PAM during the entire defluorination process.

[0025] Compared with the control group using polyaluminum silicate and polyaluminum chloride, the pH of wastewater after defluorination by polyaluminum silicate and polyaluminum chloride drops significantly to below 5.7, requiring the addition of alkali to adjust the pH to 6.5-7, and further addition of PAM coagulant to better form flocs and deeply remove fluoride ions. The method of the present invention avoids this problem.

[0026] (3) It is environmentally friendly and economically beneficial: Compared with previously reported polyaluminum silicate and polyaluminum chloride, the novel self-buffered composite defluorination agent used in this invention can effectively reduce the amount of pH-adjusting alkali and improve sedimentation PAM dosage, thereby reducing reagent costs. The product contributes to the green and low-carbon treatment of wastewater, has significant environmental protection value, and is suitable for large-scale promotion. Attached Figure Description

[0027] Figure 1 The self-buffered composite defluorination agent A prepared in Example 1 is shown. Detailed Implementation

[0028] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. These embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Experimental methods in the following embodiments, where specific conditions are not specified, are generally performed under conventional conditions in the art. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those familiar with the art.

[0029] Raw materials involved in the examples: Sodium silicate: analytical grade, commercially available.

[0030] Hydrochloric acid: analytical grade, commercially available.

[0031] Sludge: Taken from Wuxi Chengbei Wastewater Treatment Plant, it is sludge from the chemical phosphorus removal unit of the municipal wastewater treatment plant, which uses commercially available PAC reagent.

[0032] Chalk: 200 mesh, natural mineral, commercially available.

[0033] Unless otherwise specified, the solvent used in the solutions mentioned in the examples and comparative examples is water, and unless otherwise specified, the percentages mentioned refer to mass percentages (w / w).

[0034] Test methods involved in the embodiments: 1. pH test: The SL1000 / 250 portable multi-parameter water quality analyzer was purchased from Hach Instruments, Inc., USA.

[0035] 2. Fluoride ion determination: The determination was performed according to the national standard "Determination of Fluoride in Water - Fluoride Reagent Spectrophotometric Method" (HJ 488-2009).

[0036] Example 1: A self-buffered composite defluorination agent prepared by resource utilization of chemical sludge A self-buffered composite defluorination agent prepared by resource utilization of chemical sludge is prepared by the following steps: (1) Raw material pretreatment: Preparation of sludge powder containing P, Al, and Fe sources: The sludge was filtered, washed with clean water, dried at 60°C for 12 hours, and ground through an 80-mesh sieve to obtain sludge powder containing P, Al, and Fe sources.

[0037] Preparation of polysilicic acid solution: Prepare 1 L of sodium silicate solution with a concentration of 25 g / L, add 100 mL of hydrochloric acid solution with a concentration of 250 g / L dropwise under rapid stirring, ensuring pH < 3, and then let it stand for 2 h to activate to obtain polysilicic acid solution.

[0038] Preparation of polyaluminum ferric phosphate powder: 100 g of sludge powder containing P, Al and Fe sources was added to the polymeric silica solution under rapid stirring. After standing and activating for 2 h, insoluble impurities were removed by filtration. The powder was dried at 60℃ for 12 h, ground, and passed through an 80-mesh sieve to obtain polyaluminum ferric phosphate powder.

[0039] (2) Preparation of compound defluorination agents After thoroughly mixing 10 g of chalk powder and 50 g of ferric aluminum phosphate polysilicate powder, the mixture was ground and passed through an 80-mesh sieve to obtain a self-buffered composite fluoride removal agent, named Self-buffered Composite Fluoride Removal Agent A; the appearance of Self-buffered Composite Fluoride Removal Agent A is as follows. Figure 1 As shown.

[0040] Example 2: Changing the amount of chalk powder and phosphopolyalumina-iron silicate powder added The specific implementation method differs from Example 1 in that it uses 10 g of chalk powder and 100 g of aluminum iron phosphate polysilicate powder to prepare the defluorinating agent.

[0041] Comparative Example 1: Using only chalk The specific implementation method differs from Example 1 in that it does not use phosphorus polyaluminum iron silicate powder, but directly uses 60 g of chalk powder to prepare the fluoride removal agent.

[0042] Comparative Example 2: Using only phosphopolyaluminosilicate iron powder The specific implementation method differs from Example 1 in that chalk powder is not used; instead, 60 g of phosphate polyaluminum iron powder is used directly to prepare the fluoride removal agent.

[0043] Comparative Example 3: Chalk powder was replaced with calcium carbonate The specific implementation method differs from Example 1 in that chalk powder is replaced with calcium carbonate, while the other steps remain the same, to prepare a defluorinating agent.

[0044] Comparative Example 4: Direct use of commercially available polymerized aluminum silicate Commercially available polyaluminum silicate was used directly as the defluorination agent.

[0045] Example 3: Effect of the dosage of compound defluoridation agent on the removal of fluoride ions in wastewater The fluoride removal agents prepared in Examples 1-2 and Comparative Examples 1-4 were used to remove fluoride from wastewater. The steps are as follows: Weigh out 0.5 g, 1.0 g, and 1.5 g of the defluoridating agent prepared in Example 1, and 1 g of the defluoridating agent prepared in Example 2 and Comparative Examples 1-4, respectively. Add them to 1 L of photovoltaic wastewater with a fluoride ion concentration of 14.2 mg / L and pH=7.8. Stir for 5 min, let stand for 30 min to settle, take the supernatant, and monitor the pH and fluoride ion concentration of the effluent.

[0046] The measurement results are shown in Table 1. The results show that for photovoltaic wastewater with an influent fluoride concentration of 14.2 mg / L and pH=7.8, when the dosage of self-buffered compound defluoridating agent A is 0.5 g / L, 1.0 g / L and 1.5 g / L, the effluent fluoride concentrations are 1.7 mg / L, 1.0 mg / L and 0.6 mg / L, respectively, and the effluent pH is 7.1, 6.8 and 6.7, respectively. This achieves deep removal of fluoride ions and simultaneous buffering of pH.

[0047] Table 1

[0048] Comparative Example 5: Commercially available polyaluminum silicate was used as a defluorinating agent for photovoltaic wastewater treatment without adjusting the pH. An experiment was conducted using commercially available polyaluminum silicate as a fluoride removal agent to treat photovoltaic wastewater. Details are as follows: Weigh 0.5 g, 1.0 g, and 1.5 g of polyaluminum silicate, dissolve them to form a 10% solution, add them to 1 L of photovoltaic wastewater with a fluoride ion concentration of 14.2 mg / L and pH=7.8, stir for 2 min, add 1 mL of 0.1% PAM solution, let it stand for 30 min to settle, take the supernatant, and monitor the pH and fluoride ion concentration of the effluent.

[0049] The test results are shown in Table 2. For photovoltaic wastewater with an influent fluoride concentration of 14.2 mg / L and pH=7.8, when the dosage of polyaluminum silicate is 0.5 g / L, 1.0 g / L and 1.5 g / L, the effluent fluoride concentrations are 5.5 mg / L, 4.0 mg / L and 3.7 mg / L, respectively, and the effluent pH is 5.7, 4.9 and 4.5, respectively.

[0050] Table 2

[0051] Comparative Example 6: Commercially available polyaluminum silicate was used as a defluorinating agent in the treatment of photovoltaic wastewater to adjust the pH. An experiment was conducted using commercially available polyaluminum silicate as a fluoride removal agent to treat photovoltaic wastewater. Details are as follows: Weigh 0.5 g, 1.0 g, and 1.5 g of polyaluminum silicate, dissolve them to form a 10% solution, add them to 1 L of photovoltaic wastewater with a fluoride ion concentration of 14.2 mg / L and pH=7.8, stir for 2 min, add NaOH solution to adjust the pH to 6.7, then add 1 mL of 0.1% PAM solution, let it stand for 30 min to settle, take the supernatant, and monitor the pH and fluoride ion concentration of the effluent.

[0052] The test results are shown in Table 3. For photovoltaic wastewater with an influent fluoride concentration of 14.2 mg / L and pH=7.8, when the dosage of polyaluminum silicate is 0.5 g / L, 1.0 g / L and 1.5 g / L, the effluent fluoride concentrations are 3.0 mg / L, 2.1 mg / L and 1.7 mg / L, respectively, and the effluent pH is 6.7 (after adjustment).

[0053] Table 3

[0054] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Anyone skilled in the art can make various modifications and alterations without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be determined by the claims.

Claims

1. A method for preparing a self-buffered composite defluorination agent, characterized in that, Includes the following steps: A self-buffered composite fluoride removal agent was obtained by mixing and grinding chalk powder with phosphorus-polymerized aluminum iron silicate powder at a ratio of 1~2 g: 5~10 g. The preparation method of phosphorus-polymerized aluminum-iron silicate powder is as follows: sludge powder is added to the polymerized silica solution, and after standing and activating for 1-2 hours, it is filtered, dried, and ground to obtain phosphorus-polymerized aluminum-iron silicate powder.

2. The method according to claim 1, characterized in that, The concentration of sodium silicate in the polymeric silicate solution is 25~50 g / L.

3. The method according to claim 1, characterized in that, The mass ratio of sludge powder to sodium silicate is 4~6:1~2.

4. The method according to claim 1, characterized in that, The drying process involves drying at 60-100℃ for 6-10 hours.

5. The method according to claim 1, characterized in that, The grinding process involves grinding the material to a particle size of 100-200 mesh.

6. The self-buffered composite defluorination agent prepared by any one of claims 1 to 5.

7. A method for removing fluoride ions from wastewater, characterized in that, Using the self-buffered composite defluoridating agent according to claim 6, the steps are as follows: Add the self-buffered compound defluoridation agent to the wastewater at a dosage of 100~2000 mg / L, stir, and let it settle.

8. A method for simultaneously improving the removal efficiency of fluoride ions in wastewater and adjusting the pH of wastewater, characterized in that, Using the self-buffered composite defluoridating agent according to claim 6, the steps are as follows: Add the self-buffered compound defluoridation agent to the wastewater at a dosage of 100~2000 mg / L, stir, and let it settle.

9. The application of the method according to any one of claims 7 to 8 and the self-buffered composite defluorination agent according to claim 6 in the environmental field.

10. The method according to claim 9, characterized in that, The applications include reducing fluoride ions, adjusting pH, reducing the amount of alkali used, and reducing the amount of PAM used.

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