Treatment method for high-concentration fluorine-containing wastewater of glass factory

Abstract

The invention discloses a glass factory high-concentration fluorine-containing wastewater treatment method, which comprises: S1, uniformly mixing high-concentration fluorine-containing wastewater with a sodium-containing solvent, stirring, carrying out pressure filtration treatment, and separating to obtain a first precipitate and a first filtrate; s2, adding a calcium-containing solvent into the first filtrate, uniformly mixing, stirring, carrying out filter pressing treatment, and separating to obtain a second precipitate and a second filtrate; and S3, adding lime into the second filtrate, stirring until the pH value of the solution is 7-8, carrying out filter pressing treatment, and separating to obtain a third precipitate and a third filtrate. According to the defluorination method, the utilization rate of fluorine ions can reach 96.5% through the first two times of precipitation, the first-stage precipitation is sodium fluoroaluminate and sodium fluosilicate, the second-stage precipitation is calcium fluoride with the purity as high as 80%, the cost is reduced, meanwhile, precipitates with economic benefits can be obtained, the fluorine ion content of clear liquid obtained after three times of defluorination treatment is smaller than 20 mg / L, and the fluorine ion content of the clear liquid obtained after three times of defluorination treatment is smaller than 20 mg / L. And the emission standard can be reached.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, and in particular to a method for treating high-concentration fluoride-containing wastewater from a glass factory. Background Technology

[0002] Fluoride-containing wastewater refers to wastewater containing high concentrations of fluoride ions (F) from industrial production, manufacturing, or other processes. - Fluoride-containing wastewater commonly originates from wastewater treatment processes in industries such as metal smelting, chemical production, electronics, and electroplating, as well as from the use of fluoride-containing pesticides and the extraction of fluoride-containing groundwater. The fluoride content in this wastewater exceeds environmental emission standards or poses a threat to the ecological environment and human health; therefore, appropriate wastewater treatment is necessary to reduce the fluoride content to levels that meet emission standards or are acceptable.

[0003] Existing wastewater defluoridation processes include chemical precipitation, adsorption, ion exchange, reverse osmosis, and nanofiltration membrane separation technologies. However, all of these processes encounter numerous problems during implementation.

[0004] Chemical precipitation removes free fluoride ions from wastewater by adding calcium or aluminum salts to form insoluble compounds. This method can effectively reduce the fluoride content in wastewater, but excessive calcium salt addition may result in the final precipitate requiring further treatment.

[0005] The adsorption method utilizes porous materials such as activated carbon and zeolite to remove fluoride ions from wastewater. While simple to operate, the adsorption material needs to be replaced periodically, increasing maintenance costs.

[0006] Ion exchange removes fluoride ions from wastewater by reacting them with ion exchange resins. However, the resins need to be replaced regularly, and the regeneration wastewater is complex and difficult to treat.

[0007] Reverse osmosis and nanofiltration membrane separation technologies are also used to treat fluoride-containing wastewater. Through the selective permeability of semi-permeable membranes, water and other small molecules permeate under pressure, while fluoride ions and other pollutants are intercepted, thus removing fluoride ions. However, this technology is costly, and its operation and maintenance are complex. Direct discharge of the concentrated liquid can also cause serious environmental pollution.

[0008] Therefore, there is an urgent need for a defluorination method suitable for high-concentration fluoride-containing wastewater from glass factories to solve the above-mentioned technical problems. Summary of the Invention

[0009] The main objective of this invention is to propose a method for treating high-concentration fluoride-containing wastewater from glass factories, which reduces costs while the obtained filter residue precipitate also has economic benefits and increases revenue.

[0010] To achieve the above objectives, this invention proposes a method for treating high-concentration fluoride-containing wastewater from glass factories, comprising the following steps: S1. Mix high-concentration fluoride-containing wastewater with sodium-containing solvent evenly, stir, and then perform pressure filtration to separate the first precipitate and the first filtrate. S2. Add a calcium-containing solvent to the first filtrate, mix well, stir, and then perform pressure filtration to separate the second precipitate and the second filtrate. S3. Add lime to the second filtrate and stir until the pH value of the solution is 7-8. After pressure filtration, the third precipitate and the third filtrate are separated.

[0011] This invention discloses a method for treating high-concentration fluoride wastewater from glass factories. Specifically, the method involves a first-stage defluorination process: a sodium-containing solvent is added to the wastewater to obtain a first precipitate containing sodium fluoroaluminate (Na₂AlF₆) and sodium fluorosilicate (Na₂SiF₆). Sodium fluoroaluminate and sodium fluorosilicate can be used as fluxes in high-temperature metal smelting processes such as magnesium and zinc, offering good economic benefits. A second-stage defluorination process is then performed in the first filtrate by adding a calcium-containing solvent, yielding a second precipitate containing calcium fluoride (CaF₂). Lime is then added to adjust the pH to 7-8 for a third-stage defluorination process. After the first two precipitation stages, the fluoride ion utilization rate reaches 96.5%. This method is simple and low-cost, and the purity of the resulting second precipitate can reach over 80%, demonstrating good economic benefits. After the third-stage defluorination, the fluoride ion concentration is less than 20 mg / L, meeting the direct discharge standards.

[0012] Preferably, the sodium-containing solvent is one of sodium chloride and sodium hydroxide. More preferably, the sodium-containing solvent is sodium chloride.

[0013] Preferably, the amount of sodium-containing solvent added is such that the Na / F molar ratio is 1 to 4.

[0014] Preferably, the calcium-containing solvent is one of calcium chloride and calcium oxide. Preferably, the calcium-containing solvent is calcium oxide.

[0015] Preferably, the amount of calcium-containing solvent added is such that the Ca / F molar ratio is 0.7 to 2.4.

[0016] Preferably, in step S1, the stirring speed is 600~700 r / min and the stirring time is 60~120 min; In step S2, the stirring speed is 600~700 r / min and the stirring time is 60~120 min; In step S3, the stirring speed is 600~700 r / min and the stirring time is 60~120 min.

[0017] Preferably, the high-concentration fluoride-containing wastewater is a mixed solution containing silicon and sodium elements with a fluoride ion concentration higher than 30,000 mg / L.

[0018] Preferably, in step S1, the first precipitate includes sodium fluorosilicate and sodium fluoroaluminate; In step S2, the second precipitate includes calcium fluoride, and after drying, the purity of the calcium fluoride in the second precipitate is higher than 80%. In step S3, the fluoride ion content in the third filtrate is less than 20 mg / L.

[0019] Compared with existing technologies, the method for treating high-concentration fluoride-containing wastewater provided by this invention has at least the following beneficial effects: (1) The fluoride-containing wastewater treatment method of this scheme, after the first-stage defluorination, the main products of the primary precipitate are sodium fluoroaluminate and sodium fluorosilicate, which can be used as fluxing agents in metal smelting processes such as magnesium and zinc that require high-temperature smelting; after the second-stage defluorination, the main product of the secondary precipitate is calcium fluoride, and the purity reaches more than 80%, which can be directly sold and has economic benefits. (2) The fluoride-containing wastewater treatment method of this scheme does not require the use of coagulants, and the precipitates do not need to be washed. They can be separated directly by pressure filtration, vacuum filtration and other methods, which saves treatment costs. (3) After two precipitations, the utilization rate of fluoride ions reaches 96.5%. After the third defluorination, the concentration of fluoride ions in the supernatant is less than 20 mg / L, which can achieve clean discharge of the treated high-concentration fluoride wastewater. Detailed Implementation

[0020] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of this application can be combined with each other. At the same time, the raw materials mentioned below, unless otherwise specified, are all commercially available products; the process steps or preparation methods not mentioned in detail are all process steps or preparation methods known to those skilled in the art.

[0021] A method for treating high-concentration fluoride-containing wastewater from a glass factory includes the following steps: S1. Mix high-concentration fluoride-containing wastewater with sodium-containing solvent evenly, stir, and then filter under pressure to separate the first precipitate and the first filtrate; the stirring speed is 600~700 r / min, and the stirring time is 60~120 min. S2. Add a calcium-containing solvent to the first filtrate, mix well, stir, and then perform pressure filtration to separate the second precipitate and the second filtrate; the stirring speed is 600~700 r / min, and the stirring time is 60~120 min. S3. Add lime to the second filtrate and stir until the solution pH is 7-8. After pressure filtration, separate the third precipitate and the third filtrate. The stirring speed is 600-700 r / min and the stirring time is 60-120 min.

[0022] The sodium-containing solvent is either sodium chloride or sodium hydroxide, preferably sodium chloride. The amount of sodium-containing solvent added is such that the Na / F molar ratio is 1 to 4.

[0023] The calcium-containing solvent is either calcium chloride or calcium oxide, preferably calcium oxide, and the amount of calcium-containing solvent added is such that the Ca / F molar ratio is 0.7 to 2.4.

[0024] This invention provides a method for defluoridating high-concentration fluoride-containing wastewater from glass factories. It is understood that the defluoridation method described in this invention is also applicable to high-concentration fluoride-containing wastewater containing silicon and aluminum generated by other industries. This high-concentration fluoride-containing wastewater is a mixed solution containing silicon and sodium elements with a fluoride ion concentration exceeding 30,000 mg / L. In existing technologies, the treatment of high-concentration wastewater from glass factories typically involves directly adding excessive amounts of lime to the wastewater to remove fluoride ions, and then collecting the reaction precipitate and excess lime mixture for centralized landfill, which is costly and poses environmental safety risks.

[0025] This invention effectively solves the aforementioned problems. First, a sodium-containing solvent, specifically sodium chloride or sodium hydroxide, is added to fluoride-containing wastewater at a Na / F molar ratio of 1-4. After stirring, reaction, and precipitation, a first precipitate and a first filtrate are obtained. During the primary defluorination process, sodium fluoroaluminate (Na₂AlF₆) and sodium fluorosilicate (Na₂SiF₆) are produced, which can be used as fluxes in high-temperature smelting processes for metals such as magnesium and zinc, offering good economic benefits. Subsequently, a calcium-containing solvent, specifically calcium chloride or calcium oxide, is added to the first filtrate at a Ca / F molar ratio of 0.7-2.4. After stirring, reaction, and precipitation, a second precipitate and a second filtrate are obtained. After the second defluorination, calcium fluoride (CaF₂) with a purity higher than 80% can be obtained and sold directly. Then, lime is added to the second filtrate and stirred until the solution pH reaches 7-8. The solution is then filtered to separate a third precipitate and a third filtrate. The fluoride ion content in the obtained third filtrate is less than 20 mg / L. The three reactions remove fluoride ions while producing fluoride precipitates, all of which are economically beneficial, reducing costs and increasing profits.

[0026] The following examples further illustrate the present invention in detail. It should also be understood that the following examples are only for further explanation of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above description of the present invention are within the scope of protection of the present invention. The specific process parameters in the following examples are merely one example within a suitable range; that is, those skilled in the art can make appropriate selections within the range based on the description herein, and are not intended to be limited to the specific values ​​in the examples below. Where specific conditions are not specified in the examples, conventional conditions or conditions recommended by the manufacturer shall apply.

[0027] The high-concentration fluoride-containing wastewater from the glass factory used in the following examples or comparative studies was generated during the production process of a large glass factory. The composition of the raw water was analyzed using ICP and ion chromatography as follows (unit: mg / L): Example 1 A method for treating high-concentration fluoride-containing wastewater from a glass factory includes the following steps: S1. High-concentration fluoride-containing wastewater and sodium chloride are mixed evenly at a Na / F molar ratio of 3. The mixture is stirred at a stirring speed of 600 r / min for 60 min and then subjected to pressure filtration to separate the first precipitate and the first filtrate. The concentration of each element in the first filtrate is determined and the first precipitate is tested.

[0028] S2. Mix the first filtrate with lime at a Ca / F molar ratio of 2, stir at 600 r / min for 60 min, and then filter by pressure to separate the second precipitate and the second filtrate; determine the concentration of each element in the second filtrate and analyze the second precipitate. S3. Add lime to the second filtrate and stir until the pH of the solution is 7.66. Then, perform pressure filtration to separate the third precipitate and the third filtrate. Measure the concentration of each element in the third filtrate and detect the third precipitate.

[0029] The concentrations of each element in the high-concentration fluoride-containing wastewater and the clarified liquid from the third reaction in Example 1 are shown in Table 1 (unit: mg / L): Table 1 The percentage concentrations of each element and the purity of calcium fluoride in the first, second, and third precipitates of Example 1 are shown in Table 2. Table 2 Analysis revealed that the main products of the first precipitate produced after one defluorination in Example 1 were sodium fluoroaluminate and sodium fluorosilicate, both of economic value; the main product of the second precipitate produced after two defluorinations was calcium fluoride, also of economic value, with a purity of 81.78%. After the first defluorination in step S1, the fluoride ion concentration in the first filtrate decreased from 35.5 g / L to 12.3 g / L. After the second defluorination in step S2, the fluoride ion concentration decreased to 1.3 g / L. After the third defluorination in step S3, the fluoride ion concentration decreased to 14.24 mg / L, meeting the emission standards.

[0030] Example 2 A method for treating high-concentration fluoride-containing wastewater from a glass factory includes the following steps: S1. High-concentration fluoride-containing wastewater and sodium hydroxide are mixed evenly at a Na / F molar ratio of 2. The mixture is stirred at 700 r / min for 60 min and then filtered to separate the first precipitate and the first filtrate. The concentration of each element in the first filtrate is determined and the first precipitate is tested.

[0031] S2. Mix the first filtrate with calcium chloride at a Ca / F molar ratio of 1, stir at 700 r / min for 60 min, and then filter by pressure to separate the second precipitate and the second filtrate; determine the concentration of each element in the second filtrate and analyze the second precipitate. S3. Add lime to the second filtrate and stir until the solution pH is 7. Then, perform pressure filtration to separate the third precipitate and the third filtrate. Measure the concentration of each element in the third filtrate and detect the third precipitate.

[0032] The concentrations of each element in the high-concentration fluoride-containing wastewater and the clarified liquid from the third reaction in Example 2 are shown in Table 3 (unit: mg / L): Table 3 The percentage concentrations of each element and the purity of calcium fluoride in the first, second, and third precipitates of Example 2 are shown in Table 4. Table 4 Analysis revealed that the main products of the first precipitate produced after one defluorination in Example 2 were sodium fluoroaluminate and sodium fluorosilicate, both of economic value; the main product of the second precipitate produced after two defluorinations was calcium fluoride, also of economic value, with a purity of 83.19%. After the first defluorination in step S1, the fluoride ion concentration in the first filtrate decreased from 36.3 g / L to 19.4 g / L. After the second defluorination in step S2, the fluoride ion concentration decreased to 1.06 g / L. After the third defluorination in step S3, the fluoride ion concentration decreased to 17.12 mg / L, meeting the emission standards.

[0033] Comparative Example 1 A method for treating high-concentration fluoride-containing wastewater from a glass factory includes the following steps: S1. High-concentration fluoride-containing wastewater and lime are mixed evenly at a Ca / F molar ratio of 0.85. The mixture is stirred at 600 r / min for 60 min, followed by pressure filtration to separate the first precipitate and the first filtrate. The concentrations of each element in the first filtrate are determined, and the first precipitate is analyzed. S2. Mix the first filtrate with calcium chloride at a Ca / F molar ratio of 0.8, stir at 600 r / min for 60 min, and then filter by pressure to separate the second precipitate and the second filtrate.

[0034] Table 5 shows the concentrations of various elements in the high-concentration fluoride-containing wastewater of Comparative Example 1 and the clarified liquid from both reactions (unit: mg / L): Table 5 The percentage concentrations of each element and the purity of calcium fluoride in the first and second precipitates of Comparative Example 1 are shown in Table 6. Table 6 Comparative Example 1 used the traditional lime method for fluoride removal. The final filtrate concentration of fluoride ions was 5.65 mg / L. The first and second precipitates obtained included a mixture of various compounds such as aluminum hydroxide, iron hydroxide, calcium silicate, calcium fluoride, and calcium carbonate. The precipitates contained a wide variety of products, making them unrecoverable. Therefore, while the traditional lime method used in Comparative Example 1 could produce a supernatant that met emission standards, it was only a fluoride removal and purification method. New environmental pollutants were still generated during the process, and the precipitated products were difficult to recover.

[0035] In summary, the defluorination method described in this invention reduces costs while producing economically valuable sodium fluoroaluminate, sodium fluorosilicate, and calcium fluoride, achieving both wastewater treatment and substantial economic benefits.

[0036] The above description is merely a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformations made using the contents of the present invention under the inventive concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A method for treating high-concentration fluoride-containing wastewater from a glass factory, characterized in that, Includes the following steps: S1. Mix high-concentration fluoride-containing wastewater with sodium-containing solvent evenly, stir, and then perform pressure filtration to separate the first precipitate and the first filtrate. S2. Add a calcium-containing solvent to the first filtrate, mix well, stir, and then perform pressure filtration to separate the second precipitate and the second filtrate. S3. Add lime to the second filtrate and stir until the pH of the solution is 7-8. After pressure filtration, the third precipitate and the third filtrate are separated.

2. The method for treating high-concentration fluoride-containing wastewater as described in claim 1, characterized in that, In step S1, the sodium-containing solvent is either sodium chloride or sodium hydroxide.

3. The method for treating high-concentration fluoride-containing wastewater as described in claim 1, characterized in that, In step S1, the sodium-containing solvent is sodium chloride.

4. The method for treating high-concentration fluoride-containing wastewater as described in claim 1, characterized in that, In step S1, the amount of sodium-containing solvent added is such that the Na / F molar ratio is 1 to 4.

5. The method for treating high-concentration fluoride-containing wastewater as described in claim 1, characterized in that, In step S2, the calcium-containing solvent is either calcium chloride or calcium oxide.

6. The method for treating high-concentration fluoride-containing wastewater as described in claim 1, characterized in that, In step S2, the calcium-containing solvent is calcium oxide.

7. The method for treating high-concentration fluoride-containing wastewater as described in claim 1, characterized in that, In step S2, the amount of calcium-containing solvent added is such that the Ca / F molar ratio is 0.7 to 2.

4.

8. The method for treating high-concentration fluoride-containing wastewater as described in claim 1, characterized in that, The high-concentration fluoride-containing wastewater is a mixed solution containing silicon and sodium elements with a fluoride ion concentration higher than 30,000 mg / L.

9. The method for treating high-concentration fluoride-containing wastewater as described in claim 1, characterized in that, In step S1, the first precipitate includes sodium fluorosilicate and sodium fluoroaluminate; In step S2, the second precipitate includes calcium fluoride, and after drying, the purity of the calcium fluoride in the second precipitate is higher than 80%. In step S3, the fluoride ion content in the third filtrate is less than 20 mg / L.

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