Treatment methods for fluoride-containing wastewater

Abstract

This invention provides a method for treating fluoride-containing wastewater, comprising the following steps: mixing and reacting calcium salt and phosphate, then filtering; heating the precipitate in an alkaline solution to obtain a mixture; the calcium salt contains carboxyl groups; adding the mixture to the fluoride-containing wastewater, adding an aluminum source, and filtering to remove fluoride. This method significantly improves reaction efficiency, reduces the solubility of fluoride ions in water, increases the fluoride ion removal rate, and reduces treatment time. Furthermore, the mixture obtained from the reaction of calcium salt and phosphate, along with the aluminum source, acts as a buffer in the aqueous solution system, greatly expanding the pH range of the treated wastewater and demonstrating strong adaptability.

Description

Technical Field

[0001] This invention relates to the field of wastewater defluoridation technology, and in particular to a method for treating fluoride-containing wastewater. Background Technology

[0002] Excessive fluoride content in water not only leads to fluorosis in humans, causing skeletal fluorosis and dental fluorosis, but also poisons animals and plants, impacting agricultural and livestock production. The direct discharge of large quantities of fluoride-containing wastewater inevitably causes serious environmental pollution. Currently, there are various methods for treating fluoride-containing wastewater both domestically and internationally, including chemical precipitation, adsorption, coagulation sedimentation, electrocoagulation, ion exchange resin methods, reverse osmosis, liquid membrane methods, and electrodialysis. Chemical precipitation is a simple process and is currently the most widely used method for treating fluoride-containing wastewater. Traditional calcium salt precipitation methods mainly involve adding calcium salts such as calcium oxide, calcium hydroxide, and calcium chloride to the wastewater. The calcium salts react with fluoride ions in the wastewater to form CaF2 precipitate. However, this method suffers from high fluoride solubility, slow precipitation, unstable defluorination effects, and extremely high reagent consumption, causing secondary pollution. Summary of the Invention

[0003] This invention provides a method for treating fluoride-containing wastewater to solve the technical problems of unstable fluoride removal effect, long treatment time, and secondary pollution in the prior art.

[0004] To achieve the above objectives, the technical solution of the present invention is implemented as follows:

[0005] This invention provides a method for treating fluoride-containing wastewater, comprising the following steps:

[0006] S1. After reacting the calcium salt and phosphate, filter the mixture, place the precipitate in an alkaline solution and heat it to obtain a mixture; the calcium salt contains a carboxyl group;

[0007] S2. Add the mixture to the fluoride-containing wastewater, then add an aluminum source and filter to remove fluoride.

[0008] Furthermore, the molar ratio of calcium ions in the calcium salt to phosphate ions in the phosphate salt is 1.5 to 2.0:1, and the mass ratio of the mixture to the aluminum source is 1:0.05 to 0.1.

[0009] Furthermore, the calcium salt is selected from one or more of calcium carboxymethyl cellulose, calcium lignosulfonate, calcium alginate, and calcium lactobionate.

[0010] Furthermore, the molecular weight of the calcium salt is 1000 to 10000, and the mass percentage of carboxyl groups in the calcium salt is greater than 1.25%.

[0011] Furthermore, the aluminum source is selected from one or more of aluminum chloride, polyaluminum chloride, polyaluminum sulfate, aluminum sulfate, and alum.

[0012] Further, the phosphate is selected from one or more of phosphoric acid, soluble monohydrogen phosphate, soluble dihydrogen phosphate, and soluble orthophosphate.

[0013] Furthermore, in step S1, the calcium salt is dispersed in the phosphate, and the reaction temperature is 20℃~100℃.

[0014] Furthermore, in step S1, the pH value of the alkaline solution is 10 to 11.

[0015] Furthermore, in step S1, the reaction temperature of the precipitate in the alkaline solution is 85℃~95℃, and the reaction time is 4h~6h.

[0016] Further, in step S2, the mass-to-volume ratio of the mixture to the fluoride-containing wastewater is 0.5g to 20g: 1L, and the mass ratio of the mixture to the aluminum salt is 1: 0.05 to 0.1.

[0017] Furthermore, the method also includes the following steps: treating the precipitate obtained after filtration in step S2 with acid, placing it in an alkaline solution, heating it to react, and recovering the mixture.

[0018] Furthermore, the fluoride ion concentration in the fluoride-containing wastewater is less than or equal to 50 mg / L.

[0019] The method for treating fluoride-containing wastewater provided by this invention comprises two parts: a high-molecular-weight calcium salt and phosphate containing carboxyl groups, and an aluminum source. The high-molecular-weight calcium salt reacts with the phosphate to form phosphate esters. After filtration, the precipitate is placed in an alkaline solution and heated to obtain a mixture that is a hydroxyl-like calcium phosphate, which has a strong ability to adsorb fluoride ions. The aluminum source acts as a coagulant and provides acidic conditions during the fluoride removal process. Adding the hydroxyl-like calcium phosphate obtained from the reaction of calcium salt and phosphate to the fluoride-containing wastewater first, followed by the addition of the aluminum source, significantly improves the reaction efficiency, reduces the solubility of fluoride ions in water, increases the fluoride ion removal rate, and reduces the treatment time. Furthermore, the mixture obtained from the reaction of calcium salt and phosphate, along with the aluminum source, acts as a buffer in the aqueous solution system, greatly expanding the pH range of the treated wastewater and demonstrating strong adaptability. Detailed Implementation

[0020] The present invention will be further described in detail below with reference to specific embodiments.

[0021] This application provides a method for treating fluoride-containing wastewater, including the following steps: S1, mixing and reacting calcium salt and phosphate, then filtering, placing the precipitate in an alkaline solution and heating, reacting to obtain a mixture; the calcium salt contains carboxyl groups; S2, adding the mixture to the fluoride-containing wastewater, then adding an aluminum source, and filtering to remove fluoride.

[0022] In the fluoride-containing wastewater treatment method provided in this application embodiment, the treatment agent consists of two parts: one part is a high molecular weight calcium salt and phosphate containing carboxyl groups, and the other part is an aluminum source. The high molecular weight calcium salt containing carboxyl groups reacts with the phosphate to form phosphate ester compounds. After filtration, the precipitate is placed in an alkaline solution and heated to obtain a mixture that is hydroxyl-like calcium phosphate, which has a strong ability to adsorb fluoride ions. The aluminum source plays a coagulation role and provides acidic conditions during the fluoride removal process. The hydroxyl-like calcium phosphate obtained by reacting calcium salt and phosphate is first added to the fluoride-containing wastewater, and then the aluminum source is added, which greatly improves the reaction efficiency, reduces the solubility of fluoride ions in water, improves the fluoride ion removal rate, and reduces the treatment time. In addition, the mixture obtained by reacting calcium salt and phosphate and the aluminum source have a buffering effect in the aqueous solution system, which greatly improves the pH range of the treated wastewater and has strong adaptability.

[0023] In the embodiments of this application, the molar ratio of calcium ions in the calcium salt to phosphate ions in the phosphate is 1.5 to 2.0:1, and the mass ratio of the mixture to the aluminum source is 1:0.05 to 0.1.

[0024] This application utilizes calcium salts containing carboxyl groups and phosphates as raw materials to react and form hydroxyl-like calcium phosphate, which has a strong ability to adsorb fluoride ions, thereby improving reaction efficiency and fluoride ion removal rate. The calcium salt is a high-molecular-weight compound rich in carboxyl groups, selected from one or more of calcium carboxymethyl cellulose, calcium lignosulfonate, calcium alginate, and calcium lactobionate. The molecular weight of the calcium salt is 1000-10000, and the mass percentage of carboxyl groups in the calcium salt is greater than 1.25%. The phosphate is soluble and selected from one or more of phosphoric acid, soluble monohydrogen phosphate, soluble dihydrogen phosphate, and soluble orthophosphate. Specifically, examples include ammonium dihydrogen phosphate and potassium dihydrogen phosphate.

[0025] In this embodiment, the mass-to-volume ratio of the mixture to the fluoride-containing wastewater in step S2 is 0.5g to 20g:1L, and the mass ratio of the mixture to the aluminum salt is 1:0.05 to 0.1. This means that a large amount of fluoride-containing wastewater can be treated by adding a small amount of wastewater treatment agent, thus saving costs.

[0026] In this embodiment of the application, the following steps are also included: treating the precipitate obtained after filtration in step S2 with acid, placing it in an alkaline solution, heating to react, and recovering the mixture. It can be seen that the mixture obtained from the reaction of calcium salt and phosphate can be recovered through the above steps, thus enabling secondary use without pollution, reducing the cost of the treatment agent, and improving the removal efficiency.

[0027] The embodiments of this application are preferably suitable for treating fluoride-containing wastewater with a fluoride ion concentration of less than or equal to 50 mg / L, and more preferably for treating fluoride-containing wastewater with a fluoride ion concentration of about 20 mg / L.

[0028] The reagents used in the following examples are all commercially available.

[0029] Example 1

[0030] A method for treating fluoride-containing wastewater includes the following steps:

[0031] (1) Disperse 40g of calcium carboxymethyl cellulose (calcium content 10%) in 109.3g of sodium phosphate solution (sodium phosphate mass concentration 10%), heat to 50℃, and stir for 60 minutes. After the reaction is complete, filter, place the obtained precipitate in sodium hydroxide solution with pH 10, heat to 85℃, and react for 5 hours. After the reaction is complete, filter and dry, and use the resulting mixture for later use.

[0032] (2) Prepare 40 mg / L fluoride-containing wastewater and control the pH value to 3. Add the mixture obtained in step (1) to the above wastewater. Add 5 g of the above mixture to 1 L of fluoride-containing wastewater, and then immediately add 0.5 g of polyaluminum chloride. After reacting for 6 minutes, take the supernatant and measure the fluoride ion concentration to find that it is 3.6 mg / L, and the fluoride ion removal rate is 91%.

[0033] (3) The fluoride-containing wastewater treated in step (2) was filtered to obtain a precipitate, which was then dried. 10% hydrochloric acid was added, and after 30 minutes, the precipitate was filtered and washed until neutral. The precipitate was then placed in clear limewater, heated to 90°C, and reacted for 5 hours. After filtration and drying, a recovered mixture was obtained. 2g of the recovered mixture was added to 400mL of the fluoride-containing wastewater prepared in step (2), and then 0.2g of polyaluminum chloride was added. After reacting for 6 minutes, the concentration of fluoride ions in the supernatant was measured to be 3.9mg / L, and the fluoride ion removal rate was 90.25%.

[0034] Example 2

[0035] A method for treating fluoride-containing wastewater includes the following steps:

[0036] (1) Disperse 50g of calcium lignosulfonate (calcium content 7.5%) in 112.5g of sodium dihydrogen phosphate solution (sodium dihydrogen phosphate mass concentration 5%), heat to 45℃, and stir for 60 minutes. After the reaction is complete, filter, place the obtained precipitate in sodium hydroxide solution with pH 10, heat to 95℃, and react for 4 hours. After the reaction is complete, filter and dry, and use the resulting mixture for later use.

[0037] (2) Prepare 40 mg / L fluoride-containing wastewater and control the pH value to 3. Add the mixture obtained in step (1) to the above wastewater. Add 5 g of the above mixture to 1 L of fluoride-containing wastewater, and then immediately add 0.4 g of polyaluminum sulfate. After reacting for 6 minutes, take the supernatant and measure the fluoride ion concentration to find that it is 3.55 mg / L. The fluoride ion removal rate is 91.13%.

[0038] (3) The fluoride-containing wastewater treated in step (2) was filtered to obtain a precipitate, dried, and added to 10% dilute sulfuric acid. After 30 minutes, it was filtered and washed until neutral. Then, it was placed in clear limewater, heated to 90°C, and reacted for 5 hours. After filtration and drying, a recovered mixture was obtained. 2g of the above recovered mixture was added to 400mL of fluoride-containing wastewater prepared in step (2), and then 0.16g of polyaluminum sulfate was added. After reacting for 6 minutes, the concentration of fluoride ions in the supernatant was measured to be 3.65mg / L, and the fluoride ion removal rate was 90.88%.

[0039] Example 3

[0040] A method for treating fluoride-containing wastewater includes the following steps:

[0041] (1) Disperse 50g of calcium alginate (calcium content 5%) in 80g of ammonium dihydrogen phosphate solution (mass concentration of ammonium dihydrogen phosphate 5%), heat to 45℃, and stir for 60 minutes. After the reaction is complete, filter, place the obtained precipitate in sodium hydroxide solution with pH 11, heat to 95℃, and react for 4 hours. After the reaction is complete, filter and dry, and use the resulting mixture for later use.

[0042] (2) Prepare 20 mg / L fluoride-containing wastewater and control the pH value to 8. Add the mixture obtained in step (1) to the above wastewater. Add 3 g of the above mixture to 1 L of fluoride-containing wastewater, and then immediately add 0.15 g of aluminum sulfate. After reacting for 6 minutes, take the supernatant and measure the fluoride ion concentration to find that it is 1.95 mg / L, and the fluoride ion removal rate is 90.25%.

[0043] (3) The fluoride-containing wastewater treated in step (2) was filtered to obtain a precipitate, dried, and added to 10% dilute sulfuric acid. After 30 minutes, it was filtered and washed until neutral. Then, it was placed in clear limewater, heated to 90°C, and reacted for 5 hours. After filtration and drying, a recovered mixture was obtained. 2g of the above recovered mixture was added to 400mL of fluoride-containing wastewater prepared in step (2), and then 0.1g of aluminum sulfate was added. After reacting for 6 minutes, the concentration of fluoride ions in the supernatant was measured to be 2.0mg / L, and the fluoride ion removal rate was 90%.

[0044] Example 4

[0045] A method for treating fluoride-containing wastewater includes the following steps:

[0046] (1) Disperse 50g of the above-mentioned calcium lactobionate (calcium content 12.5%) in 141.7g of potassium dihydrogen phosphate solution (potassium dihydrogen phosphate mass concentration 10%), heat to 45℃, and stir for 60 minutes. After the reaction is complete, filter, place the obtained precipitate in sodium hydroxide solution with pH 11, heat to 95℃, and react for 4 hours. After the reaction is complete, filter and dry, and use the resulting mixture for later use.

[0047] (2) Prepare a fluoride-containing wastewater with a concentration of 30 mg / L and control the pH value to 11. Add the mixture obtained in step (1) to the above wastewater. Add 3 g of the above mixture to 1 L of fluoride-containing wastewater, and then immediately add 0.3 g of polyaluminum sulfate. After reacting for 6 minutes, take the supernatant and measure the fluoride ion concentration, which is 2.93 mg / L. The fluoride ion removal rate is 90.23%.

[0048] (3) The fluoride-containing wastewater treated in step (2) was filtered to obtain a precipitate, dried, and added to 10% dilute sulfuric acid. After 30 minutes, it was filtered and washed until neutral. Then, it was placed in clear limewater, heated to 90°C, and reacted for 5 hours. After filtration and drying, a recovered mixture was obtained. 2g of the above recovered mixture was added to 400mL of fluoride-containing wastewater prepared in step (2), and then 0.2g of polyaluminum sulfate was added. After reacting for 6 minutes, the concentration of fluoride ions in the supernatant was measured to be 2.66mg / L, and the fluoride ion removal rate was 91.13%.

[0049] Example 5

[0050] A method for treating fluoride-containing wastewater includes the following steps:

[0051] (1) Disperse 50g of calcium lactobionate (calcium content 12.5%) in 141.7g of potassium dihydrogen phosphate solution (potassium dihydrogen phosphate mass concentration 10%), heat to 45℃, and stir for 60 minutes. After the reaction is complete, filter, place the obtained precipitate in sodium hydroxide solution with pH 11, heat to 95℃, and react for 4 hours. After the reaction is complete, filter and dry, and use the resulting mixture for later use.

[0052] (2) Prepare 50 mg / L fluoride-containing wastewater and control the pH value to 5. Add the mixture obtained in step (1) to the above wastewater. Add 10 g of the above mixture to 1 L of fluoride-containing wastewater, and then immediately add 1 g of polyaluminum sulfate. After reacting for 6 minutes, take the supernatant and measure the fluoride ion concentration to find that it is 2.93 mg / L, and the fluoride ion removal rate is 94.14%.

[0053] (3) The fluoride-containing wastewater treated in step (2) was filtered to obtain a precipitate, dried, and added to 10% dilute sulfuric acid. After 30 minutes, it was filtered and washed until neutral. Then, it was placed in clear limewater, heated to 90°C, and reacted for 5 hours. After filtration and drying, a recovered mixture was obtained. 2g of the above recovered mixture was added to 200mL of fluoride-containing wastewater prepared in step (2), and then 0.2g of alum was added. After reacting for 6 minutes, the concentration of fluoride ions in the supernatant was measured to be 2.66mg / L, and the fluoride ion removal rate was 94.68%.

[0054] Example 6

[0055] A method for treating fluoride-containing wastewater includes the following steps:

[0056] (1) Disperse 50g of calcium lignosulfonate (calcium content 7.5%) in 163.3g of potassium monohydrogen phosphate solution (potassium monohydrogen phosphate mass concentration 5%), heat to 45℃, and stir for 60 minutes. After the reaction is complete, filter, place the obtained precipitate in sodium hydroxide solution with pH 10, heat to 95℃, and react for 4 hours. After the reaction is complete, filter and dry, and use the resulting mixture for later use.

[0057] (2) Prepare 40 mg / L fluoride-containing wastewater and control the pH value to 9. Add the mixture obtained in step (1) to the above wastewater. Add 5 g of the above mixture to 1 L of fluoride-containing wastewater, and then immediately add 0.25 g of polyaluminum sulfate. After reacting for 6 minutes, take the supernatant and measure the fluoride ion concentration to find that it is 2.97 mg / L, and the fluoride ion removal rate is 92.58%.

[0058] (3) The fluoride-containing wastewater treated in step (2) was filtered to obtain a precipitate, dried, and added to 10% dilute sulfuric acid. After 30 minutes, it was filtered and washed until neutral. Then, it was placed in clear limewater, heated to 90°C, and reacted for 5 hours. After filtration and drying, a recovered mixture was obtained. 2g of the above recovered mixture was added to 400mL of fluoride-containing wastewater prepared in step (2), and then 0.1g of polyaluminum sulfate was added. After reacting for 6 minutes, the concentration of fluoride ions in the supernatant was measured to be 3.2mg / L, and the fluoride ion removal rate was 92%.

[0059] Example 7

[0060] A method for treating fluoride-containing wastewater includes the following steps:

[0061] (1) Disperse 50g of calcium lactobionate (calcium content 12.5%) in 102g of phosphoric acid solution (phosphoric acid mass concentration 10%), heat to 45℃, and stir for 60 minutes. After the reaction is complete, filter, place the obtained precipitate in sodium hydroxide solution with pH 11, heat to 95℃, and react for 4 hours. After the reaction is complete, filter and dry, and use the resulting mixture for later use.

[0062] (2) Prepare 50 mg / L fluoride-containing wastewater and control the pH value to 5. Add the mixture obtained in step (1) to the above wastewater. Add 8 g of the above mixture to 1 L of fluoride-containing wastewater, and then immediately add 0.8 g of alum. After reacting for 6 minutes, take the supernatant and measure the fluoride ion concentration to be 3.92 mg / L. The fluoride ion removal rate is 92.16%.

[0063] (3) The fluoride-containing wastewater treated in step (2) was filtered to obtain a precipitate, dried, and added to 10% dilute sulfuric acid. After 30 minutes, it was filtered and washed until neutral. Then, it was placed in clear limewater, heated to 90°C, and reacted for 5 hours. After filtration and drying, a recovered mixture was obtained. 2g of the above recovered mixture was added to 200mL of fluoride-containing wastewater prepared in step (2), and then 0.2g of alum was added. After reacting for 6 minutes, the concentration of fluoride ions in the supernatant was measured to be 4.11mg / L, and the fluoride ion removal rate was 91.78%.

[0064] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Furthermore, the technical solutions of the various embodiments of the present invention can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for treating fluoride-containing wastewater, characterized in that, Includes the following steps: S1. After mixing and reacting the calcium salt and phosphate, the mixture is filtered. The precipitate is placed in an alkaline solution and heated to obtain a mixture. The calcium salt contains a carboxyl group. The molar ratio of calcium ions in the calcium salt to phosphate ions in the phosphate is 1.5–2.0:

1. In step S1, the calcium salt is dispersed in the phosphate, and the reaction temperature is 20°C–100°C. The reaction temperature of the precipitate in the alkaline solution is 85°C–95°C, and the reaction time is 4–6 hours. S2. Add the mixture to the fluoride-containing wastewater, then add an aluminum source and filter to remove fluoride.

2. The method for treating fluoride-containing wastewater according to claim 1, characterized in that, The mass ratio of the mixture to the aluminum source is 1:0.05 to 0.

1.

3. The method for treating fluoride-containing wastewater according to claim 1, characterized in that, The calcium salt is selected from one or more of carboxymethyl cellulose calcium, calcium lignin sulfonate, calcium alginate, and calcium lactobionate.

4. The method for treating fluoride-containing wastewater according to claim 1, characterized in that, The calcium salt has a molecular weight of 1000 to 10000, and the mass percentage of carboxyl groups in the calcium salt is greater than 1.25%.

5. The method for treating fluoride-containing wastewater according to claim 1, characterized in that, The aluminum source is selected from one or more of aluminum chloride, polyaluminum chloride, polyaluminum sulfate, aluminum sulfate, and alum; and / or The phosphate is selected from one or more of phosphoric acid, soluble monohydrogen phosphate, soluble dihydrogen phosphate, and soluble orthophosphate.

6. The method for treating fluoride-containing wastewater according to any one of claims 1 to 5, characterized in that, In step S1, the pH value of the alkaline solution is 10 to 11.

7. The method for treating fluoride-containing wastewater according to any one of claims 1 to 5, characterized in that, In step S2, the mass-to-volume ratio of the mixture to the fluoride-containing wastewater is 0.5g to 20g: 1L, and the mass-to-volume ratio of the mixture to the aluminum source is 1: 0.05 to 0.

1.

8. The method for treating fluoride-containing wastewater according to any one of claims 1 to 5, characterized in that, It also includes the following steps: The precipitate obtained after filtration in step S2 is treated with acid and then placed in an alkaline solution for heating and reaction to recover the mixture.

9. The method for treating fluoride-containing wastewater according to any one of claims 1 to 5, characterized in that, The concentration of fluoride ions in the fluoride-containing wastewater is less than or equal to 50 mg / L.