A reusable filter aid for dewatering fluorine-containing sludge and a method for preparing the same

Abstract

In order to solve the technical problems of difficult dewatering of fluorine-containing sludge and difficult recycling of ordinary chemical filter aids, the application relates to a reusable filter aid for filtering and dewatering fluorine-containing sludge and a preparation method thereof. The main component of the filter aid is alkyl carboxylic acid modified magnetic ferroferric oxide nanoparticles. The preparation method comprises the following three steps: (1) preparing magnetic ferroferric oxide nanoparticles by using a coprecipitation method, (2) amino modification of the surface of the magnetic ferroferric oxide nanoparticles, and (3) alkyl carboxylic acid modification of the magnetic ferroferric oxide nanoparticles. Compared with the prior art, the application has the advantages of simple preparation method, excellent filter aid effect (significantly shortened filtering time and significantly reduced water content of sludge filter cake), stable reuse performance and the like, and has a good application prospect.

Description

Technical Field

[0001] This invention relates to the solid-liquid separation of fluoride-containing sludge and purified water generated during the precipitation process of fluoride-containing wastewater treatment. Specifically, it relates to a reusable filter aid and its preparation method in the filtration and dewatering process of fluoride-containing sludge. Background Technology

[0002] In the etching process of solar cells and chip manufacturing, hydrofluoric acid is used extensively, and the resulting fluoride-containing etching solution is a typical type of fluoride-containing wastewater. In recent years, with the rapid development of the photovoltaic power generation and semiconductor industries, the discharge of this fluoride-containing wastewater has also increased year by year. In addition, the fluorochemical, non-ferrous metal smelting, glass, and silicon-containing electronic component industries are also important sources of fluoride-containing wastewater. As a major source of fluoride pollution in the environment, fluoride dispersed in water bodies is extremely harmful and poses a significant safety hazard to maintaining ecological stability and the healthy development of human society. Under this severe situation, the removal of fluoride from fluoride-containing wastewater has become a key research focus in the environmental protection industry in recent years. Among the many methods for treating fluoride-containing wastewater, calcium ion precipitation, coagulation sedimentation, and adsorption are three typical, highly efficient, and low-consumption methods, and are currently widely used in industry. By cleverly combining these three methods, wastewater with different fluoride contents can be treated extensively. The treated water can meet the national Class I wastewater discharge standard, with the vast majority of the fluoride transferred to the fluoride-containing sludge.

[0003] Calcium fluoride in fluoride-containing sludge is an important resource for fluoride regeneration, and numerous studies have reported on the purification of calcium fluoride from fluoride-containing sludge. Separating fluoride-containing sludge from treated wastewater is the first challenge to overcome in order to utilize calcium fluoride in fluoride-containing sludge. Currently, the main industrial method for separating fluoride-containing sludge and purifying water is plate and frame filter press. Fluoride-containing sludge not only contains calcium salt precipitates, represented by calcium fluoride, calcium carbonate, and calcium sulfate, but also various highly hydrophilic flocculant colloids. Through plate and frame filter press separation, the filter cake obtained from fluoride-containing wastewater treatment in different factories generally has a moisture content of over 50%, and in some cases as high as 75%. The high moisture content of fluoride-containing sludge undoubtedly increases the costs of sludge disposal, transportation, and subsequent drying energy consumption. Considering both economic and energy consumption issues, it is essential to explore low-energy and high-efficiency dewatering methods for fluoride-containing sludge. Similar to enhanced dewatering methods for other industrial sludge, adding filter aids during the filtration process is considered the simplest and most effective method. However, common physical filter aids such as diatomaceous earth and volcanic ash tend to remain in fluoride-containing sludge, increasing the difficulty of subsequent calcium fluoride purification; chemical filter aids such as various surfactants are easily lost into the treated water, causing secondary pollution. Therefore, how to develop a highly efficient, easily recyclable, and reusable filter aid is one of the important challenges that needs to be addressed. Summary of the Invention

[0004] This invention provides a reusable filter aid for dewatering fluoride-containing sludge and its preparation method, thereby solving the technical problems of difficult dewatering of fluoride-containing sludge and the difficulty in recycling ordinary chemical filter aids, and achieving efficient dewatering of fluoride-containing sludge.

[0005] To address the aforementioned problems, this invention discloses a reusable filter aid for filtration and dewatering of fluoride-containing sludge, characterized in that its main component is magnetic iron oxide nanoparticles modified with alkyl carboxylic acid.

[0006] This invention also discloses a method for preparing the above-mentioned reusable filter aid for fluoride-containing sludge filtration and dewatering, which is carried out according to the following steps:

[0007] (1) Magnetic iron oxide nanoparticles were prepared by co-precipitation method.

[0008] Weigh 3.89 g of ferric chloride and 3.34 g of ferrous sulfate heptahydrate and dissolve them in 400 mL of deionized water. Start stirring and heat to 50 °C at 300 rpm. Add 30 mL of 15% sodium hydroxide solution dropwise under nitrogen protection. After the addition is complete, continue crystallization for 1 hour. Separate the solid product by magnet and dry it in an oven at 120 °C for 12 hours to obtain magnetic iron oxide nanoparticles.

[0009] (2) Surface amino modification of magnetic iron oxide nanoparticles

[0010] Weigh 2g of the magnetic iron oxide nanoparticles obtained in step (1), and disperse them uniformly in 200mL of ethanol by ultrasonication. Then, add 3-aminopropyltriethoxysilane under mechanical stirring and react at 30℃ for 12 hours. Separate the solid product with a magnet, wash it with ethanol, and dry it in an oven at 120℃ for 12 hours to obtain amino-functionalized magnetic iron oxide nanoparticles (hereinafter referred to as amino-functionalized magnetic particles).

[0011] (3) Alkyl carboxylic acid modification of magnetic iron oxide nanoparticles

[0012] Weigh 1g of the aminated magnetic particles obtained in step (2), and disperse them uniformly in 100mL of organic solvent by ultrasonication. Then, add alkyl dicarboxylic acid and catalyst under mechanical stirring, and react at 120℃ for 24 hours. Collect the solid product by magnet, wash it with anhydrous ethanol, and dry it in an oven at 120℃ for 12 hours to obtain alkyl carboxylic acid modified magnetic iron oxide nanoparticles.

[0013] In step 2 of the above method, the amount of 3-aminopropyltriethoxysilane used is 0.5g to 1g.

[0014] In step 3 of the above method, the organic solvent is any one of dimethylformamide (DMF), dimethylacetamide, and dimethyl sulfoxide.

[0015] In step 3 of the above method, the alkyl dicarboxylic acid is any one of alkyl dicarboxylic acids with different carbon chain lengths, specifically any one of sebacic acid, dodecanoic acid, tetradecanoic acid, hexadecanoic acid, and octadecanoic acid.

[0016] In step 3 of the above method, the amount of the alkyl dicarboxylic acid used is 0.2g to 1g.

[0017] In step 3 of the above method, the catalyst is 4-dimethylaminopyridine, and the amount used is 0.02g to 0.1g.

[0018] The present invention has the following advantages:

[0019] (1) In this invention, magnetic iron oxide nanoparticles are used as magnetic carriers for alkyl carboxylic acid surfactants. The alkyl carboxylic acid surfactants are immobilized on the magnetic nanoparticles through chemical covalent bonds. The preparation method is simple.

[0020] (2) The alkyl carboxylic acid modified magnetic particles prepared by this invention have excellent filter aid effect in the filtration and dewatering of fluoride-containing sludge (the filtration time is significantly shortened and the moisture content of the sludge filter cake is significantly reduced). In addition, this magnetic filter aid is easy to separate from the fluoride-containing sludge by a magnet, and its repeated use performance is stable, showing good application prospects. Detailed Implementation

[0021] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0022] Example 1

[0023] Weigh 3.89 g of ferric chloride and 3.34 g of ferrous sulfate heptahydrate and dissolve them in 400 mL of deionized water. Start stirring and heat to 50 °C at 300 rpm. Under nitrogen protection, add 30 mL of 15% sodium hydroxide solution dropwise. After the addition is complete, continue crystallization for 1 hour. Separate the solid product by magnet and dry it in an oven at 120 °C for 2 hours to obtain magnetic iron oxide nanoparticles.

[0024] Weigh 2g of the above magnetic iron oxide nanoparticles and disperse them uniformly in 200mL of ethanol by ultrasonication. Then, add 1g of 3-aminopropyltriethoxysilane under mechanical stirring and react at 30℃ for 12 hours. Separate the solid product with a magnet and wash with anhydrous ethanol to remove unreacted 3-aminopropyltriethoxysilane. Dry in an oven at 120℃ for 2 hours to obtain amino-terminated functionalized magnetic iron oxide nanoparticles (hereinafter referred to as aminated magnetic particles).

[0025] Weigh 1g of the above-mentioned aminated magnetic particles and disperse them uniformly in 100mL of organic solvent DMF by ultrasonication. Then, add 0.5g of sebacic acid and 0.05g of catalyst 4-dimethylaminopyridine under mechanical stirring. React at 120℃ for 24 hours. Wash the solid product collected by the magnet with anhydrous ethanol and dry it in an oven at 120℃ for 2 hours to obtain alkyl carboxylic acid modified magnetic iron oxide nanoparticles.

[0026] Example 2

[0027] Weigh 3.89 g of ferric chloride and 3.34 g of ferrous sulfate heptahydrate and dissolve them in 400 mL of deionized water. Start stirring and heat to 50 °C at 300 rpm. Under nitrogen protection, add 30 mL of 15% sodium hydroxide solution dropwise. After the addition is complete, continue crystallization for 1 hour. Separate the solid product by magnet and dry it in an oven at 120 °C for 2 hours to obtain magnetic iron oxide nanoparticles.

[0028] Weigh 2g of the above magnetic iron oxide nanoparticles and disperse them uniformly in 200mL of ethanol by ultrasonication. Then, add 1g of 3-aminopropyltriethoxysilane under mechanical stirring and react at 30℃ for 12 hours. Separate the solid product with a magnet and wash with anhydrous ethanol to remove unreacted 3-aminopropyltriethoxysilane. Dry in an oven at 120℃ for 2 hours to obtain amino-terminated functionalized magnetic iron oxide nanoparticles (hereinafter referred to as aminated magnetic particles).

[0029] Weigh 1g of the above-mentioned aminated magnetic particles and disperse them uniformly in 100mL of organic solvent DMF by ultrasonication. Then, add 0.5g of dodecyl dicarboxylic acid and 0.05g of catalyst 4-dimethylaminopyridine under mechanical stirring. React at 120℃ for 24 hours. Wash the solid product collected by the magnet with anhydrous ethanol and dry it in an oven at 120℃ for 2 hours to obtain alkyl carboxylic acid modified magnetic iron oxide nanoparticles.

[0030] Example 3

[0031] Weigh 3.89 g of ferric chloride and 3.34 g of ferrous sulfate heptahydrate and dissolve them in 400 mL of deionized water. Start stirring and heat to 50 °C at 300 rpm. Under nitrogen protection, add 30 mL of 15% sodium hydroxide solution dropwise. After the addition is complete, continue crystallization for 1 hour. Separate the solid product by magnet and dry it in an oven at 120 °C for 2 hours to obtain magnetic iron oxide nanoparticles.

[0032] Weigh 2g of the above magnetic iron oxide nanoparticles and disperse them uniformly in 200mL of ethanol by ultrasonication. Then, add 1g of 3-aminopropyltriethoxysilane under mechanical stirring and react at 30℃ for 12 hours. Separate the solid product with a magnet and wash with anhydrous ethanol to remove unreacted 3-aminopropyltriethoxysilane. Dry in an oven at 120℃ for 2 hours to obtain amino-terminated functionalized magnetic iron oxide nanoparticles (hereinafter referred to as aminated magnetic particles).

[0033] Weigh 1g of the above-mentioned aminated magnetic particles and disperse them uniformly in 100mL of organic solvent DMF by ultrasonication. Then, add 0.5g of tetradecyl dicarboxylic acid and 0.05g of catalyst 4-dimethylaminopyridine under mechanical stirring. React at 120℃ for 24 hours. Wash the solid product collected by the magnet with anhydrous ethanol and dry it in an oven at 120℃ for 2 hours to obtain alkyl carboxylic acid modified magnetic iron oxide nanoparticles.

[0034] Example 4

[0035] Weigh 3.89 g of ferric chloride and 3.34 g of ferrous sulfate heptahydrate and dissolve them in 400 mL of deionized water. Start stirring and heat to 50 °C at 300 rpm. Under nitrogen protection, add 30 mL of 15% sodium hydroxide solution dropwise. After the addition is complete, continue crystallization for 1 hour. Separate the solid product by magnet and dry it in an oven at 120 °C for 2 hours to obtain magnetic iron oxide nanoparticles.

[0036] Weigh 2g of the above magnetic iron oxide nanoparticles and disperse them uniformly in 200mL of ethanol by ultrasonication. Then, add 1g of 3-aminopropyltriethoxysilane under mechanical stirring and react at 30℃ for 12 hours. Separate the solid product with a magnet and wash with anhydrous ethanol to remove unreacted 3-aminopropyltriethoxysilane. Dry in an oven at 120℃ for 2 hours to obtain amino-terminated functionalized magnetic iron oxide nanoparticles (hereinafter referred to as aminated magnetic particles).

[0037] Weigh 1g of the above-mentioned aminated magnetic particles and disperse them uniformly in 100mL of organic solvent DMF by ultrasonication. Then, add 0.5g of hexadecyl dicarboxylic acid and 0.05g of catalyst 4-dimethylaminopyridine under mechanical stirring. React at 120℃ for 24 hours. Wash the solid product collected by the magnet with anhydrous ethanol and dry it in an oven at 120℃ for 2 hours to obtain alkyl carboxylic acid modified magnetic iron oxide nanoparticles.

[0038] Example 5

[0039] Weigh 3.89 g of ferric chloride and 3.34 g of ferrous sulfate heptahydrate and dissolve them in 400 mL of deionized water. Start stirring and heat to 50 °C at 300 rpm. Under nitrogen protection, add 30 mL of 15% sodium hydroxide solution dropwise. After the addition is complete, continue crystallization for 1 hour. Separate the solid product by magnet and dry it in an oven at 120 °C for 2 hours to obtain magnetic iron oxide nanoparticles.

[0040] Weigh 2g of the above magnetic iron oxide nanoparticles and disperse them uniformly in 200mL of ethanol by ultrasonication. Then, add 1g of 3-aminopropyltriethoxysilane under mechanical stirring and react at 30℃ for 12 hours. Separate the solid product with a magnet and wash with anhydrous ethanol to remove unreacted 3-aminopropyltriethoxysilane. Dry in an oven at 120℃ for 2 hours to obtain amino-terminated functionalized magnetic iron oxide nanoparticles (hereinafter referred to as aminated magnetic particles).

[0041] Weigh 1g of the above-mentioned aminated magnetic particles and disperse them uniformly in 100mL of organic solvent DMF by ultrasonication. Then, add 0.5g of octadecyl dicarboxylic acid and 0.05g of catalyst 4-dimethylaminopyridine under mechanical stirring. React at 120℃ for 24 hours. Wash the solid product collected by the magnet with anhydrous ethanol and dry it in an oven at 120℃ for 2 hours to obtain alkyl carboxylic acid modified magnetic iron oxide nanoparticles.

[0042] Application Example 1

[0043] This application comparative example used three types of fluorinated sludge as raw materials and employed alkyl carboxylic acid-modified magnetic iron oxide nanoparticles (Examples 1-5) as filter aids to conduct filtration and dewatering tests on fluorinated sludge. The specific steps were as follows: 0.1–0.5 g of filter aid was weighed and added to 100 g of fluorinated sludge. The mixture was stirred for 5 minutes at room temperature and 300 rpm. Then, it was filtered through a 9 cm diameter Buchner funnel under a vacuum of 0.09 MPa until no more liquid dripped within 1 minute. The filtration time and the mass of the wet filter cake were recorded. The filter cake was then dried in a 120°C oven to constant weight, and the dry filter cake weight was recorded. The moisture content of the wet filter cake was calculated. As a blank application example, the above operations were performed without any filter aid. Table 1 shows that, compared to the blank test, all filter aids in all examples shortened the filtration time and significantly reduced the moisture content of the wet filter cake. Furthermore, among all the filter aids in the examples, the filter aid in Example 4 exhibited the best filtration performance.

[0044] Table 1. Effect of filter aid type on the filtration and dewatering performance of fluoride-containing mud.

[0045]

[0046]

[0047] Application Example 2

[0048] For application test 7 in Application Example 1, a reuse test of the filter aid was conducted, with the relevant filtration steps as described in Application Example 1. The dried fluorinated sludge and filter aid were separated using a magnet, and the recovered filter aid mass was recorded. A slight loss in filter aid mass was observed, mainly due to adhesion to the filter wall and filter paper during the filtration process. The recovered filter aid was used in the same application test, and recycled three times according to the above method. The corresponding results are shown in Table 2. The filter aid prepared in this example maintained excellent filtration and dewatering performance even after three reuses.

[0049] Table 2 shows the filtration results of the filter aid in Experiment 7 of Application Example 1, after being reused three times.

[0050] Number of times to reuse Filter aid recovery amount / g Filter aid dosage / g Filtering time / s Moisture content of wet filter cake / % 1 0.43 0.43 1126 44.52 2 0.38 0.38 1245 45.64 3 0.32 0.32 1317 46.73

[0051] The present invention and its embodiments have been described above. This description is not restrictive, and the application examples are only one embodiment of the present invention. The actual application is not limited to this. In conclusion, if those skilled in the art are inspired by this description and design similar filter aids and embodiments without departing from the spirit of the present invention, they should all fall within the protection scope of the present invention.

Claims

1. A reusable filter aid for filtration and dewatering of fluoride-containing sludge, characterized in that: The main component is magnetic iron oxide nanoparticles modified with alkyl carboxylic acids. The alkyl carboxylic acid is any one of alkyl carboxylic acids with different carbon chain lengths, specifically any one of sebacic acid, dodecanoic acid, tetradecanoic acid, hexadecanoic acid, and octadecanoic acid.

2. A method for preparing a reusable filter aid for filtration and dewatering of fluoride-containing sludge as described in claim 1, characterized in that: Including steps (1) to (3): (1) Magnetic iron oxide nanoparticles were prepared by co-precipitation method. Weigh 3.89 g of ferric chloride and 3.34 g of ferrous sulfate heptahydrate and dissolve them in 400 mL of deionized water. Start stirring and heat to 50 °C at 300 rpm. Add 30 mL of 15% sodium hydroxide solution dropwise under nitrogen protection. After the addition is complete, continue crystallization for 1 hour. Separate the solid product by magnet and dry it in an oven at 120 °C for 12 hours to obtain magnetic iron oxide nanoparticles. (2) Surface amino modification of magnetic iron oxide nanoparticles Weigh 2g of the magnetic iron oxide nanoparticles obtained in step (1), disperse them uniformly in 200mL of ethanol by ultrasonication, then add 3-aminopropyltriethoxysilane under mechanical stirring, react at 30℃ for 12 hours, separate the solid product with a magnet, wash with ethanol and dry in an oven at 120℃ for 12 hours to obtain amino-functionalized magnetic iron oxide nanoparticles. (3) Alkyl carboxylic acid modification of magnetic iron oxide nanoparticles Weigh 1g of the amino-functionalized magnetic iron oxide nanoparticles obtained in step (2), and uniformly disperse them in 100mL of organic solvent by ultrasonication. Then, add alkyl dicarboxylic acid and catalyst under mechanical stirring, and react at 120℃ for 24 hours. Collect the solid product by magnet, wash it with anhydrous ethanol, and dry it in an oven at 120℃ for 12 hours to obtain alkyl carboxylic acid modified magnetic iron oxide nanoparticles.

3. The method according to claim 2, characterized in that: The amount of 3-aminopropyltriethoxysilane used is 0.5g to 1g.

4. The method according to claim 2, characterized in that: The organic solvent is any one of dimethylformamide, dimethylacetamide, and dimethyl sulfoxide.

5. The method according to claim 2, characterized in that: The amount of the alkyl dicarboxylic acid used is 0.2g to 1g.

6. The method according to claim 2, characterized in that: The catalyst is 4-dimethylaminopyridine, and its dosage is 0.02g to 0.1g.

Images