A fluorine removal agent for coking wastewater and its preparation method

Abstract

The present invention provides a defluorinating agent for coking wastewater and a preparation method thereof, relating to the technical field of water treatment agents. The preparation method comprises the following steps: S1: Aminating and modifying lignin to obtain modified lignin. S2: Dispersing an aqueous solution containing metal oxide nanomaterials and graphene oxide in the modified lignin solution, adding a crosslinking agent and a pore-forming agent, and uniformly mixing to obtain a lignin / graphene oxide dispersion solution. S3: Dropwise adding an aqueous sodium hydroxide solution to the lignin / graphene oxide dispersion solution, and sequentially performing solidification, washing, and drying to obtain the defluorinating agent. The defluorinating agent prepared by the present invention has a wider application range, stronger defluorination efficiency, and a defluorination rate of more than 95%. In addition, the desorption rate of the defluorinating agent prepared by the present invention is more than 90%, and the regeneration ability is strong.

Description

Technical Field

[0001] The present invention relates to the technical field of water treatment agents, and more specifically, to a defluorinating agent for coking wastewater and a preparation method thereof. Background Art

[0002] Fluoride-containing wastewater is a common wastewater in the electronic industry, characterized by large water volume and strong biological toxicity. Currently, the commonly used defluorination methods include chemical precipitation method and coagulation precipitation method. The chemical precipitation method generally uses lime water as a precipitant, and the fluoride ions are separated and removed from the wastewater by forming CaF2 precipitate through the reaction of Ca 2+ and F-. The chemical precipitation method has the advantages of large water treatment capacity and low cost. However, after treatment by this method, the fluoride concentration is reduced to 10 - 20 mg / L, which is still far exceeding the national environmental protection standard of effluent F- < 1 mg / L. Therefore, the chemical precipitation method is only applicable to the primary treatment of fluoride-containing wastewater. In addition, the dosage of the medicament used in this process is large, the moisture content of the sludge is high and it is difficult to recycle. The coagulation precipitation method is to add a coagulant to the fluoride-containing wastewater. After appropriately adjusting the pH, flocculent colloids are formed. The colloids combine with the fluoride ions in the water through chemical or physical actions, and finally form precipitates to be discharged. The common coagulants mainly include aluminum salts and iron salts, such as aluminum oxide, polyaluminum chloride, polyferric sulfate, ferric chloride, etc. As a deep treatment method for fluoride-containing wastewater, the coagulation precipitation method can reduce the effluent F - concentration to below 1.0 mg / L. However, this type of coagulant has strict requirements for the reaction pH, the formed flocs are loose and have poor sedimentation performance, and the reverse dissolution of Al 3+ will cause secondary pollution and endanger human health.

[0003] The fluorine in coking wastewater mainly comes from the following aspects: First, the fluoride content in the local groundwater exceeds the standard, resulting in high-fluoride water for the enterprise's production water. Since adding a filter membrane to filter the fluoride in the groundwater in the front section of the production process will generate a large amount of production costs, most enterprises will centrally treat the fluoride ions in the fluoride-containing wastewater pool at the end of the process. And due to the large amount of industrial water consumption, the groundwater alone cannot meet the production water demand, so enterprises adopt the method of industrial water recycling to supplement the production water. The fluoride ions will accumulate in large quantities during the industrial recycling of fluoride-containing groundwater, resulting in the excessive fluoride content in the discharged water. Second, it comes from the fluorine-containing substances released during the coking process of coal, which exist in the form of fluoride ions in the surplus ammonia water, with a concentration greater than 30 mg / L. This part of the ammonia water will be discharged into the wastewater pool through the wastewater pipeline without treatment, resulting in the aggregation of a large amount of fluoride ions. Third, it comes from the desulfurization and gasification process in the synthesis gas workshop, and the fluoride content in the wastewater generated in this process is also relatively high. Therefore, the treatment of fluoride-containing coking wastewater is a hot issue in the research of the water treatment field at home and abroad. Summary of the Invention

[0004] The inventors' research found that: Lignin and its derivatives have attracted the attention of researchers due to their advantages such as being renewable, biodegradable, and easy to extract. However, lignin has low reactivity, few reactive sites, weak adsorption capacity, and does not have selective adsorption for specific ions, and its recycling performance is relatively low. Graphene oxide (GO), as an important graphene derivative, is essentially a single-layer graphite oxide with a large number of oxygen-containing functional groups introduced, such as hydroxyl groups, carboxyl groups, and epoxy groups, which can serve as adsorption sites. These oxygen-containing functional groups improve the water solubility of graphene oxide and increase the active adsorption sites, thus effectively improving its efficiency in adsorbing pollutants in wastewater. However, graphene oxide has strong hydrophilicity and is difficult to separate and recycle in water, and due to its single type of functional group and low functional group density, it limits its further application in water treatment in terms of adsorption capacity. Metal oxide nanomaterials have small sizes, large specific surface areas, strong activity, excellent adsorption performance and stability, and thus have become a research hotspot in the fields of defluorination of drinking water and fluoride-containing wastewater. However, because metal oxide nanomaterials are in the form of fine powder particles at room temperature, they are prone to agglomeration during the reaction process, difficult to recycle, resulting in serious waste and even environmental pollution. Through multiple studies, the inventors found that in the present invention, lignin is used as a substrate, lignin is modified to increase the active sites, then a pore-forming agent is added to make lignin in a porous form, and finally, under the action of a cross-linking agent, graphene oxide and metal oxide nanomaterials are loaded into the pores of the modified lignin. The obtained defluorinating agent has multiple sites for binding with fluoride ions and can effectively bind with fluoride ions in coking wastewater to remove fluoride ions from water.

[0005] On the one hand, the present invention provides a preparation method of a defluorinating agent for coking wastewater, and the preparation method includes the following steps:

[0006] S1: Aminate lignin to obtain modified lignin.

[0007] S2: Disperse an aqueous solution containing metal oxide nanomaterials and graphene oxide in the modified lignin solution, add a cross-linking agent and a pore-forming agent, and mix evenly to obtain a lignin / graphene oxide dispersion solution.

[0008] S3: Dropwise add an aqueous sodium hydroxide solution to the lignin / graphene oxide dispersion solution, and carry out curing, washing, and drying in sequence to obtain a defluorinating agent.

[0009] Wherein, the mass ratio of the lignin, graphene oxide, metal oxide nanomaterials, cross-linking agent, and pore-forming agent is: 15 - 25: 5 - 10: 5 - 10: 3 - 6: 2 - 5.

[0010] On the other hand, the present invention provides a defluorinating agent for coking wastewater. The defluorinating agent for coking wastewater uses lignin as a carrier, and a graphene oxide-metal blend is loaded on the carrier to form a chelate with multiple active sites.

[0011] Compared with the prior art, the present invention achieves at least one of the following beneficial effects:

[0012] (1) In the preparation method of the defluorinating agent for coking wastewater of the present invention, lignin is used as a carrier, and lignin is modified to increase the active sites. Then, a pore-forming agent is added to make lignin in a porous form. Finally, under the action of a cross-linking agent, graphene oxide and metal oxide nanomaterials are loaded into the pores of the modified lignin. The obtained defluorinating agent has multiple sites for binding with fluoride ions, and can effectively bind with fluoride ions in coking wastewater to remove fluoride ions from water.

[0013] (2) In the preparation method of the defluorinating agent for coking wastewater of the present invention, triethylenetetramine and ferric chloride are used to modify lignin, which can improve the selective adsorption of lignin to fluoride ions, thereby further increasing the removal rate of fluoride ions in coking wastewater.

[0014] (3) The defluorinating agent for coking wastewater prepared by the present invention has a wider application range and stronger defluorination efficiency, and the defluorination rate is above 95%. In addition, the desorption rate of the defluorinating agent prepared by the present invention is above 90%, and it has strong regeneration ability.

[0015] (4) After treating coking wastewater with the defluorinating agent for coking wastewater prepared by the present invention, the fluoride concentration reaches the effluent F- < 1mg / L specified by the national environmental protection standard. Description of the Drawings

[0016] The drawings described herein are used to provide a further understanding of the present invention, and constitute a part of the present invention. The illustrative embodiments and descriptions of the present invention are used to explain the present invention, and do not constitute an improper limitation of the present invention. In the drawings:

[0017] Figure 1 An exemplary embodiment of the process flow diagram of the preparation method of the defluorinating agent for coking wastewater of the present invention is shown. Detailed Embodiments

[0018] In order to more clearly illustrate the overall concept of the present invention, the following will be described in detail by way of examples in conjunction with the drawings of the specification.

[0019] In the following description, many specific details are set forth in order to fully understand the present invention. However, the present invention may also be implemented in other ways different from those described herein. Therefore, the protection scope of the present invention is not limited by the specific embodiments disclosed below.

[0020] In an exemplary embodiment of the present invention, the preparation method of the defluorinating agent for coking wastewater includes the following steps:

[0021] S1: Aminate and modify lignin to obtain modified lignin. Specifically, using triethylenetetramine and iron chloride to modify lignin can improve the selective adsorption of lignin to fluoride ions.

[0022] S2: Disperse an aqueous solution containing metal oxide nanomaterials and graphene oxide in the modified lignin solution, add a crosslinking agent and a pore-forming agent, and mix evenly to obtain a lignin / graphene oxide dispersion solution. Specifically, the metal oxide nanomaterials can be one or more of zirconium oxide, aluminum oxide, iron oxide, and magnesium oxide. For example, the metal oxide nanomaterials can be one or more of MgO, Fe3O4, Fe2O3, FeCO3, activated alumina Al2O3·nH2O, and ZrO(OH)2. The size of the metal oxide nanomaterials is less than 100 nm, the size of graphene oxide is less than 100 nm, and the crosslinking agent is formaldehyde or glutaraldehyde. The pore-forming agent is one or more of amino acid derivatives, polyvinyl alcohol, polymethyl methacrylate, polystyrene, and polyvinyl butyral.

[0023] S3: Dropwise add an aqueous sodium hydroxide solution to the lignin / graphene oxide dispersion solution, and successively carry out curing, washing, and drying to obtain a defluorinating agent. Specifically, the pH is controlled to be 7-10 by dropping the aqueous sodium hydroxide solution. Preferably, the pH is controlled to be 8-9 by dropping the aqueous sodium hydroxide solution. The purpose of controlling the pH is to ensure the purity of the product and the number of active sites. Drying can be freeze-drying or heat drying at a temperature not higher than 70 °C. If the drying temperature is too high, it will lead to uneven loading and thus a low defluorination rate. The flow chart of the preparation method is referred to Figure 1 as shown.

[0024] Among them, the mass ratio of the lignin, graphene oxide, metal oxide nanomaterials, crosslinking agent, and pore-forming agent is 15-25:5-10:5-10:3-6:2-5. Preferably, the mass ratio of the lignin, graphene oxide, metal oxide nanomaterials, crosslinking agent, and pore-forming agent is 18-22:6-8:6-8:4-5:3-4.

[0025] Specifically, the preparation method of the defluorinating agent for coking wastewater includes the following steps:

[0026] S1: Add lignin to a sodium hydroxide solution and stir to dissolve it, then add triethylenetetramine and formaldehyde, stir evenly, dropwise add a hydrochloric acid solution to obtain a brown precipitate, filter, and wash to obtain N-modified lignin. Add the N-modified lignin to an iron chloride solution and successively carry out a complexation reaction, filter, and wash to obtain Fe / N-modified lignin.

[0027] S2: Disperse an aqueous solution containing metal oxide nanomaterials and graphene oxide in an acidic solution of Fe / N-modified lignin with a pH of 3 - 5 for the acidic solution. Add a crosslinking agent and a pore-forming agent, and make it uniformly mixed by stirring or ultrasonic treatment to obtain a lignin / graphene oxide dispersion solution.

[0028] S3: Dropwise add an aqueous sodium hydroxide solution to the lignin / graphene oxide dispersion solution for curing. After washing with deionized water and absolute ethanol, perform freeze-drying or drying at a temperature not higher than 70 °C to obtain a defluorinating agent.

[0029] The defluorinating agent for coking wastewater of the present invention uses lignin as a carrier, and a graphene oxide-metal blend is loaded on the carrier to form a chelate with multiple active sites.

[0030] Example 1

[0031] The preparation method of the defluorinating agent for coking wastewater includes the following steps:

[0032] S1: Add 15 g of lignin to 30 ml of 0.2 mol / L sodium hydroxide solution and stir to dissolve. Then add 4 mL of triethylenetetramine and 2 mL of formaldehyde, stir evenly, and dropwise add 40% hydrochloric acid solution to obtain a brown precipitate, filter, and wash to obtain N-modified lignin. Add the N-modified lignin to 5 mol / L ferric chloride solution and carry out a complexation reaction at 70 °C. Then filter the solvent and wash with water and ethanol to obtain Fe / N-modified lignin.

[0033] S2: Disperse an aqueous solution of 5 g of Fe3O4 nanomaterials and 5 g of graphene oxide in an acidic solution of Fe / N-modified lignin with a pH of 3. Add 3 g of crosslinking agent glutaraldehyde and 2 g of pore-forming agent polyvinyl alcohol, and make it uniformly mixed by stirring or ultrasonic treatment to obtain a lignin / graphene oxide dispersion solution. Among them, the size of the Fe3O4 nanomaterials is 50 nm, and the size of the graphene oxide is 60 nm.

[0034] S3: Dropwise add an aqueous sodium hydroxide solution to the lignin / graphene oxide dispersion solution for curing. After washing with deionized water and absolute ethanol, perform freeze-drying to obtain a defluorinating agent.

[0035] Example 2

[0036] The preparation method of the defluorinating agent for coking wastewater includes the following steps:

[0037] S1: Add 20 g of lignin to 50 ml of 0.2 mol / L sodium hydroxide solution and stir to dissolve. Then add 4 mL of triethylenetetramine and 2 mL of formaldehyde, stir evenly, and dropwise add 40% hydrochloric acid solution to obtain a brown precipitate. Filter and wash to obtain N-modified lignin. Add the N-modified lignin to 5 mol / L ferric chloride solution and carry out a complexation reaction at 70 °C. Then filter the solvent and wash with water and ethanol to obtain Fe / N-modified lignin.

[0038] S2: Disperse an aqueous solution of 8 g of Al2O3·nH2O nanomaterials and 7 g of graphene oxide in the acidic solution of Fe / N-modified lignin. The pH of the acidic solution is 4. Add 4 g of crosslinking agent formaldehyde and 3 g of pore-forming agent polystyrene, and mix evenly by stirring or ultrasonic treatment to obtain a lignin / graphene oxide dispersion solution. Among them, the size of the Al2O3·nH2O nanomaterials is 20 nm, and the size of the graphene oxide is 10 nm.

[0039] S3: Dropwise add an aqueous sodium hydroxide solution to the lignin / graphene oxide dispersion solution for curing. After washing with deionized water and absolute ethanol, dry at 50 °C to obtain a defluorinating agent.

[0040] Example 3

[0041] The preparation method of the defluorinating agent for coking wastewater includes the following steps:

[0042] S1: Add 25 g of lignin to 50 ml of 0.2 mol / L sodium hydroxide solution and stir to dissolve. Then add 4 mL of triethylenetetramine and 3 mL of formaldehyde, stir evenly, and dropwise add 40% hydrochloric acid solution to obtain a brown precipitate. Filter and wash to obtain N-modified lignin. Add the N-modified lignin to 5 mol / L ferric chloride solution and carry out a complexation reaction at 70 °C. Then filter the solvent and wash with water and ethanol to obtain Fe / N-modified lignin.

[0043] S2: Disperse an aqueous solution of 10 g of MgO nanomaterials and 10 g of graphene oxide in the acidic solution of Fe / N-modified lignin. The pH of the acidic solution is 5. Add 6 g of crosslinking agent glutaraldehyde and 5 g of pore-forming agent polymethyl methacrylate, and mix evenly by stirring or ultrasonic treatment to obtain a lignin / graphene oxide dispersion solution. Among them, the size of the MgO nanomaterials is 40 nm, and the size of the graphene oxide is 10 nm.

[0044] S3: Dropwise add an aqueous sodium hydroxide solution to the lignin / graphene oxide dispersion solution for curing. After washing with deionized water and absolute ethanol, freeze-dry to obtain a defluorinating agent.

[0045] Example 4

[0046] Based on Example 1, the difference is that the lignin is not Fe-modified.

[0047] Comparative Example 1

[0048] Based on Example 1, the difference is that the lignin in Comparative Example 1 is not modified.

[0049] Comparative Example 2

[0050] Based on Example 1, the difference is that graphene oxide is not loaded in Comparative Example 2.

[0051] Comparative Example 3

[0052] Based on Example 1, the difference is that metal oxide nanomaterials are not loaded in Comparative Example 3.

[0053] For the defluorinating agents prepared in Examples 1-3 and Comparative Examples 1-3 respectively, 5 g was directly added to 1 L of coking wastewater, stirred for 20-30 min, and the supernatant was taken to detect the fluoride ion concentration. Desorption regeneration was carried out with 2 mol / L sodium hydroxide solution, and the treatment effects, defluorination rate and desorption rate, are shown in Table 1 for reference.

[0054] Table 1 Treatment effect table

[0055]

[0056] As can be seen from Table 1 for Examples 1-4, the defluorinating agent prepared by the present invention has a wider application range, stronger defluorination efficiency, and the defluorination rate is above 95%. In addition, the desorption rate of the defluorinating agent prepared by the present invention is above 90%, indicating that the defluorinating agent prepared by the present invention has strong regeneration ability, and the fluoride ions on the active sites are replaced by hydroxyl groups, so as to achieve the purpose of restoring its adsorption activity.

[0057] Compared with Example 1, in Comparative Example 1, when the lignin is not modified, the defluorination rate drops by 17.5% and the desorption rate drops by 20%. It can be seen that modifying the lignin can improve the defluorination rate and at the same time ensure the regeneration ability of the defluorinating agent.

[0058] Compared with Example 1, in Comparative Example 2, when graphene oxide is not loaded, the desorption rate remains basically unchanged, and the defluorination rate drops by 10.5%. Although graphene oxide has poor defluorination effect when used alone and is prone to agglomeration, loading it onto the modified lignin can enhance the defluorination effect.

[0059] Compared with Example 1, in Comparative Example 3, when metal oxide nanomaterials are not loaded, the desorption rate remains basically unchanged, and the defluorination rate drops by 13%. It can be seen that loading metal oxides can further enhance the defluorination effect.

[0060] The above are only embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, various modifications and variations can be made to the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the scope of the claims of the present invention.

Claims

1. A preparation method of a defluorinating agent for coking wastewater, characterized in that, The preparation method includes the following steps: S1: Aminate and modify lignin to obtain modified lignin. Specifically, dissolve lignin in a sodium hydroxide solution with stirring, then add triethylenetetramine and formaldehyde, stir evenly, dropwise add a hydrochloric acid solution thereto to obtain a brown precipitate, filter, and wash to obtain N-modified lignin. Add the N-modified lignin to a ferric chloride solution to conduct a complexation reaction, filtration, and washing in sequence to obtain Fe / N-modified lignin. S2: Disperse an aqueous solution containing metal oxide nanomaterials and graphene oxide in the modified lignin solution, add a crosslinking agent and a pore-forming agent, and mix evenly to prepare a lignin / graphene oxide dispersion solution. S3: Dropwise add an aqueous sodium hydroxide solution to the lignin / graphene oxide dispersion solution to conduct solidification, washing, and drying in sequence to obtain a defluorinating agent. Among them, the mass ratio of the lignin, graphene oxide, metal oxide nanomaterials, crosslinking agent, and pore-forming agent is 15-25:5-10:5-10:3-6:2-5. The metal oxide nanomaterials are one or more of zirconium oxide, aluminum oxide, iron oxide, and magnesium oxide.

2. The preparation method according to claim 1, characterized in that, The mass ratio of the lignin, graphene oxide, metal oxide nanomaterials, crosslinking agent, and pore-forming agent is 18-22:6-8:6-8:4-5:3-4.

3. The preparation method according to claim 1, characterized in that, The crosslinking agent is formaldehyde or glutaraldehyde.

4. The preparation method according to claim 1, characterized in that, The pore-forming agent is one or more of amino acid derivatives, polyvinyl alcohol, polymethyl methacrylate, polystyrene, and polyvinyl butyral.

5. The preparation method according to claim 1, characterized in that, In step S3, when dropping the aqueous sodium hydroxide solution, control the pH to be 7-10.

6. The preparation method according to claim 5, characterized in that, In step S3, when dropping the aqueous sodium hydroxide solution, control the pH to be 8-9.

7. In the preparation method according to claim 1, the drying in step S3 is freeze-drying or drying at 50 - 70 °C.

8. A defluorinating agent for coking wastewater prepared by the preparation method according to any one of claims 1 - 7, characterized in that, The defluorinating agent for coking wastewater uses lignin as a carrier, and a graphene oxide-metal blend is loaded on the carrier to form a chelate with multiple active sites.

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