Fluorine removal agent based on layered double hydroxide, preparation method and application thereof

Abstract

The application of layered double hydroxide fluoride removal agent and its preparation method and application belong to the technical field of fluorine-containing wastewater treatment, and aim at the shortcomings and deficiencies of the existing single aluminum fluoride removal agent, and provide a kind of layered double hydroxide fluoride removal agent and its preparation method and application, which is based on the special aluminum polymer as the base, combined with divalent metal cations to form layered double hydroxide, which can greatly improve the positive charge density, the number of surface groups and the activity of the fluoride removal agent, and is more conducive to approaching and adsorbing pollutants.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of fluorine-containing wastewater treatment, and particularly relates to a layered double hydroxide defluorination agent and a preparation method and application thereof. BACKGROUND

[0002] As an important source of industrial wastewater, fluorine-containing industrial wastewater is related to the production processes of semiconductor, fluorine chemical industry, electrolytic aluminum, pharmaceutical industry, etc., and the fluorine content in the wastewater varies from several tens to tens of thousands of mg / L. In recent years, the semiconductor electronic industry has ushered in an unprecedented wave of development, and the semiconductor production process is complex, in which etching and other processes use fluorine-containing materials such as hydrofluoric acid and ammonium fluoride, resulting in a large amount of fluorine-containing industrial wastewater discharge.

[0003] At present, the main treatment methods for fluorine-containing industrial wastewater include chemical precipitation, coagulation sedimentation, membrane filtration, electrodialysis, adsorption, etc.; among them, the adsorption method is widely favored due to its wide source of adsorbent, strong plasticity, simple operation, stable effluent, recyclable adsorbent and other advantages, and the defluorination agent as a new adsorption treatment method has the advantages of less dosage and low fluorine concentration in effluent. At present, the most commonly used defluorination agent on the market is polyaluminum chloride and activated alumina, which removes fluorine ions in water by using surface complexation, physical adsorption and other effects. However, in view of the characteristics of large amount of fluorine-containing industrial wastewater and complex water quality, the single aluminum defluorination agent has poor defluorination effect, low adsorption capacity, great influence of coexisting ions, and secondary pollution caused by aluminum dissolution, etc., which limits its application scope.

[0004] Therefore, developing an aluminum-based defluorination agent with high adsorption capacity, strong anti-interference and stable structure is an important research direction of the current defluorination technology. SUMMARY

[0005] In view of the shortcomings and deficiencies of the existing single aluminum defluorination agent, the application provides a layered double hydroxide defluorination agent and a preparation method and application thereof, which uses a specially prepared aluminum polymer as a substrate to greatly improve the positive charge density, surface group number and activity of the defluorination agent, and is more conducive to approaching and adsorbing pollutants.

[0006] In addition, the layered double hydroxide is formed by combining with divalent metal cations, and has the characteristics of structural stability and exchangeable interlayer anions, and is not easy to cause secondary pollution caused by aluminum dissolution in complex fluorine industrial wastewater, and has the advantages of enhancing the ion exchange capacity of the defluorination agent.

[0007] The above-mentioned object of the application is achieved by the following technical solutions:

[0008] adding a divalent metal cation salt into a solution containing a special aluminum high polymer; placing the mixed salt solution in a 25℃ water bath magnetic stirrer for vigorous stirring, while slowly adding a hydrolysis aid until the solution pH value remains stable, the solution pH = 9~12, preferably pH = 10; continuing to age for 12h after the reaction is completed, the obtained product is extracted and washed until the filtrate is close to neutral, and the obtained product is placed in an oven for drying at 60℃, to obtain the defluorination agent.

[0009] The divalent metal cation salt is at least one of calcium chloride, calcium nitrate tetrahydrate, magnesium chloride, calcium sulfate, and magnesium sulfate. More preferably, the divalent metal cation salt is calcium chloride.

[0010] The molar ratio of the divalent metal cation salt to the special aluminum high polymer is 1~3:1, and more preferably, the molar ratio of the divalent metal cation salt to the special aluminum high polymer is 2:1.

[0011] The hydrolysis aid is at least one of sodium hydroxide, sodium carbonate, potassium hydroxide, and potassium carbonate. More preferably, the hydrolysis aid is sodium hydroxide or sodium carbonate.

[0012] Preferably, the special aluminum high polymer is prepared by the following method:

[0013] (1) dissolving aluminum salt and urea in a molar ratio of 3~10:1 in water, and placing in a polytetrafluoroethylene cup for standby;

[0014] (2) activating the solution, stirring quickly, mixing, and obtaining the special aluminum high polymer by reaction, the stirring speed is 200~350rpm / min, and the stirring time is 30min; more preferably, the stirring speed is 250rpm / min.

[0015] Preferably, the aluminum salt is at least one of aluminum chloride, polyaluminum chloride, aluminum sulfate, and polyaluminum sulfate. More preferably, the aluminum salt is aluminum chloride.

[0016] Preferably, the activation method in the special aluminum high polymer synthesis method is at least one of microwave pyrolysis and ultrasonic. The preferred activation method is microwave pyrolysis.

[0017] The application also provides a defluorination agent prepared by the above method.

[0018] The application also provides the application of the above defluorination agent, which is used for defluorination of fluorine-containing wastewater. The defluorination agent is added to the wastewater, and the amount of the defluorination agent is determined according to the fluorine content.

[0019] Compared with the prior art, the application has the following beneficial effects:

[0020] (1) The present invention proposes a defluorinating agent based on layered bimetallic hydroxide and its preparation method and application. By synthesizing a special aluminum polymer, the aluminum polymer has a classic Keggin structure and is a nano-sized cluster compound. Thanks to its efficient charge neutralization performance and special nano-characteristics, it has high structural stability and solves the problem of excessive residual aluminum in the effluent.

[0021] (2) The present invention proposes a defluorinating agent based on layered bimetallic hydroxide and its synthesis method. By synthesizing layered bimetallic hydroxide, it has advantages such as large specific surface area, high porosity and non-toxicity. In addition, thanks to the exchangeability of interlayer anions and surface hydroxyl groups in the structure, fluoride ions can be removed through ion exchange and surface complexation.

[0022] (3) The present invention proposes a defluorinating agent based on layered bimetallic hydroxide and its synthesis method. The preparation method is simple, the operation is simple, the defluorination efficiency is high, the anti-interference ability is strong, and it is less affected by other pollutants (suspended solids, high salt, organic matter) in wastewater. It can cope with the complex changes in the water quality of industrial wastewater. Attached Figure Description

[0023] Figure 1 XRD patterns of the layered bimetallic hydroxides synthesized in Examples 1 and 3; Detailed Implementation

[0024] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all 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.

[0025] Example 1

[0026] A defluorinating agent based on layered bimetallic hydroxide comprises the following components: a specially formulated aluminum polymer, a divalent cationic metal salt, and a hydrolysis aid.

[0027] The above-mentioned layered bimetallic hydroxide defluorinating agent is synthesized as follows:

[0028] According to n (M) 2+ ): n (Al 3+ A certain amount of anhydrous calcium chloride was added to a specially prepared aluminum polymer solution in a ratio of 2:1. The solution was stirred at 25°C with a magnetic stirrer until completely dissolved and then allowed to stand for later use. Subsequently, stirring was continued and 3 mol / L NaOH solution was added dropwise to adjust the pH value to 10 and keep the pH value stable. The reaction was carried out for half an hour, and after the reaction was completed, it was aged for 12 hours to obtain flocculent material. After filtration and washing, solid-liquid separation and drying, the defluorinating agent was obtained.

[0029] The specially formulated aluminum polymer is prepared by the following method:

[0030] (1) Dissolve aluminum salt and urea in water and place them in a polytetrafluoroethylene cup for later use;

[0031] (2) Activate the polytetrafluoroethylene cup, stir rapidly, mix, and react to obtain a special aluminum polymer. The stirring speed is 250 rpm / min and the stirring time is 30 min.

[0032] Example 2

[0033] The layered bimetallic hydroxide defluorinating agent and its synthesis method in this embodiment are the same as those in Example 1, except that the divalent cation salt is replaced with calcium nitrate tetrahydrate.

[0034] Example 3

[0035] The layered bimetallic hydroxide defluorinating agent and its synthesis method in this embodiment are the same as those in Example 1, except that the divalent cation salt is replaced with anhydrous magnesium chloride.

[0036] Example 4

[0037] The layered bimetallic hydroxide defluorinating agent and its synthesis method in this embodiment are the same as those in Example 1, except that the divalent cation salt is replaced with magnesium nitrate hexahydrate.

[0038] Example 5

[0039] The defluorination effect of the layered bimetallic hydroxide defluorinating agent prepared in Example 1 was tested. The initial fluoride ion concentration was 30 mg / L. 0.2 g / L of defluorinating agent was added and the reaction was carried out under the condition of pH = 6. The fluoride ion removal rate is shown in Table 1.

[0040] Example 6

[0041] The defluorination effect experiment in this embodiment is the same as that in Example 5, except that the layered bimetallic hydroxide defluorinating agent is replaced with the defluorinating agent obtained in Example 2.

[0042] Example 7

[0043] The defluorination effect experiment in this embodiment is the same as that in Example 5, except that the layered bimetallic hydroxide defluorinating agent is replaced with the defluorinating agent obtained in Example 3.

[0044] Example 8

[0045] The defluorination effect experiment in this embodiment is the same as that in Example 5, except that the layered bimetallic hydroxide defluorinating agent is replaced with the defluorinating agent obtained in Example 4.

[0046] Comparative Example 1

[0047] In this comparative example, the layered bimetallic hydroxide of Example 5 is replaced with a specially formulated aluminum polymer, and its application is the same as that of Example 5.

[0048] Comparative Example 2

[0049] In this comparative example, the defluorinating agent used in Example 5 is a commercially available defluorinating agent, and its application is the same as in Example 5.

[0050] Table 1 shows the residual fluoride ion concentration and removal rate in each example and comparative example.

[0051]

[0052] As shown in Table 1, the layered bimetallic hydroxide of the present invention can remove fluoride ions from wastewater to a large extent. Moreover, under the same experimental conditions, the removal effect of the present invention on fluoride ions is significantly better than that of specially made aluminum polymers and commercially available defluorinating agents.

[0053] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a layered bimetallic hydroxide-based defluorinating agent, characterized in that, The method includes the following steps: (1) Add a divalent metal cation salt to a solution containing a special aluminum polymer, wherein the molar ratio of the divalent metal cation salt to the special aluminum polymer is 1~3:1; the special aluminum polymer has a classic Keggin structure and is a nano-sized cluster compound; the divalent metal cation salt is one or more of calcium chloride, calcium nitrate tetrahydrate, magnesium chloride, calcium sulfate, and magnesium sulfate; (2) Place the mixed salt solution in a 25°C water bath magnetic stirrer and stir vigorously, while slowly adding the hydrolysis aid dropwise until the pH value of the solution remains stable, wherein the solution pH=9~12; the hydrolysis aid is one or more of sodium hydroxide, sodium carbonate, potassium hydroxide, and potassium carbonate; (3) After the reaction is complete, continue aging, filter and wash the obtained product until the filtrate is close to neutral, place the product in an oven and dry at 60°C to obtain the defluorinating agent; The specially formulated aluminum polymer is prepared by the following method: (1.1) Dissolve aluminum salt and urea in water at a molar ratio of 3~10:1 and place in a polytetrafluoroethylene cup for later use; the aluminum salt is one or more of aluminum chloride, polyaluminum chloride, aluminum sulfate and polyaluminum sulfate; (1.2) The solution is activated by microwave pyrolysis or ultrasound, and stirred rapidly at 200~350 rpm / min for 30 min. The mixture and reaction are then carried out to obtain a special aluminum polymer. Using a specially formulated aluminum polymer as a base, the positive charge density, surface group quantity and activity of the defluorinating agent are increased, making it less prone to aluminum leaching in complex fluorine industrial wastewater.

2. The preparation method according to claim 1, characterized in that, In step (1), the molar ratio of divalent metal cation salt to specially formulated aluminum polymer is 2:

1.

3. A defluorinating agent based on layered bimetallic hydroxides, characterized in that, The defluorinating agent is prepared by the preparation method described in any one of claims 1-2.

4. The application of the defluorinating agent as described in claim 3, characterized in that, The defluorinating agent is used to remove fluoride from fluoride-containing wastewater.

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