Aluminum-based composite coagulant coupled with zirconium and calcium, its preparation method and application

Abstract

The application provides an aluminum-based composite coagulant coupled with zirconium and calcium, a preparation method and application thereof, and belongs to the technical field of environment and chemistry. The preparation method of the aluminum-based composite coagulant coupled with zirconium and calcium comprises the following steps: dissolving an aluminum salt in water to obtain an aluminum salt aqueous solution; adding a zirconium salt into the aluminum salt aqueous solution to perform a first hydrolysis reaction according to a molar ratio of aluminum ions to zirconium ions of 5-30:1, so as to obtain a polymeric mixture; adding a calcium salt into the polymeric mixture to perform a second hydrolysis reaction according to a molar ratio of the sum of aluminum ions and zirconium ions to calcium ions of 1-30:1, so as to obtain the aluminum-based composite coagulant coupled with zirconium and calcium.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of environment and chemistry, and particularly relates to an aluminum-based composite coagulant coupled with zirconium and calcium as well as a preparation method and application thereof. BACKGROUND

[0002] With the rapid development of China's industry, more and more fluorine resources are applied to modern industry, such as semiconductor industry, photovoltaic industry, glass manufacturing industry, etc., and more and more fluorine-containing wastewater is produced, and the fluorine concentration in the wastewater gradually increases, and the acidity gradually increases. If the fluorine-containing wastewater is directly discharged without treatment, it will seriously harm the surrounding ecological environment and human health. Therefore, the skilled person in the art has explored various defluorination methods, such as membrane separation method, ion exchange method, adsorption method and electrochemical method, etc.

[0003] The membrane separation method has high removal efficiency for fluorine ions, but has high requirements for the water quality of the influent, the treatment equipment is easy to be contaminated and scaled, and the treatment cost is high, so it is not suitable for treating large-scale industrial wastewater. Although the ion exchange method has high defluorination efficiency and simple regeneration, it produces a large amount of fluorine-loaded waste, which may cause secondary pollution; and the production cost and regeneration cost of the resin used are high, so it is also not suitable for treating large-scale industrial wastewater. The adsorption method is mainly affected by the adsorption capacity and adsorption efficiency, and is commonly used for treating wastewater with low fluorine concentration (less than 50 mg / L). The coagulation and sedimentation method has the characteristics of low treatment cost, simple equipment and easy operation, and is therefore considered to be the best choice for treating industrial wastewater. The fluorine ions in the wastewater can form insoluble substances with a variety of substances, and then the solid phase is removed from the solution by some means, so as to achieve the purpose of defluorination. However, the coagulants on the current market have a narrow pH range of application, and have low efficiency when used for treating fluorine-containing wastewater, and may produce other pollutants. Alternatively, an excessive amount of coagulant is added during the treatment of fluorine-containing wastewater, which increases the cost and easily causes the residual metal ions in the coagulant in the effluent. SUMMARY

[0004] In view of the above technical problems, the present application provides an aluminum-based composite coagulant coupled with zirconium and calcium as well as a preparation method and application thereof, in order to at least partially solve the above technical problems, and thus the specific technical solutions provided by the present application are as follows.

[0005] As a first aspect of the present application, a preparation method of an aluminum-based composite coagulant coupled with zirconium and calcium is provided, comprising:

[0006] dissolving an aluminum salt in water to obtain an aluminum salt aqueous solution;

[0007] adding a zirconium salt to the aluminum salt aqueous solution to carry out a first hydrolysis reaction according to a molar ratio of aluminum ions to zirconium ions of 5-30:1, to obtain a polymeric mixture;

[0008] The second hydrolysis reaction is carried out by adding calcium salt to the polymeric mixture in a molar ratio of the sum of the moles of aluminum ions and zirconium ions to the moles of calcium ions being 1-30:1, to obtain the aluminum-based composite coagulant coupled with zirconium and calcium.

[0009] As a second aspect of the present application, an aluminum-based composite coagulant coupled with zirconium and calcium is provided, which is prepared by the above method.

[0010] As a third aspect of the present application, the use of the above aluminum-based composite coagulant coupled with zirconium and calcium in wastewater treatment is provided.

[0011] In the embodiments of the present application, the aluminum salt is dissolved in water, and then the zirconium salt is added to the aqueous aluminum salt solution to carry out the first hydrolysis reaction. Through the interaction of the aluminum salt and the zirconium salt, a polymeric mixture containing Al-O-Al, Zr-O-Zr and / or Al-O-Zr bonds is formed, so as to provide more binding sites for the coagulant to pollutants in the wastewater. At the same time, the introduction of the zirconium salt promotes the hydrolysis polymerization of the aluminum salt, promotes the transformation of the aluminum salt to polymeric states such as Al-O-Al and Al-O-Zr, and the H + The addition of calcium salt to the polymeric mixture will significantly affect the form of Al in the coagulant. Through the second hydrolysis reaction, Ca couples with Al and / or Zr during the hydrolysis process, so that the polymeric mixture is converted into a more complex polymeric mixture, and the aluminum-based composite coagulant coupled with zirconium and calcium (hereinafter referred to as composite coagulant) is obtained. The preparation method of the composite coagulant provided by the present application is simple to operate and controllable in process, and is suitable for large-scale promotion and has a wide application prospect. Compared with the aluminum-based coagulant used alone, the coagulation efficiency of the composite coagulant provided by the present application is significantly improved, the dosage of aluminum salt can be reduced under the condition of ensuring effective coagulation effect, and the concentration of aluminum in the effluent is significantly lower than that of the aluminum-based coagulant used alone. At the same time, compared with the aluminum-based coagulant, the zirconium-based coagulant and the calcium-based coagulant used alone, the composite coagulant provided by the present application can maintain good coagulation effect in a wider pH range and pollutant concentration range. BRIEF DESCRIPTION OF DRAWINGS

[0012] Figure 1 Figure for the treatment effect of the Al-Zr composite coagulant in Comparative Examples 1-6 on the fluorine-containing wastewater;

[0013] Figure 2 Figure for the defluorination effect of the composite coagulant in Example 1-Example 10 on the wastewater containing 10 mg / L of fluorine concentration;

[0014] Figure 3 Figure for the defluorination effect of the composite coagulant in Example 1-Example 10 on the wastewater containing 50 mg / L of fluorine concentration;

[0015] Figure 4Figure for fluoride removal effect of composite coagulant and AlCl3 coagulant in wastewater containing fluoride with concentration of 50 mg / L in Example 4, Comparative Example 1, Comparative Example 7, Comparative Example 8;

[0016] Figure 5 Figure for fluoride removal effect of composite coagulant and AlCl3 coagulant in wastewater containing fluoride with concentration of 10 mg / L in Example 9, Comparative Example 1, Comparative Example 7, Comparative Example 8;

[0017] Figure 6 Figure for fluoride removal effect of composite coagulant in wastewater containing fluoride with concentration of 50 mg / L in Example 4, Comparative Example 9, Comparative Example 10;

[0018] Figure 7 Figure for fluoride removal effect of composite coagulant in wastewater containing fluoride with concentration of 50 mg / L in Example 4, Comparative Example 9, Comparative Example 10;

[0019] Figure 8 Figure for fluoride removal effect of AlCl3 coagulant in wastewater containing fluoride with different dosages;

[0020] Figure 9 Figure for fluoride removal effect of composite coagulant in wastewater containing fluoride with different pH values in Example 4;

[0021] Figure 10 Figure for fluoride removal effect of AlCl3 coagulant in wastewater containing fluoride with different pH values;

[0022] Figure 11 Figure for fluoride removal effect of composite coagulant and AlCl3 coagulant in wastewater containing fluoride in Example 4, Comparative Example 1, Comparative Example 7, Comparative Example 8;

[0023] Figure 12 Figure for ESI-MS detection result of composite coagulant in Example 4;

[0024] Figure 13 Figure for ESI-MS detection result of AlCl3 coagulant;

[0025] Figure 14 Figure for infrared spectrum of flocculation in fluoride removal process of composite coagulant and AlCl3 coagulant in Example 4. DETAILED DESCRIPTION

[0026] In order to make the objects, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to specific examples and drawings.

[0027] There are many problems to be solved in the current coagulation sedimentation method for treating wastewater. For example, in the treatment of wastewater containing fluorine, most of them are through the way of adding excess calcium oxide to form calcium fluoride, but other ions existing in the wastewater will affect the formation and precipitation of calcium fluoride, such as sodium chloride, sodium sulfate and other salts will increase the solubility of calcium fluoride, while calcium chloride, calcium sulfate and other salts will reduce its solubility. Some use aluminum salt coagulation, but a large amount of aluminum salt coagulant needs to be added, and high concentration of aluminum ions is easily left in the wastewater. Zirconium salt has good biocompatibility, and zirconium salt also has strong fluoride removal ability, but it is easy to agglomerate in the application process, the pH suitable range is narrow, and when removing fluoride, it may also have certain adsorption effect on other ions, resulting in poor selectivity.

[0028] Based on this, the application provides an aluminum-based composite coagulant coupled with zirconium and calcium and a preparation method and application thereof. Zirconium ions and calcium ions are sequentially introduced into the aluminum-based coagulant to promote the transformation of aluminum ions to a polymeric state that is easier to combine with pollutants in wastewater. The prepared composite coagulant can maintain good coagulation effect in a wider pH range and pollutant concentration range.

[0029] Specifically, as a first aspect of the application, a preparation method of an aluminum-based composite coagulant coupled with zirconium and calcium is provided, comprising:

[0030] Dissolving the aluminum salt in water to obtain an aluminum salt aqueous solution;

[0031] According to a molar ratio of aluminum ions to zirconium ions of 5-30:1, zirconium salt is added to the aluminum salt aqueous solution to perform a first hydrolysis reaction, to obtain a polymeric mixture;

[0032] According to a molar ratio of the sum of aluminum ions and zirconium ions to calcium ions of 1-30:1, calcium salt is added to the polymeric mixture to perform a second hydrolysis reaction, to obtain the aluminum-based composite coagulant coupled with zirconium and calcium.

[0033] In the embodiment of the application, the aluminum salt is dissolved in water, and then the zirconium salt is added to the aluminum salt aqueous solution to perform the first hydrolysis reaction. Through the interaction of the aluminum salt and the zirconium salt, a polymeric mixture containing Al-O-Al, Zr-O-Zr and / or Al-O-Zr bonds is formed, so as to provide more binding sites for the coagulant and the pollutants in the wastewater. At the same time, the introduction of the zirconium salt promotes the hydrolysis polymerization of the aluminum salt, promotes the transformation of the aluminum salt to Al-O-Al, Al-O-Zr and other polymeric states, and the H +The morphology of Al in the coagulant will be significantly affected. The second hydrolysis reaction is carried out by adding calcium salt into the polymeric mixture, and the coupling between Ca and Al and / or Zr occurs during the hydrolysis process, so that the polymeric mixture is converted into a more complex polymeric mixture, and an aluminum-based composite coagulant coupled with zirconium and calcium (hereinafter referred to as a composite coagulant) is obtained. The preparation method of the composite coagulant provided by the present application is simple to operate, controllable in process, suitable for large-scale promotion, and has a wide application prospect.

[0034] In the embodiments of the present application, after the aluminum salt is added into water, after the zirconium salt is added into the aqueous solution of the aluminum salt, and after the calcium salt is added into the polymeric mixture, the aluminum ions, the zirconium ions and the calcium ions are stirred for 0.5-1.5 h to undergo hydrolysis and polymerization. The H + The morphology of the aluminum ions in the composite coagulant is significantly affected, and too much content of the zirconium salt will cause the precipitation of aluminum hydroxide and zirconium hydroxide after the water-soluble zirconium salt is added, which is not conducive to the formation of the polymeric mixture. Changing the adding sequence of the zirconium salt and the calcium salt, or adding the aluminum salt, the zirconium salt and the calcium salt at the same time, will quickly form particulate substances such as aluminum hydroxide, zirconium hydroxide and calcium hydroxide, which cannot form the composite coagulant. Therefore, the aluminum salt, the zirconium salt and the calcium salt are sequentially added, so that the hydrolysis gradually occurs, and the transition to the polymeric mixture and to a more complex polymeric mixture is more easily controlled.

[0035] According to the embodiments of the present application, the above method further comprises: aging the aluminum-based composite coagulant coupled with zirconium and calcium, wherein the aging time is 24-72 h. In the aging process, the hydrolysis reaction between the aluminum ions, the zirconium ions and the calcium ions is further promoted, so that they are converted into a more complex polymeric mixture, and the dispersion and suspension of the composite coagulant in water are facilitated, thereby improving the coagulation effect. Further, with the extension of the aging time, the coagulation effect is gradually improved. However, when the aging time reaches 72 h, the coagulation effect of the composite coagulant will decrease, because the too long aging time will cause the aluminum ions, the zirconium ions and the calcium ions in the composite coagulant to be converted into aluminum hydroxide, zirconium hydroxide and calcium hydroxide precipitates, thereby affecting the coagulation effect.

[0036] According to the embodiments of the present application, the aluminum salt includes any one of aluminum chloride and aluminum sulfate, the zirconium salt includes any one of zirconium chloride and zirconium sulfate, and the calcium salt includes any one of calcium chloride and calcium sulfate. The influence of chloride ions and sulfate ions on the hydrolysis of aluminum ions, zirconium ions and calcium ions is small. At the same time, it also needs to be considered whether other impurities will be introduced into the effluent. It should be noted that the present application only provides two kinds of optional anion species, and other water-soluble aluminum salts, zirconium salts and calcium salts can also be selected as long as the anion species does not affect the hydrolysis effect of aluminum ions, zirconium ions and calcium ions.

[0037] As a second aspect of the present application, there is provided an aluminum-based composite coagulant coupled with zirconium and calcium, which is prepared by the above method.

[0038] According to an embodiment of the present application, the aluminum-based composite coagulant coupled with zirconium and calcium is a colorless clear transparent solution.

[0039] As a third aspect of the present application, there is provided an application of the above aluminum-based composite coagulant coupled with zirconium and calcium in wastewater treatment.

[0040] In an embodiment of the present application, the composite coagulant provided by the present application has significantly improved coagulation efficiency compared with the use of aluminum-based coagulant alone. The dosage of aluminum salt can be reduced to significantly reduce the concentration of aluminum ions in the effluent while ensuring effective coagulation effect. This is because, in the first hydrolysis reaction, aluminum ions and zirconium ions undergo hydrolysis and polymerization to form compounds with Al-O-Al, Zr-O-Zr and / or Al-O-Zr bonds. The introduction of zirconium ions further promotes the hydrolysis and polymerization of aluminum ions, and promotes the transformation of aluminum ions to a polymeric state that is more easily combined with pollutants in wastewater. In the second hydrolysis reaction, calcium ions are introduced, which also undergo hydrolysis and polymerization, and further react with compounds with Al-O-Al, Zr-O-Zr and / or Al-O-Zr bonds to increase the molecular weight of the hydrolysis product and lengthen the molecular chain, forming a more complex polymeric mixture with increased binding sites for pollutants in wastewater. In the coagulation process, larger flocculants can be produced, which can shorten the sedimentation time and improve the coagulation effect of the composite coagulant.

[0041] According to an embodiment of the present application, the above wastewater includes fluorine-containing wastewater and fluorine-containing groundwater. The pH of the wastewater is 2-10, preferably 4-9, and more preferably 4-6. The concentration of fluorine in the wastewater is 1-70 mg / L, preferably 10-50 mg / L. Compared with aluminum-based coagulants alone (suitable for wastewater treatment with pH 5-7), zirconium-based coagulants (suitable for wastewater treatment with pH 2-4), and calcium-based coagulants (suitable for wastewater treatment with pH 7-8), the composite coagulant provided by the present application can maintain good defluorination effect in a wider pH range. Due to the common ion effect of calcium ions, the solubility of the insoluble precipitate is reduced, and the flocculants produced by the composite coagulant are more easily precipitated, thereby having higher defluorination effect at a wider fluorine concentration.

[0042] According to an embodiment of the present application, when the concentration of fluorine in the wastewater is 1-30 mg / L, the molar ratio of aluminum ions to zirconium ions (i.e. n Al / n Zr ) in the aluminum-based composite coagulant coupled with zirconium and calcium is 5:1, and the molar ratio of the sum of aluminum ions and zirconium ions to calcium ions (i.e. (n Al +n Zr / n Ca ))for 25:1; in the case that the concentration of fluorine in the wastewater is 30-70 mg / L, the molar ratio of aluminum ions and zirconium ions in the aluminum-based composite coagulant coupled with zirconium and calcium is 5:1, and the molar ratio of the sum of aluminum ions and zirconium ions to calcium ions is 4:1. The molar ratio of aluminum ions and zirconium ions is preferably 5:1. In the preferred molar ratio of aluminum ions and zirconium ions, the polymeric mixture formed by aluminum ions and zirconium ions is optimal in form and is more conducive to complexing with subsequent calcium ions.

[0043] The present application is further illustrated by the following examples and related test experiments. In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the embodiments of the present application. It will be apparent, however, that one or more embodiments can be practiced without these specific details. In other instances, well-known methods have not been described in detail in order to not unnecessarily obscure the present application. Also, well-known instruments, materials, and methods have not been described in detail in order to not unnecessarily obscure the present application. Details of the embodiments of the present application can be combined with each other in any combination, unless the context clearly dictates otherwise.

[0044] To investigate the effect of the molar ratio of aluminum ions and zirconium ions on the defluorination effect of the composite coagulant, the present application prepared the aluminum-zirconium composite coagulants (Al-Zr composite coagulants) of Comparative Example 1-Comparative Example 6.

[0045] Comparative Example 1

[0046] In the Al-Zr composite coagulant of this comparative example 1, the water-soluble aluminum salt is aluminum chloride hexahydrate, and the water-soluble zirconium salt is zirconium chloride. The molar ratio of aluminum chloride hexahydrate and zirconium chloride is 5:1, and the specific preparation method is as follows.

[0047] 2.4143 g of aluminum chloride hexahydrate was weighed into 100 ml of ultrapure water, stirred for 1 h to obtain an aluminum chloride aqueous solution; zirconium chloride was added to the aluminum chloride aqueous solution, and stirred for 1 h to obtain a first mixed solution; the first mixed solution was aged for 48 h to obtain the Al-Zr composite coagulant of Comparative Example 1.

[0048] Comparative Example 2-Comparative Example 6

[0049] In the Al-Zr composite coagulants of Comparative Example 2-Comparative Example 6, the molar ratios of aluminum chloride hexahydrate and zirconium chloride are 10:1, 15:1, 20:1, 25:1, and 30:1, respectively, and the specific preparation method is the same as that of Comparative Example 1.

[0050] Further, the Al-Zr composite coagulants in Comparative Example 1-Comparative Example 6 were applied to wastewater containing fluorine at a concentration of 10 mg / L to investigate their defluorination effect, wherein the addition amount of the composite coagulant was 0.5 mmol / L.

[0051] Figure 1The graphs show the treatment effects of Al-Zr composite coagulants on fluoride-containing wastewater in Comparative Examples 1-6.

[0052] Depend on Figure 1 It can be seen that the fluoride removal effect increases with the increase of the molar ratio of aluminum chloride hexahydrate to zirconium chloride. The fluoride removal rate reaches its highest when the molar ratio of aluminum chloride hexahydrate to zirconium chloride is 5:1. Since Al-Zr composite coagulants with a molar ratio of aluminum chloride hexahydrate to zirconium chloride below 5:1 cannot be successfully prepared (a large amount of aluminum hydroxide and zirconium hydroxide precipitates are generated when zirconium salt is added to aluminum salt aqueous solution), when preparing calcium-containing composite coagulants, the molar ratio of aluminum chloride hexahydrate to zirconium chloride is fixed at 5:1, and a series of composite coagulants with different calcium contents are prepared to explore the fluoride removal ability of multiple metal ions.

[0053] To investigate the effect of the calcium ion ratio on the defluorination effect of the composite coagulant, the composite coagulants of Examples 1-10 were prepared in this invention.

[0054] Example 1

[0055] In the composite coagulant of Example 1, the water-soluble aluminum salt is aluminum chloride hexahydrate, the water-soluble zirconium salt is zirconium chloride, and the water-soluble calcium salt is calcium chloride. The molar ratio of aluminum chloride hexahydrate to zirconium chloride is 5:1, and the sum of the molar ratios of aluminum chloride hexahydrate and zirconium chloride to calcium chloride is 1:1. The specific preparation method is as follows.

[0056] Weigh 2.4143g of aluminum chloride hexahydrate and dissolve it in 100ml of ultrapure water. Stir for 1h to obtain an aluminum chloride aqueous solution. Add zirconium chloride to the aluminum chloride aqueous solution and stir for 1h to obtain a first mixed solution. Add calcium chloride to the first mixed solution and stir for 1h to obtain a second mixed solution. Let the second mixed solution mature for 48h to obtain the composite coagulant of Example 1.

[0057] Examples 2-10

[0058] In the composite coagulants of Examples 2-10, the molar ratio of aluminum chloride hexahydrate and zirconium chloride is 5:1, and the molar ratio of the sum of the molars of aluminum chloride hexahydrate and zirconium chloride to calcium chloride is 2:1, 3:1, 4:1, 5:1, 10:1, 15:1, 20:1, 25:1, and 30:1, respectively. The specific preparation method is the same as in Example 1.

[0059] Furthermore, the composite coagulants from Examples 1-10 were applied to wastewater with fluoride concentrations of 10 mg / L and 50 mg / L, respectively, to investigate their fluoride removal effect, wherein the amount of composite coagulant added was 0.5 mmol / L.

[0060] Figure 2The graphs show the defluoridation effect of the composite coagulant in Examples 1-10 on wastewater with a fluoride concentration of 10 mg / L. Figure 3 The graphs show the defluoridation effect of the composite coagulant in Examples 1-10 on wastewater with a fluoride concentration of 50 mg / L.

[0061] Depend on Figure 2 It can be seen that, when treating low-concentration fluoride wastewater (10 mg / L), the composite coagulant in Example 9 achieved the highest fluoride ion removal efficiency, superior to composite coagulants with other proportions. Figure 3 It can be seen that when treating high-concentration fluoride-containing wastewater (50 mg / L), the composite coagulant in Example 4 achieved the highest fluoride ion removal efficiency, which was superior to other composite coagulants with different proportions.

[0062] To investigate the effects of aluminum and calcium salts alone, as well as zirconium and calcium salts, on the defluorination effect of composite coagulants, the present invention prepared aluminum-calcium composite coagulant (Al-Ca composite coagulant) of Comparative Example 7 and zirconium-calcium composite coagulant (Zr-Ca composite coagulant) of Comparative Example 8.

[0063] Comparative Example 7

[0064] Comparative Example 7 prepared an Al-Ca composite coagulant with a molar ratio of aluminum chloride hexahydrate and calcium chloride of 4:1. The specific preparation method is as follows.

[0065] 2.4143 g of aluminum chloride hexahydrate was weighed and dissolved in 100 ml of ultrapure water. The mixture was stirred for 1 h to obtain an aluminum chloride aqueous solution. Calcium chloride was added to the aluminum chloride aqueous solution, and the mixture was stirred for 1 h and then matured for 48 h to obtain the Al-Ca composite coagulant of Comparative Example 7.

[0066] Comparative Example 8

[0067] Comparative Example 8 prepared a Zr-Ca composite coagulant with a zirconium chloride and calcium chloride molar ratio of 4:1. The specific preparation method is as follows.

[0068] 2.3304 g of zirconium chloride was weighed and dissolved in 100 ml of ultrapure water. The mixture was stirred for 1 h to obtain an aqueous solution of zirconium chloride. Calcium chloride was added to the aqueous solution of zirconium chloride, and the mixture was stirred for 1 h and then matured for 48 h to obtain the Zr-Ca composite coagulant of Comparative Example 8.

[0069] Furthermore, the composite coagulant from Example 4, along with the AlCl3 coagulant and the composite coagulants from Comparative Examples 1, 7, and 8, were applied to wastewater with a fluoride concentration of 50 mg / L. The composite coagulant from Example 9, along with the AlCl3 coagulant and the composite coagulants from Comparative Examples 1, 7, and 8, were applied to wastewater with a fluoride concentration of 10 mg / L to investigate their fluoride removal effect. The amount of composite coagulant added was 0.5 mmol / L.

[0070] Figure 4 The graph shows the defluoridation effect of the composite coagulant and AlCl3 coagulant in wastewater with a fluoride concentration of 50 mg / L in Examples 4, 1, 7, and 8. Figure 5 The graph shows the defluoridation effect of the composite coagulant and AlCl3 coagulant in wastewater with a fluoride concentration of 10 mg / L in Examples 9, Comparative Examples 1, 7, and 8.

[0071] Depend on Figure 4 It can be seen that when treating high-concentration fluoride wastewater (50 mg / L), the composite coagulant shows a more significant improvement in fluoride ion removal efficiency compared to AlCl3 coagulant. The composite coagulant in Example 4 achieved the highest fluoride ion removal efficiency, at 70.8%. In contrast, the AlCl3 coagulant only achieved a fluoride ion removal efficiency of 50.6%, representing an improvement of 20.2%. Figure 5 It can be seen that when treating low-concentration fluoride wastewater (10 mg / L), the composite coagulant significantly improves the removal efficiency of fluoride ions compared to AlCl3 coagulant. This demonstrates that the addition of zirconium chloride can enhance the removal efficiency of fluoride ions. In Example 9, the composite coagulant achieved the highest fluoride ion removal efficiency, with a removal rate of 83%.

[0072] To investigate the effect of the order of addition of aluminum salt, zirconium salt and calcium salt on the defluorination effect of composite coagulant, the present invention prepared aluminum-calcium-zirconium composite coagulant (Al-Ca-Zr composite coagulant) of Comparative Example 9 and calcium-zirconium-aluminum composite coagulant (Zr-Ca-Al composite coagulant) of Comparative Example 10.

[0073] Comparative Example 9

[0074] Comparative Example 9 prepared an Al-Ca-Zr composite coagulant. The specific preparation method was the same as in Example 4, except that the order of adding aluminum salt, zirconium salt and calcium salt was: aluminum salt first, then calcium salt, and finally zirconium salt.

[0075] Comparative Example 10

[0076] Comparative Example 10 prepared a Zr-Ca-Al composite coagulant. The specific preparation method was the same as in Example 4, except that the order of adding aluminum salt, zirconium salt and calcium salt was: calcium salt first, then zirconium salt, and finally aluminum salt.

[0077] Furthermore, the composite coagulant in Example 4 and the composite coagulants in Comparative Examples 9 and 10 were applied to wastewater with a fluoride concentration of 50 mg / L to investigate their fluoride removal effect, wherein the amount of composite coagulant added was 0.5 mmol / L.

[0078] Figure 6The graphs show the defluoridation effect of the composite coagulant in Example 4, Comparative Example 9, and Comparative Example 10 on wastewater with a fluoride concentration of 50 mg / L.

[0079] Depend on Figure 6 It is known that the order in which aluminum, zirconium, and calcium salts are added affects the metallic form of the coagulant during polymerization, thus leading to differences in coagulation and defluorination effects. Adding aluminum salt first, followed by zirconium salt, promotes the formation of polymerized aluminum, and the resulting polymeric mixture is more conducive to complexing with fluoride ions. Adding calcium salt afterwards further enhances the binding ability of the composite coagulant with fluoride ions. Conversely, if zirconium salt is added first, its easier hydrolysis makes it less conducive to complexing with aluminum salts, and also weakens its optimization effect on the hydrolysis form of aluminum salts, hindering the formation of a more favorable polymeric mixture for complexing with fluoride ions, and also impeding further complexing with calcium ions. Calcium salt, due to the strong alkalinity of its hydrolysis products, preferentially complexes with aluminum salts, which is also unfavorable for forming a more favorable form for complexing fluoride ions. Therefore, adding calcium salt after the aluminum and zirconium salts can weaken the adverse effect of calcium ions on the aluminum ion form, generating a composite coagulant with stronger complexing ability with fluoride ions, thereby enhancing the coagulation effect of the composite coagulant.

[0080] To investigate the effect of the dosage of the composite coagulant on the defluorination effect, the composite coagulant and AlCl3 coagulant in Example 4 were applied to wastewater with a fluoride concentration of 50 mg / L at different dosages.

[0081] Figure 7 Figure 4 shows the effect of the composite coagulant on the treatment of fluoride-containing wastewater under different dosages. Figure 8 The graph shows the effect of AlCl3 coagulant on the treatment of fluoride-containing wastewater at different dosages.

[0082] Depend on Figure 7 and Figure 8 It can be seen that as the dosage of the composite coagulant increases, the removal efficiency of fluoride ions also increases. At a dosage of 10 mmol / L, the composite coagulant removes 85% of fluoride ions, and at a dosage of 14 mmol / L, the removal efficiency reaches 99%. AlCl3 coagulant also shows the same trend, but at the same dosage, the composite coagulant has a better fluoride removal effect than AlCl3 coagulant.

[0083] To investigate the effect of pH on the defluorination effect of fluoride-containing wastewater, the composite coagulant and AlCl3 coagulant in Example 4 were applied to wastewater with a fluoride concentration of 50 mg / L at different pH values, with the amount of composite coagulant added being 0.5 mmol / L.

[0084] Figure 9 Figure 4 shows the effect of the composite coagulant on the treatment of fluoride-containing wastewater under different pH conditions.Figure 10 The treatment effect of AlCl3 coagulant on fluorine-containing wastewater under different pH conditions.

[0085] From Figure 9 and Figure 10 It can be seen that under alkaline conditions (pH>7), the treatment effect of the composite coagulant and the AlCl3 coagulant on fluorine-containing wastewater is poor, while under acidic conditions (pH<7), the treatment effect of the composite coagulant and the AlCl3 coagulant on fluorine-containing wastewater is good, but the composite coagulant is better than the traditional AlCl3 coagulant in the pH range of 4-9. With the decrease of pH, the removal rate gradually increases. At pH 4, the removal effect of the composite coagulant reaches the best, and the residual fluoride ion concentration is 7.2 mg / L, and the removal rate is 85.6%. Therefore, the removal effect of the composite coagulant on fluoride ions under acidic conditions is much better than that under alkaline conditions.

[0086] In order to better simulate the fluorine-containing wastewater in nature, tap water is used to configure simulated wastewater, in which the fluoride ion is 50 mg / L, COD=20 mg / L, SO4 2- =190 mg / L, the composite coagulant in Example 4, Comparative Example 1, Comparative Example 7, Comparative Example 8 and AlCl3 coagulant are applied to the treatment of fluorine-containing wastewater, and the addition amount of the composite coagulant is 0.5 mmol / L.

[0087] Figure 11 The treatment effect of the composite coagulant in Example 4, Comparative Example 1, Comparative Example 7, Comparative Example 8 and AlCl3 coagulant on simulated natural fluorine-containing wastewater is shown in the figure.

[0088] From Figure 11 It can be seen that when treating wastewater with a fluoride ion concentration of 50 mg / L, a COD concentration of 20 mg / L, and a SO4 2- concentration of 190 mg / L, the treatment effect of the composite coagulant in Example 4 is the best, and the efficiency is increased by 7% compared with the use of AlCl3 coagulant alone. The treatment effect of the composite coagulant in Comparative Example 8 is the worst, and the removal rate is only 42.8%. The treatment effect of the composite coagulant in Example 4 is decreased compared with the treatment of wastewater containing only fluoride ions, because the pH value of the wastewater solution is high, and SO4 2- has a certain inhibitory effect on defluorination, resulting in a decrease in the defluorination effect of the composite coagulant.

[0089] In order to detect the form of aluminum in the composite coagulant, the composite coagulant in Example 4 and AlCl3 coagulant were detected by electrospray ionization mass spectrometry (ESI-MS).

[0090] Figure 12 The ESI-MS detection results of the composite coagulant in Example 4 are shown in the figure; Figure 13Figure 1 shows the ESI-MS detection results of the AlCl3 coagulant.

[0091] It can be seen from Figure 12 and Figure 13 that the main form of aluminum in the composite coagulant and the AlCl3 coagulant is monomeric aluminum, and the strength of monomeric aluminum in the composite coagulant is weaker than that of the AlCl3 coagulant, but the relative intensity of total Al 13 in the composite coagulant is 2.28%, which is higher than the intensity of total Al 13 in the AlCl3 coagulant. Therefore, the excellent coagulation effect of the composite coagulant is not only due to the coupling effect of multiple metals, but also due to the fact that the hydrolysis process of aluminum ions is significantly affected after the multiple metals are compounded, so that the composite coagulant shows a stronger defluorination effect than the AlCl3 coagulant.

[0092] In order to detect how the composite coagulant plays a role in the defluorination process, the flocculants in the defluorination process of the composite coagulant and the AlCl3 coagulant in Example 4 were detected by infrared spectroscopy (FTIR).

[0093] Figure 14 Figure 2 shows the infrared spectra of the flocculants in the defluorination process of the composite coagulant and the AlCl3 coagulant in Example 4.

[0094] It can be seen from Figure 14 that the characteristic peak at 980 cm -1 is caused by the vibration of M (Al / Zr / Ca)-O, and the characteristic peak at 605 cm -1 is caused by the vibration of the O-M (Al / Zr / Ca)-O bond. It can be seen that the intensity of this peak in the composite coagulant is significantly enhanced, which is due to the fact that Zr and Ca promote the polymerization of Al, and also due to the generation of multiple metal bonds of Al-O-Zr, Zr-O-Ca and Al-O-Ca. And the stretching vibration of the -OH bond and the bending vibration caused by the adsorption of the water H-O-H group due to intermolecular bonding are observed at 3500 cm -1 , which proves that there are a large number of hydroxyl polymers in the flocculants. By comparing the infrared spectra of the two coagulants, it is found that the peak intensity and peak area in the 750-1000 cm -1 region of the composite coagulant are larger than those of AlCl3, which is due to the vibration of the Zr-O bond and the Zr-F bond caused by the addition of zirconium ions. This indicates that zirconium ions also participate in the defluorination process, and the peak area and peak intensity of -OH in the composite coagulant are higher than those of AlCl3, which is due to the fact that zirconium ions themselves hydrolyze and polymerize, and zirconium ions promote the hydrolysis and polymerization of aluminum ions.

[0095] The above-described specific embodiments further illustrate the purpose, technical solutions and beneficial effects of the present application, and it should be understood that the above-described is only a specific embodiment of the present application and is not intended to limit the present application, and any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. A method for preparing an aluminum-based composite coagulant coupled with zirconium and calcium, comprising: dissolving an aluminum salt in water to obtain an aqueous aluminum salt solution; adding a zirconium salt to the aqueous aluminum salt solution to perform a first hydrolysis reaction, according to a molar ratio of aluminum ions to zirconium ions of 5-30: 1, to obtain a polymeric mixture; adding a calcium salt to the polymeric mixture to perform a second hydrolysis reaction, according to a molar ratio of the sum of aluminum ions and zirconium ions to calcium ions of 1-30: 1, to obtain an aluminum-based composite coagulant coupled with zirconium and calcium. aging the obtained aluminum-based composite coagulant coupled with zirconium and calcium; wherein the aging time is 24-72 h. The aluminum salt comprises any one of aluminum chloride and aluminum sulfate, the zirconium salt comprises any one of zirconium chloride and zirconium sulfate, and the calcium salt comprises any one of calcium chloride and calcium sulfate. The polymeric mixture comprises a compound having Al-O-Al, Zr-O-Zr and / or Al-O-Zr bonds.

2. The method of claim 1, further comprising: 5.An aluminum-based composite coagulant coupled with zirconium and calcium, prepared by the method of any one of claims 1-4. 6.Use of the aluminum-based composite coagulant coupled with zirconium and calcium of claim 5 in wastewater treatment.

3. The method of claim 1, wherein, The wastewater comprises fluorine-containing wastewater and fluorine-containing underground water.

4. The method of claim 1, wherein, The pH of the wastewater is 2-10. The concentration of fluorine in the wastewater is 1-70 mg / L. When the concentration of fluorine in the wastewater is 1-30 mg / L, the molar ratio of aluminum ions to zirconium ions in the aluminum-based composite coagulant coupled with zirconium and calcium is 5: 1, and the molar ratio of the sum of aluminum ions and zirconium ions to calcium ions is 25: 1; or 7. Use according to claim 6, wherein, When the concentration of fluorine in the wastewater is 30-70 mg / L, the molar ratio of aluminum ions to zirconium ions in the aluminum-based composite coagulant coupled with zirconium and calcium is 5: 1, and the molar ratio of the sum of aluminum ions and zirconium ions to calcium ions is 4:

1.

8. Use according to claim 7, wherein, ​ 9. Use according to claim 7, wherein, ​ 10. Use according to claim 9, wherein, ​ ​

Images