A method for treating high-concentration fluorine-containing wastewater by using modified aluminate cement and a fluorine removal agent for high-concentration fluorine-containing wastewater

Abstract

The application discloses a method for treating high-concentration fluorine-containing wastewater by using modified aluminate cement and a defluorination agent for high-concentration fluorine-containing wastewater, and belongs to the technical field of environmental protection and water treatment. The method comprises the following steps: putting defluorination agent pellets made of aluminate cement into fluorine-containing wastewater to perform primary defluorination; adjusting the pH value of effluent after the primary defluorination treatment, adding a flocculant to promote precipitation, and performing secondary defluorination; and wherein, the pH value of the effluent after the primary defluorination treatment is adjusted to 7-9. The application uses the hydrated aluminate cement pellet defluorination agent to treat the fluorine-containing wastewater, and optimizes the specific treatment process, especially after two-stage defluorination treatment, the deep defluorination of the high-concentration fluorine-containing wastewater can be realized, the defluorination agent has the advantages of high defluorination rate, fast defluorination speed, high strength, large specific surface area, easy separation and the like, and the production process is simple, raw materials are easy to obtain, and the cost is low.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of environmental protection and water treatment, and particularly relates to a method for treating high-concentration fluorine-containing wastewater by using modified aluminate cement and a defluorination agent for high-concentration fluorine-containing wastewater. BACKGROUND

[0002] Fluorine pollution in water bodies mainly comes from nature, life and industrial production, among which the fluorine pollution caused by industrial production is the most serious. With the increasing production scale of various fluorine-related industries, the development and use of fluorine-containing materials are increasing, and the concentration of fluorine-containing materials in industrial wastewater is also increasing. For example, the concentration of fluorine-containing materials in wastewater generated in the production process of copper smelting industry can reach 1000 mg / L. The direct discharge concentration of industrial fluorine-containing wastewater in China is regulated to be below 10 mg / L, and the concentration of chlorides in surface water is controlled to be below 1.5 mg / L at most. Therefore, direct discharge will also cause the concentration of fluorine-containing materials in surface water to exceed the standard, and the wastewater is discharged into the wastewater treatment system of the park, and then discharged after being treated by the centralized wastewater treatment plant of the park. However, the centralized wastewater treatment process of the park does not involve defluorination. Therefore, at present, most enterprises require the discharge standard of fluorine-containing materials in wastewater to be lower than 10 mg / L, mostly 5 mg / L, or even lower. At present, there are various types of defluorination agents, but there are still some limitations in actual production and application, especially in the treatment of high-concentration fluorine-containing wastewater. The fluorine ion concentration cannot be reduced to below 1.5 mg / L by one-time addition, and if deep removal of fluorine-containing materials is required, multiple treatments are needed, which increases the cost budget.

[0003] There are some technical achievements in the research of using cement to prepare defluorination agents. For example, the patent application file with the patent application number CN201310015854.2 and the application publication date of May 10, 2013 discloses a defluorination adsorbent and a preparation method and application thereof. The defluorination agent is prepared by using Portland cement as raw material through hydration, filtration, calcination and grinding, and has a high removal rate for high-fluorine wastewater. However, aluminum sulfate needs to be added in proportion during the preparation process, and the preparation process needs to be filtered, which is not suitable for mass production. The patent application file with the patent application number CN201310097724.8 and the application publication date of June 12, 2013 discloses a method for preparing a defluorination agent by using high-aluminate cement as raw material. The defluorination agent with large specific surface area and porosity is prepared by mixing cement with calcium chloride dihydrate, followed by hydration, crushing, screening, washing and drying. However, the defluorination agent is not suitable for high-concentration fluorine-containing wastewater, and the kinetic process is slow and the adsorption capacity is small.

[0004] For example, the patent application file with the patent application number CN201811509831.6 and the application publication date of April 26, 2019 discloses a high-temperature modified aluminate cement defluorination adsorbent, a preparation method and application thereof. The defluorination agent is prepared by using aluminate cement as raw material through grinding, hydration, curing, crushing, washing, and calcination. The obtained defluorination agent has the advantages of rough surface, high porosity, rich micro-porous structure distribution, large specific surface area, and high strength, and the theoretical maximum adsorption capacity is 223.72 mg / g. However, a large amount of washing wastewater is generated during the washing process of the aluminate cement, and it is difficult to achieve deep removal. The patent application file with the patent application number CN202210309452.2 and the application publication date of June 21, 2022 discloses a high-concentration defluorination agent and a preparation method thereof. The defluorination agent is prepared by using waste concrete as raw material through crushing, calcination, screening, and surface treatment. However, the surface treatment requires the use of organic substances, which will generate a large amount of organic wastewater.

[0005] Therefore, in order to better treat high-concentration fluorine-containing wastewater to below 1.5 mg / L, it is of great significance to develop a new type of high-efficiency, environmentally friendly, low-cost, and simple-process fluorine-containing wastewater treatment material. SUMMARY

[0006] The purpose of the present application is to provide a method for treating high-concentration fluorine-containing wastewater using modified aluminate cement and a defluorination agent for high-concentration fluorine-containing wastewater, so as to overcome the defects of high production cost, pollution during production process, insufficient removal depth, and complicated operation of existing defluorination agents.

[0007] To achieve the above-mentioned purpose, the technical solution provided by the present application is as follows:

[0008] The present application provides a method for treating high-concentration fluorine-containing wastewater using modified aluminate cement, which comprises:

[0009] The defluorination agent pellets made of aluminate cement are put into fluorine-containing wastewater for primary defluorination; and

[0010] The pH value of the effluent after primary defluorination treatment is adjusted, and the step of secondary defluorination is performed;

[0011] The pH value of the effluent after primary defluorination treatment is adjusted to 7-9.

[0012] The present application uses aluminate cement as raw material to prepare defluorination agent pellets, and after curing and calcination, the pellets are added to fluorine-containing wastewater for primary defluorination. The pH value of the effluent after primary defluorination is adjusted, and then a flocculating agent is added for secondary defluorination. Thus, deep defluorination of high-concentration fluorine-containing wastewater can be achieved, and the stability of the defluorination effect is ensured when the pH value of the fluorine-containing wastewater to be treated changes between 3 and 12. The adaptability to fluorine-containing wastewater is good.

[0013] Furthermore, the main chemical composition of the aluminate cement is Al2O3, CaO, and SiO2, and it may also contain small amounts of Fe2O3 and MgO. The main mineral components are monocalcium aluminate (CaO·Al2O3), monocalcium dialuminate (CaO·2Al2O3), dicalcium silicate (2CaO·SiO2), and dodecacalcium heptaaluminate (12CaO·7Al2O3). Preferably, the mass content of calcium aluminate in the aluminate cement is ≥50%. After modification, the monocalcium aluminate and dicalcium aluminate in the material will transform into dodecacalcium heptaaluminate after hydration and calcination. Therefore, the calcium aluminate mineral can be monocalcium aluminate, monocalcium dialuminate, or dodecacalcium heptaaluminate. When a defluorinating agent made from this aluminate cement is added to high-concentration fluoride-containing wastewater, Ca2+ will dissolve. 2+ And Al 3+ Among them, the dissolved Ca 2+ Precipitation and the adsorption properties of the adsorbent itself can achieve primary fluoride removal from fluoride-containing wastewater. Simultaneously, this process further promotes the formation of Al in the material. 3+ Further release of Al2+ can be induced by adjusting the pH of the effluent after primary fluoride removal treatment to 7-9. 3+ Precipitation is carried out to further capture fluoride ions in the solution and reduce their concentration to below 1.5 mg / L, achieving deep removal. The entire process is simple to operate.

[0014] It should be noted that this application applies to different types of aluminate cement, as long as its main mineral composition is calcium aluminate. The main requirement is for the quality composition of calcium aluminate mineral, while there are no special requirements for the quality composition of other components. Therefore, commercially available aluminate cement of models CA50, CA60, CA70, and CA80, or even pure calcium aluminate powder, as well as industrial solid waste mainly containing these three minerals, can be used directly.

[0015] Specifically, this invention can achieve deep defluoridation of high-concentration fluoride-containing wastewater with a fluoride ion concentration not exceeding 400 mg / L and a pH value of 3–12, with a defluoridation rate of over 99%. Using the modified aluminate cement pellet defluoridator of this invention, a single defluoridation treatment can reduce the concentration of high-concentration fluoride-containing wastewater to approximately 10 mg / L. Then, by adjusting the pH of the effluent and performing a second defluoridation treatment, the fluoride ion concentration can be further reduced to below 1.5 mg / L, achieving deep treatment of fluoride-containing wastewater.

[0016] Furthermore, the mass concentration of the added defluorinating agent pellets is 2-5 g / L, preferably 3-5 g / L, which is a relatively small amount.

[0017] Furthermore, the particle size range of the defluorinating agent pellets is controlled to be 1–3 mm.

[0018] Further, the fluoride removal agent pellet is prepared by granulating, curing and calcining the aluminate cement.

[0019] Further, the specific preparation process of the fluoride removal agent pellet is as follows:

[0020] Pelletizing: the aluminate cement is placed in a granulator, and is granulated into spherical particles by spraying water;

[0021] Curing: the prepared aluminate cement pellet is cured in steam, the curing time is controlled to be 3-7 days, and the curing temperature is 20-80 DEG C;

[0022] Calcining: the aluminate cement pellet after curing is calcined, and finally the fluoride removal agent pellet is obtained; the calcining temperature is controlled to be 400-800 DEG C, and the calcining time is controlled to be 1-3 hours.

[0023] Further, a flocculating agent is added to promote precipitation when secondary fluoride removal is performed.

[0024] Further, the polyacrylamide flocculating agent is used, and further preferably, an anionic polyacrylamide flocculating agent is used.

[0025] Further, the addition amount of the flocculating agent is 3-10 mg / L, and the secondary fluoride removal precipitation time is 20-60 minutes.

[0026] Further, the pH value of the effluent after the primary fluoride removal treatment is adjusted by hydrochloric acid or sulfuric acid.

[0027] The application further provides a fluoride removal agent for high-concentration fluoride-containing wastewater, which is prepared by granulating, curing and calcining the aluminate cement.

[0028] In summary, compared with the prior art, the technical solution provided by the application has the following beneficial effects:

[0029] (1) The modified aluminate cement pellet fluoride removal agent is used to treat the fluoride-containing wastewater, and the specific treatment process is optimized, especially after two-stage fluoride removal treatment, so that the deep fluoride removal of the high-concentration fluoride-containing wastewater can be realized, the fluoride removal agent has the advantages of high fluoride removal rate, fast fluoride removal rate, high strength, large specific surface area, easy separation and the like, and the production process is simple, the raw materials are easy to obtain, and the cost is low;

[0030] (2) The modified aluminate cement pellet defluorination agent used in the application has stable physical and chemical properties, can be used for efficient treatment of high-concentration fluorine-containing wastewater (fluorine ion concentration not higher than 400 mg / L), and the defluorination rate is more than 99% at pH of 3-12; meanwhile, in the engineering practical application, the pH of the influent does not need to be adjusted before primary treatment, and the pH of the finally discharged wastewater also does not need to be adjusted, the defluorination reaction rate is fast, and the defluorination balance can be basically reached in 5-10 min, effectively reducing the treatment period of the fluorine-containing wastewater.

[0031] (3) The main raw materials of the modified aluminate cement pellet defluorination agent used in the application are aluminate cement and water, which have good resource reserves in China, and the production process is simple and clean, which has the possibility of large-scale production, and the final product is safe and environmentally friendly, and all functional auxiliary materials are green and non-toxic, which will not cause secondary pollution to water quality. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 The flow chart of the method for treating high-concentration fluorine-containing wastewater by using the modified aluminate cement of the embodiments of the application;

[0033] Figure 2 The SEM image of the defluorination agent prepared in Example 2. DETAILED DESCRIPTION

[0034] In order to make the purpose, technical scheme and advantages of the application clearer, the technical scheme in the embodiments of the application will be described clearly and completely in combination with the embodiments of the application. It should be understood by those skilled in the art that the embodiments are only used to help understand the application, and should not be regarded as a specific limitation on the application. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the application.

[0035] The embodiments of the application are implemented on the premise of the technical scheme of the application, and detailed implementation modes and processes are given, but the protection scope of the application is not limited to the following embodiments. The endpoints and any values in the scope disclosed in the application are not limited to the exact range or value, and these ranges or values should be understood as containing values close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and individual point values can be combined with each other to obtain one or more new numerical ranges, which should be regarded as specifically disclosed in the application.

[0036] Example 1

[0037] The embodiment provides a method for treating high-concentration fluorine-containing wastewater by using modified aluminate cement, which adopts a fluorine removal agent made of aluminate cement as raw material to perform two-stage fluorine removal treatment on high-concentration fluorine-containing wastewater, and combines Figure 1 and specifically comprises the following steps:

[0038] Step one, balling: high-alumina cement is placed in a granulator, then water is sprayed, and the aluminate cement is made into spherical particles, and the particle size of the obtained aluminate cement ball is 1 mm;

[0039] Step two, curing: the prepared aluminate cement ball particles are placed in steam for curing, the curing time is 3d, and the curing temperature is 80 DEG C;

[0040] Step three, calcination: the aluminate cement ball particles after curing are sent to a kiln to be calcined at 400 DEG C for 3h, and finally the fluorine removal agent particles are obtained;

[0041] Step four, first-stage fluorine removal: the obtained fluorine removal agent ball particles are put into fluorine-containing wastewater to perform first-stage fluorine removal, the fluorine ion concentration of the fluorine-containing wastewater is 300 mg / L, and the mass concentration of the added fluorine removal agent ball particles is 5 g / L;

[0042] Step five, second-stage fluorine removal: hydrochloric acid is added to adjust the pH of the effluent after the first-stage fluorine removal, and the pH is finally adjusted to 8, so that the second-stage fluorine removal is realized, and further preferably, a PAM type flocculant is added to promote precipitation, the mass concentration of the PAM type flocculant is 5 mg / L, and the second-stage fluorine removal precipitation time is about 30 min.

[0043] Example 2

[0044] The method for treating high-concentration fluorine-containing wastewater by using modified aluminate cement in the embodiment is different from that in example 1 in that the calcination temperature of the aluminate cement ball particles is controlled at about 600 DEG C, and the structure and morphology of the prepared fluorine removal agent in the embodiment are as shown in Figure 2 .

[0045] Example 3

[0046] The method for treating high-concentration fluorine-containing wastewater by using modified aluminate cement in the embodiment is different from that in example 1 in that the calcination temperature of the aluminate cement ball particles is controlled at about 800 DEG C.

[0047] Example 4

[0048] The method for treating high-concentration fluorine-containing wastewater by using modified aluminate cement in the embodiment is different from that in example 1 in that the steam curing time of the aluminate cement ball particles is 5d, and the curing temperature is 50 DEG C.

[0049] Example 5

[0050] The method for treating high-concentration fluorine-containing wastewater by using modified aluminate cement in this example is different from that in Example 1 in that the steam curing time of the aluminate cement pellets is 7 days and the curing temperature is 20°C.

[0051] Example 6

[0052] The method for treating high-concentration fluorine-containing wastewater by using modified aluminate cement in this example is different from that in Example 1 in that the particle size of the obtained aluminate cement pellets is 3 mm.

[0053] Example 7

[0054] The method for treating high-concentration fluorine-containing wastewater by using modified aluminate cement in this example is different from that in Example 1 in that the particle size of the obtained aluminate cement pellets is 2 mm.

[0055] Example 8

[0056] The method for treating high-concentration fluorine-containing wastewater by using modified aluminate cement in this example is different from that in Example 1 in that the actual calcination time of the aluminate cement pellets is 1 h.

[0057] Example 9

[0058] The method for treating high-concentration fluorine-containing wastewater by using modified aluminate cement in this example is different from that in Example 1 in that the actual calcination time of the aluminate cement pellets is 2 h.

[0059] Example 10

[0060] The method for treating high-concentration fluorine-containing wastewater by using modified aluminate cement in this example is different from that in Example 1 in that the mass concentration of the PAM-type flocculant for secondary fluorine removal is 3 mg / L, and the secondary fluorine removal precipitation time is about 20 min.

[0061] Example 11

[0062] The method for treating high-concentration fluorine-containing wastewater by using modified aluminate cement in this example is different from that in Example 1 in that the mass concentration of the PAM-type flocculant for secondary fluorine removal is 10 mg / L, and the secondary fluorine removal precipitation time is about 60 min.

[0063] Comparative Example 1

[0064] In this comparative example, the original aluminate cement without any modification is directly used for the treatment of fluorine-containing wastewater.

[0065] Comparative Example 2

[0066] In this comparative example, the fluorine removal agent is a commercially available polyaluminum chloride (PAC) prepared into a 30% solution.

[0067] Comparative Example 3

[0068] The defluorination agent of the present comparative example uses the commercially available MT-701 type solid defluorination agent of Guangzhou Miaotong Water Treatment Technology Co., Ltd.

[0069] Performance test

[0070] First group of performance tests:

[0071] The defluorination agents in Examples 1-11 and Comparative Examples 1-3 were used to test the material defluorination performance, and the fluorine ion selective electrode was used to determine and analyze the fluorine ion concentration in the supernatant. The test steps are as follows:

[0072] (1) Take an equal amount of 0.5 g of the defluorination materials of each example and comparative example, and add them into 250 mL conical flasks, add 100 mL of fluorine-containing solution with a concentration of 300 mg / L, and take samples under 25℃, 150 r / min for 1 h, filter through a 0.45 um filter membrane, and determine and analyze with a fluorine ion selective electrode;

[0073] (2) Take the filtrate after reaction in (1), adjust the pH to 8 and add 5 mg / L of PAM to precipitate for 30 min, then take the supernatant and determine and analyze with a fluorine ion selective electrode;

[0074] (3) Two parallel samples were prepared for each example and comparative example.

[0075] Table 1 shows the experimental results of each example and comparative example

[0076]

[0077]

[0078] The experimental results show that for high-concentration fluorine-containing wastewater, the materials of Examples 1-11 all exhibit excellent defluorination performance, and the defluorination performance is significantly better than that of some commercially available defluorination agents. The pH needs to be adjusted during the induction process, and the subsequent process will not change. The adjusted pH is consistent with the value required in the discharge standard, which confirms the advantages of the defluorination agent of the present application in application.

[0079] Second group of performance tests:

[0080] Examples 1, 3, 6, and 8 were used to test the effect of defluorination agent dosage on the defluorination performance of the materials. The fluorine ion selective electrode was used to determine and analyze the fluorine ion concentration in the supernatant. The test steps are as follows:

[0081] (1) Take 0.2g, 0.3g and 0.5g of the fluoride removal material of each example respectively, add them to 250mL conical flasks, add 100mL of fluoride solution with a concentration of 300mg / L, shake at 25℃ and 150r / min for 1h, take samples, filter through a 0.45um filter membrane, and determine and analyze using a fluoride ion selective electrode;

[0082] (2) Take the filtrate after the reaction in (1), adjust the pH to 8 and add 5 mg / L PAM precipitate for 30 min, then take the supernatant and analyze it using a fluoride ion selective electrode.

[0083] (3) Two parallel samples were made for each embodiment and comparative example.

[0084] Table 2 shows the performance test results for each embodiment.

[0085]

[0086] As can be seen from the table above, adding a defluorinating agent to a 300 mg / L fluoride ion solution with a mass concentration of about 3 g / L can effectively remove fluoride-containing wastewater. In practical applications, the dosage can be adjusted according to the effluent concentration standard, which helps to reduce the cost of defluorinating agents.

[0087] Third group of performance tests:

[0088] The effects of different pH values ​​on defluorination performance in secondary treatment were tested using Examples 1, 3, 6, and 8. The difference from the second group of performance tests was that the pH values ​​of the effluent after primary treatment of the fluoride-containing wastewater were adjusted to 5, 7, and 9, respectively.

[0089] Table 3. Test results of the third group of performance tests

[0090]

[0091] Experimental results show that the present invention can effectively achieve deep fluoride removal by adjusting the pH to 5-9 in the secondary treatment. Combined with the pH requirements of the wastewater discharge standards, the optimal pH range is 7-9. Therefore, this process can simultaneously achieve pH adjustment and fluoride removal of the effluent, and has great potential in practical applications.

[0092] Fourth group of performance tests:

[0093] The effects of different concentrations of fluoride-containing wastewater on defluorination performance were tested using Examples 1, 3, 6, and 8. The difference from the second group of performance tests was that the initial concentrations of the fluoride-containing wastewater were 200 mg / L, 300 mg / L, and 400 mg / L.

[0094] Table 4 shows the test results of the fourth group of performance tests.

[0095]

[0096] The experimental results show that the fluorine removal agent prepared by the application can treat 200-400 mg / L fluorine-containing wastewater to below 20 mg / L in the first stage of treatment, and further reduce the fluorine content in the wastewater to below 1.5 mg / L through the second stage of treatment.

Claims

1. A method for treating high concentration fluoride-containing wastewater using a modified aluminate cement, characterized by, The method comprises the following steps: The fluoride removal agent pellets made of aluminate cement are put into the fluoride-containing wastewater for primary fluoride removal; The pH value of the effluent after the primary fluoride removal is adjusted to 7-9, and the secondary fluoride removal is performed; The fluoride ion concentration of the fluoride-containing wastewater to be treated is not more than 400 mg / L, and the pH value is 3-12; the mass concentration of the fluoride removal agent pellets to be added is 2-5 g / L; and a flocculant is added to promote precipitation during the secondary fluoride removal; The fluoride removal agent pellets are prepared by granulation, curing and calcination of aluminate cement, and the specific preparation process is as follows: Pelletizing: the aluminate cement is placed in a pelletizer, and is granulated into spherical particles by water spraying; Curing: the prepared aluminate cement pellets are cured in steam, the curing time is controlled to be 3-7 days, and the curing temperature is 20-80 DEG C; Calcination: the cured aluminate cement pellets are calcined, and the fluoride removal agent pellets are finally obtained; the calcination temperature is controlled to be 400-800 DEG C, and the calcination time is controlled to be 1-3 hours.

2. The method for treating high concentration fluorine-containing wastewater using modified aluminate cement according to claim 1, characterized in that, The particle size of the fluoride removal agent pellets is controlled to be 1-3 mm.

3. The method for treating high concentration fluorine-containing wastewater with modified aluminate cement according to claim 1 or 2, characterized in that, The flocculant is an anionic polyacrylamide flocculant, and the dosage of the flocculant is 3-10 mg / L; and the secondary fluoride removal precipitation time is 20-60 min.

4. The method of treating with a modified aluminate cement according to claim 1 or 2, characterized in that, The pH value of the effluent after the primary fluoride removal is adjusted by hydrochloric acid or sulfuric acid.

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