Fluorine-containing wastewater zero discharge treatment method and system

Abstract

The invention discloses a zero-discharge treatment method and system for fluorine-containing wastewater, and belongs to the technical field of water treatment. The system comprises a water inlet tank, a first fluorine removal device, a first softening device, a first filtering device, a second fluorine removal device, a first nanofiltration device, a reverse osmosis device, a pure salt evaporative crystallization device, an ozone reaction device, a second softening device, a second filtering device, a second nanofiltration device, a fluorine removal agent cleaning and separating device and a carnallite evaporative crystallization device. The water inlet tank is sequentially connected with a first defluorination device, a first softening device, a first filtering device, a second defluorination device, a first nanofiltration device, a reverse osmosis device and a pure salt evaporative crystallization device; the ozone reaction device is arranged, so that an organic scale inhibitor in a concentrated solution is destroyed, recycling of an inorganic salt fluorine removal agent is realized, the problem of organic matter enrichment pollution after wastewater is concentrated by the first nanofiltration device is prevented, and the overall water outlet effect of the zero discharge system is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of water treatment, and specifically relates to a zero-discharge treatment method and system for fluorine-containing wastewater. Background Art

[0002] Due to the extremely low solubility of calcium fluoride, the presence of fluoride ions can cause equipment scaling problems in industrial wastewater treatment. In reverse osmosis devices and evaporation concentration devices, as the material continues to concentrate, calcium fluoride will reach an oversaturated state and then precipitate on the membrane surface or the heat exchanger surface. Once scaling occurs, it is difficult to remove by conventional pickling, and usually requires high-speed flushing or chelating agent immersion, which is difficult and costly to maintain. In addition, fluoride ions are highly corrosive to metal materials, especially under acidic conditions (low pH), which will accelerate the corrosion of metal materials and shorten the service life of the evaporator. In particular, titanium materials, although generally corrosion-resistant, have limited tolerance to fluoride ions, and long-term contact will cause corrosion problems. Therefore, in the face of fluoride-containing industrial wastewater, fluoride ions need to be removed through pretreatment. The pretreatment methods for fluoride-containing wastewater mainly include chemical precipitation, coagulation precipitation, adsorption, and ion exchange.

[0003] Chemical precipitation is a common method for treating high-concentration fluoride-containing wastewater. It removes fluoride ions by adding chemicals such as lime to the wastewater to generate insoluble fluoride precipitates. This method is simple to operate and low in cost, but the treated effluent is difficult to meet high standards, and the generated sludge settles slowly and is difficult to dehydrate.

[0004] The coagulation and sedimentation method uses the cations in the coagulant to form a complex with the fluoride ions in the water, and removes the fluoride ions by precipitation. This method needs to consider multiple factors such as the amount of coagulant added and the pH value of the raw water, which has a great influence on the fluoride removal effect.

[0005] The adsorption method uses adsorbents such as activated alumina, clinoptilolite, activated magnesium oxide, etc. to remove fluoride ions through adsorption. This method is suitable for deep treatment of drinking water with a small amount of water, and the effect is obvious, but the operation is complicated and the cost is high.

[0006] The ion exchange method uses ion exchange resins and other materials to remove fluoride ions through ion exchange. This method is suitable for high-purity separation and purification, and has the advantages of strong removal capacity and regeneration, but the resin capacity is limited, the regeneration process is complicated, and the cost is high. It is suitable for deep removal of low-concentration fluoride ions.

[0007] CN116639853B discloses a system and method for achieving zero discharge of wastewater and salt recovery, which uses a two-stage defluorination system and adds lime to form calcium fluoride precipitation to achieve the defluorination effect. CN116022965B discloses a zero discharge treatment system and process for coking wastewater, which uses a first-stage defluorination high-density tank for defluorination treatment and adds calcium chloride to form calcium fluoride precipitation to achieve the defluorination effect.

[0008] The existing wastewater zero-discharge treatment system mainly uses chemical precipitation to remove fluorine. Usually, the fluorine ion concentration in the effluent of the chemical precipitation method can reach about 10-20 mg / L. If the fluorine ion concentration is to be further reduced, excessive addition of calcium-based defluorinating agents is required, and the cost of adding agents is high. In addition, the fluctuation of the fluorine ion concentration in the inlet water can easily lead to excessive fluorine ion concentration in the effluent of the defluoridation treatment, which in turn affects the stability of the subsequent reverse osmosis system and evaporation crystallization system. Summary of the invention

[0009] The purpose of the present invention is to solve the above problems and propose a method and system for defluoridation by utilizing inorganic salts from wastewater itself, thereby reducing the amount of reagents added in the chemical precipitation method and adopting deep defluoridation technology in combination to prevent the harm caused by fluoride ions in the zero-emission treatment system.

[0010] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0011] A zero-discharge treatment system for fluorine-containing wastewater, the system comprising a water inlet tank, a first defluorination device, a first softening device, a first filtering device, a second defluorination device, a first nanofiltration device, a reverse osmosis device, a pure salt evaporation crystallization device, an ozone reaction device, a second softening device, a second filtering device, a second nanofiltration device, a defluorination agent cleaning and separation device, and a miscellaneous salt evaporation crystallization device;

[0012] The water inlet tank is connected in sequence to the first defluorination device, the first softening device, the first filtering device, the second defluorination device, the first nanofiltration device, the reverse osmosis device, and the pure salt evaporation crystallization device;

[0013] The concentrated liquid outlet of the first nanofiltration device is connected to the ozone reaction device, the second softening device, the second filtering device, the second nanofiltration device, and the mixed salt evaporation crystallization device in sequence;

[0014] The water output outlets of the first nanofiltration device and the second nanofiltration device are connected to the water inlet of the reverse osmosis device;

[0015] The solid product obtained by the ozone reaction device is added to the first defluorination device after being treated by the defluorination agent cleaning and separation device.

[0016] Furthermore, the first defluorination device is a reaction clarification tank, which includes a reaction tank and a clarification tank. The reaction tank is provided with a solid-liquid mixing component, and the solid-liquid mixing component is one of a mechanical agitator and an aeration mixer, or a combination of the two; the clarification tank is one of an inclined tube sedimentation tank and an inclined plate sedimentation tank; the second defluorination device is an ion exchange resin.

[0017] Furthermore, the first softening device and the second softening device are a kind of high-density clarification tank or flocculation sedimentation tank; the first filtration device and the second filtration device are a combination of one or more of multi-media filtration, microfiltration, and ultrafiltration; the first nanofiltration device and the second nanofiltration device are both primary and at least one stage; the reverse osmosis device includes at least two stages and two sections (the first stage water production entering the second stage is called two stages, and the first stage (which is also the first section) concentrated water enters the second section, that is, the water production and desalination are called the second stage, and the concentrated water is called the second stage. This is an industry term and there is no ambiguity in the industry).

[0018] Furthermore, the ozone reaction device comprises a reaction zone, an ozone dosing component, a mechanical stirring component, a clarification zone, and a sedimentation zone; the ozone dosing component adopts a mechanical mixed dissolved air dosing device or an ejector dosing device, one of the two dosing devices is selected, and the generated ozone is added inside the reaction zone; the mechanical stirring component is a paddle stirrer, which is arranged in the reaction zone, and the stirring speed is 20-100r / min; the reaction zone is a column or tower reactor; the clarification zone is at the top of the reaction zone, and a trapezoidal weir or a triangular weir is arranged; the sedimentation zone is at the bottom of the reaction zone, and the generated inorganic salt defluorination agent crystalline solid is collected.

[0019] Furthermore, the wastewater zero discharge system also includes a pre-defluorination device, which is installed after the water inlet tank and before the first defluorination device to pre-defluorinate the wastewater with high fluoride ion concentration; the pre-defluorination device is a high-density clarification tank, which adds calcium oxide or calcium chloride to form calcium fluoride precipitation to reduce the fluoride ion concentration to below 50 mg / L. In this field, a fluoride ion concentration greater than 500 mg / L is considered high-concentration fluoride-containing wastewater.

[0020] Furthermore, the system also includes an inlet water online fluoride ion detector, a first online fluoride ion detector and a second online fluoride ion detector, which are respectively installed on the outlet pipe of the water inlet tank, the first defluorination device and the second defluorination device outlet pipe.

[0021] A method for treating wastewater using the above-mentioned fluorine-containing wastewater zero-discharge treatment system, the method comprising:

[0022] Step 1: First defluorination treatment: The fluorine-containing wastewater enters the first defluorination device from the water inlet tank, an inorganic salt defluoridant is added to the reaction tank of the first defluorination device, and the solid-liquid separation of the wastewater is achieved through the clarification tank;

[0023] Step 2: First softening treatment: the effluent from the first defluorination device enters the first softening device, and a softener is added to the first softening device to reduce the concentration of calcium and magnesium;

[0024] Step 3: First filtration treatment: The effluent from the first softening device enters the first filtration device, and the effluent from the first softening treatment is finely filtered to deeply remove suspended solid particles;

[0025] Step 4: Second defluorination treatment: The effluent from the second filtration device enters the second defluorination device to further remove residual fluoride ions, and ensures that the effluent fluoride ion concentration meets the standard in the debugging stage, water quality fluctuations, and failures of the first defluorination device.

[0026] Step 5: First nanofiltration separation: Separate the monovalent salt and the divalent salt in the wastewater discharged from the second defluorination device to obtain the first nanofiltration product water and the first nanofiltration concentrate;

[0027] Step 6: Reverse osmosis desalination and concentration: Desalination treatment is performed on the water produced by the first nanofiltration device and the water produced by the second nanofiltration device to obtain product water and reverse osmosis device concentrate;

[0028] Step 7: Pure salt evaporation and crystallization: Concentrate and crystallize the concentrated liquid of the reverse osmosis device to obtain a sodium chloride salt product;

[0029] Step 8: Ozone oxidation and clarification treatment: The ozone reaction device performs ozone oxidation and clarification treatment (organic matter removal and inorganic salt resource utilization) on the concentrated liquid of the first nanofiltration device to obtain ozone oxidation effluent and inorganic salt defluorinating agent; the ozone action oxidizes the scale inhibitor, destroys its chelating or dispersion effect, and makes the metastable wastewater realize solid crystallization; the inorganic salt defluorinating agent is cleaned with tap water or desalted water to remove impurities carried on the surface, and the inorganic salt defluorinating agent is separated by filtration, centrifugation or gravity precipitation; the separated inorganic salt defluorinating agent is added to the first defluorinating device;

[0030] Step 9: Second softening treatment: Soften and clarify the effluent from the ozone reaction device to further remove calcium and magnesium ions;

[0031] Step 10: Second filtration treatment: fine filtration of the water effluent from the second softening device;

[0032] Step 11: Second nanofiltration treatment: further concentrate and reduce the effluent from the second filtration device, further separate the sodium chloride therein, improve the resource utilization rate of sodium chloride, reduce the amount of water to be processed by the impurity salt evaporation and crystallization device, and obtain the second nanofiltration device produced water and the second device nanofiltration concentrate;

[0033] Step 12: Evaporation treatment of impure salts: concentrating and crystallizing the concentrated liquid from the second nanofiltration device to obtain impure salt solid waste.

[0034] Furthermore, in step one, the solid content of the inorganic salt defluorinating agent in the first defluorinating device is 1%-5%; the residence time of the first defluorinating device is 0.5h-3h; the first nanofiltration device and the second nanofiltration device are added with organic scale inhibitors, and the scale inhibitor dosage is 0.5-5mg / L, and the scale inhibitor can be one or more of PBTCA (2-phosphonobutane-1,2,4-tricarboxylic acid), HEDP (hydroxyethylidene diphosphonic acid) or ATMP (aminotrimethylene phosphonic acid); the first nanofiltration treatment and the second nanofiltration treatment are both primary and at least one stage; the reverse osmosis treatment process includes at least two-stage treatment and two-stage treatment (the first-stage produced water entering the second stage is called two-stage, and the first-stage (also the first stage) concentrated water enters the second stage, that is, the produced water is desalted and called the second stage, and the concentrated water is concentrated and called the second stage, which is an industry term and has no ambiguity in the industry).

[0035] Furthermore, the first softening device and the second softening device are added with softening agents selected from the group consisting of calcium oxide, calcium hydroxide, sodium carbonate, sodium hydroxide, polyferric chloride, polyaluminium chloride, ferric chloride, aluminium chloride, ferric sulfate, aluminium sulfate and polyacrylamide; the pre-defluorination device is added with one or more selected from the group consisting of calcium chloride, calcium oxide, calcium hydroxide, aluminium sulfate and polyaluminium and polyferric.

[0036] Furthermore, the second defluorination device is filled with a second defluorination adsorbent which is a selective defluorination resin, and the defluorination functional group of the selective defluorination resin is aminophosphoric acid-supported aluminum (existing product); the method also includes a regeneration process of the second defluorination adsorbent, and the regeneration agent is 15-25% concentration aluminum sulfate, and the regeneration time is 30min-120min.

[0037] The beneficial effects of the present invention compared to the prior art are:

[0038] 1. The present invention adds a scale inhibitor to the first nanofiltration device. After the wastewater is concentrated by the first nanofiltration device, calcium ions and sulfate ions in the concentrate are enriched, and a stable metastable state is maintained under the action of the scale inhibitor. In the ozone reaction device, the metastable state under the action of the scale inhibitor is destroyed to form a crystalline solid mainly composed of calcium sulfate. After the defluorination agent is cleaned and separated, the formed inorganic salt defluorination agent (calcium sulfate) is added to the first defluorination device to remove fluoride ions in the wastewater, realize the recycling of inorganic salt resources in the wastewater, and reduce the use of agents and transportation costs.

[0039] 2. The present invention is provided with a second defluorination device to deeply remove fluoride ions in the wastewater, thereby avoiding the scaling problem of calcium fluoride caused by the concentration process of the membrane system and the evaporation system, and the corrosion problem of the evaporator caused by fluoride ions.

[0040] 3. The second nanofiltration device is provided in the present invention, which increases the reverse osmosis water production of the overall zero-discharge system and reduces the amount of evaporation and crystallization of impurities. At the same time, the concentrated liquid of the first nanofiltration device after the inorganic salt resource recycling reduces the ion concentration in the wastewater, reduces the salt content of the inlet water of the second nanofiltration device, and reduces the operating load of the nanofiltration membrane.

[0041] 4. The present invention is provided with an ozone reaction device, which not only destroys the organic scale inhibitor in the concentrated liquid and realizes the recycling of the inorganic salt defluorinating agent, but also prevents the organic matter enrichment pollution problem after the wastewater is concentrated by the first nanofiltration device, thereby improving the overall water discharge effect of the zero emission system. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 This is a process flow chart of low-concentration fluoride ion treatment of the present invention;

[0043] Figure 2 The figure is a process flow chart of the high concentration fluoride ion treatment process of the present invention. DETAILED DESCRIPTION

[0044] The technical solution of the present invention is further described below in conjunction with the accompanying drawings and embodiments, but is not limited thereto. Any modification or equivalent replacement of the technical solution of the present invention that does not depart from the spirit and scope of the technical solution of the present invention should be included in the protection scope of the present invention.

[0045] Embodiment 1:

[0046] A zero-discharge treatment system for fluorine-containing wastewater, the system comprising a water inlet tank, a first defluorination device, a first softening device, a first filtering device, a second defluorination device, a first nanofiltration device, a reverse osmosis device, a pure salt evaporation crystallization device, an ozone reaction device, a second softening device, a second filtering device, a second nanofiltration device, a defluorination agent cleaning and separation device, and a miscellaneous salt evaporation crystallization device;

[0047] The water inlet tank is connected in sequence to the first defluorination device, the first softening device, the first filtering device, the second defluorination device, the first nanofiltration device, the reverse osmosis device, and the pure salt evaporation crystallization device;

[0048] The concentrated liquid outlet of the first nanofiltration device is connected to the ozone reaction device, the second softening device, the second filtering device, the second nanofiltration device, and the mixed salt evaporation crystallization device in sequence;

[0049] The water output outlets of the first nanofiltration device and the second nanofiltration device are connected to the water inlet of the reverse osmosis device;

[0050] The solid product obtained by the ozone reaction device is added to the first defluorination device after being treated by the defluorination agent cleaning and separation device.

[0051] The first defluorination device is a reaction clarification tank, which includes a reaction tank and a clarification tank. The reaction tank is provided with a solid-liquid mixing component, which is a mechanical agitator; the clarification tank is an inclined plate sedimentation tank; and the second defluorination device is an ion exchange resin.

[0052] The first softening device and the second softening device are a kind of high-density clarification tank or flocculation sedimentation tank; the first filtration device and the second filtration device are multi-media filtration; the first nanofiltration device and the second nanofiltration device are both primary and at least one stage; the reverse osmosis device includes at least two stages and two sections (the primary water production entering the secondary stage is called two stages, and the concentrated water of the primary stage (which is also the first section) enters the second section, that is, the water production and desalination are called the second stage, and the concentrated water is called the second stage, which is an industry term and there is no ambiguity in the industry).

[0053] The ozone reaction device comprises a reaction zone, an ozone dosing component, a mechanical stirring component, a clarification zone, and a precipitation zone; the ozone dosing component adopts an ejector dosing device, and the generated ozone is added inside the reaction zone; the mechanical stirring component is a paddle stirrer, which is arranged in the reaction zone, and the stirring speed is 60-70r / min; the reaction zone is a column reactor; the clarification zone is at the top of the reaction zone, and a trapezoidal weir or a triangular weir is arranged; the precipitation zone is at the bottom of the reaction zone, and the generated inorganic salt defluorination agent crystalline solid is collected.

[0054] The system also includes an inlet water online fluoride ion detector, a first online fluoride ion detector and a second online fluoride ion detector, which are respectively installed on the outlet pipe of the water inlet tank, the first defluorination device and the outlet pipe of the second defluorination device.

[0055] Example 2

[0056] A method for treating wastewater using the fluorine-containing wastewater zero-discharge treatment system of Example 1, the method comprising:

[0057] Step 1: First defluorination treatment: Fluorine-containing wastewater enters the first defluorination device from the water inlet tank, an inorganic salt defluoridant is added to the reaction tank of the first defluorination device, and solid-liquid separation of the wastewater is achieved through a clarification tank;

[0058] Step 2: First softening treatment: the effluent from the first defluorination device enters the first softening device, and a softener is added to the first softening device to reduce the concentration of calcium and magnesium;

[0059] Step 3: First filtration treatment: The effluent from the first softening device enters the first filtration device, and the effluent from the first softening treatment is finely filtered to deeply remove suspended solid particles;

[0060] Step 4: Second defluorination treatment: The effluent from the second filtration device enters the second defluorination device to further remove residual fluoride ions. In addition, the fluoride ion concentration in the effluent is guaranteed to meet the standard in the debugging stage, water quality fluctuations, and failures of the first defluorination device.

[0061] Step 5: First nanofiltration separation: Separate the monovalent salt and the divalent salt in the wastewater discharged from the second defluorination device to obtain the first nanofiltration product water and the first nanofiltration concentrate;

[0062] Step 6: Reverse osmosis desalination and concentration: Desalination treatment is performed on the water produced by the first nanofiltration device and the water produced by the second nanofiltration device to obtain product water and reverse osmosis device concentrate;

[0063] Step 7: Pure salt evaporation and crystallization: Concentrate and crystallize the concentrated liquid of the reverse osmosis device to obtain a sodium chloride salt product;

[0064] Step 8: Ozone oxidation and clarification treatment: The ozone reaction device performs ozone oxidation and clarification treatment (organic matter removal and inorganic salt resource utilization) on the concentrated liquid of the first nanofiltration device to obtain ozone oxidation effluent and inorganic salt defluorinating agent; the ozone action oxidizes the scale inhibitor, destroys its chelating or dispersion effect, and makes the metastable wastewater realize solid crystallization; the inorganic salt defluorinating agent is cleaned with tap water or desalted water to remove impurities carried on the surface, and the inorganic salt defluorinating agent is separated by filtration, centrifugation or gravity precipitation; the separated inorganic salt defluorinating agent is added to the first defluorinating device;

[0065] Step 9: Second softening treatment: Soften and clarify the effluent from the ozone reaction device to further remove calcium and magnesium ions;

[0066] Step 10: Second filtration treatment: fine filtration of the water effluent from the second softening device;

[0067] Step 11: Second nanofiltration treatment: further concentrate and reduce the effluent from the second filtration device, further separate the sodium chloride therein, improve the resource utilization rate of sodium chloride, reduce the amount of water to be processed by the impurity salt evaporation and crystallization device, and obtain the second nanofiltration device produced water and the second device nanofiltration concentrate;

[0068] Step 12: Evaporation treatment of impure salts: concentrating and crystallizing the concentrated liquid from the second nanofiltration device to obtain impure salt solid waste.

[0069] In step one, the solid content of the inorganic salt defluorinating agent in the first defluorinating device is 2%-4%; the residence time of the first defluorinating device is 0.5h-1.5h; the first nanofiltration device and the second nanofiltration device are added with organic antiscalant, and the dosage of the antiscalant is 3-5mg / L; the first nanofiltration treatment and the second nanofiltration treatment are both one-stage and at least one-stage; the reverse osmosis treatment process includes at least two-stage treatment and two-stage treatment (the first-stage produced water entering the second stage is called two-stage, and the concentrated water of the first stage (which is also the first stage) enters the second stage, that is, the produced water is desalted again, which is called the second stage, and the concentrated water is concentrated again, which is an industry term and there is no ambiguity in the industry).

[0070] Softening agents such as calcium oxide, calcium hydroxide and sodium carbonate are added into the first softening device and the second softening device.

[0071] The second defluorination device is filled with a second defluorination adsorbent which is a selective defluorination resin, and the defluorination functional group of the selective defluorination resin is aminophosphoric acid-supported aluminum (existing product); the method also includes a regeneration process of the second defluorination adsorbent, the regeneration agent is 15-25% concentration aluminum sulfate, and the regeneration time is 30min-120min.

[0072] Example 3

[0073] Based on Example 1, this embodiment further includes a pre-defluorination device, which is installed after the water inlet tank and before the first defluorination device to pre-defluorinate the wastewater with high fluoride ion concentration; the pre-defluorination device is a high-density clarification tank, which adds calcium oxide or calcium chloride to form calcium fluoride precipitation, thereby reducing the fluoride ion concentration to below 50 mg / L.

[0074] The method for treating wastewater using the system of this embodiment is as follows:

[0075] Step 1: First defluorination treatment: Fluorine-containing wastewater enters the first defluorination device from the water inlet tank, an inorganic salt defluoridant is added to the reaction tank of the first defluorination device, and solid-liquid separation of the wastewater is achieved through a clarification tank;

[0076] Step 2: First softening treatment: the effluent from the first defluorination device enters the first softening device, and a softener is added to the first softening device to reduce the concentration of calcium and magnesium;

[0077] Step 3: First filtration treatment: The effluent from the first softening device enters the first filtration device, and the effluent from the first softening treatment is finely filtered to deeply remove suspended solid particles;

[0078] Step 4: Second defluorination treatment: The effluent from the second filtration device enters the second defluorination device to further remove residual fluoride ions. In addition, the fluoride ion concentration in the effluent is guaranteed to meet the standard in the debugging stage, water quality fluctuations, and failures of the first defluorination device.

[0079] Step 5: First nanofiltration separation: Separate the monovalent salt and the divalent salt in the wastewater discharged from the second defluorination device to obtain the first nanofiltration product water and the first nanofiltration concentrate;

[0080] Step 6: Reverse osmosis desalination and concentration: Desalination treatment is performed on the water produced by the first nanofiltration device and the water produced by the second nanofiltration device to obtain product water and reverse osmosis device concentrate;

[0081] Step 7: Pure salt evaporation and crystallization: Concentrate and crystallize the concentrated liquid of the reverse osmosis device to obtain a sodium chloride salt product;

[0082] Step 8: Ozone oxidation and clarification treatment: The ozone reaction device performs ozone oxidation and clarification treatment (organic matter removal and inorganic salt resource utilization) on the concentrated liquid of the first nanofiltration device to obtain ozone oxidation effluent and inorganic salt defluorinating agent; the ozone action oxidizes the scale inhibitor, destroys its chelating or dispersion effect, and makes the metastable wastewater realize solid crystallization; the inorganic salt defluorinating agent is cleaned with tap water or desalted water to remove impurities carried on the surface, and the inorganic salt defluorinating agent is separated by filtration, centrifugation or gravity precipitation; the separated inorganic salt defluorinating agent is added to the first defluorinating device;

[0083] Step 9: Second softening treatment: Soften and clarify the effluent from the ozone reaction device to further remove calcium and magnesium ions;

[0084] Step 10: Second filtration treatment: fine filtration of the water effluent from the second softening device;

[0085] Step 11: Second nanofiltration treatment: further concentrate and reduce the effluent from the second filtration device, further separate the sodium chloride therein, improve the resource utilization rate of sodium chloride, reduce the amount of water to be processed by the impurity salt evaporation and crystallization device, and obtain the second nanofiltration device produced water and the second device nanofiltration concentrate;

[0086] Step 12: Evaporation treatment of impure salts: concentrating and crystallizing the concentrated liquid from the second nanofiltration device to obtain impure salt solid waste.

[0087] In step one, the solid content of the inorganic salt defluorinating agent in the first defluorinating device is 3%-5%; the residence time of the first defluorinating device is 2h-3h; the first nanofiltration device and the second nanofiltration device are added with organic antiscalant, and the dosage of the antiscalant is 3-5mg / L; the first nanofiltration treatment and the second nanofiltration treatment are both one-stage and at least one-stage; the reverse osmosis treatment process includes at least two-stage treatment and two-stage treatment (the first-stage produced water entering the second stage is called two-stage, and the first-stage (also the first stage) concentrated water enters the second stage, that is, the produced water is desalted again, which is called the second stage, and the concentrated water is concentrated again, which is an industry term and there is no ambiguity in the industry).

[0088] Softening agents such as polyaluminium chloride, ferric chloride, aluminium chloride and ferric sulfate are added to the first softening device and the second softening device; calcium chloride, calcium oxide and calcium hydroxide are added to the pre-defluorination device.

[0089] The second defluorination device is filled with a second defluorination adsorbent which is a selective defluorination resin, and the defluorination functional group of the selective defluorination resin is aminophosphoric acid-supported aluminum (existing product); the method also includes a regeneration process of the second defluorination adsorbent, the regeneration agent is 15-25% concentration aluminum sulfate, and the regeneration time is 30min-120min.

[0090] The two fluorine-containing wastewaters were treated using the methods of Examples 2 and 3, respectively, and the data obtained are shown in the following table:

[0091]

[0092]

Claims

1. A zero-discharge treatment system for fluorine-containing wastewater, characterized in that: The system comprises a water inlet tank, a first defluorination device, a first softening device, a first filtering device, a second defluorination device, a first nanofiltration device, a reverse osmosis device, a pure salt evaporation crystallization device, an ozone reaction device, a second softening device, a second filtering device, a second nanofiltration device, a defluorination agent cleaning and separation device and a miscellaneous salt evaporation crystallization device; The water inlet tank is connected in sequence to the first defluorination device, the first softening device, the first filtering device, the second defluorination device, the first nanofiltration device, the reverse osmosis device, and the pure salt evaporation crystallization device; The concentrated liquid outlet of the first nanofiltration device is connected to the ozone reaction device, the second softening device, the second filtering device, the second nanofiltration device, and the mixed salt evaporation crystallization device in sequence; The water output outlets of the first nanofiltration device and the second nanofiltration device are connected to the water inlet of the reverse osmosis device; The solid product obtained by the ozone reaction device is added to the first defluorination device after being treated by the defluorination agent cleaning and separation device.

2. A zero-discharge treatment system for fluorine-containing wastewater according to claim 1, characterized in that: The first defluorination device comprises a reaction tank and a clarification tank. The reaction tank is provided with a solid-liquid mixing component, which is one of a mechanical agitator and an aeration mixer or a combination of the two. The clarification tank is one of an inclined tube sedimentation tank and an inclined plate sedimentation tank. The second defluorination device is an ion exchange resin.

3. A zero-discharge treatment system for fluorine-containing wastewater according to claim 1, characterized in that: The first softening device and the second softening device are a kind of high-density clarification tank or flocculation sedimentation tank; the first filtration device and the second filtration device are a combination of one or more of multi-media filtration, microfiltration, and ultrafiltration; the first nanofiltration device and the second nanofiltration device are both one-stage and at least one section; the reverse osmosis device includes at least two stages and two sections.

4. A zero-discharge treatment system for fluorine-containing wastewater according to claim 1, characterized in that: The ozone reaction device comprises a reaction zone, an ozone dosing component, a mechanical stirring component, a clarification zone, and a precipitation zone; the ozone dosing component adopts a mechanical mixed dissolved air dosing device or an ejector dosing device, and the generated ozone is dosed inside the reaction zone; the mechanical stirring component is a paddle stirrer, which is arranged in the reaction zone, and the stirring speed is 20-100r / min; the reaction zone is a column or tower reactor; the clarification zone is at the top of the reaction zone, and a trapezoidal weir or a triangular weir is arranged; the precipitation zone is at the bottom of the reaction zone, and the generated inorganic salt defluorination agent crystalline solid is collected.

5. A zero-discharge treatment system for fluorine-containing wastewater according to any one of claims 1 to 4, characterized in that: The wastewater zero discharge system also includes a pre-defluorination device, which is installed after the water inlet tank and before the first defluorination device to pre-defluorinate wastewater with high fluoride ion concentration; the pre-defluorination device is a high-density clarification tank, which adds calcium oxide or calcium chloride to form calcium fluoride precipitation, thereby reducing the fluoride ion concentration to below 50 mg / L.

6. A zero-discharge treatment system for fluorine-containing wastewater according to any one of claims 1 to 4, characterized in that: The system also includes an inlet water online fluoride ion detector, a first online fluoride ion detector and a second online fluoride ion detector, which are respectively installed on the outlet pipe of the water inlet tank, the first defluorination device and the outlet pipe of the second defluorination device.

7. A method for treating wastewater using the zero-discharge treatment system for fluorine-containing wastewater according to any one of claims 1 to 6, characterized in that: The method is: Step 1: First defluorination treatment: Fluorine-containing wastewater enters the first defluorination device from the water inlet tank, an inorganic salt defluoridant is added to the reaction tank of the first defluorination device, and solid-liquid separation of the wastewater is achieved through a clarification tank; Step 2: First softening treatment: the effluent from the first defluorination device enters the first softening device, and a softener is added to the first softening device to reduce the concentration of calcium and magnesium; Step 3: First filtration treatment: The effluent from the first softening device enters the first filtration device, and the effluent from the first softening treatment is finely filtered to deeply remove suspended solid particles; Step 4: Second defluorination treatment: The effluent from the second filtration device enters the second defluorination device to further remove residual fluoride ions to ensure that the fluoride ion concentration of the effluent meets the standard; Step 5: First nanofiltration separation: Separate the monovalent salt and the divalent salt in the wastewater discharged from the second defluorination device to obtain the first nanofiltration product water and the first nanofiltration concentrate; Step 6: Reverse osmosis desalination and concentration: Desalination treatment is performed on the water produced by the first nanofiltration device and the water produced by the second nanofiltration device to obtain product water and reverse osmosis device concentrate; Step 7: Pure salt evaporation and crystallization: Concentrate and crystallize the concentrated liquid of the reverse osmosis device to obtain a sodium chloride salt product; Step 8: Ozone oxidation and clarification treatment: The ozone reaction device performs ozone oxidation and clarification treatment on the concentrated liquid of the first nanofiltration device to obtain ozone oxidation effluent and inorganic salt defluorination agent; Step 9: Second softening treatment: Soften and clarify the effluent from the ozone reaction device to further remove calcium and magnesium ions; Step 10: Second filtration treatment: fine filtration of the water effluent from the second softening device; Step 11: Second nanofiltration treatment: further concentrate and reduce the effluent from the second filtration device, further separate the sodium chloride therein, improve the resource utilization rate of sodium chloride, reduce the amount of water to be processed by the impurity salt evaporation and crystallization device, and obtain the second nanofiltration device produced water and the second device nanofiltration concentrate; Step 12: Evaporation treatment of impure salts: concentrating and crystallizing the concentrated liquid from the second nanofiltration device to obtain impure salt solid waste.

8. A zero-discharge treatment method for fluorine-containing wastewater according to claim 7, characterized in that: In step one, the solid content of the inorganic salt defluoridant in the first defluoridation device is 1%-5%; the residence time of the first defluoridation device is 0.5h-3h; the first nanofiltration device and the second nanofiltration device are added with organic antiscalant, and the dosage of the antiscalant is 0.5-5mg / L; the first nanofiltration treatment and the second nanofiltration treatment are both one-stage and at least one-stage; the reverse osmosis treatment process includes at least two-stage treatment and two-stage treatment.

9. A zero-discharge treatment method for fluorine-containing wastewater according to claim 7, characterized in that: The first softening device and the second softening device are added with softening agents selected from the group consisting of calcium oxide, calcium hydroxide, sodium carbonate, sodium hydroxide, polyferric chloride, polyaluminium chloride, ferric chloride, aluminium chloride, ferric sulfate, aluminium sulfate and polyacrylamide; the pre-defluorination device is added with one or more selected from the group consisting of calcium chloride, calcium oxide, calcium hydroxide, aluminium sulfate and polyaluminium and polyferric.

10. A zero-discharge treatment method for fluorine-containing wastewater according to claim 7, characterized in that: The second defluorination device is filled with a selective defluorination resin, and the defluorination functional group of the selective defluorination resin is aminophosphoric acid-supported aluminum.

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