Fluorine-containing wastewater treatment method and system

Abstract

The invention discloses a fluorine-containing wastewater treatment method and system, and belongs to the technical field of water treatment. According to the invention, a high-adsorption-capacity double-metal hydroxide defluorination adsorbent (an agent added in a reaction tank) is used for defluorination treatment, and an aluminum flocculant is used for assisting in solid-liquid separation of the adsorbent and strengthening removal of fluorine ions at the same time; through sludge circulation of the clarification tank, aluminum hydroxide formed by the defluorination adsorbent and the aluminum flocculant which do not reach adsorption saturation is circulated to the reaction tank for defluorination treatment again, and the adsorption capacity of the adsorbent is utilized to the maximum extent. The two-stage defluorination treatment can effectively cope with the following different application scenes: the two-stage defluorination treatment needs to be carried out at the same time so as to achieve a stable and standard water outlet effect; when the effluent of the first-stage defluorination unit meets the requirement, the second-stage defluorination unit can be skipped, so that the loss and the power consumption of a second-stage defluorination adsorbent are reduced; when the first-stage defluorination unit is saturated in adsorption, a recovery mode is started, and the second-stage defluorination unit is matched to ensure that the effluent reaches the standard.

Description

Technical Field

[0001] The invention belongs to the technical field of water treatment, and specifically relates to a method and system for treating 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. In recent years, new adsorbents such as hydroxyapatite and zirconium oxide have attracted attention due to their high adsorption capacity.

[0006] The ion exchange method uses materials such as ion exchange resins 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.

[0007] For wastewater with high fluoride content, the fluoride ion concentration is usually reduced to about 10-15 mg / L through chemical precipitation and coagulation precipitation, and then deep defluorination treatment is carried out through adsorption or ion exchange to control the fluoride ion concentration below 1 mg / L. However, the material cost and regeneration cost of adsorbents and ion exchange resins are high.

[0008] CN118307090B discloses a system and method for deep defluorination of wastewater, which uses a fluoride ion exchange column of calcium fluoride chemical precipitation and zirconium resin to perform two-stage defluorination treatment. The secondary deep treatment uses a zirconium-loaded resin. Although the removal effect is good and the effluent water quality is relatively stable, the resin cost and regeneration cost are high. CN105688865B discloses a biosorbent obtained by ball-milling and modifying tea residues, and its preparation method and application, and the tea residues are modified and applied in defluorination. Although the tea residue raw material is a waste utilization, the adsorption capacity is low and frequent regeneration is required. CN117510888B discloses an adsorption-assisted defluorination polymer material, and its preparation method and application, in which a defluorination polymer material containing an organic rare earth material is added to the wastewater, and then solid-liquid separation is completed by a flocculation and clarification method. However, the defluorination material is difficult to recover and the operating cost is high. Summary of the invention

[0009] The purpose of the present invention is to solve the problem of defluorination of wastewater and to provide a method and system for treating fluorine-containing wastewater.

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

[0011] A fluorine-containing wastewater treatment system, the system comprising a water inlet tank, a primary defluorination unit, a secondary defluorination unit, a dosing unit, an online monitoring unit, a collection water tank, and an emergency water tank;

[0012] The primary defluorination unit comprises a reaction tank, a flocculation clarification tank, a sludge concentration tank, a sludge dewatering machine and a multi-media filter; the reaction tank is equipped with a stirring device with a residence time of 0.5-2h; the water inlet tank is connected to the reaction tank, the flocculation clarification tank and the multi-media filter in sequence;

[0013] The flocculation clarification tank includes a flocculation tank and a clarification tank, equipped with a 50-80r / min low-speed mechanical agitator, and the clarification tank is equipped with an inclined tube (the inclined tube is placed on the upper layer of the clarification tank, and the inclined tube is at an angle of 60° to the horizontal plane to assist in accelerating the sedimentation of the precipitate); the flocculation clarification tank is connected to the sludge thickening tank and the sludge dewatering machine in sequence;

[0014] The secondary defluorination unit includes a second defluorination device; the second defluorination device is equipped with a selective defluorination resin, the amount of which is determined according to the size of the device, and its outlet water is connected to a collection water tank and an accident water tank respectively;

[0015] The dosing unit comprises a dosing device 1 and a dosing device 2, wherein the dosing device 1 comprises a first dosing water tank and a first dosing pump, and the dosing device 2 comprises a second dosing water tank and a second dosing pump; the reagent in the first dosing water tank is added to the reaction tank through the first dosing pump; the reagent in the second dosing water tank is added to the flocculation tank of the flocculation clarification tank through the second dosing pump; the first dosing water tank and the second dosing water tank are equipped with agitators;

[0016] The online monitoring unit includes a primary water outlet online detector and a secondary water outlet online detector. The primary water outlet online detector is used to detect the water outlet of the multi-media filter, and the secondary water outlet online detector is used to detect the water outlet of the second defluorination device. The online detector is a fluoride ion online detector, which is an ion selective electrode detector or an ion chromatograph analyzer.

[0017] A method for treating wastewater using the above-mentioned fluorine-containing wastewater treatment system comprises the following steps:

[0018] Step 1: Send the wastewater to be treated from the water inlet tank into the reaction tank for primary defluorination treatment. When the solid content of the reaction tank is less than 3%, add the first defluorination adsorbent to the reaction tank. When the solid content of the reaction tank is greater than 3%, stop adding the adsorbent.

[0019] Step 2: The effluent from the reaction tank is sent to the flocculation clarification tank for solid-liquid separation. Aluminum flocculants are added to the flocculation tank, and the sludge from the clarification tank is returned to the reaction tank. The solid content of the reaction tank is controlled to be 1-3%. When the solid content of the reaction tank exceeds 3%, the sludge from the clarification tank is sent to the sludge concentration tank for further concentration and then to the sludge dewatering machine for dehydration treatment; the effluent from the sludge dewatering machine can be returned to the reaction tank for further treatment;

[0020] Step 3: Send the effluent from the flocculation clarification tank to a multi-media filter for deep solid-liquid separation treatment;

[0021] Step 4: Detect the fluoride ion concentration of the effluent from the multi-media filter. The fluoride ion concentration at the initial stage of the system operation is recorded as C10, and the current fluoride ion concentration of the system is recorded as C1t. If (C1t-C10) / C10>25%, enter the recovery mode of the first defluorination unit, that is, stop the sludge return from the flocculation clarification tank, and start the dosing device 1; if the fluoride ion concentration is less than 0.5ppm, send the effluent from the multi-media filter to the collection water tank, and do not start the second defluorination device at this time; if the fluoride ion concentration of the effluent from the multi-media is greater than 0.5ppm, send the effluent from the multi-media to the second defluorination device;

[0022] Step 5: Defluorination is carried out through the second defluorination device, and the effluent from the second defluorination device is tested for fluoride ions. If the fluoride ion concentration of the effluent is >0.5ppm, the effluent from the second defluorination device is sent to the accident water tank and then to the water inlet tank.

[0023] Furthermore, in step 1, the preparation method of the first defluorination adsorbent is:

[0024] (1) preparing a mixture 1 of 0.2-0.3 M aluminum salt, 0.7-0.8 M magnesium salt and 0.1-0.2 M background salt with fresh distilled water; preparing a 1.5-2 M alkaline mixture 2 with fresh distilled water;

[0025] (2) maintaining the temperature of the mixed solution 1 at 65-75° C. by heating in a water bath and maintaining high-speed stirring, adding the mixed solution 2 to the mixed solution 1, controlling the pH at 11-12 by controlling the dosing speed, and reacting for 24 hours;

[0026] (3) centrifuging and washing the obtained precipitate for multiple times until the conductivity of the centrifugal supernatant is less than 500 μS / cm, thereby obtaining a washed precipitate;

[0027] (4) The washed precipitate is vacuum dried and then calcined at 400-450° C. for 2-3 hours to obtain a first defluorination adsorbent.

[0028] Furthermore, in step (1), the aluminum salt includes one of aluminum sulfate, polyaluminum chloride or potassium aluminum sulfate dodecahydrate; the magnesium salt includes one of magnesium chloride, magnesium nitrate or magnesium sulfate; the background salt is sodium chloride or sodium sulfate; and the solute of the alkaline mixed solution is a mixture of any two of sodium hydroxide, calcium hydroxide or magnesium hydroxide.

[0029] Furthermore, in step 2, the aluminum flocculant includes one or more of aluminum chloride, aluminum sulfate, polyaluminum sulfate, polyaluminum chloride, and sodium aluminate, and the dosage is 5-50 ppm.

[0030] Furthermore, in step 2, the wastewater retention time in the flocculation tank is 0.5-1h, and the wastewater retention time in the clarification tank is 0.5-4h.

[0031] Furthermore, in step three, the filter media of the multi-media filter are quartz sand and anthracite, which are used for deep filtration.

[0032] Furthermore, the volume ratio of quartz sand to anthracite is 2-4:1, with quartz sand at the lower layer and anthracite at the upper layer.

[0033] Furthermore, the treatment method also includes, before step 1, adding an acid-base regulator to the reaction tank to control the pH of the reaction tank to be 6-8.

[0034] Furthermore, the method also includes a first defluorination adsorbent regeneration and reuse step, specifically: (1) soaking the dehydrated sludge obtained by the sludge dewatering machine in an alkali with a pH of 12-14 for 24-48 hours; (2) performing solid-liquid separation and clean water washing on the suspension after the alkali soaking, and the solid-liquid separation method includes filtration, sedimentation, and centrifugation; (3) repeating (2) until the pH of the solid-liquid separation supernatant is 7-8.

[0035] The beneficial effects of the present invention compared to the prior art are:

[0036] (1) The present invention achieves a stable defluorination effect by performing two-stage defluorination treatment using high-performance double metal hydroxides and selective defluorination resins. The first stage uses double metal hydroxide defluorination adsorbents coupled with aluminum-based agents to enhance defluorination while achieving solid-liquid separation in the clarification tank, and maximizes the utilization rate of the defluorination agent through sludge circulation in the sedimentation tank.

[0037] (2) The two-stage defluorination treatment of the present invention can effectively cope with the following different application scenarios: two-stage defluorination needs to be operated simultaneously to achieve a stable effluent effect that meets the standards; when the effluent of the first-stage defluorination unit alone meets the requirements, the second-stage defluorination unit can be skipped to reduce the loss and power consumption of the second-stage defluorination adsorbent; when the first-stage defluorination unit is saturated with adsorption, it enters the recovery mode and cooperates with the second-stage defluorination unit to ensure that the effluent meets the standards.

[0038] (3) The first-stage defluorination device reaction tank maintains a high solid content, high fluorine adsorption efficiency, and maximizes the adsorption capacity of the defluorination adsorbent through sludge return; the time point of adsorbent saturation is quickly identified through online fluoride ion detection. The solid content is the sludge content formed by the first defluorination adsorbent and the aluminum flocculant. The first defluorination adsorbent adsorbs fluoride ions in the wastewater, and then forms sludge under the action of the aluminum flocculant. After cleaning, it is converted back into the first defluorination adsorbent and returned to the first-stage defluorination device reaction tank.

[0039] (4) The aluminum-based flocculant added to the flocculation and clarification tank can produce a synergistic effect with the first defluorination adsorbent. First, in the flocculation tank of the flocculation and clarification tank, the precipitation process of the aluminum-based coagulant can enhance the defluorination effect. In addition, the aluminum-based flocculant precipitate is returned to the reaction tank together with the first defluorination adsorbent, which can enhance the defluorination effect of the reaction tank.

[0040] (5) The solution has a high degree of automation, simple operation, and stable water output effect.

[0041] (6) The defluorination adsorbent has a high specific surface area and good adsorption performance, and can be regenerated and reused through this solution, reducing the cost of purchasing consumables. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 It is a system block diagram of the present invention.

[0043] Figure 2 This is the flow chart of the regeneration and reuse of the first defluorination adsorbent.

[0044] Figure 3 It is the sewage treatment flow chart of the present invention.

[0045] Figure 4 This is a flow chart for preparing the first defluorination adsorbent. DETAILED DESCRIPTION

[0046] 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.

[0047] When the present invention detects that the primary defluorination unit has a tendency of fluoride ion penetration (rising), the defluorination adsorbent regeneration mode (reaction tank regeneration) is switched, and the saturated adsorbent is continuously removed from the system while the regenerated or fresh adsorbent is supplemented. After the effluent of the primary defluorination unit reaches a preset value, the reaction tank production mode is restored.

[0048] The present invention utilizes a high adsorption capacity double metal hydroxide defluorination adsorbent (agent added to the reaction tank) for defluorination treatment, and utilizes an aluminum-based flocculant to assist the solid-liquid separation of the adsorbent while strengthening the removal of fluoride ions; through the circulation of clarification tank sludge, the defluorination adsorbent that has not reached adsorption saturation and the aluminum-based flocculant formed by the aluminum-based hydroxide are circulated to the reaction tank for re-defluorination treatment, thereby maximizing the utilization of the adsorption capacity of the adsorbent. A two-stage linkage defluorination treatment method, with the primary defluorination as the main defluorination unit and the secondary defluorination as the protection unit. Through online fluoride ion monitoring, after identifying that the primary defluorination unit has reached adsorption saturation, the primary defluorination unit enters the recovery mode, and the secondary defluorination unit ensures that the effluent meets the standard without the need for shutdown treatment. The dehydrated sludge is subjected to fluoride ion desorption and regeneration treatment to realize the reuse of the discarded adsorbent. The primary defluorination device maximizes the utilization rate of the defluorination agent adsorption capacity through sludge reflux, and the effluent fluoride ion concentration detection quickly identifies adsorption saturation and replaces the adsorbent in time; at the same time, the adsorbent can be recovered, regenerated and reused.

[0049] Embodiment 1:

[0050] A fluorine-containing wastewater treatment system, the system comprising a water inlet tank, a primary defluorination unit, a secondary defluorination unit, a dosing unit, an online monitoring unit, a collection water tank, and an emergency water tank;

[0051] The primary defluorination unit comprises a reaction tank, a flocculation clarification tank, a sludge concentration tank, a sludge dewatering machine and a multi-media filter; the reaction tank is equipped with a stirring device with a residence time of 0.5-2h; the water inlet tank is connected to the reaction tank, the flocculation clarification tank and the multi-media filter in sequence;

[0052] The flocculation clarification tank includes a flocculation tank and a clarification tank, equipped with a 50-80r / min low-speed mechanical agitator, and the clarification tank is equipped with an inclined tube (the inclined tube is placed on the upper layer of the clarification tank, and the inclined tube is at an angle of 60° to the horizontal plane to assist in accelerating the sedimentation of the precipitate); the flocculation clarification tank is connected to the sludge thickening tank and the sludge dewatering machine in sequence;

[0053] The secondary defluorination unit includes a second defluorination device; the second defluorination device is equipped with a selective defluorination resin, the amount of which is determined according to the size of the device, and its outlet water is connected to a collection water tank and an accident water tank respectively;

[0054] The dosing unit comprises a dosing device 1 and a dosing device 2, wherein the dosing device 1 comprises a first dosing water tank and a first dosing pump, and the dosing device 2 comprises a second dosing water tank and a second dosing pump; the reagent in the first dosing water tank is added to the reaction tank through the first dosing pump; the reagent in the second dosing water tank is added to the flocculation tank of the flocculation clarification tank through the second dosing pump; the first dosing water tank and the second dosing water tank are equipped with agitators;

[0055] The online monitoring unit includes a primary water outlet online detector and a secondary water outlet online detector. The primary water outlet online detector is used to detect the water outlet of the multi-media filter, and the secondary water outlet online detector is used to detect the water outlet of the second defluorination device. The online detector is a fluoride ion online detector, which is an ion selective electrode detector or an ion chromatograph analyzer.

[0056] Embodiment 2:

[0057] The method for treating photovoltaic enterprise production wastewater using the fluorine-containing wastewater treatment system of the above-mentioned embodiment 1 comprises the following steps:

[0058] Step 1: Send the wastewater to be treated from the water inlet tank into the reaction tank for primary defluorination treatment. When the solid content of the reaction tank is less than 3%, add the first defluorination adsorbent to the reaction tank. When the solid content of the reaction tank is greater than 3%, stop adding the adsorbent.

[0059] Step 2: The effluent from the reaction tank is sent to the flocculation clarification tank for solid-liquid separation. Aluminum flocculants are added to the flocculation tank, and the sludge from the clarification tank is returned to the reaction tank. The solid content of the reaction tank is controlled to be 3%. When the solid content of the reaction tank exceeds 3%, the sludge from the clarification tank is sent to the sludge concentration tank for further concentration and then to the sludge dewatering machine for dehydration treatment; the effluent from the sludge dewatering machine can be returned to the reaction tank for further treatment;

[0060] Step 3: Send the effluent from the flocculation clarification tank to a multi-media filter for deep solid-liquid separation treatment;

[0061] Step 4: Detect the fluoride ion concentration of the effluent from the multi-media filter. The fluoride ion concentration at the initial stage of the system operation is recorded as C10, and the current fluoride ion concentration of the system is recorded as C1t. If (C1t-C10) / C10>25%, enter the recovery mode of the first defluorination unit, that is, stop the sludge return from the flocculation clarification tank, and start the dosing device 1; if the fluoride ion concentration is less than 0.5ppm, send the effluent from the multi-media filter to the collection water tank, and do not start the second defluorination device at this time; if the fluoride ion concentration of the effluent from the multi-media is greater than 0.5ppm, send the effluent from the multi-media to the second defluorination device;

[0062] Step 5: Defluorination is carried out through the second defluorination device, and the effluent from the second defluorination device is tested for fluoride ions. If the fluoride ion concentration of the effluent is >0.5ppm, the effluent from the second defluorination device is sent to the accident water tank and then to the water inlet tank.

[0063] In step 1, the preparation method of the first defluorination adsorbent is:

[0064] (1) preparing a mixture 1 of 0.2 M aluminum salt, 0.7 M magnesium salt and 0.1 M background salt with fresh distilled water; preparing a 1.5 M alkaline mixture 2 with fresh distilled water;

[0065] (2) maintaining the temperature of the mixed solution 1 at 65° C. by heating in a water bath and maintaining high-speed stirring, adding the mixed solution 2 to the mixed solution 1, controlling the pH at 11-12 by controlling the dosing speed, and reacting for 24 hours;

[0066] (3) centrifuging and washing the obtained precipitate for multiple times until the conductivity of the centrifugal supernatant is less than 500 μS / cm, thereby obtaining a washed precipitate;

[0067] (4) The washed precipitate is vacuum dried and then calcined at 400° C. for 2-3 hours to obtain a first defluorination adsorbent.

[0068] In step (1), the aluminum salt includes aluminum sulfate; the magnesium salt includes magnesium chloride; the background salt is sodium chloride; and the solutes of the alkaline mixed solution are sodium hydroxide and calcium hydroxide.

[0069] In step 2, the aluminum-based flocculants include aluminum chloride and aluminum sulfate, and the dosage is 25 ppm.

[0070] In step 2, the wastewater retention time in the flocculation tank is 0.5 h, and the wastewater retention time in the clarification tank is 0.5 h.

[0071] In step three, the filter media of the multi-media filter are quartz sand and anthracite, which are used for deep filtration.

[0072] The volume ratio of quartz sand and anthracite is 2:1, with quartz sand at the bottom and anthracite at the top.

[0073] The treatment method further comprises, before step 1, adding an acid-base regulator to the reaction tank to control the pH of the reaction tank to be 6-8.

[0074] The method also includes a first defluorination adsorbent regeneration and reuse step, specifically: (1) soaking the dehydrated sludge obtained by the sludge dewatering machine in an alkali with a pH of 12-14 for 24-48 hours; (2) performing solid-liquid separation and clean water washing on the suspension after the alkali soaking, and the solid-liquid separation method includes filtration, precipitation, and centrifugation; (3) repeating (2) until the pH of the solid-liquid separation supernatant is 7-8.

[0075] Embodiment 3:

[0076] The method for treating photovoltaic enterprise production wastewater using the fluorine-containing wastewater treatment system of the above-mentioned embodiment 1 comprises the following steps:

[0077] Step 1: Send the wastewater to be treated from the water inlet tank into the reaction tank for primary defluorination treatment. When the solid content of the reaction tank is less than 3%, add the first defluorination adsorbent to the reaction tank. When the solid content of the reaction tank is greater than 3%, stop adding the adsorbent.

[0078] Step 2: The effluent from the reaction tank is sent to the flocculation clarification tank for solid-liquid separation. Aluminum flocculants are added to the flocculation tank, and the sludge from the clarification tank is returned to the reaction tank. The solid content of the reaction tank is controlled to be 3%. When the solid content of the reaction tank exceeds 3%, the sludge from the clarification tank is sent to the sludge concentration tank for further concentration and then to the sludge dewatering machine for dehydration treatment; the effluent from the sludge dewatering machine can be returned to the reaction tank for further treatment;

[0079] Step 3: Send the effluent from the flocculation clarification tank to a multi-media filter for deep solid-liquid separation treatment;

[0080] Step 4: Detect the fluoride ion concentration of the effluent from the multi-media filter. The fluoride ion concentration at the initial stage of the system operation is recorded as C10, and the current fluoride ion concentration of the system is recorded as C1t. If (C1t-C10) / C10>25%, enter the recovery mode of the first defluorination unit, that is, stop the sludge return from the flocculation clarification tank, and start the dosing device 1; if the fluoride ion concentration is less than 0.5ppm, send the effluent from the multi-media filter to the collection water tank, and do not start the second defluorination device at this time; if the fluoride ion concentration of the effluent from the multi-media is greater than 0.5ppm, send the effluent from the multi-media to the second defluorination device;

[0081] Step 5: Defluorination is carried out through the second defluorination device, and the effluent from the second defluorination device is tested for fluoride ions. If the fluoride ion concentration of the effluent is >0.5ppm, the effluent from the second defluorination device is sent to the accident water tank and then to the water inlet tank.

[0082] In step 1, the preparation method of the first defluorination adsorbent is:

[0083] (1) preparing a mixture 1 of 0.3 M aluminum salt, 0.8 M magnesium salt and 0.2 M background salt with fresh distilled water; preparing a 2 M alkaline mixture 2 with fresh distilled water;

[0084] (2) maintaining the temperature of the mixed solution 1 at 75° C. by heating in a water bath and maintaining high-speed stirring, adding the mixed solution 2 to the mixed solution 1, controlling the pH at 11-12 by controlling the dosing speed, and reacting for 24 hours;

[0085] (3) centrifuging and washing the obtained precipitate for multiple times until the conductivity of the centrifugal supernatant is less than 500 μS / cm, thereby obtaining a washed precipitate;

[0086] (4) The washed precipitate is vacuum dried and then calcined at 450° C. for 2-3 hours to obtain a first defluorination adsorbent.

[0087] In step (1), the aluminum salt includes aluminum sulfate; the magnesium salt includes magnesium chloride; the background salt is sodium chloride; and the solutes of the alkaline mixed solution are sodium hydroxide and calcium hydroxide.

[0088] In step 2, the aluminum-based flocculants include aluminum chloride and aluminum sulfate, and the dosage is 25 ppm.

[0089] In step 2, the wastewater retention time in the flocculation tank is 0.5-1h, and the wastewater retention time in the clarification tank is 3h.

[0090] In step three, the filter media of the multi-media filter are quartz sand and anthracite, which are used for deep filtration.

[0091] The volume ratio of quartz sand and anthracite is 2-4:1, with quartz sand at the bottom and anthracite at the top.

[0092] The treatment method further comprises, before step 1, adding an acid-base regulator to the reaction tank to control the pH of the reaction tank to be 6-8.

[0093] The method also includes a first defluorination adsorbent regeneration and reuse step, specifically: (1) soaking the dehydrated sludge obtained by the sludge dewatering machine in an alkali with a pH of 12-14 for 24-48 hours; (2) performing solid-liquid separation and clean water washing on the suspension after the alkali soaking, and the solid-liquid separation method includes filtration, precipitation, and centrifugation; (3) repeating (2) until the pH of the solid-liquid separation supernatant is 7-8.

[0094] Comparative Example 1:

[0095] The present invention is different from Example 2 in that the first defluorination adsorbent and aluminum flocculant are not added, but lime is added to the reaction tank to remove fluorine. The fluoride ion exceeds 20 mg / L and the addition amount is 1200 mg / L. The other steps are the same as Example 2.

[0096] Comparative Example 2:

[0097] The present invention is different from Example 3 in that the first defluorination adsorbent and the aluminum flocculant are not added, but magnesium salt is added to the reaction tank, and the amount of magnesium salt added is 850 mg / L. The other steps are the same as Example 3.

[0098] The two fluorine-containing wastewaters were treated using the methods of Examples 2 and 3 and Comparative Examples 1 and 2, respectively, and the data obtained are shown in the following table:

[0099]

[0100]

Claims

1. A fluorine-containing wastewater treatment system, characterized in that: The system includes a water inlet tank, a primary defluorination unit, a secondary defluorination unit, a dosing unit, an online monitoring unit, a collection water tank, and an emergency water tank; The primary defluorination unit comprises a reaction tank, a flocculation clarification tank, a sludge concentration tank, a sludge dewatering machine and a multi-media filter; the water inlet tank is connected to the reaction tank, the flocculation clarification tank and the multi-media filter in sequence; The flocculation clarification tank includes a flocculation tank and a clarification tank, which is equipped with a 50-80r / min low-speed mechanical agitator, and the clarification tank is equipped with an inclined tube; the flocculation clarification tank is connected to the sludge thickening tank and the sludge dewatering machine in sequence; The secondary defluorination unit comprises a second defluorination device; the second defluorination device is equipped with a selective defluorination resin, and its outlet water is connected to a collection water tank and an emergency water tank respectively; The dosing unit comprises a dosing device 1 and a dosing device 2, wherein the dosing device 1 comprises a first dosing water tank and a first dosing pump, and the dosing device 2 comprises a second dosing water tank and a second dosing pump; the first dosing pump is used to add the reagent in the first dosing water tank to the reaction tank; the second dosing pump is used to add the reagent in the second dosing water tank to the flocculation tank of the flocculation clarification tank; The online monitoring unit includes a primary water outlet online detector and a secondary water outlet online detector. The primary water outlet online detector is used to detect the water outlet of the multi-media filter, and the secondary water outlet online detector is used to detect the water outlet of the second defluorination device.

2. A method for treating wastewater using the fluorine-containing wastewater treatment system according to claim 1, characterized in that: The steps include: Step 1: Send the wastewater to be treated from the water inlet tank into the reaction tank for primary defluorination treatment. When the solid content of the reaction tank is less than 3%, add the first defluorination adsorbent to the reaction tank. When the solid content of the reaction tank is greater than 3%, stop adding the adsorbent. Step 2: The effluent from the reaction tank is sent to a flocculation clarification tank for solid-liquid separation. Aluminum flocculants are added to the flocculation tank, and the sludge from the clarification tank is returned to the reaction tank. The solid content of the reaction tank is controlled to be 1-3%. When the solid content of the reaction tank exceeds 3%, the sludge from the clarification tank is sent to a sludge thickening tank for further concentration and then to a sludge dewatering machine for dehydration. The effluent from the sludge dewatering machine can be returned to the reaction tank for further treatment; Step 3: Send the effluent from the flocculation clarification tank to a multi-media filter for deep solid-liquid separation treatment; Step 4: Detect the fluoride ion concentration of the effluent from the multi-media filter. The fluoride ion concentration at the initial stage of the system operation is recorded as C10, and the current fluoride ion concentration of the system is recorded as C1t. If (C1t-C10) / C10>25%, enter the recovery mode of the first defluorination unit, that is, stop the sludge return from the flocculation clarification tank, and start the dosing device 1; if the fluoride ion concentration is less than 0.5ppm, send the effluent from the multi-media filter to the collection water tank; if the fluoride ion concentration of the effluent from the multi-media is greater than 0.5ppm, send the effluent from the multi-media to the second defluorination device; Step 5: Defluorination is carried out through the second defluorination device, and the effluent from the second defluorination device is tested for fluoride ions. If the fluoride ion concentration of the effluent is >0.5ppm, the effluent from the second defluorination device is sent to the accident water tank and then to the water inlet tank.

3. A method for treating fluorine-containing wastewater according to claim 2, characterized in that: In step 1, the preparation method of the first defluorination adsorbent is: (1) preparing a mixture 1 of 0.2-0.3 M aluminum salt, 0.7-0.8 M magnesium salt and 0.1-0.2 M background salt with fresh distilled water; preparing a 1.5-2 M alkaline mixture 2 with fresh distilled water; (2) maintaining the temperature of the mixed solution 1 at 65-75° C. by heating in a water bath and maintaining high-speed stirring, adding the mixed solution 2 to the mixed solution 1, controlling the pH at 11-12 by controlling the dosing speed, and reacting for 24 hours; (3) centrifuging and washing the obtained precipitate for multiple times until the conductivity of the centrifugal supernatant is less than 500 μS / cm, thereby obtaining a washed precipitate; (4) The washed precipitate is vacuum dried and then calcined at 400-450° C. for 2-3 hours to obtain a first defluorination adsorbent.

4. A method for treating fluorine-containing wastewater according to claim 3, characterized in that: In step (1), the aluminum salt includes one of aluminum sulfate, polyaluminum chloride or potassium aluminum sulfate dodecahydrate; the magnesium salt includes one of magnesium chloride, magnesium nitrate or magnesium sulfate; the background salt is sodium chloride or sodium sulfate; and the solute of the alkaline mixed solution is a mixed solution of any two of sodium hydroxide, calcium hydroxide or magnesium hydroxide.

5. A method for treating fluorine-containing wastewater according to claim 2, characterized in that: In step 2, the aluminum flocculant includes one or more of aluminum chloride, aluminum sulfate, polyaluminum sulfate, polyaluminum chloride, and sodium aluminate, and the dosage is 5-50 ppm.

6. A method for treating fluorine-containing wastewater according to claim 2, characterized in that: In step 2, the wastewater retention time in the flocculation tank is 0.5-1h, and the wastewater retention time in the clarification tank is 0.5-4h.

7. A method for treating fluorine-containing wastewater according to claim 2, characterized in that: In step three, the filter media of the multi-media filter are quartz sand and anthracite.

8. A method for treating fluorine-containing wastewater according to claim 7, characterized in that: The volume ratio of quartz sand and anthracite is 2-4:1, with quartz sand at the bottom and anthracite at the top.

9. A method for treating fluorine-containing wastewater according to any one of claims 2 to 8, characterized in that: The treatment method further comprises, before step 1, adding an acid-base regulator to the reaction tank to control the pH of the reaction tank to be 6-8.

10. A method for treating fluorine-containing wastewater according to claim 2, characterized in that: The method also includes a first defluorination adsorbent regeneration and reuse step, specifically: (1) soaking the dehydrated sludge obtained by the sludge dewatering machine in an alkali with a pH of 12-14 for 24-48 hours; (2) performing solid-liquid separation and clean water washing on the suspension after the alkali soaking, and the solid-liquid separation method includes filtration, precipitation, and centrifugation; (3) repeating (2) until the pH of the solid-liquid separation supernatant is 7-8.

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