Method for treating and recycling fluorine-containing wastewater

Abstract

The invention belongs to the technical field of fluorine-containing wastewater treatment, and discloses a fluorine-containing wastewater treatment and reuse method which comprises the following steps: (1) adding chemicals into fluorine-containing wastewater to remove fluorine; (2) carrying out suspended matter removal treatment on the wastewater treated in the step (1) by adopting a roll type ultrafiltration unit; (3) carrying out desalination treatment on the ultrafiltration produced water treated in the step (2) by adopting a primary reverse osmosis unit; (4) carrying out further desalination treatment on the primary reverse osmosis produced water treated in the step (3) by adopting a secondary reverse osmosis unit to obtain secondary reverse osmosis produced water; secondary reverse osmosis produced water is recycled to the chemical water replenishing unit. According to the method disclosed by the invention, the wastewater can be recycled, the discharge of the wastewater is reduced, the advanced treatment and reuse of the wastewater are realized, and the utilization value of the wastewater is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of treatment of fluorine-containing wastewater, and more specifically, to a method for treating and reusing fluorine-containing wastewater. Background Art

[0002] Fluoride-containing wastewater is widely present in industrial production, such as the smelting of non-ferrous metals and rare earth metals, aluminum electrolytic refining, stainless steel pickling and other traditional industries. A large amount of fluoride-containing wastewater is also discharged in modern chemical industrial production such as the petrochemical industry, coal chemical industry, atomic energy industry, and electronics industry. Direct discharge of fluoride-containing wastewater without treatment or discharge that does not meet treatment standards will seriously pollute the environment and pose a serious threat to human health.

[0003] The main pollutant of fluoride-containing wastewater is fluorine, which usually exists in the form of hydrofluoric acid and fluorosilicic acid. Usually, depending on the production process, the wastewater also contains other pollutants such as inorganic salts or organic matter. There are many studies on fluoride-containing wastewater in China, mainly analyzing and discussing the graded treatment of fluoride-containing wastewater, sludge recycling co-precipitation, and the combined application of reagents.

[0004] Production enterprises generally use sedimentation treatment to treat fluoride-containing wastewater, initially reduce the content of fluoride ions in the wastewater, and then discharge it through dilution treatment, without effective comprehensive utilization. Therefore, the development of efficient fluoride-containing wastewater treatment and reuse technology is of great significance in industrial water treatment. At present, common defluorination methods include: chemical defluorination, resin defluorination and flocculation process defluorination, but due to the different wastewater systems, there is no unified standard for the use of defluorination technology. In the defluorination process, due to strict control parameters and difficult operation, the treatment effect is unstable, which affects the further recycling of wastewater.

[0005] At present, the existing fluorine removal technologies can be divided into two categories in principle. One is through precipitation, that is, the fluorine removal agent forms an ionic bond with the fluorine ions in the wastewater to generate a substance with a small solubility product, such as calcium salt or magnesium salt used to precipitate fluorine ions; the other is through adsorption, such as using alumina, bone char or resin as a fluorine removal agent. This type of fluorine removal agent is solid, and it adsorbs fluorine ions on the solid of the above fluorine removal agent through the attraction between anions and cations, thereby reducing the concentration of fluorine ions in the water. The problem with the first type of precipitation method is that it is currently difficult to find a precipitant with high cost performance to achieve deep fluorine removal while having a low cost. Although traditional calcium salts or magnesium salts are cheap, their solubility product is not small enough to meet the requirements of deep fluorine removal. The problem with the second type of adsorption method is that although most of them can achieve deep fluorine removal, they face many problems in the field of wastewater treatment, such as wastewater pretreatment, treatment cost, and treatment of resin regeneration liquid. The regeneration of adsorbent materials and the treatment of wastewater after regeneration are also issues. Moreover, the number of times that adsorbent materials can be regenerated is limited, usually no more than a few dozen times. Therefore, in actual use, not only is the investment cost high, but the defluorination process is also complicated. Therefore, it is necessary to seek an effective, cheap, and simple defluorination method to provide technical support for the subsequent recycling of wastewater. Summary of the invention

[0006] The purpose of the present invention is to provide a method for treating and reusing fluorine-containing wastewater in view of the defects in the prior art.

[0007] In order to achieve the above object, the present invention provides a method for treating and reusing fluorine-containing wastewater, which comprises:

[0008] (1) Treat fluoride-containing wastewater by adding chemicals to remove fluoride;

[0009] (2) using a roll-type ultrafiltration unit to remove suspended solids from the wastewater treated in step (1);

[0010] (3) using a primary reverse osmosis unit to desalinate the ultrafiltration water after the treatment in step (2);

[0011] (4) further desalting the primary reverse osmosis water after the treatment in step (3) using a secondary reverse osmosis unit to obtain secondary reverse osmosis water; the secondary reverse osmosis water is recycled to the chemical water replenishment unit.

[0012] Compared with the prior art, the present invention has the following advantages:

[0013] 1. The defluorination agent of the present invention is used to defluorinate wastewater, and a roll-type ultrafiltration unit is used as a solid-liquid separation method, so that the fluoride ion in the influent is less than 500 mg / L and the fluoride ion in the effluent is less than 5 mg / L after treatment.

[0014] 2. The present invention adopts the process of adding defluorinating agent + rolled ultrafiltration membrane + two-stage reverse osmosis, which can effectively treat fluorine-containing wastewater. At the same time, the wastewater is treated by the rolled ultrafiltration membrane + reverse osmosis membrane process, which can recycle the wastewater, reduce the discharge of wastewater, realize the deep treatment and reuse of wastewater, and improve the utilization value of wastewater.

[0015] 3. Compared with the prior art, the technical equipment involved in the present invention is easy to operate and maintain, has strong environmental adaptability, and has good technical and economic performance.

[0016] 4. The method of the present invention is used to treat and reuse fluorine-containing wastewater, which solves the problem of wastewater treatment difficulties in related enterprises and achieves water resource utilization.

[0017] Other features and advantages of the present invention will be described in detail in the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Exemplary embodiments of the present invention will be described in more detail with reference to the accompanying drawings.

[0019] Figure 1 A process flow chart of a method for treating and reusing fluorine-containing wastewater according to an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0020] The preferred embodiments of the present invention will be described in more detail below. Although the preferred embodiments of the present invention are described below, it should be understood that the present invention can be implemented in various forms and should not be limited to the embodiments set forth herein.

[0021] The present invention provides a method for treating and reusing fluorine-containing wastewater, which comprises:

[0022] (1) Treat fluoride-containing wastewater by adding chemicals to remove fluoride;

[0023] (2) using a roll-type ultrafiltration unit to remove suspended solids from the wastewater treated in step (1);

[0024] (3) using a primary reverse osmosis unit to desalinate the ultrafiltration water after the treatment in step (2);

[0025] (4) further desalting the primary reverse osmosis water after the treatment in step (3) using a secondary reverse osmosis unit to obtain secondary reverse osmosis water; the secondary reverse osmosis water is recycled to the chemical water replenishment unit.

[0026] In the present invention, fluorine ions in wastewater form particles with the defluorination agent and are suspended in the solution under the action of the flocculant component in the defluorination agent; a roll-type ultrafiltration unit is used to remove suspended matter from the wastewater to remove fluorine-containing particles and other suspended matter in the wastewater; a primary reverse osmosis unit is used to desalinate the wastewater to remove soluble ions in the wastewater.

[0027] According to the present invention, preferably, the primary reverse osmosis concentrated water treated in step (3) is used as the ultrafiltration backwash water in step (2);

[0028] The secondary reverse osmosis concentrated water treated in step (4) is returned to the primary reverse osmosis unit for use as reverse osmosis feed water.

[0029] In the present invention, preferably, the water produced by the spiral ultrafiltration enters the primary reverse osmosis unit, and the primary reverse osmosis concentrated water returns to the backwash water tank of the spiral ultrafiltration process for use as backwash water, the purpose of which is to improve water utilization.

[0030] According to the present invention, preferably, in the step (1), the defluoridation agent in the defluoridation agent aqueous solution used comprises at least two of calcium oxide, calcium chloride, sodium aluminate, magnesium chloride, potassium dihydrogen phosphate, aluminum trichloride and polyaluminum chloride;

[0031] The mass concentration of the defluorination agent aqueous solution used is preferably 5-35%, and more preferably 10-20%.

[0032] In the present invention, the main concentration range of the defluorination agent aqueous solution is selected mainly based on the solubility of the defluorination agent, and the preferred mass concentration of the prepared solution is 10-20%.

[0033] According to the present invention, preferably, in the step (1), the amount of the defluorination agent added is 2-10 times, preferably 2-4 times, the mass content of fluoride ions in the fluoride-containing wastewater;

[0034] The reaction time of the defluorination agent and the fluorine-containing wastewater is 30-360 minutes, preferably 60-120 minutes;

[0035] The pH value of the reaction between the defluorination agent and the fluorine-containing wastewater is controlled at 6.5-10, preferably 7-8.5.

[0036] In the present invention, the defluorination agent refers to the solute in the defluorination agent aqueous solution used, that is, the agent component.

[0037] According to the present invention, preferably, the ultrafiltration membrane used in the rolled ultrafiltration unit is a large-channel rolled ultrafiltration membrane;

[0038] Preferably, the large-channel rolled ultrafiltration membrane is made of polyvinylidene fluoride (PVDF), the channel uses a PP plate as a support layer, and the channel diameter is 0.8-1.5 mm.

[0039] In the present invention, the large-channel rolled ultrafiltration membrane used has strong suspended matter resistance performance.

[0040] According to the present invention, preferably, in step (2), the concentration of suspended solids in the inlet water is 50-5000 mg / L, and the turbidity of the outlet water is less than 0.1 NTU;

[0041] The operating pressure of the spiral ultrafiltration unit is 0-0.25Mpa, preferably 0-0.15Mpa;

[0042] The operating flux of the roll-type ultrafiltration unit is 25-500L / m 2 h, preferably 25-150 L / m 2 ·h;

[0043] The scroll type ultrafiltration unit adopts an internal circulation operation mode, and the internal circulation flow rate is 2-15 times of the water inlet volume, preferably 6-10 times;

[0044] The scroll ultrafiltration unit runs for 30-150 minutes for automatic backwashing, preferably for 60-90 minutes for automatic backwashing.

[0045] In the present invention, the large-channel rolled ultrafiltration membrane adopts an internal circulation operation mode, which can effectively reduce membrane surface pollution and has a long operation cycle.

[0046] In the present invention, the large-channel rolled ultrafiltration membrane is operated for 30-150 minutes for automatic backwashing to remove pollutants retained in the membrane channel. After optimization and screening, the water production flux is stable in a 60-90 minute operation period, which is taken as the optimal operation time.

[0047] According to the present invention, preferably, in the step (3), the reverse osmosis membrane used in the primary reverse osmosis unit is a pollution-resistant reverse osmosis membrane;

[0048] Preferably, the anti-pollution reverse osmosis membrane is made of polyamide composite membrane material, and the membrane area of ​​a single 8040 module of the anti-pollution reverse osmosis membrane is 34m 2 .

[0049] According to the present invention, preferably, in step (3), the operating pressure of the primary reverse osmosis unit is 1-3 MPa, preferably 1.5-2.5 MPa;

[0050] During operation, the forward flushing method is adopted, the forward flushing cycle is once / 4-8 hours, and the flushing time is 30-60 seconds;

[0051] The pH value of the influent water is 6-9, preferably 7.5-8.6.

[0052] In the present invention, the operating pressure is optimized according to the salt content of the influent water.

[0053] In the present invention, in step 3, by adjusting the wastewater operation mode and adopting a forward flushing method during operation, the concentration polarization on the membrane surface can be effectively reduced, the membrane surface pollution can be reduced, and the operation stability can be improved.

[0054] In step 3, the pH value of the influent is adjusted to 6-9 by adding alkali. After optimization, the pH range is 7.5-8.6, and the system desalination rate is the highest, stably reaching more than 99%.

[0055] According to the present invention, preferably, in the step (4), the reverse osmosis membrane used in the secondary reverse osmosis unit is an ultra-low pressure reverse osmosis membrane;

[0056] Preferably, the material of the ultra-low pressure reverse osmosis membrane is a polyamide composite membrane material, and the membrane area of ​​a single 8040 membrane assembly of the ultra-low pressure reverse osmosis membrane is 40.7 m 2 .

[0057] According to the present invention, preferably, in step (4), the operating pressure of the secondary reverse osmosis unit is 0.5-0.8Mpa;

[0058] During operation, the forward flushing method is adopted, the forward flushing cycle is once / 4-8 hours, and the flushing time is 30-60 seconds;

[0059] The pH value of the influent water is 8.2-8.5;

[0060] Preferably, the conductivity of the secondary reverse osmosis produced water is less than 5 us / cm.

[0061] According to the present invention, preferably, the main water quality characteristics of the fluoride-containing wastewater include: conductivity of 2000-10000 mg / L, fluoride ion content of 50-500 mg / L, chloride ion content of 650-7800 mg / L, sulfate ion content of 130-2460 mg / L, calcium ion content of 50-120 mg / L, magnesium ion content of 15-68 mg / L, COD of 10-80 mg / L, pH of 6-9, suspended matter of 10-200 mg / L, and turbidity of 5-120 NTU.

[0062] In the present invention, the water quality characteristics of the secondary reverse osmosis water produced by the treatment method of the present invention include the following: conductivity <5μS / cm, COD <2mg / L, Cl- <1mg / L, SO4 2- <0.1mg / L, Ca 2+ <0.1mg / L,Mg 2+<0.1mg / L, F-<0.001mg / L, meeting the requirements of chemical water replenishment and reuse.

[0063] The present invention is further described below by examples:

[0064] In the following embodiments:

[0065] The ultrafiltration membrane used in the rolled ultrafiltration unit is a large-channel rolled ultrafiltration membrane; the material of the large-channel rolled ultrafiltration membrane is polyvinylidene fluoride (PVDF), the channel uses a PP plate as a support layer, and the channel diameter is 1.2 mm.

[0066] The reverse osmosis membrane used in the primary reverse osmosis unit is an anti-pollution reverse osmosis membrane; the anti-pollution reverse osmosis membrane is made of a polyamide composite membrane material, and the membrane area of ​​a single 8040 module of the anti-pollution reverse osmosis membrane is 34m 2 .

[0067] The reverse osmosis membrane used in the secondary reverse osmosis unit is an ultra-low pressure reverse osmosis membrane; the material of the ultra-low pressure reverse osmosis membrane is a polyamide composite membrane material, and the membrane area of ​​a single 8040 membrane assembly of the ultra-low pressure reverse osmosis membrane is 40.7m 2 .

[0068] In the following examples, the determination method of each parameter is as follows: Ca 2+ : Reference standard GB / T 6910-2006; Mg 2+ :Reference standard HJ812-2016; Cl - : Reference standard GB / T 15453-2008; SO4 2- : Reference standard GB / T 14642-2009; pH value: Reference standard GB / T 6920-1986; Conductivity: Reference standard GB / T 6908-2008; F - : Refer to standard GB / T7484-1987; COD: Refer to standard GB 11914-89; SS value: Refer to standard GB / T1901-89; Turbidity: Measured by portable turbidity meter using standard scattering method.

[0069] Example 1

[0070] The main water quality characteristics of fluoride-containing wastewater from a coal chemical enterprise are: wastewater conductivity 3520μS / cm, pH 6.7, suspended solids 58mg / L, turbidity: 98NTU, F - :112mg / L、Cl - :1863mg / L、SO4 2- :212mg / L、Mg 2+ :21mg / L、Ca 2+ :75mg / L, COD:35mg / L.

[0071] like Figure 1 As shown, the processing steps are as follows:

[0072] Step 1, the fluorine-containing wastewater enters the defluorination reactor for defluorination treatment by adding a defluorination agent aqueous solution for chemical defluorination, wherein a defluorination agent aqueous solution with a mass concentration of 12% is prepared by using a defluorination agent, the defluorination agent is a mixture of calcium chloride, sodium aluminate and aluminum chloride, based on the total weight of the mixture, calcium chloride accounts for 10wt%, sodium aluminate accounts for 88wt%, and aluminum chloride accounts for 2wt%, the amount of defluorination agent added is 2.5 times the mass content of fluoride ions in the fluoride-containing wastewater, the reaction time is 60 minutes, and the reaction pH is controlled at 7.2 by adding a sodium hydroxide aqueous solution with a mass concentration of 30%. After the reaction is completed, all the mixed wastewater enters a spiral ultrafiltration membrane unit for suspended matter separation (suspended matter removal treatment);

[0073] Step 2, after the addition of the drug and the defluorination reaction, the mixed wastewater enters the roll-type ultrafiltration unit to produce ultrafiltration water and ultrafiltration backwash water; the ultrafiltration water enters the primary reverse osmosis membrane unit for desalination treatment, and the ultrafiltration backwash water is discharged into the factory sewage treatment plant;

[0074] The operating conditions of the roll ultrafiltration unit are: operating pressure (operating pressure) is 0.05MPa, and the operating flux is 50L / m 2 h, adopting the internal circulation operation mode, the internal circulation flow is 8 times of the inlet water volume; running for 80 minutes for automatic backwashing; under this condition, the spiral ultrafiltration membrane can operate stably for a long period of time; among which, the inlet suspended solids concentration is 658mg / L, and the outlet turbidity is less than 0.1NTU;

[0075] Step 3, the ultrafiltration water enters the primary reverse osmosis unit for desalination treatment, removes dissolved ions in the wastewater, obtains primary reverse osmosis water and primary reverse osmosis concentrated water, and the primary reverse osmosis concentrated water is returned to the ultrafiltration backwash water tank for use as ultrafiltration backwash water, further improving the utilization rate of wastewater, and the primary reverse osmosis water enters the secondary reverse osmosis unit for further treatment;

[0076] The operating conditions of the primary reverse osmosis unit are: the pH of the influent water is adjusted to 8.2 by adding a sodium hydroxide aqueous solution with a mass concentration of 30%, the influent pressure (operating pressure) is 1.2 MPa, the recovery rate is 78%, the positive flushing cycle is 1 time / 8 hours, and the positive flushing time is 30 seconds;

[0077] Step 4: the primary reverse osmosis product water enters the secondary reverse osmosis unit for further desalination treatment, and the secondary reverse osmosis concentrated water produced is returned to the primary reverse osmosis inlet water for reuse, and the secondary reverse osmosis product water obtained enters the recycled water system for reuse in the chemical water replenishment unit;

[0078] The operating conditions of the secondary reverse osmosis unit are: the pH of the inlet water is adjusted to 8.3 by adding a sodium hydroxide aqueous solution with a mass concentration of 30%, the inlet water pressure (operating pressure) is 0.75 MPa, and the recovery rate is 85%; the forward flushing cycle is 1 time / 6 hours, and the flushing time is 60 seconds.

[0079] Analysis results of water quality treated by each unit

[0080] project Fluoride-containing wastewater Ultrafiltration water First-stage reverse osmosis water Secondary reverse osmosis water Conductivity(us / cm) 3520 3880 35 2.3 pH 6.7 7.2 7.8 7.1 SS(mg / L) 58 Not detected Not detected Not detected Turbidity (NTU) 98 0.08 0 0 <![CDATA[F - (mg / L)]]> 112 4.6 0.1 <0.001 <![CDATA[Cl - (mg / L)]]> 1863 1852 11.8 0.8 <![CDATA[SO4 2- (mg / L)]]> 212 210 5.9 <0.1 <![CDATA[Ca 2+ (mg / L)]]> 75 98 6.6 <0.1 <![CDATA[Mg 2+ (mg / L)]]> 21 20 3.2 <0.1 COD(mg / L) 35 35 10 <2

[0081] Example 2

[0082] The main water quality characteristics of fluoride-containing wastewater from a petrochemical enterprise are: wastewater conductivity 8650μS / cm, pH 7.8, suspended solids 136mg / L, turbidity: 105NTU, F - :321mg / L、Cl - :4853mg / L、SO4 2- :1389mg / L、Mg 2+ :45mg / L、Ca 2+ :118mg / L, COD:55mg / L.

[0083] like Figure 1 As shown, the processing steps are as follows:

[0084] Step 1, the fluorine-containing wastewater enters the defluorination reactor for defluorination treatment by adding a defluorination agent aqueous solution for chemical defluorination, wherein a defluorination agent aqueous solution with a mass concentration of 18% is prepared by using a defluorination agent, the defluorination agent is a mixture of magnesium chloride, sodium aluminate and aluminum chloride, and based on the total weight of the mixture, magnesium chloride accounts for 25wt%, sodium aluminate accounts for 73wt%, and aluminum chloride accounts for 2wt%. The amount of defluorination agent added is 4 times the mass content of fluoride ions in the fluoride-containing wastewater, the reaction time is 90 minutes, and the pH is adjusted to 7.5 by adding a sodium hydroxide aqueous solution with a mass concentration of 30%. After the reaction is completed, all the mixed wastewater enters a spiral ultrafiltration membrane unit for suspended matter separation (suspended matter removal treatment);

[0085] Step 2, after the addition of the drug and the defluorination reaction, the mixed wastewater enters the scroll ultrafiltration unit to produce ultrafiltration water and ultrafiltration backwash water; the ultrafiltration water enters the primary reverse osmosis unit for desalination treatment, and the ultrafiltration backwash water is discharged into the factory sewage treatment plant;

[0086] The operating conditions of the spiral ultrafiltration unit are: operating pressure (operating pressure) is 0.08MPa, and the operating flux is 45L / m 2h, adopting the internal circulation operation mode, the internal circulation flow rate is 10 times the inlet water volume; automatic backwashing is performed after 60 minutes of operation; under this condition, the spiral ultrafiltration membrane can operate stably for a long period of time; the inlet suspended solids concentration is 998 mg / L, and the outlet turbidity is less than 0.1 NTU;

[0087] Step 3, the ultrafiltration water enters the primary reverse osmosis unit for desalination treatment, removes dissolved ions in the wastewater, obtains primary reverse osmosis water and primary reverse osmosis concentrated water, and the primary reverse osmosis concentrated water is returned to the ultrafiltration backwash water tank for use as ultrafiltration backwash water, further improving the utilization rate of wastewater, and the primary reverse osmosis water enters the secondary reverse osmosis unit for further treatment;

[0088] The operating conditions of the first-stage reverse osmosis unit are: the pH of the influent water is adjusted to 7.9 by adding a sodium hydroxide aqueous solution with a mass concentration of 30%, the influent pressure (operating pressure) is 2.2 MPa, the recovery rate is 73%, the positive flushing cycle is 1 time / 4 hours, and the positive flushing time is 60 seconds;

[0089] Step 4: the primary reverse osmosis product water enters the secondary reverse osmosis unit for further desalination treatment, and the secondary reverse osmosis concentrated water produced is returned to the primary reverse osmosis inlet water for reuse, and the secondary reverse osmosis product water obtained enters the recycled water system for reuse in the chemical water replenishment unit;

[0090] The operating conditions of the secondary reverse osmosis unit are: the pH of the inlet water is adjusted to 8.1 by adding a sodium hydroxide aqueous solution with a mass concentration of 30%, the inlet water pressure (operating pressure) is 0.75 MPa, and the recovery rate is 85%; the forward flushing cycle is 1 time / 8 hours, and the flushing time is 30 seconds.

[0091] Analysis results of water quality treated by each unit

[0092] project Fluoride-containing wastewater Ultrafiltration water First-stage reverse osmosis water Secondary reverse osmosis water Conductivity(us / cm) 8650 9680 88 3.8 pH 7.8 7.5 7.6 7.0 SS(mg / L) 136 Not detected Not detected Not detected Turbidity (NTU) 105 0.06 0 0 <![CDATA[F - (mg / L)]]> 321 4.3 0.1 <0.001 <![CDATA[Cl - (mg / L)]]> 4853 4821 56.9 1.2 <![CDATA[SO4 2- (mg / L)]]> 1389 1376 9.8 <0.1 <![CDATA[Ca 2+ (mg / L)]]> 123 103 5.4 <0.1 <![CDATA[Mg 2+ (mg / L)]]> 45 37 2.7 <0.1 COD(mg / L) 55 51 8 <2

[0093] The embodiments of the present invention have been described above, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and changes will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A method for treating and reusing fluorine-containing wastewater, characterized in that: The treatment and reuse methods include: (1) Treat fluoride-containing wastewater by adding chemicals to remove fluoride; (2) using a roll-type ultrafiltration unit to remove suspended solids from the wastewater treated in step (1); (3) using a primary reverse osmosis unit to desalinate the ultrafiltration water after the treatment in step (2); (4) further desalting the primary reverse osmosis water after the treatment in step (3) using a secondary reverse osmosis unit to obtain secondary reverse osmosis water; the secondary reverse osmosis water is recycled to the chemical water replenishment unit.

2. The method for recycling according to claim 1, wherein: The primary reverse osmosis concentrated water treated in step (3) is used as the ultrafiltration backwash water in step (2); The secondary reverse osmosis concentrated water treated in step (4) is returned to the primary reverse osmosis unit for use as reverse osmosis feed water.

3. The treatment and reuse method according to claim 1, wherein: In the step (1), the defluoridation agent in the defluoridation agent aqueous solution used includes at least two of calcium oxide, calcium chloride, sodium aluminate, magnesium chloride, potassium dihydrogen phosphate, aluminum trichloride and polyaluminum chloride; The mass concentration of the defluorination agent aqueous solution used is preferably 5-35%, and more preferably 10-20%.

4. The method for recycling according to claim 1, wherein: In the step (1), the amount of the defluorination agent added is 2-10 times, preferably 2-4 times, the mass content of fluoride ions in the fluoride-containing wastewater; The reaction time of the defluorination agent and the fluorine-containing wastewater is 30-360 minutes, preferably 60-120 minutes; The pH value of the reaction between the defluorination agent and the fluorine-containing wastewater is controlled at 6.5-10, preferably 7-8.

5.

5. The treatment and reuse method according to claim 1, wherein: The ultrafiltration membrane used in the rolled ultrafiltration unit is a large-channel rolled ultrafiltration membrane; Preferably, the large-channel rolled ultrafiltration membrane is made of polyvinylidene fluoride, the channel uses a PP plate as a support layer, and the channel diameter is 0.8-1.5 mm.

6. The method for recycling according to claim 1, wherein: In step (2), the concentration of suspended solids in the inlet water is 50-5000 mg / L, and the turbidity of the outlet water is less than 0.1 NTU; The operating pressure of the spiral ultrafiltration unit is 0-0.25Mpa, preferably 0-0.15Mpa; The operating flux of the roll-type ultrafiltration unit is 25-500L / m 2 h, preferably 25-150 L / m 2 ·h; The scroll type ultrafiltration unit adopts an internal circulation operation mode, and the internal circulation flow rate is 2-15 times of the water inlet volume, preferably 6-10 times; The scroll ultrafiltration unit runs for 30-150 minutes for automatic backwashing, preferably for 60-90 minutes for automatic backwashing.

7. The method for recycling according to claim 1, wherein: In the step (3), the reverse osmosis membrane used in the primary reverse osmosis unit is a pollution-resistant reverse osmosis membrane; Preferably, the anti-pollution reverse osmosis membrane is made of polyamide composite membrane material, and the membrane area of ​​a single 8040 module of the anti-pollution reverse osmosis membrane is 34m 2 .

8. The treatment and reuse method according to claim 1, wherein: In the step (3), the operating pressure of the primary reverse osmosis unit is 1-3 MPa, preferably 1.5-2.5 MPa; During operation, the forward flushing method is adopted, the forward flushing cycle is once / 4-8 hours, and the flushing time is 30-60 seconds; The pH value of the influent water is 6-9, preferably 7.5-8.

6.

9. The method for recycling according to claim 1, wherein: In the step (4), the reverse osmosis membrane used in the secondary reverse osmosis unit is an ultra-low pressure reverse osmosis membrane; Preferably, the material of the ultra-low pressure reverse osmosis membrane is a polyamide composite membrane material, and the membrane area of ​​a single 8040 membrane assembly of the ultra-low pressure reverse osmosis membrane is 40.7 m 2 .

10. The treatment and reuse method according to claim 1, wherein: In the step (4), the operating pressure of the secondary reverse osmosis unit is 0.5-0.8 MPa; During operation, the forward flushing method is adopted, the forward flushing cycle is once / 4-8 hours, and the flushing time is 30-60 seconds; The pH value of the inlet water is 8.2-8.5; Preferably, the conductivity of the secondary reverse osmosis produced water is less than 5 us / cm.

11. The method for recycling according to claim 1, wherein: The main water quality characteristics of the fluoride-containing wastewater include: conductivity of 2000-10000 mg / L, fluoride ion content of 50-500 mg / L, chloride ion content of 650-7800 mg / L, sulfate ion content of 130-2460 mg / L, calcium ion content of 50-120 mg / L, magnesium ion content of 15-68 mg / L, COD of 10-80 mg / L, pH of 6-9, suspended solids of 10-200 mg / L, and turbidity of 5-120 NTU.

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