Process and system for deeply treating high-concentration fluorine-containing wastewater

Abstract

The invention discloses a process and a system for deeply treating high-concentration fluorine-containing wastewater. The process comprises a first-stage defluorination reaction process section, a second-stage defluorination reaction process section and a third-stage defluorination reaction process section which are arranged in sequence, the first-stage defluorination reaction process section adopts a chemical precipitation method to perform first-stage defluorination, the second-stage defluorination reaction process section adopts a coagulation precipitation method to perform second-stage defluorination, and the third-stage defluorination reaction process section adopts an electric flocculation method to perform third-stage defluorination. According to the method, the chemical precipitation method is used for primary fluorine removal, so that the high-fluorine-content wastewater is changed into the low-concentration fluorine-containing wastewater, then the coagulating precipitation method is used for further removing fluorine ions, and finally the electric flocculation method is used for deep fluorine removal, so that the problem that the fluorine ion concentration of the effluent is difficult to reach 1.5 mg / L or below after the high-fluorine-content wastewater is treated in the prior art can be solved. The amount of sludge generated by the electric flocculation method is relatively small, no coagulant aid needs to be additionally added, and the content of Al ions in effluent can be obviously reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of fluorine-containing wastewater treatment, and in particular to a process and system for deep treatment of high-concentration fluorine-containing wastewater. Background Art

[0002] With the development of the industry, my country's photovoltaic industry, new energy industry and semiconductor industry are developing rapidly. In the production process of these enterprises, a large amount of hydrofluoric acid and other fluorine-containing agents are used, resulting in a large amount of fluoride ions in the production wastewater, and the discharge scale of fluoride-containing wastewater is expanding. At present, the engineering treatment process for high-concentration fluoride-containing wastewater mainly uses a chemical-coagulation combination process, which can treat the fluoride ions in high-fluoride wastewater to below 10 mg / L. However, with the improvement of emission standards, the fluoride ion concentration in the effluent of this process can no longer meet the standards, and the current effluent needs to be deeply re-treated to reduce the fluoride ion concentration in the effluent to below 1.5 mg / L.

[0003] At present, the main deep treatment processes for fluoride-containing wastewater include coagulation and sedimentation, ion exchange, adsorption, membrane separation and electrocoagulation. The coagulation and sedimentation method for fluoride removal usually uses the addition of coagulants and coagulants to the water, and adjusts the various parameters of the wastewater, and then quickly stirs and then slowly flocculates and precipitates. The coagulation and sedimentation technology has the advantages of high removal efficiency, high sedimentation efficiency and large water treatment volume. Patent CN118495740A adds a third-stage coagulation and defluoridation after the second-stage coagulation and defluoridation to achieve the removal of fluoride ion concentration to below 1ppm. However, the defluoridation effect of this method is easily affected by water quality conditions and operating factors, and the amount of coagulant added needs to be accurately calculated. In addition, the residual iron ions and aluminum ions will cause damage to the water body and the human body respectively. We also need to control the iron and aluminum content in the effluent.

[0004] In addition, ion exchange, adsorption and membrane separation methods are relatively expensive and require the regeneration and recycling of the medium or biofilm. The operation is complicated, the requirements for staff are high, and the operating costs are increased. Therefore, the economic efficiency of the project is low.

[0005] Electroflocculation is a technology that generates floccules by in-situ hydrolysis during the electrolysis process. It does not require additional reagents, and the in-situ generated flocculants are more active. At the same time, this technology has the advantages of simple equipment, small footprint and easy operation. Its main operating parameters include voltage and current. The overall process of this technology can be highly automated, and the operation and maintenance management are relatively simple. The floc particles generated by the electroflocculation process are large and stable, which can be used for mud and water separation.

[0006] Therefore, the electrocoagulation process can be combined with other processes and applied to the treatment of fluoride-containing wastewater, but there is no publicly available and reliable solution. Summary of the invention

[0007] The technical problem to be solved by the present invention is to provide a process and system for deep treatment of high-concentration fluorine-containing wastewater in view of the deficiencies in the above-mentioned prior art.

[0008] In order to solve the above technical problems, the technical solution adopted by the present invention is: in the first aspect of the present invention, a process for deep treatment of high-concentration fluorine-containing wastewater is provided, comprising a first-stage defluorination reaction process section, a second-stage defluorination reaction process section and a third-stage defluorination reaction process section which are arranged in sequence;

[0009] The first stage defluorination reaction process section adopts chemical precipitation method to carry out primary defluorination, the second stage defluorination reaction process section adopts coagulation precipitation method to carry out secondary defluorination, and the third stage defluorination reaction process section adopts electric flocculation method to carry out tertiary defluorination.

[0010] Preferably, the process for deep treatment of high-concentration fluorine-containing wastewater comprises the following process steps:

[0011] S1, first stage defluorination reaction process section:

[0012] S11, allowing the fluorine-containing wastewater and the recycled water to enter the primary defluorination reaction tank together;

[0013] S12, adding lime milk into the primary defluorination reaction tank, and then adjusting the pH to 8-9 with sulfuric acid, stirring the reaction;

[0014] S13, the effluent from the primary defluorination reaction tank enters the primary flocculation tank, and PAM (polyacrylamide) is added to carry out flocculation reaction;

[0015] S14, the effluent from the primary flocculation tank enters the primary sedimentation tank for solid-liquid separation;

[0016] S2, the second stage defluorination reaction process section:

[0017] S21, the supernatant of the primary sedimentation tank enters the secondary defluorination reaction tank, PAC is added, liquid alkali is added to control the pH to 7-8, and the reaction is stirred;

[0018] S22, the effluent from the secondary defluorination reaction tank enters the secondary flocculation tank, and PAM is added for flocculation reaction;

[0019] S23, the effluent from the secondary flocculation reaction tank enters the secondary sedimentation tank for solid-liquid separation;

[0020] S3, the third defluorination reaction process section:

[0021] S31. The supernatant of the secondary sedimentation tank enters the electro-flocculation defluorination device, sulfuric acid is added to adjust the pH to 6-6.5, and the electro-flocculation defluorination device is started to perform the electro-flocculation defluorination reaction;

[0022] S32. The effluent from the electro-flocculation defluorination device enters the tertiary sedimentation tank for solid-liquid separation, and the supernatant is directly discharged into the clear water tank for external discharge.

[0023] Preferably, the bottom sludge of the primary sedimentation tank, the secondary sedimentation tank and the tertiary sedimentation tank first enters the sludge thickening tank, and the concentrated sludge then enters the filter press for solid-liquid separation, the filter cake is transported out for treatment, and the recycled water enters the primary defluorination reaction tank, and the recycled water includes: the filtrate of the filter press and the supernatant of the sludge thickening tank.

[0024] Preferably, the process for deep treatment of high-concentration fluorine-containing wastewater comprises the following process steps:

[0025] S1, first stage defluorination reaction process section:

[0026] S11, allowing high-concentration fluoride-containing wastewater with a fluoride ion concentration of ≥2500 mg / L and recycled water to enter the primary defluorination reaction tank;

[0027] S12, add lime milk to the primary defluorination reaction tank to make the calcium-fluorine molar ratio in the water 0.3-0.7, then adjust the pH to 8-9 with sulfuric acid, and stir the reaction for 1 hour;

[0028] S13, the effluent from the primary defluorination reaction tank enters the primary flocculation tank, and PAM is added for flocculation reaction. The amount of PAM added is 2-6 mg / L, and the reaction time is 10-20 min;

[0029] S14, the effluent from the primary flocculation tank enters the primary sedimentation tank for solid-liquid separation, and the fluoride ion concentration in the supernatant of the primary sedimentation tank is 20-35 mg / L;

[0030] S2, the second stage defluorination reaction process section:

[0031] S21. The supernatant of the primary sedimentation tank enters the secondary defluorination reaction tank, PAC (polyaluminium chloride) is added in an amount of 200-600 mg / L, and liquid alkali (sodium hydroxide) is added to control the pH to 7-8, and the reaction is stirred for 1 hour;

[0032] S22, the effluent from the secondary defluorination reaction tank enters the secondary flocculation tank, and PAM is added for flocculation reaction. The amount of PAM added is 2-6 mg / L, and the reaction time is 10-20 min;

[0033] S23, the effluent from the secondary flocculation reaction tank enters the secondary sedimentation tank for solid-liquid separation, and the fluoride ion concentration in the supernatant of the secondary sedimentation tank is 3-8 mg / L;

[0034] S3, the third defluorination reaction process section:

[0035] S31. The supernatant of the secondary sedimentation tank enters the electro-flocculation defluorination device, sulfuric acid is added to adjust the pH to 6-6.5, the electro-flocculation defluorination device is turned on, and the electro-flocculation defluorination reaction is carried out for 30 minutes;

[0036] S32. The effluent from the electro-flocculation defluorination device enters the tertiary sedimentation tank for solid-liquid separation, and the supernatant is directly discharged into the clear water tank for external discharge. The fluoride ion concentration in the supernatant is ≤1.5mg / L.

[0037] Preferably, the process for deep treatment of high-concentration fluorine-containing wastewater comprises the following process steps:

[0038] S1, first stage defluorination reaction process section:

[0039] S11, allowing high-concentration fluoride-containing wastewater with a fluoride ion concentration greater than or equal to 2500 mg / L and recycled water to enter the primary defluorination reaction tank;

[0040] S12, add lime milk to the primary defluorination reaction tank to make the calcium-fluorine molar ratio in the water 0.5, then adjust the pH to 8-9 with sulfuric acid, and stir the reaction for 1 hour;

[0041] S13, the effluent from the primary defluorination reaction tank enters the primary flocculation tank, and PAM is added for flocculation reaction. The amount of PAM added is 4 mg / L, and the reaction time is 15 min;

[0042] S14, the effluent from the primary flocculation tank enters the primary sedimentation tank for solid-liquid separation, and the fluoride ion concentration in the supernatant of the primary sedimentation tank is 20-35 mg / L;

[0043] S2, the second stage defluorination reaction process section:

[0044] S21. The supernatant of the primary sedimentation tank enters the secondary defluorination reaction tank, PAC is added at an amount of 500 mg / L, and liquid alkali is added to control the pH to 7-8, and the reaction is stirred for 1 hour;

[0045] S22, the effluent from the secondary defluorination reaction tank enters the secondary flocculation tank, and PAM is added for flocculation reaction. The amount of PAM added is 4 mg / L, and the reaction time is 15 min;

[0046] S23, the effluent from the secondary flocculation reaction tank enters the secondary sedimentation tank for solid-liquid separation, and the fluoride ion concentration in the supernatant of the secondary sedimentation tank is 3-8 mg / L;

[0047] S3, the third defluorination reaction process section:

[0048] S31. The supernatant of the secondary sedimentation tank enters the electro-flocculation defluorination device, sulfuric acid is added to adjust the pH to 6-6.5, the electro-flocculation defluorination device is turned on, and the electro-flocculation defluorination reaction is carried out for 30 minutes;

[0049] S32. The effluent from the electro-flocculation defluorination device enters the tertiary sedimentation tank for solid-liquid separation, and the supernatant is directly discharged into the clear water tank for external discharge. The fluoride ion concentration in the supernatant is ≤1.5mg / L.

[0050] Preferably, the electro-flocculation defluorination device comprises a device housing, a first graphite electrode and a second graphite electrode fixedly mounted in the device housing, a plurality of metal electrodes fixedly embedded between the first graphite electrode and the second graphite electrode, a stirring device arranged at the bottom of the device housing, a temperature control device arranged in the device housing, and a DC power supply whose positive and negative electrodes are respectively connected to the first graphite electrode and the second graphite electrode.

[0051] The lower part of the device shell is provided with a water inlet, and the upper part is provided with a water outlet.

[0052] Preferably, the plurality of metal electrodes are evenly spaced and arranged, and the metal electrodes are aluminum electrodes or iron electrodes.

[0053] Preferably, when the electro-flocculation defluorination device is used for wastewater treatment, the first graphite electrode, the second graphite electrode and the plurality of metal electrodes in the device housing are completely immersed in water.

[0054] Preferably, the metal electrodes are aluminum electrodes, and the number is 3.

[0055] The second aspect of the present invention provides a system for deep treatment of high-concentration fluorine-containing wastewater, which uses the process as described above to treat the fluorine-containing wastewater, and the system comprises: a first-stage defluorination reaction subsystem, a second-stage defluorination reaction subsystem, a third-stage defluorination reaction subsystem, and a sludge thickening tank and a filter press for treating sludge generated by the three subsystems.

[0056] The first-stage defluorination reaction subsystem comprises a first-stage defluorination reaction tank, a first-stage flocculation tank and a first-stage sedimentation tank which are arranged in sequence;

[0057] The second-stage defluorination reaction subsystem includes a secondary defluorination reaction tank, a secondary flocculation tank and a secondary sedimentation tank which are arranged in sequence;

[0058] The third-stage defluorination reaction subsystem includes an electric flocculation defluorination device and a three-stage sedimentation tank.

[0059] The beneficial effects of the present invention are:

[0060] The present invention provides a process and system for deep treatment of high-concentration fluorine-containing wastewater. In the present invention, a chemical precipitation method is used for primary defluorination to convert high-fluorine-containing wastewater into low-concentration fluorine-containing wastewater, and then a coagulation sedimentation method is used to further remove fluorine ions. Finally, an electric flocculation method is used for deep defluorination, which can solve the problem that the fluorine ion concentration of the effluent after the existing high-fluorine-containing wastewater treatment is difficult to reach below 1.5 mg / L. In addition, since the electric flocculation defluorination device occupies a small area, it is not necessary to expand the sewage treatment plant with two-stage defluorination. In addition, compared with the coagulation sedimentation method as a three-stage defluorination method, the electric flocculation method generates relatively less sludge and does not require additional coagulant aid for sedimentation, which can significantly reduce the Al ion content in the effluent. In addition, the main influencing factors for the electric flocculation defluorination device to treat fluorine wastewater are parameters such as current density, pH, electrolysis time and plate spacing. These parameters can be easily adjusted, have low requirements for professional knowledge, can be highly automated, and reduce operating costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] Figure 1 This is a process flow chart for deep treatment of high-concentration fluorine-containing wastewater in the present invention;

[0062] Figure 2 It is a schematic diagram of the structure of the electrocoagulation defluorination device in the present invention.

[0063] Description of reference numerals:

[0064] 1—device housing; 2—first graphite electrode; 3—second graphite electrode; 4—metal electrode; 5—stirring device; 6—temperature control device; 7—DC power supply; 8—water inlet; 9—water outlet. DETAILED DESCRIPTION

[0065] The present invention is further described in detail below in conjunction with embodiments so that those skilled in the art can implement the invention with reference to the description.

[0066] It should be understood that the terms such as “having”, “including” and “comprising” used herein do not exclude the existence or addition of one or more other elements or combinations thereof.

[0067] The test methods used in the following examples are conventional methods unless otherwise specified. The materials and reagents used in the following examples are all commercially available unless otherwise specified. In the following examples, if no specific conditions are specified, the experiments were carried out under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used, if the manufacturer is not specified, are all conventional products that can be purchased commercially.

[0068] Reference Figure 1The present invention provides a process for deep treatment of high-concentration fluorine-containing wastewater, comprising a first-stage defluorination reaction process section, a second-stage defluorination reaction process section and a third-stage defluorination reaction process section which are sequentially arranged;

[0069] Among them, the first stage defluorination reaction process section adopts chemical precipitation method for primary defluorination, the second stage defluorination reaction process section adopts coagulation sedimentation method for secondary defluorination, and the third stage defluorination reaction process section adopts electric flocculation method for tertiary defluorination.

[0070] In a preferred embodiment, the process for deep treatment of high-concentration fluoride-containing wastewater comprises the following process steps:

[0071] S1, first stage defluorination reaction process section:

[0072] S11, allowing high-concentration fluoride-containing wastewater with a fluoride ion concentration of ≥2500 mg / L and recycled water to enter the primary defluorination reaction tank;

[0073] S12, add lime milk to the primary defluorination reaction tank to make the calcium-fluorine molar ratio in the water 0.3-0.7, then adjust the pH to 8-9 with sulfuric acid, and stir at high speed for 1 hour;

[0074] S13, the effluent from the primary defluorination reaction tank enters the primary flocculation tank, and PAM is added for flocculation reaction. The amount of PAM added is 2-6 mg / L, and the reaction time is 10-20 min;

[0075] S14, the effluent from the primary flocculation tank enters the primary sedimentation tank for solid-liquid separation, and the fluoride ion concentration in the supernatant of the primary sedimentation tank is 20-35 mg / L;

[0076] S2, the second stage defluorination reaction process section:

[0077] S21. The supernatant of the primary sedimentation tank enters the secondary defluorination reaction tank, PAC (polyaluminium chloride) is added in an amount of 200-600 mg / L, and liquid alkali (sodium hydroxide) is added to control the pH to 7-8, and the reaction is carried out with high speed and strong stirring for 1 hour;

[0078] S22, the effluent from the secondary defluorination reaction tank enters the secondary flocculation tank, and PAM is added for flocculation reaction. The amount of PAM added is 2-6 mg / L, and the reaction time is 10-20 min;

[0079] S23, the effluent from the secondary flocculation reaction tank enters the secondary sedimentation tank for solid-liquid separation, and the fluoride ion concentration in the supernatant of the secondary sedimentation tank is 3-8 mg / L;

[0080] S3, the third defluorination reaction process section:

[0081] S31. The supernatant of the secondary sedimentation tank enters the electro-flocculation defluorination device, sulfuric acid is added to adjust the pH to 6-6.5, the electro-flocculation defluorination device is turned on, and the electro-flocculation defluorination reaction is carried out for 30 minutes;

[0082] S32. The effluent from the electro-flocculation defluorination device enters the tertiary sedimentation tank for solid-liquid separation, and the supernatant is directly discharged into the clear water tank for external discharge. The fluoride ion concentration in the supernatant is ≤1.5mg / L.

[0083] Among them, the bottom sludge of the primary sedimentation tank, the secondary sedimentation tank, and the tertiary sedimentation tank first enters the sludge thickening tank, and the concentrated sludge then enters the filter press for solid-liquid separation, the filter cake is transported out for treatment, and the recycled water enters the primary defluorination reaction tank. The recycled water includes: the filtrate from the filter press and the supernatant from the sludge thickening tank.

[0084] Reference Figure 2 In a preferred embodiment, the electro-flocculation defluorination device includes a device housing 1, a first graphite electrode 2 and a second graphite electrode 3 fixedly installed in the device housing 1, a plurality of metal electrodes 4 fixedly embedded between the first graphite electrode 2 and the second graphite electrode 3, a stirring device 5 arranged at the bottom of the device housing 1, a temperature control device 6 arranged in the device housing 1, and a DC power supply 7 whose positive and negative poles are connected to the first graphite electrode 2 and the second graphite electrode 3 respectively.

[0085] A water inlet 8 is provided at the lower part of the device housing 1 , and a water outlet 9 is provided at the upper part.

[0086] In a preferred embodiment, a plurality of metal electrodes 4 are evenly spaced and arranged, and the metal electrodes 4 are aluminum electrodes or iron electrodes. The aluminum electrodes or the iron electrodes may be used alone or in combination.

[0087] In a preferred embodiment, when the electro-flocculation defluorination device is used for wastewater treatment, the first graphite electrode 2, the second graphite electrode 3, and the plurality of metal electrodes 4 in the device housing 1 are all completely immersed in water.

[0088] In a preferred embodiment, the metal electrodes 4 are aluminum electrodes, and the number of the metal electrodes 4 is three.

[0089] The present invention also provides a system for deep treatment of high-concentration fluorine-containing wastewater, which uses the above process to treat fluorine-containing wastewater, and the system comprises: a first-stage defluorination reaction subsystem, a second-stage defluorination reaction subsystem, a third-stage defluorination reaction subsystem, and a sludge concentration tank and a filter press for treating sludge generated by the three subsystems;

[0090] The first-stage defluorination reaction subsystem includes a first-stage defluorination reaction tank, a first-stage flocculation tank and a first-stage sedimentation tank which are arranged in sequence;

[0091] The second-stage defluorination reaction subsystem includes a secondary defluorination reaction tank, a secondary flocculation tank and a secondary sedimentation tank which are arranged in sequence;

[0092] The third-stage defluorination reaction subsystem includes an electrocoagulation defluorination device and a third-stage sedimentation tank.

[0093] The above is the overall concept of the present invention, and detailed embodiments and comparative examples are provided below on the basis of the overall concept of the present invention to further illustrate the present invention.

[0094] Example 1

[0095] A system for deep treatment of high-concentration fluoride-containing wastewater, the system comprising: a first-stage defluorination reaction subsystem, a second-stage defluorination reaction subsystem, a third-stage defluorination reaction subsystem, and a sludge concentration tank and a filter press for treating sludge generated by the three subsystems;

[0096] The first-stage defluorination reaction subsystem includes a first-stage defluorination reaction tank, a first-stage flocculation tank and a first-stage sedimentation tank which are arranged in sequence;

[0097] The second-stage defluorination reaction subsystem includes a secondary defluorination reaction tank, a secondary flocculation tank and a secondary sedimentation tank which are arranged in sequence;

[0098] The third-stage defluorination reaction subsystem includes an electrocoagulation defluorination device and a third-stage sedimentation tank.

[0099] The electro-flocculation defluorination device comprises a device housing 1, a first graphite electrode 2 and a second graphite electrode 3 fixedly installed in the device housing 1, a plurality of metal electrodes 4 fixedly embedded between the first graphite electrode 2 and the second graphite electrode 3, a stirring device 5 arranged at the bottom of the device housing 1, a temperature control device 6 arranged in the device housing 1, and a DC power supply 7 whose positive and negative poles are connected to the first graphite electrode 2 and the second graphite electrode 3 respectively; a water inlet 8 is arranged at the lower part of the device housing 1, and a water outlet 9 is arranged at the upper part.

[0100] The stirring device 5 can ensure that the wastewater in the device and the coagulant produced by electrolysis can be mixed evenly. The temperature control device 6 is used to adjust the temperature in the device. By increasing the temperature, the adsorption of fluoride ions by the flocs can be enhanced, so that the defluorination effect of the device is increased. Both the temperature control device 6 and the stirring device 5 are powered by the above-mentioned DC power supply 7.

[0101] The metal electrodes 4 are aluminum electrodes, the number of which is 3 and are evenly spaced with a spacing of 1.2 cm. When treating wastewater, all electrodes need to be completely immersed in water.

[0102] Example 2

[0103] Fluorine-containing wastewater from a photovoltaic plant was used as a sample, and the system of Example 1 was used to perform a treatment test using the following process. The water quality indicators of the fluorine-containing wastewater are shown in Table 1 below:

[0104] Table 1

[0105]

[0106] The process for deep treatment of the fluorine-containing wastewater using the system of Example 1 comprises the following steps:

[0107] S1, first stage defluorination reaction process section:

[0108] S11, allowing the fluorine-containing wastewater and the recycled water to enter the primary defluorination reaction tank together;

[0109] S12, add lime milk to the primary defluorination reaction tank to make the calcium-fluorine molar ratio in the water 0.5, then adjust the pH to 8-9 with sulfuric acid, and react at high speed and strong stirring (speed of 150r / min) for 1h;

[0110] S13, the effluent from the primary defluorination reaction tank enters the primary flocculation tank, and PAM is added for flocculation reaction. The amount of PAM added is 4 mg / L, and the reaction time is 15 min;

[0111] S14, the effluent from the primary flocculation tank enters the primary sedimentation tank for solid-liquid separation. The fluoride ion concentration in the supernatant of the primary sedimentation tank is measured to be 23.7 mg / L;

[0112] S2, the second stage defluorination reaction process section:

[0113] S21. The supernatant of the primary sedimentation tank enters the secondary defluorination reaction tank, PAC (polyaluminium chloride) is added, the amount of PAC added is 500 mg / L, liquid alkali (sodium hydroxide) is added to control the pH to 7-8, and the reaction is carried out for 1 hour with high speed strong stirring (speed of 150 r / min);

[0114] S22, the effluent from the secondary defluorination reaction tank enters the secondary flocculation tank, and PAM is added for flocculation reaction. The amount of PAM added is 4 mg / L, and the reaction time is 15 min;

[0115] S23, the effluent from the secondary flocculation reaction tank enters the secondary sedimentation tank for solid-liquid separation. It is determined that the fluoride ion concentration in the supernatant of the secondary sedimentation tank is 6.53 mg / L;

[0116] S3, the third defluorination reaction process section:

[0117] S31, the supernatant of the secondary sedimentation tank enters the electro-flocculation defluorination device, sulfuric acid is added to adjust the pH to 6-6.5, the electro-flocculation defluorination device is turned on (the speed of the stirring device 5 is 300r / min), and the electro-flocculation defluorination reaction is carried out. The reaction temperature is 30°C, the reaction time is 30min; the current density is 30A / m 2 ;

[0118] S32, the effluent from the electro-flocculation defluorination device enters the tertiary sedimentation tank for solid-liquid separation, and the supernatant is directly discharged into the clear water tank for discharge. The fluoride ion concentration in the supernatant is 0.97 mg / L, Al 3+ The concentration is 0.19mg / L.

[0119] Comparative Example

[0120] This example is basically the same as Example 2, except that in the third defluorination reaction process stage, this example adopts a coagulation precipitation method, and the specific steps are as follows:

[0121] S3, the third defluorination reaction process section:

[0122] The supernatant of the secondary defluorination was introduced into the tertiary defluorination reaction tank, and PAC (polyaluminium chloride) was added for high-speed strong stirring reaction. The amount of PAC added was 500 mg / L. Sodium hydroxide and sulfuric acid were used to adjust the pH to 6.5-7.5, and the reaction time was 1 hour.

[0123] The effluent from the third-stage defluorination reaction tank enters the third-stage flocculation tank, where PAM is added for flocculation reaction. The amount of PAM added is 4 mg / L, and the reaction time is 15 min.

[0124] The effluent from the three-stage flocculation tank enters the three-stage sedimentation tank for solid-liquid separation, and the supernatant is directly discharged into the clear water tank for discharge. The effluent fluoride ion concentration is 1.42 mg / L, Al 3+ Content: 0.76mg / L.

[0125] Although the embodiments of the present invention have been disclosed as above, they are not limited to the applications listed in the specification and the implementation modes. They can be fully applied to various fields suitable for the present invention. For those familiar with the art, additional modifications can be easily implemented. Therefore, without departing from the general concept defined by the claims and the scope of equivalents, the present invention is not limited to specific details.

Claims

1. A process for deep treatment of high-concentration fluorine-containing wastewater, characterized in that: It includes a first-stage defluorination reaction process section, a second-stage defluorination reaction process section and a third-stage defluorination reaction process section which are arranged in sequence; The first stage defluorination reaction process section adopts chemical precipitation method to carry out primary defluorination, the second stage defluorination reaction process section adopts coagulation precipitation method to carry out secondary defluorination, and the third stage defluorination reaction process section adopts electric flocculation method to carry out tertiary defluorination.

2. The process for deep treatment of high-concentration fluorine-containing wastewater according to claim 1, characterized in that: The process steps include: S1, first stage defluorination reaction process section: S11, allowing the fluorine-containing wastewater and the recycled water to enter the primary defluorination reaction tank together; S12, adding lime milk into the primary defluorination reaction tank, and then adjusting the pH to 8-9 with sulfuric acid, stirring the reaction; S13, the effluent from the primary defluorination reaction tank enters the primary flocculation tank, and PAM is added for flocculation reaction; S14, the effluent from the primary flocculation tank enters the primary sedimentation tank for solid-liquid separation; S2, the second stage defluorination reaction process section: S21, the supernatant of the primary sedimentation tank enters the secondary defluorination reaction tank, PAC is added, liquid alkali is added to control the pH to 7-8, and the reaction is stirred; S22, the effluent from the secondary defluorination reaction tank enters the secondary flocculation tank, and PAM is added for flocculation reaction; S23, the effluent from the secondary flocculation reaction tank enters the secondary sedimentation tank for solid-liquid separation; S3, the third defluorination reaction process section: S31. The supernatant of the secondary sedimentation tank enters the electro-flocculation defluorination device, sulfuric acid is added to adjust the pH to 6-6.5, and the electro-flocculation defluorination device is started to perform the electro-flocculation defluorination reaction; S32. The effluent from the electro-flocculation defluorination device enters the tertiary sedimentation tank for solid-liquid separation, and the supernatant is directly discharged into the clear water tank for external discharge.

3. The process for deep treatment of high-concentration fluorine-containing wastewater according to claim 2, characterized in that: The bottom sludge of the primary sedimentation tank, the secondary sedimentation tank and the tertiary sedimentation tank first enters the sludge thickening tank, and the concentrated sludge then enters the filter press for solid-liquid separation, the filter cake is transported out for treatment, and the recycled water enters the primary defluorination reaction tank, and the recycled water includes: the filtrate of the filter press and the supernatant of the sludge thickening tank.

4. The process for deep treatment of high-concentration fluorine-containing wastewater according to claim 3, characterized in that: The process steps include: S1, first stage defluorination reaction process section: S11, allowing high-concentration fluoride-containing wastewater with a fluoride ion concentration of ≥2500 mg / L and recycled water to enter the primary defluorination reaction tank; S12, add lime milk to the primary defluorination reaction tank to make the calcium-fluorine molar ratio in the water 0.3-0.7, then adjust the pH to 8-9 with sulfuric acid, and stir the reaction for 1 hour; S13, the effluent from the primary defluorination reaction tank enters the primary flocculation tank, and PAM is added for flocculation reaction. The amount of PAM added is 2-6 mg / L, and the reaction time is 10-20 min; S14, the effluent from the primary flocculation tank enters the primary sedimentation tank for solid-liquid separation, and the fluoride ion concentration in the supernatant of the primary sedimentation tank is 20-35 mg / L; S2, the second stage defluorination reaction process section: S21. The supernatant of the primary sedimentation tank enters the secondary defluorination reaction tank, PAC is added in an amount of 200-600 mg / L, liquid alkali is added to control the pH to 7-8, and the reaction is stirred for 1 hour; S22, the effluent from the secondary defluorination reaction tank enters the secondary flocculation tank, and PAM is added for flocculation reaction. The amount of PAM added is 2-6 mg / L, and the reaction time is 10-20 min; S23, the effluent from the secondary flocculation reaction tank enters the secondary sedimentation tank for solid-liquid separation, and the fluoride ion concentration in the supernatant of the secondary sedimentation tank is 3-8 mg / L; S3, the third defluorination reaction process section: S31. The supernatant of the secondary sedimentation tank enters the electro-flocculation defluorination device, sulfuric acid is added to adjust the pH to 6-6.5, the electro-flocculation defluorination device is turned on, and the electro-flocculation defluorination reaction is carried out for 30 minutes; S32. The effluent from the electro-flocculation defluorination device enters the tertiary sedimentation tank for solid-liquid separation, and the supernatant is directly discharged into the clear water tank for external discharge. The fluoride ion concentration in the supernatant is ≤1.5mg / L.

5. The process for deep treatment of high-concentration fluorine-containing wastewater according to claim 4, characterized in that: The process steps include: S1, first stage defluorination reaction process section: S11, allowing high-concentration fluoride-containing wastewater with a fluoride ion concentration greater than or equal to 2500 mg / L and recycled water to enter the primary defluorination reaction tank; S12, add lime milk to the primary defluorination reaction tank to make the calcium-fluorine molar ratio in the water 0.5, then adjust the pH to 8-9 with sulfuric acid, and stir the reaction for 1 hour; S13, the effluent from the primary defluorination reaction tank enters the primary flocculation tank, and PAM is added for flocculation reaction. The amount of PAM added is 4 mg / L, and the reaction time is 15 min; S14, the effluent from the primary flocculation tank enters the primary sedimentation tank for solid-liquid separation, and the fluoride ion concentration in the supernatant of the primary sedimentation tank is 20-35 mg / L; S2, the second stage defluorination reaction process section: S21. The supernatant of the primary sedimentation tank enters the secondary defluorination reaction tank, PAC is added at an amount of 500 mg / L, and liquid alkali is added to control the pH to 7-8, and the reaction is stirred for 1 hour; S22, the effluent from the secondary defluorination reaction tank enters the secondary flocculation tank, and PAM is added for flocculation reaction. The amount of PAM added is 4 mg / L, and the reaction time is 15 min; S23, the effluent from the secondary flocculation reaction tank enters the secondary sedimentation tank for solid-liquid separation, and the fluoride ion concentration in the supernatant of the secondary sedimentation tank is 3-8 mg / L; S3, the third defluorination reaction process section: S31. The supernatant of the secondary sedimentation tank enters the electro-flocculation defluorination device, sulfuric acid is added to adjust the pH to 6-6.5, the electro-flocculation defluorination device is turned on, and the electro-flocculation defluorination reaction is carried out for 30 minutes; S32. The effluent from the electro-flocculation defluorination device enters the tertiary sedimentation tank for solid-liquid separation, and the supernatant is directly discharged into the clear water tank for external discharge. The fluoride ion concentration in the supernatant is ≤1.5mg / L.

6. The process for deep treatment of high-concentration fluorine-containing wastewater according to claim 2, characterized in that: The electro-flocculation defluorination device comprises a device housing, a first graphite electrode and a second graphite electrode fixedly installed in the device housing, a plurality of metal electrodes fixedly embedded between the first graphite electrode and the second graphite electrode, a stirring device arranged at the bottom of the device housing, a temperature control device arranged in the device housing, and a DC power supply whose positive and negative electrodes are connected to the first graphite electrode and the second graphite electrode respectively; The lower part of the device shell is provided with a water inlet, and the upper part is provided with a water outlet.

7. The process for deep treatment of high-concentration fluorine-containing wastewater according to claim 6, characterized in that: A plurality of metal electrodes are evenly spaced and arranged, and the metal electrodes are aluminum electrodes or iron electrodes.

8. The process for deep treatment of high-concentration fluorine-containing wastewater according to claim 7, characterized in that: When the electro-flocculation defluorination device is used for wastewater treatment, the first graphite electrode, the second graphite electrode and a plurality of metal electrodes in the device housing are completely immersed in water.

9. The process for deep treatment of high-concentration fluorine-containing wastewater according to claim 8, characterized in that: The metal electrodes are aluminum electrodes, and there are three of them.

10. A system for deep treatment of high-concentration fluorine-containing wastewater, characterized in that: The process as claimed in any one of claims 1 to 9 is used to treat fluorine-containing wastewater, and the system comprises: a first-stage defluorination reaction subsystem, a second-stage defluorination reaction subsystem, a third-stage defluorination reaction subsystem, and a sludge thickening tank and a filter press for treating sludge generated by the three subsystems; The first-stage defluorination reaction subsystem comprises a first-stage defluorination reaction tank, a first-stage flocculation tank and a first-stage sedimentation tank which are arranged in sequence; The second-stage defluorination reaction subsystem includes a secondary defluorination reaction tank, a secondary flocculation tank and a secondary sedimentation tank which are arranged in sequence; The third-stage defluorination reaction subsystem includes an electric flocculation defluorination device and a three-stage sedimentation tank.

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