A method for treating fluorine-containing wastewater

Abstract

The present invention provides a method for treating fluorine-containing wastewater. A multi-tower adsorption system is used to treat the fluorine-containing wastewater. The method for treating the fluorine-containing wastewater comprises the following steps: S1. At least two adsorption towers perform adsorption operations. The fluorine-containing wastewater is introduced into one adsorption tower and then flows out, and subsequently enters the remaining adsorption towers performing adsorption operations, and qualified water is obtained at the outlet; at least two adsorption towers perform desorption and regeneration operations. The regenerant is introduced into one adsorption tower performing desorption and regeneration operations and then flows out, and subsequently enters the remaining adsorption towers performing desorption and regeneration operations, and a fluorine-rich solution is obtained at the outlet; S2. The qualified water is stored or discharged, the adsorption towers performing desorption and regeneration operations are cleaned, and the cleaning liquid is returned to the fluorine-containing wastewater storage tank; S3. The fluorine-rich solution is treated, and the fluorine-depleted liquid after treatment is returned to the fluorine-containing wastewater storage tank; S4. Steps S1 to S3 are cycled in sequence. The method for treating fluorine-containing wastewater according to the present invention prolongs the adsorption time of the adsorption tower and improves the utilization rate of the adsorption tower.

Description

Technical Field

[0001] The present application relates to the technical field of fluorine-containing wastewater treatment, and in particular to a method for treating fluorine-containing wastewater. Background Art

[0002] Most of the fluorinated elastomers are obtained by emulsion polymerization of various fluoroolefins. The emulsion polymerization synthesizes fluorinated elastomers to obtain fluorinated elastomer emulsions. After degassing, the solid content of the emulsion is usually 20-35%. The emulsion composition is complex, mainly including: the target product fluorinated elastomer obtained by monomer polymerization, and also includes emulsifiers, initiators, pH regulators, chain transfer agents, low molecular weight polymers and water. Some of these components must be removed during the flocculation, washing, drying and other processes to avoid affecting the performance of the final product. Fluorine-containing wastewater is generated during the flocculation and washing processes.

[0003] At the same time, with the rapid development of information technology, new energy, new materials and other industries in recent years, a large amount of fluoride-containing wastewater has also been discharged. At present, fluoride-containing wastewater accounts for about 5% of the total industrial wastewater discharge in the country, and has gradually become an important source of environmental fluoride pollution. If this type of fluoride-containing wastewater is discharged without meeting the treatment standards, it is very easy to cause pollution of surface water, soil and groundwater. At the same time, it is also a waste of fluoride resources.

[0004] Since the emission requirements for fluorinated organic substances such as perfluoroalkyl and polyfluoroalkyl substances (PFAS) are more stringent, it is particularly important to choose a reasonable and advanced defluorination process. At present, the large-scale industrial treatment methods for this type of wastewater at home and abroad are mainly "lime precipitation" and "ion exchange". However, the above treatment methods have the characteristics of frequent regeneration and high reagent costs, resulting in high treatment costs and low defluorination efficiency. Summary of the invention

[0005] Therefore, a new technical solution is needed to achieve the goal of stable drainage up to standard and low fluorine removal cost during the treatment of fluorine-containing wastewater.

[0006] The object of the present invention is to provide a method for treating fluorine-containing wastewater.

[0007] In order to solve the above problems, the first aspect of the present invention provides a method for treating fluorine-containing wastewater, wherein the fluorine-containing wastewater is treated by a multi-tower adsorption system, wherein the multi-tower adsorption system comprises a plurality of adsorption towers, a flow control valve unit, a pipeline part and a control unit, wherein the plurality of adsorption towers are connected through a pipeline of the pipeline part, the flow control valve unit comprises a plurality of flow control valves arranged on the pipeline, and the control unit controls the opening or closing of the flow control valve to realize that the fluorine-containing wastewater and the regeneration agent enter different adsorption towers, and the effluent that meets the discharge standards and the fluorine-rich solution flow out of different adsorption towers. The method for treating fluorine-containing wastewater covers the adsorption process, the desorption process and the regeneration process, and comprises the following steps:

[0008] S1. At least two adsorption towers perform adsorption operations. The fluorine-containing wastewater is introduced into one of the adsorption towers and then flows out, and subsequently enters the remaining adsorption towers performing adsorption operations, and qualified water is obtained at the outlet.

[0009] At least two adsorption towers perform desorption and regeneration operations. The regenerant is introduced into one of the adsorption towers performing desorption and regeneration operations and then flows out, and subsequently enters the remaining adsorption towers performing desorption and regeneration operations, and a fluorine-rich solution is obtained at the outlet.

[0010] S2. The qualified water is stored or discharged, the tower performing desorption and regeneration operations is cleaned, and the cleaning liquid is returned to the fluorine-containing wastewater storage tank.

[0011] S3. The fluorine-rich solution is treated, and the defluorinated liquid after treatment is returned to the fluorine-containing wastewater storage tank.

[0012] S4. Steps S1 to S3 are cycled in sequence.

[0013] In one embodiment, the number N of the adsorption towers is estimated from the underutilized zone LUB:

[0014] ;

[0015] In the formula, L0 is the effective filling height of the adsorption tower, that is, the height of the filled adsorbent.

[0016] In one embodiment, the multi-tower adsorption system has 4 adsorption towers: the first adsorption tower, the second adsorption tower, the third adsorption tower and the fourth adsorption tower, including a cycle switching step:

[0017] First switching: Two adsorption towers are used to perform adsorption operations. The fluorine-containing wastewater enters the first adsorption tower. The first adsorption tower adsorbs the adsorbate in the fluorine-containing wastewater. After the water flows out, it enters the second adsorption tower. The effluent of the second adsorption tower is discharged or stored up to standard.

[0018] Meanwhile, the heated regenerant enters the third adsorption tower for desorption and regeneration. The desorbed liquid flowing out of the third adsorption tower enters the fourth adsorption tower. The fluorine-rich solution flowing out of the fourth adsorption tower enters the fluorine-rich solution storage tank.

[0019] Second switching: The fluorine-containing wastewater enters the second adsorption tower. The second adsorption tower adsorbs the adsorbate in the fluorine-containing wastewater. After the water flows out, it enters the third adsorption tower. The effluent of the third adsorption tower is discharged or stored up to standard.

[0020] Meanwhile, the heated regenerant enters the fourth adsorption tower for desorption and regeneration. The desorbed liquid flowing out of the fourth adsorption tower enters the first adsorption tower. The fluorine-rich solution flowing out of the first adsorption tower enters the fluorine-rich solution storage tank.

[0021] Third switching: The fluorine-containing wastewater enters the third adsorption tower. The third adsorption tower adsorbs the adsorbate in the fluorine-containing wastewater, and after discharging water, it enters the fourth adsorption tower. The effluent of the fourth adsorption tower meets the standards for discharge or storage.

[0022] Meanwhile, the heated regenerant enters the first adsorption tower for desorption regeneration. The desorbed liquid flowing out of the first adsorption tower enters the second adsorption tower, and the fluorine-rich solution flowing out of the second adsorption tower enters the fluorine-rich solution storage tank.

[0023] Fourth switching: The fluorine-containing wastewater enters the fourth adsorption tower. The fourth adsorption tower adsorbs the adsorbate in the fluorine-containing wastewater, and after discharging water, it enters the first adsorption tower. The effluent of the first adsorption tower meets the standards for discharge or storage.

[0024] Meanwhile, the heated regenerant enters the second adsorption tower for desorption regeneration. The desorbed liquid flowing out of the second adsorption tower enters the third adsorption tower, and the fluorine-rich solution flowing out of the third adsorption tower enters the fluorine-rich solution storage tank.

[0025] Return to the first switching.

[0026] In one embodiment, the adsorption tower is filled with one adsorbent or multiple adsorbents, and the adsorbent includes any one or a mixture of natural zeolite, synthetic molecular sieve, activated carbon, and adsorption resin.

[0027] In one embodiment, the adsorption process includes a physical adsorption process and a chemical adsorption process. The desorption process is determined according to the characteristics of the physical or chemical adsorption process, including hot water desorption of temperature swing adsorption, acid-base desorption of chemical adsorption, and activation of the adsorbent.

[0028] In one embodiment, the fluorine-containing wastewater includes fluorine-containing organic wastewater, fluorine-containing inorganic wastewater, or a mixture thereof.

[0029] In one embodiment, when steps S1 to S3 are cycled, the time for adsorption, desorption, and regeneration is the same.

[0030] In one embodiment, the fluorine-rich solution is further treated by chemical precipitation or evaporation concentration. The treatment process produces precipitates or concentrated solutions, and at the same time, produces fluorine-poor wastewater.

[0031] In one embodiment, the fluorine-containing wastewater to be treated includes two parts. One is the raw fluorine-containing wastewater, and the other is the fluorine-poor wastewater generated during the regeneration, cleaning, or treatment of the fluorine-rich solution.

[0032] In one embodiment, the regenerant is prepared from the effluent meeting the discharge standards or deionized water.

[0033] In one embodiment, the regeneration process includes a desorption process using a regenerant and a cleaning process using the effluent meeting the discharge standards or deionized water.

[0034] Compared with the prior art, the advantages of the present invention are as follows:

[0035] In this embodiment, a multi-tower adsorption system is designed based on the less utilized zone (LUB) of the adsorption process, so that the LUB of the adsorption tower is fully utilized, the adsorption time is extended, and the utilization rate of the adsorption tower is improved.

[0036] Furthermore, under the condition of maintaining the same removal rate, the concentration of the fluorine-rich solution obtained by regeneration is high, which can significantly improve the treatment efficiency of the fluorine-containing wastewater and is beneficial to the further treatment of the fluorine-rich solution. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 is the concentration profile along the adsorption tower at the adsorption breakthrough;

[0038] Figure 2a is a schematic diagram of the adsorption bed after regeneration;

[0039] Figure 2b is a schematic diagram of the first step in multi-step purification;

[0040] Figure 2c is a schematic diagram of the second step in multi-step purification;

[0041] Figure 2d is a schematic diagram of the third step in multi-step purification;

[0042] Figure 2e is a schematic diagram of the fourth step in multi-step purification;

[0043] Figure 3a is a schematic diagram of the first switching of the four-tower cyclic adsorption;

[0044] Figure 3b is a schematic diagram of the second switching of the four-tower cyclic adsorption;

[0045] Figure 3c is a schematic diagram of the third switching of the four-tower cyclic adsorption;

[0046] Figure 3d is a schematic diagram of the fourth switching of the four-tower cyclic adsorption;

[0047] Figure 4 is a process flow diagram of the four-tower continuous adsorption. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0048] The embodiments of the present application will be described in detail below with reference to the accompanying drawings.

[0049] The following describes the embodiments of the present application through specific specific examples. Those skilled in the art can easily understand the other advantages and effects of the present application from the content disclosed in this specification. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all embodiments. The present application can also be implemented or applied through other different specific implementation manners. Various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present application. It should be noted that, without conflict, the following embodiments and the features in the embodiments can be combined with each other. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without making creative efforts belong to the scope of protection of the present application.

[0050] It should be noted that the following describes various aspects of the embodiments within the scope of the appended claims. It should be obvious that the aspects described herein can be embodied in a wide variety of forms, and any specific structure and / or function described herein is illustrative only. Based on the present application, those skilled in the art should understand that one aspect described herein can be implemented independently of any other aspect, and two or more of these aspects can be combined in various ways. For example, any number and aspects described herein can be used to implement the device and / or practice the method. Additionally, this device and / or this method can be implemented using other structures and / or functionality in addition to one or more of the aspects described herein.

[0051] It should also be noted that the drawings provided in the following embodiments only illustrate the basic concept of the present application schematically. The drawings only show the components related to the present application and are not drawn according to the number, shape, and size of the components in actual implementation. The type, quantity, and ratio of each component in its actual implementation can be an arbitrary change, and the component layout type may also be more complex.

[0052] In addition, in the following description, specific details are provided to facilitate a thorough understanding of the examples. However, those skilled in the art will understand that the described aspects can be practiced without these specific details.

[0053] Embodiment

[0054] The fluorine-containing wastewater includes fluorine-containing organic wastewater, fluorine-containing inorganic wastewater, or a mixture thereof. The fluorine-containing wastewater to be treated includes two parts. One is the raw fluorine-containing wastewater, and the other is the poor-fluorine wastewater generated during the regeneration, cleaning, or treatment of the fluorine-rich solution.

[0055] The treatment of fluoride-containing wastewater by adsorption is considered an effective, low-energy-consuming, and environmentally friendly method. Currently, there are numerous adsorbents, such as natural zeolites, synthetic molecular sieves, activated carbon, adsorption resins, or their mixtures, which have been widely used to adsorb pollutants in aqueous solutions.

[0056] Due to the more stringent emission requirements for fluorinated organic substances such as per- and polyfluoroalkyl substances (PFAS), it is particularly important to select a reasonable and advanced defluorination process. Currently, the main large-scale industrial treatment methods for this type of wastewater at home and abroad are "lime precipitation" and "ion exchange". However, the above treatment methods have high treatment costs and low defluorination efficiency due to frequent regeneration and high reagent costs.

[0057] The perfluoroether elastomer is prepared by emulsion polymerization. In one example, the solid content of the residual liquid obtained after centrifugal coagulation and washing of the emulsion is 3.35%. The addition amount of the emulsifier perfluorooctanoic acid (PFOA) during polymerization is about 0.47% (weight ratio), and the residual amount in the emulsion is about 1350 mg / L. The discharge standard after treatment is 0.1 - 1 mg / L.

[0058] Ion exchange resins are generally used to treat and separate small molecule pollutants in water. However, the molecular volume of perfluoro organic pollutants is relatively large, and as surfactants, they may form micelles and semi-micelles. It is difficult to activate and regenerate ion exchange resins saturated with adsorbed perfluoro organic pollutants by ion exchange resin regeneration technology. Therefore, in this application, activated carbon adsorption is first used to remove most of the perfluoro organic pollutants, making the concentration of perfluoro organic pollutants reach the milligram level, and then ion exchange resin treatment is used.

[0059] The acid dissociation constant pKa of perfluoro organic pollutants is relatively small. For example, the pKa of PFOA is about -0.5, and most of it exists in the fluoride-containing wastewater in the form of negatively charged anions. The perfluoro organic pollutants treated by activated carbon adsorption are mainly PFOA, which is a weakly adsorbed component due to its small molecular weight. In subsequent experiments, the breakthrough curve of adsorption was characterized by measuring the concentration change of PFOA.

[0060] The surface of the ion exchange resin has a large number of ion exchange sites, and the perfluoro organic surfactant PFOA in water can be removed through the ion exchange process occurring on the resin surface. In addition, perfluoro organic pollutants have a hydrophobic carbon-fluorine chain structure, and the ion exchange resin can also adsorb and remove them through hydrophobic effects.

[0061] In this embodiment, the meanings of desorption and regeneration are different. Desorption includes the process of using a regenerant to separate the adsorbed substances in the fluorine-containing wastewater from the adsorbent and flowing out of the adsorption tower with the regenerant; regeneration includes the desorption process, but also includes temperature reduction (such as hot water regeneration), neutralization (such as alkali solution regeneration), activation of the adsorbent, and replacement and cleaning processes using up-to-standard discharged effluent or deionized water, so that the regenerated adsorption tower is in a state of entering the next cycle. The adsorption process includes physical adsorption and chemical adsorption processes. The desorption process is determined according to the characteristics of the physical adsorption process, including hot water desorption of temperature swing adsorption, acid-base desorption of chemical adsorption, and activation of the adsorbent. The regeneration process includes the desorption process using a regenerant and the replacement and cleaning processes using up-to-standard discharged effluent or deionized water. The desorption process using a regenerant produces a fluorine-rich solution, and the solution produced by the replacement and cleaning process is returned to the fluorine-containing wastewater treatment system.

[0062] The multi-tower adsorption system designed according to the less utilized zone (LUB) in this embodiment makes full use of the LUB of the adsorption tower, prolongs the adsorption time, and the concentration of the fluorine-rich solution obtained by regeneration is high, which is beneficial to the further treatment of the fluorine-rich solution and improves the utilization rate of the adsorption tower.

[0063] As Figure 1 shown, the size of the mass transfer zone (MTZ) of adsorption is determined by the diffusion trend caused by non-equilibrium adsorption or backmixing and the sharpening trend caused by the non-linearity of adsorption equilibrium. The size of the less utilized zone (LUB) is related to the MTZ and depends on the concentration of the given breakthrough point, that is, the concentration of the up-to-standard discharged effluent. After the adsorption system is determined, the outlet concentration of up-to-standard discharge largely determines the efficiency of the adsorption system. Among them, Figure 1 the serial number 1 in it represents the diffusion trend caused by non-equilibrium adsorption or backmixing; the serial number 2 represents the sharpening trend caused by the non-linearity of adsorption equilibrium; the serial number 3 represents that the low concentration zone is controlled by adsorption equilibrium. Wherein, SZ is the saturation zone; MTZ is the mass transfer zone; LUB is the less utilized zone.

[0064] Figure 1 describes the axial change of the concentration of the adsorbed substance in the fluorine-containing wastewater at a typical moment during the adsorption process. The filling height of the adsorption tower refers to the height of the adsorbent filled in the adsorption tower, excluding the height of the head and demister of the adsorption tower, etc. The concentration in the SZ saturation zone is the concentration of the adsorbed substance in the fluorine-containing wastewater when the adsorbent adsorption reaches saturation, that is, the initial concentration C0 of the adsorbed substance in the fluorine-containing wastewater; the MTZ mass transfer zone contains an adsorption front, and the concentration of the adsorbed substance in the fluorine-containing wastewater decreases sharply. The size of the MTZ is jointly controlled by adsorption equilibrium and mass transfer diffusion effects. If the adsorption equilibrium constant of adsorption equilibrium is large or the mass transfer diffusion effect is small, the MTZ is small, that is, the adsorption process is controlled by adsorption equilibrium, otherwise the adsorption process is controlled by mass transfer diffusion; LUB is the less utilized zone. Let the concentration of the breakthrough point be C b ., if Cb / C0 = 0.01, that is, when the concentration at the outlet of the adsorption tower reaches the breakthrough point concentration C b the adsorbent in the adsorption tower needs to be regenerated. Obviously, the concentration of the adsorbed substance adsorbed by the adsorbent in the LUB region is low. Especially when the emission requirements are strict and the initial concentration is relatively high, the adsorbent in the LUB section is not fully utilized, resulting in a low concentration multiple of the adsorbed substance during the regeneration of the adsorption tower, an increase in the amount of regenerant consumed per unit of adsorbed substance, and a decrease in the post-treatment efficiency of the concentrated solution of the adsorbed substance.

[0065] To make the underutilized LUB region be utilized, a multi-tower structure needs to be adopted.

[0066] For gas-phase adsorption, the main purpose of adopting multi-tower adsorption is the pressure equalization process, and multi-step pressure equalization in multiple towers is used to recover pressure energy. For liquid-phase adsorption, adopting multiple towers does not have the direct benefits similar to gas-phase adsorption. However, from the perspectives of improving the utilization rate of the adsorbent, increasing the concentration multiple of the adsorbed substance, and reducing the amount of regenerant consumed per unit of adsorbed substance, it has certain economic benefits.

[0067] Figures 2a - 2e is a schematic diagram of simulating the adsorption of two towers and the desorption and regeneration of two towers in multiple steps by one tower according to the underutilized LUB region of the adsorption system, where CZ is the clean zone.

[0068] First, it is the regenerated adsorption tower in the standby stage as shown in Figure 2a which is associated with the 4th step as shown in Figure 2e . The feed inlet of the fluorine-containing wastewater in the adsorption process is the discharge outlet of the regeneration process. The regeneration process does not require complete regeneration, and a part of the MTZ region is left. The 1st step as shown in Figure 2b is a conventional treatment process, that is, the fluorine-containing wastewater is treated by the adsorption tower to obtain the up-to-standard discharged water. As the adsorption process proceeds, the adsorption front in the MTZ region moves forward, forming the SZ saturation zone and the LUB zone, and the concentration of the adsorbed substance at the outlet has reached the breakthrough point. The traditional adsorption process enters the regeneration stage at this time. However, in this application, the adsorption potential of the LUB region is utilized to continue treating the fluorine-containing wastewater in the 2nd step as shown in Figure 2c .

[0069] Obviously, when treating the fluorine-containing wastewater in the 2nd step, the concentration of the adsorbed substance at the outlet has exceeded the breakthrough point and cannot meet the discharge standard. The method adopted in this application is to connect the outlet to the second adsorption tower until the concentration at the outlet of the first adsorption tower is relatively high and the adsorption process approaches the MTZ, then the first adsorption tower enters the regeneration stage.

[0070] As shown in Figure 2dThe third step shown involves the regeneration stage. The regeneration stage includes the process of regeneration using a regenerant and displacement cleaning after regeneration with a cleaning agent such as deionized water. With the continuous addition of the regenerant, a CZ clean area gradually forms at the upper end of the adsorption tower, while the SZ saturated area gradually moves downward and is discharged from the adsorption tower to form a fluorine-rich solution until the MTZ mass transfer zone moves down to the outlet. After displacement cleaning with deionized water, the entire regeneration stage is completed. Among them, the regeneration stage is also a two-tower series connection. In the third step, one tower completes partial regeneration and then is connected in series with another tower to be regenerated. Due to the series connection of two towers, the concentration of the concentrated solution obtained by regeneration is high. Although the amount of regenerant used is more than that for single-tower adsorption and single-tower regeneration, it is less than the amount for two runs. Therefore, it increases the concentration multiple of the adsorbate and reduces the amount of regenerant consumed per unit of adsorbate obtained, having certain economic benefits.

[0071] Figures 3a - 3d is a schematic diagram of the four-tower cyclic adsorption switching process. The four adsorption towers are adsorption tower I, adsorption tower II, adsorption tower III, and adsorption tower IV. In the figure, FS is fluorine-containing wastewater; BS is the up-to-standard discharge water; ZS is the regenerant; FY is the fluorine-rich solution.

[0072] Table 1 is related to Figures 3a - 3d the operating status and timing during the operation of the four-tower adsorption process for fluorine-containing wastewater corresponding thereto.

[0073] Table 1 Operating Status and Timing during the Operation of the Four-Tower Adsorption Process for Fluorine-Containing Wastewater

[0074]

[0075] A method for treating fluorine-containing wastewater uses a multi-tower adsorption system to treat fluorine-containing wastewater. The multi-tower adsorption system includes multiple adsorption towers, a flow control valve unit, a pipeline section, and a control unit. The multiple adsorption towers are connected through the pipelines of the pipeline section. The flow control valve unit has multiple flow control valves arranged on the pipelines. The control unit controls the opening or closing of the flow control valves to enable fluorine-containing wastewater and the regenerant to enter different adsorption towers, and the up-to-standard discharge water and the fluorine-rich solution to flow out from different adsorption towers.

[0076] Figure 4 is the process flow diagram of the four-tower continuous adsorption process in the embodiment.

[0077] The adsorption system in the embodiment includes four adsorption towers, as Figure 4As shown, the four adsorption towers are adsorption tower I, adsorption tower II, adsorption tower III, and adsorption tower IV. The adsorption system further includes a flow control valve unit, a pipeline section, storage tanks, a control unit, a pump, and a regeneration system (heating or chemical agent). The flow control valve unit includes multiple fluoride-containing wastewater inlet valves (valve 104, valve 204, valve 304, valve 404, valve 601-1 are respectively connected to the upper fluoride-containing wastewater inlet pipeline 601; valve 105, valve 205, valve 305, valve 405, valve 602-1 are respectively connected to the lower fluoride-containing wastewater inlet pipeline 602), multiple up-to-standard discharge outlet valves (valve 102, valve 202, valve 302, valve 402, valve 701-1 are respectively connected to the upper up-to-standard discharge outlet pipeline 701; valve 107, valve 207, valve 307, valve 407, valve 702-1 are respectively connected to the lower up-to-standard discharge outlet pipeline 702), multiple regenerant inlet valves (valve 103, valve 203, valve 303, valve 403, valve 801-1 are respectively connected to the upper regenerant inlet pipeline 801; valve 106, valve 206, valve 306, valve 406, valve 802-1 are respectively connected to the lower regenerant inlet pipeline 802), and multiple fluorine-rich solution valves (valve 101, valve 201, valve 301, valve 401, valve 501-1 are respectively connected to the upper fluorine-rich solution pipeline 501; valve 108, valve 208, valve 308, valve 408, valve 502-1 are respectively connected to the lower fluorine-rich solution pipeline 502). The pipeline section includes a fluoride-containing waste liquid inlet pipeline, an up-to-standard discharge outlet pipeline, a regenerant inlet pipeline, and a fluorine-rich solution pipeline. The storage tanks include a fluoride-containing wastewater storage tank, an up-to-standard discharge outlet storage tank, a regenerant storage tank, and a fluorine-rich solution storage tank. The bottom and top of each adsorption tower are both connected to the fluoride-containing wastewater inlet pipeline. One fluoride-containing wastewater inlet valve is provided on each fluoride-containing wastewater inlet pipeline and is connected to the fluoride-containing wastewater inlet storage tank; at the same time, the bottom or top of each adsorption tower is both connected to the up-to-standard discharge outlet pipeline. One up-to-standard discharge outlet valve is provided on each up-to-standard discharge outlet pipeline and is connected to the up-to-standard discharge outlet storage tank; at the same time, the bottom or top of each adsorption tower is both connected to the regenerant inlet pipeline. One regenerant inlet valve is provided on each regenerant inlet pipeline and is connected to the regenerant inlet storage tank; at the same time, the bottom or top of each adsorption tower is both connected to the fluorine-rich solution pipeline. One fluorine-rich solution valve is provided on each concentrated solution pipeline and is connected to the fluorine-rich solution storage tank. The pipelines at the bottom and top are respectively connected and are respectively connected to the pump. The control unit controls the opening or closing of the flow control valves and the on and off of the pump. The discharged water meeting the standards and the fluorine-rich solution are detected by detection equipment; the adsorption towers, pipelines, valves, and storage tanks are insulated.

[0078] In one embodiment, the regenerant is hot water at a certain temperature. The hot water is heated by electricity or steam. After hot water regeneration, normal temperature water is used for replacement to cool down the adsorption tower for the next cycle operation.

[0079] In one embodiment, the regenerant is an acidic solution. After regeneration, it is neutralized with an alkaline solution and replaced with normal temperature water for the next cycle operation. The regenerant in this application is prepared with the effluent meeting the discharge standards or deionized water.

[0080] A method for treating fluoride-containing wastewater, comprising the following steps:

[0081] S1. At least two adsorption towers perform adsorption operations. The fluoride-containing wastewater is introduced into one of the adsorption towers and then flows out, and subsequently enters the remaining adsorption towers performing adsorption operations, and qualified water is obtained at the outlet.

[0082] At least two adsorption towers perform desorption and regeneration operations. The regenerant is introduced into one of the adsorption towers performing desorption and regeneration operations and then flows out, and subsequently enters the remaining adsorption towers performing desorption and regeneration operations, and a fluoride-rich solution is obtained at the outlet.

[0083] S2. The qualified water is stored or discharged, and the adsorption tower performing desorption and regeneration operations is cleaned, and the cleaning liquid is returned to the fluoride-containing wastewater storage tank.

[0084] S3. The fluoride-rich solution is treated, and the defluorinated liquid after treatment is returned to the fluoride-containing wastewater storage tank.

[0085] S4. Steps S1 to S3 are cycled in sequence.

[0086] In one embodiment, when steps S1 to S3 are cycled, the time for adsorption is the same as that for desorption and regeneration.

[0087] In one embodiment, the multi-tower adsorption system has at least 4 adsorption towers: the first adsorption tower, the second adsorption tower, the third adsorption tower and the fourth adsorption tower, including the following cycle switching steps:

[0088] First switch: Two adsorption towers are used to perform adsorption operations. The fluoride-containing wastewater enters the first adsorption tower. The first adsorption tower adsorbs the adsorbate in the fluoride-containing wastewater. After the water flows out, it enters the second adsorption tower. The effluent of the second adsorption tower is discharged or stored up to the standard.

[0089] At the same time, the heated regenerant enters the third adsorption tower for desorption and regeneration. The desorbed liquid flowing out of the third adsorption tower enters the fourth adsorption tower. The fluoride-rich solution flowing out of the fourth adsorption tower enters the fluoride-rich solution storage tank.

[0090] Second switch: The fluoride-containing wastewater enters the second adsorption tower. The second adsorption tower adsorbs the adsorbate in the fluoride-containing wastewater. After the water flows out, it enters the third adsorption tower. The effluent of the third adsorption tower is discharged or stored up to the standard.

[0091] Meanwhile, the heated regenerant enters the fourth adsorption tower for desorption regeneration. The desorbed liquid flowing out of the fourth adsorption tower enters the first adsorption tower, and the fluorine-rich solution flowing out of the first adsorption tower enters the fluorine-rich solution storage tank;

[0092] Third switching: The fluorine-containing wastewater enters the third adsorption tower. The third adsorption tower adsorbs the adsorbate in the fluorine-containing wastewater. After the water outlet, it enters the fourth adsorption tower. The water outlet of the fourth adsorption tower meets the discharge standard or is stored;

[0093] Meanwhile, the heated regenerant enters the first adsorption tower for desorption regeneration. The desorbed liquid flowing out of the first adsorption tower enters the second adsorption tower, and the fluorine-rich solution flowing out of the second adsorption tower enters the fluorine-rich solution storage tank;

[0094] Fourth switching: The fluorine-containing wastewater enters the fourth adsorption tower. The fourth adsorption tower adsorbs the adsorbate in the fluorine-containing wastewater. After the water outlet, it enters the first adsorption tower. The water outlet of the first adsorption tower meets the discharge standard or is stored;

[0095] Meanwhile, the heated regenerant enters the second adsorption tower for desorption regeneration. The desorbed liquid flowing out of the second adsorption tower enters the third adsorption tower, and the fluorine-rich solution flowing out of the third adsorption tower enters the fluorine-rich solution storage tank,

[0096] Return to the first switching.

[0097] Specifically, this embodiment adopts a 4-tower system (except as otherwise specified, all valves are in the normally closed state), including the following 4 cyclic switches (in combination Figures 3a - 3d and Figure 4 ):

[0098] 1. First switching: Two adsorption towers are used to perform the adsorption operation. Valve 601-1 and valve 104 are opened, and the fluorine-containing wastewater FS enters from the top of adsorption tower I. Adsorption tower I that performs the adsorption operation adsorbs the adsorbate in the fluorine-containing wastewater FS. After the water outlet, it enters adsorption tower II from the bottom through valve 105 via pipeline 602 (valve 602-1 is closed) and valve 205. The water outlet BS is discharged up to the standard or stored through valve 202 and valve 701-1 via pipeline 701 (valve 702-1 is closed); Meanwhile, the heated regenerant ZS enters adsorption tower III from the bottom through pipeline 802 via valve 802-1 and valve 306 for desorption regeneration. The desorbed concentrated liquid coming out from the top enters adsorption tower IV from the top through valve 304 via pipeline 601 and valve 404. The discharged fluorine-rich solution FY flows out from the bottom of adsorption tower IV and enters the fluorine-rich solution storage tank through valve 408 and valve 502-1 via pipeline 502, completing one cycle. Corresponding Figure 3a to the first switching in and the first cycle in Table 1.

[0099] 2. Second switch: Open valve 602-1 and valve 205 to introduce fluorine-containing wastewater FS from the bottom of Adsorption Tower II. Adsorption Tower II performing the adsorption operation adsorbs the adsorbate in the fluorine-containing wastewater FS. After the water outlet, it enters Adsorption Tower III from the top through valve 204 via pipeline 601 and valve 304. The effluent BS is discharged up to standard or stored through valve 307 and valve 702-1 via pipeline 702; meanwhile, the heated regenerant ZS enters Adsorption Tower IV from the top through valve 801-1 via pipeline 801 and valve 403 for desorption regeneration. The concentrated liquid desorbed from the bottom of the tower enters Adsorption Tower I from the bottom through valve 408 via pipeline 502 and valve 108. The discharged fluorine-rich solution FY flows out from the top of Adsorption Tower I and enters the fluorine-rich solution storage tank through valve 101 and valve 501-1 via pipeline 501, completing one cycle. Corresponding to Figure 3b the second switch in

[0100] 3. Third switch: Open valve 601-1 and valve 304 to introduce fluorine-containing wastewater FS from the top of Adsorption Tower III. Adsorption Tower III performing the adsorption operation adsorbs the adsorbate in the fluorine-containing wastewater FS. After the water outlet, it enters Adsorption Tower IV from the bottom through valve 305 via pipeline 601 and valve 405 (valve 602-1 is closed). The effluent BS is discharged up to standard or stored through valve 402 and valve 701-1 via pipeline 701; meanwhile, the heated regenerant ZS enters Adsorption Tower I from the bottom through pipeline 802 and valve 802-1 and valve 106 for desorption regeneration. The concentrated liquid desorbed from the top of the tower enters Adsorption Tower II from the top through valve 103 via pipeline 801 and valve 203. The discharged fluorine-rich solution FY flows out from the bottom of Adsorption Tower II and enters the fluorine-rich solution storage tank through valve 208 and valve 502-1 via pipeline 502, completing one cycle. Corresponding to Figure 3c the third switch in

[0101] 4. Fourth switch: Open valve 602-1 and valve 405 to introduce fluorine-containing wastewater FS from the bottom of Adsorption Tower IV. Adsorption Tower IV performing the adsorption operation adsorbs the adsorbate in the fluorine-containing wastewater FS. After the water outlet, it enters Adsorption Tower I from the top through valve 404 via pipeline 601 and valve 104 (valve 601-1 is closed). The effluent BS is discharged up to standard or stored through valve 107 and valve 702-1 via pipeline 702; meanwhile, the heated regenerant ZS enters Adsorption Tower II from the top through pipeline 801 and valve 801-1 and valve 203 for desorption regeneration. The concentrated liquid desorbed from the bottom of the tower enters Adsorption Tower III from the bottom through valve 206 via pipeline 802 and valve 306 (valve 802-1 is closed). The discharged fluorine-rich solution FY flows out from the top of Adsorption Tower III and enters the fluorine-rich solution storage tank through valve 301 and valve 501-1 via pipeline 501, completing one cycle. Corresponding to Figure 3d the fourth switch in

[0102] 5. Treat the fluorine-rich solution, and the fluorine-rich solution is further treated by chemical precipitation or evaporation and concentration methods. During the treatment process, precipitates or concentrated solutions are generated, and at the same time, fluorine-depleted wastewater is generated. The treated fluorine-depleted wastewater is returned to the fluorine-containing wastewater storage tank.

[0103] 6. Cycle steps 1 and 5 in sequence.

[0104] The above desorption process ensures that the desorbent inlet is the low-concentration area of the tower, while the outlet of the adsorption process is the low-concentration area of the tower.

[0105] The design of the pipeline and the selection of the valve should consider the volume relative to the adsorption tower. The dead volume of the pipeline and the valve should be small, and the dead volume of the head and distributor of the adsorption tower should also be considered. Of course, it is more accurate to consider the throughput of each adsorption tower.

[0106] The number N of adsorption towers in this application is estimated from the underutilized zone LUB:

[0107] ;

[0108] where L0 is the packed height of the adsorption tower.

[0109] It should be noted that for a specific adsorption system (i.e., the adsorbent, adsorbate, and regeneration method are certain), the size of LUB has a great relationship with the set outlet concentration.

[0110] For example, C0 = 200 ppm, the breakthrough point C b = 10 ppm, the adsorption equilibrium is of the Langmuir type, the SZ saturated adsorption zone is relatively long, and the MTZ adsorption mass transfer zone is close to 10 ppm. Single-tower adsorption and single-tower desorption can be adopted.

[0111] Under the same conditions, if the breakthrough point is C b = 0.5 ppm, which is the discharge requirement for the treatment of F-ion-containing wastewater in a certain area at the present stage. Then the SZ saturated adsorption zone is relatively short, the LUB zone is relatively long, close to half of the effective length of the adsorption tower, then

[0112] ;

[0113] Rounding 1.82 gives 2.

[0114] That is, two-tower adsorption and two-tower desorption are adopted. Because the breakthrough point concentration is low and the adsorption tower breaks through quickly, two-tower adsorption and two-tower regeneration are more beneficial.

[0115] Generally, N is less than 1.2, rounded to 1; N = 1.2 - 2.2, rounded to 2; N = 2.2 - 3.2, rounded to 3, and so on.

[0116] Measurement of PFOA

[0117] Using n-hexane and acetone as solvents for extracting PFOA, after centrifugation (high-speed centrifuge TG-19, Sichuan Shuke Instrument Co., Ltd.), the supernatant was taken and the content of PFOA was determined by GC / MS (Agilent 8860-5977C). The detection limit was 0.1 mg / L.

[0118] In a residue of an emulsion in one example, the concentration of perfluorooctanoic acid PFOA after activated carbon adsorption was C0 = 12 mg / L, and the pH was about 5.8. It was denoted as fluorine-containing wastewater FS and reserved for use.

[0119] Example 1

[0120] Treatment of fluorine-containing wastewater FS with single-column adsorption / single-column desorption of strongly basic adsorption resin

[0121] The 201×7 gel-type strongly basic anion exchange resin (Hebei Meifeng Chemical Building Materials Co., Ltd.) is an anion exchange resin with quaternary ammonium groups [-N(CH3)3OH] on a cross-linked 7% styrene-divinylbenzene copolymer. Its alkalinity is equivalent to that of general quaternary amine bases, and it shows ion exchange function in acidic, neutral, and even alkaline media. The mass total exchange capacity (dry) ≥ 3.60 mmol / g, the wet true density is 1.07 - 1.10 g / ml, and it is in the Cl -1 type when leaving the factory.

[0122] After cleaning with deionized water, 4 - 5% dilute hydrochloric acid, and 4 - 5% sodium hydroxide solution, it was treated with 4 - 5% NaOH for transformation. It was packed into a column wetly. The diameter d of the adsorption column was 3.5 cm, and the packing height L was 80 cm. The temperature was controlled at 45 ± 2 °C by a constant-temperature water jacket. An empty volume was left at the upper part of the ion exchange column to accommodate a transformation expansion rate of about 20%.

[0123] Let the empty tower operating flow rate be u (unit: m / h), then the unit time treatment capacity Q is u / L (unit: BV, BV is the effective empty tower volume of the bed), and the average residence time t R is L / u (unit: h).

[0124] Collect the volume V1 and concentration C1 of the solution flowing out during the adsorption process; after the adsorption is completed, it is regenerated by countercurrent with 4 - 5% dilute hydrochloric acid. After regeneration, it is neutralized and transformed with 4 - 5% NaOH. Collect the volume V2 and concentration C2 of the regenerant. Finally, it is washed and replaced with deionized water, and the solution generated during the replacement washing process is returned to the fluorine-containing wastewater treatment system.

[0125] The removal rate and concentration multiple of PFOA were calculated respectively as follows:

[0126] ;

[0127] ;

[0128] The calculation results are shown in Table 2.

[0129] Table 2 Breakthrough curve data and estimated parameters during single-column adsorption operation

[0130]

[0131] Example 2

[0132] Treatment of fluoride-containing wastewater FS with strongly basic anion exchange resin by two-column adsorption / two-column regeneration

[0133] According to Example 1, the diameter of the adsorption column is 3.5 cm, and the packing height is half of that in Example 1, i.e., 40 cm. The temperature is controlled at 45 ± 2 °C by a constant-temperature water jacket, and an empty volume is left at the upper part of the ion exchange column to accommodate a transformation expansion rate of about 20%.

[0134] The adsorption time is the same as that in Example 1, and the regeneration treatment is the same as that in Example 1.

[0135] The experimental results are shown in Table 3.

[0136] Table 3 Breakthrough curve data and estimated parameters during four-column adsorption operation

[0137]

[0138] As can be seen from Table 2, under the condition of maintaining the same removal rate (99%), when a lower flow rate is adopted, the breakthrough time is correspondingly extended (from 20 BV to 30 BV), and the concentration multiple is increased (from 2.8 times to 3.3 times).

[0139] As can be seen from Table 3, under the condition of maintaining the same removal rate (99%) and adsorption time, by adopting a four-column cycle, the concentration multiple is significantly increased, from 3.3 times to 5.5 times (lower flow rate) and from 2.8 times to 4.2 times (higher flow rate), respectively.

[0140] In this specification, the same or similar parts among the various embodiments can be referred to each other, and each embodiment focuses on the differences from other embodiments. In particular, for the embodiments described later, the description is relatively simple, and the relevant parts can be referred to the partial description of the foregoing embodiments.

[0141] The above are only specific embodiments of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed in the present application should be covered by the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A method for treating fluoride-containing wastewater, which uses a multi-tower adsorption system to treat the fluoride-containing wastewater, is characterized in that The multi-tower adsorption system is designed based on the underutilized area, and includes multiple adsorption towers, a flow control valve unit, a pipeline section and a control unit. The multiple adsorption towers are connected through the pipelines of the pipeline section. The flow control valve unit has multiple flow control valves arranged on the pipelines. The control unit controls the opening or closing of the flow control valves to enable the fluorine-containing wastewater and the regenerant to enter different adsorption towers, and the up-to-standard discharged water and the fluorine-rich solution to flow out from different adsorption towers. A method for treating fluorine-containing wastewater covers an adsorption process, a desorption process and a regeneration process, and includes the following steps: S1. At least two adsorption towers perform adsorption operations. After the fluorine-containing wastewater is introduced into one adsorption tower and then flows out, it then enters the remaining adsorption towers performing adsorption operations, and up-to-standard water is obtained at the outlet. At least two adsorption towers perform desorption and regeneration operations. After the regenerant is introduced into one adsorption tower performing desorption and regeneration operations and then flows out, it then enters the remaining adsorption towers performing desorption and regeneration operations, and a fluorine-rich solution is obtained at the outlet. The multi-tower adsorption system has at least 4 adsorption towers: the first adsorption tower, the second adsorption tower, the third adsorption tower and the fourth adsorption tower, and includes a cycle switching step: First switching: Two adsorption towers are used to perform adsorption operations. The fluorine-containing wastewater enters the first adsorption tower. The first adsorption tower adsorbs the adsorbate in the fluorine-containing wastewater. After the water flows out, it enters the second adsorption tower. The water discharged from the second adsorption tower is discharged up to standard or stored. At the same time, the heated regenerant enters the third adsorption tower for desorption and regeneration. The desorbed liquid flowing out of the third adsorption tower enters the fourth adsorption tower. The fluorine-rich solution flowing out of the fourth adsorption tower enters the fluorine-rich solution storage tank. Second switching: The fluorine-containing wastewater enters the second adsorption tower. The second adsorption tower adsorbs the adsorbate in the fluorine-containing wastewater. After the water flows out, it enters the third adsorption tower. The water discharged from the third adsorption tower is discharged up to standard or stored. At the same time, the heated regenerant enters the fourth adsorption tower for desorption and regeneration. The desorbed liquid flowing out of the fourth adsorption tower enters the first adsorption tower. The fluorine-rich solution flowing out of the first adsorption tower enters the fluorine-rich solution storage tank. Among them, when the adsorption process of the first adsorption tower performing the adsorption operation approaches the mass transfer zone, it enters the regeneration stage. S2. The up-to-standard water is stored or discharged, and the adsorption towers performing desorption and regeneration operations are cleaned, and the cleaning liquid returns to the fluorine-containing wastewater storage tank. S3. The fluorine-rich solution is treated, and the poor fluorine liquid after treatment returns to the fluorine-containing wastewater storage tank. S4. Steps S1 to S3 are cycled in sequence.

2. The method for treating fluorine-containing wastewater according to claim 1, wherein The number of the adsorption towers is determined by the underutilized area of the adsorption system.

3. The method for treating fluorine-containing wastewater according to claim 1, wherein The cycle switching step in S1 further includes: Third switching: The fluorine-containing wastewater enters the third adsorption tower. The third adsorption tower adsorbs the adsorbate in the fluorine-containing wastewater. After the water flows out, it enters the fourth adsorption tower. The water discharged from the fourth adsorption tower is discharged up to standard or stored. At the same time, the heated regenerant enters the first adsorption tower for desorption and regeneration. The desorbed liquid flowing out of the first adsorption tower enters the second adsorption tower. The fluorine-rich solution flowing out of the second adsorption tower enters the fluorine-rich solution storage tank. Fourth switching: The fluorine-containing wastewater enters the fourth adsorption tower. The fourth adsorption tower adsorbs the adsorbate in the fluorine-containing wastewater. After the water outlet, it enters the first adsorption tower, and the water outlet of the first adsorption tower is discharged up to standard or stored. Meanwhile, the heated regenerant enters the second adsorption tower for desorption regeneration. The desorption liquid flowing out of the second adsorption tower enters the third adsorption tower, and the fluorine-rich solution flowing out of the third adsorption tower enters the fluorine-rich solution storage tank. Return to the first switching.

4. The method for treating fluorine-containing wastewater according to claim 1, wherein The adsorption tower is filled with one adsorbent or multiple adsorbents. The adsorbent includes any one or a mixture of natural zeolite, synthetic molecular sieve, activated carbon, and adsorption resin.

5. The method for treating fluorine-containing wastewater according to claim 1, wherein The adsorption process includes a physical adsorption process and a chemical adsorption process. The desorption process is determined according to the characteristics of the physical or chemical adsorption process, including hot water desorption of temperature swing adsorption, acid-base desorption of chemical adsorption, and activation of the adsorbent.

6. The method for treating fluorine-containing wastewater according to claim 1, characterized in that, The fluorine-containing wastewater includes fluorine-containing organic wastewater, fluorine-containing inorganic wastewater, or a mixture thereof.

7. The method for treating fluorine-containing wastewater according to claim 1, wherein, When steps S1 to S3 are cycled, the time for adsorption, desorption, and regeneration is the same.

8. The method for treating fluorine-containing wastewater according to claim 1, wherein The fluorine-containing wastewater includes two parts. One is the raw fluorine-containing wastewater, and the other is the fluorine-depleted wastewater generated during the regeneration, cleaning, or treatment of the fluorine-rich solution.

9. The method for treating fluorine-containing wastewater according to claim 1, wherein The regenerant is prepared from the water outlet discharged up to standard or deionized water.

10. The method for treating fluorine-containing wastewater according to claim 1, wherein The regeneration process includes a desorption process using the regenerant and a replacement cleaning process using the water outlet discharged up to standard or deionized water. The desorption process using the regenerant produces a fluorine-rich solution. The fluorine-rich solution is further treated by chemical precipitation or evaporation concentration. The treatment process produces precipitates or concentrated solutions, and at the same time, fluorine-depleted wastewater is generated and returned to the fluorine-containing wastewater treatment system.

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