Method for treating fluorine-containing wastewater

Abstract

The invention provides a method for treating fluorine-containing wastewater, which adopts a multi-tower adsorption system to treat the fluorine-containing wastewater, and the method for treating the fluorine-containing wastewater comprises the following steps: S1, at least two adsorption towers execute adsorption operation, the fluorine-containing wastewater flows out after being introduced into one adsorption tower, and then enters the other adsorption towers executing the adsorption operation, and standard water is obtained at an outlet; at least two adsorption towers execute desorption and regeneration operations, a regenerant flows out after being introduced into one adsorption tower executing the desorption and regeneration operations, and then enters the other adsorption towers executing the desorption and regeneration operations, and a fluorine-rich solution is obtained at an outlet; s2, storing or discharging water reaching the standard, cleaning the adsorption tower executing desorption and regeneration operation, and returning a cleaning solution to a fluorine-containing wastewater storage tank; s3, treating the fluorine-rich solution, and returning the treated fluorine-poor solution to the fluorine-containing wastewater storage tank; and S4, the step S1 to the step S3 are cycled in sequence. According to the method for treating the fluorine-containing wastewater, the adsorption time of the adsorption tower is prolonged, and the utilization rate of the adsorption tower is increased.

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: S1. At least two adsorption towers perform adsorption operation, and the fluorine-containing wastewater is introduced into one of the adsorption towers and then flows out, and then enters the other adsorption towers performing adsorption operation, and the outlet obtains qualified water; At least two adsorption towers perform desorption and regeneration operations, the regeneration agent is introduced into one of the adsorption towers performing desorption and regeneration operations and then flows out, and then enters the remaining adsorption towers performing desorption and regeneration operations, and a fluorine-rich solution is obtained at the outlet; S2, storage or discharge of qualified water, cleaning of the tower performing desorption and regeneration operations, and return of the cleaning liquid to the fluorine-containing wastewater storage tank; S3, treating the fluorine-rich solution, and returning the treated fluorine-poor liquid to the fluorine-containing wastewater storage tank; S4, looping steps S1 to S3 in sequence.

[0008] In one embodiment, the number N of the adsorption towers is estimated by the underutilized area LUB: ; Where L0 is the effective filling height of the adsorption tower, that is, the height of the filled adsorbent.

[0009] In one embodiment, the multi-tower adsorption system has four adsorption towers: a first adsorption tower, a second adsorption tower, a third adsorption tower and a fourth adsorption tower, and includes a cyclic switching step: First switching, using two adsorption towers to perform adsorption operation, fluorine-containing wastewater enters the first adsorption tower, the first adsorption tower adsorbs the adsorbate in the fluorine-containing wastewater, and the effluent enters the second adsorption tower after effluent, and the effluent of the second adsorption tower meets the standards for discharge or storage; At the same time, the heated regenerant enters the third adsorption tower for desorption and regeneration, the desorption liquid flowing out of the third adsorption tower enters the fourth adsorption tower, and 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, and the effluent enters the third adsorption tower, and the effluent of the third adsorption tower meets the standards for discharge or storage; At the same time, the heated regenerant enters the fourth adsorption tower for desorption and regeneration, the desorption 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; The third switching, the fluorine-containing wastewater enters the third adsorption tower, the third adsorption tower adsorbs the adsorbate in the fluorine-containing wastewater, and the effluent enters the fourth adsorption tower, and the effluent of the fourth adsorption tower meets the standards for discharge or storage; At the same time, the heated regenerant enters the first adsorption tower for desorption and regeneration, the desorption 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; The fourth switch, the fluorine-containing wastewater enters the fourth adsorption tower, the fourth adsorption tower adsorbs the adsorbate in the fluorine-containing wastewater, and the effluent enters the first adsorption tower after being discharged or stored after the effluent meets the standards; At the same time, the heated regeneration agent enters the second adsorption tower for desorption and 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 switch.

[0010] In one embodiment, the adsorption tower is filled with one adsorbent or multiple adsorbents, and the adsorbent includes any one of natural zeolite, synthetic molecular sieve, activated carbon, adsorption resin, or a mixture thereof.

[0011] In one embodiment, the adsorption process includes a physical adsorption process and a chemical adsorption process, and 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.

[0012] In one embodiment, the fluorine-containing wastewater includes fluorine-containing organic wastewater or fluorine-containing inorganic wastewater or a mixture thereof.

[0013] In one embodiment, the time of adsorption, desorption and regeneration during the cycle from step S1 to step S3 is the same.

[0014] In one embodiment, the fluorine-rich solution is further treated by chemical precipitation or evaporative concentration, and the treatment process produces a precipitate or a concentrated solution, and simultaneously produces fluorine-poor wastewater.

[0015] 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.

[0016] In one embodiment, the regenerant is prepared from effluent that meets discharge standards or deionized water.

[0017] In one embodiment, the regeneration process includes a desorption process using a regeneration agent and a cleaning process using effluent water that meets emission standards or deionized water.

[0018] Compared with the prior art, the advantages of the present invention are: This embodiment designs a multi-tower adsorption system based on the underutilized area LUB of the adsorption process, so that the underutilized area LUB of the adsorption tower is fully utilized, the adsorption time is extended, and the utilization rate of the adsorption tower is improved.

[0019] Furthermore, under the condition of maintaining the same removal rate, the regenerated fluorine-rich solution has a high concentration, which can significantly improve the treatment efficiency of fluorine-containing wastewater and is beneficial to the further treatment of the fluorine-rich solution. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is the concentration profile along the adsorption tower when adsorption breaks through; Figure 2a is a schematic diagram of the adsorption bed after regeneration; Figure 2b Schematic diagram of the first step in a multi-step purification; Figure 2c It is a schematic diagram of the second step in the multi-step purification; Figure 2d It is a schematic diagram of the third step in the multi-step purification; Figure 2e It is a schematic diagram of the fourth step in the multi-step purification; Figure 3a This is a schematic diagram of the first switch of the four-tower cyclic adsorption; Figure 3b This is a schematic diagram of the second switch of the four-tower cyclic adsorption; Figure 3c This is a schematic diagram of the third switch of the four-tower cyclic adsorption; Figure 3d This is a schematic diagram of the fourth switch of the four-tower cyclic adsorption; Figure 4 This is a four-tower continuous adsorption process flow chart. DETAILED DESCRIPTION

[0021] The embodiments of the present application are described in detail below with reference to the accompanying drawings.

[0022] The following describes the implementation methods of the present application through specific specific embodiments, and those skilled in the art can easily understand other advantages and effects of the present application from the contents disclosed in this specification. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. The present application can also be implemented or applied through other different specific implementation methods, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present application. It should be noted that the following embodiments and features in the embodiments can be combined with each other in the absence of conflict. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without making creative work belong to the scope of protection of the present application.

[0023] It should be noted that various aspects of the embodiments within the scope of the appended claims are described below. It should be apparent that the aspects described herein can be embodied in a wide variety of forms, and any specific structure and / or function described herein is merely illustrative. Based on the present application, it should be understood by those skilled in the art that an 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 aspect described herein can be used to implement the device and / or practice the method. In addition, other structures and / or functionalities other than one or more of the aspects described herein can be used to implement this device and / or practice this method.

[0024] It should also be noted that the illustrations provided in the following embodiments are only schematic illustrations of the basic concept of the present application. The drawings only show components related to the present application rather than being drawn according to the number, shape and size of components in actual implementation. In actual implementation, the type, quantity and proportion of each component may be changed arbitrarily, and the component layout may also be more complicated.

[0025] Additionally, in the following description, specific details are provided to facilitate a thorough understanding of the examples. However, it will be understood by those skilled in the art that the aspects described may be practiced without these specific details.

[0026] Example

[0027] Fluoride-containing wastewater includes fluoride-containing organic wastewater or fluoride-containing inorganic wastewater or a mixture thereof. The fluoride-containing wastewater to be treated includes two parts, one is the fluoride-containing wastewater raw water, and the other is the fluoride-poor wastewater generated during the regeneration, cleaning or treatment of fluoride-rich solution.

[0028] Adsorption is considered to be an effective, low-energy, and environmentally friendly method for treating fluoride-containing wastewater. Currently, there are many types of 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.

[0029] 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 high treatment costs and low defluorination efficiency due to the characteristics of frequent regeneration and high reagent costs.

[0030] The perfluoroether elastomer is prepared by emulsion polymerization. In one embodiment, the solid content of the residual liquid obtained after centrifugal coagulation and washing of the emulsion is 3.35%, wherein the emulsifier perfluorooctanoic acid PFOA is added in an amount of about 0.47% (weight ratio) during polymerization, and the residue in the emulsion is about 1350 mg / L. The emission standard achieved after treatment is 0.1-1 mg / L.

[0031] Ion exchange resins are generally used to treat and separate small molecular pollutants in water, while the molecular volume of perfluorinated organic pollutants is relatively large, and as surfactants, they may also form micelles and semi-micelles. Ion exchange resin regeneration technology is difficult to activate and regenerate ion exchange resins that are saturated with perfluorinated organic matter. Therefore, this application first uses activated carbon adsorption to remove most of the perfluorinated organic pollutants, so that the concentration of perfluorinated organic pollutants becomes milligram level, and then uses ion exchange resin for treatment.

[0032] The acid dissociation constant pKa of perfluorinated organic compounds is relatively small. For example, the pKa of PFOA is about -0.5. Most of them exist in the fluorine-containing wastewater in the form of negatively charged anions. The perfluorinated 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 concentration change of PFOA was measured to characterize the adsorption breakthrough curve.

[0033] The surface of ion exchange resin has a large number of ion exchange sites, which can remove the perfluorinated organic surfactant PFOA in water through the ion exchange process occurring on the resin surface. In addition, perfluorinated organic matter has a hydrophobic carbon fluorine chain structure, and ion exchange resin can also adsorb and remove it through the hydrophobic effect.

[0034] In this embodiment, the meanings of desorption and regeneration are different. Desorption includes the process of using a regeneration agent to separate the adsorbed material in the fluorine-containing wastewater from the adsorbent and flow out of the adsorption tower with the regeneration agent; regeneration includes the desorption process, but also includes cooling (such as regeneration using hot water), neutralization (such as regeneration using alkali solution), activation of the adsorbent, and the use of qualified discharge water or deionized water replacement and cleaning process to put the regenerated adsorption tower into the next cycle state. 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 adsorption process, including hot water desorption of variable temperature adsorption, acid-base desorption of chemical adsorption, and activation of the adsorbent. The regeneration process includes a desorption process using a regeneration agent and a replacement and cleaning process using qualified discharge water or deionized water. The regeneration agent desorption process produces a fluorine-rich solution, and the solution produced in the replacement and cleaning process is returned to the fluorine-containing wastewater treatment system.

[0035] The multi-tower adsorption system of this embodiment is designed based on the underutilized area LUB, so that the underutilized area LUB of the adsorption tower is fully utilized, the adsorption time is extended, and the concentration of the regenerated fluorine-rich solution is high, which is beneficial to the further treatment of the fluorine-rich solution and improves the utilization rate of the adsorption tower.

[0036] like Figure 1 As shown, the size of the adsorption mass transfer zone MTZ is determined by the diffusion trend caused by non-equilibrium adsorption or backmixing and the sharpening trend caused by the nonlinearity of adsorption equilibrium, while the size of the underutilized area LUB is related to the MTZ and depends on the concentration of the given breakthrough point, that is, the effluent concentration that meets the emission standards. After the adsorption system is determined, the outlet concentration that meets the emission standards determines the efficiency of the adsorption system to a large extent. Among them, Figure 1 The serial number 1 in the figure indicates the diffusion trend caused by non-equilibrium adsorption or back-mixing; the serial number 2 indicates the sharpening trend caused by the nonlinearity of adsorption equilibrium; the serial number 3 indicates that the low concentration area is controlled by adsorption equilibrium. Among them, SZ is the saturated zone; MTZ is the mass transfer zone; LUB is the underutilized zone.

[0037] Figure 1 The axial variation of the concentration of the adsorbent in the fluorine-containing wastewater at a typical moment during the adsorption process in the adsorption tower is described. 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. The concentration in the SZ saturation zone is the concentration of the adsorbent in the fluorine-containing wastewater when the adsorbent reaches saturation, that is, the initial concentration of the adsorbent in the fluorine-containing wastewater C0; the MTZ mass transfer zone contains the adsorption front, and the concentration of the adsorbent in the fluorine-containing wastewater drops sharply. The size of the MTZ is controlled by the adsorption equilibrium and the mass transfer diffusion effect. If the adsorption equilibrium constant of the adsorption equilibrium is large or the mass transfer diffusion effect is small, the MTZ is small, that is, the adsorption process is controlled by the adsorption equilibrium, otherwise the adsorption process is controlled by the mass transfer diffusion; LUB is the underutilized zone, and the concentration of the breakthrough point is set to C b , if C b / C0=0.01, that is, the concentration at the outlet of the adsorption tower reaches the breakthrough point concentration C b The adsorption tower needs to be regenerated. Obviously, the adsorbate concentration adsorbed by the adsorbent in the LUB area 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 adsorbate during regeneration of the adsorption tower, an increase in the regeneration agent consumed per unit of adsorbate, and a decrease in the post-treatment efficiency of the adsorbate concentrate.

[0038] In order to make use of the underutilized areas of LUB, a multi-tower structure should be adopted.

[0039] The purpose of using multiple towers for gas phase adsorption is mainly to equalize the pressure process, and multiple towers and multiple steps equalize the pressure to recover the pressure energy. The use of multiple towers for liquid phase adsorption does not have the same direct benefits as gas phase adsorption. However, from the perspective of improving the utilization rate of adsorbents, increasing the concentration multiples of adsorbates, and reducing the consumption of regenerators to obtain unit adsorbates, it has certain economic benefits.

[0040] Figure 2a-2eIt is a schematic diagram of multi-step simulation of two-tower adsorption and two-tower desorption regeneration by one tower based on the underutilized zone LUB of the adsorption system, where CZ is the clean zone.

[0041] First, in the standby stage Figure 2a The regenerated adsorption tower shown in FIG. Figure 2e The feed port of the fluorine-containing wastewater in the adsorption process is the discharge port of the regeneration process. The regeneration process does not require complete regeneration, leaving part of the MTZ area. Figure 2b The first step shown is the conventional treatment process, that is, the fluorine-containing wastewater is treated in the adsorption tower to obtain qualified discharge water. As the adsorption process proceeds, the adsorption front in the MTZ area moves forward to form the SZ saturation zone and the LUB zone, and the adsorbate concentration at the outlet has reached the breakthrough point. The traditional adsorption process enters the regeneration stage at this time. However, this application uses the adsorption potential of the LUB area to enter Figure 2c Step 2 shown continues to treat the fluoride-containing wastewater.

[0042] Obviously, when treating fluorine-containing wastewater in the second step, the adsorbent concentration at the outlet has exceeded the breakthrough point and cannot meet the emission standards. The method adopted in this application is to connect the outlet to the second adsorption tower until the outlet concentration of the first adsorption tower is higher and the adsorption process is close to MTZ, then the first adsorption tower enters the regeneration stage.

[0043] like Figure 2d The third step shown involves the regeneration stage. The regeneration stage includes regeneration using a regenerant and a cleaning agent such as deionized water replacement cleaning process used after regeneration. With the continuous addition of the regenerant, a CZ clean area is gradually formed at the upper end of the adsorption tower, and the SZ saturated area gradually moves down and discharges the adsorption tower to form a fluorine-rich solution, until the MTZ mass transfer area moves down to the outlet, and the entire regeneration stage is completed after replacement cleaning with deionized water. Among them, the regeneration stage is also two towers in series. In the third step, one tower completes partial regeneration and then connects to another tower to be regenerated. Since the two towers are connected in series, the concentration of the concentrated solution obtained by regeneration is high. Although the amount of regenerant used in single-tower regeneration is more than that of single-tower adsorption, it is less than the amount of two operations. Therefore, it has certain economic benefits to increase the concentration multiple of the adsorbate and reduce the amount of regeneration consumed to obtain unit adsorbate.

[0044] Figure 3a-3d It 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. FS in the figure is fluorine-containing wastewater; BS is standard discharge water; ZS is regeneration agent; FY is fluorine-rich solution.

[0045] Table 1 is Figure 3a-3d The corresponding operating status and timing of the four-tower adsorption process for fluorine-containing wastewater.

[0046] Table 1 Operation status and timing of the four-tower adsorption process for fluorine-containing wastewater

[0047] A method for treating fluorine-containing wastewater adopts a multi-tower adsorption system to treat the fluorine-containing wastewater. The multi-tower adsorption system comprises a plurality of adsorption towers, a flow control valve unit, a pipeline part and a control unit. The plurality of adsorption towers are connected through pipelines of the pipeline part. The flow control valve unit has a plurality of flow control valves arranged on the pipeline. The control unit controls the opening or closing of the flow control valves to realize that the fluorine-containing wastewater and the regeneration agent enter different adsorption towers, and the effluent meeting the discharge standards and the fluorine-rich solution flow out from different adsorption towers.

[0048] Figure 4 It is a process flow chart of continuous adsorption in the fourth tower of Example 4.

[0049] The adsorption system in the embodiment includes four adsorption towers, such as Figure 4As shown, the four adsorption towers are respectively adsorption tower I, adsorption tower II, adsorption tower III and adsorption tower IV. The adsorption system also includes a flow control valve unit, a pipeline part, a storage tank, a control unit, a pump and a regeneration system (heating or chemical agent). The flow control valve unit includes a plurality of fluorine-containing wastewater inlet valves (valve 104, valve 204, valve 304, valve 404, valve 601-1 are respectively connected to the fluorine-containing wastewater upper inlet pipeline 601; valve 105, valve 205, valve 305, valve 405, valve 602-1 are respectively connected to the fluorine-containing wastewater lower inlet pipeline 602), a plurality of standard discharge outlet valves (valve 102, valve 202, valve 302, valve 402, valve 701-1 are respectively connected to the standard discharge upper outlet pipeline 701; valve 107, valve 207, valve 307, valve 407, valve 702-1 are respectively connected to the standard discharge lower outlet pipeline The invention relates to a method for manufacturing a fluorine-rich solution device comprising: a fluorine-containing waste liquid inlet pipeline, a standard discharge water outlet pipeline, a regenerant liquid inlet pipeline and a fluorine-rich solution pipeline. The fluorine-rich solution device comprises a fluorine-containing waste liquid inlet pipeline, a standard discharge water outlet pipeline, a regenerant liquid inlet pipeline and a fluorine-rich solution pipeline. The storage tank comprises a fluorine-containing waste water storage tank, a standard discharge water outlet storage tank, a regenerant storage tank and a fluorine-rich solution storage tank. The bottom and top of each adsorption tower are connected to the fluorine-containing wastewater inlet pipeline, and each fluorine-containing wastewater inlet pipeline is provided with a fluorine-containing wastewater inlet valve, which is connected to the fluorine-containing wastewater inlet storage tank; at the same time, the bottom or top of each adsorption tower is connected to the standard discharge outlet pipeline, and each standard discharge outlet pipeline is provided with a standard discharge outlet valve, which is connected to the standard discharge outlet storage tank; at the same time, the bottom or top of each adsorption tower is connected to the regeneration agent inlet pipeline, and each regeneration agent inlet pipeline is provided with a regeneration agent inlet valve, which is connected to the regeneration agent inlet storage tank; at the same time, the bottom or top of each adsorption tower is connected to the fluorine-rich solution pipeline, and each concentrated liquid pipeline is provided with a fluorine-rich solution valve, which is connected to the fluorine-rich solution storage tank. The pipelines at the bottom and top of the tower are connected to each other and are connected to the pump respectively. The control unit controls the opening or closing of the flow control valve and the opening and closing of the pump. The effluent and fluorine-rich solution that meet the discharge standards are detected by the detection equipment. The adsorption tower, pipeline, valve and storage tank are insulated.

[0050] In one embodiment, the regeneration agent is hot water at a certain temperature, which is heated by electricity or steam. After the hot water is regenerated, it is replaced by water at normal temperature to cool the adsorption tower for the next cycle operation.

[0051] In one embodiment, the regenerant is an acidic solution, which is neutralized with an alkaline solution after regeneration and replaced with water at room temperature for the next cycle. The regenerant of the present application is configured with effluent water or deionized water that meets the discharge standards.

[0052] The method for treating fluoride-containing wastewater comprises the following steps: S1. At least two adsorption towers perform adsorption operation, and the fluorine-containing wastewater is introduced into one of the adsorption towers and then flows out, and then enters the other adsorption towers performing adsorption operation, and the outlet obtains qualified water; At least two adsorption towers perform desorption and regeneration operations, the regeneration agent is introduced into one of the adsorption towers performing desorption and regeneration operations and then flows out, and then enters the remaining adsorption towers performing desorption and regeneration operations, and a fluorine-rich solution is obtained at the outlet; S2, storing or discharging qualified water, cleaning the adsorption tower that performs desorption and regeneration operations, and returning the cleaning liquid to the fluorine-containing wastewater storage tank; S3, treating the fluorine-rich solution, and returning the treated fluorine-poor liquid to the fluorine-containing wastewater storage tank; S4, looping steps S1 to S3 in sequence.

[0053] In one embodiment, the time of adsorption, desorption and regeneration during the cycle from step S1 to step S3 is the same.

[0054] In one embodiment, the multi-tower adsorption system has at least four adsorption towers: a first adsorption tower, a second adsorption tower, a third adsorption tower, and a fourth adsorption tower, and includes the following cycle switching steps: First switching, using two adsorption towers to perform adsorption operation, fluorine-containing wastewater enters the first adsorption tower, the first adsorption tower adsorbs the adsorbate in the fluorine-containing wastewater, and the effluent enters the second adsorption tower after effluent, and the effluent of the second adsorption tower meets the standards for discharge or storage; At the same time, the heated regenerant enters the third adsorption tower for desorption and regeneration, the desorption liquid flowing out of the third adsorption tower enters the fourth adsorption tower, and 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, and the effluent enters the third adsorption tower, and the effluent of the third adsorption tower meets the standards for discharge or storage; At the same time, the heated regenerant enters the fourth adsorption tower for desorption and regeneration, the desorption 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; The third switching, the fluorine-containing wastewater enters the third adsorption tower, the third adsorption tower adsorbs the adsorbate in the fluorine-containing wastewater, and the effluent enters the fourth adsorption tower, and the effluent of the fourth adsorption tower meets the standards for discharge or storage; At the same time, the heated regenerant enters the first adsorption tower for desorption and regeneration, the desorption 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; The fourth switch, the fluorine-containing wastewater enters the fourth adsorption tower, the fourth adsorption tower adsorbs the adsorbate in the fluorine-containing wastewater, and the effluent enters the first adsorption tower after being discharged or stored after the effluent meets the standards; At the same time, the heated regeneration agent enters the second adsorption tower for desorption and 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 switch.

[0055] Specifically, this embodiment adopts a 4-tower system (unless otherwise specified, all valves are in a normally closed state), including the following 4 cycle switching (combined with Figure 3a-3d and Figure 4 ): 1. For the first switch, two adsorption towers are used to perform the adsorption operation. Open valve 601-1 and valve 104 to let fluorine-containing wastewater FS enter from the top of adsorption tower I. Adsorption tower I that performs the adsorption operation adsorbs the adsorbent in the fluorine-containing wastewater FS. After the effluent is discharged, it passes through valve 105 through pipeline 602 (valve 602-1 is closed) and valve 205 from the bottom of the tower to adsorption tower II. The effluent BS is discharged or stored through valve 202 and valve 701-1 through pipeline 701 (valve 702-1 is closed). At the same time, the heated regeneration agent ZS enters adsorption tower III from the bottom of the tower through pipeline 802 through valve 802-1 and valve 306 for desorption and regeneration. The desorbed concentrated liquid from the top of the tower passes through valve 304 through pipeline 601 and valve 404 from the top of the tower to adsorption tower IV. 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 through pipeline 502, completing a cycle. Figure 3a The first switch in and the first cycle in Table 1.

[0056] 2. The second switch, open valve 602-1 and valve 205 to let fluorine-containing wastewater FS enter from the bottom of adsorption tower II. Adsorption tower II, which performs adsorption operation, adsorbs the adsorbent in the fluorine-containing wastewater FS. After the water is discharged, it passes through valve 204, pipeline 601 and valve 304 from the top of the tower to adsorption tower III. The effluent BS passes through valve 307 and valve 702-1 through pipeline 702 to meet the standards for discharge or storage. At the same time, the heated regeneration agent ZS passes through valve 801-1, pipeline 801 and valve 403 from the top of the tower to enter adsorption tower IV for desorption and regeneration. The desorbed concentrated liquid from the bottom of the tower passes through valve 408, pipeline 502, valve 108 from the bottom of the tower to enter adsorption tower I. The discharged fluorine-rich solution FY flows out from the top of adsorption tower I and passes through valve 101 and valve 501-1 through pipeline 501 to enter the fluorine-rich solution storage tank, completing a cycle. Corresponding Figure 3bThe second switch in and the second cycle in Table 1.

[0057] 3. The third switch, open valve 601-1 and valve 304 to let fluorine-containing wastewater FS enter from the top of adsorption tower III. Adsorption tower III, which performs adsorption operation, adsorbs the adsorbent in the fluorine-containing wastewater FS. After the water is discharged, it passes through valve 305, pipeline 601 and valve 405 from the bottom of the tower to adsorption tower IV (valve 602-1 is closed). The effluent BS passes through valve 402 and valve 701-1 pipeline and is discharged or stored in compliance with the standards through pipeline 701. At the same time, the heated regeneration agent ZS enters adsorption tower I from the bottom of the tower through pipeline 802, valve 802-1 and valve 106 for desorption and regeneration. The desorbed concentrated liquid from the top of the tower passes through valve 103, pipeline 801, valve 203 and the top of the tower to enter adsorption tower II. 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 through pipeline 502, completing a cycle. Figure 3c The third switch in and the third cycle in Table 1.

[0058] 4. The fourth switch, open valve 602-1 and valve 405 to let fluorine-containing wastewater FS enter from the bottom of adsorption tower IV. Adsorption tower IV, which performs adsorption operation, adsorbs the adsorbent in the fluorine-containing wastewater FS. After the effluent, it passes through valve 404 through pipeline 601 and valve 104 from the top of the tower to adsorption tower I (valve 601-1 is closed). The effluent BS passes through valve 107 and valve 702-1 through pipeline 702 to meet the standards for discharge or storage. At the same time, the heated regeneration agent ZS passes through pipeline 801, valve 801-1 and valve 203 from the top of the tower to enter adsorption tower II for desorption and regeneration. The desorbed concentrated liquid from the bottom of the tower passes through valve 206 through pipeline 802 and valve 306 from the bottom of the tower to enter adsorption tower III (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 through pipeline 501, completing a cycle. Corresponding Figure 3d The fourth switch in and the fourth cycle in Table 1.

[0059] 5. Treat the fluorine-rich solution. The fluorine-rich solution is further treated by chemical precipitation or evaporation concentration. The treatment process produces a precipitate or a concentrated solution, and at the same time produces fluorine-poor wastewater. The treated fluorine-poor wastewater is returned to the fluorine-containing wastewater storage tank.

[0060] 6. Repeat steps 1 and 5 in sequence.

[0061] The above-mentioned desorption process ensures that the desorbent inlet is the low concentration zone of the tower, while the outlet of the adsorption process is the low concentration zone of the tower.

[0062] The design of pipelines and the selection of valves should take into account the small dead volume of pipelines and valves relative to the volume of the adsorption tower, 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 processing capacity of each adsorption tower.

[0063] The number of adsorption towers N in this application is estimated by the underutilized area LUB: ; Where L0 is the filling height of the adsorption tower.

[0064] It should be pointed out that for a specific adsorption system (i.e., adsorbent, adsorbate and regeneration method are certain), the size of LUB is closely related to the set outlet concentration.

[0065] For example, C0=200 ppm, the breakthrough point C b =10 ppm, the adsorption equilibrium is Langmuir type, the SZ saturated adsorption zone is longer, and the MTZ adsorption mass transfer zone is close to 10 ppm. Single-tower adsorption and single-tower desorption can be used.

[0066] Under the same conditions, if the breakthrough point is C b =0.5 ppm, which is the discharge requirement for the treatment of wastewater containing F ions in a certain area at this stage. Then the SZ saturated adsorption zone is shorter, and the LUB zone is longer, which is close to half of the effective length of the adsorption tower. ; 1.82 is rounded to 2.

[0067] That is, double tower adsorption and double tower desorption are used. Because the breakthrough point concentration is low and the adsorption tower breaks through quickly, it is more advantageous to use double tower adsorption and double tower regeneration.

[0068] Generally, if N is less than 1.2, it is rounded to 1; if N=1.2-2.2, it is rounded to 2; if N=2.2-3.2, it is rounded to 3, and so on.

[0069] Measurement of PFOA

[0070] Hexane and acetone were used as solvents to extract PFOA. After centrifugation (high-speed centrifuge TG-19, Sichuan Shuke Instrument Co., Ltd.), the supernatant was taken and the PFOA content was determined by GC / MS (Agilent 8860-5977C) with a detection limit of 0.1 mg / L.

[0071] In one embodiment, after the residual liquid in the emulsion is adsorbed by activated carbon, the concentration of perfluorooctanoic acid PFOA is C0=12 mg / L, and the pH is about 5.8, which is recorded as fluorine-containing wastewater FS and set aside.

[0072] Example 1 Single tower adsorption / single tower desorption strong alkaline adsorption resin treatment of fluoride-containing wastewater FS 201×7 gel-type strongly basic anion exchange resin (Hebei Meifeng Chemical Building Materials Co., Ltd.) is an anion exchange resin with a quaternary ammonium group [-N(CH3)3OH] on a 7% cross-linked styrene-divinylbenzene copolymer. Its alkalinity is equivalent to that of a general quaternary ammonium base. It exhibits ion exchange function in acidic, neutral and even alkaline media. The total exchange capacity (dry) is ≥3.60mmol / g, the wet true density is 1.07-1.10 g / ml, and the ex-factory is Cl -1 type.

[0073] After washing with deionized water, 4-5% dilute hydrochloric acid and 4-5% sodium hydroxide solution, it was transformed with 4-5% NaOH and wet packed. The adsorption column diameter d was 3.5 cm, the filling height L was 80 cm, the temperature was controlled at 45±2 ℃ by a constant temperature water jacket, and an empty volume was left on the top of the ion exchange column to accommodate a transformation expansion rate of about 20%.

[0074] Assuming the empty tower flow rate is u (unit m / h), the processing volume per unit time Q is u / L (unit BV, BV is the effective empty tower volume of the bed); the average residence time t R It is L / u (unit: h).

[0075] The volume of the solution flowing out during the adsorption process is V1, and the concentration is C1. After the adsorption is completed, 4-5% dilute hydrochloric acid is used for countercurrent regeneration. After regeneration, it is neutralized and transformed with 4-5% NaOH. The volume of the regenerated liquid is V2, and the concentration of the regenerated liquid is C2. Finally, deionized water is used for cleaning and replacement. The solution generated in the replacement and cleaning process is returned to the fluorine-containing wastewater treatment system.

[0076] The removal rate and concentration multiple of PFOA are calculated as follows: ; ; The calculation results are shown in Table 2.

[0077] Table 2 Breakthrough curve data and estimated parameters during single tower adsorption operation

[0078] Example 2 Double tower adsorption / double tower regeneration strong alkaline adsorption resin for treating fluoride-containing wastewater FS According to Example 1, the adsorption column has a diameter of 3.5 cm, a filling height of half that of Example 1, i.e., 40 cm, a constant temperature water jacket is used to control the temperature at 45±2° C., and an empty volume is left at the top of the ion exchange column to accommodate a transformation expansion rate of about 20%.

[0079] The adsorption time is the same as that in Example 1, and the regeneration process is the same as that in Example 1.

[0080] The experimental results are shown in Table 3.

[0081] Table 3 Breakthrough curve data and estimated parameters during the adsorption operation of the 4-tower

[0082] It can be seen from Table 2 that, under the condition of maintaining the same removal rate (99%), a lower flow rate is used, 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).

[0083] It can be seen from Table 3 that, under the same conditions of removal rate (99%) and adsorption time, the concentration multiple is significantly improved by using four-tower circulation, from 3.3 times to 5.5 times (lower flow rate) and from 2.8 times to 4.2 times (higher flow rate).

[0084] In this specification, the same or similar parts between 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 previous embodiments.

[0085] The above is only a specific implementation 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 a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application shall be based on the protection scope of the claims.

Claims

1. A method for treating fluorine-containing wastewater, using a multi-tower adsorption system to treat fluorine-containing wastewater, characterized in that: The multi-tower adsorption system comprises a plurality of adsorption towers, a flow control valve unit, a pipeline part and a control unit. The plurality of adsorption towers are connected through pipelines of the pipeline part. The flow control valve unit has a plurality of flow control valves arranged on the pipeline. The control unit controls the opening or closing of the flow control valves to achieve the fluorine-containing wastewater and regeneration agent entering different adsorption towers, and the effluent that meets the discharge standards and the fluorine-rich solution flowing out of different adsorption towers. A method for treating fluoride-containing wastewater includes an adsorption process, a desorption process and a regeneration process, and comprises the following steps: S1. At least two adsorption towers perform adsorption operation, and the fluorine-containing wastewater is introduced into one of the adsorption towers and then flows out, and then enters the other adsorption towers performing adsorption operation, and the outlet obtains qualified water; At least two adsorption towers perform desorption and regeneration operations, the regeneration agent is introduced into one of the adsorption towers performing desorption and regeneration operations and then flows out, and then enters the remaining adsorption towers performing desorption and regeneration operations, and a fluorine-rich solution is obtained at the outlet; S2, storing or discharging qualified water, cleaning the adsorption tower that performs desorption and regeneration operations, and returning the cleaning liquid to the fluorine-containing wastewater storage tank; S3, treating the fluorine-rich solution, and returning the treated fluorine-poor liquid to the fluorine-containing wastewater storage tank; S4, looping steps S1 to S3 in sequence.

2. The method for treating fluorine-containing wastewater according to claim 1, characterized in that: The number of adsorption towers is determined by the underutilized areas of the adsorption system.

3. The method for treating fluorine-containing wastewater according to claim 1, characterized in that: The multi-tower adsorption system has at least four adsorption towers: a first adsorption tower, a second adsorption tower, a third adsorption tower and a fourth adsorption tower, and includes a cycle switching step: First switching, using two adsorption towers to perform adsorption operation, fluorine-containing wastewater enters the first adsorption tower, the first adsorption tower adsorbs the adsorbate in the fluorine-containing wastewater, and the effluent enters the second adsorption tower after effluent, and the effluent of the second adsorption tower meets the standards for discharge or storage; At the same time, the heated regenerant enters the third adsorption tower for desorption and regeneration, the desorption liquid flowing out of the third adsorption tower enters the fourth adsorption tower, and 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, and the effluent enters the third adsorption tower, and the effluent of the third adsorption tower meets the standards for discharge or storage; At the same time, the heated regenerant enters the fourth adsorption tower for desorption and regeneration, the desorption 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; The third switching, the fluorine-containing wastewater enters the third adsorption tower, the third adsorption tower adsorbs the adsorbate in the fluorine-containing wastewater, and the effluent enters the fourth adsorption tower, and the effluent of the fourth adsorption tower meets the standards for discharge or storage; At the same time, the heated regenerant enters the first adsorption tower for desorption and regeneration, the desorption 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; The fourth switch, the fluorine-containing wastewater enters the fourth adsorption tower, the fourth adsorption tower adsorbs the adsorbate in the fluorine-containing wastewater, and the effluent enters the first adsorption tower after being discharged or stored after the effluent meets the standards; At the same time, the heated regenerant enters the second adsorption tower for desorption and 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 switch.

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

5. The method for treating fluorine-containing wastewater according to claim 1, characterized in that: The adsorption process includes physical adsorption process and 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 or fluorine-containing inorganic wastewater or a mixture thereof.

7. The method for treating fluorine-containing wastewater according to claim 1, characterized in that: The time for adsorption, desorption and regeneration is the same during the cycle from step S1 to step S3.

8. The method for treating fluorine-containing wastewater according to claim 1, characterized in that: The fluorine-containing wastewater 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.

9. The method for treating fluorine-containing wastewater according to claim 1, characterized in that: The regeneration agent is prepared from effluent water that meets discharge standards or deionized water.

10. The method for treating fluorine-containing wastewater according to claim 1, characterized in that: The regeneration process includes a desorption process using a regeneration agent and a replacement and cleaning process using effluent water that meets the discharge standards or deionized water. The desorption process using the regeneration agent produces a fluorine-rich solution, and the fluorine-rich solution is further treated by chemical precipitation or evaporation concentration. The treatment process produces a precipitate or a concentrated solution, and at the same time, produces fluorine-poor wastewater, which is returned to the fluorine-containing wastewater treatment system.

Images