A system and method for recovering salt and removing hardness from dyed brine

Abstract

The invention provides a system and method for recovering salt and simultaneously removing hardness from dyed brine. The system comprises a wastewater collection tank, a mesh filter, a tubular membrane device, an alkalinity removal tank, a pH regulating tank, an ultrafiltration device, an ozone tower, a nanofiltration device, a sodium sulfate concentration regulating tank, a sodium hydroxide solution storage tank, and a sulfuric acid storage tank. The outlet of the wastewater collection tank is connected to the inlet of the mesh filter, the outlet of the mesh filter is connected to the inlet of the tubular membrane device, the outlet of the tubular membrane device is connected to the inlet of the pH regulating tank via a pipeline via the alkalinity removal tank, the outlet of the pH regulating tank is connected to the inlet of the ultrafiltration device, the outlet of the ultrafiltration device is connected to the liquid inlet of the ozone tower, the liquid outlet of the ozone tower is connected to the dyed brine inlet of the nanofiltration device, and the dyed brine outlet of the nanofiltration device is connected to the sodium sulfate concentration regulating tank; the outlet of the sodium hydroxide solution storage tank is respectively connected to the dosing ports of the wastewater collection tank and the pH regulating tank; and the outlet of the sulfuric acid storage tank is connected to the dosing port of the alkalinity removal tank.

Description

Technical Field

[0001] The invention relates to a system and method for recovering salt and removing hardness from dyed brine, belonging to the technical field of environmental protection and resource recovery. Background Art

[0002] The reactive dyeing process requires the addition of large amounts of salt and alkali to promote dye dispersion. Typically, the salt concentration in the dyeing residue / dyeing brine is 20-100g / L, the alkali concentration is 2-30g / L, the dye concentration is 0.1-2g / L, the COD is 500-3000mg / L, the chroma is 500-5000 times, and the hardness is 50-300mg / L. Discharging the dyeing residue directly into the sewage system will greatly increase the wastewater treatment load. In particular, the high salt content of the dyeing residue will not only affect the efficiency of the sewage treatment biochemical system, but also the overall wastewater reuse rate. If the salt in the wastewater can be recovered through appropriate methods and reused in production, it will not only reduce its impact on the overall sewage treatment, but also turn waste into resources, achieving better environmental and economic benefits.

[0003] Therefore, providing a new system and method for recovering salt from dyed brine and removing hardness at the same time has become a technical problem that needs to be solved urgently in this field. Summary of the Invention

[0004] In order to solve the above-mentioned shortcomings and deficiencies, an object of the present invention is to provide a system for recovering salt and removing hardness from dyed brine at the same time.

[0005] Another object of the present invention is to provide a method for recovering salt and removing hardness from dyed brine.

[0006] To achieve the above objectives, the present invention provides a system for recovering salt and removing hardness from dyed brine, wherein the system comprises: a wastewater collection tank, a mesh filter, a tubular membrane device, an alkalinity removal tank, a pH adjustment tank, an ultrafiltration device, an ozone tower, a nanofiltration device, a sodium sulfate concentration adjustment tank, a sodium hydroxide solution storage tank, and a sulfuric acid storage tank.

[0007] Wherein, the outlet of the wastewater collection tank is connected to the inlet of the mesh filter through a pipeline, the outlet of the mesh filter is connected to the inlet of the tubular membrane device through a pipeline via a circulation pump, the outlet of the tubular membrane device is connected to the inlet of the pH adjustment tank through a pipeline via the alkalinity removal tank, the outlet of the pH adjustment tank is connected to the inlet of the ultrafiltration device through a pipeline via an ultrafiltration circulation pump, the outlet of the ultrafiltration device (the outlet of the dyed brine after the dye is removed) is connected to the liquid inlet of the ozone tower through a pipeline, the liquid outlet of the ozone tower is connected to the dyed brine inlet of the nanofiltration device through a pipeline via a nanofiltration high-pressure pump, and the dyed brine outlet of the nanofiltration device is connected to the sodium sulfate concentration regulating tank through a pipeline;

[0008] The outlet of the sodium hydroxide solution storage tank is connected to the dosing port of the wastewater collection tank and the dosing port of the pH adjustment tank through pipelines respectively;

[0009] The outlet of the sulfuric acid storage tank is connected to the dosing port of the alkalinity removal tank through a pipeline.

[0010] As a specific embodiment of the system for recovering salt and removing hardness from dyed brine described above, the system further includes a nanofiltration water production tank, and the water production port of the nanofiltration device is connected to the nanofiltration water production tank through a pipeline.

[0011] As a specific embodiment of the system for recovering salt and removing hardness from dyed brine described above, the system further includes an ozone generator, and the gas outlet of the ozone generator is connected to the gas inlet of the ozone tower through a pipeline.

[0012] As a specific embodiment of the system for recovering salt and removing hardness from dyed brine described above, the height of the ozone tower is greater than 4m.

[0013] As a specific embodiment of the system for recovering salt and removing hardness from dyed brine described above, the system further includes a recovered salt storage tank, and the liquid outlet of the sodium sulfate concentration regulating tank is connected to the recovered salt storage tank through a pipeline.

[0014] As a specific embodiment of the system for recovering salt and simultaneously removing hardness from dyed brine of the present invention, the system further comprises a first dosing pump, a second dosing pump, and a third dosing pump, and the outlet of the sodium hydroxide solution storage tank is connected to the dosing port of the wastewater collection tank and the dosing port of the pH adjustment tank via pipelines via the first dosing pump and the third dosing pump, respectively;

[0015] The outlet of the sulfuric acid storage tank is connected to the dosing port of the alkalinity removal tank through a pipeline via a second dosing pump.

[0016] As a specific embodiment of the system for recovering salt and removing hardness from dyed brine described above, the system further includes a wastewater treatment device, and the concentrated water outlet of the ultrafiltration device is connected to the wastewater treatment device through a pipeline.

[0017] As a specific embodiment of the system for recovering salt and removing hardness from dyed brine described above, the filtration accuracy of the mesh filter is 150-300 meshes.

[0018] As a specific embodiment of the system for recovering salt and removing hardness from dyed brine described above, the tubular membrane used in the tubular membrane device has a molecular weight cutoff of 5000-100 kDa.

[0019] As a specific embodiment of the system for recovering salt and removing hardness from dyed brine described above, the ultrafiltration membrane element used in the ultrafiltration device has a molecular weight cutoff of 1000-10000 Da.

[0020] As a specific embodiment of the system for recovering salt and removing hardness from dyed brine described above, the nanofiltration membrane element used in the nanofiltration device has a molecular weight cutoff of 200-500 Da.

[0021] On the other hand, the present invention also provides a method for recovering salt and removing hardness from dyed brine, wherein the method is implemented by using the above-mentioned system for recovering salt and removing hardness from dyed brine, and comprises:

[0022] 1) Collecting the dyeing brine in a wastewater collection tank and then adding sodium hydroxide solution to adjust it to alkaline. Under alkaline conditions, the metal ions in the dyeing brine form metal hydroxide colloids and metal carbonate colloids;

[0023] 2) filtering the dyed brine obtained in step 1) through a mesh filter to remove suspended matter and trichomes;

[0024] 3) filtering the dyed brine obtained in step 2) in a tubular membrane device to remove the metal hydroxide colloid and the metal carbonate colloid therein, thereby removing the hardness of the dyed brine and obtaining the dyed brine after the hardness is removed;

[0025] 4) the dyed brine obtained in step 3) enters an alkalinity removal tank, and sulfuric acid is added to adjust its pH to 3.0-4.5, so that carbonate (mainly residual sodium carbonate) therein is converted into carbon dioxide and overflows from the dyed brine, thereby achieving the purpose of removing alkalinity;

[0026] 5) allowing the dyed brine obtained in step 4) to enter a pH adjustment tank and adding sodium hydroxide solution to adjust the pH to neutral;

[0027] 6) passing the dyed brine obtained in step 5) into an ultrafiltration device to separate the dye and salt to obtain concentrated water and dyed brine after the dye is removed;

[0028] 7) performing deep ozone decolorization on the dyed brine obtained in step 6) in an ozone tower to obtain decolorized dyed brine;

[0029] 8) concentrating the dyed brine obtained in step 7) in a nanofiltration device to obtain concentrated dyed brine;

[0030] 9) The dyed brine obtained in step 8) enters a sodium sulfate concentration regulating tank to complete salt recovery and hardness removal in the dyed brine.

[0031] As a specific embodiment of the method for recovering salt and removing hardness from dyed brine described above, the method further comprises:

[0032] 10) adding solid sodium sulfate to the dyeing brine obtained in step 9) to adjust the sodium sulfate concentration to the target concentration and then returning the brine to the dyeing process.

[0033] As a specific embodiment of the method for recovering salt and removing hardness from dyed brine described above, in step 1), sodium hydroxide solution is added to adjust the pH value thereof to 11.0-13.0.

[0034] As a specific embodiment of the method for recovering salt and removing hardness from dyed brine described above, in step 3), the operating pressure of the tubular membrane device is 0.2-0.6 MPa, and the hardness of the dyed brine after hardness removal is less than 50 mg / L.

[0035] As a specific embodiment of the method for recovering salt and removing hardness from dyed brine described above, in step 6), the operating pressure of the ultrafiltration device is 0.2-1.0 MPa, and the retention rate of the dye (chromaticity) is greater than 90%.

[0036] As a specific embodiment of the method for recovering salt and removing hardness from dyed brine described above, in step 7), the ozone dosage of the ozone tower is 50-200 mg / L, the residence time is 1-4 hours, and the chroma of the decolorized dyed brine is less than 8 times based on the dilution multiple method.

[0037] As a specific embodiment of the method for recovering salt and removing hardness from dyed brine described above, in step 8), the operating pressure of the nanofiltration device is 2-8 MPa, the retention rate of sodium sulfate is greater than 99%, and the concentration of sodium sulfate in the concentrated dyed brine is 100-200 g / L.

[0038] As a specific embodiment of the method for recovering salt and removing hardness from dyed brine described above, in step 1) and step 5), the concentration of the sodium hydroxide solution is 10-30%.

[0039] As a specific embodiment of the method for recovering salt and removing hardness from dyed brine described above, in step 4), the sulfuric acid is concentrated sulfuric acid with a concentration of 94-98%.

[0040] The system and method for recovering salt and simultaneously removing hardness from dyed brine provided by the present invention utilizes membrane fractionation to reuse salt from the dyed brine and remove hardness, offering advantages such as simple operation and low shipping costs. The sodium sulfate concentration in the dyed brine obtained after salt recovery and hardness removal is adjusted to a target concentration and then reused in the dyeing process, achieving acceptable color difference and levelness. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0042] Figure 1 This is a schematic structural diagram of the system for recovering salt and removing hardness from dyed brine provided in Example 1 of the present invention.

[0043] Description of main figures:

[0044] 1-wastewater collection tank, 2-mesh filter, 3-circulation pump, 4-tubular membrane device, 5-alkalinity removal tank, 6-pH adjustment tank, 7-ultrafiltration circulation pump, 8-ultrafiltration device, 9-ozone tower, 10-nanofiltration high-pressure pump, 11-nanofiltration device, 12-sodium sulfate concentration adjustment tank, 13-recovered salt storage tank, 14-nanofiltration water storage tank, 15-sodium hydroxide solution storage tank, 16-sulfuric acid storage tank, 17-ozone generator, 18-first dosing pump, 19-second dosing pump, 20-third dosing pump. DETAILED DESCRIPTION

[0045] It should be noted that the term "comprise" and any variations thereof in the specification and claims of the present invention and the above-mentioned drawings are intended to cover non-exclusive inclusions. For example, a process, method, system, product or apparatus that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or are inherent to these processes, methods, products or apparatus.

[0046] The "range" disclosed in the present invention is given in the form of a lower limit and an upper limit. It can be one or more lower limits, and one or more upper limits respectively. A given range is defined by selecting a lower limit and an upper limit. The selected lower limit and upper limit define the boundaries of a particular range. All ranges defined in this way are combinable, i.e., any lower limit can be combined with any upper limit to form a range. For example, a range of 60-120 and 80-110 is listed for a particular parameter, and it is understood that a range of 60-110 and 80-120 is also expected. In addition, if the minimum range values ​​listed are 1 and 2, and the maximum range values ​​listed are 3, 4, and 5, then the following ranges can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5.

[0047] In the present invention, unless otherwise specified, the numerical range "ab" is an abbreviation for any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" are listed in this invention, and "0-5" is merely an abbreviation for these numerical combinations.

[0048] In the present invention, unless otherwise specified, all embodiments and preferred embodiments mentioned in the present invention can be combined with each other to form a new technical solution.

[0049] In the present invention, unless otherwise specified, all technical features and preferred features mentioned in the present invention can be combined with each other to form a new technical solution.

[0050] In the present invention, unless otherwise specified, all steps mentioned herein may be performed sequentially or randomly, but are preferably performed sequentially. For example, the method comprising steps (a) and (b) indicates that the method may comprise steps (a) and (b) performed sequentially, or may comprise steps (b) and (a) performed sequentially. For example, the method further comprising step (c) indicates that step (c) may be added to the method in any order, for example, the method may comprise steps (a), (b) and (c), or may comprise steps (a), (c) and (b), or may comprise steps (c), (a) and (b), etc.

[0051] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention is further described in detail below in conjunction with the attached table, drawings and examples. The following embodiments are some embodiments of the present invention, rather than all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of the present invention. If specific conditions are not specified in the examples, they are carried out according to conventional conditions or the conditions recommended by the manufacturer. If the manufacturer is not specified for the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0052] Example 1

[0053] This embodiment provides a system for recovering salt from dyed brine and removing hardness at the same time, and its structural diagram is shown as follows: Figure 1 As shown, from Figure 1 It can be seen that the system for recovering salt and removing hardness of the dyed brine at the same time includes: a wastewater collection tank 1, a screen filter 2, a tubular membrane device 4, an alkalinity removal tank 5, a pH adjustment tank 6, an ultrafiltration device 8, a wastewater treatment device (not shown in the figure), an ozone tower 9, a nanofiltration device 11, a sodium sulfate concentration adjustment tank 12, a recovered salt storage tank 13, a nanofiltration water storage tank 14, a sodium hydroxide solution storage tank 15, a sulfuric acid storage tank 16 and an ozone generator 17;

[0054] The outlet of the wastewater collection tank 1 is connected to the inlet of the mesh filter 2 through a pipeline, the outlet of the mesh filter 2 is connected to the inlet of the tubular membrane device 4 through a pipeline via a circulation pump 3, the outlet of the tubular membrane device 4 is connected to the inlet of the pH adjustment tank 6 through a pipeline via the alkalinity removal tank 5, the outlet of the pH adjustment tank 6 is connected to the inlet of the ultrafiltration device 8 through a pipeline via an ultrafiltration circulation pump 7, the dyed brine outlet of the ultrafiltration device 8 after the dye is removed is connected to the liquid inlet of the ozone tower 9 through a pipeline, and the concentrated brine of the ultrafiltration device 8 is connected to the liquid inlet of the ozone tower 9. The water outlet is connected to the wastewater treatment device through a pipeline, the gas outlet of the ozone generator 17 is connected to the gas inlet of the ozone tower 9 through a pipeline, the liquid outlet of the ozone tower 9 is connected to the dyeing brine inlet of the nanofiltration device 11 through a pipeline via the nanofiltration high-pressure pump 10, the water production port of the nanofiltration device 11 is connected to the nanofiltration water production storage tank 14 through a pipeline, the dyeing brine outlet of the nanofiltration device 11 is connected to the sodium sulfate concentration regulating tank 12 through a pipeline, and the liquid outlet of the sodium sulfate concentration regulating tank 12 is connected to the recovered salt storage tank 13 through a pipeline;

[0055] The outlet of the sodium hydroxide solution storage tank 15 is connected to the dosing port of the wastewater collection tank 1 and the dosing port of the pH adjustment tank 6 through pipelines via a first dosing pump 18 and a third dosing pump 20 respectively;

[0056] The outlet of the sulfuric acid storage tank 16 is connected to the dosing port of the alkalinity removal tank 5 through a pipeline via a second dosing pump 19 .

[0057] In this embodiment, the height of the ozone tower 9 is greater than 4m;

[0058] The filtration accuracy of the mesh filter 2 is 150-300 mesh;

[0059] The tubular membrane used in the tubular membrane device 4 has a molecular weight cut-off of 5000-100 kDa;

[0060] The ultrafiltration membrane element used in the ultrafiltration device 8 has a molecular weight cut-off of 1000-10000 Da.

[0061] The nanofiltration membrane element used in the nanofiltration device has a molecular weight cut-off of 200-500 Da.

[0062] Example 2

[0063] This embodiment provides a method for recovering salt and removing hardness from dyed brine, which is implemented using the system for recovering salt and removing hardness from dyed brine provided in Example 1. The method includes the following specific steps:

[0064] 1) collecting dyeing brine and passing it into a wastewater collection tank, wherein the dyeing brine has a dye concentration of 1.0 g / L, a chroma of 2560 times (calculated by a dilution multiple method), a sodium sulfate concentration of 80 g / L, a soda ash concentration of 15 g / L, a total hardness of 250 mg / L, and contains a small amount of trichome; adding a 10% mass concentration of sodium hydroxide solution to the wastewater collection tank to adjust the pH to 12.0. Under alkaline conditions, metal ions in the dyeing brine form metal hydroxide and metal carbonate colloids;

[0065] 2) filtering the dyed brine obtained in step 1) through a mesh filter to remove large suspended solids and trichomes;

[0066] 3) finely filtering the dyed brine obtained in step 2) in a tubular membrane device (tubular ultrafiltration membrane device) to remove remaining suspended matter and metal salt colloids, thereby removing the hardness of the dyed brine and obtaining a dyed brine after hardness removal;

[0067] The operating pressure of the tubular ultrafiltration membrane device is 0.2 MPa, and the total hardness of the dyed brine after hardness removal is 45 mg / L, and the chromaticity is 2000 times (calculated by the dilution multiple method);

[0068] 4) the dyeing brine obtained in step 3) is passed into an alkalinity removal tank, and 98% concentrated sulfuric acid is added thereto to adjust its pH to 4.0. Aeration is performed for 1 hour to convert the carbonate therein into carbon dioxide, which overflows from the dyeing brine, thereby achieving the purpose of removing alkalinity;

[0069] 5) the dyed brine obtained in step 4) enters a pH adjustment tank and is then added with a 10% sodium hydroxide solution to adjust its pH to 7.0;

[0070] 6) passing the dyed brine obtained in step 5) into an ultrafiltration device (a spiral ultrafiltration membrane device) to separate the dye and salt to obtain concentrated water and dyed brine after the dye is removed;

[0071] The operating pressure of the spiral ultrafiltration membrane device is 0.4 MPa, the dye retention rate is greater than 90%, and the concentration of sodium sulfate in the dyeing brine after the dye is removed in step 6) is 71 g / L, and the chroma is 128 times (calculated by the dilution multiple method);

[0072] 7) performing deep ozone decolorization on the dyed brine obtained in step 6) in an ozone tower to obtain decolorized dyed brine;

[0073] The ozone dosage in the ozone tower is 200 mg / L, the residence time is 1 hour, and the chromaticity of the decolorized dyed brine is 4 times (calculated by the dilution multiple method);

[0074] 8) concentrating the completely decolorized dyed brine obtained in step 7) in a nanofiltration device to obtain concentrated dyed brine;

[0075] The operating pressure of the nanofiltration device is 6 MPa, the retention rate of sodium sulfate is greater than 99%, and the concentration of sodium sulfate in the concentrated dyeing brine is 143 g / L.

[0076] 9) The dyed brine obtained in step 8) enters a sodium sulfate concentration adjustment tank to complete salt recovery and hardness removal in the dyed brine. The final water produced has a sodium sulfate concentration of 143 g / L, a chromaticity of 8 times (calculated by the dilution multiple method), a total hardness of 90 mg / L, and a total alkalinity of 135 mg / L.

[0077] Application Example 1

[0078] This application example reuses the dyeing brine stored in the sodium sulfate concentration regulating tank in step 9) of Example 2 in the dyeing process, including:

[0079] First, a dyeing solution is prepared using dyeing salt water. The formula of the resulting dyeing solution is as follows:

[0080]

[0081] Wherein, the "%" in the dyeing solution formula is the weight percentage calculated based on the total weight of the fabric to be dyed, and the "g / L" is calculated based on the total volume of the dyeing solution;

[0082] Then, 20-count single-knitted fabric was dyed at 60°C for 60 minutes with a bath ratio of 1:10.

[0083] Dyeing effect: The color difference ΔE is 0.4, which is acceptable, and the visual levelness is also acceptable.

[0084] Application Example 2

[0085] This application example reuses the dyeing brine stored in the sodium sulfate concentration regulating tank in step 9) of Example 2 in the dyeing process, including:

[0086] First, a dyeing solution is prepared using dyeing salt water. The formula of the resulting dyeing solution is as follows:

[0087]

[0088]

[0089] Wherein, the "%" in the dyeing solution formula is the weight percentage calculated based on the total weight of the fabric to be dyed, and the "g / L" is calculated based on the total volume of the dyeing solution;

[0090] Then, 20-count single-knitted fabric was dyed at 60°C for 60 minutes with a bath ratio of 1:10.

[0091] Dyeing effect: The color difference ΔE is 0.58, which is acceptable, and the visual levelness is also acceptable.

[0092] In summary, the system and method for recovering salt and simultaneously removing hardness from dyed brine provided by the embodiments of the present invention utilize membrane fractionation to reuse salt from the dyed brine and achieve the goal of removing hardness. This method is characterized by simple operation and low shipping costs. The sodium sulfate concentration in the dyed brine obtained after salt recovery and hardness removal according to the embodiments of the present invention is adjusted to the target concentration and then reused in the dyeing process, achieving acceptable color difference and levelness.

[0093] The above description is merely a specific embodiment of the present invention and should not be construed as limiting the scope of the invention. Therefore, substitutions of equivalent components, or equivalent changes and modifications made within the scope of patent protection, should still fall within the scope of this patent. Furthermore, the technical features of this invention may be freely combined with one another, with other technical inventions, and with other technical inventions.

Claims

1. A system for recovering salt and removing hardness from dyed brine, characterized in that: The system for recovering salt and removing hardness from dyed brine comprises: a wastewater collection tank, a mesh filter, a tubular membrane device, an alkalinity removal tank, a pH adjustment tank, an ultrafiltration device, an ozone tower, a nanofiltration device, a sodium sulfate concentration adjustment tank, a sodium hydroxide solution storage tank, and a sulfuric acid storage tank; Wherein, the outlet of the wastewater collection tank is connected to the inlet of the mesh filter through a pipeline, the outlet of the mesh filter is connected to the inlet of the tubular membrane device through a pipeline via a circulation pump, the outlet of the tubular membrane device is connected to the inlet of the pH adjustment tank through a pipeline via the alkalinity removal tank, the outlet of the pH adjustment tank is connected to the inlet of the ultrafiltration device through a pipeline via an ultrafiltration circulation pump, the outlet of the ultrafiltration device is connected to the liquid inlet of the ozone tower through a pipeline, the liquid outlet of the ozone tower is connected to the dyed brine inlet of the nanofiltration device through a pipeline via a nanofiltration high-pressure pump, and the dyed brine outlet of the nanofiltration device is connected to the sodium sulfate concentration regulating tank through a pipeline; The outlet of the sodium hydroxide solution storage tank is connected to the dosing port of the wastewater collection tank and the dosing port of the pH adjustment tank through pipelines respectively; The outlet of the sulfuric acid storage tank is connected to the dosing port of the alkalinity removal tank through a pipeline; Wherein, the filtration accuracy of the mesh filter is 150-300 mesh; The tubular membrane used in the tubular membrane device has a molecular weight cut-off of 5000-100 kDa; The ultrafiltration membrane element used in the ultrafiltration device has a molecular weight cut-off of 1000-10000Da; The nanofiltration membrane element used in the nanofiltration device has a molecular weight cut-off of 200-500 Da.

2. The system for recovering salt and removing hardness from dyed brine according to claim 1, characterized in that: The system further comprises a nanofiltration water production storage tank, and the water production port of the nanofiltration device is connected to the nanofiltration water production storage tank via a pipeline.

3. The system for recovering salt and removing hardness from dyed brine according to claim 1 or 2, characterized in that: The system further comprises an ozone generator, wherein a gas outlet of the ozone generator is connected to a gas inlet of the ozone tower via a pipeline.

4. The system for recovering salt and removing hardness from dyed brine according to claim 3, characterized in that: The height of the ozone tower is greater than 4m.

5. The system for recovering salt and removing hardness from dyed brine according to claim 1 or 2, characterized in that: The system further comprises a recovered salt storage tank, and the liquid outlet of the sodium sulfate concentration regulating tank is connected to the recovered salt storage tank via a pipeline.

6. The system for recovering salt and removing hardness from dyed brine according to claim 1 or 2, characterized in that: The system further comprises a first dosing pump, a second dosing pump and a third dosing pump, and the outlet of the sodium hydroxide solution storage tank is connected to the dosing port of the wastewater collection tank and the dosing port of the pH adjustment tank through pipelines via the first dosing pump and the third dosing pump respectively; The outlet of the sulfuric acid storage tank is connected to the dosing port of the alkalinity removal tank through a pipeline via a second dosing pump.

7. A method for recovering salt and removing hardness from dyed brine, characterized in that: The method for recovering salt and removing hardness from dyed brine is achieved by using the system for recovering salt and removing hardness from dyed brine according to any one of claims 1 to 6, which comprises: 1) collecting the dyeing brine in a wastewater collection tank and adding sodium hydroxide solution to adjust the pH value thereof to 11.0-13.0, so that the metal ions in the dyeing brine form metal hydroxide colloid and metal carbonate colloid; 2) filtering the dyed brine obtained in step 1) through a mesh filter to remove suspended matter and trichomes; 3) filtering the dyed brine obtained in step 2) in a tubular membrane device to remove metal hydroxide colloids and metal carbonate colloids therein, thereby obtaining a dyed brine after hardness removal; wherein the operating pressure of the tubular membrane device is 0.2-0.6 MPa, and the hardness of the dyed brine after hardness removal is less than 50 mg / L; 4) allowing the dyed brine obtained in step 3) to enter an alkalinity removal tank and adding sulfuric acid to adjust its pH to 3.0-4.5, so that the carbonate therein is converted into carbon dioxide and overflows from the dyed brine; 5) allowing the dyed brine obtained in step 4) to enter a pH adjustment tank and adding sodium hydroxide solution to adjust the pH to neutral; 6) passing the dyed brine obtained in step 5) into an ultrafiltration device to separate the dye and salt to obtain concentrated water and dyed brine after the dye is removed; wherein the operating pressure of the ultrafiltration device is 0.2-1.0 MPa and the dye retention rate is greater than 90%; 7) deep decolorizing the dyed brine obtained in step 6) with ozone in an ozone tower to obtain decolorized dyed brine; wherein the ozone dosage in the ozone tower is 50-200 mg / L, the residence time is 1-4 hours, and the chroma of the decolorized dyed brine is less than 8 times as calculated by the dilution multiple method; 8) concentrating the dyeing brine obtained in step 7) in a nanofiltration device to obtain concentrated dyeing brine; wherein the operating pressure of the nanofiltration device is 2-8 MPa, the retention rate of sodium sulfate is greater than 99%, and the concentration of sodium sulfate in the concentrated dyeing brine is 100-200 g / L; 9) The dyed brine obtained in step 8) enters a sodium sulfate concentration regulating tank to complete salt recovery and hardness removal in the dyed brine.

8. The method for recovering salt and removing hardness from dyed brine according to claim 7, characterized in that: The method further comprises: 10) adding solid sodium sulfate to the dyeing brine obtained in step 9) to adjust the sodium sulfate concentration to the target concentration and then returning the brine to the dyeing process.

9. The method for recovering salt and removing hardness from dyed brine according to claim 7 or 8, characterized in that: In step 1) and step 5), the concentration of the sodium hydroxide solution is 10-30%.

10. The method for recovering salt and removing hardness from dyed brine according to claim 7 or 8, characterized in that: In step 4), the sulfuric acid is concentrated sulfuric acid with a concentration of 94-98%.

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