Method and system for extracting and removing chloride ions in industrial wastewater

Abstract

The invention belongs to the technical field of wastewater treatment, and relates to a method and a system for extracting and removing chloride ions in industrial wastewater, and the method comprises the following steps: feeding chlorine-containing wastewater into a first extraction tower, and contacting the chlorine-containing wastewater with an extraction solvent for extraction to obtain a chloride ion extract and raffinate wastewater; the raffinate wastewater enters a second extraction tower to be in contact with a diluent for extraction, the residual extraction agent is recovered into a diluent phase, the recovered wastewater enters a diluent stripping tower, an azeotrope of the diluent and water is obtained from the tower top, and treated wastewater is obtained from the tower bottom; pumping an azeotrope of the diluent and water to a diluent recovery tower, and carrying out rectification separation to obtain a pure diluent and kettle liquid; and feeding the chloride ion extract into an extracting agent regeneration tower, and carrying out reverse extraction regeneration by using alkali liquor to obtain an extracting agent and chloride ion enriched liquid. According to the method, chloride ions in the wastewater can be efficiently removed, meanwhile, the residual extractant and diluent in the wastewater are thoroughly recycled, secondary pollution can be eliminated, and the method has the advantages of being clean and environmentally friendly.

Description

Technical Field

[0001] The present invention belongs to the field of wastewater treatment technology, and specifically relates to a method and system for extracting and removing chloride ions from industrial wastewater. This method and system remove chloride ions from industrial wastewater, thereby reducing the equilibrium concentration of chloride ions and eliminating corrosion problems caused by high chloride ion concentrations. Background Art

[0002] Chloride ion accumulation is a common problem in many industrial systems. When the accumulated amount of chloride ions reaches a certain level, it will cause serious corrosion to the system. For example, the coal chemical wastewater generated during the processing of high-chloride coal can contain chlorine levels of up to 3,000 mg / L or more; and the concentration of chloride ions in industrial circulating cooling water systems often reaches over 10,000 mg / L after enrichment. Therefore, measures need to be taken to promptly remove chloride ions from wastewater. Currently, methods for removing chloride ions from wastewater include evaporation, electrolysis-electrodialysis, ion exchange, and membrane exchange. However, these methods cannot be used in some scenarios. For example, for wastewater from industries such as coal chemical industry with high pollution loads and complex composition, membrane exchange, evaporation, and ion exchange cannot be used. To this end, it is necessary to develop a chloride ion removal process that is widely applicable, efficient, and stable.

[0003] Traditional extraction methods utilize extractants to remove chloride-containing compounds. However, this method is subject to secondary pollution, such as residual extractants and diluents used in traditional extraction methods. To address this issue, the present invention proposes a highly efficient, stable, and widely applicable process for removing chloride ions from wastewater. This process not only removes chloride ions but also completely recovers residual extractants and diluents in the wastewater, eliminating secondary pollution. Summary of the Invention

[0004] The purpose of the present invention is to solve the above-mentioned problems existing in the prior art, and a method and system for extracting and removing chloride ions from industrial wastewater are proposed. On the one hand, the method takes solubility and recyclability into consideration when selecting the extractant and diluent; for example, the extractant selected has a low solubility, and when selecting the diluent, a high distribution coefficient for the extractant is also used as an evaluation indicator to reduce the residual amount of the extractant in the wastewater; on the other hand, a recovery unit is also provided in the system to fully recover the extractant and diluent; in addition, a secondary extraction recovery of the extractant is also provided, so that the content of the extractant can be reduced to below 30 mg / L; and the selected diluent forms an azeotropic reaction with water and can be completely recovered by steam stripping.

[0005] Through the above-mentioned optimized method and system, the present invention can efficiently remove chloride ions from wastewater, and at the same time completely recover residual extractant and diluent in the wastewater, thereby eliminating secondary pollution and having the advantages of being clean and environmentally friendly.

[0006] The technical solution of the present invention is:

[0007] The present invention provides a method for extracting and removing chloride ions from industrial wastewater, comprising the following steps:

[0008] (1) Extraction dechlorination: Chlorine-containing wastewater is fed into the first extraction tower and brought into contact with the extraction solvent for extraction to obtain chloride ion extract and raffinate wastewater;

[0009] (2) Extractant recovery: The raffinate wastewater enters the second extraction tower, contacts with the diluent for extraction, and the residual extractant in the raffinate wastewater is recovered into the diluent phase to obtain the recovered wastewater and diluent phase;

[0010] (3) Diluent stripping: The recovered wastewater enters the diluent stripping tower, and the azeotrope of diluent and water is obtained from the top of the tower, and the treated wastewater is obtained at the bottom of the tower;

[0011] (4) Diluent recovery: The azeotrope of diluent and water is pumped to the diluent recovery tower for distillation separation to obtain pure diluent and kettle liquid;

[0012] (5) Extractant regeneration: The chloride ion extract obtained in step (1) is fed into an extractant regeneration tower and regenerated by stripping with alkaline solution to obtain an extractant and a chloride ion enriched solution.

[0013] Furthermore, when the chloride ion content in the chlorine-containing wastewater exceeds 2000 mg / L, iron oxide or iron salt is added to the chlorine-containing wastewater before extraction to reduce the mass ratio of the extraction solvent to the chlorine-containing wastewater, and the molar ratio of iron ions to chloride ions is controlled at 1:5 to 1:2;

[0014] When iron ions are added before extraction or the chlorine-containing wastewater contains iron ions, the chloride ion-enriched liquid obtained after extraction needs to enter the solid-liquid separator to separate the iron-containing precipitate, and the iron-containing precipitate can be added back to the wastewater before extraction for recycling.

[0015] Furthermore, the extraction solvent in step (1) is an organic phase obtained by mixing an extractant and a diluent in a mass ratio of 1:10 to 1:2.

[0016] Furthermore, the extractant includes trioctylamine (TOA), and the diluent includes methyl isobutyl ketone.

[0017] Furthermore, the mass ratio of the extraction solvent (a mixture of the extractant and the diluent) to the chlorine-containing wastewater is 1:6 to 1:2.

[0018] Furthermore, the first extraction tower is not limited to an extraction tower, and can also be one or more of a multi-stage mixer-settler, a static mixer, and an oil-water separator.

[0019] Furthermore, the chlorine-containing wastewater in step (1) is extracted with the extraction solvent pumped from the extractant circulation tank in the first extraction tower, and the chloride ion extract is obtained from the top of the first extraction tower and sent to the extractant regeneration tower, and the raffinate wastewater is obtained at the bottom of the first extraction tower and sent to the second extraction tower.

[0020] Furthermore, in step (1), the theoretical number of stages of the first extraction tower is 1-6, and the extraction temperature is 20-65°C.

[0021] Furthermore, in the step (2), the extract wastewater after extraction and dechlorination is countercurrently contacted and extracted with the diluent sent from the diluent circulation tank in the second extraction tower, and the residual extractant in the extract wastewater is extracted and recovered into the diluent phase. The recovered wastewater comes out from the bottom of the tower and then enters the diluent stripping tower, and the diluent phase comes out from the top of the tower and enters the diluent circulation tank.

[0022] Furthermore, in step (2), the theoretical number of stages of the second extraction tower is 1-6, and the extraction temperature is 20-65°C.

[0023] Furthermore, in the step (2), the mass ratio of the diluent to the raffinate wastewater is 1:4 to 1:1.

[0024] Furthermore, in the step (3), the recovered wastewater enters the diluent stripping tower from the bottom of the second extraction tower, and the diluent is recovered by heating and stripping by utilizing the azeotropic property of the diluent and water. The vapor phase obtained at the top of the tower is the azeotropic mixture of the diluent and water, which enters the diluent circulation tank after condensation, and the treated wastewater is obtained at the bottom of the tower and sent out of the boundary area.

[0025] Furthermore, in step (3), the operating pressure of the diluent stripping tower is atmospheric pressure, the number of theoretical plates is 5-15, and the tower top temperature is 90-98°C.

[0026] Furthermore, in the step (4), the azeotropic mixture of the condensed diluent and water is pumped to a diluent recovery tower for dilution separation, and the pure diluent obtained at the top of the tower is sent to a diluent circulation tank. The kettle liquid with a composition ratio of extractant to diluent similar to that of the extraction solvent is obtained in the bottom of the tower and is sent to the extractant circulation tank.

[0027] Because the diluent in the diluent recirculation tank contains a low concentration of extractant, it is pumped to the diluent recovery tower for fractionation. Pure diluent is obtained from the top of the tower and returned to the diluent recirculation tank. The bottom of the tower, containing a ratio of extractant to diluent similar to that of the extraction solvent feed to the first extraction tower, produces a kettle liquid that is fed to the extractant recirculation tank.

[0028] Furthermore, in step (4), the operating pressure of the diluent recovery tower is atmospheric pressure, the number of theoretical plates is 5-16, and the tower top temperature is 109-112°C.

[0029] Furthermore, in the step (5), the chloride ion extract obtained in the step (1) is sent to the extractant regeneration tower, and is regenerated by stripping with a dilute alkali solution with a concentration of 8-20%. The regenerated chloride ion-enriched liquid is sent out of the boundary area and used as a biochemical alkali supplement, a membrane cleaner, or a raw material for chlor-alkali production, etc. according to the situation; the regenerated extractant is returned to the extractant circulation tank for recycling.

[0030] Furthermore, the theoretical number of stages of the extractant regeneration tower is 1-6, and the extraction temperature is 20-65°C.

[0031] Furthermore, the mass ratio between the alkali solution and the chloride ion extract is 1:5 to 1:2.

[0032] The present invention also provides a system for extracting and removing chloride ions from industrial wastewater, comprising:

[0033] The first extraction tower is used to extract chloride ions from the chlorine-containing wastewater;

[0034] An extractant circulation tank, used for storing the extractant and pumping the extractant into the first extraction tower;

[0035] a chloride ion extract tank for storing the chloride ion extract obtained from the first extraction tower and pumping it to the extractant regeneration tower;

[0036] The extractant regeneration tower is used for stripping and regenerating the extractant, and sending the regenerated extractant to the extractant circulation tank for recycling, and sending the regenerated chloride ion enriched liquid out of the boundary area;

[0037] The second extraction tower is used to receive the raffinate wastewater after dechlorination in the first extraction tower, and use the diluent to extract and recover the residual extractant in the raffinate wastewater, and then send it to the diluent circulation tank after condensation. The recovered wastewater is sent to the diluent stripping tower;

[0038] a diluent circulation tank, used for storing the diluent and feeding the diluent into the second extraction tower;

[0039] The diluent recovery tower is used to receive the diluent containing low concentration of extractant from the diluent circulation tank and perform distillation separation, return the obtained pure diluent to the diluent circulation tank, and send the kettle liquid containing diluent and extractant to the extractant circulation tank;

[0040] The diluent stripping tower is used to strip and recover the diluent in the wastewater coming out of the second extraction tower, and to send the obtained azeotrope of diluent and water into the diluent circulation tank.

[0041] Furthermore, the system also includes a solid-liquid separator for separating the iron-containing precipitate from the chloride ion-enriched liquid obtained after regeneration. The obtained iron-containing precipitate can be added back to the wastewater before extraction for recycling.

[0042] Beneficial effects of the present invention:

[0043] (1) The method provided by the present invention is used to remove chloride ions with a high removal efficiency, which can reach more than 99% or reduce the chloride ion content to below 100 mg / L.

[0044] (2) The method of the present invention has a wide range of applications and is suitable for various chlorine-containing wastewater systems. It is not affected by the organic matter, suspended matter, and other salt content in the wastewater. It can efficiently remove chloride ions from the wastewater and simultaneously achieve complete recovery of residual extractants and diluents in the wastewater, eliminating secondary pollution.

[0045] (3) The diluent selected in the present invention forms a minimum azeotrope with water, allowing the diluent to be completely recovered by steam stripping. Furthermore, the recycled diluent can be used to recover residual TOA in the water, eliminating the need for an exogenous extractant. This present invention is clean, environmentally friendly, and free of secondary pollution. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 A process flow chart of the system for extracting and removing chloride ions from industrial wastewater provided by the present invention;

[0047] Figure 2 This is a process flow chart of the system for extracting and removing chloride ions from industrial wastewater with added iron ions provided by the present invention.

[0048] In the figure, 1. first extraction tower; 2. extractant circulation tank; 3. chloride ion extractant tank; 4. extractant regeneration tower; 5. second extraction tower; 6. diluent circulation tank; 7. diluent recovery tower; 8. diluent stripping tower; 9. solid-liquid separator. DETAILED DESCRIPTION

[0049] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0050] In order to further understand the present invention, the present invention will be further described with reference to the accompanying drawings and embodiments.

[0051] Example 1

[0052] In a coal-to-chemical fertilizer plant, the coal gasification wastewater flow rate is 95 tons / hour and the chloride ion content is about 1600 mg / L. Figure 1 The flow chart shown is used to extract chlorine and recover the extractant. The steps are as follows:

[0053] (1) Using TOA as the extractant and methyl isobutyl ketone as the diluent, TOA and methyl isobutyl ketone were mixed in a mass ratio of 1:8 and used as the extraction solvent;

[0054] The chlorine-containing wastewater and the extraction solvent pumped from the extractant circulation tank 2 are extracted in the first extraction tower 1 at a mass ratio of 6:1. The theoretical number of stages of the first extraction tower 1 is 3, and the extraction temperature is 60°C; the chloride ion extract is obtained at the top of the extraction tower and sent to the extractant regeneration tower 4; the raffinate wastewater is obtained at the bottom of the extraction tower and sent to the second extraction tower 5.

[0055] (2) After extraction and dechlorination, the wastewater is sent to the second extraction tower 5 and subjected to countercurrent contact extraction with the diluent sent from the diluent circulation tank 6; the second extraction tower 5 has three theoretical stages, the extraction temperature is about 60°C, and the mass ratio of diluent to wastewater is 1:4; the TOA remaining in the wastewater is extracted and recovered into the diluent phase; the wastewater flows out of the bottom of the tower and then enters the diluent stripping tower 8; the diluent phase flows out of the top of the tower and enters the diluent circulation tank 6.

[0056] (3) The wastewater from the bottom of the second extraction tower 5 enters the diluent stripping tower 8, and is recovered by heating stripping using the azeotropic property of the diluent and water. The operating pressure of the diluent stripping tower 8 is atmospheric pressure, the number of theoretical plates is 5, and the tower top temperature is 92°C; the vapor phase obtained at the top of the tower is the azeotropic mixture of the diluent and water, which enters the diluent circulation tank 6 after condensation; the treated wastewater obtained at the bottom of the tower is sent out of the boundary area.

[0057] (4) The diluent in the diluent circulation tank 6 contains a low concentration of TOA and is pumped to the diluent recovery tower 7. The operating pressure of the diluent recovery tower 7 is atmospheric pressure, the number of theoretical plates is 6, and distillation separation is performed by distillation. The top temperature of the diluent recovery tower 7 is 109°C, and the pure diluent obtained from the top is returned to the diluent circulation tank 6. The bottom of the tower obtains a bottom liquid with a TOA to diluent ratio similar to that of the extraction solvent feed of the first extraction tower 1, and is sent to the extractant circulation tank 2.

[0058] (5) The chloride ion extract obtained in step (1) is pumped into the extractant regeneration tower 4 through the chloride ion extract tank 3, and is regenerated by stripping with a dilute alkali solution with a concentration of 10%. The theoretical number of stages of the extractant regeneration tower 4 is 2, the extraction temperature is 60°C, and the mass ratio of the alkali solution to the chloride ion extract is 1:5; the regenerated chloride ion enriched liquid is sent out of the boundary area and used for biochemical alkali supplementation, membrane cleaning agent or chlor-alkali production raw material according to the situation; the regenerated extractant is returned to the extractant circulation tank 2 for recycling.

[0059] After treatment using this method, the chloride ion content in the wastewater can be reduced to below 80 mg / L, eliminating equipment corrosion issues in subsequent wastewater treatment facilities. The TOA residual in the wastewater is below 20 mg / L, and the diluent can be reduced to undetectable levels.

[0060] Example 2

[0061] In a coal-to-chemical fertilizer plant, the coal gasification wastewater flow rate is 95 tons / hour and the chloride ion content is about 1600 mg / L. Figure 1 The extraction and recovery of chlorine and the extraction agent are performed in the flowchart shown. The extraction and recovery process is basically the same as in Example 1, except that the parameters such as temperature and solvent ratio are adjusted. The specific steps are as follows:

[0062] (1) Using TOA as the extractant and methyl isobutyl ketone as the diluent, TOA and methyl isobutyl ketone were mixed in a mass ratio of 1:10 and used as the extraction solvent;

[0063] The chlorine-containing wastewater and the extraction solvent pumped from the extractant circulation tank 2 are extracted in the first extraction tower 1 at a mass ratio of 4:1. The theoretical number of stages of the first extraction tower 1 is 2, and the extraction temperature is 30°C; the chloride ion extract is obtained at the top of the extraction tower and sent to the extractant regeneration tower 4; the raffinate wastewater is obtained at the bottom of the extraction tower and sent to the second extraction tower 5.

[0064] (2) After extraction and dechlorination, the wastewater is sent to the second extraction tower 5 and subjected to countercurrent contact extraction with the diluent sent from the diluent circulation tank 6; the second extraction tower 5 has two theoretical stages, the extraction temperature is about 30°C, and the mass ratio of diluent to wastewater is 1:3; the TOA remaining in the wastewater is extracted and recovered into the diluent phase; the wastewater flows out of the bottom of the tower and then flows into the diluent stripping tower 8; the diluent phase flows out of the top of the tower and then flows into the diluent circulation tank 6.

[0065] (3) The wastewater from the bottom of the second extraction tower 5 enters the diluent stripping tower 8, and is recovered by heating stripping using the azeotropic property of the diluent and water. The operating pressure of the diluent stripping tower 8 is atmospheric pressure, the number of theoretical plates is 10, and the tower top temperature is 95°C; the vapor phase obtained at the top of the tower is the azeotropic mixture of the diluent and water, which enters the diluent circulation tank 6 after condensation; the treated wastewater obtained at the bottom of the tower is sent out of the boundary area.

[0066] (4) The diluent in the diluent circulation tank 6 contains a low concentration of TOA and is pumped to the diluent recovery tower 7. The operating pressure of the diluent recovery tower 7 is atmospheric pressure, the number of theoretical plates is 10, and distillation separation is performed by distillation. The top temperature of the diluent recovery tower 7 is 110°C, and the pure diluent obtained from the top is returned to the diluent circulation tank 6. The bottom of the tower obtains a bottom liquid with a TOA to diluent ratio similar to that of the extraction solvent feed of the first extraction tower 1, which is sent to the extractant circulation tank 2.

[0067] (5) The chloride ion extract obtained in step (1) is pumped into the extractant regeneration tower 4 through the chloride ion extract tank 3, and is regenerated by stripping with a dilute alkali solution with a concentration of 14%. The theoretical number of stages of the extractant regeneration tower 4 is 4, the extraction temperature is 30°C, and the mass ratio of the alkali solution to the chloride ion extract is 1:3; the regenerated chloride ion enriched liquid is sent out of the boundary area and used for biochemical alkali supplementation, membrane cleaning agent or chlor-alkali production raw material according to the situation; the regenerated extractant is returned to the extractant circulation tank 2 for recycling.

[0068] After treatment using this method, the chloride ion content in the wastewater can be reduced to below 80 mg / L, eliminating equipment corrosion issues in subsequent wastewater treatment facilities. The TOA residual in the wastewater is below 20 mg / L, and the diluent can be reduced to undetectable levels.

[0069] Example 3

[0070] In a coal-to-chemical fertilizer plant, the coal gasification wastewater flow rate is 95 tons / hour and the chloride ion content is about 1600 mg / L. Figure 1 The extraction and recovery of chlorine and the extraction agent are performed in the flowchart shown. The extraction and recovery process is basically the same as in Example 1, except that the parameters such as temperature and solvent ratio are adjusted. The specific steps are as follows:

[0071] (1) Using TOA as the extractant and methyl isobutyl ketone as the diluent, TOA and methyl isobutyl ketone were mixed in a mass ratio of 1:2 and used as the extraction solvent;

[0072] The chlorine-containing wastewater and the extraction solvent pumped from the extractant circulation tank 2 are extracted in the first extraction tower 1 at a mass ratio of 2:1. The first extraction tower 1 has 6 theoretical stages and the extraction temperature is 50°C. The chloride ion extract is obtained at the top of the extraction tower and sent to the extractant regeneration tower 4. The raffinate wastewater is obtained at the bottom of the extraction tower and sent to the second extraction tower 5.

[0073] (2) After extraction and dechlorination, the wastewater is sent to the second extraction tower 5 and subjected to countercurrent contact extraction with the diluent sent from the diluent circulation tank 6; the second extraction tower 5 has 6 theoretical stages, the extraction temperature is about 50°C, and the mass ratio of diluent to wastewater is 1:1; the TOA remaining in the wastewater is extracted and recovered into the diluent phase; the wastewater flows out of the bottom of the tower and then flows into the diluent stripping tower 8; the diluent phase flows out of the top of the tower and then flows into the diluent circulation tank 6.

[0074] (3) The wastewater from the bottom of the second extraction tower 5 enters the diluent stripping tower 8, and is recovered by heating and stripping using the azeotropic property of the diluent and water. The operating pressure of the diluent stripping tower 8 is atmospheric pressure, the number of theoretical plates is 15, and the tower top temperature is 98°C; the vapor phase obtained at the top of the tower is the azeotropic mixture of the diluent and water, which enters the diluent circulation tank 6 after condensation; the treated wastewater obtained at the bottom of the tower is sent out of the boundary area.

[0075] (4) The diluent in the diluent circulation tank 6 contains a low concentration of TOA and is pumped to the diluent recovery tower 7. The operating pressure of the diluent recovery tower 7 is atmospheric pressure, the number of theoretical plates is 16, and distillation separation is performed by distillation. The top temperature of the diluent recovery tower 7 is 112°C, and the pure diluent obtained from the top is returned to the diluent circulation tank 6. The bottom of the tower obtains a bottom liquid with a TOA to diluent ratio similar to that of the extraction solvent feed of the first extraction tower 1, and is sent to the extractant circulation tank 2.

[0076] (5) The chloride ion extract obtained in step (1) is pumped into the extractant regeneration tower 4 through the chloride ion extract tank 3, and is regenerated by stripping with a dilute alkali solution with a concentration of 20%. The theoretical number of stages of the extractant regeneration tower 4 is 6, the extraction temperature is 40°C, and the mass ratio of the alkali solution to the chloride ion extract is 1:2; the regenerated chloride ion enriched liquid is sent out of the boundary area and used for biochemical alkali supplementation, membrane cleaning agent or chlor-alkali production raw material according to the situation; the regenerated extractant is returned to the extractant circulation tank 2 for recycling.

[0077] After treatment using this method, the chloride ion content in the wastewater can be reduced to below 80 mg / L, eliminating equipment corrosion issues in subsequent wastewater treatment facilities. The TOA residual in the wastewater is below 20 mg / L, and the diluent can be reduced to undetectable levels.

[0078] Example 4

[0079] A steel plant with a coking wastewater flow rate of 80 tons / hour and a chloride ion content of about 2800 mg / L (about 79 mmol / L) was used to extract chlorine from the wastewater and recover the extractant. The extraction and recovery process was the same as in Example 1.

[0080] After treatment according to the method and steps of Example 1, the chloride ion content in the wastewater can be reduced to below 80 mg / L, eliminating the problem of equipment corrosion in the wastewater subsequent treatment device. The TOA residual content in the wastewater is below 20 mg / L, and the diluent can be reduced to undetectable levels.

[0081] The extraction and recovery process of the same wastewater system is basically the same as that of Example 1, except that iron ions are added to promote extraction.

[0082] like Figure 2 As shown, the pickling wastewater of our factory (to supplement iron ions) is added to the wastewater before extraction. After mixing, the iron ion content in the wastewater is about 16-27 mmol / L, that is, the molar ratio of iron ions to chloride ions is controlled at 1:5-1:3. The mass ratio of wastewater to extraction solvent can be reduced from 1.5:1 to 4:1, and the chloride ion content in the effluent can also be reduced to the same level.

[0083] The chloride ion-rich liquid obtained after extraction from the extractant regeneration tower 4 enters the solid-liquid separator 9 to separate the iron-containing precipitate, which can be added back to the wastewater before extraction for recycling.

[0084] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art may still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein with equivalents. Any modifications, equivalent replacements, and modifications made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for extracting and removing chloride ions from industrial wastewater, characterized in that: The following steps are involved: (1) Extraction dechlorination: Chlorine-containing wastewater is fed into the first extraction tower and brought into contact with the extraction solvent for extraction to obtain chloride ion extract and raffinate wastewater; (2) Extractant recovery: The raffinate wastewater enters the second extraction tower, contacts with the diluent for extraction, and the residual extractant in the raffinate wastewater is recovered into the diluent phase to obtain the recovered wastewater and diluent phase; (3) Diluent stripping: The recovered wastewater enters the diluent stripping tower, and the azeotrope of diluent and water is obtained from the top of the tower, and the treated wastewater is obtained at the bottom of the tower; (4) Diluent recovery: The azeotrope of diluent and water is pumped to the diluent recovery tower for distillation separation to obtain pure diluent and kettle liquid; (5) Extractant regeneration: The chloride ion extract obtained in step (1) is fed into an extractant regeneration tower and regenerated by stripping with alkaline solution to obtain an extractant and a chloride ion enriched solution.

2. The method according to claim 1, characterized in that When the chloride ion content in the chlorine-containing wastewater exceeds 2000 mg / L, iron oxide or iron salt is added to the chlorine-containing wastewater before extraction to reduce the mass ratio of the extraction solvent to the chlorine-containing wastewater, and the molar ratio of iron ions to chloride ions is controlled at 1:5 to 1:2; When iron ions are added before extraction or the chlorine-containing wastewater contains iron ions, the chloride ion-enriched liquid obtained after extraction is sent to a solid-liquid separator to separate the iron-containing precipitate, which is then added back into the chlorine-containing wastewater before extraction for recycling.

3. The method according to claim 1, characterized in that The extraction solvent in step (1) is obtained by mixing an extractant and a diluent in a mass ratio of 1:10 to 1:2, the extractant includes trioctylamine, and the diluent includes methyl isobutyl ketone; the mass ratio of the extraction solvent to the chlorine-containing wastewater is 1:6 to 1:

2.

4. The method according to claim 1, wherein The chlorine-containing wastewater in step (1) is extracted with the extraction solvent pumped from the extractant circulation tank in a first extraction tower, and the chloride ion extract is obtained from the top of the first extraction tower and sent to the extractant regeneration tower, and the raffinate wastewater is obtained from the bottom and sent to the second extraction tower; the theoretical number of stages of the first extraction tower is 1-6, and the extraction temperature is 20-65°C.

5. The method according to claim 1, wherein In the step (2), the extracting wastewater after extraction and dechlorination is countercurrently contacted with the diluent sent from the diluent circulation tank in the second extraction tower for extraction, and the residual extractant in the extracting wastewater is extracted and recovered into the diluent phase. The recovered wastewater enters the diluent stripping tower from the bottom of the tower, and the diluent phase enters the diluent circulation tank from the top of the tower; the theoretical number of stages of the second extraction tower is 1-6, the extraction temperature is 20-65°C, and the mass ratio of the diluent to the extracting wastewater is 1:4 to 1:

1.

6. The method according to claim 1, characterized in that In the step (3), the recovered wastewater enters a diluent stripping tower, and the diluent is recovered by heating and stripping. The vapor phase obtained at the top of the tower is an azeotrope of the diluent and water, which enters the diluent circulation tank after condensation, and the treated wastewater is obtained at the bottom of the tower; the operating pressure of the diluent stripping tower is atmospheric pressure, the number of theoretical plates is 5-15, and the top temperature is 90-98°C.

7. The method according to claim 1, characterized in that In the step (4), the azeotropic mixture of the condensed diluent and water is pumped to a diluent recovery tower for dilution separation, the pure diluent obtained at the top of the tower is fed into a diluent circulation tank, and the kettle liquid having an extractant to diluent composition ratio similar to that of the extraction solvent is obtained at the bottom of the tower and fed into the extractant circulation tank; wherein the operating pressure of the diluent recovery tower is atmospheric pressure, the number of theoretical plates is 5-16, and the top temperature is 109-112°C.

8. The method according to claim 1, characterized in that In the step (5), the chloride ion extract obtained in the step (1) is sent to an extractant regeneration tower, and is stripped and regenerated using a dilute alkali solution with a concentration of 8-20%. The regenerated chloride ion-enriched solution is sent out of the boundary area, and the regenerated extractant is returned to the extractant circulation tank for recycling; wherein the theoretical number of stages of the extractant regeneration tower is 1-6, the extraction temperature is 20-65°C, and the mass ratio between the alkali solution and the chloride ion extract is 1:5 to 1:

2.

9. A system for extracting and removing chloride ions from industrial wastewater, characterized in that: include: The first extraction tower is used to extract chloride ions from the chlorine-containing wastewater; An extractant circulation tank, used for storing the extractant and pumping the extractant into the first extraction tower; a chloride ion extract tank for storing the chloride ion extract obtained from the first extraction tower and pumping it to the extractant regeneration tower; The extractant regeneration tower is used for stripping and regenerating the extractant, and sending the regenerated extractant to the extractant circulation tank for recycling, and sending the regenerated chloride ion enriched liquid out of the boundary area; The second extraction tower is used to receive the raffinate wastewater after dechlorination in the first extraction tower, and use the diluent to extract and recover the residual extractant in the raffinate wastewater, and then send it to the diluent circulation tank after condensation. The recovered wastewater is sent to the diluent stripping tower; a diluent circulation tank, used for storing the diluent and feeding the diluent into the second extraction tower; The diluent recovery tower is used to receive the diluent containing low concentration of extractant from the diluent circulation tank and perform distillation separation, return the obtained pure diluent to the diluent circulation tank, and send the kettle liquid containing diluent and extractant to the extractant circulation tank; The diluent stripping tower is used to strip and recover the diluent in the wastewater coming out of the second extraction tower, and to send the obtained azeotrope of diluent and water into the diluent circulation tank.

10. The system according to claim 9, characterized in that The system also includes a solid-liquid separator for separating the iron-containing precipitate from the chloride ion-enriched liquid obtained after regeneration. The obtained iron-containing precipitate can be added back into the wastewater before extraction for recycling.

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