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

Abstract

The application belongs to the technical field of wastewater treatment, and relates to a method and system for extracting and removing chlorine ions in industrial wastewater, which comprises the following steps: sending chlorine-containing wastewater into a first extraction tower to contact with an extraction solvent for extraction, so as to obtain a chlorine ion extract and raffinate wastewater; the raffinate wastewater enters a second extraction tower to contact with a diluent for extraction, the residual extraction agent is recovered into the diluent phase, the recovered wastewater enters a diluent stripping tower, an azeotrope of the diluent and water is obtained from the top of the tower, and treated wastewater is obtained from the bottom of the tower; the azeotrope of the diluent and water is pumped into a diluent recovery tower for rectification and separation, so as to obtain pure diluent and still liquid; and the chlorine ion extract is sent into an extraction agent regeneration tower to be regenerated by back extraction with lye, so as to obtain the extraction agent and a chlorine ion concentrate. The application can efficiently remove the chlorine ions in the wastewater, simultaneously realizes complete recovery of the residual extraction agent and diluent in the wastewater, can eliminate secondary pollution, and has the advantages of being clean and environmentally friendly.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment technology, specifically relating 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 levels. Background Technology

[0002] Chloride ion accumulation is a problem in many industrial systems, and high levels of accumulated chloride ions can cause severe corrosion. For example, wastewater from high-chloride coal processing can contain chloride levels exceeding 3000 mg / L; in industrial circulating cooling water systems, chloride ion concentrations often reach over 10000 mg / L. Therefore, measures are needed to remove chloride ions from wastewater promptly. Current methods for chloride ion removal include evaporation, electrolysis-electrodialysis, ion exchange, and membrane exchange. However, these methods are unsuitable in certain scenarios. For instance, membrane exchange, evaporation, and ion exchange are not applicable to wastewater from industries with high pollution loads and complex compositions, such as coal chemical engineering. Therefore, a widely applicable, efficient, and stable chloride ion removal process needs to be developed.

[0003] Traditional extraction methods remove chloride-containing compounds by using extractants. However, these methods suffer from secondary pollution problems, such as secondary pollution caused by residual extractants and diluents. To address these issues, this 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 from the wastewater, eliminating secondary pollution. Summary of the Invention

[0004] The purpose of this invention is to solve the aforementioned problems existing in the prior art, and to propose a method and system for chloride ion extraction and removal from industrial wastewater. On the one hand, this method considers solubility and recyclability when selecting the extractant and diluent; for example, the selected extractant has low solubility, and when selecting the diluent, a high partition coefficient to the extractant is also used as an evaluation indicator to reduce the residual amount of extractant in the wastewater. On the other hand, a recovery unit is also set up in the system to fully recover the extractant and diluent; in addition, a secondary extraction and recovery of the extractant is set up, thereby reducing the extractant content to below 30 mg / L; and the selected diluent forms an azeotrope with water and can be completely recovered through stripping.

[0005] Through the optimized method and system described above, the present invention can efficiently remove chloride ions from wastewater, while achieving complete recovery of residual extractants and diluents in the wastewater, thus eliminating secondary pollution and possessing the advantages of being clean and environmentally friendly.

[0006] The technical solution of this invention is:

[0007] This invention provides a method for chloride ion extraction and removal from industrial wastewater, comprising the following steps:

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

[0009] (2) Extractant recovery: The raffinate wastewater enters the second extraction tower and is extracted by contacting the diluent. The extractant remaining in the raffinate wastewater is recovered into the diluent phase, resulting in 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, while the treated wastewater is obtained from 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 bottom liquid;

[0012] (5) Extractant regeneration: The chloride ion extract obtained in step (1) is sent to the extractant regeneration tower and regenerated by alkaline back-extraction to obtain the extractant and chloride ion enrichment 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. The molar ratio of iron ions to chloride ions is controlled at 1:5 to 1:2.

[0014] If iron ions were added before extraction or if the chlorine-containing wastewater contains iron ions, the chloride ion enrichment solution obtained after extraction needs to enter a solid-liquid separator to separate the iron-containing precipitate. 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 the extractant and the 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 extractant and 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, but can also be one or more of a multi-stage mixer-clarifier, a static mixer, and an oil-water separator.

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

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

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

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

[0024] Furthermore, in step (3), the recovered wastewater enters the diluent stripping tower from the bottom of the second extraction tower. The diluent is recovered by heating and stripping using the azeotropic properties of the diluent and water. The vapor phase obtained at the top of the tower is the azeotrope of the diluent and water. After condensation, it enters the diluent circulation tank. 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 theoretical number of plates is 5-15, and the temperature at the top of the tower is 90-98℃.

[0026] Furthermore, in step (4), the azeotrope of the condensed diluent and water is pumped to the diluent recovery tower for distillation separation. The pure diluent obtained from the top of the tower is sent to the diluent circulation tank, and the bottom liquid obtained from the tower, which has a composition ratio of extractant and diluent similar to that of the extraction solvent, is sent to the extractant circulation tank.

[0027] Because the diluent in the diluent circulation tank contains a low concentration of extractant, it is pumped to the diluent recovery tower for distillation separation. Pure diluent is obtained from the top of the tower and returned to the diluent circulation tank; the bottom liquid, with an extractant-to-diluent composition ratio similar to that of the first extraction tower feed solvent, is sent to the extractant circulation tank.

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

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

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

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

[0032] This invention also provides a system for chloride ion extraction and removal from industrial wastewater, comprising:

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

[0034] The extractant circulation tank is used to store the extractant and pump it to the first extraction tower;

[0035] A chloride ion extract tank is used to store the chloride ion extract obtained from the first extraction tower and to pump it to the extractant regeneration tower.

[0036] The extractant regeneration tower is used for back-extraction and regeneration of the extractant, and the regenerated extractant is sent to the extractant circulation tank for recycling. The regenerated chloride ion enrichment solution is sent 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 to use diluent to extract and recover the residual extractant in the raffinate wastewater. After condensation, the wastewater is sent to the diluent circulation tank, and the recovered wastewater is sent to the diluent stripping tower.

[0038] A diluent circulation tank is used to store the diluent and send it to the second extraction tower;

[0039] The diluent recovery tower is used to receive diluent containing a low concentration of extractant from the diluent circulation tank and perform distillation separation. The obtained pure diluent is sent back to the diluent circulation tank, and the kettle liquid containing diluent and extractant is sent into the extractant circulation tank.

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

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

[0042] The beneficial effects of this invention are:

[0043] (1) The method provided by the present invention can remove chloride ions with high removal efficiency, which can reach more than 99% or reduce the chloride ion content to less than 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 content of organic matter, suspended solids, and other salts in the wastewater. It can efficiently remove chloride ions from the wastewater and at the same time achieve the complete recovery of residual extractant and diluent in the wastewater, eliminating secondary pollution.

[0045] (3) The diluent selected in this invention can form a minimum azeotrope with water, so the diluent can be completely recovered by stripping, and the reused diluent can be used to recover residual TOA in the water without the need to introduce exogenous extractants. This invention has the advantages of being clean, environmentally friendly, and free from secondary pollution. Attached Figure Description

[0046] Figure 1 The system process flow diagram for chloride ion extraction and removal from industrial wastewater provided by the present invention;

[0047] Figure 2 The present invention provides a process flow diagram for the extraction and removal of chloride ions from industrial wastewater with added iron ions.

[0048] In the diagram, 1 is the first extraction tower; 2 is the extractant circulation tank; 3 is the chloride ion extract tank; 4 is the extractant regeneration tower; 5 is the second extraction tower; 6 is the diluent circulation tank; 7 is the diluent recovery tower; 8 is the diluent stripping tower; and 9 is the solid-liquid separator. Detailed Implementation

[0049] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0050] To further understand the present invention, it will be further described in conjunction with the accompanying drawings and embodiments.

[0051] Example 1

[0052] A coal-to-fertilizer plant has a coal gasification wastewater flow rate of 95 tons / hour and a chloride ion content of approximately 1600 mg / L. According to... Figure 1 The flowchart shown illustrates the steps for chlorine extraction and extractant recovery:

[0053] (1) TOA was used as the extractant and methyl isobutyl ketone was used as the diluent. TOA and methyl isobutyl ketone were mixed at a mass ratio of 1:8 and then used as the extraction solvent.

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

[0055] (2) After extraction and dechlorination, the wastewater is sent into the second extraction tower 5 and is subjected to countercurrent contact extraction with the diluent sent from the diluent circulation tank 6. The theoretical number of stages in the second extraction tower 5 is 3, the extraction temperature is about 60℃, and the mass ratio of diluent to wastewater is 1:4. The residual TOA in the wastewater is extracted and recovered into the diluent phase. After the wastewater comes out from the bottom of the tower, it enters the diluent stripping tower 8. After the diluent phase comes out from the top of the tower, it 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. The diluent is recycled by heating and stripping, taking advantage of the azeotropic properties of the diluent and water. The operating pressure of the diluent stripping tower 8 is atmospheric pressure, the theoretical number of plates is 5, and the temperature at the top of the tower is 92°C. The vapor phase obtained at the top of the tower is the azeotrope of the diluent and water. After condensation, it enters the diluent circulation tank 6. 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, and it has 6 theoretical plates. Distillation separation is performed by distillation. The top temperature of the diluent recovery tower 7 is 109°C. The pure diluent obtained from the top of the tower is returned to the diluent circulation tank 6. The bottom liquid obtained from the bottom of the tower has a TOA to diluent composition 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 via the chloride ion extract tank 3. It is regenerated by back-extraction with a dilute alkali solution of 10% concentration. The theoretical number of stages in the extractant regeneration tower 4 is 2, the extraction temperature is 60℃, and the mass ratio of alkali solution to chloride ion extract is 1:5. The regenerated chloride ion enrichment solution is sent out of the boundary area and used as a biochemical alkali supplement, membrane cleaner, or raw material for chlor-alkali production, depending on the situation. The regenerated extractant is returned to the extractant circulation tank 2 for recycling.

[0059] After treatment using the above method, the chloride ion content in the wastewater can be reduced to below 80 mg / L, eliminating the equipment corrosion problem in subsequent wastewater treatment devices. The TOA residue in the wastewater is below 20 mg / L, and the diluent can reduce it to undetectable levels.

[0060] Example 2

[0061] A coal-to-fertilizer plant has a coal gasification wastewater flow rate of 95 tons / hour and a chloride ion content of approximately 1600 mg / L. According to... Figure 1 The flowchart shown illustrates the extraction of chlorine and the recovery of the extractant. The extraction and recovery process is essentially the same as in Example 1, except for adjustments to parameters such as temperature and solvent ratio. The specific steps are as follows:

[0062] (1) TOA was used as the extractant and methyl isobutyl ketone was used as the diluent. TOA and methyl isobutyl ketone were mixed at a mass ratio of 1:10 and then used as the extraction solvent.

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

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

[0065] (3) The wastewater from the bottom of the second extraction tower 5 enters the diluent stripping tower 8. The diluent is recycled by heating stripping using the azeotropic properties of the diluent and water. The operating pressure of the diluent stripping tower 8 is atmospheric pressure, the theoretical number of plates is 10, and the temperature at the top of the tower is 95℃. The vapor phase obtained at the top of the tower is the azeotrope of the diluent and water. After condensation, it enters the diluent circulation tank 6. 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, with 10 theoretical plates, and distillation separation is performed. The top temperature of the diluent recovery tower 7 is 110°C. The pure diluent obtained from the top of the tower is returned to the diluent circulation tank 6. The bottom liquid obtained from the bottom of the tower has a TOA to diluent composition ratio similar to that of the extraction solvent feed of the first extraction tower 1 and 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 via the chloride ion extract tank 3. It is regenerated by back-extraction with a dilute alkali solution of 14%. The theoretical number of stages in the extractant regeneration tower 4 is 4, the extraction temperature is 30℃, and the mass ratio of alkali solution to chloride ion extract is 1:3. The regenerated chloride ion enrichment solution is sent out of the boundary area and used as a biochemical alkali supplement, membrane cleaner, or raw material for chlor-alkali production, depending on the situation. The regenerated extractant is returned to the extractant circulation tank 2 for recycling.

[0068] After treatment using the above method, the chloride ion content in the wastewater can be reduced to below 80 mg / L, eliminating the equipment corrosion problem in subsequent wastewater treatment devices. The TOA residue in the wastewater is below 20 mg / L, and the diluent can reduce it to undetectable levels.

[0069] Example 3

[0070] A coal-to-fertilizer plant has a coal gasification wastewater flow rate of 95 tons / hour and a chloride ion content of approximately 1600 mg / L. According to... Figure 1 The flowchart shown illustrates the extraction of chlorine and the recovery of the extractant. The extraction and recovery process is essentially the same as in Example 1, except for adjustments to parameters such as temperature and solvent ratio. The specific steps are as follows:

[0071] (1) TOA was used as the extractant and methyl isobutyl ketone was used as the diluent. TOA and methyl isobutyl ketone were mixed at a mass ratio of 1:2 and then used as the extraction solvent.

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

[0073] (2) After extraction and dechlorination, the wastewater is sent into the second extraction tower 5 and is extracted in a countercurrent manner with the diluent sent from the diluent circulation tank 6. The theoretical number of stages in the second extraction tower 5 is 6, the extraction temperature is about 50℃, and the mass ratio of diluent to wastewater is 1:1. The residual TOA in the wastewater is extracted and recovered into the diluent phase. After the wastewater comes out from the bottom of the tower, it enters the diluent stripping tower 8. After the diluent phase comes out from the top of the tower, it enters the diluent circulation tank 6.

[0074] (3) The wastewater from the bottom of the second extraction tower 5 enters the diluent stripping tower 8. The diluent is recycled by heating stripping using the azeotropic properties of the diluent and water. The operating pressure of the diluent stripping tower 8 is atmospheric pressure, the theoretical number of plates is 15, and the temperature at the top of the tower is 98°C. The vapor phase obtained at the top of the tower is the azeotrope of the diluent and water. After condensation, it enters the diluent circulation tank 6. 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, and it has 16 theoretical plates. Distillation separation is performed by distillation. The top temperature of the diluent recovery tower 7 is 112°C. The pure diluent obtained from the top of the tower is returned to the diluent circulation tank 6. The bottom liquid obtained from the bottom of the tower has a TOA to diluent composition 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 via the chloride ion extract tank 3. It is regenerated by back-extraction with a dilute alkali solution of 20% concentration. The theoretical number of stages in the extractant regeneration tower 4 is 6, the extraction temperature is 40℃, and the mass ratio of alkali solution to chloride ion extract is 1:2. The regenerated chloride ion enrichment solution is sent out of the boundary area and used as a biochemical alkali supplement, membrane cleaner, or raw material for chlor-alkali production, depending on the situation. The regenerated extractant is returned to the extractant circulation tank 2 for recycling.

[0077] After treatment using the above method, the chloride ion content in the wastewater can be reduced to below 80 mg / L, eliminating the equipment corrosion problem in subsequent wastewater treatment devices. The TOA residue in the wastewater is below 20 mg / L, and the diluent can reduce it to undetectable levels.

[0078] Example 4

[0079] A steel plant has a coking wastewater flow rate of 80 tons / hour and a chloride ion content of approximately 2800 mg / L (about 79 mmol / L). Chlorine extraction and extractant recovery were performed on the wastewater, following the same extraction and recovery process as in Example 1.

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

[0081] The extraction and recovery process of this 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 plant's own pickling wastewater (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 enriched liquid obtained after extraction in 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 invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, alterations, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for removing chloride ions from industrial wastewater by extraction, characterized in that, Includes the following steps: (1) Extraction and dechlorination: Chlorine-containing wastewater is fed into the first extraction tower and extracted by contacting the extraction solvent to obtain chloride ion extract and raffinate wastewater; (2) Extractant recovery: The raffinate wastewater enters the second extraction tower and is extracted by contacting the diluent. The extractant remaining in the raffinate wastewater is recovered into the diluent phase, and the recovered wastewater and diluent phase are obtained. (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, while the treated wastewater is obtained from 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 bottom liquid; (5) Extractant regeneration: The chloride ion extract obtained in step (1) is sent to the extractant regeneration tower and regenerated by alkaline back-extraction to obtain the extractant and chloride ion enrichment solution. The extractant is trioctylamine, the diluent is methyl isobutyl ketone, and the extraction solvent is obtained by mixing the extractant and the diluent in a mass ratio of 1:10 to 1:

2.

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. The molar ratio of iron ions to chloride ions is controlled at 1:5 to 1:

2. If iron ions were added before extraction or if the chlorine-containing wastewater contains iron ions, the chloride ion-enriched solution obtained after extraction is sent to a solid-liquid separator to separate the iron-containing precipitate. The iron-containing precipitate is then added back to the chlorine-containing wastewater before extraction for recycling.

3. The method according to claim 1, characterized in that, The mass ratio of the extraction solvent to the chlorine-containing wastewater in step (1) is 1:6 to 1:

2.

4. The method according to claim 1, characterized in that, In step (1), the chlorine-containing wastewater and the extraction solvent pumped from the extractant circulation tank are extracted in the first extraction tower. Chloride ion extract is obtained from the top of the first extraction tower and sent to the extractant regeneration tower. Raffinate wastewater is obtained from the bottom and sent to the second extraction tower. The theoretical number of stages in the first extraction tower is 1-6, and the extraction temperature is 20-65℃.

5. The method according to claim 1, characterized in that, In step (2), the raffinate wastewater after extraction and dechlorination is subjected to countercurrent contact extraction with the diluent from the diluent circulation tank in the second extraction tower. The residual extractant in the raffinate 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 in the second extraction tower is 1-6, the extraction temperature is 20-65℃, and the mass ratio of the diluent to the raffinate wastewater is 1:4 to 1:

1.

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

7. The method according to claim 1, characterized in that, In step (4), the condensed diluent and water azeotrope is pumped to the diluent recovery tower for distillation separation. The pure diluent obtained at the top of the tower is sent to the diluent circulation tank, and the bottom liquid obtained from the bottom of the tower, which has a composition ratio of extractant and diluent similar to that of the extraction solvent, is sent to the extractant circulation tank. The operating pressure of the diluent recovery tower is atmospheric pressure, the theoretical number of plates is 5-16, and the temperature at the top of the tower is 109-112℃.

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

2.

9. A system for chloride ion extraction and removal from industrial wastewater, characterized in that, include: The first extraction tower is used to extract chloride ions from chlorine-containing wastewater; The extractant circulation tank is used to store the extractant trioctylamine and pump the trioctylamine to the first extraction tower; A chloride ion extract tank is used to store the chloride ion extract obtained from the first extraction tower and to pump it to the extractant regeneration tower. The extractant regeneration tower is used for back-extraction and regeneration of trioctylamine, and the regenerated trioctylamine is sent to the extractant circulation tank for recycling. The regenerated chloride ion enrichment solution is sent out of the boundary area. The second extraction tower is used to receive the raffinate wastewater after dechlorination in the first extraction tower, and to extract and recover the residual trioctylamine in the raffinate wastewater using the diluent methyl isobutyl ketone. After condensation, the wastewater is sent to the diluent circulation tank, and the recovered wastewater is sent to the diluent stripping tower. A diluent circulation tank is used to store methyl isobutyl ketone and to send methyl isobutyl ketone into the second extraction tower; The diluent recovery tower is used to receive methyl isobutyl ketone containing a low concentration of trioctylamine from the diluent circulation tank and to perform distillation separation. The obtained pure methyl isobutyl ketone is sent back to the diluent circulation tank, and the bottom liquid containing methyl isobutyl ketone and trioctylamine is sent to the extractant circulation tank. The diluent stripping tower is used to strip and recover methyl isobutyl ketone from the wastewater coming out of the second extraction tower, and the resulting methyl isobutyl ketone and water azeotrope is sent to the diluent circulation tank.

10. The system according to claim 9, characterized in that, The system also includes a solid-liquid separator, which is used to separate the iron-containing precipitate from the chloride ion enrichment solution obtained after regeneration. The iron-containing precipitate is then added back to the wastewater before extraction for recycling.

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