Treatment system for wastewater containing inorganic salt

Abstract

The utility model discloses a treatment system for wastewater containing inorganic salt. The treatment system comprises a sodium chloride evaporative crystallization unit for obtaining sodium chloride crystals B and evaporative crystallization mother liquor; the salting-out unit is connected with the sodium chloride evaporative crystallization unit to obtain sodium chloride crystals D and salting-out separation mother liquor, and the salting-out separation mother liquor is discharged to the potassium nitrate freezing crystallization unit; the potassium nitrate freezing crystallization unit is connected with the salting-out unit to obtain potassium nitrate crystals E and potassium nitrate freezing crystallization mother liquor; and the nanofiltration unit is connected with the potassium nitrate freezing and crystallizing unit and is used for carrying out nanofiltration treatment on effluent of the potassium nitrate freezing and crystallizing unit and discharging nanofiltration permeate to the sodium chloride evaporation and crystallization unit at the same time.

Description

Technical Field

[0001] The utility model belongs to the field of wastewater treatment, and in particular relates to a treatment system for wastewater containing inorganic salts. Background Art

[0002] In the wastewater zero discharge or waste salt comprehensive utilization projects, high-salt wastewater will eventually be formed. It is necessary to use evaporation and crystallization to crystallize the inorganic salts in the wastewater to obtain products such as sodium chloride and sodium sulfate, and discharge part of the evaporation and crystallization mother liquor or further evaporate and crystallize the mother liquor to obtain part of the mixed salt. + In addition, it also contains some K + Ions, usually Na + The content is greater than K + , and the anions in the wastewater except Cl - In addition, it also contains SO4 2- and NO3 - ions, these K + 、NO3 - 、SO4 2- Ions cause the final mixed salt amount to reach more than 10%. Not only can it not become a product, but it also requires additional high-cost processing, which seriously affects the application and promotion of zero wastewater discharge and the economic benefits of comprehensive utilization of waste salt projects. An economical and efficient treatment technology is urgently needed. Utility Model Content

[0003] In view of the above-mentioned defects and needs in the treatment of inorganic salt-containing wastewater, the utility model provides a treatment system for inorganic salt-containing wastewater, which is used to treat Cl - 、SO4 2- 、NO3 - 、Na + and K + The salt-containing wastewater is subjected to salt recovery to prepare high-purity sodium chloride and potassium nitrate, which specifically includes the following processing units:

[0004] A sodium chloride evaporation and crystallization unit is used to perform evaporation and crystallization treatment on the inorganic salt-containing wastewater to obtain sodium chloride crystals B and evaporation and crystallization mother liquor;

[0005] A salting-out unit is connected to the sodium chloride evaporation and crystallization unit, and is used to process the evaporation and crystallization mother liquor of the sodium chloride evaporation and crystallization unit, add potassium chloride to the evaporation and crystallization mother liquor, obtain sodium chloride crystals D and salting-out separation mother liquor, and discharge the salting-out separation mother liquor to the potassium nitrate freezing and crystallization unit;

[0006] The potassium nitrate freezing crystallization unit is connected to the salting-out unit, and is used to add dilution water to the salting-out separation mother liquor of the salting-out unit, and perform freezing crystallization treatment to obtain potassium nitrate crystals E and potassium nitrate freezing crystallization mother liquor.

[0007] The nanofiltration unit is connected to the potassium nitrate freezing crystallization unit and is used for nanofiltration treatment of the effluent of the potassium nitrate freezing crystallization unit and discharge the nanofiltration permeate to the sodium chloride evaporation crystallization unit.

[0008] According to a specific embodiment of the utility model, the sodium chloride evaporation and crystallization unit is provided with an evaporation crystallizer for performing evaporation and crystallization treatment on the inorganic salt-containing wastewater.

[0009] According to a specific embodiment of the utility model, the sodium chloride evaporation crystallization unit is provided with a centrifugal separation device for separating sodium chloride crystals from the solution to obtain solid sodium chloride crystals B and the evaporation crystallization mother liquor.

[0010] According to a specific embodiment of the utility model, the salting-out unit is provided with a salting-out crystallizer for performing salting-out treatment on the evaporation crystallization mother liquor.

[0011] According to a specific embodiment of the utility model, the salting-out unit is provided with a crystal separation device for separating sodium chloride crystals from the solution to obtain the sodium chloride crystals D and the salting-out separation mother liquor.

[0012] According to a specific embodiment of the utility model, the potassium nitrate freezing crystallization unit is provided with a freezing crystallizer for performing freezing crystallization treatment on the salting-out separation mother liquor.

[0013] According to a specific embodiment of the utility model, the potassium nitrate freezing crystallization unit is provided with a centrifugal separation device for separating potassium nitrate crystals from the solution to obtain potassium nitrate crystals E and potassium nitrate freezing crystallization mother liquor.

[0014] According to a specific embodiment of the utility model, in the potassium nitrate freezing crystallization unit, the added amount of the dilution water accounts for 5% to 400% by volume of the water output of the salting-out unit, preferably 5% to 100%, and more preferably 5% to 20%.

[0015] According to a specific embodiment of the utility model, the freezing crystallization temperature of the potassium nitrate freezing crystallization unit is -5 to 30°C, preferably 0 to 10°C.

[0016] According to a specific embodiment of the utility model, the treatment system also includes a medium filtration unit, which is connected to the potassium nitrate freezing crystallization unit and the nanofiltration unit, and is used for performing medium filtration treatment on the effluent potassium nitrate freezing crystallization mother liquor of the potassium nitrate freezing crystallization unit, removing suspended matter in the effluent of the potassium nitrate freezing crystallization unit, and conveying the effluent of the medium filtration unit to the nanofiltration unit.

[0017] According to a specific embodiment of the utility model, the treatment system also includes a silicon removal unit, which is connected to the potassium nitrate freezing crystallization unit and the medium filtration unit, and is used to treat the effluent potassium nitrate freezing crystallization mother liquor of the potassium nitrate freezing crystallization unit, by adding a silicon removal chemical agent to cause silicon to chemically react and form a precipitate to remove the silicon therein, and the effluent after silicon removal is transported to the medium filtration unit.

[0018] According to a specific embodiment of the utility model, the desiliconization unit is provided with a chemical desiliconization reaction precipitation device for treating the potassium nitrate frozen crystallization mother liquor to obtain a supernatant and precipitated sludge, and the supernatant is transported to the medium filtration unit.

[0019] According to a specific embodiment of the utility model, the desiliconization unit is provided with a precipitated sludge dewatering device for filtering and separating the precipitated sludge. The dewatered sludge after separation is transported out, and the sludge dewatered filtrate is returned to the inlet of the chemical desiliconization reaction precipitation device for further processing.

[0020] According to a specific embodiment of the utility model, the water inlet of the nanofiltration unit not only comes from the medium filtration unit, but also receives a part of the water inlet of the sodium chloride evaporation crystallization unit, that is, the inorganic salt-containing wastewater to be treated, so as to reduce the Cl in the nanofiltration retentate. - 、NO3 - 、Na + and K + The content.

[0021] According to a specific embodiment of the utility model, the flow rate of the inorganic salt-containing wastewater to be treated received by the nanofiltration unit is 0.5 to 10 times the effluent flow rate of the medium filtration unit.

[0022] Beneficial effects:

[0023] The utility model provides a method for treating Cl - 、SO4 2- 、NO3 - 、Na + and K +The salt-containing wastewater treatment system is equipped with a sodium chloride evaporation crystallization unit, a salting-out unit, a potassium nitrate freezing crystallization unit and a nanofiltration unit in sequence. By designing the type and sequence of each treatment unit, high-purity and high-yield products of sodium chloride and potassium nitrate are prepared.

[0024] The system and method provided by the utility model can recover the salt in the wastewater containing inorganic salts in the form of sodium chloride and potassium nitrate products, remove impurities such as silicon and prevent their accumulation, and recover SO4 2- After ion concentration, it is discharged for separate treatment and recovery, while the discharge of other inorganic salts is reduced as much as possible, thereby improving the salt recovery efficiency, saving energy consumption, and realizing the resource treatment of wastewater containing inorganic salts. There is no secondary pollution of waste salt, which has significant environmental and economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a schematic diagram of the inorganic salt-containing wastewater treatment system provided by the utility model.

[0026] The reference numerals are described as follows:

[0027] 1. Sodium chloride evaporation crystallization unit; 2. Evaporation crystallization mother liquor; 3. Salting-out unit; 4. Potassium nitrate freezing crystallization unit; 5. Potassium nitrate freezing crystallization mother liquor; 6. Silicon removal unit; 7. Settled sludge; 8. Supernatant; 9. Settled sludge dehydration device; 10. Sludge dehydration filtrate; 11. Medium filtration unit; 12. Nanofiltration unit; 13. Nanofiltration rinse liquid; 14. Nanofiltration permeate; 15. Nanofiltration retentate;

[0028] A. Wastewater containing inorganic salts; B. Sodium chloride crystals B; C. Potassium chloride; D. Sodium chloride crystals D; E. Potassium nitrate crystals E; F. Dilution water; G. Chemical agents; H. Dewatered sludge. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical scheme and advantages of the utility model clearer, the example embodiments will now be described more fully with reference to the accompanying drawings. However, the example embodiments can be implemented in various forms and should not be understood as being limited to the embodiments set forth herein; on the contrary, these embodiments are provided so that the utility model will be comprehensive and complete and the concept of the example embodiments will be fully conveyed to those skilled in the art. The same reference numerals in the figures represent the same or similar structures, and thus their detailed description will be omitted.

[0030] The first aspect of the utility model provides a treatment system for inorganic salt-containing wastewater, which is used for treating wastewater containing Cl - 、SO4 2- 、NO3 - 、Na + and K +The salt-containing wastewater is subjected to salt recovery to prepare high-purity sodium chloride and potassium nitrate, which specifically includes the following processing units:

[0031] Sodium chloride evaporation and crystallization unit 1 is used to perform evaporation and crystallization treatment on the inorganic salt-containing wastewater to obtain sodium chloride crystals B and evaporation and crystallization mother liquor;

[0032] The salting-out unit 3 is connected to the sodium chloride evaporation crystallization unit 1, and is used to process the evaporation crystallization mother liquor of the sodium chloride evaporation crystallization unit, add potassium chloride to the evaporation crystallization mother liquor, obtain sodium chloride crystals D and salting-out separation mother liquor, and discharge the salting-out separation mother liquor to the potassium nitrate freezing crystallization unit;

[0033] A potassium nitrate freezing crystallization unit 4 is connected to the salting-out unit 3, and is used to add dilution water to the salting-out separation mother liquor of the salting-out unit 3, and perform freezing crystallization treatment to obtain potassium nitrate crystals E and potassium nitrate freezing crystallization mother liquor;

[0034] The nanofiltration unit 12 is connected to the potassium nitrate freezing crystallization unit 4, and is used to perform nanofiltration treatment on the effluent of the potassium nitrate freezing crystallization unit, and at the same time discharge the nanofiltration permeate to the sodium chloride evaporation crystallization unit.

[0035] The utility model is provided with a salting-out unit between a sodium chloride evaporation crystallization unit and a potassium nitrate freezing crystallization unit. By adding potassium chloride into the evaporation crystallization mother liquor, more sodium ions can be precipitated in the form of NaCl, thereby improving the purity and yield of NaCl; in addition, nitrate can also be precipitated in the form of KNO3 during freezing crystallization, thereby reducing the content of NaNO3 and improving the purity and yield of the product KNO3.

[0036] The utility model can prevent the crystallization of other salts except potassium nitrate in the subsequent freezing crystallization process by adding dilution water to the salting-out separation mother liquor of the salting-out unit, which is helpful to improve the purity and yield of the product KNO3.

[0037] In an optional embodiment, the sodium chloride evaporation and crystallization unit is provided with an evaporation crystallizer for performing evaporation and crystallization treatment on the inorganic salt-containing wastewater.

[0038] The utility model has no special limitation on the sodium chloride evaporation crystallizer, for example, the multi-effect evaporation or MVR evaporation crystallization known in the art can be adopted.

[0039] In an optional embodiment, the sodium chloride evaporation and crystallization unit is provided with a centrifugal separation device for separating sodium chloride crystals from the solution to obtain solid sodium chloride crystals B and the evaporation and crystallization mother liquor.

[0040] The utility model has no special limitation on the centrifugal separation equipment. For example, a horizontal screw centrifuge or a pusher centrifuge and auxiliary equipment commonly used in the art can be selected, as long as the separation of sodium chloride crystals and solution can be achieved.

[0041] In an optional embodiment, in the salting-out unit, the amount of potassium chloride added is based on the amount of potassium chloride in the evaporation crystallization mother liquor. + With NO3 - An appropriate amount is added to achieve an equal molar concentration.

[0042] In an optional embodiment, the salting-out unit is provided with a salting-out crystallizer for performing salting-out treatment on the evaporation crystallization mother liquor.

[0043] The present invention has no special limitation on the salting-out crystallizer, and any salting-out crystallizer known in the art can be used.

[0044] In an optional embodiment, the salting-out unit is provided with a crystal separation device for separating sodium chloride crystals from the solution to obtain the sodium chloride crystals D and the salting-out separation mother liquor.

[0045] The utility model has no special limitation on the crystal separation equipment. For example, a horizontal screw centrifuge or a pusher centrifuge and auxiliary equipment commonly used in the art can be selected, as long as the separation of sodium chloride crystals and solution can be achieved.

[0046] In an optional embodiment, the potassium nitrate freeze crystallization unit is provided with a freeze crystallizer for performing freeze crystallization treatment on the salting-out separation mother liquor.

[0047] The present invention has no special limitation on the freezing crystallizer, and the common OSLO crystallizer or DTB crystallizer in the art can be used.

[0048] In an optional embodiment, the potassium nitrate freeze crystallization unit is provided with a centrifugal separation device for separating potassium nitrate crystals from the solution to obtain potassium nitrate crystals E and potassium nitrate freeze crystallization mother liquor.

[0049] The utility model has no special limitation on the centrifugal separation device. For example, a horizontal screw centrifuge or a pusher centrifuge and auxiliary equipment commonly used in the art can be selected, as long as the potassium nitrate crystals and the solution can be separated.

[0050] In an optional embodiment, in the potassium nitrate freezing crystallization unit, the added amount of the dilution water accounts for 5% to 400% by volume of the water output of the salting-out unit, preferably 5% to 100%, and more preferably 5% to 20%.

[0051] The utility model has no special limitation on the dilution water, as long as it contains a lower concentration of sodium chloride than the separated mother liquor of the salting-out crystallization unit and does not bring in additional other impurities. For example, the inlet water A of the evaporation crystallization unit can be used, or desalted water can be used.

[0052] In an optional embodiment, the freezing crystallization temperature of the potassium nitrate freezing crystallization unit is -5 to 60°C, preferably 0 to 20°C, and more preferably 0 to 10°C.

[0053] In an optional embodiment, the treatment system also includes a media filtration unit, which is connected to the potassium nitrate freezing crystallization unit and the nanofiltration unit, and is used to perform media filtration treatment on the effluent potassium nitrate freezing crystallization mother liquor of the potassium nitrate freezing crystallization unit, remove suspended matter in the effluent of the potassium nitrate freezing crystallization unit, and convey the effluent of the media filtration unit to the nanofiltration unit.

[0054] In an optional embodiment, the treatment system also includes a silicon removal unit, which is connected to the potassium nitrate freezing crystallization unit and the medium filtration unit, and is used to treat the effluent potassium nitrate freezing crystallization mother liquor of the potassium nitrate freezing crystallization unit, by adding a silicon removal chemical agent to cause silicon to chemically react and form a precipitate to remove silicon therein, and the effluent after silicon removal is transported to the medium filtration unit.

[0055] The utility model has no special limitation on the silicon removal unit, and can adopt the equipment and reagents commonly used in the field for removing impurities such as silicon and hardness, for example, sodium aluminate, PAC and PAM, or silicon removal magnesium agent can be used for chemical silicon removal, and lime or soda ash, flocculant and other reagents can be used for clarification and softening, as long as these equipment can achieve the same treatment effect.

[0056] In an optional embodiment, the desiliconization unit is provided with a chemical desiliconization reaction precipitation device for treating the potassium nitrate frozen crystallization mother liquor to obtain a supernatant and precipitated sludge, and the supernatant is conveyed to the media filtration unit.

[0057] In an optional embodiment, the desiliconization unit is provided with a precipitated sludge dewatering device for filtering and separating the precipitated sludge. The dewatered sludge after separation is transported outward, and the sludge dewatered filtrate is returned to the inlet of the chemical desiliconization reaction precipitation device for further treatment.

[0058] The utility model has no special limitation on the sludge dewatering equipment, and common filter press or centrifugal separation equipment in the art can be used.

[0059] In an optional embodiment, the influent of the nanofiltration unit, in addition to coming from the media filtration unit, also receives a portion of the influent of the sodium chloride evaporation crystallization unit, i.e., the inorganic salt-containing wastewater to be treated, so as to reduce the Cl in the nanofiltration retentate. - 、NO3 - 、Na + and K + The content.

[0060] In an optional embodiment, the flow rate of the inorganic salt-containing wastewater to be treated received by the nanofiltration unit is 0.5 to 10 times the effluent flow rate of the medium filtration unit.

[0061] The following combination Figure 1 The processing system of the utility model is explained in detail.

[0062] The inorganic salt-containing wastewater A to be treated enters the sodium chloride evaporation crystallization unit 1. The sodium chloride evaporation crystallization unit 1 is used to perform evaporation crystallization treatment on the inorganic salt-containing wastewater, recover sodium chloride crystals, and discharge evaporation crystallization mother liquor at the same time. The sodium chloride evaporation crystallization unit 1 is provided with an evaporation crystallizer and a centrifugal separation device. Steam heating is used in the evaporation crystallizer to evaporate the water in the inorganic salt-containing wastewater. As the evaporation continues, the concentration of sodium chloride in the solution continues to increase until it reaches an oversaturated state and precipitates in the form of crystals. Then, the sodium chloride crystals are separated from the solution by a centrifugal separation device to obtain a solid sodium chloride product B and an evaporation crystallization mother liquor. The obtained sodium chloride has a high purity (dry basis purity can reach more than 99%) and can meet industrial grade standards. The evaporated gas is condensed into evaporation condensate for recycling.

[0063] As evaporation proceeds, in addition to maintaining saturation with sodium chloride, SO4 2- 、NO3 - and K + The concentration of sodium chloride is increasing. In addition, silicon in the wastewater is gradually enriched. In order to prevent these ions from crystallizing out as sodium sulfate, sodium nitrate or potassium nitrate, or the concentration is high enough to affect the product quality of sodium chloride, it is necessary to discharge part of the evaporation and crystallization mother liquor of the sodium chloride evaporation and crystallization unit. The sodium chloride evaporation and crystallization mother liquor 2 is sent to the salting-out unit 3.

[0064] The sodium chloride evaporation crystallization mother liquor 2 enters the salting-out unit 3. The salting-out unit 3 is connected to the sodium chloride evaporation crystallization unit 1. The salting-out unit 3 is provided with a salting-out crystallizer and a crystal separation device for salting out the sodium chloride centrifugal separation mother liquor 2. First, potassium chloride crystals C are added to the evaporation crystallization mother liquor 2. Since the sodium chloride in the evaporation crystallization mother liquor is saturated, while KCl is unsaturated, as Cl -The sodium chloride dissolved in the solution continues to precipitate in the form of crystals, while the added potassium chloride is dissolved, and then the sodium chloride crystals are separated from the solution by a crystal separation device to obtain sodium chloride crystals D and a salting-out separation mother liquor, and the salting-out separation mother liquor is discharged to the potassium nitrate freezing crystallization unit 4;

[0065] The salting-out separation mother liquor enters the potassium nitrate freezing crystallization unit 4, and the potassium nitrate freezing crystallization unit 4 is connected to the salting-out unit 3, and is used to add dilution water containing low sodium chloride to dilute the salting-out separation mother liquor discharged from the salting-out unit 3, and perform freezing crystallization treatment, recover potassium nitrate crystals, and discharge the potassium nitrate freezing crystallization mother liquor. When the salting-out separation mother liquor enters the potassium nitrate freezing crystallization unit 4, dilution water F is added to the salting-out separation mother liquor to dilute it, so as to prevent other salts other than potassium nitrate from crystallizing in the subsequent freezing crystallization process. The addition amount of dilution water F can be 5-400% of the volume of the salting-out separation mother liquor, preferably 5-100%, and more preferably 5-20%. The potassium nitrate freezing crystallization unit 4 includes a freezing crystallizer and a centrifugal separation device, and the salting-out centrifugal separation mother liquor is frozen and cooled by an external cooling medium. As the temperature decreases, the potassium nitrate dissolved in the water reaches a supersaturated state and precipitates in the form of crystals and is separated from the solution. Other ions in the solution still exist in the form of solution and will not precipitate. After centrifugation, potassium nitrate crystals E and potassium nitrate freezing crystallization mother liquor 5 are obtained. The freezing temperature is -5 to 60°C, preferably 0 to 20°C, and more preferably 0 to 10°C, the purpose of which is to crystallize potassium nitrate from the solution as much as possible with lower energy consumption and without precipitation of other impurities. The potassium nitrate freezing crystallization mother liquor 5 of the potassium nitrate freezing crystallization unit is transported to the silicon removal unit 6 for further treatment.

[0066] The potassium nitrate frozen crystallization mother liquor 5 enters the silicon removal unit 6, which is connected to the potassium nitrate frozen crystallization unit 4 and is used to perform chemical silicon removal on the potassium nitrate frozen crystallization mother liquor 5. The silicon removal unit 6 includes a chemical silicon removal reaction precipitation device and a sedimentation sludge dehydration device, and removes silicon and other impurities therein by adding chemical agent G, so that the SiO2 in the wastewater is less than 20 mg / L; chemical agents for removing hardness can also be added at the same time to remove impurities such as calcium, magnesium, hardness, and some organic matter, suspended matter and colloids. Thereby, the hardness in the wastewater is less than 150 mg / L (in terms of CaCO3), and the SDI is less than 3, so that the concentration of these impurities will not affect the operation of subsequent nanofiltration treatment, frozen crystallization, evaporation crystallization and other units and the quality of the product.

[0067] The supernatant 8 of the desiliconization reaction precipitation device is transported to the medium filtration unit 11 for further treatment, and the formed precipitated sludge 7 is filtered and separated by the sludge dewatering device 9. The separated dewatered sludge H is transported out, and the sludge dewatered filtrate 10 can be returned to the inlet of the desiliconization reaction precipitation device for further treatment.

[0068] The medium filtration unit 11 is connected to the silicon removal unit 6 to perform medium filtration treatment on the effluent of the silicon removal unit 6, remove suspended matter in the effluent of the silicon removal unit 6, and transport the effluent of the medium filtration unit 11 to the nanofiltration unit 12. The medium filtration unit 11 is provided with a medium filter, and filtering is performed in the presence of one or more filter media to further reduce the suspended matter content in the wastewater to below 5 mg / L and the turbidity to below 5 NTU.

[0069] The utility model has no special limitation on the form of the media filter, and can adopt the multi-media filter commonly used in the art. The multi-media filter can be vertical, single-layer horizontal or double-layer horizontal, and can also be a filter tank.

[0070] The utility model does not specifically limit the type of filter medium, and one or more filter media commonly used in the art can be used, such as quartz sand, anthracite, etc. In a preferred embodiment, dual-medium filtration is used, and the filter medium can be quartz sand and anthracite. More preferably, the particle size of the filter medium can be: quartz sand 0.4-0.6mm, anthracite 0.8-1.2mm, and the filter layer thickness can preferably be: quartz sand 800mm, anthracite 400mm, and can also be appropriately adjusted according to the water quality.

[0071] The effluent of the medium filtration unit 11 enters the nanofiltration unit 12, which is connected to the medium filtration unit 11 to perform nanofiltration treatment on the effluent of the medium filtration unit 11 and discharge the nanofiltration permeate to the sodium chloride evaporation and crystallization unit 1; the nanofiltration unit 12 is provided with a nanofiltration membrane assembly, and most monovalent ions such as Cl - 、NO3 - 、Na + , K + and water can pass through the nanofiltration membrane, while most organic matter and SO4 2- Therefore, the nanofiltration membrane module divides the effluent from the medium filtration unit into two streams, namely, organic matter-rich and SO4 2- The nanofiltration retentate 15 and the Cl-rich - 、NO3 - The nanofiltration permeate 14 is produced. The nanofiltration retentate 15 is sent out to recover sulfate alone, remove other impurities that have been enriched, and then continue to be used. The nanofiltration permeate 14 enters the sodium chloride evaporation crystallization unit 1.

[0072] Since nanofiltration membrane can - 、NO3 - The retention rate is very low, and the Cl - and NO3 - The concentration changes are small, while the Cl - 、NO3- 、Na + and K + The concentration is very high, so in order to reduce the removal of SO4 2- The efflux of other salts reduces the Cl content in the nanofiltration retentate - 、NO3 - 、Na + and K + A portion of the inorganic salt-containing wastewater A to be treated (i.e., the nanofiltration rinse liquid 13) is diverted into the nanofiltration unit 12, and filtered through the nanofiltration membrane together with the effluent of the medium filtration unit 11, and the filtered permeate enters the sodium chloride evaporation crystallization device 1;

[0073] The utility model has no special limitation on the nanofiltration membrane assembly, and the nanofiltration membrane assembly commonly used in the art can be used. In a preferred embodiment, the nanofiltration membrane assembly can be selected to filter organic matter and SO4 2- In a preferred embodiment, the water inlet temperature of the nanofiltration membrane can be 5-40°C, preferably 20-25°C, so that SO4 in the medium filtration unit 11 can be removed. 2- The concentration is concentrated to an ideal value as much as possible without saturation, so as to reduce the amount of wastewater (i.e., nanofiltration retentate) that needs to be discharged and save energy. The nanofiltration membrane assembly can be one-stage or multi-stage. In a preferred embodiment, one-stage nanofiltration is used.

[0074] The utility model also provides a method for treating wastewater containing inorganic salts, which is used to treat wastewater containing Cl - 、SO4 2- 、NO3 - 、Na + and K + The salt-containing wastewater is subjected to salt recovery to prepare high-purity sodium chloride and potassium nitrate, which specifically comprises the following steps:

[0075] Sodium chloride evaporation and crystallization step, subjecting the inorganic salt-containing wastewater to evaporation and crystallization treatment to obtain sodium chloride crystals B and evaporation and crystallization mother liquor;

[0076] A salting-out step, treating the evaporation crystallization mother liquor of the sodium chloride evaporation crystallization step, adding potassium chloride to the evaporation crystallization mother liquor to obtain sodium chloride crystals D and a salting-out separation mother liquor, and simultaneously discharging the salting-out separation mother liquor to the potassium nitrate freezing crystallization step;

[0077] A potassium nitrate freeze crystallization step, wherein dilution water containing sodium chloride is added to the effluent salting-out separation mother liquor of the salting-out step to dilute the mother liquor, and a freeze crystallization treatment is performed to recover potassium nitrate crystals;

[0078] The nanofiltration step is to perform nanofiltration on the effluent from the potassium nitrate freezing crystallization step, and at the same time, discharge the nanofiltration permeate to the sodium chloride evaporation crystallization step.

[0079] In an optional embodiment, in the potassium nitrate freeze crystallization step, the amount of dilution water added is 5wt% to 20wt% of the water output of the salting-out step.

[0080] In an optional embodiment, the freezing crystallization temperature of the potassium nitrate freezing crystallization step is -5 to 60°C, preferably 0 to 20°C, and more preferably 0 to 10°C.

[0081] In an optional embodiment, the dilution water can be pure water or an aqueous solution containing low concentration of sodium chloride; when the dilution water is an aqueous solution containing low concentration of sodium chloride, the concentration of sodium chloride is lower than the concentration of sodium chloride in the salting-out separation mother liquor. By adding dilution water to the effluent of the salting-out unit, other salts except potassium nitrate are prevented from crystallizing in the subsequent freezing crystallization process.

[0082] In an optional embodiment, the treatment method further includes a medium filtration step, wherein the effluent potassium nitrate frozen crystallization mother liquor of the potassium nitrate frozen crystallization step is subjected to medium filtration treatment to remove suspended matter in the potassium nitrate frozen crystallization mother liquor, and the effluent of the medium filtration step is conveyed to the nanofiltration step.

[0083] In an optional embodiment, the treatment method further includes a desiliconization step, in which the effluent potassium nitrate freeze crystallization mother liquor from the potassium nitrate freeze crystallization step is treated by adding a desiliconizing chemical agent to cause silicon to chemically react and form a precipitate to remove silicon therein, and the effluent after desiliconization is conveyed to the medium filtration step.

[0084] In an optional embodiment, the desiliconization unit includes a chemical desiliconization reaction precipitation device, the chemical reaction is carried out in the chemical desiliconization reaction precipitation device, and the precipitated sludge generated by the chemical reaction is dehydrated and the filtrate is returned to the inlet end of the chemical desiliconization reaction precipitation device.

[0085] In an optional embodiment, the influent of the nanofiltration step not only comes from the medium filtration step, but also receives a portion of the influent of the sodium chloride evaporation and crystallization step, that is, the inorganic salt-containing wastewater to be treated, so as to reduce the Cl in the nanofiltration retentate. - 、NO3 - 、Na + and K + The content.

[0086] In an optional embodiment, the flow rate of the inorganic salt-containing wastewater to be treated received by the nanofiltration step is 0.5 to 10 times the effluent flow rate of the medium filtration unit.

[0087] The inorganic salt wastewater treatment system and treatment method of the utility model can be applied to inorganic salt wastewater generated by various industries such as petrochemical, coal chemical, fine chemical, power plants, etc., which usually contain a large amount of Cl - 、SO4 2- 、NO3 - 、Na + and K + The wastewater is very suitable for using the treatment system and treatment method of the utility model.

[0088] Below, the utility model is further described in detail through embodiments.

[0089] Example 1

[0090] Follow the steps below to treat wastewater containing inorganic salts.

[0091] a. Wastewater containing inorganic salts to be treated, flow rate 21.03t / h, including Na + Concentration 37665mg / l, K + Concentration 440mg / l, Cl - Concentration 54939mg / l, SO4 2- Concentration 64.7mg / l, NO3 - Concentration: 6251mg / l, SiO2 concentration: 43mg / l.

[0092] b. 5.38t / h of inorganic salt-containing wastewater is diverted to the inlet of the rear-end nanofiltration device, and the remaining part directly enters the sodium chloride evaporation crystallization device, and is mixed with the permeate of the nanofiltration device and treated by triple-effect reduced pressure evaporation. The evaporator discharge temperature is 71°C, and the sodium chloride crystal B obtained after centrifugation is 1744kg / h. The dry basis purity of the sodium chloride product B can reach 99.5%, which meets the requirements of industrial application. The Na in the obtained evaporation crystallization mother liquor is 1.38t / h. + Concentration 166546mg / l, K + Concentration 29208mg / l, Cl - Concentration 172159mg / l, SO4 2- Concentration 908mg / l, NO3 - Concentration: 211842mg / l.

[0093] c. 1.55t / h of evaporation crystallization mother liquor enters the salting-out reactor, 114.8kg / h of KCl crystals are added to the salting-out reactor, and after reaction, centrifugation is performed to obtain 48.2kg / h of sodium chloride crystals D. The dry basis purity of the sodium chloride product D can reach 99.5%. + Concentration 146607mg / l, K + Concentration 78754mg / l, Cl -Concentration 189092mg / l, SO4 2- Concentration 886mg / l, NO3 - Concentration: 206590mg / l, SiO2 concentration: 800mg / l.

[0094] d. Add 0.24t / h of sodium chloride evaporation crystallization unit water to the salting-out separation mother liquor, and then send it to the freezing crystallization separation device. In the freezing crystallization separation device, the water temperature is first cooled to 7-10°C, potassium nitrate reaches a supersaturated state and precipitates in the form of crystals, and then the potassium nitrate crystals are separated from the solution by centrifugation. The potassium nitrate crystals E obtained are 168.6kg / h, and the Na in the freezing crystallization mother liquor is 1.25t / h. + Concentration 139829mg / l, K + Concentration 22254mg / l, Cl - Concentration 181389mg / l, SO4 2- Concentration 810mg / l, NO3 - Concentration: 110753mg / l.

[0095] e. Add 830 mg / l of sodium aluminate, 20 mg / l of PAC and 1.0 mg / l of PAM to the discharged frozen crystallization mother liquor, and let it enter the reaction sedimentation tank for silicon removal reaction and precipitation separation. The SiO2 concentration in the effluent of the sedimentation tank is 20 mg / l. The sludge settled at the bottom of the reaction sedimentation tank is dehydrated by a filter press, and the filtrate is returned to the entrance of the reaction sedimentation tank.

[0096] f. The supernatant in the reaction sedimentation tank is pumped into the multi-media filter, which is filled with quartz sand and anthracite. The filling height of quartz sand is 800mm, the filling height of anthracite is 400mm, and the filtration rate is 7.0m / h. The suspended solids in the effluent of the multi-media filter are less than 2mg / L, and the turbidity is less than 5NTU.

[0097] g. The effluent from the multi-media filter is mixed with the inorganic salt-containing wastewater to be treated and directly diverted to the nanofiltration device, and then enters the membrane module system of the nanofiltration unit. The nanofiltration membrane module adopts the GE DK8040 nanofiltration membrane module. SO4 in the nanofiltration membrane interception liquid 2- The concentration of Na in the nanofiltration membrane permeate reaches about 2181 mg / L and is discharged. + Concentration 61500mg / l, K + Concentration 5810mg / l, Cl - Concentration 84294mg / l, SO4 2- Concentration 10mg / l, NO3 - The concentration is 31840 mg / l and is transported to the sodium chloride evaporation crystallization device for evaporation crystallization treatment.

[0098] Comparative Example 1

[0099] Other conditions are the same as those in Example 1, except that the salting-out unit is not provided, and the evaporation crystallization mother liquor obtained by the sodium chloride evaporation crystallization unit directly enters the potassium nitrate freezing crystallization unit.

[0100] Comparative Example 2

[0101] Other conditions are the same as those in Example 1, except that the mother liquor of salting-out separation in step d is not added with dilution water or sodium chloride to feed the evaporation crystallization unit.

[0102] The purity and yield of the products obtained in Example 1 and Comparative Examples 1-2 are shown in Table 1:

[0103] Table 1

[0104]

[0105] As can be seen from the examples, a sodium chloride solid product is obtained by evaporating and crystallizing the inorganic salt-containing wastewater, and a sodium chloride solid product is further obtained by adding potassium chloride for salting out and crystallizing. - The concentration remains unchanged while K + The concentration is greatly improved, and potassium nitrate solid product is obtained by freezing crystallization. Adding dilution water before freezing crystallization prevents the saturation precipitation of sodium chloride during the freezing crystallization process, and the reflux of part of the freezing crystallization mother liquor reduces the K + The concentration was increased while reducing the flow of dilution water, preventing the precipitation of potassium chloride during the freezing crystallization process. Silicon in the wastewater was removed by adding a silicon removal magnesium agent, preventing the accumulation of silicon in the wastewater during evaporation. Most of the suspended matter and colloids in the wastewater after silicon removal were removed by medium filtration, and sulfate was intercepted and concentrated after treatment by the nanofiltration unit. By diverting part of the salt-containing wastewater to be treated to the inlet side of the nanofiltration membrane, the Cl in the nanofiltration retentate was reduced. - 、NO3 - 、Na + and K + Through these treatment steps, the salt and water in the inorganic salt wastewater can be separated to obtain high-quality sodium chloride and potassium nitrate products, SO4 2- The enriched and separated products are sent out for separate treatment. The method and system of the utility model can also ensure that the system can operate long-term, stably, economically and reliably without secondary pollution, and has significant economic and environmental benefits.

[0106] Although the utility model has been described with reference to typical embodiments, it should be understood that the terms used are illustrative and exemplary, rather than restrictive. Since the utility model can be implemented in a variety of forms without departing from the spirit or essence of the utility model, it should be understood that the above embodiments are not limited to any of the aforementioned details, but should be widely interpreted within the spirit and scope defined by the attached claims, so all changes and modifications falling within the scope of the claims or their equivalents should be covered by the attached claims.

Claims

1. A treatment system for inorganic salt wastewater, used for treating wastewater containing Cl - 、SO4 2- 、NO3 - 、Na + and K + The salt-containing wastewater is used for salt recovery to prepare sodium chloride and potassium nitrate products, characterized in that: include: A sodium chloride evaporation and crystallization unit is used to perform evaporation and crystallization treatment on the inorganic salt-containing wastewater to obtain sodium chloride crystals B and evaporation and crystallization mother liquor; A salting-out unit is connected to the sodium chloride evaporation and crystallization unit, and is used to process the evaporation and crystallization mother liquor of the sodium chloride evaporation and crystallization unit, add potassium chloride to the evaporation and crystallization mother liquor, obtain sodium chloride crystals D and salting-out separation mother liquor, and discharge the salting-out separation mother liquor to the potassium nitrate freezing crystallization unit; The potassium nitrate freezing crystallization unit is connected to the salting-out unit, and is used to add dilution water to the salting-out separation mother liquor of the salting-out unit, and perform freezing crystallization treatment to obtain potassium nitrate crystals E and potassium nitrate freezing crystallization mother liquor; The nanofiltration unit is connected to the potassium nitrate freezing crystallization unit and is used for nanofiltration treatment of the effluent of the potassium nitrate freezing crystallization unit and discharge the nanofiltration permeate to the sodium chloride evaporation crystallization unit.

2. The processing system according to claim 1, characterized in that The sodium chloride evaporation and crystallization unit is provided with an evaporation crystallizer for performing evaporation and crystallization treatment on the inorganic salt-containing wastewater.

3. The processing system according to claim 1, characterized in that The sodium chloride evaporation and crystallization unit is provided with a centrifugal separation device for separating sodium chloride crystals from the solution to obtain solid sodium chloride crystals B and the evaporation and crystallization mother liquor.

4. The processing system according to claim 1, characterized in that The salting-out unit is provided with a salting-out crystallizer for performing salting-out treatment on the evaporation crystallization mother liquor.

5. The processing system according to claim 1, characterized in that The salting-out unit is provided with a crystal separation device for separating sodium chloride crystals from the solution to obtain the sodium chloride crystals D and the salting-out separation mother liquor.

6. The processing system according to claim 1, characterized in that The potassium nitrate freezing crystallization unit is provided with a freezing crystallizer for performing freezing crystallization treatment on the salting-out separation mother liquor.

7. The processing system according to claim 1, characterized in that The potassium nitrate freezing crystallization unit is provided with a centrifugal separation device for separating potassium nitrate crystals from the solution to obtain potassium nitrate crystals E and potassium nitrate freezing crystallization mother liquor.

8. The processing system according to claim 1, characterized in that The treatment system also includes a medium filtration unit, which is connected to the potassium nitrate freezing crystallization unit and the nanofiltration unit, and is used to perform medium filtration treatment on the effluent potassium nitrate freezing crystallization mother liquor of the potassium nitrate freezing crystallization unit, remove suspended matter in the effluent of the potassium nitrate freezing crystallization unit, and transport the effluent of the medium filtration unit to the nanofiltration unit.

9. The processing system according to claim 8, characterized in that The treatment system also includes a silicon removal unit, which is connected to the potassium nitrate freezing crystallization unit and the medium filtration unit, and is used to treat the effluent potassium nitrate freezing crystallization mother liquor of the potassium nitrate freezing crystallization unit, by adding a silicon removal chemical agent to cause silicon to undergo a chemical reaction to form a precipitate and remove the silicon therein, and the effluent after silicon removal is transported to the medium filtration unit.

10. The processing system according to claim 9, characterized in that The desiliconization unit is provided with a chemical desiliconization reaction precipitation device for treating the potassium nitrate freezing crystallization mother liquor to obtain a supernatant and precipitated sludge, and the supernatant is transported to the medium filtration unit.

11. The processing system according to claim 10, characterized in that The desiliconization unit is provided with a precipitated sludge dewatering device for filtering and separating the precipitated sludge. The dewatered sludge after separation is transported outward, and the sludge dewatering filtrate is returned to the inlet of the chemical desiliconization reaction precipitation device for further processing.

12. The processing system according to claim 8, characterized in that The influent of the nanofiltration unit not only comes from the medium filtration unit, but also receives a portion of the influent of the sodium chloride evaporation crystallization unit, that is, the inorganic salt-containing wastewater to be treated, so as to reduce the Cl in the nanofiltration retentate. - 、NO3 - 、Na + and K + The content.

13. The processing system according to claim 12, characterized in that The flow rate of the inorganic salt-containing wastewater to be treated received by the nanofiltration unit is 0.5 to 10 times the effluent flow rate of the medium filtration unit.

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