A method for resource-based treatment of high-salinity wastewater

Abstract

This invention discloses a method for the resource-based treatment of high-salinity wastewater, belonging to the field of high-salinity wastewater resource-based treatment in the metallurgical industry. The treatment method includes passing high-salinity wastewater from a primary nanofiltration inlet tank into a primary nanofiltration device for primary nanofiltration to separate primary nanofiltration concentrate and product water; passing the obtained primary nanofiltration concentrate into a freeze crystallization device for crystallization, and then into a metathesis reactor for metathesis reaction, and passing the reaction product into a vacuum belt filter for heavy alkali filtration; passing the separated sodium bicarbonate solid into a calcining furnace; this invention employs a treatment system with "primary nanofiltration + freeze crystallization device + ammonia production device" + "primary nanofiltration + secondary nanofiltration + high-pressure reverse osmosis + evaporation device" as its core to produce high-value-added ammonium sulfate, soda ash, sodium chloride salts, and qualified recycled water, thereby increasing the value of the product salts.

Description

Technical Field

[0001] This invention belongs to the technical field of resource utilization treatment of high-salinity wastewater in the metallurgical industry, and specifically relates to a method for resource utilization treatment of high-salinity wastewater. Background Technology

[0002] High-salinity wastewater generally refers to wastewater containing a total dissolved salt content of not less than 1% by mass. The main ions present in this type of wastewater are... Na + Ca 2+ K + High-salinity wastewater contains a variety of components, including soluble inorganic salts and organic matter in some industries, making it relatively difficult to treat.

[0003] The main process flow used in the resource recovery system for high-salinity wastewater treatment is as follows: high-efficiency clarification tank → ozone catalytic oxidation → aerated biological filter → multi-media filter → ultrafiltration system → weak acid cation bed → primary reverse osmosis system → high-pressure reverse osmosis system → nanofiltration desalination → evaporation crystallization. Through the above methods, the separation and recovery of the main components in high-salinity wastewater are achieved.

[0004] However, the target salts separated and recovered by the current high-salinity wastewater treatment and resource recovery system are still mainly sodium chloride and sodium sulfate. The utilization rate of high-salinity wastewater is low, resulting in overproduction of product salts, which have low value and are difficult to sell. Therefore, a high-salinity wastewater resource recovery treatment method is proposed. Summary of the Invention

[0005] The purpose of this invention is to provide a method for the resource-based treatment of high-salinity wastewater to solve the problems mentioned in the background art.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a method for resource-based treatment of high-salinity wastewater, the method comprising the following steps:

[0007] Step S1: The high-salinity wastewater in the primary nanofiltration inlet tank is passed into the primary nanofiltration unit for primary nanofiltration to separate the primary nanofiltration concentrate (TDS: around 160,000 mg / L) and the permeate (TDS: around 160,000 mg / L, mainly sodium sulfate); the permeate is passed into the secondary nanofiltration unit and the primary nanofiltration concentrate is passed into the subsequent treatment unit.

[0008] Step S2: Pass the first-stage nanofiltration concentrate obtained in step S1 into a cryogenic crystallization device for low-temperature crystallization.

[0009] Step S3: Pass the reaction product from step S2 into a metathesis reactor to carry out a metathesis reaction.

[0010] Step S4: The reaction product of step S3 is passed into a vacuum belt filter for heavy alkali filtration; the separated sodium bicarbonate solid is passed into a calcining furnace, and the remaining mother liquor is sent to the subsequent processing device.

[0011] Step S5: Pass the remaining mother liquor from step S4 into the ammonia stripping tower for thermal separation. The precipitated sodium sulfate solid is returned to the metathesis reactor, and the remaining mother liquor is sent to the subsequent processing unit.

[0012] Step S6: Pass the remaining mother liquor 2 from step S5 into the cryogenic crystallization equipment 2 for low-temperature treatment to separate solid and liquid. The resulting double salt is returned to the sodium sulfate / ammonium sulfate mixture, and the remaining mother liquor 3 is sent to the subsequent processing device.

[0013] Step S7: Pass the remaining mother liquor from step S6 into a multi-effect evaporator for solid-liquid separation to obtain ammonium sulfate and mother liquor IV.

[0014] Furthermore, the secondary nanofiltration permeate in step S1 is concentrated by high-pressure reverse osmosis (TDS: 100000 mg / L, mainly sodium chloride) and then enters a sodium chloride evaporation and crystallization device to prepare sodium chloride salt and recycled water.

[0015] Furthermore, in step S2, the mother liquor produced by the first-stage nanofiltration concentrate is mixed with the high-pressure reverse osmosis concentrate and then fed into the sodium chloride evaporation and crystallization equipment to prepare sodium chloride salt and recycled water.

[0016] Furthermore, in step S3, ammonium bicarbonate is prepared by introducing ammonia and CO2 into the absorption equipment in a certain proportion to prepare an aqueous solution of ammonium bicarbonate, which is then pumped into the carbonation tower and the cleaning tower for further carbonation to generate an ammonium bicarbonate solid-liquid mixture. The CO2 content introduced is 90% to 100%, and the mass fraction of the generated ammonium bicarbonate solid-liquid mixture is 12% to 24%.

[0017] Furthermore, in step S4, the sodium bicarbonate solid is separated by a vacuum belt filter, washed countercurrently with deionized water to dissolve and remove impurities, and then passed into a calcining furnace for high-temperature drying to obtain soda ash.

[0018] Furthermore, in step S5, the mother liquor processed in step S4 is introduced into the ammonia stripping tower for heating to release ammonia gas. The released ammonia gas is compressed and returned to the absorption equipment to mix with CO2 and participate in the ammonium bicarbonate section. The temperature of the ammonia stripping tower is controlled above 75°C and the heating time is above 2 hours.

[0019] Furthermore, in step S5, the ammonia gas that escapes is mixed with the remaining liquid and the sodium sulfate / ammonium sulfate mixture. The solubility of sodium sulfate decreases, and sodium sulfate precipitates out. The separated sodium sulfate solid is returned to the metathesis reactor as a recycled raw material to participate in the metathesis reaction. The remaining liquid after separation is the mother liquor II.

[0020] Furthermore, in steps S6 and S7, mother liquor two is mixed with refluxed mother liquor four and fed into the freeze crystallization device two. After mixing, double salt and mother liquor three are precipitated. Mother liquor three enters the multi-effect evaporation device for solid-liquid separation, and mother liquor four is recycled into the freeze crystallization device two.

[0021] Compared with the prior art, the beneficial effects of the present invention are:

[0022] This invention employs a processing system comprised of "primary nanofiltration + freezing crystallization equipment + ammonia production equipment" + "primary nanofiltration + secondary nanofiltration + high-pressure reverse osmosis + evaporation equipment" to produce high-value-added ammonium sulfate, soda ash, sodium chloride salt, and qualified recycled water, thereby increasing the value of the product salts. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the process for the resource-based treatment of high-salt wastewater in the metallurgical industry according to the present invention.

[0024] In the diagram: 1. Primary nanofiltration inlet tank; 2. Primary nanofiltration; 3. Primary nanofiltration concentrate tank; 4. Freeze crystallization equipment one; 5. Metathesis reactor; 6. Secondary nanofiltration; 7. High-pressure reverse osmosis; 8. Sodium chloride evaporation equipment; 9. Recycled water collection tank; 10. Belt filter; 11. Ammonia stripping tower; 12. Freeze crystallization equipment two; 13. Multi-effect evaporation equipment; 14. Absorption equipment; 15. Reaction tower; 16. Calcination furnace. Detailed Implementation

[0025] The present invention will be further described below with reference to embodiments.

[0026] The following embodiments are used to illustrate the present invention, but should not be used to limit the scope of protection of the present invention. The conditions in the embodiments can be further adjusted according to specific conditions, and simple improvements to the method of the present invention under the premise of the concept of the present invention are all within the scope of protection claimed by the present invention.

[0027] Please see Figure 1 This invention provides a method for the resource-based treatment of high-salinity wastewater, comprising the following steps:

[0028] Step S1: Separate the primary nanofiltration concentrate (TDS: around 160,000 mg / L) and the permeate (TDS: around 160,000 mg / L, mainly sodium sulfate); pass the permeate into the secondary nanofiltration unit and pass the primary nanofiltration concentrate into the subsequent treatment unit.

[0029] Step S2: Pass the first-stage nanofiltration concentrate obtained in step S1 into a cryogenic crystallization device for low-temperature crystallization.

[0030] Step S3: Pass the reaction product from step S2 into a metathesis reactor to carry out a metathesis reaction.

[0031] Step S4: The reaction product of step S3 is passed through a belt filter for heavy alkali filtration; the separated sodium bicarbonate solid is passed into a calcining furnace, and the remaining mother liquor is sent to the subsequent processing device.

[0032] Step S5: Pass the remaining mother liquor from step S4 into the ammonia stripping tower for thermal separation. The precipitated sodium sulfate solid is returned to the metathesis reactor, and the remaining mother liquor is sent to the subsequent processing unit.

[0033] Step S6: Pass the remaining mother liquor 2 from step S5 into the cryogenic crystallization equipment 2 for low-temperature treatment to separate solid and liquid. The resulting double salt is returned to the sodium sulfate / ammonium sulfate mixture, and the remaining mother liquor 3 is sent to the subsequent processing device.

[0034] Step S7: Pass the remaining mother liquor from step S6 into a multi-effect evaporator for solid-liquid separation to obtain ammonium sulfate and mother liquor IV.

[0035] In step S1, the high-salt wastewater in the primary nanofiltration inlet tank 1 is pressurized by a booster pump and then fed into the primary nanofiltration device 2 for primary nanofiltration separation, completing the initial separation and concentration of chloride and sulfate. The separated permeate is fed into the secondary nanofiltration device 6 for secondary nanofiltration to produce secondary nanofiltration permeate. The secondary nanofiltration permeate is treated and concentrated by high-pressure reverse osmosis 7, and the resulting mother liquor is mixed and then fed into the sodium chloride evaporation and crystallization equipment 8 to prepare sodium chloride salt and recycled water. The recycled water is fed into the recycling water collection tank 9 for utilization, the prepared sodium chloride salt is recovered, and the primary nanofiltration concentrate enters the primary nanofiltration concentrate tank 3.

[0036] In step S2, the water in the primary nanofiltration concentrate tank 3 is transported to the freeze crystallization device 4 by the action of the booster pump. The temperature of the freeze crystallization device 4 is controlled to be below 5°C, and sodium sulfate is crystallized to form sodium sulfate. The sodium sulfate is then fed into the metathesis reactor 5, and the remaining solution is fed into the sodium chloride evaporation crystallization device 8 to prepare sodium chloride and recycled water.

[0037] The nanofiltration membranes used in steps S1 and S2 above have a molecular weight between that of ultrafiltration and reverse osmosis, approximately 100-2000 Da. Their salt rejection capacity ranges from 20% to 98%, and their removal rate for soluble monovalent ions is lower than that for high-valent ions. They can be used for the separation of chloride and sulfate ions in high-salt wastewater applications. By pressurizing the raw water side of the nanofiltration membrane, a portion of the pure water and chloride ions permeate through the membrane in a direction perpendicular to the membrane. Most of the sulfate ions in the water concentrate on the membrane surface. The remaining raw water carries away the concentrated substances in a direction parallel to the membrane. The water permeating through the membrane contains a large amount of chloride ions, thus achieving effective separation of sodium chloride and sodium sulfate.

[0038] The high-pressure reverse osmosis in step S1 above utilizes the property of a semi-permeable membrane that allows water to pass through but not salt to remove various salts from the water. Pressure is applied to the raw water side of the reverse osmosis membrane, causing a portion of the pure water to permeate through the membrane in a direction perpendicular to the membrane. Salts in the water concentrate on the membrane surface. The remaining raw water carries away the concentrated substances in a direction parallel to the membrane. Only a small amount of salt remains in the water that permeates through the membrane. Collecting and utilizing this permeate achieves the purpose of desalination (removing more than 95% of the salt).

[0039] In step S3, sodium sulfate is mixed with refluxed sodium sulfate and ammonium bicarbonate in metathesis reactor 5 to carry out a metathesis reaction.

[0040] In step S3 above, ammonium bicarbonate is prepared by passing ammonia and CO2 into the absorption device 14 in a certain proportion to prepare an aqueous solution of ammonium bicarbonate, which is then pumped into the carbonization tower and the cleaning tower 15 for further carbonization with carbon dioxide (content 90% to 100%) to become a solid-liquid mixture of ammonium bicarbonate (mass fraction 12% to 24%).

[0041] In step S3 above, in the metathesis reactor 5, the molar ratio of ammonium bicarbonate to sodium sulfate is 2.5 to 3.5:1, the reaction temperature is controlled at 25 to 35°C, and the reaction time is 1.5 to 2.5 hours, finally forming a composite mixture of sodium sulfate, ammonium sulfate and sodium bicarbonate.

[0042] In step S4, the composite mixture from step S3 is passed into a vacuum belt filter 10. The composite mixture undergoes heavy alkali filtration in the vacuum belt filter 10, and the water in the composite mixture is evaporated under negative pressure to obtain dried sodium bicarbonate solid.

[0043] In step S4 above, the sodium bicarbonate solid is separated and washed countercurrently with deionized water to dissolve and remove impurities. Then it is fed into calcining furnace 16. The sodium bicarbonate is decomposed in calcining furnace 16 at a temperature of 130~140℃ to obtain sodium carbonate solid. After being transported and packaged by airflow, soda ash product is obtained. The calcination tail gas is compressed and returned to the ammonium bicarbonate section for secondary recycling.

[0044] In step S5, the remaining liquid from step S4 is sent to the ammonia stripping tower 11, where the temperature is controlled above 75°C and the heating time is above 2 hours. During heating, a portion of the ammonia gas escapes and enters the next step of the sodium sulfate and ammonium sulfate mixture, while the other portion is compressed and returned to the absorption device 14 to mix with CO2 and participate in the ammonium bicarbonate process.

[0045] In step S5 above, the remaining liquid is mixed with the sodium sulfate / ammonium sulfate mixture and ammonia gas output from the ammonia stripping tower 11 is introduced. The introduced ammonia gas is used to reduce the solubility of sodium sulfate and precipitate sodium sulfate in the solution, thereby performing solid-liquid separation on the reaction liquid. The separated sodium sulfate solid is returned to the metathesis reactor 5 as a recycled raw material to participate in the metathesis reaction. The remaining liquid after separation is mother liquor II.

[0046] In step S6, the mother liquor 2 from step S5 is mixed with the refluxed mother liquor 4 and introduced into the cryogenic crystallization device 2 12. The temperature inside the cryogenic crystallization device 2 12 is controlled to be below 5°C. After mixing, the complex salt and mother liquor 3 are precipitated. After solid-liquid separation of the solution, the separated complex salt is returned to the sodium sulfate / ammonium sulfate mixture for recycling.

[0047] In step S7, mother liquor 3 enters the next stage multi-effect evaporator 13 for solid-liquid separation to obtain ammonium sulfate and mother liquor 4. Mother liquor 4 is circulated into step S6 and mixed with mother liquor 2 before being fed into the second freeze crystallization device 12.

[0048] The freezing / evaporation device used in the above processing steps utilizes the characteristic that salt has different solubilities at different temperatures and pressures. Under the action of external heating, the temperature of the incoming water is increased and the pressure inside the equipment is reduced, which reduces the solubility, causes water molecules to evaporate, and the solution concentration is continuously concentrated. When the solute is nearly saturated, it will crystallize out from the water. After the thick liquid completes solid-liquid separation, the crystals are further dried to become product salt, the steam is further condensed and used as recycled water, and the mother liquor is further refluxed or dried to become mixed salt.

[0049] Operating Procedure: Water in the primary nanofiltration inlet tank 1 is pressurized by a lift pump and enters the primary nanofiltration unit 2 through a pipeline. After the primary nanofiltration completes the initial separation and concentration of chlorides and sulfates, the primary nanofiltration concentrate enters the primary nanofiltration concentrate tank 3, while the permeate enters the secondary nanofiltration unit 6. The secondary nanofiltration permeate is concentrated by high-pressure reverse osmosis 7 and then mixed with the mother liquor from the low-temperature cryogenic crystallization unit 4 before entering the sodium chloride evaporation crystallization unit 8 to prepare sodium chloride and recycled water. The recycled water enters the recovery water collection tank 9 for reuse. Water in the primary nanofiltration concentrate tank 3 is transported to the cryogenic crystallization unit 4 by a lift pump. Under low-temperature conditions, sodium sulfate is formed. The sodium sulfate then reacts with reflux sodium sulfate and ammonium bicarbonate. After solid-liquid mixing, the mixture enters the double decomposition reactor 5 for double decomposition reaction to prepare a composite mixture of sodium sulfate, ammonium sulfate, and sodium bicarbonate. Sodium bicarbonate solid is separated from the mixture in the double decomposition reactor 5 using a vacuum belt filter 10. The mixture is then washed countercurrently with deionized water to dissolve and remove impurities. The remaining liquid is sent to the ammonia stripping tower 11, where the overflowing ammonia gas mixes with the sodium sulfate / ammonium sulfate mixture to precipitate sodium sulfate solid and mother liquor II. Mother liquor II and mother liquor IV are combined and then separated into solid and liquid in the freeze crystallization device II 12 at a low temperature of 5°C to obtain double salt and mother liquor III. The double salt is returned to the sodium sulfate / ammonium sulfate mixture, and mother liquor III is separated into solid and liquid in the multi-effect evaporation device 13 to obtain ammonium sulfate and mother liquor IV. Example 1

[0050] The molar ratio of ammonium bicarbonate to sodium sulfate in the metathesis reactor 5 was controlled at 2.5:1, the reaction temperature was controlled at 25℃, and the reaction time was 1.5h, finally forming a composite mixture of sodium sulfate, ammonium sulfate and sodium bicarbonate.

[0051] Ammonia and carbon dioxide are introduced into absorption equipment 14 at a molar ratio of 1:1.5 to prepare an ammonium bicarbonate aqueous solution, which is then pumped into carbonation tower and washing tower 15 for further carbonation with 90% carbon dioxide to form an ammonium bicarbonate solid-liquid mixture with a mass fraction of 12%. Example 2

[0052] The molar ratio of ammonium bicarbonate to sodium sulfate in the metathesis reactor 5 was controlled at 3.5:1, the reaction temperature was controlled at 35℃, and the reaction time was 2.5h, finally forming a composite mixture of sodium sulfate, ammonium sulfate and sodium bicarbonate.

[0053] Ammonia and carbon dioxide are introduced into absorption device 14 at a molar ratio of 1:2 to prepare ammonium bicarbonate aqueous solution, which is then pumped into carbonation tower and washing tower 15 for further carbonation with 100% carbon dioxide to form ammonium bicarbonate solid-liquid mixture with a mass fraction of 24%. Example 3

[0054] The molar ratio of ammonium bicarbonate to sodium sulfate in the metathesis reactor 5 was controlled at 3:1, the reaction temperature was controlled at 30℃, and the reaction time was 2h, finally forming a composite mixture of sodium sulfate, ammonium sulfate and sodium bicarbonate.

[0055] Ammonia and carbon dioxide are introduced into absorption equipment 14 at a molar ratio of 1:1.8 to prepare an ammonium bicarbonate aqueous solution, which is then pumped into carbonation tower and washing tower 15 for further carbonation with 95% carbon dioxide to form an ammonium bicarbonate solid-liquid mixture with a mass fraction of 18%.

[0056] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for resource-based treatment of high-salinity wastewater, characterized in that: The processing method includes the following steps: Step S1: Pass the high-salt wastewater in the first-stage nanofiltration inlet tank (1) into the first-stage nanofiltration device (2) for first-stage nanofiltration to separate the first-stage nanofiltration concentrate and product water; pass the product water into the second-stage nanofiltration device (6) and pass the first-stage nanofiltration concentrate into the subsequent treatment device. Step S2: Pass the first-stage nanofiltration concentrate obtained in step S1 into the cryogenic crystallization equipment (4) for low-temperature crystallization. Step S3: Pass the reaction product of step S2 into the metathesis reactor (5) to carry out the metathesis reaction; Step S4: The reaction product of step S3 is passed into a vacuum belt filter (10) for heavy alkali filtration; the separated sodium bicarbonate solid is passed into a calcining furnace (16), and the remaining mother liquor is sent to the subsequent processing device. Step S5: The remaining mother liquor from step S4 is passed into the ammonia stripping tower for thermal separation. The precipitated sodium sulfate solid is returned to the metathesis reactor (5), and the remaining mother liquor is sent to the subsequent processing device. Step S6: Pass the remaining mother liquor 2 from step S5 into the cryogenic crystallization equipment 2 (12) for low-temperature treatment to separate solid and liquid. The resulting double salt is returned to the sodium sulfate / ammonium sulfate mixture, and the remaining mother liquor 3 is sent to the subsequent processing device. Step S7: The remaining mother liquor from step S6 is passed into a multi-effect evaporator (13) for solid-liquid separation to obtain ammonium sulfate and mother liquor IV. In step S3, ammonium bicarbonate is prepared by introducing ammonia and CO2 into the absorption device (14) in a certain proportion to prepare an ammonium bicarbonate aqueous solution, which is then pumped into the carbonation tower and the washing tower (15) for further carbonation to generate an ammonium bicarbonate solid-liquid mixture. The CO2 content introduced is 90% to 100%, and the mass fraction of the generated ammonium bicarbonate solid-liquid mixture is 12% to 24%. In step S4, the vacuum belt filter (10) separates the sodium bicarbonate solid and washes it with deionized water in a countercurrent manner. After dissolving and removing the impurities, it is introduced into the calcining furnace (16) for high-temperature drying to obtain soda ash. In step S5, the mother liquor after step S4 is introduced into the ammonia stripping tower (11) for heating to release ammonia gas. Part of the released ammonia gas is compressed and returned to the absorption device. The ammonia gas is mixed with CO2 in the preparation (14) to participate in the ammonium bicarbonate process. The temperature of the ammonia stripping tower (11) is controlled above 75°C and the heating time is above 2 hours. In step S5, the other part of the ammonia gas escapes is mixed with the remaining liquid and the sodium sulfate / ammonium sulfate mixture. The solubility of sodium sulfate decreases and sodium sulfate is precipitated. The separated sodium sulfate solid is returned to the metathesis reactor (5) as a recycled raw material to participate in the metathesis reaction. The remaining liquid after separation is mother liquor II. In steps S6 and S7, mother liquor II is mixed with the refluxed mother liquor IV and then passed into the freeze crystallization equipment II (12). After mixing, double salt and mother liquor III are precipitated. Mother liquor III enters the multi-effect evaporation equipment (13) for solid-liquid separation and mother liquor IV is circulated into the freeze crystallization equipment II (12).

2. The method for resource-based treatment of high-salinity wastewater according to claim 1, characterized in that: The product water in step S1 is fed into a secondary nanofiltration device (6) to produce secondary nanofiltration water which is then treated and concentrated by high-pressure reverse osmosis (7) and then fed into a sodium chloride evaporation and crystallization device (8) to prepare sodium chloride salt and recycled water.

3. The method for resource-based treatment of high-salinity wastewater according to claim 2, characterized in that: In step S2, the primary nanofiltration concentrate enters the low-temperature freezing crystallization equipment (4), and the mother liquor produced is mixed with the high-pressure reverse osmosis concentrate and then fed into the sodium chloride evaporation crystallization equipment (8) to prepare sodium chloride salt and recycled water.

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