Method for comprehensive utilization of potassium sulfate-rich concentrated water

Abstract

The application provides a comprehensive utilization method of potassium sulfate-rich concentrated water, which comprises the following steps: precipitating nitrate from the concentrated water at 0 DEG C; adding potassium chloride into the mother liquor of the precipitated nitrate to precipitate potassium sulfate when the temperature of the mother liquor is increased to 20-25 DEG C; evaporating and concentrating the mother liquor after the potassium sulfate is precipitated, and then cooling and crystallizing to obtain fresh water and potassium chloride, and the potassium chloride is returned to the preparation of potassium sulfate; introducing the mother liquor of the precipitated nitrate into the mother liquor after the potassium chloride is prepared, and then performing nanofiltration, and returning the nanofiltration concentrated liquid containing sulfate to the preparation of potassium sulfate; evaporating and concentrating the nanofiltration permeate to obtain fresh water and concentrated material; centrifuging the concentrated material to obtain industrial salt and sodium chloride crystallization mother liquor; cooling and crystallizing the sodium chloride crystallization mother liquor, and then centrifuging to obtain potassium chloride and potassium precipitation mother liquor; returning the potassium chloride to the preparation of potassium sulfate; combining the potassium precipitation mother liquor with the nanofiltration permeate; when the content of impurity ions in the potassium precipitation mother liquor exceeds the standard, evaporating and concentrating the potassium precipitation mother liquor to obtain fresh water and mixed salt. The method has reasonable process flow design, low operation condition requirement, low running cost and good economy.

Description

Technical Field

[0001] This invention belongs to the field of environmental protection technology, and in particular relates to a method for the comprehensive utilization of concentrated water rich in potassium sulfate. Background Technology

[0002] With industrial development, global freshwater resources are becoming increasingly scarce, leading to the development of concentrated brine utilization technology. This technology not only provides freshwater but also enables the production of many industrial raw materials. Industries such as chemicals, dyes, and pesticides generate large amounts of saline organic wastewater. For wastewater with a salt content of 3%–5%, halophilic bacteria can be introduced for biochemical treatment, or the wastewater can be diluted before biochemical treatment. However, when the salt content exceeds 20%, its treatment becomes a major challenge. Direct discharge would severely impact surface water, soil, and groundwater. Concentrated brine utilization technology allows high-concentration brine to be used as a raw material in the chlor-alkali industry, while simultaneously providing freshwater resources, achieving the recycling of wastewater resources. This is of great significance for sustainable development and the ecological environment. However, existing concentrated brine utilization technologies suffer from long and cumbersome processes, demanding operating conditions, high energy consumption, high operating costs, and poor economic efficiency. Summary of the Invention

[0003] In view of this, in order to solve the above problems, this invention proposes a comprehensive utilization method for potassium sulfate-rich concentrated water, which has a reasonable process flow design, low operating condition requirements, low energy consumption, low operating cost, good economic efficiency, and no secondary pollution to the environment, so as to realize the recycling of wastewater resources.

[0004] To achieve the above objectives, the technical solution of the present invention is implemented as follows:

[0005] A method for the comprehensive utilization of potassium sulfate-rich concentrated water includes the following steps:

[0006] S1. Preparation process of sodium sulfate: The concentrated water used as raw material is basically saturated with sodium sulfate at 0°C, and then directly frozen to precipitate decahydrate. The decahydrate is then processed to obtain sodium sulfate product.

[0007] S2. Potassium sulfate preparation process: The mother liquor after the decahydrate of nitrate is precipitated is heated to 20-25°C, and potassium chloride is added to precipitate potassium sulfate. After processing, potassium sulfate product is obtained.

[0008] S3, Potassium Chloride Recovery Process: The mother liquor after potassium sulfate precipitation has a low sulfate concentration. It is directly evaporated and concentrated to obtain fresh water and potassium chloride. The liquid is then cooled and crystallized to precipitate potassium chloride. The potassium chloride obtained from evaporation, concentration and cooling crystallization is returned to S2 for the production of potassium sulfate.

[0009] S4, Nanofiltration-Reverse Osmosis Separation Process: Nitrate mother liquor from S1 is introduced into the mother liquor after potassium chloride production. After nanofiltration, monovalent and divalent ions are separated. The nanofiltration concentrate containing sulfate is returned to S2 to continue potassium sulfate production. The nanofiltration permeate is further concentrated by reverse osmosis to obtain fresh water and reverse osmosis concentrate.

[0010] S5. Industrial salt preparation process: Evaporate and concentrate the reverse osmosis concentrate to obtain fresh water and concentrate; centrifuge the concentrate to obtain industrial salt and sodium chloride crystallization mother liquor;

[0011] S6. Potassium chloride recovery and industrial salt preparation process: Cool the sodium chloride crystallization mother liquor to crystallize, centrifuge to separate potassium chloride and potassium precipitation mother liquor; return potassium chloride to S2 for potassium sulfate production; return the potassium precipitation mother liquor to S5 and combine it with the nanofiltration permeate, continue to evaporate and concentrate until the impurity ion content in the potassium precipitation mother liquor exceeds the standard.

[0012] S7. Mixed salt preparation process: When the impurity ion content in the potassium precipitation mother liquor exceeds the standard, the potassium precipitation mother liquor is evaporated and concentrated to obtain fresh water and mixed salt.

[0013] Furthermore, in S1, the total salinity of the concentrated water used as the raw material solution is 35,000–50,000 mg / L; wherein, SO4 2- 100,000–110,000 mg / L, Na + 30000~40000mg / L, Cl - 2000~3000mg / L, K + 35000~40000mg / L, HNO3 - 60–80 mg / L, Ca 2+ 10–20 mg / L, HCO3 3- 30–45 mg / L, Mg 2+ : 3-8mg / L, SiO220~30mg / L, COD300~350.

[0014] Furthermore, in S1, the specific gravity of the concentrated water used as the raw material liquid is calculated as 1 to 1.15. The material is analyzed using the phase diagram of the quaternary aqueous salt system at different temperatures. It is determined that under 0°C conditions, sodium sulfate is saturated and decahydrate nitrate can be directly precipitated.

[0015] Furthermore, in S1, the decahydrate nitrate is concentrated by MVR evaporation, centrifuged and dried to obtain sodium sulfate product.

[0016] Furthermore, in step S2, after potassium sulfate precipitates, it is separated by centrifugation and dried to obtain the potassium sulfate product.

[0017] Furthermore, in S3, the evaporation and concentration temperature is 107–113°C, and the cooling and crystallization temperature is 40°C.

[0018] Furthermore, in S4, during the nanofiltration process, the pressure difference across the nanofiltration membrane is 1.6–1.9 MPa, and the inlet temperature is 22–26 °C.

[0019] Furthermore, in step S6, the excessive impurity ion content refers to HNO3. - Reaching 4g / L, Ca 2+ Reaching 857.14 g / L, HCO3 - Reaching 2673.75 g / L, Mg 2+ It reached 392.87 g / L.

[0020] Compared with existing technologies, the method for comprehensive utilization of potassium sulfate-rich concentrated water described in this invention has the following advantages:

[0021] (1) The process flow design of the comprehensive utilization method of potassium sulfate-rich concentrated water described in this invention is reasonable, with low requirements for operating conditions and low operating costs; the decahydrate nitrate is separated by freezing crystallization to obtain sodium sulfate product; potassium chloride + sodium sulfate are converted by metathesis reaction to produce potassium sulfate product and sodium chloride; sulfate ions and sodium chloride are separated by nanofiltration and further separated and concentrated by reverse osmosis; metathesis reaction and freezing crystallization can improve the separation effect; the nanofiltration process has low osmotic pressure, low operating pressure, low energy consumption and good separation effect; the further separation and concentration by reverse osmosis can reduce the subsequent evaporation and reduce the cost of treating concentrated water, while obtaining industrial raw materials and fresh water resources with added value, realizing the recycling of wastewater resources, with good economic benefits and no secondary pollution to the environment;

[0022] (2) In the process flow of the potassium sulfate-rich concentrated water comprehensive utilization method of the present invention, the preceding and following processes complement each other. The potassium chloride generated in the process is recycled to the potassium sulfate production process, which reduces the cost of purchasing potassium chloride, effectively reduces the processing cost, and improves the economy. Attached Figure Description

[0023] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0024] Figure 1 This is a schematic diagram of the process flow for the comprehensive utilization method of potassium sulfate-rich concentrated water according to the present invention;

[0025] Figure 2 This is a schematic diagram of the process flow for the comprehensive utilization method of potassium sulfate-rich concentrated water according to Embodiment 2 of the present invention. Detailed Implementation

[0026] Unless otherwise defined, the technical terms used in the following embodiments have the same meanings as commonly understood by those skilled in the art. Unless otherwise specified, the experimental reagents used in the following embodiments are conventional biochemical reagents; and the experimental methods described are conventional methods.

[0027] The present invention will now be described in detail with reference to the embodiments and accompanying drawings.

[0028] This invention provides a method for the comprehensive utilization of potassium sulfate-rich concentrated water. The composition of the concentrated water used as the raw material solution is as follows: total salinity of 35,000–50,000 mg / L; wherein, SO42- 2- 100,000–110,000 mg / L, Na + 30000~40000mg / L, Cl - 2000~3000mg / L, K + 35000~40000mg / L, HNO3 - 60–80 mg / L, Ca 2+ 10–20 mg / L, HCO3 3- 30–45 mg / L, Mg 2 + 3~8mg / L, SiO220~30mg / L, COD 300~350.

[0029] like Figure 1 As shown, the steps are as follows:

[0030] S1. Preparation process of sodium sulfate: The specific gravity of the concentrated water is calculated according to 1 to 1.15. The phase diagram of the quaternary aqueous salt system at different temperatures is used to analyze the material and determine that sodium sulfate in the concentrated water is saturated at 0℃. The temperature of the concentrated water is controlled at 0℃ to precipitate decahydrate. The decahydrate is concentrated by MVR evaporation, centrifugation and drying to obtain sodium sulfate product.

[0031] S2. Potassium sulfate preparation process: The mother liquor after the decahydrate of nitrate is precipitated is heated to 20-25°C, and potassium chloride is added to precipitate potassium sulfate. After centrifugation and drying, potassium sulfate product is obtained.

[0032] S3, Potassium Chloride Recovery Process: The mother liquor after potassium sulfate precipitation has a low sulfate concentration. The evaporation and concentration temperature is controlled at 110℃ to obtain fresh water and potassium chloride. The liquid is then cooled down, and the cooling crystallization temperature is controlled at 40℃ to precipitate potassium chloride. The potassium chloride obtained from evaporation, concentration and cooling crystallization is returned to S2 for the production of potassium sulfate.

[0033] S4, Nanofiltration-Reverse Osmosis Separation Process: Sulfate is enriched in the mother liquor after potassium chloride production. The nitrate-precipitated mother liquor from S1 is then introduced into the mother liquor after potassium chloride production for nanofiltration treatment. The effective membrane area of ​​the nanofiltration membrane during the nanofiltration process is 0.38 m². 2 The pressure difference across the membrane is 1.60-1.90 MPa, and the inlet water temperature is 22℃-26℃. After nanofiltration, monovalent ions and divalent ions (sulfate and chloride) are separated. The nanofiltration concentrate containing sulfate is returned to S2 to continue the production of potassium sulfate. The nanofiltration permeate is further concentrated by reverse osmosis to obtain fresh water and reverse osmosis concentrate.

[0034] S5. Industrial salt preparation process: Evaporate and concentrate the reverse osmosis concentrate to obtain fresh water and concentrate; centrifuge the concentrate to obtain industrial salt and sodium chloride crystallization mother liquor;

[0035] S6. Potassium chloride recovery and industrial salt preparation process: Cool the sodium chloride crystallization mother liquor to crystallize, centrifuge to separate potassium chloride and potassium precipitation mother liquor; return potassium chloride to S2 for potassium sulfate production; return the potassium precipitation mother liquor to S5 and combine it with the nanofiltration permeate, continue to evaporate and concentrate until the impurity ion content in the potassium precipitation mother liquor exceeds the standard.

[0036] S7. Mixed salt preparation process: When the impurity ions HNO3 in the potassium precipitation mother liquor... - Ca 2+ HCO3 - Mg 2+ Excessive content, HNO3 - Reaching 4g / L, Ca 2+ Reaching 857.14 g / L, HCO3 - Reaching 2673.75 g / L, Mg 2+ When the concentration reaches 392.87 g / L, the potassium precipitation mother liquor is evaporated and concentrated to obtain fresh water and mixed salt.

[0037] Example 1

[0038] The composition of the concentrated water used as the feed solution is as follows: total salinity is 37500 mg / L; of which, SO42- 2- 105000mg / L, Na + 35000 mg / L, Cl - 2500mg / L, K + 37500mg / L, HNO3 - 70mg / L, Ca 2+ 15mg / L, HCO 3- 37.5 mg / L, Mg 2+ 5.5mg / L, SiO225mg / L, COD 325.

[0039] The concentrated water is treated using the comprehensive utilization method for potassium sulfate-rich concentrated water described in this invention, and the process is as follows:

[0040] S1. Preparation process of sodium sulfate: The specific gravity of the concentrated water is calculated as 1. 786t of concentrated water is taken as raw material. The temperature of the concentrated water is controlled at 0℃ to precipitate decahydrate. The decahydrate is concentrated by MVR evaporation, centrifugation and drying to obtain about 34t of sodium sulfate product.

[0041] S2. Potassium sulfate preparation process: The mother liquor after the decahydrate of nitrate is precipitated is heated to 20°C, and 40t of purchased potassium chloride is added to precipitate potassium sulfate. After centrifugation and drying, about 78t of potassium sulfate product is obtained.

[0042] S3, Potassium Chloride Recovery Process: The sulfate concentration in the mother liquor after potassium sulfate precipitation is low. The evaporation and concentration temperature is controlled at 110℃ to obtain about 500t of fresh water and 20t of potassium chloride. The liquid is then cooled down and the cooling crystallization temperature is controlled at 40℃ to precipitate 4t of residual potassium chloride. The potassium chloride obtained from evaporation, concentration and cooling crystallization is returned to S2 for the production of potassium sulfate.

[0043] S4. Nanofiltration Separation Process: Sulfate ions are enriched in the mother liquor after potassium chloride production. The nitrate precipitation mother liquor from S1 is introduced into the mother liquor after potassium chloride production for nanofiltration treatment. The effective membrane area of ​​the nanofiltration membrane during the nanofiltration process is 0.38m². 2 The pressure difference across the membrane is controlled at 1.60 MPa, and the inlet water temperature is controlled at 22℃. After nanofiltration, monovalent ions and divalent ions (sulfate and chloride) are separated. The nanofiltration concentrate containing sulfate is returned to S2 to continue the production of potassium sulfate. The nanofiltration permeate is further concentrated by reverse osmosis to obtain fresh water and reverse osmosis concentrate.

[0044] S5. Industrial salt preparation process: The reverse osmosis concentrate contains virtually no sulfate. The reverse osmosis concentrate is evaporated and concentrated to obtain approximately 90t of fresh water. The concentrate is centrifuged to obtain approximately 20t of industrial salt and the separated sodium chloride crystallization mother liquor.

[0045] S6. Potassium chloride recovery and industrial salt preparation process: Cool the sodium chloride crystallization mother liquor to crystallize, centrifuge to separate it, and obtain potassium precipitation mother liquor and about 20t of potassium chloride; return the potassium chloride to S2 for the production of potassium sulfate; return the potassium precipitation mother liquor to S5 and combine it with the nanofiltration permeate, continue to evaporate and concentrate until the impurity ion content in the potassium precipitation mother liquor exceeds the standard.

[0046] S7. Mixed salt preparation process: When the impurity ions HNO3 in the potassium precipitation mother liquor... - Ca 2+ HCO3 - Mg 2+ When the content exceeds the standard, the potassium precipitation mother liquor is evaporated and concentrated to obtain approximately 23 tons of fresh water and 9 tons of mixed salt of potassium chloride and sodium chloride.

[0047] Example 2

[0048] The composition of the concentrated water used as the feed solution is as follows: total salinity is 38000 mg / L; of which, SO42- 2- 110000mg / L, Na + 40000mg / L, Cl - 3000mg / L, K + 40000mg / L, HNO3 - 80mg / L, Ca 2+ 20mg / L, HCO 3- 45mg / L, Mg 2+ 8mg / L, SiO230mg / L, COD 350.

[0049] like Figure 2 As shown, the concentrated water is treated using the comprehensive utilization method for potassium sulfate-rich concentrated water described in this invention. The process is as follows:

[0050] S1. Preparation process of sodium sulfate: The specific gravity of the concentrated water is calculated as 1.15. 786t of concentrated water is taken as raw material. The temperature of the concentrated water is controlled at 0℃ to precipitate decahydrate. The decahydrate is concentrated by MVR evaporation, centrifugation and drying to obtain about 34t of sodium sulfate product.

[0051] S2. Potassium sulfate preparation process: The mother liquor after the decahydrate of nitrate is precipitated is heated to 25°C, and 40t of purchased potassium chloride is added to precipitate potassium sulfate. After centrifugation and drying, about 90t of potassium sulfate product is obtained.

[0052] S3, Potassium Chloride Recovery Process: The sulfate concentration in the mother liquor after potassium sulfate precipitation is low. The evaporation and concentration temperature is controlled at 110℃ to obtain about 500t of fresh water and 16t of potassium chloride. The liquid is then cooled down and the cooling crystallization temperature is controlled at 40℃ to precipitate 4t of residual potassium chloride. The potassium chloride obtained from evaporation, concentration and cooling crystallization is returned to S2 for the production of potassium sulfate.

[0053] S4, Nanofiltration-Reverse Osmosis Separation Process: Sulfate is enriched in the mother liquor after potassium chloride production. The nitrate-precipitated mother liquor from S1 is then introduced into the mother liquor after potassium chloride production for nanofiltration treatment. The effective membrane area of ​​the nanofiltration membrane during the nanofiltration process is 0.38 m². 2 The pressure difference across the membrane is controlled at 1.90 MPa, and the inlet water temperature is controlled at 25℃. After nanofiltration, monovalent ions and divalent ions (sulfate and chloride) are separated. The nanofiltration concentrate containing sulfate is returned to S2 to continue the production of potassium sulfate. The nanofiltration permeate is further concentrated by reverse osmosis to obtain fresh water and reverse osmosis concentrate.

[0054] S5. Industrial salt preparation process: The reverse osmosis concentrate contains virtually no sulfate. About 30t of reverse osmosis concentrate is evaporated and concentrated to obtain about 90t of fresh water. The concentrate is centrifuged to obtain about 25t of industrial salt and the separated sodium chloride crystallization mother liquor.

[0055] S6. Potassium chloride recovery and industrial salt preparation process: Cool the sodium chloride crystallization mother liquor to crystallize, centrifuge to separate it, and obtain potassium precipitation mother liquor and about 20t of potassium chloride; return the potassium chloride to S2 for the production of potassium sulfate; return the potassium precipitation mother liquor to S5 and combine it with the nanofiltration permeate, continue to evaporate and concentrate until the impurity ion content in the potassium precipitation mother liquor exceeds the standard.

[0056] S7. Mixed salt preparation process: When the impurity ions HNO3 in the potassium precipitation mother liquor... - Ca 2+ HCO3 - Mg 2+ When the content exceeds the standard, the potassium precipitation mother liquor is evaporated and concentrated to obtain approximately 23 tons of fresh water and 11 tons of mixed salt of potassium chloride and sodium chloride.

[0057] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, 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 comprehensive utilization of potassium sulfate-rich concentrated water, characterized in that, Includes the following steps: S1. Preparation process of sodium sulfate: The concentrated water used as raw material solution is precipitated at 0℃ to obtain sodium sulfate decahydrate. The sodium sulfate decahydrate is then processed to obtain sodium sulfate product. S2. Potassium sulfate preparation process: The mother liquor after the decahydrate of nitrate is precipitated is heated to 20-25°C, potassium chloride is added, potassium sulfate is precipitated, and potassium sulfate product is obtained after treatment. S3, Potassium chloride recovery process: The mother liquor after potassium sulfate precipitation is evaporated and concentrated to obtain fresh water and potassium chloride. The liquid is then cooled and crystallized to precipitate potassium chloride. The potassium chloride obtained from evaporation, concentration and cooling crystallization is returned to S2 for the production of potassium sulfate. S4, Nanofiltration-Reverse Osmosis Separation Process: Nitrate mother liquor from S1 is introduced into the mother liquor after potassium chloride production. After nanofiltration, monovalent and divalent ions are separated. The nanofiltration concentrate containing sulfate is returned to S2 to continue potassium sulfate production. The nanofiltration permeate is further concentrated by reverse osmosis to obtain fresh water and reverse osmosis concentrate. S5. Industrial salt preparation process: Evaporate and concentrate the reverse osmosis concentrate to obtain fresh water and concentrate; The concentrate was centrifuged to obtain industrial salt and sodium chloride crystallization mother liquor; S6. Potassium chloride recovery and industrial salt preparation process: Cool the sodium chloride crystallization mother liquor to crystallize, centrifuge to separate potassium chloride and potassium precipitation mother liquor; return potassium chloride to S2 for potassium sulfate production; return the potassium precipitation mother liquor to S5 and combine it with the nanofiltration permeate, continue to evaporate and concentrate until the impurity ion content in the potassium precipitation mother liquor exceeds the standard. S7. Mixed salt preparation process: When the impurity ion content in the potassium precipitation mother liquor exceeds the standard, the potassium precipitation mother liquor is evaporated and concentrated to obtain fresh water and mixed salt.

2. The method for comprehensive utilization of potassium sulfate-rich concentrated water according to claim 1, characterized in that: In S1, sodium decahydrate is concentrated by MVR evaporation, centrifuged and dried to obtain sodium sulfate product.

3. The method for comprehensive utilization of potassium sulfate-rich concentrated water according to claim 1, characterized in that: In step S2, after potassium sulfate precipitates, it is separated by centrifugation and dried to obtain the potassium sulfate product.

4. The method for comprehensive utilization of potassium sulfate-rich concentrated water according to claim 1, characterized in that: In step S3, the evaporation and concentration temperature is 107–113°C, and the cooling and crystallization temperature is 40°C.

5. The method for comprehensive utilization of potassium sulfate-rich concentrated water according to claim 1, characterized in that: In step S4, during nanofiltration, the pressure difference across the nanofiltration membrane is 1.6–1.9 MPa, and the inlet temperature is 22–26 °C.

6. The method for comprehensive utilization of potassium sulfate-rich concentrated water according to claim 1, characterized in that: The S6, impurity ion content exceeds the standard HNO3 - reach 4g / L, Ca 2+ reach 857.14g / L, HCO3 - reach 2673.75g / L, Mg 2+ reach 392.87g / L.

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