CN111153456A

CN111153456A - High-salt-content wastewater quality-divided crystallization treatment system and method

Info

Publication number: CN111153456A
Application number: CN201910578307.2A
Authority: CN
Inventors: 赛世杰; 余占军; 张娜; 党平; 李思序; 李战胜; 刘慧�; 樊璐; 康花
Original assignee: Inner Mongolia Jiuke Kangrui Environmental Technology Co ltd
Current assignee: Inner Mongolia Jiuke Kangrui Environmental Technology Co ltd
Priority date: 2019-06-28
Filing date: 2019-06-28
Publication date: 2020-05-15

Abstract

The invention discloses a high-salinity wastewater quality-divided crystallization treatment system and a method, wherein the system comprises an adjusting tank, a first sodium chloride evaporative crystallization system, a sodium chloride mother liquor cache tank, a potassium nitrate frozen crystallization system, a second sodium chloride evaporative crystallization system and a miscellaneous salt evaporative crystallization system; the method comprises the following steps: (1) homogenizing and uniformly treating the wastewater; (2) evaporating and crystallizing the first sodium chloride; (3) adding potassium chloride into the sodium chloride mother liquor to obtain a mixed liquor; (4) freezing to separate out potassium nitrate; (5) and (4) evaporating and crystallizing the frozen potassium nitrate mother liquor. The method has the advantages of low wastewater treatment cost, various product types, small impurity salt amount, high purity of the produced sodium chloride more than 99%, high purity of the sodium sulfate more than 99%, high purity of the potassium nitrate more than 99% and high impurity salt yield less than or equal to 10%.

Description

High-salt-content wastewater quality-divided crystallization treatment system and method

The technical field is as follows:

the invention relates to the field of water treatment, in particular to a high-salt-content wastewater quality-divided crystallization treatment system and method.

Background art:

the high-salt-content wastewater is wastewater generated in the industries of coal mines, chemical industry, coal chemical industry, power plants, metallurgy, pharmacy and the like, is mainly used for producing circulating water, sewage, plant domestic sewage and the like, mainly comprises sodium chloride, sodium sulfate and sodium nitrate, and also comprises calcium magnesium, silicon dioxide, refractory organic matters and the like.

At present, with the technological progress and the development of times, the national environmental protection requirements for various industries are increasingly strict, and the stealing, burying and emission are strictly forbidden. This is a serious test for the enterprises which are continuously producing all the time and the enterprises which build the evaporation ponds.

In recent years, a large amount of wastewater zero-discharge treatment devices are put into operation, and the main process routes include pretreatment, double-membrane, nanofiltration, high-pressure reverse osmosis (DTRO, electrodialysis), evaporative crystallization and the like. After the processes are carried out, most of wastewater can be recycled, and sodium chloride and sodium sulfate are subjected to fractional crystallization, but the processes are unstable in operation, the produced sodium chloride and sodium sulfate are low in quantity, the purity is lower than 98%, the whiteness does not reach the standard, and the sodium chloride and sodium sulfate cannot be recycled; meanwhile, the content of sodium nitrate in water is high, so that the yield of miscellaneous salt in the wastewater is up to 25%.

In conclusion, although the prior art can realize the recycling of most wastewater and the quality separation and crystallization of sodium chloride and sodium sulfate, the prior art has the problems of unstable operation, high salt yield of miscellaneous salts, low yield of crystallized salts, poor quality, incapability of resource utilization and the like. Therefore, the system and the method for efficiently realizing sodium chloride and sodium sulfate dual crystallization, improving the purity of the crystallized salt and reducing the salt yield of the miscellaneous salt are urgently found.

The invention content is as follows:

the high-salt-content wastewater quality-divided crystallization treatment system and method provided by the invention can obtain high-purity sodium chloride and sodium sulfate, can convert sodium nitrate which is difficult to treat into potassium nitrate with a high added value, ensure the purity of crystallized salt, reduce the salt yield of miscellaneous salts, and simultaneously recycle the produced high-purity sodium chloride, sodium sulfate and potassium nitrate, realize certain economic benefit and reduce the wastewater treatment pressure of enterprises.

The invention aims to provide the high-salt-content wastewater quality-divided crystallization treatment system which has the advantages of stable process operation, high purity of produced sodium chloride and sodium sulfate, high yield and high quality of crystallization salt, multiple types of crystallization salt, low treatment cost and realization of resource utilization of wastewater.

The second purpose of the invention is to provide a high-salt-content wastewater quality-divided crystallization treatment method which has the advantages of stable process operation, high purity of produced sodium chloride and sodium sulfate, high yield and high quality of crystallization salt, multiple types of crystallization salt, low treatment cost and realization of resource utilization of wastewater.

The first purpose of the invention is implemented by the following technical scheme: a high salt-containing wastewater quality-divided crystallization treatment system comprises a regulating reservoir, a first sodium chloride evaporative crystallization system, a sodium chloride mother liquor cache pool, a potassium nitrate freezing crystallization system, a second sodium chloride evaporative crystallization system and a miscellaneous salt evaporative crystallization system;

the equalizing basin delivery port with the water inlet of first sodium chloride evaporative crystallization system is connected, the sodium chloride evaporative crystallization mother liquor export of first sodium chloride evaporative crystallization system with the sodium chloride mother liquor access connection of sodium chloride mother liquor buffer memory pond, the liquid outlet of sodium chloride mother liquor buffer memory pond with the inlet of the frozen crystallization system of potassium nitrate is connected, the mother liquor export of the frozen crystallization system of potassium nitrate with the inlet of the sodium chloride evaporative crystallization system of second, the sodium chloride evaporative crystallization mother liquor export of the sodium chloride evaporative crystallization system of second respectively with the sodium chloride mother liquor import of sodium chloride mother liquor buffer memory pond with the sodium chloride mother liquor access connection of miscellaneous salt evaporative crystallization system.

Furthermore, the high-salt-content wastewater quality-separating crystallization treatment system further comprises a nanofiltration system, wherein a water outlet of the regulating reservoir is connected with a water inlet of the nanofiltration system, and a water production outlet of the nanofiltration system is connected with a water inlet of the first sodium chloride evaporative crystallization system.

Furthermore, the high-salt-content wastewater quality-divided crystallization treatment system further comprises an advanced oxidation system, a mirabilite freezing and crystallization system and a mirabilite melting or dissolving and crystallization system; a concentrated water outlet of the nanofiltration system is connected with a water inlet of the advanced oxidation system, a water outlet of the advanced oxidation system is connected with a water inlet of the mirabilite freezing and crystallizing system, and a freezing mother liquor outlet of the mirabilite freezing and crystallizing system is respectively connected with a water inlet of the regulating tank and a freezing mother liquor inlet of the miscellaneous salt evaporative crystallization system; and a mirabilite outlet of the mirabilite freezing and crystallizing system is connected with a feed inlet of the mirabilite melting or dissolving and crystallizing system.

Further, the high-salt-content wastewater quality-divided crystallization treatment system further comprises a pretreatment device, wherein the pretreatment device comprises a high-density sedimentation tank, ultrafiltration, ion exchange resin and a carbon remover which are sequentially connected; and the water outlet of the carbon remover is connected with the water inlet of the regulating tank. The pretreatment device is used for removing calcium and magnesium ions, particles, microorganisms, silicon dioxide and alkalinity in the wastewater.

Furthermore, the system for treating the high-salinity wastewater by fractional crystallization also comprises a first wastewater concentration device; and the water outlet of the regulating tank is connected with the water inlet of the first wastewater concentration device, and the concentrated water outlet of the first wastewater concentration device is connected with the water inlet of the first sodium chloride evaporative crystallization system.

Further, the first wastewater concentration device is any one of a high-pressure reverse osmosis device, a disc type reverse osmosis Device (DTRO), an electrodialysis device, a forward osmosis device, an MVR or a multi-effect evaporation system.

Furthermore, the high-salinity wastewater quality-divided crystallization treatment system also comprises an evaporation concentration system; the liquid outlet of sodium chloride mother liquor buffer pool with the inlet of evaporative concentration system is connected, the concentrate export of evaporative concentration system with the inlet of potassium nitrate freeze crystallization system is connected.

Furthermore, the system for treating the high-salinity wastewater by fractional crystallization also comprises a first wastewater concentration device; and a water outlet of the nanofiltration system is connected with a water inlet of the first wastewater concentration device, and a concentrated water outlet of the first wastewater concentration device is connected with a water inlet of the first sodium chloride evaporative crystallization device.

Furthermore, the system for treating the high-salinity wastewater by the fractional crystallization also comprises a second wastewater concentration device; and the water outlet of the advanced oxidation system is connected with the water inlet of the second wastewater concentration device, and the concentrated water outlet of the second wastewater concentration device is connected with the water inlet of the mirabilite freezing and crystallizing system.

The second purpose of the invention is implemented by the following technical scheme: a high-salt-content wastewater quality-divided crystallization treatment method comprises the following steps: (1) homogenizing and uniformly treating the wastewater; (2) evaporating and crystallizing the first sodium chloride; (3) adding potassium chloride into the sodium chloride mother liquor to obtain a mixed liquor; (4) freezing to separate out potassium nitrate; (5) evaporating and crystallizing the frozen potassium nitrate mother liquor; wherein,

(1) homogenizing and uniformly treating the wastewater: the wastewater enters a regulating tank for homogenizing and uniform treatment;

(2) first sodium chloride evaporative crystallization: feeding the homogenized and uniform amount of wastewater into the first sodium chloride evaporation crystallization device, evaporating and crystallizing to separate out sodium chloride, and stopping evaporation crystallization when the COD content in the sodium chloride mother liquor is more than or equal to 25000mg/L or the mass concentration ratio of chloride ions to nitrate ions is 1:2.2-1: 1; directly recycling the condensed water, and enabling the sodium chloride mother liquor to enter a sodium chloride mother liquor buffer pool;

the concentrated solution of nanofiltration water production mainly comprises sodium chloride and sodium nitrate, and simultaneously contains a small amount of organic matters, silicon dioxide and other impurities. With continuous concentration and crystallization, the contents of organic matters, silicon dioxide and the like are multiplied, and the content of sodium nitrate is also multiplied, so that the boiling point is increased, the evaporation capacity is reduced, and the purity of sodium chloride is influenced. Therefore, the COD content in the sodium chloride mother liquor and the mass concentration ratio of chloride ions to nitrate ions are controlled, so that sodium chloride is precipitated as much as possible under the condition that the boiling point rise is not increased, and the purity of the precipitated sodium chloride is ensured.

(3) Adding potassium chloride into the sodium chloride mother liquor to obtain a mixed solution: after sodium chloride mother liquor enters a sodium chloride mother liquor buffer tank, adding potassium chloride into the sodium chloride mother liquor buffer tank to obtain mixed liquor; the mass ratio of sodium nitrate to potassium chloride in the mixed solution is 1:0.95-1:1.2, and the mixed solution enters a freezing and crystallizing system;

(4) freezing to separate out potassium nitrate: the mixed solution enters a freezing crystallization system, potassium nitrate is separated out through freezing crystallization, and a potassium nitrate freezing mother solution enters a second sodium chloride evaporation crystallization system;

(5) and (3) evaporating and crystallizing potassium nitrate frozen mother liquor: the frozen potassium nitrate mother liquor enters a second sodium chloride evaporative crystallization system to be evaporated, crystallized and separated to obtain sodium chloride, condensed water is directly recycled, and 60-70% of the total mass of the sodium chloride mother liquor flows back to a sodium chloride mother liquor buffer pool; and the residual sodium chloride mother liquor enters a mixed salt evaporation crystallization system to evaporate and crystallize the mixed salt.

The frozen mother liquor of potassium nitrate gets into second sodium chloride evaporative crystallization system, and along with the continuous going on of evaporation, further concentration and precipitation sodium chloride, in-process potassium nitrate and impurity also can accumulate, for the purity of guaranteeing to precipitate out sodium chloride, need the regular discharge sodium chloride mother liquor. Meanwhile, in order to recycle sodium chloride and sodium nitrate in the system as much as possible and improve the recycling rate of the crystallized salt, part of sodium chloride mother liquor is refluxed in the system, and the impurity content in the refluxed mother liquor is further ensured to be maintained in a certain range.

Further, the quality-dividing crystallization treatment method for the high-salt-content wastewater further comprises a nanofiltration salt-dividing step between the wastewater homogenization and uniform-quantity treatment in the step (1) and the first sodium chloride evaporative crystallization in the step (2): the homogeneous and uniform amount of wastewater enters a nanofiltration system to carry out first-stage salt separation, the nanofiltration membrane adopts a conventional commercial nanofiltration membrane, the rejection rate of divalent salt reaches more than 99 percent, and the rejection effect of monovalent salt is almost not achieved. After nanofiltration treatment, the nanofiltration water production side mainly contains sodium chloride and sodium nitrate, and the nanofiltration concentrated water side mainly contains sodium sulfate, sodium chloride and sodium nitrate; the nanofiltration produced water enters the first sodium chloride evaporation crystallization device; and carrying out salt separation and crystallization treatment on the nanofiltration concentrated water.

Further, the salt separation and crystallization treatment of the nanofiltration concentrated water comprises the following steps: (1) removing COD by advanced oxidation; (2) freezing and crystallizing to separate out mirabilite; wherein,

(1) advanced oxidation to remove COD: the nanofiltration concentrated water enters an advanced oxidation system, organic matters in the water are removed by the advanced oxidation system, the COD content of the treated effluent is less than 1000mg/L, and the advanced oxidation effluent enters a mirabilite freezing crystallization system;

(2) freezing and crystallizing to separate out mirabilite: the high-grade oxidation effluent enters a mirabilite freezing crystallization system to be frozen to separate out mirabilite, and when the concentration of sulfate ions in the mirabilite freezing crystallization mother liquor is less than or equal to 15000mg/L, the freezing crystallization is terminated; the mirabilite enters a mirabilite melting or dissolving crystallization system to separate out sodium sulfate; refluxing 60-70% of the total mass of the mirabilite freezing crystallization mother liquor to a regulating tank; and the residual mirabilite freezing crystallization mother liquor enters a mixed salt evaporation crystallization system to evaporate and crystallize mixed salt.

After mirabilite crystals are separated out by freezing crystallization, the content of sodium sulfate in the frozen mother liquor is reduced, the frozen mother liquor flows back to the regulating reservoir, the mother liquor can be returned to the crystallization recycling system again, and then the mirabilite is separated out by freezing, so that the yield of the mirabilite can be improved, the yield of miscellaneous salt is reduced, and sodium chloride and sodium nitrate enriched in the frozen mother liquor can enter a sodium chloride evaporation crystallization system again for cyclic separation and recovery by backflow. And the content of the organic matters and other impurities enriched in the solution is gradually increased in the processes of continuous concentration and freezing circulation, so that a certain amount of mother liquor needs to be discharged to a mixed salt evaporation crystallization system, the organic matters in the frozen crystallization mother liquor are maintained, and the purity of the produced mirabilite is ensured.

Further, a second wastewater concentration step is included between the step (1) of removing COD through advanced oxidation and the step (2) of freezing, crystallizing and separating out mirabilite, the advanced oxidation effluent enters a second wastewater concentration device and is concentrated until TDS is more than 200000mg/L, and then the concentrated solution enters a mirabilite freezing and crystallizing system.

Further, a step of homogenizing and homogenizing wastewater concentration is also included between the wastewater homogenizing and homogenizing treatment in the step (1) and the first sodium chloride evaporative crystallization in the step (2), after the wastewater homogenizing and homogenizing is concentrated by the first wastewater concentration device, TDS reaches more than 100000mg/L, and then the wastewater enters the first sodium chloride evaporative crystallization device.

Further, a first evaporation concentration step is included between the step (3) of adding potassium chloride into the sodium chloride mother liquor to obtain a mixed liquor and the step (4) of freezing and separating out the potassium nitrate, and the mixed liquor enters an evaporation concentration system for concentration until the concentration is 180000mg/L or more and the TDS or less and 250000mg/L or less. Otherwise, part of sodium chloride is brought out in the later freezing process, so that the quality of potassium nitrate is reduced.

And further, a nanofiltration water production concentration step is also included between the nanofiltration salt separation step and the first sodium chloride evaporation crystallization step, after the nanofiltration water production is concentrated by a first wastewater concentration device, the TDS reaches more than 100000mg/L, and then the nanofiltration water production enters a first sodium chloride evaporation crystallization device for sodium chloride evaporation crystallization.

Further, a first evaporation concentration step is included between the step of adding potassium chloride into the sodium chloride mother liquor to obtain a mixed liquor and the step of freezing and separating out potassium nitrate, the mixed liquor enters an evaporation concentration system for concentration until the concentration is that TDS is more than or equal to 180000mg/L and less than or equal to 250000 mg/L.

Further, before the step (1), a pretreatment step is further included, specifically: the wastewater is pretreated by a high-density sedimentation tank, ultrafiltration, ion exchange resin and a carbon remover respectively to remove calcium and magnesium ions, particles, microorganisms, silicon dioxide and alkalinity in the wastewater; and (4) the wastewater after pretreatment enters an adjusting tank.

The boiling point of the solution is mainly related to the type, composition and operating pressure of the solution. When the pressure is constant, the vapor pressure of the solvent in the sodium chloride solution is reduced by the presence of the solute sodium chloride, and to achieve boiling, the temperature must be raised to increase the vapor pressure of the solvent. The boiling point of the solution is increased due to different contents of sodium chloride and sodium nitrate in the solution. For example, when the sodium chloride solution is evaporated under 101.325kPa, the sodium chloride mass fraction in the solution is 20.32%, that is, when the sodium chloride content is about 200000mg/L, the boiling point of the solution is 105 ℃ and the boiling point thereof is 5 ℃. As the evaporation process progresses, the content of sodium chloride in the solution gradually increases, and when the mass fraction of sodium chloride in the solution reaches 26.09%, namely the content of sodium chloride is about 260000mg/L, the boiling point of the solution is 107 ℃ and the boiling point rises to 7 ℃. When sodium chloride and sodium nitrate are present in the solution, the content of sodium nitrate also affects the boiling point of the solution. On the premise of ensuring the purity of sodium chloride, the content of sodium nitrate causes the difference of boiling point rise of 2-4 ℃ in evaporative crystallization design.

The invention has the advantages that:

1. firstly, a nanofiltration system is used for primary salt separation, and sodium chloride, sodium nitrate and sodium sulfate are separated into two streams of water; then, the mixed water of sodium chloride and sodium nitrate is firstly evaporated to obtain sodium chloride, potassium chloride is added for blending, potassium nitrate is separated out by freezing, and finally sodium chloride is separated out again by evaporation, so that the boiling point rise caused by sodium nitrate enrichment in the traditional salt separation process is avoided, the efficient separation of three crystal salts of sodium chloride, sodium nitrate and sodium sulfate is realized, and simultaneously sodium chloride and potassium nitrate with higher purity can be obtained;

2. the invention skillfully combines the nanofiltration salt separation with the cold-hot salt separation and the chemical composite reaction, realizes the primary separation of monovalent ions and divalent ions through the primary salt separation of nanofiltration, then cooperates with the composite reaction of medicaments, and the reflux of evaporation mother liquor and freezing mother liquor, and continuously enriches and separates nitrate ions in the wastewater from the nanofiltration water production side, and simultaneously increases the yield of sodium chloride, thereby achieving multiple purposes.

3. By means of evaporative crystallization, frozen crystallization, potassium chloride adding and blending and the like, the quality-classified crystallization of sodium chloride, sodium sulfate and potassium nitrate is effectively realized, high-purity crystalline salt is obtained, the phenomenon that sodium nitrate is discharged in the form of miscellaneous salt after being enriched in the traditional quality-classified crystallization process is changed, and the miscellaneous salt rate is reduced;

4. the method converts the sodium nitrate in the wastewater into the potassium nitrate which has high added value and large market space and can be used for fertilizers, and improves the economic value of byproducts and the economic benefit of enterprises. Meanwhile, sodium nitrate in the sodium chloride solution is continuously converted into potassium nitrate and separated out, so that the content of sodium nitrate in the solution is reduced, and the boiling point rise caused by the content of sodium nitrate is reduced. Therefore, when the evaporation system is designed and selected, parameters such as temperature rise and energy consumption of the compressor, area of the heat exchanger and the like can be changed, the investment and operation cost of the evaporation crystallization device are finally reduced, and the wastewater treatment cost is reduced;

5. the method has stable process operation, high purity of the produced sodium chloride and sodium sulfate, high yield of the crystallized salt and high quality of the crystallized salt can reach the standard, and realizes the resource utilization of the wastewater; the purity of the produced sodium chloride is more than 99 percent, the purity of the sodium sulfate is more than 99 percent, the purity of the potassium nitrate is more than 99 percent, and the yield of miscellaneous salts is less than or equal to 10 percent.

Description of the drawings:

in order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.

FIG. 1 is a schematic diagram of system connection in example 1.

FIG. 2 is a schematic diagram of system connection according to embodiment 2.

FIG. 3 is a schematic diagram of system connection according to embodiment 3.

FIG. 4 is a process flow diagram of example 4.

FIG. 5 is a flow chart of the process of examples 5-7.

The device comprises a pretreatment device 1, a high-density sedimentation tank 1-1, ultrafiltration 1-2, ion exchange resin 1-3, a carbon remover 1-4, an adjusting tank 2, a first wastewater concentration device 3, a nanofiltration system 4, a first sodium chloride evaporative crystallization device 5, a sodium chloride mother liquor cache tank 6, an evaporative concentration system 7, a potassium nitrate freezing crystallization system 8, a second sodium chloride evaporative crystallization system 9, a high-grade oxidation system 10, a second wastewater concentration device 11, a mirabilite freezing crystallization system 12, a mirabilite melting or dissolving crystallization system 13 and a miscellaneous salt evaporative crystallization system 14.

The specific implementation mode is as follows:

the technical solutions in the embodiments of the present invention will be clearly and completely described below, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Example 1: a high salt waste water quality-separating crystallization treatment system comprises a pretreatment device 1, an adjusting tank 2, a first waste water concentration device 3, a nanofiltration system 4, a first sodium chloride evaporative crystallization device 5, a sodium chloride mother liquor cache tank 6, an evaporative concentration system 7, a potassium nitrate freezing crystallization system 8, a second sodium chloride evaporative crystallization system 9, a high-grade oxidation system 10, a second waste water concentration device 11, a mirabilite freezing crystallization system 12, a mirabilite melting or dissolving crystallization system 13 and a miscellaneous salt evaporative crystallization system 14;

the pretreatment device 1 comprises a high-density sedimentation tank 1-1, an ultrafiltration 1-2, an ion exchange resin 1-3 and a carbon remover 1-4 which are connected in sequence; the water outlets of the carbon removers 1 to 4 are connected with the water inlet of the regulating tank 2. The pretreatment device 1 is used for removing calcium and magnesium ions, particles, microorganisms, silicon dioxide and alkalinity in wastewater.

The water outlet of the regulating tank 2 is connected with the water inlet of the nanofiltration system 4, the water outlet of the nanofiltration system 4 is connected with the water inlet of the first wastewater concentration device 3, and the concentrated water outlet of the first wastewater concentration device 3 is connected with the water inlet of the first sodium chloride evaporative crystallization device 5. Wherein, first waste water enrichment facility 3 can be high pressure reverse osmosis unit, disc formula reverse osmosis unit, electrodialysis device, forward osmosis unit, MVR or multiple-effect evaporation system, and the embodiment chooses for use high pressure reverse osmosis unit. The first sodium chloride evaporative crystallization device 5 may be any one or more of a multi-effect evaporative crystallization device, a TVR evaporative crystallization device, an MVR evaporative crystallization device, and a falling film + forced circulation evaporative crystallization device, and the MVR evaporative crystallization device is selected in this embodiment.

The sodium chloride evaporative crystallization mother liquor outlet of the first sodium chloride evaporative crystallization device 5 is connected with the sodium chloride mother liquor inlet of the sodium chloride mother liquor buffer pool 6, the liquid outlet of the sodium chloride mother liquor buffer pool 6 is connected with the liquid inlet of the evaporative concentration system 7, the concentrated solution outlet of the evaporative concentration system 7 is connected with the liquid inlet of the potassium nitrate evaporative crystallization system 8, the mother liquor outlet of the potassium nitrate evaporative crystallization system 8 is connected with the liquid inlet of the second sodium chloride evaporative crystallization system 9, the sodium chloride evaporative crystallization mother liquor outlet of the second sodium chloride evaporative crystallization system 9 is respectively connected with the sodium chloride mother liquor inlet of the sodium chloride mother liquor buffer pool 6 and the sodium chloride mother liquor inlet of the miscellaneous salt evaporative crystallization system 14. The evaporation concentration system 7 can adopt any one or more of multi-effect evaporation and MVR evaporation, and the multi-effect evaporation device is adopted in the embodiment. The potassium nitrate freezing and crystallizing system 8 may be any one or more of an FC continuous freezing and crystallizing device, an OSLO continuous freezing and crystallizing device, and a DTB continuous freezing and crystallizing device, and in this embodiment, an OSLO continuous freezing and crystallizing device is used. The second sodium chloride evaporative crystallization system 9 may be any one or more of a multi-effect evaporative crystallization device, a TVR evaporative crystallization device, an MVR evaporative crystallization device, and a falling film + forced circulation evaporative crystallization device, and in this embodiment, the multi-effect evaporative crystallization device is selected. The miscellaneous salt evaporative crystallization system 14 can be any one or more of a multi-effect evaporative crystallization device, a single-effect evaporative crystallization device, a spray drying device and a paddle drying device, and the multi-effect evaporative crystallization device is selected in the embodiment.

A concentrated water outlet of the nanofiltration system 4 is connected with a water inlet of the advanced oxidation system 10, a water outlet of the advanced oxidation system 10 is connected with a water inlet of the second wastewater concentration device 11, a concentrated water outlet of the second wastewater concentration device 11 is connected with a water inlet of the mirabilite freezing and crystallizing system 12, and a freezing mother liquor outlet of the mirabilite freezing and crystallizing system 12 is respectively connected with a water inlet of the regulating tank 2 and a freezing mother liquor inlet of the miscellaneous salt evaporative crystallization system 14; the mirabilite outlet of the mirabilite freezing and crystallizing system 12 is connected with the feed inlet of the mirabilite melting or dissolving and crystallizing system 13.

The advanced oxidation system 10 may select any one or more of catalytic oxidation with ozone, electrocatalytic oxidation, multi-element synergetic catalytic oxidation, fenton oxidation, wet catalytic oxidation, and ultraviolet catalytic oxidation, and the catalytic oxidation with ozone is selected in this embodiment. The second wastewater concentration device 11 may be any one or more of a multi-effect evaporation crystallization device, a TVR evaporation crystallization device, an MVR evaporation crystallization device, and a falling film + forced circulation evaporation crystallization device, and the MVR evaporation crystallization device is selected in this embodiment. The mirabilite freezing and crystallizing system 12 may be any one or more of an FC continuous freezing and crystallizing device, an OSLO continuous freezing and crystallizing device, and a DTB continuous freezing and crystallizing device, and in this embodiment, an OSLO continuous freezing and crystallizing device is used. The mirabilite melting or dissolving crystallization system 13 may be any one or more of a multiple-effect evaporation crystallization device, a TVR evaporation crystallization device, and an MVR evaporation crystallization device, and in this embodiment, the multiple-effect evaporation crystallization device is selected.

Example 2: a high salt-containing wastewater quality-divided crystallization treatment system comprises an adjusting tank 2, a first sodium chloride evaporative crystallization device 5, a sodium chloride mother liquor cache tank 6, a potassium nitrate freezing crystallization system 8, a second sodium chloride evaporative crystallization system 9 and a miscellaneous salt evaporative crystallization system 14;

the water outlet of the regulating tank 2 is connected with the water inlet of the first sodium chloride evaporative crystallization device 5. The first sodium chloride evaporative crystallization device 5 can be any one or more of a multi-effect evaporative crystallization melting crystallization device, a TVR evaporative crystallization melting crystallization device, an MVR evaporative crystallization melting crystallization device, and a falling film + MVR forced circulation evaporative crystallization melting crystallization device, and the falling film + MVR forced circulation evaporative crystallization device is selected in the embodiment.

The sodium chloride evaporative crystallization mother liquor outlet of the first sodium chloride evaporative crystallization device 5 is connected with the sodium chloride mother liquor inlet of the sodium chloride mother liquor cache pool 6, the liquid outlet of the sodium chloride mother liquor cache pool 6 is connected with the liquid inlet of the potassium nitrate freezing crystallization system 8, the mother liquor outlet of the potassium nitrate freezing crystallization system 8 is connected with the liquid inlet of the second sodium chloride evaporative crystallization system 9, and the sodium chloride evaporative crystallization mother liquor outlet of the second sodium chloride evaporative crystallization system 9 is respectively connected with the sodium chloride mother liquor inlet of the sodium chloride mother liquor cache pool 6 and the sodium chloride mother liquor inlet of the miscellaneous salt evaporative crystallization system 14. The potassium nitrate freezing and crystallizing system 8 may be any one or more of an FC continuous freezing and crystallizing device, an OSLO continuous freezing and crystallizing device, and a DTB continuous freezing and crystallizing device, and in this embodiment, an FC continuous freezing and crystallizing device is used. The second sodium chloride evaporative crystallization system 9 may be any one or more of a multi-effect evaporative crystallization device, a TVR evaporative crystallization device, an MVR evaporative crystallization device, and a falling film + MVR forced circulation evaporative crystallization device, and the multi-effect evaporative crystallization device is selected in this embodiment. The miscellaneous salt evaporative crystallization system 14 may be any one or more of multiple-effect evaporative crystallization, single-effect evaporative crystallization, a spray drying device, and a paddle drying device, and in this embodiment, the spray drying device is used.

Example 3: a high salt waste water quality-separating crystallization treatment system comprises a pretreatment device 1, an adjusting tank 2, a nanofiltration system 4, a first sodium chloride evaporative crystallization device 5, a sodium chloride mother liquor cache tank 6, a potassium nitrate freezing crystallization system 8, a second sodium chloride evaporative crystallization system 9, an advanced oxidation system 10, a mirabilite freezing crystallization system 12, a mirabilite melting or dissolving crystallization system 13 and a miscellaneous salt evaporative crystallization system 14;

The water outlet of the regulating tank 2 is connected with the water inlet of the nanofiltration system 4, and the water outlet of the nanofiltration system 4 is connected with the water inlet of the first sodium chloride evaporative crystallization device 5. Wherein, the first sodium chloride evaporative crystallization device 5 can select a multi-effect evaporative crystallization device, a TVR evaporative crystallization device, an MVR evaporative crystallization device, a falling film + MVR forced circulation evaporative crystallization device, and the embodiment selects the multi-effect evaporative crystallization device.

The sodium chloride evaporative crystallization mother liquor outlet of the first sodium chloride evaporative crystallization device 5 is connected with the sodium chloride mother liquor inlet of the sodium chloride mother liquor cache pool 6, the liquid outlet of the sodium chloride mother liquor cache pool 6 is connected with the liquid inlet of the potassium nitrate freezing crystallization system 8, the mother liquor outlet of the potassium nitrate freezing crystallization system 8 is connected with the liquid inlet of the second sodium chloride evaporative crystallization system 9, and the sodium chloride evaporative crystallization mother liquor outlet of the second sodium chloride evaporative crystallization system 9 is respectively connected with the sodium chloride mother liquor inlet of the sodium chloride mother liquor cache pool 6 and the sodium chloride mother liquor inlet of the miscellaneous salt evaporative crystallization system 14. The potassium nitrate freezing and crystallizing system 8 may be an FC continuous freezing and crystallizing device, an OSLO continuous freezing and crystallizing device, or a DTB continuous freezing and crystallizing device, but in this embodiment, a DTB continuous freezing and crystallizing device is used. The second sodium chloride evaporative crystallization system 9 may be any one or more of a multiple-effect evaporative crystallization device, a TVR evaporative crystallization device, an MVR evaporative crystallization device, and a falling film + MVR forced circulation evaporative crystallization device, and the TVR evaporative crystallization device is selected in this embodiment. The miscellaneous salt evaporative crystallization system 14 may be any one or more of a multi-effect evaporative crystallization device, a single-effect evaporative crystallization device, a spray drying device, and a paddle drying device, and in this embodiment, the single-effect evaporative crystallization device is selected.

A concentrated water outlet of the nanofiltration system 4 is connected with a water inlet of the advanced oxidation system 10, a water outlet of the advanced oxidation system 10 is connected with a water inlet of the mirabilite freezing and crystallizing system 12, and a freezing mother liquor outlet of the mirabilite freezing and crystallizing system 12 is respectively connected with a water inlet of the regulating tank 2 and a freezing mother liquor inlet of the miscellaneous salt evaporative crystallization system 14; the mirabilite outlet of the mirabilite freezing and crystallizing system 12 is connected with the feed inlet of the mirabilite melting or dissolving and crystallizing system 13.

The advanced oxidation system 10 may select any one or more of ozone catalytic oxidation, electrocatalytic oxidation, multi-element synergetic catalytic oxidation, fenton oxidation, wet catalytic oxidation, and ultraviolet catalytic oxidation, and in this embodiment, the electrocatalytic oxidation is selected. The mirabilite freezing and crystallizing system 12 may be any one or more of an FC continuous freezing and crystallizing device, an OSLO continuous freezing and crystallizing device, and a DTB continuous freezing and crystallizing device, and in this embodiment, an OSLO continuous freezing and crystallizing device is used. The mirabilite melting or dissolving crystallization system 13 may be any one or more of multiple-effect evaporation crystallization, TVR evaporation crystallization, and MVR evaporation crystallization, and the MVR evaporation crystallization device is used in this embodiment.

Example 4:

the quality-divided crystallization treatment method for the high-salt-content wastewater by using the system of the embodiment 2 comprises the following steps: (1) homogenizing and uniformly treating the wastewater; (2) evaporating and crystallizing the first sodium chloride; (3) adding potassium chloride into the sodium chloride mother liquor to obtain a mixed liquor; (4) freezing to separate out potassium nitrate; (5) evaporating and crystallizing the frozen potassium nitrate mother liquor; wherein,

(1) homogenizing and uniformly treating the wastewater: the wastewater enters a regulating tank for homogenizing and uniform treatment; the specific water quality is as follows;

quality of water	TDS(mg/L)	NaCl(mg/L)	Na₂SO₄(mg/L)	NaNO₃(mg/L)	COD(mg/L)
						Inflow water	97500	84500	120	12850	200

(2) First sodium chloride evaporative crystallization: feeding the homogenized and uniform amount of wastewater into the first sodium chloride evaporation crystallization device, evaporating and crystallizing to separate out sodium chloride, and stopping evaporation crystallization when the mass concentration ratio of chloride ions to nitrate ions in sodium chloride mother liquor is 1: 1.9; directly recycling the condensed water, and enabling the sodium chloride mother liquor to enter a sodium chloride mother liquor buffer pool;

the main components of the wastewater are sodium chloride and sodium nitrate, and the wastewater simultaneously contains a small amount of organic matters, silicon dioxide and other impurities. With continuous concentration and crystallization, the contents of organic matters, silicon dioxide and the like are multiplied, and the content of sodium nitrate is also multiplied, so that the boiling point is increased, the evaporation capacity is reduced, and the purity of sodium chloride is influenced. Therefore, the mass concentration ratio of the chloride ions to the nitrate ions is controlled, so that the sodium chloride is precipitated as much as possible under the condition of ensuring that the boiling point rise is not increased, and the purity of the precipitated sodium chloride is ensured.

The water quality of the sodium chloride mother liquor in the step is as follows:

quality of water	TDS(mg/L)	NaCl(mg/L)	Na₂SO₄(mg/L)	NaNO₃(mg/L)
					Mother liquor of sodium chloride	425000	165000	2400	257000

(3) Adding potassium chloride into the sodium chloride mother liquor to obtain a mixed solution: after sodium chloride mother liquor enters a sodium chloride mother liquor buffer tank, adding potassium chloride into the sodium chloride mother liquor buffer tank to obtain mixed liquor; the mass ratio of sodium nitrate to potassium chloride in the mixed solution is 1:0.95, and the mixed solution enters a freezing and crystallizing system;

(5) and (3) evaporating and crystallizing potassium nitrate frozen mother liquor: the frozen potassium nitrate mother liquor enters a second sodium chloride evaporative crystallization system to be evaporated, crystallized and separated to obtain sodium chloride, condensed water is directly recycled, and 70 percent of the total mass of the sodium chloride mother liquor flows back to a sodium chloride mother liquor buffer pool; and the residual sodium chloride mother liquor enters a mixed salt evaporation crystallization system to evaporate and crystallize the mixed salt.

The frozen mother liquor of potassium nitrate gets into second sodium chloride evaporative crystallization system, and along with the continuous going on of evaporation, further concentration and precipitation sodium chloride, in-process potassium nitrate and impurity also can accumulate, for the purity of guaranteeing to precipitate out sodium chloride, need the mother liquor of regularly discharging. Meanwhile, in order to recycle sodium chloride and sodium nitrate in the system as much as possible and improve the recycling rate of the crystallized salt, part of the evaporated and crystallized mother liquor in the system is refluxed, and the impurity content in the refluxed mother liquor is further ensured to be maintained in a certain range.

In the step, the water quality of the sodium chloride mother liquor of the second sodium chloride evaporation crystallization system is as follows:

example 4 comparative example: the quality and the inflow of the inflow water of the embodiment are the same as those of the embodiment 4, and the method comprises the following steps: (1) homogenizing and uniformly treating the wastewater; (2) evaporating and crystallizing sodium chloride; wherein,

(1) homogenizing and uniformly treating the wastewater: the wastewater enters a regulating tank for homogenizing and uniform treatment; the water amount is 100m³The specific water quality is as follows:

quality of water	TDS(mg/L)	NaCl(mg/L)	Na₂SO₄(mg/L)	NaNO3(mg/L)	COD(mg/L)
						Inflow water	97500	84500	120	12850	200

(2) Sodium chloride evaporative crystallization: feeding the homogenized and uniform amount of wastewater into the first sodium chloride evaporation crystallization device, and evaporating and crystallizing to separate out sodium chloride; the condensed water is directly recycled, and the sodium chloride mother liquor enters a mixed salt evaporation crystallization system to be evaporated and crystallized to obtain mixed salt.

to process 100m³The effluent, example 4, is compared to the comparative example of example 4, and comparative data on product purity and production cost are shown in the following table:

example 4 comparative example compared with example 4, without the steps of adding potassium chloride and precipitating potassium nitrate, sodium nitrate was completely incorporated into the mixed saltThe yield is obviously increased, and the yield of sodium chloride is reduced. In the embodiment, according to the market prices of various industrial salts, the selling price of sodium chloride per ton is 200 yuan, the selling price of potassium nitrate per ton is 4000 yuan, the selling price of potassium chloride per ton is 2400 yuan, the treatment cost of miscellaneous salt is 3000 yuan per ton, and the treatment cost is 100m³Compared with the comparative example 4, the wastewater of the example 4 saves the comprehensive treatment cost of 6730-.

Example 5: the method for performing the quality-divided crystallization treatment on the high-salt-content wastewater by using the system in the embodiment 1 comprises the following steps:

(1) wastewater pretreatment: the wastewater is pretreated by a high-density sedimentation tank, ultrafiltration, ion exchange resin and a carbon remover respectively to remove calcium and magnesium ions, particles, microorganisms, silicon dioxide and alkalinity in the wastewater; and (4) the wastewater after pretreatment enters an adjusting tank.

The design water quantity is 100m³The water quality of inlet water and outlet water of the pretreatment is shown in the following table:

(2) homogenizing and uniformly treating pretreated wastewater: the pretreated wastewater enters a regulating tank for homogenizing and uniform treatment;

(3) and (3) nanofiltration salt separation: the homogeneous and uniform amount of wastewater enters a nanofiltration system to carry out first-stage salt separation, the nanofiltration membrane adopts a conventional commercial nanofiltration membrane, the rejection rate of divalent salt reaches more than 99 percent, and the rejection effect of monovalent salt is almost not achieved. After nanofiltration treatment, the nanofiltration water production side mainly contains sodium chloride and sodium nitrate, and the nanofiltration concentrated water side mainly contains sodium sulfate, sodium chloride and sodium nitrate; the nanofiltration produced water enters a first wastewater concentration device; and carrying out salt separation and crystallization treatment on the nanofiltration concentrated water.

The nanofiltration concentrated water and the produced water have the following quality:

quality of water	TDS(mg/L)	NaCl(mg/L)	Na₂SO₄(mg/L)	NaNO₃(mg/L)
					Nanofiltration concentrated water	81857	25582	51139	5136
Nanofiltration water production	38972	32042	189	6741

(4) And (4) nanofiltration water production concentration: after the nanofiltration produced water is concentrated by the first wastewater concentration device, the TDS reaches more than 100000mg/L, and then the nanofiltration produced water enters the first sodium chloride evaporative crystallization device to carry out sodium chloride evaporative crystallization.

And (3) carrying out nanofiltration on the concentrated water:

(5) first sodium chloride evaporative crystallization: the concentrated nanofiltration produced water enters the first sodium chloride evaporation crystallization device, partial sodium chloride is separated by evaporation crystallization at 95 ℃, and when the mass concentration ratio of chloride ions to nitrate ions in the sodium chloride mother liquor is 1:1.8, the evaporation crystallization is stopped; directly recycling the condensed water, and enabling the sodium chloride mother liquor to enter a sodium chloride mother liquor buffer pool;

The water quality of the sodium chloride mother liquor generated by evaporating and crystallizing the first sodium chloride in the step is as follows:

quality of water	TDS(mg/L)	NaCl(mg/L)	Na₂SO₄(mg/L)	NaNO₃(mg/L)
					Mother liquor of sodium chloride	417000	165000	6873	245127

(6) Adding potassium chloride into the sodium chloride mother liquor to obtain a mixed solution: after sodium chloride mother liquor enters a sodium chloride mother liquor buffer tank, adding potassium chloride into the sodium chloride mother liquor buffer tank to obtain mixed liquor; the mass ratio of sodium nitrate to potassium chloride in the mixed solution is 1:0.98, and the mixed solution is fed into an evaporation concentration system;

(7) first evaporation and concentration: and the mixed solution enters an evaporation concentration system for concentration to 240000 mg/L. Otherwise, part of sodium chloride is brought out in the later freezing process, so that the quality of potassium nitrate is reduced.

(8) Freezing to separate out potassium nitrate: the concentrated mixed solution enters a freezing crystallization system, potassium nitrate is separated out through freezing crystallization, and the frozen potassium nitrate mother solution enters a second sodium chloride evaporation crystallization system;

(9) and (3) evaporating and crystallizing potassium nitrate frozen mother liquor: the frozen potassium nitrate mother liquor enters a second sodium chloride evaporative crystallization system to be evaporated, crystallized and separated to obtain sodium chloride, condensed water is directly recycled, and 70 percent of the total mass of the sodium chloride mother liquor flows back to a sodium chloride mother liquor buffer pool; and the residual sodium chloride mother liquor enters a mixed salt evaporation crystallization system to evaporate and crystallize the mixed salt. The frozen mother liquor of potassium nitrate gets into second sodium chloride evaporative crystallization system, and along with the continuous going on of evaporation, further concentration and precipitation sodium chloride, in-process potassium nitrate and impurity also can accumulate, for the purity of guaranteeing to precipitate out sodium chloride, need the mother liquor of regularly discharging. Meanwhile, in order to recycle sodium chloride and sodium nitrate in the system as much as possible and improve the recycling rate of the crystallized salt, part of the evaporated and crystallized mother liquor in the system is refluxed, and the impurity content in the refluxed mother liquor is further ensured to be maintained in a certain range.

The water quality of the sodium chloride mother liquor generated by evaporating and crystallizing the second sodium chloride in the step is as follows:

(10) the salt separation and crystallization treatment of the nanofiltration concentrated water comprises the following steps:

I. advanced oxidation to remove COD: the nanofiltration concentrated water enters an advanced oxidation system, organic matters in the water are removed by the advanced oxidation system, the COD content of the treated effluent is less than 1000mg/L, and the advanced oxidation effluent enters a second wastewater concentration device;

the quality of the advanced oxidation inlet water and the advanced oxidation outlet water is as follows:

quality of water	Advanced oxidation feed water	High grade oxidation effluent
			COD(mg/L)	580	270

II. A second wastewater concentration step: the advanced oxidation effluent enters a second wastewater concentration device, the TDS is concentrated to 224000mg/L, and then the concentrated solution enters a mirabilite freezing crystallization system;

III, freezing and crystallizing to separate out mirabilite: the concentrated solution enters a mirabilite freezing and crystallizing system, mirabilite is separated out by circulating freezing at the temperature of 0 ℃, and freezing and crystallizing are terminated when the concentration of sulfate ions in the mirabilite freezing and crystallizing mother solution reaches 14738 mg/L; introducing mirabilite into a mirabilite melting or dissolving crystallization system, and evaporating and crystallizing at 95 ℃ to separate sodium sulfate; refluxing 70 percent of the total mass of the mirabilite freezing and crystallizing mother liquor to the regulating tank; and the residual mirabilite freezing crystallization mother liquor enters a mixed salt evaporation crystallization system to evaporate and crystallize mixed salt.

The water quality of the mirabilite freezing crystallization mother liquor in the step is as follows:

example 6:

the method for performing the quality-divided crystallization treatment on the high-salt-content wastewater by using the system in the embodiment 1 comprises the following steps:

(1) wastewater pretreatment: respectively pretreating the wastewater by a high-density sedimentation tank, ultrafiltration, ion exchange resin and a carbon remover to remove alkaline substances such as calcium and magnesium ions, particles, microorganisms, silicon dioxide, alkalinity and the like in the wastewater; and (4) the wastewater after pretreatment enters an adjusting tank.

The water quality of the inlet water and the outlet water of the pretreatment is shown in the following table:

(4) And (4) nanofiltration water production concentration: after the nanofiltration produced water is concentrated by the first wastewater concentration device, the TDS can reach 100000mg/L, and then the nanofiltration produced water enters the first sodium chloride evaporation crystallization device for sodium chloride evaporation crystallization.

And (3) carrying out nanofiltration on the concentrated water:

(5) first sodium chloride evaporative crystallization: the concentrated nanofiltration produced water enters the first sodium chloride evaporation crystallization device, partial sodium chloride is separated by evaporation crystallization at 95 ℃, and when the mass concentration ratio of chloride ions to nitrate ions in the sodium chloride mother liquor is 1:2, the evaporation crystallization is stopped; directly recycling the condensed water, and enabling the sodium chloride mother liquor to enter a sodium chloride mother liquor buffer pool;

quality of water	TDS(mg/L)	NaCl(mg/L)	Na₂SO₄(mg/L)	NaNO₃(mg/L)
					Mother liquor of sodium chloride	443747	166200	7569	269977

(6) Adding potassium chloride into the sodium chloride mother liquor to obtain a mixed solution: after sodium chloride mother liquor enters a sodium chloride mother liquor buffer tank, adding potassium chloride into the sodium chloride mother liquor buffer tank to obtain mixed liquor; the mass ratio of sodium nitrate to potassium chloride in the mixed solution is 1:1, and the mixed solution enters an evaporation concentration system;

(7) first evaporation and concentration: and the mixed liquor enters an evaporation concentration system for concentration until the TDS of the solution is 24000 mg/L. Otherwise, part of sodium chloride is brought out in the later freezing process, so that the quality of potassium nitrate is reduced.

(9) and (3) evaporating and crystallizing potassium nitrate frozen mother liquor: the frozen potassium nitrate mother liquor enters a second sodium chloride evaporative crystallization system to be evaporated, crystallized and separated to obtain sodium chloride, condensed water is directly recycled, and 65 percent of the total mass of the sodium chloride mother liquor flows back to a sodium chloride mother liquor buffer pool; and the residual sodium chloride mother liquor enters a mixed salt evaporation crystallization system to evaporate and crystallize the mixed salt.

II. A second wastewater concentration step: the advanced oxidation effluent enters a second wastewater concentration device, the TDS is concentrated to 228000mg/L, and then the concentrated solution enters a mirabilite freezing crystallization system;

III, freezing and crystallizing to separate out mirabilite: the concentrated solution enters a mirabilite freezing and crystallizing system, mirabilite is separated out by circulating freezing at the temperature of 0 ℃, and when the concentration of sulfate ions in the mirabilite freezing and crystallizing mother solution is 13800mg/L, the freezing and crystallizing are stopped; introducing mirabilite into a mirabilite melting or dissolving crystallization system, and evaporating and crystallizing at 95 ℃ to separate sodium sulfate; 65 percent of the total mass of the mirabilite freezing crystallization mother liquor flows back to the regulating tank; and the residual mirabilite freezing crystallization mother liquor enters a mixed salt evaporation crystallization system to evaporate and crystallize mixed salt.

example 7: the method for performing the quality-divided crystallization treatment on the high-salt-content wastewater by using the system in the embodiment 1 comprises the following steps:

And (3) carrying out nanofiltration on the concentrated water:

(5) first sodium chloride evaporative crystallization: the concentrated nanofiltration produced water enters the first sodium chloride evaporation crystallization device, partial sodium chloride is separated by evaporation crystallization at 95 ℃, and when the mass concentration ratio of chloride ions to nitrate ions in the sodium chloride mother liquor is 1:2.2, the evaporation crystallization is stopped; directly recycling the condensed water, and enabling the sodium chloride mother liquor to enter a sodium chloride mother liquor buffer pool;

quality of water	TDS(mg/L)	NaCl(mg/L)	Na₂SO₄(mg/L)	NaNO₃(mg/L)
					Mother liquor of sodium chloride	471200	163200	8400	299600

(6) Adding potassium chloride into the sodium chloride mother liquor to obtain a mixed solution: after sodium chloride mother liquor enters a sodium chloride mother liquor buffer tank, adding potassium chloride into the sodium chloride mother liquor buffer tank to obtain mixed liquor; the mass ratio of sodium nitrate to potassium chloride in the mixed solution is 1:1.2, and the mixed solution is fed into an evaporation concentration system;

(7) first evaporation and concentration: and the mixed liquor enters an evaporation concentration system for concentration until the TDS of the solution reaches 239000 mg/L. Otherwise, part of sodium chloride is brought out in the later freezing process, so that the quality of potassium nitrate is reduced.

(9) and (3) evaporating and crystallizing potassium nitrate frozen mother liquor: the frozen potassium nitrate mother liquor enters a second sodium chloride evaporative crystallization system to be evaporated, crystallized and separated to obtain sodium chloride, condensed water is directly recycled, and 60 percent of the total mass of the sodium chloride mother liquor flows back to a sodium chloride mother liquor buffer pool; and the residual sodium chloride mother liquor enters a mixed salt evaporation crystallization system to evaporate and crystallize the mixed salt.

II. A second wastewater concentration step: the advanced oxidation effluent enters a second wastewater concentration device, is concentrated until TDS reaches 214000mg/L, and then the concentrated solution enters a mirabilite freezing crystallization system;

III, freezing and crystallizing to separate out mirabilite: the concentrated solution enters a mirabilite freezing and crystallizing system, mirabilite is separated out by circulating freezing at the temperature of 0 ℃, and freezing and crystallizing are stopped when the concentration of sulfate ions in the mirabilite freezing and crystallizing mother solution is 12000 mg/L; introducing mirabilite into a mirabilite melting or dissolving crystallization system, and evaporating and crystallizing at 95 ℃ to separate sodium sulfate; refluxing 60 percent of the total mass of the mirabilite freezing and crystallizing mother liquor to the regulating tank; and the residual mirabilite freezing crystallization mother liquor enters a mixed salt evaporation crystallization system to evaporate and crystallize mixed salt.

example 8: this example is different from example 5 in that the first sodium chloride evaporation crystallization in step (5) was not performed, and the other steps were completely the same.

Example 9: the difference between the embodiment and the embodiment 5 is that the sodium chloride mother liquor in the step (9) is completely discharged into a miscellaneous salt evaporative crystallization system; in the step (10), all the mirabilite freezing crystallization mother liquor is discharged into a miscellaneous salt evaporation crystallization system, and miscellaneous salt is evaporated and crystallized, and other steps are completely the same as those in the example 4.

Examples 5 to 9 were compared to treat 100m³The comparative data of the wastewater meter, the product purity and the production cost are shown in the following table:

example 8 compared with example 5, the yield of sodium sulfate was not significantly changed, the yield of potassium nitrate and sodium chloride was reduced, the yield of total salt was reduced, the yield of miscellaneous salt was increased, and the water treatment cost was increased. The selling price of sodium chloride per ton is 200 yuan, the selling price of sodium sulfate per ton is 300 yuan, the selling price of potassium nitrate per ton is 4000 yuan, the selling price of potassium chloride per ton is 2400 yuan, the treatment cost of miscellaneous salt is 3000 yuan per ton, and the treatment cost is 100m³Waste water, example 5, saves the cost of waste water treatment 410 yuan compared with example 8.

In example 9, the yields of sodium chloride and sodium sulfate were significantly reduced, the yields of miscellaneous salts were significantly increased, and the water treatment costs were significantly increased, as compared with example 5.

The above embodiments are illustrative and not restrictive of the present invention, and several embodiments may be enumerated in accordance with the scope of the definitions set forth, so that changes and modifications may be made without departing from the general concept of the present invention and fall within the scope of the present invention.

Claims

1. The system for treating the high-salt-content wastewater through the fractional crystallization is characterized by comprising an adjusting tank, a first sodium chloride evaporative crystallization system, a sodium chloride mother liquor cache tank, a potassium nitrate frozen crystallization system, a second sodium chloride evaporative crystallization system and a miscellaneous salt evaporative crystallization system;

2. The system for treating high-salinity wastewater through fractional crystallization according to claim 1, further comprising a nanofiltration system, wherein the water outlet of the regulating tank is connected with the water inlet of the nanofiltration system, and the water outlet of the nanofiltration system is connected with the water inlet of the first sodium chloride evaporative crystallization system.

3. The system for treating the high-salinity wastewater through the fractional crystallization according to claim 2, characterized by further comprising an advanced oxidation system, a mirabilite freezing and crystallizing system and a mirabilite melting or dissolving and crystallizing system; a concentrated water outlet of the nanofiltration system is connected with a water inlet of the advanced oxidation system, a water outlet of the advanced oxidation system is connected with a water inlet of the mirabilite freezing and crystallizing system, and a freezing mother liquor outlet of the mirabilite freezing and crystallizing system is respectively connected with a water inlet of the regulating tank and a freezing mother liquor inlet of the miscellaneous salt evaporative crystallization system; and a mirabilite outlet of the mirabilite freezing and crystallizing system is connected with a feed inlet of the mirabilite melting or dissolving and crystallizing system.

4. The system for treating the high-salinity wastewater through fractional crystallization according to claim 2 or 3, characterized by further comprising a pretreatment device, wherein the pretreatment device comprises a high-density sedimentation tank, ultrafiltration, ion exchange resin and a carbon remover which are connected in sequence; and the water outlet of the carbon remover is connected with the water inlet of the regulating tank.

5. The system for treating high-salinity wastewater by fractional crystallization according to claim 1, characterized by further comprising a first wastewater concentration device; and the water outlet of the regulating tank is connected with the water inlet of the first wastewater concentration device, and the concentrated water outlet of the first wastewater concentration device is connected with the water inlet of the first sodium chloride evaporative crystallization system.

6. The system for fractional crystallization treatment of wastewater containing high salt content according to claim 5, wherein the first wastewater concentration device is any one of a high pressure reverse osmosis device, a disc reverse osmosis device, an electrodialysis device, a forward osmosis device, an MVR or a multi-effect evaporation system.

7. The system for treating the high-salinity wastewater through fractional crystallization according to claim 1, 5 or 6, characterized by further comprising an evaporation concentration system; the liquid outlet of sodium chloride mother liquor buffer pool with the inlet of evaporative concentration system is connected, the concentrate export of evaporative concentration system with the inlet of potassium nitrate freeze crystallization system is connected.

8. The system for treating the high-salinity wastewater through fractional crystallization according to claim 2, characterized by further comprising a first wastewater concentration device; and a water outlet of the nanofiltration system is connected with a water inlet of the first wastewater concentration device, and a concentrated water outlet of the first wastewater concentration device is connected with a water inlet of the first sodium chloride evaporative crystallization system.

9. The system for fractional crystallization treatment of wastewater containing high salt content according to claim 8, wherein the first wastewater concentration device is any one of a high pressure reverse osmosis device, a disc reverse osmosis device, an electrodialysis device, a forward osmosis device, an MVR or a multi-effect evaporation system.

10. The system for treating the high-salinity wastewater by fractional crystallization according to claim 8 or 9, characterized by further comprising an evaporation concentration system; the liquid outlet of sodium chloride mother liquor buffer pool with the inlet of evaporative concentration system is connected, the concentrate export of evaporative concentration system with the inlet of potassium nitrate freeze crystallization system is connected.

11. The system for treating high-salinity wastewater by fractional crystallization according to claim 3, characterized by further comprising a second wastewater concentration device; and the water outlet of the advanced oxidation system is connected with the water inlet of the second wastewater concentration device, and the concentrated water outlet of the second wastewater concentration device is connected with the water inlet of the mirabilite freezing and crystallizing system.

12. The method for treating the high-salt-content wastewater through mass separation and crystallization is characterized by comprising the following steps of: (1) homogenizing and uniformly treating the wastewater; (2) evaporating and crystallizing the first sodium chloride; (3) adding potassium chloride into the sodium chloride mother liquor to obtain a mixed liquor; (4) freezing to separate out potassium nitrate; (5) evaporating and crystallizing the frozen potassium nitrate mother liquor; wherein,

(2) first sodium chloride evaporative crystallization: the homogenized and uniform amount of wastewater enters the first sodium chloride evaporative crystallization system, sodium chloride is separated out through evaporative crystallization, and when the COD content in the sodium chloride mother liquor is more than or equal to 25000mg/L or the mass concentration ratio of chloride ions to nitrate ions is 1:2.2-1:1, the evaporative crystallization is stopped; directly recycling the condensed water, and enabling the sodium chloride mother liquor to enter a sodium chloride mother liquor buffer pool;

13. The method for treating wastewater with high salt content by fractional crystallization according to claim 12, further comprising a salt nanofiltration step between the step (1) of wastewater homogeneous and uniform treatment and the step (2) of first sodium chloride evaporative crystallization: the homogeneous and uniform amount of wastewater enters a nanofiltration system to be subjected to first-stage salt separation, and after nanofiltration treatment, the nanofiltration water production side mainly contains sodium chloride and sodium nitrate, and the nanofiltration concentrated water side mainly contains sodium sulfate, sodium chloride and sodium nitrate; the nanofiltration produced water enters the first sodium chloride evaporative crystallization system; and carrying out salt separation and crystallization treatment on the nanofiltration concentrated water.

14. The method for treating the high-salinity wastewater through fractional crystallization according to claim 13, wherein the step of subjecting the nanofiltration concentrated water to fractional crystallization comprises the following steps: (1) removing COD by advanced oxidation; (2) freezing and crystallizing to separate out mirabilite; wherein,

15. The method according to claim 14, wherein a second wastewater concentration step is further included between the step (1) of removing COD by advanced oxidation and the step (2) of freezing and crystallizing to separate out mirabilite, the effluent of advanced oxidation enters a second wastewater concentration device and is concentrated to TDS > 200000mg/L, and then the concentrated solution enters the mirabilite freezing and crystallizing system.

16. The method for treating wastewater containing high salt content by fractional crystallization according to claim 12, further comprising a step of concentrating wastewater with uniform concentration between the step (1) of wastewater with uniform concentration and the step (2) of first sodium chloride evaporative crystallization, wherein after the wastewater with uniform concentration is concentrated by the first wastewater concentration device, the TDS is more than 100000mg/L, and then the wastewater enters the first sodium chloride evaporative crystallization system.

17. The method for treating the high-salinity wastewater through fractional crystallization according to claim 12 or 16, wherein a first evaporation concentration step is further included between the step (3) of adding potassium chloride into the sodium chloride mother liquor to obtain a mixed liquor and the step (4) of freezing and separating out potassium nitrate, and the mixed liquor enters an evaporation concentration system for concentration until the concentration is 180000mg/L to 250000 mg/L.

18. The method for treating wastewater with high salinity according to any one of claims 13-15, characterized by further comprising a nanofiltration product water concentration step between the nanofiltration salt separation step and the first sodium chloride evaporative crystallization step, wherein after the nanofiltration product water is concentrated by the first wastewater concentration device, the TDS reaches more than 100000mg/L, and then the concentrated product water enters the first sodium chloride evaporative crystallization system to perform sodium chloride evaporative crystallization.

19. The method for treating the high-salinity wastewater through the fractional crystallization according to any one of claims 13 to 15, wherein a first evaporation concentration step is further included between the step of adding potassium chloride to sodium chloride mother liquor to obtain a mixed liquor and the step of freezing to precipitate potassium nitrate, and the mixed liquor is concentrated in an evaporation concentration system until the concentration is 180000mg/L to 250000mg/L TDS.

20. The method for treating the high-salinity wastewater through fractional crystallization according to claim 18, wherein a first evaporation concentration step is further included between the step of adding potassium chloride to sodium chloride mother liquor to obtain a mixed liquor and the step of freezing to precipitate potassium nitrate, and the mixed liquor is concentrated in an evaporation concentration system until the concentration is 180000mg/L to 250000mg/L TDS.

21. The method for treating high-salinity wastewater by fractional crystallization according to claim 12, 13, 14, 15, 16 or 20, characterized by further comprising a pretreatment step before the step (1), specifically: the wastewater is pretreated by a high-density sedimentation tank, ultrafiltration, ion exchange resin and a carbon remover respectively to remove calcium and magnesium ions, particles, microorganisms, silicon dioxide and alkalinity in the wastewater; and (4) the wastewater after pretreatment enters an adjusting tank.

22. The method for treating high-salinity wastewater through fractional crystallization according to claim 17, characterized by further comprising a pretreatment step before the step (1), specifically: the wastewater is pretreated by a high-density sedimentation tank, ultrafiltration, ion exchange resin and a carbon remover respectively to remove calcium and magnesium ions, particles, microorganisms, silicon dioxide and alkalinity in the wastewater; and (4) the wastewater after pretreatment enters an adjusting tank.

23. The method for treating high-salinity wastewater through fractional crystallization according to claim 18, characterized by further comprising a pretreatment step before the step (1), specifically: the wastewater is pretreated by a high-density sedimentation tank, ultrafiltration, ion exchange resin and a carbon remover respectively to remove calcium and magnesium ions, particles, microorganisms, silicon dioxide and alkalinity in the wastewater; and (4) the wastewater after pretreatment enters an adjusting tank.

24. The method for treating high-salinity wastewater through fractional crystallization according to claim 19, characterized by further comprising a pretreatment step before the step (1), specifically: the wastewater is pretreated by a high-density sedimentation tank, ultrafiltration, ion exchange resin and a carbon remover respectively to remove calcium and magnesium ions, particles, microorganisms, silicon dioxide and alkalinity in the wastewater; and (4) the wastewater after pretreatment enters an adjusting tank.