CN113651478A - Purification and recovery device and method for treating saline-alkali soil salt-washing effluent - Google Patents
Purification and recovery device and method for treating saline-alkali soil salt-washing effluent Download PDFInfo
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Classifications
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- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F9/00—Multistage treatment of water, waste water or sewage
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01D—COMPOUNDS OF ALKALI METALS, i.e. LITHIUM, SODIUM, POTASSIUM, RUBIDIUM, CAESIUM, OR FRANCIUM
- C01D7/00—Carbonates of sodium, potassium or alkali metals in general
- C01D7/22—Purification
- C01D7/24—Crystallisation
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
- C01F11/00—Compounds of calcium, strontium, or barium
- C01F11/20—Halides
- C01F11/24—Chlorides
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
- C01F5/00—Compounds of magnesium
- C01F5/40—Magnesium sulfates
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
- C02F1/001—Processes for the treatment of water whereby the filtration technique is of importance
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
- C02F1/02—Treatment of water, waste water, or sewage by heating
- C02F1/04—Treatment of water, waste water, or sewage by heating by distillation or evaporation
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
- C02F1/02—Treatment of water, waste water, or sewage by heating
- C02F1/04—Treatment of water, waste water, or sewage by heating by distillation or evaporation
- C02F1/06—Flash evaporation
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
- C02F1/44—Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis
- C02F1/441—Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis by reverse osmosis
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
- C02F1/44—Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis
- C02F1/442—Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis by nanofiltration
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
- C02F1/44—Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis
- C02F1/444—Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis by ultrafiltration or microfiltration
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
- C02F1/46—Treatment of water, waste water, or sewage by electrochemical methods
- C02F1/469—Treatment of water, waste water, or sewage by electrochemical methods by electrochemical separation, e.g. by electro-osmosis, electrodialysis, electrophoresis
- C02F1/4693—Treatment of water, waste water, or sewage by electrochemical methods by electrochemical separation, e.g. by electro-osmosis, electrodialysis, electrophoresis electrodialysis
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- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Life Sciences & Earth Sciences (AREA)
- Inorganic Chemistry (AREA)
- Geology (AREA)
- Engineering & Computer Science (AREA)
- Hydrology & Water Resources (AREA)
- Environmental & Geological Engineering (AREA)
- Water Supply & Treatment (AREA)
- Materials Engineering (AREA)
- Heat Treatment Of Water, Waste Water Or Sewage (AREA)
- Separation Using Semi-Permeable Membranes (AREA)
Abstract
The invention discloses a purification and recovery device and a method for treating saline-alkali soil salt-washing effluent, wherein the device comprises a filtering unit; the nanofiltration unit is used for separating monovalent ions in saline-alkali soil salt washing effluent after being filtered by the filtering unit to obtain a solution containing the monovalent ions; an ion determination unit for inputting the monovalent ion-containing solution and determining Cl in the solution‑With HCO3 ‑Comparing the molar content ratio with a preset threshold value, and dividing the input solution containing the monovalent ions into a solution with the molar ratio more than or equal to the preset threshold value and a solution with the molar ratio less than the preset threshold value according to a comparison result; a first evaporative concentration crystallization unit for extractingObtaining NaCl; a first flash evaporation cooling crystallization unit for extracting and obtaining NaHCO3. The invention can realize the grading separation and the high-efficiency recovery of various salts in the saline-alkali soil salt washing effluent.
Description
Technical Field
The invention belongs to the technical field of purification and separation, and particularly relates to a purification and recovery device and method for treating saline-alkali soil salt-washing effluent.
Background
At present, the salinized land increases year by year, and the alkalization degree is generally higher, so that the problems of harming the growth of crops, hindering agricultural production and the like exist.
At present, the irrigation salt-washing technology is generally adopted, so that soil salt is dissolved in salt-washing effluent and laterally seeps into a drainage ditch to be discharged, and the aim of reducing the salt content in soil is fulfilled. However, the high-salt water generated by the traditional irrigation salt-washing technology directly discharges into the natural environment without being treated, so that serious environmental pollution and harm exist, and the irrigation process also has a serious water resource waste problem.
In summary, a new device and method for purifying and recovering saline-alkali soil salt-washing effluent are needed.
Disclosure of Invention
The invention aims to provide a purification and recovery device and a method for treating saline-alkali soil salt-washing effluent so as to solve one or more technical problems. The invention can realize the grading separation and the high-efficiency recovery of various salts in the saline-alkali soil salt washing effluent.
In order to achieve the purpose, the invention adopts the following technical scheme:
the invention relates to a purification and recovery device for treating saline-alkali soil salt-washing effluent, which comprises:
the filtering unit is used for filtering the saline-alkali soil salt-washing effluent;
the nanofiltration unit is used for separating monovalent ions in saline-alkali soil salt washing effluent after being filtered by the filtering unit to obtain a solution containing the monovalent ions; wherein the monovalent ion comprises Na+、HCO3 -、Cl-；
An ion determination unit for inputting the monovalent ion-containing solution and determining Cl in the solution-With HCO3 -Comparing the molar content ratio with a preset threshold value, and dividing the input solution containing the monovalent ions into a solution with the molar ratio more than or equal to the preset threshold value and a solution with the molar ratio less than the preset threshold value according to a comparison result;
an evaporation concentration crystallization I unit used for inputting the solution with the mole ratio more than or equal to the preset threshold value output by the ion judgment unit, extracting to obtain NaCl until Cl is in the solution-With HCO3 -Outputting a solution with the molar ratio smaller than a preset threshold value when the molar content ratio is smaller than the preset threshold value;
a flash evaporation temperature reduction crystallization I unit used for inputting a solution with the mole ratio of the output of the ion judgment unit and the output of the first evaporation concentration crystallization unit being less than a preset threshold value, and inputting low-salt water used for maintaining Cl of the mother liquor in the first flash evaporation temperature reduction crystallization unit-Less than 6.1mol/L, extracting to obtain NaHCO3。
In a further development of the invention, the predetermined threshold is Cl-With HCO3 -The molar ratio is 2.7: 1.
In a further development of the invention, in the first evaporative concentration crystallization unit, the step of extracting NaCl comprises: circularly evaporating, concentrating, crystallizing and extracting at 60-100 ℃ to obtain NaCl; extracting to obtain NaHCO in the flash evaporation cooling crystallization I unit3The method specifically comprises the following steps: carrying out flash evaporation, cooling, crystallization and extraction at 0-10 ℃ to obtain NaHCO3。
The invention relates to a purification and recovery device for treating saline-alkali soil salt-washing effluent, which comprises:
the filtering unit is used for filtering the saline-alkali soil salt-washing effluent;
the nanofiltration unit is used for separating divalent ions in saline-alkali soil salt washing effluent after being filtered by the filtering unit to obtain solution containing the divalent ions; wherein the divalent ions comprise Ca2+、Mg2+、SO4 2-；
The concentration unit is used for inputting the solution containing the divalent ions and concentrating the solution to obtain a concentrated solution;
evaporating and concentrating a crystallization II unit for inputting the concentrated solution and extracting to obtain MgSO4；
Flash evaporation cooling crystallization II unit for inputting and extracting MgSO4Extracting the mother liquor to obtain CaCl2And MgSO4Mixing the salts.
In a further improvement of the invention, in the evaporative concentration crystallization II unit, MgSO is obtained by extraction4The method specifically comprises the following steps: circularly evaporating, concentrating, crystallizing and extracting at 80-100 ℃ to obtain MgSO4(ii) a Extracting CaCl from the flash evaporation cooling crystallization II unit2And MgSO4The step of mixing the salt specifically comprises: performing flash evaporation, cooling, crystallization and extraction at 0-10 ℃ to obtain CaCl2And MgSO4Mixing the salts.
The invention relates to a purification and recovery device for treating saline-alkali soil salt-washing effluent, which comprises:
the filtering unit is used for filtering the saline-alkali soil salt-washing effluent;
the nanofiltration unit is used for separating monovalent ions and divalent ions in saline-alkali soil salt washing effluent filtered by the filtering unit to respectively obtain a solution containing the monovalent ions and a solution containing the divalent ions; wherein the monovalent ion comprises Na+、HCO3 -、Cl-The divalent ion includes Ca2+、Mg2+、SO4 2-；
An ion determination unit for inputting the monovalent ion-containing solution and determining Cl in the solution-With HCO3 -The molar content ratio is compared with a preset threshold value, and the input solution containing monovalent ions is divided into two parts according to the comparison resultThe solution with the molar ratio more than or equal to a preset threshold value and the solution with the molar ratio less than the preset threshold value;
an evaporation concentration crystallization I unit used for inputting the solution with the mole ratio more than or equal to the preset threshold value output by the ion judgment unit, extracting to obtain NaCl until Cl is in the solution-With HCO3 -Outputting a solution with the molar ratio smaller than a preset threshold value when the molar content ratio is smaller than the preset threshold value;
a flash evaporation temperature reduction crystallization I unit used for inputting the solution with the mole ratio smaller than the preset threshold value output by the ion judgment unit and the first evaporation concentration crystallization unit, and the input low-salt water is used for maintaining the Cl of the mother liquor in the flash evaporation temperature reduction crystallization I unit-Less than 6.1mol/L, extracting to obtain NaHCO3；；
The concentration unit is used for inputting the solution containing the divalent ions and concentrating the solution to obtain a concentrated solution;
evaporating and concentrating a crystallization II unit for inputting the concentrated solution and extracting to obtain MgSO4；
Flash evaporation cooling crystallization II unit for inputting and extracting MgSO4Extracting the mother liquor to obtain CaCl2And MgSO4Mixing the salts.
A further development of the invention is that the filter unit comprises: the pretreatment unit is used for filtering saline-alkali soil salt-washing effluent for the first time; the preprocessing unit includes: a filtering grid and a sedimentation tank; the ultrafiltration unit is used for carrying out secondary filtration on the saline-alkali soil salt-washing effluent after primary filtration; the ultrafiltration unit adopts a hollow fiber type component, a filter membrane arranged in the ultrafiltration unit is of a porous asymmetric structure, and the screening pore diameter is 0.002-0.1 mu m; the concentration unit includes: the reverse osmosis unit is used for inputting a solution containing divalent ions and performing primary concentration; wherein the reverse osmosis unit at least comprises two stages of reverse osmosis membrane modules connected in series; the electrodialysis unit is used for carrying out secondary concentration on the solution containing the divalent ions after the primary concentration; the electrodialysis unit comprises positive and negative electrodes at two ends, and anion and cation exchange membranes alternately arranged between the positive and negative electrodes.
The invention has the further improvement that the nanofiltration membrane of the nanofiltration unit is a separation membrane made of aromatic polyamide, the membrane aperture is 1nm, a primary two-section structure is adopted, and the number ratio of one-section membrane shell to two-section membrane shell is 2: 1.
The invention is further improved in that the first flash evaporation temperature-reduction crystallization unit is also used for obtaining NaHCO through extraction3The solution is input into an evaporation concentration crystallization I unit to improve NaCl and NaHCO in the washing brine3Recovery rate of (a); the flash evaporation cooling crystallization II unit is also used for extracting CaCl2And MgSO4The solution after mixing the salt is input into a second evaporation concentration crystallization unit to increase MgSO in the brine4And CaCl2Recovery rate of (a); the low-salt water input by the flash evaporation temperature-reducing crystallization I unit is the low-salt water output by the concentration unit.
The invention relates to an operation method of a purification and recovery device for treating saline-alkali soil salt-washing effluent, which comprises the following steps:
filtering saline-alkali soil salt-washing effluent to remove preset kinds of impurities;
separating monovalent ions and divalent ions in saline-alkali soil salt washing effluent after removing impurities to respectively obtain a solution containing the monovalent ions and a solution containing the divalent ions; wherein the monovalent ion comprises Na+、HCO3 -、Cl-The divalent ion includes Ca2+、Mg2+、SO4 2-；
Adding Cl in the solution containing the monovalent ions-With HCO3 -Comparing the molar content ratio with a preset threshold value, and dividing the input solution containing the monovalent ions into a solution with the molar ratio more than or equal to the preset threshold value and a solution with the molar ratio less than the preset threshold value according to a comparison result; based on the solution with the molar ratio more than or equal to the preset threshold value, evaporating, concentrating, crystallizing and extracting to obtain NaCl until Cl is contained in the solution-With HCO3 -The molar content ratio is smaller than the preset threshold value, and a solution with the molar ratio smaller than the preset threshold value is output; based on the solution with the molar ratio smaller than the preset threshold value and the input of low salt water, carrying out flash evaporation, cooling, crystallization and extraction to obtain NaHCO3(ii) a It is composed ofIn the process, the input low-salt water is used for maintaining Cl of mother liquor in the flash evaporation cooling crystallization I unit-＜6.1mol/L；
Concentrating the solution containing divalent ions to obtain a concentrated solution; evaporating, concentrating, crystallizing and extracting to obtain MgSO4(ii) a Based on extraction of MgSO4The subsequent mother liquor is subjected to flash evaporation, temperature reduction, crystallization and extraction to obtain CaCl2And MgSO4Mixing the salts.
Compared with the prior art, the invention has the following beneficial effects:
in the invention, the membrane separation, evaporative crystallization and temperature step regulation and control combined technology is adopted to realize the fractional separation and high-efficiency recovery of various salts in saline-alkali soil salt washing effluent. Specifically, the saline-alkali soil is rich in water-soluble salt, and the direct discharge of the salt-washing effluent not only threatens the surrounding ecological environment, but also causes serious salt-water resource loss; according to the solubility law of each salt, the invention separates and separates out each salt composition by low-pressure evaporation and temperature control and matching with a membrane separation technology, and each purified salt can become a product (such as salt, baking soda, farmland fertilizer and the like) meeting the market standard, thereby obtaining considerable economic benefit.
In the invention, the removal rate of impurities such as suspended matters, colloids and the like in the washing brine by the ultrafiltration system can reach more than 90 percent, the main function of the ultrafiltration system is to prevent the problem of membrane blockage of the nanofiltration system and improve the purity of salt products obtained in the later evaporation crystallization process so as to meet the market requirement. The nanofiltration system can realize the separation of the primary and the divalent ions in the salt washing water, the separation rate can reach 90 percent, the effect is not only for the ion separation, but also more importantly, the problem of poor salt separation effect in a mixed salt system is solved, and the efficient recovery of salt in the evaporation crystallization process is realized. In the invention, the evaporative crystallization device comprises evaporative concentration crystallization and flash evaporation cooling crystallization, and NaCl and MgSO in salt-containing mother liquor which is subjected to membrane filtration systems such as ultrafiltration, nanofiltration and reverse osmosis by temperature regulation and control4And NaHCO3A single salt component, and CaCl2And MgSO4The mixed salt is separated efficiently, and the recovery rate can reach more than 99 percent; the purity of each single salt component obtained by recovery reaches more than 98 percent,meets the purity requirement of various commercially sold salts, and obtains the recovered CaCl2And MgSO4The mixed salt can be used as fertilizer to be applied to agriculture. In the invention, the reverse osmosis and electrodialysis membrane treatment can not only realize the purpose of brine concentration, but also obtain low brine which can be used for supplementing moisture required by a flash evaporation crystallization link. The whole device realizes the organic combination of membrane separation, evaporative crystallization and temperature regulation, and realizes the stable and efficient operation of the device by the ring-to-ring buckling.
In order to ensure that the saline-alkali content of the drained saline-alkali soil reaches the standard, the amount of water irrigated to the saline-alkali soil is generally increased, and a large amount of water resources are wasted. The brine purification and recovery system can effectively separate the salt in the brine washing effluent to obtain low-salt reclaimed water, and can greatly reduce the water consumption of the original saline-alkali soil by more than 70 percent in the form of recharging the saline-alkali soil.
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 are briefly introduced below; it is obvious that the drawings in the following description are some embodiments of the invention, and that for a person skilled in the art, other drawings can be derived from them without inventive effort.
FIG. 1 is a schematic block diagram of a process for purifying and recovering saline-alkali soil saline-washing effluent according to an embodiment of the present invention;
FIG. 2 is a schematic block diagram of a process of another method for purifying and recycling saline-alkali soil saline-washing effluent according to an embodiment of the present invention.
Detailed Description
In order to make the purpose, technical effect and technical solution of the embodiments of the present invention clearer, the following clearly and completely describes the technical solution of the embodiments of the present invention with reference to the drawings in the embodiments of the present invention; it is to be understood that the described embodiments are only some of the embodiments of the present invention. Other embodiments, which can be derived by one of ordinary skill in the art from the disclosed embodiments without inventive faculty, are intended to be within the scope of the invention.
Referring to fig. 1, a purification and recovery apparatus for treating saline-alkali soil saline-washing effluent according to an embodiment of the present invention includes:
the filtering unit is used for filtering the saline-alkali soil salt-washing effluent;
the nanofiltration unit is used for separating monovalent ions in saline-alkali soil salt washing effluent after being filtered by the filtering unit to obtain a solution containing the monovalent ions; wherein the monovalent ion comprises Na+、HCO3 -、Cl-；
An ion determination unit for inputting the monovalent ion-containing solution and determining Cl in the solution-With HCO3 -Comparing the molar content ratio with a preset threshold value, and dividing the input solution containing the monovalent ions into a solution with the molar ratio more than or equal to the preset threshold value and a solution with the molar ratio less than the preset threshold value according to a comparison result;
an evaporation concentration crystallization I unit used for inputting the solution with the mole ratio more than or equal to the preset threshold value output by the ion judgment unit, extracting to obtain NaCl until Cl is in the solution-With HCO3 -Outputting a solution with the molar ratio smaller than a preset threshold value when the molar content ratio is smaller than the preset threshold value;
a flash evaporation temperature reduction crystallization I unit used for inputting a solution with the mole ratio of the output of the ion judgment unit and the output of the first evaporation concentration crystallization unit being less than a preset threshold value, and inputting low-salt water used for maintaining Cl of the mother liquor in the first flash evaporation temperature reduction crystallization unit-Less than 6.1mol/L, extracting to obtain NaHCO3。
Wherein the preset threshold is Cl-With HCO3 -The molar ratio is 2.7: 1; in the first evaporation concentration crystallization unit, the step of extracting and obtaining NaCl comprises the following steps: circularly evaporating, concentrating, crystallizing and extracting at 60-100 ℃ to obtain NaCl; extracting to obtain NaHCO in the flash evaporation cooling crystallization I unit3The method specifically comprises the following steps: carrying out flash evaporation, cooling, crystallization and extraction at 0-10 ℃ to obtain NaHCO3。
Referring to fig. 2, the saline-alkali soil salt-washing effluent purification and recovery device according to the embodiment of the present invention includes: the device comprises a pretreatment unit, an ultrafiltration unit, a nanofiltration unit, a reverse osmosis unit, an electrodialysis unit, an evaporation concentration crystallization unit, a flash evaporation cooling crystallization unit, a low-salt water recovery system and a solar energy supply and storage unit.
In the embodiment of the invention, the pretreatment unit is used for intercepting insoluble impurities such as large-particle impurities, suspended matters and the like in the saline-alkali soil washing brine, the input end of the pretreatment unit is connected with the saline-alkali soil washing brine outlet, and the output end of the pretreatment unit is connected with the input end of the ultrafiltration system through a pipeline. Preferably, the pretreatment unit comprises a filter grid and a sedimentation tank; preferably, the inclination angle of the filtering grating is 60-75 degrees, and the net spacing of the grating bars is 5-10 mm.
In the embodiment of the invention, the ultrafiltration unit is used for removing suspended matters, colloids and macromolecular substances in pretreated washing brine so as to prevent a nanofiltration system from having a membrane blockage problem and ensure the purity grade of a salinity product in an evaporation crystallization link. The output end of the ultrafiltration unit is connected with the input end of the nanofiltration system through a pipeline; the ultrafiltration unit adopts a hollow fiber type component, a filter membrane arranged in the ultrafiltration unit is of a porous asymmetric structure, and the screening pore diameter of the ultrafiltration unit is 0.002-0.1 mu m.
In the embodiment of the invention, the nanofiltration unit is used for separating monovalent (Na) in washing brine+、HCO3 -、Cl-) And divalent ions (Ca)2+、Mg2+、SO4 2-) Improving NaCl and NaHCO in the salt washing water3、MgSO4Iso-monosalt and CaCl2And MgSO4Separation effect of mixed salt components and product purity. A monovalent ion output end of the nanofiltration unit is connected with an input end of an ion determination system, and a divalent ion output end is connected with a primary reverse osmosis input end; the nanofiltration membrane of the nanofiltration unit is a separation membrane made of aromatic polyamide, the membrane aperture is 1nm, a first-stage two-stage design is adopted, and the number ratio of first-stage membrane shells to second-stage membrane shells is 2: 1.
In the embodiment of the invention, the ion determination system is used for detecting Cl in the saline solution flowing out of the nanofiltration system in real time-With HCO3 -Molar content ratio in Cl-With HCO3 -Mole ofThe solution was split according to a 2.7:1 ratio. The salt solution with the molar ratio of more than or equal to 2.7:1 flows into the evaporation concentration crystallization I unit through a pipeline, the salt solution with the molar ratio of less than 2.7:1 flows into the flash evaporation cooling crystallization I unit through a pipeline, the output end of the ion determination unit is connected with the evaporation concentration crystallization I unit and the input end of the flash evaporation cooling crystallization I unit through an intelligent control three-way ball valve, the three-way ball valve is made of stainless steel materials resistant to salt corrosion, and the selection of the channel is controlled by the ion determination system unit.
In the embodiment of the invention, the reverse osmosis unit is used for concentrating saline water, the separation efficiency of salinity in an evaporation crystallization link is improved, and meanwhile, the obtained low-salinity water can be used for supplementing the moisture in a flash evaporation cooling crystallization I unit and a saline-alkali soil salt washing link. The first-stage reverse osmosis strong brine output end is connected with the second-stage reverse osmosis input end through a pipeline, and the second-stage reverse osmosis strong brine output end is connected with the electrodialysis system input end through a pipeline. The first-stage reverse osmosis low-salt water output end and the second-stage reverse osmosis low-salt water output end are connected with the input end of the low-salt water collecting tank through pipelines; the reverse osmosis unit at least comprises two stages of reverse osmosis membrane assemblies which are connected in series, and the reverse osmosis unit comprises a booster pump, a filter, a high-pressure pump and a reverse osmosis membrane device.
In the embodiment of the invention, the electrodialysis unit is used for further concentrating the saline water after reverse osmosis treatment, so that the separation efficiency of salt in the evaporation crystallization link is improved, and the obtained low-salt water can be used for supplementing the water in the flash evaporation cooling crystallization I unit and the saline-alkali soil salt washing link. The strong brine output end of the electrodialysis unit is connected with the input end of the evaporation concentration crystallization II unit through a pipeline, and the low brine output end is connected with the input end of the low brine collecting tank through a pipeline; the electrodialysis unit comprises positive and negative electrodes at two ends, anion and cation exchange membranes alternately arranged between the positive and negative electrodes, and fresh water channels and concentrated water channels alternately arranged between adjacent anion and cation exchange membranes.
In the embodiment of the invention, two evaporative crystallization devices are respectively arranged behind the electrodialysis unit and the nanofiltration unit; wherein, the evaporation crystallization device II positioned behind the electrodialysis unit can extract MgSO with high purity by controlling the evaporation temperature to be between 80 and 100 DEG C4. Selecting the so-called MgSO 80-100 DEG C4With CaCl2The separation temperature of (a) is based on the solubility law of the two salts, MgSO in this temperature range4Has a solubility far lower than that of CaCl2And MgSO with increasing temperature4The dissolution of (A) is in a downward trend, and experiments show that the extracted MgSO is in a range of 80-100 DEG C4The purity is highest and can reach 98 percent. And the evaporation crystallization device I positioned behind the nanofiltration unit can extract NaCl with higher purity by controlling the evaporation temperature to be 60-100 ℃.
In the embodiment of the invention, the ion determination system mainly identifies Cl in the solution-And HCO3 -The ratio of the molar concentration to the content of the sodium chloride is used for judging the type of the land (saline land or alkaline land) and carrying out split-flow treatment, and high-purity NaCl and NaHCO are extracted step by step3。
The evaporative crystallization device I and the flash evaporation cooling crystallization device I can realize NaCl and NaHCO3In particular, the identification of Cl in salt-containing solutions according to an ion determination system-And HCO3 -In a molar ratio of (1) when Cl-：HCO3 -More than or equal to 2.7:1, the solution enters an evaporative crystallization device I for recovering NaCl through a pipeline, and is circularly evaporated and crystallized at the temperature of 60-100 ℃ and high-purity NaCl is extracted until Cl is reached-：HCO3 -Less than 2.7: 1. Introducing the mother liquor into a flash evaporation cooling crystallization I, introducing part of low-salt water generated by the system into the flash evaporation cooling crystallization I system, and introducing the low-salt water to keep Cl in the mother liquor-Less than 6.1mol/L, and extracting high-purity NaHCO at the temperature of 0-10 DEG C3Up to Cl-：HCO3 -And (4) refluxing the mother liquor again to enter an evaporation crystallization device I to continuously recover high-purity NaCl, wherein the ratio of the mother liquor to the mother liquor is 6.3: 1. When the salt solution contains Cl-：HCO3 -Less than 2.7:1, directly introducing the solution into flash evaporation cooling crystallization I, and extracting high-purity NaHCO at the temperature of 0-10 DEG C3Up to Cl-：HCO3 -And (4) refluxing the mother liquor to enter a salt field treatment system evaporation crystallization device I to continuously recover high-purity NaCl, wherein the ratio of the mother liquor to the mother liquor is 6.3: 1.
In the embodiment of the invention, flash evaporation cooling crystallization is adoptedTwo are respectively positioned after the two evaporative crystallization devices. The flash evaporation cooling crystallization II device can extract CaCl by reducing the temperature to 0-10 DEG C2And MgSO4The mixed salt can be used as fertilizer residual mother liquor to continuously flow back to the evaporation crystallization device II for recovering high-purity MgSO4。
In the embodiment of the invention, 2.7:1 is selected as a split flow basis of evaporative concentration crystallization II and flash evaporation cooling crystallization II, and the specific reasons are as follows: according to NaCl and NaHCO3The solubility rule of (A) is that Cl is saturated at the temperature of 60-100 ℃ under the condition that two salts are saturated-With HCO3 -The molar ratio of (1) to (2.7) to (3.3) to (1), when Cl is contained in a salt solution-With HCO3 -When the molar ratio is more than or equal to 2.7:1, evaporating water in an environment of 60-100 ℃, and separating out NaCl single salt from a salt solution because the concentration of NaCl exceeds the solubility; and for Cl-and HCO3 -When the molar ratio is less than 2.7:1, the NaCl and NaHCO can not be effectively separated by evaporating water at the temperature of 60-100 DEG C3According to the condition of NaHCO under the temperature of 0-10 DEG C3Characteristic crystallization separated NaHCO with solubility far less than NaCl3A mono-salt. In particular, due to the continuous precipitation of NaCl monosalt in the evaporative crystals I, Cl-and HCO in the salt solution thereof3 -The mol ratio can be reduced to below 2.7:1, and the mother liquor in the evaporation concentration crystallization unit I needs to be introduced into the flash evaporation temperature reduction crystallization unit I through a pipeline. For the flash cooling crystallization I unit, the temperature reduction can cause NaCl and NaHCO3The solubility is reduced, so to ensure the separated NaHCO3The product does not contain NaCl, and a certain amount of low-salt water needs to be introduced to reduce the concentration of NaCl. When both the two salts are saturated, Cl is generated under the environment of 0-10 DEG C-With HCO3 -The molar ratio of (A) to (B) is 6.3:1, so that Cl contained in the mother liquor in the flash evaporation cooling crystallization I unit-With HCO3 -When the molar ratio of (A) to (B) is 6.3:1, the mother liquor is introduced into an evaporative concentration crystallization II unit to carry out NaCl extraction. Finally, NaCl and NaHCO extracted by the unit of evaporation concentration crystallization I and flash evaporation cooling crystallization I3The purity of the product reaches more than 98 percent, and the product meets the requirement of market purity.
In the embodiment of the invention, the low-salt water recovery unit is connected with a fresh water outlet of the reverse osmosis, electrodialysis and evaporative crystallization device through a pipeline, one part of the collected low-salt water is used for supplementing flash evaporation crystallization I, and the other part of the collected low-salt water is conveyed to a water inlet end of a spraying system through a pipeline.
In the embodiment of the invention, the removal rate of suspended matters, colloid and other impurities in the washing brine by the early-stage ultrafiltration system is up to more than 90 percent, the main function of the ultrafiltration system is to prevent the problem of membrane blockage of the nanofiltration system and improve the purity of salt products obtained in the later-stage evaporative crystallization process so as to meet the market requirement. The nanofiltration system can realize the separation of the primary and the divalent ions in the salt washing water, the separation rate is up to 90 percent, the effect is not only for the ion separation, but also more importantly, the problem of poor salt separation effect in a mixed salt system is solved, and the efficient recovery of salt in the evaporation crystallization link is realized. The evaporative crystallization device comprises evaporative concentration crystallization and flash evaporation cooling crystallization, and NaCl and MgSO in salt-containing mother liquor of membrane filtration systems such as ultrafiltration, nanofiltration and reverse osmosis are controlled by temperature4And NaHCO3A single salt component, and CaCl2And MgSO4The mixed salt is separated efficiently, and the recovery rate reaches more than 99 percent. Wherein the purity of each single salt component obtained by recovery reaches more than 98 percent, the purity requirement of each salt on products sold in the market is met, and CaCl obtained by recovery2And MgSO4The mixed salt can be used as fertilizer to be applied to agriculture. And reverse osmosis and electrodialysis membrane treatment can realize the purpose of brine concentration, and the obtained low brine can be used for supplementing moisture required in the flash evaporation crystallization I link. The whole device realizes the organic combination of membrane separation, evaporative crystallization and temperature regulation, and the rings are buckled with each other, so that the stable and efficient operation of the device is realized.
In the embodiment of the invention, the solar energy conversion and storage unit consists of a solar cell panel, a photovoltaic water pumping inverter and a storage battery, the required energy of the whole device is supplied by a solar energy conversion and storage system, the solar cell panel is used for daily energy supply in the daytime, and the solar energy conversion and storage unit is operated by using the electric energy stored by the storage battery at night.
In the embodiment of the invention, the energy required by the whole set of device is from a solar energy conversion and storage system, no additional energy input is needed, no substances including greenhouse gases are emitted, no noise and no pollution are caused, and the aims of energy conservation, emission reduction, environmental protection and high efficiency are really realized.
In conclusion, the system provided by the embodiment of the invention adopts the combined technology of evaporative crystallization, temperature step regulation and membrane separation to realize the fractional separation and high-efficiency recovery of various salts in saline-alkali soil salt washing effluent. The saline-alkali soil is rich in water-soluble salt, and the direct discharge of the salt-washing effluent not only threatens the surrounding ecological environment, but also causes serious salt-water resource loss. The system separates out the components of each salt by low-pressure evaporation and temperature regulation according to the solubility rule of each salt and matching with a membrane separation technology, and each purified salt can become salt, baking soda and farmland fertilizer products meeting the market standard, thereby obtaining considerable economic benefit. In order to ensure that the saline-alkali content of the drained saline-alkali soil reaches the standard, the amount of water irrigated to the saline-alkali soil is generally increased, and a large amount of water resources are wasted. The brine purification and recovery system can effectively separate the salt in the brine washing effluent to obtain low-salt reclaimed water, and can greatly reduce the water consumption of the original saline-alkali soil by more than 70 percent in the form of recharging the saline-alkali soil. And the energy required by the whole set of device is from a solar energy conversion and storage system, no additional energy input is needed, no substances including greenhouse gases are emitted, no noise and no pollution exist, and the aims of energy conservation, emission reduction, green and high efficiency are really achieved.
Example 1
The high-salinity effluent related to the embodiment of the invention is obtained in the process of leaching saline-alkali soil in northwest arid areas, and the saline-alkali soil is a general term of saline soil and alkaline earth. The saline soil mainly refers to saline soil with high chloride or sulfate content, the soil is alkaline, but the pH value is not necessarily high, and the content of ions in a typical saline-alkali soil is shown in table 1.
TABLE 1 statistics of soil salt ion content in certain saline and alkaline land
The purification and recovery device for saline-alkali soil salt leaching effluent in the embodiment of the invention comprises a leaching system, a pretreatment system, an ultrafiltration system, a nanofiltration system, a reverse osmosis system, an electrodialysis system, an evaporation concentration crystallization system, a flash evaporation cooling crystallization system, a low-salt water recovery system and a solar energy conversion and storage system.
The leaching system comprises a salt discharge concealed pipe, an irrigation concealed pipe and a salt discharge ditch. The salt discharge concealed pipe with the water seepage micropores is laid in parallel and is perpendicular to the direction of the salt discharge ditch, the laying depth is l-1.5 m, the laying distance is l 0-50 m, the laying depth is higher than the bottom of the salt discharge ditch, and two ends of the salt discharge concealed pipe enter the salt discharge ditch; the laying depth of the irrigation underground pipes is 0.8-1.3 m, the laying depth is higher than that of the salt-removing underground pipes, and water outlets of the irrigation underground pipes are formed in the surface of the terrace.
The pretreatment system comprises a filter grid and an inclined tube sedimentation tank, the inclination angle of the filter grid is 60-75 degrees, more preferably 60 degrees, and the gap between grid bars is 5-10 mm, more preferably 5 mm. The inclined tube has an inclination angle of 50-70 degrees, more preferably 60 degrees, the inclined tube sedimentation tank is positioned behind the grating of the filter tank, the inclined tube is arranged in the inclined tube sedimentation tank, the incoming water flows through the inclined tube from bottom to top from the bottom of the tank after entering the tank, and the inclined tube makes small particles in the salt washing effluent settle to the bottom of the inclined tube sedimentation tank.
The ultrafiltration system adopts a hollow fiber type component, a filter membrane is of a porous asymmetric structure and is mainly used for intercepting macromolecules in water, the application pressure of the ultrafiltration system is 0.1-0.6 Mpa, the screening aperture is 0.002-0.1 mu m, almost all bacteria, colloidal particles, proteins and macromolecular organic matters in liquid can be intercepted, and the water body after being filtered and precipitated by a grating is further finely filtered.
The nanofiltration system adopts a separation membrane made of aromatic polyamide material, the membrane aperture is 1nm, a first-stage two-stage design (6-core membrane shell) is adopted, and the number ratio of the first-stage membrane shell to the second-stage membrane shell is 2: 1. The nanofiltration system can intercept the molecular weight within the range of 200-1000 daltons, has negative charges on the surface, can efficiently intercept divalent or high-valent ions, particularly anions, and has the interception rate of sodium chloride of 96%.
Said two-stage reactionThe osmosis unit is mainly used for further concentrating the salt in water and mainly comprises a booster pump, a filter, a high-pressure pump and a reverse osmosis membrane device. The additional pump is used for increasing the pressure of water, and the incoming water forms reverse osmosis conditions; the filter be used for filtering the incoming water, be provided with reverse osmosis membrane in the reverse osmosis unit, the salt water of straining is one-level reverse osmosis RO through reverse osmosis membrane again, reverse osmosis membrane is the pellicle, can prevent Cl-，Na+When large ions pass through the reverse osmosis membrane, in order to ensure the reverse osmosis effect and protect the reverse osmosis membrane, a scale inhibitor is continuously added into a reverse osmosis container, meanwhile, the water temperature is ensured to be above 25 ℃, a steam heat exchanger is used in winter, certain water pressure is ensured, a vertical pump is used, under certain pressure, ion-containing water is extruded to pass through the reverse osmosis membrane, so that two kinds of water are formed, low salt water passing through the reverse osmosis membrane enters a reuse water tank, concentrated water enters a secondary reverse osmosis RO to be continuously concentrated, the desalination rate of the primary reverse osmosis reaches 80%, and the desalination rate of the secondary reverse osmosis reaches 60%. And the low-salt water produced by the secondary reverse osmosis RO also enters a reuse water pool, and the concentrated water enters an electrodialysis device in the next link.
The Electrodialysis (EDR) system comprises a positive electrode and a negative electrode which are arranged at two ends, anion-cation exchange membranes which are alternately arranged between the positive electrode and the negative electrode, and a fresh water channel and a concentrated water channel which are alternately arranged between adjacent anion-cation exchange membranes, wherein salt ions such as MgSO (MgSO) are generated after the concentrated brine which passes through the two-stage reverse osmosis enters the Electrodialysis (EDR) system4And CaCl2And the low-salt water enters a reuse water system and is used for the leaching operation of the saline-alkali soil again.
The two evaporative crystallization devices are respectively positioned behind the electrodialysis system and the nanofiltration system. Located after the electrodialysis system is an evaporative crystallization unit II, known as CaCl with increasing temperature2Gradually increases in solubility over MgSO4The solubility of the compound shows a rule of decreasing after increasing, so that the evaporation temperature is increased to be more than 80 ℃ to make MgSO4Crystallization is separated out, and the purity is as high as 98%; and CaCl2Still remaining in the mother liquor.
For nanofiltration systemsAn evaporation crystallization device I arranged behind the system is provided with an ion judgment device which is mainly used for identifying Cl in salt-containing solution-And HCO3 -In the molar ratio of Cl in the salt-washing effluent of this example-And HCO3 -Up to 209: 1 (more than 2.7:1), the solution enters an evaporative crystallization device I for recovering NaCl through a pipeline, and is circularly evaporated and crystallized at 100 ℃ to extract NaCl, and the purity of the NaCl reaches 98%.
When Cl is in mother liquor of the evaporation concentration crystallization device I-：HCO3 -When the concentration is less than 2.7:1, introducing the mother liquor into a flash evaporation cooling crystallization I, introducing part of low-salt water generated by the system into a flash evaporation cooling crystallization I device, introducing the low-salt water to keep Cl < -6.1 mol/L, and extracting NaHCO at the temperature of 0-10 DEG C3The purity of the product reaches 98 percent. Until Cl in mother liquor of flash evaporation cooling crystallization I device-：HCO3 -The mother liquor is refluxed again into the evaporative crystallization device I to continue to recover NaCl when the ratio is 6.3: 1.
The flash evaporation cooling crystallization unit of system has two, is located two evaporation crystallization device respectively after. Wherein the flash evaporation cooling crystallization II device can extract CaCl by reducing the temperature to 0-10 DEG C2And MgSO4The mixed salt meets the requirements of the sulfur fertilizer sold in the market. The liquid after flash evaporation, temperature reduction and crystallization treatment flows back to an evaporation crystallization device II, and the residual Mg is continuously utilized2+、SO4 2-Ions.
The low-salt water recovery system is connected with fresh water outlets of the two-stage reverse osmosis and electrodialysis devices through pipelines, one part of the collected low-salt water is used for supplementing flash evaporation crystallization I, the other part of the collected low-salt water is directly conveyed to a water inlet end of the spraying system through the pipelines and is used for the alkaline land leaching operation, the separated low-salt water is reused for the irrigation and salt leaching treatment of the saline-alkali land, and compared with the traditional irrigation and salt leaching process, the water consumption is reduced by more than 70%.
Solar energy conversion and storage system constitute by solar cell panel, photovoltaic pumping inverter and battery, the required energy of complete equipment is supplied with by solar energy conversion and storage system, relies on solar cell panel to carry out daily energy supply daytime, utilizes the electric energy operation of battery storage night. The solar photovoltaic power generation process is simple, no mechanical rotating part is arranged, no fuel is consumed, no substance including greenhouse gas is emitted, and no noise and no pollution are caused. Solar energy resources are available everywhere, power can be supplied nearby, long-distance transmission is not needed, and electric energy loss caused by long-distance transmission lines is avoided; and secondly, cooling water is not needed in the photovoltaic power generation process, and the photovoltaic power generation system can be even installed on the gobi in the desert without water, so that the whole power generation system is stable and reliable in working performance and long in service life (more than 30 years).
Example 2
In the purification and recovery device for treating saline-alkali soil salt washing effluent, NaCl is obtained by circularly evaporating, concentrating, crystallizing and extracting in the evaporation, concentration and crystallization I under the environment of low pressure and 60 ℃; in the flash evaporation cooling crystallization I, the NaHCO is obtained by flash evaporation cooling crystallization extraction at the temperature of 0 DEG C3。
The screening aperture of a filtering membrane arranged in the ultrafiltration unit is 0.002 mu m;
in the evaporation concentration crystallization II unit, the MgSO is obtained by circulating evaporation concentration crystallization extraction at the temperature of 80 DEG C4(ii) a In the flash evaporation cooling crystallization II unit, CaCl is obtained by flash evaporation cooling crystallization extraction at 0 DEG C2And MgSO4Mixing the salts.
Example 3
In the purification and recovery device for treating saline-alkali soil salt washing effluent, NaCl is obtained by circularly evaporating, concentrating, crystallizing and extracting at low pressure and 80 ℃ in the evaporation, concentration and crystallization I unit; in the flash evaporation cooling crystallization I unit, the NaHCO is obtained by flash evaporation cooling crystallization extraction at the temperature of 5 DEG C3。
The screening aperture of the filtering membrane arranged in the ultrafiltration unit is 0.01 mu m.
In the evaporation concentration crystallization II unit, the MgSO is obtained by circulating evaporation concentration crystallization extraction under the environment of low pressure and 90 DEG C4(ii) a In the flash evaporation cooling crystallization II unit, CaCl is obtained by flash evaporation cooling crystallization extraction at the temperature of 5 DEG C2And MgSO4Mixing the salts.
Example 4
In the purification and recovery device for treating saline-alkali soil salt washing effluent, NaCl is obtained by circularly evaporating, concentrating, crystallizing and extracting at 100 ℃ in the evaporation, concentration and crystallization I unit; in the evaporation cooling crystallization I unit, the NaHCO is obtained by flash evaporation cooling crystallization extraction at the temperature of 10 DEG C3。
The screening aperture of the filtering membrane arranged in the ultrafiltration unit is 0.1 mu m.
In the evaporation concentration crystallization II unit, the MgSO is obtained by circulating evaporation concentration crystallization extraction at the temperature of 100 DEG C4(ii) a In the flash evaporation cooling crystallization II unit, CaCl is obtained by flash evaporation cooling crystallization extraction at 10 DEG C2And MgSO4Mixing the salts.
Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art can make modifications and equivalents to the embodiments of the present invention without departing from the spirit and scope of the present invention, which is set forth in the claims of the present application.
Claims (10)
1. The utility model provides a purify recovery unit for handling saline and alkaline land salt leaching goes out water which characterized in that includes:
the filtering unit is used for filtering the saline-alkali soil salt-washing effluent;
the nanofiltration unit is used for separating monovalent ions in saline-alkali soil salt washing effluent after being filtered by the filtering unit to obtain a solution containing the monovalent ions; wherein the monovalent ion comprises Na+、HCO3 -、Cl-；
An ion determination unit for inputting the monovalent ion-containing solution and determining Cl in the solution-With HCO3 -The molar content ratio is compared with a preset threshold value, the input solution containing monovalent ions is divided into a solution with the molar ratio more than or equal to the preset threshold value and a solution with the molar ratio less than or equal to the preset threshold value according to the comparison resultPresetting a threshold value solution;
an evaporation concentration crystallization I unit used for inputting the solution with the mole ratio more than or equal to the preset threshold value output by the ion judgment unit, extracting to obtain NaCl until Cl is in the solution-With HCO3 -Outputting a solution with the molar ratio smaller than a preset threshold value when the molar content ratio is smaller than the preset threshold value;
a flash evaporation temperature reduction crystallization I unit for inputting the solution with the mole ratio less than the preset threshold value output by the ion judgment unit and the evaporation concentration crystallization I unit, inputting the low-salt water, and extracting to obtain NaHCO3(ii) a Wherein, Cl is contained in the low-salt water-＜6.1mol/L。
2. The device for purifying and recycling saline-alkali soil salt-washing effluent according to claim 1, wherein the preset threshold is Cl-With HCO3 -The molar ratio is 2.7: 1.
3. The purification and recovery device for treating saline-alkali soil salt-washing effluent according to claim 1,
in the evaporation concentration crystallization I unit, the step of extracting and obtaining NaCl comprises the following steps: circularly evaporating, concentrating, crystallizing and extracting at 60-100 ℃ to obtain NaCl;
extracting to obtain NaHCO in the flash evaporation cooling crystallization I unit3The method specifically comprises the following steps: carrying out flash evaporation, cooling, crystallization and extraction at 0-10 ℃ to obtain NaHCO3。
4. The utility model provides a purify recovery unit for handling saline and alkaline land salt leaching goes out water which characterized in that includes:
the filtering unit is used for filtering the saline-alkali soil salt-washing effluent;
the nanofiltration unit is used for separating divalent ions in saline-alkali soil salt washing effluent after being filtered by the filtering unit to obtain solution containing the divalent ions; wherein the divalent ions comprise Ca2+、Mg2+、SO4 2-；
The concentration unit is used for inputting the solution containing the divalent ions and concentrating the solution to obtain a concentrated solution;
evaporating and concentrating a crystallization II unit for inputting the concentrated solution and extracting to obtain MgSO4；
Flash evaporation cooling crystallization II unit for inputting and extracting MgSO4Extracting the mother liquor to obtain CaCl2And MgSO4Mixing the salts.
5. The purification and recovery device for treating saline-alkali soil salt-washing effluent according to claim 4,
in the evaporation concentration crystallization II unit, MgSO is obtained by extraction4The method specifically comprises the following steps: circularly evaporating, concentrating, crystallizing and extracting at 80-100 ℃ to obtain MgSO4；
Extracting CaCl from the flash evaporation cooling crystallization II unit2And MgSO4The step of mixing the salt specifically comprises: performing flash evaporation, cooling, crystallization and extraction at 0-10 ℃ to obtain CaCl2And MgSO4Mixing the salts.
6. The utility model provides a purify recovery unit for handling saline and alkaline land salt leaching goes out water which characterized in that includes:
the filtering unit is used for filtering the saline-alkali soil salt-washing effluent;
the nanofiltration unit is used for separating monovalent ions and divalent ions in saline-alkali soil salt washing effluent filtered by the filtering unit to respectively obtain a solution containing the monovalent ions and a solution containing the divalent ions; wherein the monovalent ion comprises Na+、HCO3 -、Cl-The divalent ion includes Ca2+、Mg2+、SO4 2-；
An ion determination unit for inputting the monovalent ion-containing solution and determining Cl in the solution-With HCO3 -The molar content ratio is compared with a preset threshold value, the input solution containing monovalent ions is divided into a solution with the molar ratio more than or equal to the preset threshold value and a solution with the molar ratio less than the preset threshold value according to the comparison resultThe solution of (1);
an evaporation concentration crystallization I unit used for inputting the solution with the mole ratio more than or equal to the preset threshold value output by the ion judgment unit, extracting to obtain NaCl until Cl is in the solution-With HCO3 -Outputting a solution with the molar ratio smaller than a preset threshold value when the molar content ratio is smaller than the preset threshold value;
a flash evaporation temperature reduction crystallization I unit used for inputting a solution with the mole ratio of the output of the ion judgment unit and the output of the evaporation concentration crystallization I unit being less than a preset threshold value, and the input low-salt water enables Cl of the mother liquor in the first flash evaporation temperature reduction crystallization unit-Less than 6.1mol/L, extracting to obtain NaHCO3；；
The concentration unit is used for inputting the solution containing the divalent ions and concentrating the solution to obtain a concentrated solution;
evaporating and concentrating a crystallization II unit for inputting the concentrated solution and extracting to obtain MgSO4；
Flash evaporation cooling crystallization II unit for inputting and extracting MgSO4Extracting the mother liquor to obtain CaCl2And MgSO4Mixing the salts.
7. The device for purifying and recycling saline-alkali soil effluent according to claim 6, wherein the filtering unit comprises: the pretreatment unit is used for filtering saline-alkali soil salt-washing effluent for the first time; the preprocessing unit includes: a filtering grid and a sedimentation tank; the ultrafiltration unit is used for carrying out secondary filtration on the saline-alkali soil salt-washing effluent after primary filtration; the ultrafiltration unit adopts a hollow fiber type component, a filter membrane arranged in the ultrafiltration unit is of a porous asymmetric structure, and the screening pore diameter is 0.002-0.1 mu m;
the concentration unit includes: the reverse osmosis unit is used for inputting a solution containing divalent ions and performing primary concentration; wherein the reverse osmosis unit at least comprises two stages of reverse osmosis membrane modules connected in series; the electrodialysis unit is used for carrying out secondary concentration on the solution containing the divalent ions after the primary concentration; the electrodialysis unit comprises positive and negative electrodes at two ends, and anion and cation exchange membranes alternately arranged between the positive and negative electrodes.
8. The device for purifying and recovering saline-alkali soil effluent according to claim 6, wherein the nanofiltration membrane of the nanofiltration unit is a separation membrane made of aromatic polyamide, the membrane aperture is 1nm, a one-stage two-stage structure is adopted, and the number ratio of one-stage membrane shell to two-stage membrane shell is 2: 1.
9. The purification and recovery device for treating saline-alkali soil salt-washing effluent according to claim 6,
the flash evaporation cooling crystallization I unit is also used for obtaining NaHCO through extraction3The solution is input into a first evaporation concentration crystallization unit to improve NaCl and NaHCO in the washing brine3Recovery rate of (a);
the flash evaporation cooling crystallization II unit is also used for extracting CaCl2And MgSO4The solution after mixing the salt is input into an evaporative concentration crystallization II unit to increase MgSO in the brine4And CaCl2Recovery rate of (a);
the low salt water of first flash of vaporization cooling crystallization unit input is the low salt water of concentration unit output.
10. An operation method of a purification and recovery device for treating saline-alkali soil salt-washing effluent is characterized by comprising the following steps:
filtering saline-alkali soil salt-washing effluent to remove preset kinds of impurities;
separating monovalent ions and divalent ions in saline-alkali soil salt washing effluent after removing impurities to respectively obtain a solution containing the monovalent ions and a solution containing the divalent ions; wherein the monovalent ion comprises Na+、HCO3 -、Cl-The divalent ion includes Ca2+、Mg2+、SO4 2-；
Adding Cl in the solution containing the monovalent ions-With HCO3 -The molar content ratio is compared with a preset threshold value, and the input content is compared according to the comparison resultThe solution of the monovalent ions is divided into a solution with a molar ratio of more than or equal to a preset threshold value and a solution with a molar ratio of less than a preset threshold value; based on the solution with the molar ratio more than or equal to the preset threshold value, evaporating, concentrating, crystallizing and extracting to obtain NaCl until Cl is contained in the solution-With HCO3 -The molar content ratio is smaller than the preset threshold value, and a solution with the molar ratio smaller than the preset threshold value is output; based on the solution with the molar ratio smaller than the preset threshold value and the input of low salt water, carrying out flash evaporation, cooling, crystallization and extraction to obtain NaHCO3(ii) a Wherein the input low salt water enables the Cl of the mother liquor in the flash evaporation cooling crystallization I unit-＜6.1mol/L；
Concentrating the solution containing divalent ions to obtain a concentrated solution; evaporating, concentrating, crystallizing and extracting to obtain MgSO4(ii) a Based on extraction of MgSO4The subsequent mother liquor is subjected to flash evaporation, temperature reduction, crystallization and extraction to obtain CaCl2And MgSO4Mixing the salts.
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