A method for incrementally recovering salt from high-salinity wastewater

Abstract

The present invention discloses a method for incrementally recovering salt from high-salinity wastewater, the steps of which are as follows: (1) pre-treatment of high-salinity wastewater to obtain a first mixed solution; (2) feature discrimination of the first mixed solution; (3) determining the main product salt and its associated compound, adding the associated compound to the first mixed solution to form a second mixed solution; (4) membrane separation of the second mixed solution to obtain a first concentrated solution and a first permeate; (5) membrane concentration of the first concentrated solution and the first permeate respectively to obtain a second concentrated solution, a second permeate and membrane permeate; (6) crystallization of the second concentrated solution and the second permeate respectively to obtain a main product salt, an associated compound, a byproduct salt and a crystallization mother liquor; (7) the associated compound obtained in step (6) is returned to step (3); (8) the crystallization mother liquor is returned to the first mixed solution. The present application can recover various salts in high-salinity wastewater, realize resource utilization, and achieve the purpose of energy saving, regeneration, cost reduction and efficiency improvement.

Description

Technical Field

[0001] The invention relates to a method for incrementally recovering salt in high-salinity wastewater, and in particular to deep treatment and resource utilization of high-salinity wastewater, belonging to the field of wastewater treatment. Background Art

[0002] In recent years, with the rapid development of petrochemical, pharmaceutical, pesticide and other industries, more and more high-salt wastewater has been generated. At present, the amount of high-salt wastewater in my country accounts for about 5% of the total wastewater, and it is still increasing at a certain rate every year, causing serious environmental pollution. High-salt wastewater refers to wastewater with a total salt mass fraction of ≥1%. This type of wastewater not only has a high COD concentration, but also contains high concentrations of soluble inorganic salt ions such as sodium, potassium, magnesium, calcium, chlorine and sulfate. It has the characteristics of strong acidity and alkalinity, complex chemical composition, and difficulty in treatment.

[0003] At present, the treatment technologies for high-salinity wastewater mainly include physical method, chemical method, biological method and their combined processes. Among them, the physical method mainly adopts flotation, sedimentation, mechanical compression evaporation, activated carbon adsorption and other technologies; the chemical method mainly adopts incineration, reaction precipitation, deep oxidation and other technologies; the biological method mainly adopts active microbial sludge, membrane bioreactor and other technologies. The current methods are mostly used for the treatment of high-salinity wastewater discharge in compliance with standards, and are less used in the resource recovery of valuable salts in high-salinity wastewater. The main reasons are: ①. Compared with the crystallization concentration of salt, the initial concentration of each salt in high-salinity wastewater is still low, and the conventional thermal concentration method has high energy consumption and large investment; ②. The quality of recovered salt is low and difficult to commercialize; ③. The cost of salt recovery is high and the profit margin is low. It is precisely because of the above problems in the current methods that wastewater production enterprises lack motivation for the resource utilization of high-salinity wastewater, and their enthusiasm is generally low. Most of them are only willing to treat high-salinity wastewater for discharge in compliance with standards. A large amount of salt in the wastewater is disposed of as solid waste, resulting in a huge waste of resources. Therefore, under the environmental protection requirements of low-carbon energy saving and green circulation, there is an urgent need for a salt recovery method for high-salt wastewater that combines low-cost treatment and high-value conversion. Summary of the invention

[0004] In order to solve the above problems, the present application proposes a method for incrementally recovering salt from high-salinity wastewater, which specifically comprises the following steps:

[0005] (1) Preliminary treatment of high-salinity wastewater to obtain a first mixed solution;

[0006] (2) performing characteristic discrimination on the first mixed solution;

[0007] (3) determining the main product salt and its related compounds based on characteristic discrimination, measuring the related compounds and adding them to the first mixed solution to form a second mixed solution;

[0008] (4) subjecting the second mixed liquid to separation by a separation membrane to obtain a first concentrated liquid and a first permeate;

[0009] (5) re-concentrating the first concentrated solution and the first permeate by membrane method to obtain a second concentrated solution, a second permeate and membrane permeate;

[0010] (6) crystallizing the second concentrated solution to obtain a main product salt and a first crystallization mother liquor, and fractionally crystallizing the second permeate to obtain a related compound, a by-product salt, and a second crystallization mother liquor;

[0011] (7) using the associated compound obtained by crystallization in step (6) as the associated compound of step (3) and returning it to the first mixed solution;

[0012] (8) Returning the first crystallization mother liquor and the second crystallization mother liquor to the first mixed liquor for mixing and reuse.

[0013] In step (5), the first concentrated liquid is re-concentrated by membrane method to obtain a second concentrated liquid and membrane permeate water, and the first permeate is re-concentrated by membrane method to obtain a second permeate and membrane permeate water; the membrane permeate water obtained from the first concentrated liquid and the first permeate can be used as recycled water and returned to the production system.

[0014] The present application increases the concentration of one ion in the anions and cations of the high-value main product salt by adding low-value associated compounds, and matches it with the concentration of another ion in the main product salt in the high-salt wastewater, so as to separate the high-salt wastewater in the form of the main product salt to the greatest extent possible, and obtain the main product salt with higher value than the associated compounds. Since the present application utilizes the characteristic that the separation membrane has a higher retention rate for high-valent ions than low-valent ions, the high-valent ions and low-valent ions with the same charge are separated, achieving the goal of using low-value raw materials in exchange for high-value products; and separation by separation membrane can make the ion components in the first concentrated solution and the first permeate simpler than the second mixed solution, which is conducive to the high-purity recovery of the high-value main product salt therein, and is also conducive to the extraction of other salt substances in the high-salt wastewater.

[0015] Compared with existing conventional methods such as evaporation and concentration, the present application utilizes a separation membrane separation coupled membrane re-concentration process, which can not only separate ions of different valence states, but also reduce the concentration cost of high-salt wastewater; compared with conventional methods such as evaporation and concentration, this method has a simple operation process, high efficiency, and energy saving, the equipment has large adjustability, is easy to integrate, has strong practicality, and has high application value.

[0016] Compared with the existing step-by-step reaction precipitation method, since the method of the present application performs membrane separation on ions of different valence states, the main product salt obtained has higher purity, does not require further purification, and has greater recycling value.

[0017] Compared with simply using step-by-step crystallization to recover salt from high-salt wastewater, due to the complex composition of high-salt wastewater and the low salt concentration, when direct step-by-step crystallization is performed, the crystallization yield of the main product salt is not high and the purity is low, and further purification is required to remove the impurity ions therein, which greatly increases the recovery cost of the main product salt, reduces the recovery efficiency, and reduces the value of resource utilization.

[0018] By using the present application, high-value multivalent ions in high-salt wastewater can be recovered in the form of high-purity main product salt, and other salts can also be recovered at the same time, thereby achieving resource utilization of salt in high-salt wastewater and realizing the goals of energy conservation and environmental protection, resource regeneration, cost reduction and efficiency improvement.

[0019] Specifically, in step (1), the preliminary treatment includes but is not limited to pH adjustment, activated carbon adsorption decolorization, physicochemical treatment, precipitation and separation, and membrane filtration processes; after the high-salt wastewater is subjected to preliminary treatment, the pH value of the first mixed solution obtained is in the range of 2 to 13, SS (suspended solids) is less than 50 mg / L, TOC (total organic carbon) is less than 50 mg / L, COD (chemical oxygen demand) is less than 40 mg / L, and SDI (silt density index) is less than 5.

[0020] In this application, the purpose of pre-treatment of high-salinity wastewater is to obtain a qualified first mixed solution. On the premise of meeting the above-mentioned indicators, the specific procedures of the pre-treatment can be selected and combined. After the pre-treatment, most of the impurities in the high-salinity wastewater are removed, avoiding the blockage or damage of the separation membrane pores by the impurities, and ensuring the service life of the separation membrane device.

[0021] The specific pH value of the first mixed solution is determined according to the appropriate acid-base environment for salt crystallization in the high-salt wastewater. For details, please refer to the prior art and will not be described in detail.

[0022] When any of the indicators SS, TOC, COD and SDI is too high, it means that the concentration of impurities in the first mixed wastewater exceeds the standard, which can easily cause a decrease in the permeation flux of the separation membrane device, thereby affecting the membrane separation and concentration effect of high-salt wastewater.

[0023] Specifically, in step (2), the first mixed solution after preliminary treatment is mainly an aqueous solution of inorganic salts, and its characteristics are identified, including identifying the types of ions contained therein, clarifying the valence distribution of each ion and determining the concentration of each ion. Among them, the anions in the first mixed solution can be determined by ion chromatography and titration; the cations can be determined by atomic absorption spectroscopy, inductively coupled plasma emission spectroscopy, and titration.

[0024] Specifically, in step (3), the main product salt and its associated compound are determined according to the characteristic discrimination result of the first mixed solution, the main product salt is composed of a first anion and a first cation, one of which has a valence of monovalent and the other has a valence of polyvalent; the associated compound is composed of a second anion and a second cation, and the valence of the second anion and the second cation are both monovalent;

[0025] One of the second anion and the second cation of the associated compound is the same as the first anion and the first cation of the main product salt, which has a valence of one, and the other is the same as an ion other than the first anion and the first cation in the high-salinity wastewater;

[0026] The first anion, the first cation, the second anion and the second cation are all ions already present in the high-salinity wastewater.

[0027] The multivalent state in the present application means that the valence of the ion is greater than or equal to 2, specifically +2 to +8, and -2 to -8.

[0028] In the present application, under the premise of determining the main product salt, a monovalent ion other than the main product salt ion is selected from the anions and cations already existing in the first mixed solution, and paired with the monovalent anion or monovalent cation of the main product salt to form an associated compound; that is, one of the second anion and the second cation constituting the associated compound is the same as the first anion and the first cation of the main product salt, which are monovalent, and the other is the same as an ion other than the first anion and the first cation in the high-salt wastewater. The second anion and the second cation are both ions already present in the high-salt wastewater to avoid the introduction of new ions.

[0029] The second anion and the second cation of the above-mentioned related compound can both pass through the separation membrane during the separation process of the separation membrane in step (4) and be enriched in the first permeate.

[0030] In the present application, the molar ratio of the third ion to the fourth ion in the second mixed solution is (3-8):1, wherein the third ion is the ion with a valence of one among the first anion and the first cation of the main product salt, and the fourth ion is an ion with the same charge and valence as the third ion except the third ion.

[0031] In the present application, the amount of the associated compound to be added is calculated by combining the test data of the concentration of each ion in the first mixed solution and the molar ratio of the third ion to the fourth ion in the second mixed solution.

[0032] When the molar ratio of the third ion to the fourth ion in the second mixed liquor is too low, the amount of the associated compound added is too small, the concentration of the main product salt ions is not significantly increased, the incremental recovery effect is poor, and it is difficult to maximize the recovery of the multivalent ions in the form of the main product salt; when the molar ratio of the third ion to the fourth ion in the second mixed liquor is too high, the amount of the associated compound added is too large, in addition to meeting the main product salt ion requirements, a large number of excess ions are introduced, which brings difficulty and additional burden to the membrane separation process, increases the loss of the separation membrane, prolongs the membrane separation time, and reduces the service life and work efficiency of the separation membrane.

[0033] Specifically, in step (4), the charge of the separation membrane is the same as the charge of the multivalent ion among the first anion and the first cation of the main product salt.

[0034] The second mixed liquor is separated by a separation membrane, which has three effects: ①. Separation effect: using a charged separation membrane that meets the requirements, the main product salt ions in the second mixed liquor are selectively separated, providing a guarantee for the efficient and high-purity preparation of the main product salt; ②. Purification effect: by separating the monovalent and multivalent ions in the second mixed liquor by a separation membrane, the ion composition in the first concentrated liquid and the first permeate is simpler than that in the second mixed liquor, which is more conducive to the crystallization of high-purity main product salt, related compounds and by-product salt in step (6); ③. Concentration effect: by separating the second mixed liquor by a separation membrane, the first concentrated liquid containing the main product salt is concentrated, the concentration of the main product salt is increased, and the crystallization process of the main product salt is facilitated.

[0035] The types of separation membranes in step (4) of the present application include tubular separation membranes, rolled separation membranes, flat separation membranes and hollow fiber separation membranes; the charge of the separation membrane is the same as the charge of the multivalent ions in the first anion and the first cation of the main product salt, that is, when the multivalent ions in the main product salt are cations, the separation membrane selects a positively charged membrane; when the multivalent ions in the main product salt are anions, the separation membrane selects a negatively charged membrane.

[0036] Furthermore, in step (4), the pore size of the separation membrane is 0.5-10 nm, the porosity is 30-70%, the pressure range is 0-8 MPa, and the interception rate of the multivalent ions of the main product salt is greater than 90%. Furthermore, preferably, the pore size of the separation membrane is 0.5-5 nm, the porosity is 35-55%, the pressure range is 0-6 MPa, and the interception rate of the multivalent ions of the main product salt is greater than 95%.

[0037] Furthermore, in step (4), the volume distribution ratio of the first concentrated liquid separated by the separation membrane to the first permeate is in the range of 1:2 to 1:20.

[0038] Specifically, in step (5), the first concentrated liquid and the first permeate are respectively subjected to membrane re-concentration, with the concentration multiple being 1.2 to 15 times; the membrane re-concentration method includes any one of thermal drive type, pressure drive type and electric field drive type or a combination of at least two thereof.

[0039] Further, in step (5), the membrane device used in the reconcentration process includes but is not limited to a membrane distillation device, a reverse osmosis membrane device and an electrodialysis membrane device. Among them, the membrane materials used in the membrane distillation device include but are not limited to a hydrophobic ceramic membrane, a hydrophobic PVDF (polyvinylidene fluoride) membrane, a hydrophobic PVDF-HFP (polyvinylidene fluoride-hexafluoropropylene) membrane, the pore size of the membrane is 0.8 to 100 nm, the porosity is 35 to 65%, the working pressure tolerance is 0 to -0.1 MPa, and the membrane retention rate is greater than 95%; the membrane materials used in the reverse osmosis membrane device include but are not limited to polytetrafluoroethylene membrane, aromatic polyamide membrane, cellulose acetate membrane, composite membrane, the pore size of the membrane is 0.1 to 1 nm, the pressure range is 0 to 10 MPa, and the membrane desalination rate is greater than 96%; the membrane materials used in the electrodialysis membrane device include but are not limited to polymer membrane, hydrogel membrane, fiber membrane, the water content of the membrane is 30 to 50%, the membrane surface resistance is less than 15Ω·cm2, the membrane exchange capacity is 1.5 to 5mmol / g, and the selective permeability is greater than 85%.

[0040] When the concentration multiple is too low, the ideal concentration effect cannot be achieved, and the recovery amount of the main product salt in the subsequent crystallization step will be affected; when the concentration multiple is too high, the concentration of the membrane inlet solution is high, which is prone to concentration polarization, resulting in a decrease in membrane flux, and easy to produce crystals on the membrane surface, blocking or destroying the membrane pores, and reducing the service life of the membrane material.

[0041] In the present application, the incremental recovery of the main product salt is achieved through four major steps: determining the associated compounds, controlling the amount of associated compounds added, optimizing the separation membrane separation process, and adjusting the membrane reconcentration process. The four steps complement each other and are indispensable. Among them, determining the associated compounds is the basis for the effectiveness of the method of the present application and is of great significance to improving the salt concentration of the main product; controlling the amount of associated compounds added determines the molar ratio of key ions in the second mixed solution, which is crucial to adjusting the reasonable composition of the separation membrane inlet material and is the basis for the specific implementation of the method of the present application; optimizing the separation membrane separation process is the core step to achieve the membrane method to improve the salt concentration of the main product and is a specific way to achieve the goal of the method of the present application; adjusting the membrane reconcentration process can further achieve the concentration increase of the first concentrated solution and the first permeate, and has the advantages of low energy consumption, high operating process safety, and integration, and provides an initial crystallization solution of appropriate concentration for the crystallization process of step (6).

[0042] Specifically, in step (6), the second concentrated liquid and the second permeate are crystallized respectively, and the crystallization method is evaporation crystallization, cooling crystallization or freezing crystallization. The specific crystallization method is selected according to the crystallization characteristics of the crystallization product. For details, please refer to the prior art and will not be described in detail.

[0043] Specifically, in step (7), the associated compound obtained by crystallization in step (6) needs to be measured before returning to the first mixed solution.

[0044] In the present application, the associated compound obtained in step (6) is returned to the first mixed solution as the associated compound of step (3) after being measured;

[0045] In the present application, when the salt concentration in the high-salt wastewater remains stable, all the related compounds obtained in step (6) are returned to step (3), and an appropriate amount of related compounds are supplemented as needed; when the salt concentration of the high-salt wastewater fluctuates, related compounds are added according to actual needs. When adding related compounds, the related compounds obtained from step (6) are first used. When the needs cannot be met, fresh related compounds are supplemented.

[0046] Specifically, in step (8), the mass ratio of the first crystallization mother liquor, the second crystallization mother liquor and the first mixed liquor for reuse is (10-20):(10-30):(50-80). When the mass ratio of the first mixed liquor is too low, the ion concentration of the main product salt in the mixed wastewater solution is low, affecting its product yield; when the mass ratio of the first mixed liquor is too high, the reuse amount of the first crystallization mother liquor and the second crystallization mother liquor is small, which is easy to cause backlog and is not conducive to the stable and continuous operation of the product line.

[0047] In this application, for the sake of clarity, the ions in the high-salt wastewater are divided into effective ions and impure ions, with the total molar number of all detected salt ions (i.e., metal ions and acid radical ions) as the benchmark, where the ions with a molar concentration percentage of <0.5% are impure ions, and the remaining ions are effective ions. The ions described in this application are all effective ions. There is only one type of multivalent cation or multivalent anion in the high-salt wastewater, that is, it does not contain multivalent cations and multivalent anions at the same time, and after the multivalent cations or multivalent anions are converted into monovalent ions, the molar concentration percentage of the multivalent cations or multivalent anions is ≥40%. For example, SO 4 2- After converting to monovalent ions, when calculating the molar concentration, one mole of SO 4 2- In terms of two moles; Mg 2+ After converting to monovalent ions, when calculating molar concentration, one mole of Mg 2+ In terms of two moles; Al 3+After converting to monovalent ions, when calculating the molar concentration, one mole of Al 3+ Calculated as three moles, and so on.

[0048] In the present application, when there are too many impurity ions in the first crystallization mother liquor and the second crystallization mother liquor, and have affected the crystallization purity of the main product salt, the by-product salt and the associated compounds, they are no longer returned to the first mixed liquor, but directly enter the wastewater treatment system for discharge in compliance with the standards; the crystallization purity of the main product salt, the by-product salt and the associated compounds can be determined according to specific needs.

[0049] Compared with the common high-salinity wastewater resource utilization method, the beneficial effects of this application are:

[0050] 1. The method in the present application increases the concentration of one ion in the main product salt by adding related compounds to match another ion of the main product salt with a higher content in high-salt wastewater, thereby providing a basis for incremental recovery of the main product salt from high-salt wastewater; then, the second mixed liquor is separated by a separation membrane, and the monovalent ions and part of the water are permeated out by utilizing the characteristic that the separation membrane has a much higher retention rate for multivalent ions than for monovalent ions, thereby achieving the purpose of separating, purifying and increasing the concentration of the main product salt in the second mixed liquor; compared with directly concentrating the first mixed liquor, the method of the present application effectively adjusts the concentration ratio of key ions in the second mixed liquor, and realizes the separation of solutions with different salts, thereby providing a guarantee for the step-by-step and high-purity recovery of each salt.

[0051] 2. This application cooperates with each other through the four steps of related compound determination + related compound addition control + separation membrane separation + membrane re-concentration to jointly achieve the adjustment, separation, concentration and purification recovery of high-salt wastewater. Compared with the method of increasing the salt concentration of the main product by evaporation and concentration, the energy consumption of this application method is greatly reduced, which is more environmentally friendly and more in line with the national carbon emission policy; compared with the chemical precipitation method with a more complex reaction environment, the method of this application makes the obtained first concentrated solution and first permeate liquid simpler and more concentrated due to the membrane separation effect of the separation membrane on the second mixed liquid. Therefore, the main product salt, related compounds and by-product salts finally crystallized are purer than the salt substances obtained by the chemical precipitation method, and the recycling value is higher; compared with the direct crystallization method of high-salt wastewater, due to the complex composition of high-salt wastewater and the low salt concentration, the direct crystallization method has a low yield of salt substances, a large amount of residual crystallization mother liquor, high disposal difficulty, and the purity of the salt substances obtained by crystallization is not high, and the economic value is limited.

[0052] 3. The related compounds in this application, under the premise of meeting the requirements, can be combined with the market price to select suitable compounds with lower prices, so as to achieve the purpose of adding low-value salt substances to obtain high-value main product salt output, which can reduce the treatment cost of high-salt wastewater and improve economic benefits. Compared with other methods for resource utilization of high-salt wastewater, it has greater cost advantages.

[0053] In summary, the present application provides a high-purity, low-cost, incremental method for recovering salt from high-salinity wastewater, which provides a new solution for the resource utilization of high-salinity wastewater and has significant technical and economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 It is the process flow chart of this application. DETAILED DESCRIPTION

[0055] Reference Figure 1 , the method of the present application is described in detail below through specific embodiments.

[0056] Example 1

[0057] A NH 4 + 、Na + , Cl - 、SO 4 2- The total salt weight fraction of high-salt chemical wastewater is about 1.5wt%. The method of the present application is used to increase the main product salt (NH 4 ) 2 SO 4 The concentration of the main product salt (NH 4 ) 2 SO 4 , the specific steps are as follows:

[0058] (1) For NH 4 + 、Na + , Cl - 、SO 4 2- The high-salt chemical wastewater is pre-treated, and the first mixed liquid is obtained through the steps of pH adjustment, activated carbon adsorption decolorization, physicochemical treatment, precipitation filtration and ultrafiltration membrane separation. The pH value of the first mixed liquid is 5.7, SS is 38.2 mg / L, TOC is 13.5 mg / L, COD is 15.7 mg / L, and SDI is 1.8.

[0059] (2) The first mixed solution is characterized by using ion chromatography to determine the anions and inductively coupled plasma emission spectrometry to determine the cations. The specific ion types and concentration test data are as follows:

[0060] Ion name Test Method Test data mg / L Converted molar concentration mol / L <![CDATA[NH 4 + ]]> Inductively Coupled Plasma Optical Emission Spectrometry 1575 0.0875 <![CDATA[Na + ]]> Inductively Coupled Plasma Optical Emission Spectrometry 3017.6 0.1312 <![CDATA[Cl - ]]> Ion chromatography 491 0.0138 <![CDATA[SO 4 2- ]]> Ion chromatography 9837.2 0.1025

[0061] (3) According to the above characteristics, determine (NH 4 ) 2 SO 4The main product salt was further determined as NH 4 Cl is its associated compound, according to NH 4 + with Na + The molar ratio of NH 4 Material measurement of Cl, calculation of NH 4 The addition amount of Cl was 30.41 g / L, and NH 4 Cl is added to the first mixed solution, and stirred to dissolve to form a second mixed solution, in which the concentration data of each ion are as follows:

[0062] Ion name Test Method Test data mg / L Converted molar concentration mol / L <![CDATA[NH 4 + ]]> Inductively Coupled Plasma Optical Emission Spectrometry 11806.4 0.6559 <![CDATA[Na + ]]> Inductively Coupled Plasma Optical Emission Spectrometry 3017.6 0.1312 <![CDATA[Cl - ]]> Ion chromatography 20669.6 0.5822 <![CDATA[SO 4 2- ]]> Ion chromatography 9837.2 0.1025

[0063] (4) using a negatively charged tubular separation membrane device to perform membrane separation on the second mixed liquid, wherein the membrane pore size of the separation membrane of the membrane device is 0.5 to 3 nm, the porosity is 45%, and the actual working pressure is 2.5 MPa; using the membrane device to perform membrane separation on the second mixed liquid to obtain a first concentrated liquid and a first permeate; the separation membrane is used to separate SO 4 2- The rejection rate is 98%. After membrane separation, the volume distribution ratio of the first concentrate and the first permeate is 1:3.4, that is, the first concentrate is concentrated 4.4 times, and the first permeate is concentrated 1.294 times. The ion concentration data in the first concentrate and the first permeate are as follows:

[0064]

[0065]

[0066] (5) The first concentrated liquid and the first permeate are respectively re-concentrated by reverse osmosis membrane method, wherein the first concentrated liquid is re-concentrated by membrane method using a polytetrafluoroethylene reverse osmosis membrane with a pore size of 0.1-0.8 nm, an actual working pressure of 4 MPa, a membrane desalination rate of 98%, and a re-concentration multiple of 3.5 times to obtain a second concentrated liquid; the second concentrated liquid and the main product salt (NH 4 ) 2 SO 4 The concentration data of each ion are as follows:

[0067]

[0068] The first permeate membrane method re-concentration also uses a polytetrafluoroethylene reverse osmosis membrane, the pore size of the membrane is 0.1-0.8nm, the actual working pressure is 5MPa, the membrane desalination rate is 98%, and the concentration multiple is 5.5 times to obtain the second permeate; the ion concentration data in the second permeate are as follows:

[0069]

[0070] The membrane permeate produced by membrane re-concentration of the first concentrated liquid and the first permeate reaches the process water standard and is returned to the system for reuse.

[0071] (6) The second concentrated solution is cooled and crystallized to obtain the main product salt (NH 4 ) 2 SO 4 and the first crystallization mother liquor; the second permeate is subjected to step-by-step crystallization, using evaporation crystallization followed by cooling crystallization to obtain by-product salt NaCl and associated compound NH 4 Cl and the second crystallization mother liquor.

[0072] (7) After measuring the related compound obtained from the above crystallization, return to step (3), mix it with fresh related compounds, and then measure and add it to the first mixed solution for reuse.

[0073] (8) Returning the first crystallization mother liquor and the second crystallization mother liquor to the first mixed liquor for mixed reuse, the mixed reuse mass ratio of the first crystallization mother liquor: the second crystallization mother liquor: the first mixed liquor is 15:20:65.

[0074] In this embodiment, NH 4 Cl is used as a related compound to increase the NH 4 + concentration, the main product salt (NH 4 ) 2 SO 4 Provide sufficient cations; then separate the monovalent ions and divalent ions through the negatively charged separation membrane, and separate the Cl - Seepage, SO 4 2- 98% intercepted, NH 4 + and Na + The first concentrated solution and the first permeate are both present in a molar ratio of 5:1; the first concentrated solution and the first permeate are further concentrated to the crystallization concentration through a reverse osmosis membrane, and finally the main product salt (NH 4 ) 2 SO 4 、Related compounds NH 4 Cl and by-product salt NaCl.

[0075] Compared with the initial first mixed solution, the main product salt (NH 4 ) 2 SO 4 The mass and molar concentration were both increased by 2845.7%. It can be seen that the method of this embodiment has achieved the main product salt (NH 4 ) 2 SO4 The separation, purification and concentration of the main product salt (NH 4 ) 2 SO 4 The purpose of concentration enhancement and incremental recovery.

[0076] This embodiment also realizes the recovery of related compounds and by-product salts, and has a high total salt recovery rate for high-salt wastewater. After the obtained related compounds are reused, the amount of external related compounds added is greatly reduced, the operating investment is reduced, and the production cost is saved; the obtained by-product salt is sold as finished salt, which broadens the economic value of high-salt wastewater resource recovery.

[0077] Example 2

[0078] A NH 4 + 、Na + , Cl - 、SO 4 2- The total salt weight fraction of high-salt chemical wastewater is about 1.5wt%. The method of the present application is used to increase the main product salt (NH 4 ) 2 SO 4 The concentration of the main product salt (NH 4 ) 2 SO 4 , the specific steps are as follows:

[0079] (1) For NH 4 + 、Na + , Cl - 、SO 4 2- The high-salt chemical wastewater is pre-treated, and the first mixed liquid is obtained through the steps of pH adjustment, activated carbon adsorption decolorization, physicochemical treatment, precipitation filtration and ultrafiltration membrane separation. The pH value of the first mixed liquid is 5.7, SS is 38.2 mg / L, TOC is 13.5 mg / L, COD is 15.7 mg / L, and SDI is 1.8.

[0080] (2) The first mixed solution is characterized by using ion chromatography to determine the anions and inductively coupled plasma emission spectrometry to determine the cations. The specific ion types and concentration test data are as follows:

[0081] Ion name Test Method Test data mg / L Converted molar concentration mol / L <![CDATA[NH 4 + ]]> Inductively Coupled Plasma Optical Emission Spectrometry 1575 0.0875 <![CDATA[Na + ]]> Inductively Coupled Plasma Optical Emission Spectrometry 3017.6 0.1312 <![CDATA[Cl - ]]> Ion chromatography 491 0.0138 <![CDATA[SO 4 2- ]]> Ion chromatography 9837.2 0.1025

[0082] (3) According to the above characteristics, determine (NH 4 ) 2SO 4 The main product salt was further determined as NH 4 Cl is its associated compound, according to NH 4 + with Na + The molar ratio of NH 4 Material calculation of Cl, calculate NH 4 The addition amount of Cl was 44.453 g / L, and NH 4 Cl is added to the first mixed solution, and stirred to dissolve to form a second mixed solution, in which the concentration data of each ion are as follows:

[0083] Ion name Test Method Test data mg / L Converted molar concentration mol / L <![CDATA[NH 4 + ]]> Inductively Coupled Plasma Optical Emission Spectrometry 16531.2 0.9184 <![CDATA[Na + ]]> Inductively Coupled Plasma Optical Emission Spectrometry 3017.6 0.1312 <![CDATA[Cl - ]]> Ion chromatography 29986.85 0.8447 <![CDATA[SO 4 2- ]]> Ion chromatography 9837.2 0.1025

[0084] (4) using a negatively charged tubular separation membrane device to perform membrane separation on the second mixed liquid, wherein the membrane pore size of the separation membrane of the membrane device is 0.5 to 3 nm, the porosity is 45%, and the actual working pressure is 2.5 MPa; using the membrane device to perform membrane separation on the second mixed liquid to obtain a first concentrated liquid and a first permeate; the separation membrane is used to separate SO 4 2- The rejection rate is 98%. After membrane separation, the volume distribution ratio of the first concentrate and the first permeate is 1:4.2, that is, the first concentrate is concentrated 5.2 times, and the first permeate is concentrated 1.238 times. The ion concentration data of the first concentrate and the first permeate after membrane separation are as follows:

[0085]

[0086] (5) The first concentrated liquid and the first permeate are respectively re-concentrated by reverse osmosis membrane method, wherein the first concentrated liquid membrane method re-concentration uses a polytetrafluoroethylene reverse osmosis membrane with a pore size of 0.1-0.8 nm, an actual working pressure of 4 MPa, a membrane desalination rate of 97%, and a concentration multiple of 3 times to obtain a second concentrated liquid; the second concentrated liquid and the main product salt (NH 4 ) 2 SO 4 The concentration data of each ion are as follows:

[0087]

[0088] The first permeate membrane method re-concentration also uses a polytetrafluoroethylene reverse osmosis membrane, the pore size of the membrane is 0.1-0.8nm, the actual working pressure is 5MPa, the membrane desalination rate is 97%, and the concentration multiple is 3 times to obtain the second permeate; the ion concentration data in the second permeate are as follows:

[0089]

[0090] The membrane permeate produced by membrane re-concentration of the first concentrated liquid and the first permeate reaches the process water standard and is returned to the system for reuse.

[0091] (6) The second concentrated solution is cooled and crystallized to obtain the main product salt (NH 4 ) 2 SO 4 and the first crystallization mother liquor; the second permeate is subjected to step-by-step crystallization, using evaporation crystallization followed by cooling crystallization to obtain by-product salt NaCl and associated compound NH 4 Cl and the second crystallization mother liquor.

[0092] (7) After measuring the related compound obtained from the above crystallization, return to step (3), mix it with fresh related compounds, and then measure and add it to the first mixed solution for reuse.

[0093] (8) Returning the first crystallization mother liquor and the second crystallization mother liquor to the first mixed liquor for mixed reuse, the mixed reuse mass ratio of the first crystallization mother liquor: the second crystallization mother liquor: the first mixed liquor is 15:20:65.

[0094] In this embodiment, NH 4 Cl is used as a related compound to increase the NH 4 + concentration, the main product salt (NH 4 ) 2 SO 4 Provide sufficient cations; then separate the monovalent ions and divalent ions through the negatively charged separation membrane, and separate the Cl - Seepage, SO 4 2- 98% intercepted, NH 4 + and Na + The first concentrated solution and the first permeate are both present in a molar ratio of 7:1; the first concentrated solution and the first permeate are further concentrated to the crystallization concentration through a reverse osmosis membrane, and finally the main product salt (NH 4 ) 2 SO 4 、Related compounds NH 4 Cl and by-product salt NaCl.

[0095] Compared with the initial first mixed solution, the main product salt (NH 4 ) 2 SO 4 The mass and molar concentration were both increased by 2969.21%. It can be seen that the method of this embodiment has achieved the main product salt (NH 4 ) 2 SO4 The separation, purification and concentration of the main product salt (NH 4 ) 2 SO 4 The purpose of concentration enhancement and incremental recovery.

[0096] In addition, this embodiment also recovers the related compound NH 4 Cl and by-product salt NaCl are recovered and reused or sold to the outside, thereby improving the salt recovery rate of high-salt wastewater; at the same time, the membrane seepage water produced in the re-concentration process is reused as process water, and the first and second crystallization mother liquors are also reasonably reused. The salt recovery method of this embodiment has the characteristics of high yield, low cost and low emission, and has obvious technical and economic value.

[0097] Example 3

[0098] A Mg-containing 2+ 、Na + , Cl - 、NO 3 - The total salt weight fraction of high-salt industrial wastewater is about 1.6wt%. The method of the present application is used to increase the main product salt Mg(NO 3 ) 2 The concentration is reduced, and finally the main product salt Mg(NO is recovered by crystallization. 3 ) 2 , the specific steps are as follows:

[0099] (1) For Mg 2+ 、Na + , Cl - 、NO 3 - The high-salt industrial wastewater was pre-treated, and successively went through activated carbon adsorption decolorization, physicochemical treatment, precipitation filtration, pH adjustment and ultrafiltration membrane separation processes to obtain the first mixed liquid. The pH value of the first mixed liquid was 6.8, SS was 31.2 mg / L, TOC was 24.9 mg / L, COD was 22.8 mg / L, and SDI was 2.5.

[0100] (2) The first mixed solution is characterized by using ion chromatography to determine the anions and atomic absorption spectroscopy to determine the cations. The specific ion types and concentration test data are as follows:

[0101] Ion name Test Method Test data mg / L Converted molar concentration mol / L <![CDATA[Mg 2+ ]]> Atomic absorption spectroscopy 2880 0.12 <![CDATA[Na + ]]> Atomic absorption spectroscopy 460 0.02 <![CDATA[Cl - ]]> Ion chromatography 4792.5 0.135 <![CDATA[NO 3 - ]]> Ion chromatography 7750 0.125

[0102] (3) According to the above characteristics, determine Mg(NO 3 ) 2 The main product is salt, and further determine the lower selling price of NaNO3 As its related compound, according to the NO in the second mixed solution 3 - With Cl - The molar ratio of NaNO was 5:1. 3 Material calculation, calculate NaNO 3 The addition amount is 46.75g / L, and NaNO 3 Add to the first mixed solution, stir and dissolve to form a second mixed solution, the concentration data of each ion are as follows:

[0103] Ion name Test Method Test data mg / L Converted molar concentration mol / L <![CDATA[Mg 2+ ]]> Atomic absorption spectroscopy 2880 0.12 <![CDATA[Na + ]]> Atomic absorption spectroscopy 13110 0.57 <![CDATA[Cl - ]]> Ion chromatography 4792.5 0.135 <![CDATA[NO 3 - ]]> Ion chromatography 41850 0.675

[0104] (4) using a positively charged flat plate separation membrane device to perform membrane separation on the second mixed liquid, wherein the membrane pore size of the separation membrane of the membrane device is 0.7-4 nm, the porosity is 54%, and the actual working pressure is 3.5 MPa; using the membrane device to perform separation membrane separation on the second mixed liquid to obtain a first concentrated liquid and a first permeate; the separation membrane is charged to Mg 2+ The rejection rate is 99%. After membrane separation, the volume distribution ratio of the first concentrate and the first permeate is 1:4, that is, the first concentrate is concentrated 5 times, and the first permeate is concentrated 1.25 times. The ion concentration data in the first concentrate and the first permeate are as follows:

[0105]

[0106] (5) The first concentrated liquid and the first permeate are respectively re-concentrated by reverse osmosis membrane method, wherein the first concentrated liquid membrane method re-concentration uses a composite reverse osmosis membrane with a pore size of 0.5-1 nm, an actual working pressure of 5 MPa, a membrane desalination rate of 98.5%, and a re-concentration multiple of 2.5 times to obtain a second concentrated liquid; the second concentrated liquid and the main product salt Mg(NO 3 ) 2 The concentration data of each ion are as follows:

[0107]

[0108] The first permeate membrane method re-concentration also uses a composite reverse osmosis membrane, the pore size of the membrane is 0.5-1nm, the actual working pressure is 5MPa, the membrane desalination rate is 98.5%, and the concentration multiple is 3.5 times to obtain the second permeate; the ion concentration data in the second permeate are as follows:

[0109]

[0110] The membrane permeate produced by membrane re-concentration of the first concentrated liquid and the first permeate reaches the process water standard and is returned to the system for reuse.

[0111] (6) The second concentrated solution is subjected to freeze crystallization to obtain the main product salt Mg(NO 3 ) 2 and the first crystallization mother liquor; the second permeate is subjected to step-by-step crystallization, using evaporation crystallization followed by cooling crystallization to obtain by-product salt NaCl and associated compound NaNO 3 and the second crystallization mother liquor.

[0112] (7) After measuring the related compound obtained from the above crystallization, return to step (3), mix it with fresh related compounds, and then measure and add it to the first mixed solution for reuse.

[0113] (8) Returning the first crystallization mother liquor and the second crystallization mother liquor to the first mixed liquor for mixing and reuse, the mixed reuse mass ratio of the first crystallization mother liquor: the second crystallization mother liquor: the first mixed liquor is 10:25:65.

[0114] In this embodiment, NaNO is selected, which has a lower market price. 3 As an associated compound, to increase the NO in the first mixed solution 3 - concentration, the main product salt Mg(NO 3 ) 2 Provide sufficient anions; then separate the monovalent ions and divalent ions through the positively charged separation membrane, and separate the Na + Permeation, Mg 2+ 99% intercepted, NO 3 - and Cl - The first concentrated solution and the first permeate are both present in a molar ratio of 5:1; the first concentrated solution and the first permeate are further concentrated to the crystallization concentration through the composite reverse osmosis membrane, and finally the main product salt Mg(NO 3 ) 2 、Related compounds NaNO 3 and by-product salt NaCl.

[0115] Compared with the initial first mixed solution, the Mg(NO 3 ) 2 The mass and molar concentration were increased by 1880%, which shows that the method of this embodiment has achieved the main product salt Mg(NO 3 ) 2 The separation, purification and concentration of the main product salt Mg(NO 3 ) 2 The purpose of incremental recycling.

[0116] This embodiment also realizes the related compound NaNO 3The recovery of the by-product salt NaCl has a high total recovery rate of salt in high-salinity wastewater. In addition, this embodiment adds NaNO 3 , and obtain the main product salt Mg(NO 3 ) 2 , has considerable economic value.

[0117] Example 4

[0118] A kind of Al 3+ , K + 、Na + , Cl - 、NO 3 - The total salt weight fraction of high-salinity industrial wastewater is about 2.2wt%. The method of the present application is used to increase the main product salt Al(NO 3 ) 3 concentration, and finally crystallize to recover the main product salt Al(NO 3 ) 3 , the specific steps are as follows:

[0119] (1) For Al 3+ , K + 、Na + , Cl - 、NO 3 - The high-salt industrial wastewater was pre-treated, and successively went through the steps of pH adjustment, activated carbon adsorption decolorization, physicochemical treatment, sedimentation filtration and ultrafiltration membrane separation to obtain the first mixed liquid. The pH value of the first mixed liquid was 4.5, SS was 28.2 mg / L, TOC was 26.5 mg / L, COD was 24.9 mg / L, and SDI was 1.9.

[0120] (2) The first mixed solution is characterized by using ion chromatography to test anions and atomic absorption spectroscopy to test cations. The specific ion types and concentration test data are as follows:

[0121] Ion name Test Method Test data mg / L Converted molar concentration mol / L <![CDATA[Al 3+ ]]> Atomic absorption spectroscopy 2970 0.11 <![CDATA[K + ]]> Atomic absorption spectroscopy 604.5 0.0155 <![CDATA[Na + ]]> Atomic absorption spectroscopy 299 0.013 <![CDATA[Cl - ]]> Ion chromatography 5502.5 0.155 <![CDATA[NO 3 - ]]> Ion chromatography 12617 0.2035

[0122] (3) According to the above characteristics, determine Al(NO 3 ) 3 The main product is salt, and further determine the lower selling price of NaNO 3 As its related compound, according to the NO in the second mixed solution 3 - With Cl - The molar concentration ratio of NaNO was 5:1. 3 Material calculation, calculate NaNO 3The addition amount is 48.58g / L, and NaNO 3 Add to the first mixed solution, stir and dissolve to form a second mixed solution, the concentration data of each ion are as follows:

[0123] Ion name Test Method Test data mg / L Converted molar concentration mol / L <![CDATA[Al 3+ ]]> Atomic absorption spectroscopy 2970 0.11 <![CDATA[K + ]]> Atomic absorption spectroscopy 604.5 0.0155 <![CDATA[Na + ]]> Atomic absorption spectroscopy 13443.5 0.5845 <![CDATA[Cl - ]]> Ion chromatography 5502.5 0.155 <![CDATA[NO 3 - ]]> Ion chromatography 48050 0.775

[0124] (4) A positively charged hollow fiber separation membrane device is used to perform membrane separation on the second mixed liquid. The membrane pore size of the separation membrane of the membrane device is in the range of 0.5 to 5 nm, the porosity is 57%, and the actual working pressure is 3.3 MPa. The second mixed liquid is separated by a separation membrane using the membrane device to obtain a first concentrated liquid and a first permeate. The separation membrane is used to separate the Al 3+ The rejection rate is 99%. After membrane separation, the volume distribution ratio of the first concentrate and the first permeate is 1:5, that is, the first concentrate is concentrated 6 times, and the first permeate is concentrated 1.2 times. The ion concentration data in the first concentrate and the first permeate are as follows:

[0125]

[0126] (5) The first concentrated liquid and the first permeate are respectively re-concentrated by electrodialysis membrane method, and a polymer membrane is selected. The water content of the membrane is 40%, and the membrane surface resistance is 12Ω·cm 2 The membrane exchange capacity was 2.5 mmol / g, the selectivity was 89%, and the concentration multiple was 6 times to obtain the second concentrated solution; the second concentrated solution and the main product salt Al(NO 3 ) 3 The concentration data of each ion are as follows:

[0127]

[0128] The first permeate membrane reconcentration also uses a polymer electrodialysis membrane, the water content of which is 40% and the membrane surface resistance is 12Ω·cm 2 , the membrane exchange capacity is 2.5mmol / g, the selective permeability is 89%, the concentration multiple is 2 times, and the second permeate is obtained; the ion concentration data in the second permeate are as follows:

[0129]

[0130]

[0131] The membrane permeate produced by membrane re-concentration of the first concentrated liquid and the first permeate reaches the process water standard and is returned to the system for reuse.

[0132] (6) The second concentrated solution is subjected to freeze crystallization to obtain the main product salt Al(NO 3 ) 3and the first crystallization mother liquor; the second permeate is subjected to step-by-step crystallization, and the step-by-step crystallization adopts the existing mature technology to obtain the related compound NaNO 3 , by-product salt NaCl and the second crystallization mother liquor.

[0133] (7) After measuring the related compound obtained from the above crystallization, return to step (3), mix it with fresh related compounds, measure it and add it to the first mixed solution for reuse.

[0134] (8) Returning the first crystallization mother liquor and the second crystallization mother liquor to the first mixed liquor for mixing and reuse, the mass ratio of the first crystallization mother liquor: the second crystallization mother liquor: the first mixed liquor for mixing and reuse is 15:25:60.

[0135] In this embodiment, NaNO, which has a lower market price, is selected 3 As an associated compound, to increase the NO in the first mixed solution 3 - concentration, the main product salt Al(NO 3 ) 3 Provide sufficient anions; then separate the monovalent ions and trivalent ions through the positively charged separation membrane, and separate the Na + , K + Permeate, Al 3+ 99% was retained, while NO 3 - and Cl - The first concentrated solution and the first permeate are both present in a molar ratio of 5:1; the first concentrated solution and the first permeate are further concentrated to a crystallization concentration through a polymer electrodialysis membrane, and finally the main product salt Al(NO 3 ) 3 、Related compounds NaNO 3 and by-product salt NaCl.

[0136] Compared with the initial first mixed solution, the Al(NO 3 ) 3 The mass and molar concentration were increased by 4716.22%, which shows that the main product salt Al(NO 3 ) 3 The separation, purification and concentration of the main product salt Al(NO 3 ) 3 In addition, this embodiment adds NaNO, which has a lower market price, to the first mixed solution. 3 , and obtain the main product salt Al(NO 3 ) 3, the economic benefits are very considerable.

Claims

1. A method for incrementally recovering salt from high-salinity wastewater, characterized in that: The steps include: (1) Preliminary treatment of high-salinity wastewater to obtain a first mixed solution; (2) performing characteristic discrimination on the first mixed solution; (3) determining the main product salt and its associated compounds based on characteristic discrimination, measuring the associated compounds and adding them to the first mixed solution to form a second mixed solution; One of the first anion and the first cation of the main product salt has a valence of monovalent and the other has a valence of polyvalent; the valence of the second anion and the second cation of the associated compound are both monovalent; One of the second anion and the second cation of the associated compound is the same as the first anion and the first cation of the main product salt, which has a valence of one, and the other is the same as an ion other than the first anion and the first cation in the high-salinity wastewater; The first anion, the first cation, the second anion, and the second cation are all ions already present in the high-salinity wastewater; In the second mixed solution, the molar ratio of the third ion to the fourth ion is (3-8):1, wherein the third ion is an ion with a valence of one of the first anion and the first cation of the main product salt, and the fourth ion is an ion with the same charge and valence as the third ion except the third ion; (4) separating the second mixed liquid by a separation membrane to obtain a first concentrated liquid and a first permeate; (5) re-concentrating the first concentrated solution and the first permeate by a membrane method to obtain a second concentrated solution, a second permeate and membrane permeate; (6) crystallizing the second concentrated solution to obtain a main product salt and a first crystallization mother liquor, and fractionally crystallizing the second permeate to obtain a related compound, a by-product salt, and a second crystallization mother liquor; (7) using the associated compound obtained by crystallization in step (6) as the associated compound of step (3) and returning it to the first mixed solution; (8) Returning the first crystallization mother liquor and the second crystallization mother liquor to the first mixed liquor for mixing and reuse.

2. The method for incrementally recovering salt from high-salinity wastewater according to claim 1, characterized in that: In step (1), after the high-salinity wastewater is pre-treated, the pH value of the first mixed solution obtained is in the range of 2 to 13, SS is less than 50 mg / L, TOC is less than 50 mg / L, COD is less than 40 mg / L, and SDI is less than 5.

3. The method for incrementally recovering salt from high-salinity wastewater according to claim 1, characterized in that: In step (2), the first mixed solution is subjected to characteristic identification, including identifying the types of ions contained therein, clarifying the valence distribution of each ion, and determining the concentration of each ion.

4. The method for incrementally recovering salt from high-salinity wastewater according to claim 1, characterized in that: In step (4), the charge of the separation membrane is the same as the charge of the multivalent ions in the first anion and the first cation of the main product salt; the pore size of the separation membrane is 0.5 to 10 nm, the porosity is 30 to 70%, the pressure range is 0 to 8 MPa, and the retention rate of the multivalent ions of the main product salt is >90%.

5. The method for incrementally recovering salt from high-salinity wastewater according to claim 1, characterized in that: In step (5), the first concentrated liquid and the first permeate are respectively subjected to membrane re-concentration, and the concentration multiple is 1.2 to 15 times; the membrane re-concentration method includes any one of thermal drive type, pressure drive type and electric field drive type or a combination of at least two thereof.

6. The method for incrementally recovering salt from high-salinity wastewater according to claim 1, characterized in that: In step (6), the second concentrated solution and the second permeate are crystallized respectively, and the crystallization method is evaporation crystallization, cooling crystallization or freezing crystallization.

7. The method for incrementally recovering salt from high-salinity wastewater according to claim 1, characterized in that: In step (7), the associated compound obtained by crystallization in step (6) needs to be measured before returning to the first mixed solution.

8. The method for incrementally recovering salt from high-salinity wastewater according to claim 1, characterized in that: In step (8), the mass ratio of the first crystallization mother liquor, the second crystallization mother liquor and the first mixed liquor for mixing and recycling is (10-20):(10-30):(50-80).

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