Resource utilization method and resource utilization system for highly-mineralized mine water

Abstract

According to the resource utilization method and the resource utilization system for the high-mineralization-degree mine water, the chemical consumption and the energy consumption can be reduced, and the resource utilization of the high-mineralization-degree mine water can be realized. The method comprises the following steps: 1) feeding the highly-mineralized mine water into a first chemical softening unit for treatment, and then feeding the treated highly-mineralized mine water into a first reverse osmosis unit for treatment; 2) feeding the first reverse osmosis concentrated water into a first crystallizer to obtain a first mother solution; 3) filtering the first mother liquor, and feeding the filtered first mother liquor into a nanofiltration unit for treatment; or the first mother liquor is fed into a second chemical softening unit to be treated to obtain calcium carbonate mixed liquor, and the calcium carbonate mixed liquor is fed into a nanofiltration unit to be treated after being filtered; 4) returning the concentrated water to the first crystallizer for continuous treatment; 5) concentrating the produced water rich in sodium chloride in a concentration unit; and 6) treating the concentrated solution in a post-treatment unit to obtain a product containing sodium chloride.

Description

Technical Field

[0001] The invention relates to the technical field of treatment of high-mineralization mine water, and in particular to a resource utilization method and resource utilization system of high-mineralization mine water. Background Art

[0002] At present, the mine water produced by coal mining in my country is 1.87m 3 , coal mine water is about 6.88×10 9 m 3 , the average utilization rate of coal mine water is about 35%. According to the research and prediction of coal production development trend, by 2035, my country's coal mine water can be stabilized at 6.0×10 9 m 3 As mentioned above, coal mine water will be a long-term and stable unconventional water resource in my country, and the efficient use of mine water will have significant economic and social benefits.

[0003] The traditional method of treating high-mineralized mine water uses pretreatment, membrane concentration and evaporation crystallization to treat concentrated brine. It has high chemical consumption and treatment costs, and the resulting mixed salts cannot be recycled and can only be disposed of as hazardous waste. The disposal cost is as high as 3,000-5,000 yuan / ton. The disposal cost may be even higher in some local areas, which is not conducive to the development and utilization of mine water resources.

[0004] Therefore, it is necessary to further improve the system and method for resource utilization of high-mineralized mine water, so as to reduce the treatment cost of high-mineralized mine water and realize resource utilization. Summary of the invention

[0005] The present invention provides a resource utilization method and a resource utilization system for high-mineralized mine water. The scheme of the present invention can not only reduce drug consumption and energy consumption and lower pretreatment costs, but also realize resource utilization of high-mineralized mine water, convert the miscellaneous salts therein into industrial salt products, and realize the transformation of waste into treasure.

[0006] To achieve the purpose, the present invention provides the following technical solutions:

[0007] In one aspect, the present invention provides a method for resource utilization of high-mineralization mine water, the method comprising the following steps:

[0008] 1) sending the high-mineralization mine water to a first chemical softening unit for treatment to remove magnesium hardness, and then sending it to a first reverse osmosis unit for treatment to obtain first reverse osmosis product water and first reverse osmosis concentrated water;

[0009] 2) sending the first reverse osmosis concentrated water into a first crystallizer to induce crystallization, so that sulfate and calcium ions in the first reverse osmosis concentrated water are crystallized to form calcium sulfate dihydrate, and obtaining a first mother liquor;

[0010] 3) After filtering the first mother liquor, the mother liquor is sent to a nanofiltration unit for treatment to obtain concentrated water rich in sodium sulfate and produced water rich in sodium chloride;

[0011] Alternatively, the first mother liquor is sent to a second chemical softening unit for treatment, so that calcium ions in the first mother liquor react with carbonate ions to obtain a calcium carbonate mixed solution, and then the calcium carbonate mixed solution is filtered and sent to a nanofiltration unit for treatment to obtain concentrated water rich in sodium sulfate and produced water rich in sodium chloride;

[0012] 4) returning the concentrated water rich in sodium sulfate in step 3) to the first crystallizer in step 2) for further treatment;

[0013] 5) concentrating the produced water rich in sodium chloride in a concentration unit to obtain a concentrated solution;

[0014] 6) treating the concentrated solution in a post-treatment unit to obtain a product including sodium chloride.

[0015] Further, in step 1), a first softening agent is added into the first chemical softening unit to remove the magnesium hardness, and the first softening agent is preferably lime or sodium hydroxide;

[0016] In step 3), a second softening agent capable of providing the carbonate ions is added into the second chemical softening unit. Preferably, the second softening agent is sodium carbonate.

[0017] Preferably, in step 1), the apparent salt rejection rate of the first reverse osmosis unit is preferably not less than 97%.

[0018] Preferably, the recovery rate of the first reverse osmosis unit is adjusted so that the calcium sulfate saturation in the first reverse osmosis concentrated water obtained by the first reverse osmosis unit does not exceed 700%;

[0019] Preferably, in step 1), before the high-mineralization mine water is fed into the first chemical softening unit, the high-mineralization mine water is subjected to coagulation and sedimentation treatment to remove suspended matter and coal powder therein;

[0020] Preferably, in step 1), the high-mineralization mine water is treated by the first chemical softening unit, filtered and ultrafiltered, and then sent to the first reverse osmosis unit.

[0021] In a preferred embodiment, in step 2), during the induced crystallization process, an inducer is added to the first crystallizer. Preferably, the inducer is added to make the mass concentration of calcium sulfate dihydrate crystals in the first crystallizer be 3-10%.

[0022] Preferably, the inducer is calcium sulfate dihydrate powder.

[0023] Preferably, the induced crystallization does not require additional heating; further preferably, the induced crystallization is carried out at 10-45°C.

[0024] In a preferred embodiment, in step 3), the filtration is performed in a bag microfiltration device;

[0025] In a preferred embodiment, in step 3), the nanofiltration unit includes a secondary nanofiltration device; preferably, the nanofiltration unit includes a primary nanofiltration device and a secondary nanofiltration device connected in series; preferably, the nanofiltration membrane used in the nanofiltration unit is a material separation membrane; preferably, the separation rate of monovalent salts and divalent salts of the nanofiltration unit is not less than 95%.

[0026] In some embodiments, in step 5), the concentration unit includes a second reverse osmosis unit connected to the nanofiltration unit, and an evaporator connected to the second reverse osmosis unit, the second reverse osmosis unit is used to perform reverse osmosis treatment on the produced water rich in sodium chloride, and the evaporator is used to evaporate and concentrate the second reverse osmosis concentrated water obtained by the second reverse osmosis unit;

[0027] Preferably, the second reverse osmosis unit obtains second reverse osmosis concentrated water with a TDS of about 13-18%;

[0028] Preferably, the evaporator uses steam exhaust or low-pressure steam to provide heat energy, and the water production ratio of the evaporator is preferably 5-12;

[0029] Preferably, in step 5), the sodium chloride-rich produced water is concentrated to a TDS of 23%-30% by the treatment of the concentration unit.

[0030] In a preferred embodiment, in step 6), the post-processing unit includes a second crystallizer and a mother liquor purification device;

[0031] sending the concentrated solution into the second crystallizer for evaporation and crystallization to obtain sodium chloride and a second mother liquor;

[0032] sending the second mother liquor into the mother liquor purification device for treatment to remove organic matter and residual hardness therein to obtain a purified second mother liquor;

[0033] Preferably, the post-treatment unit further comprises a bipolar membrane electrodialysis device or a sodium hypochlorite generator; the purified second mother liquor is passed into the bipolar membrane electrodialysis device for treatment to obtain acid and alkali; or, the purified second mother liquor is passed into the sodium hypochlorite generator for treatment to obtain sodium hypochlorite.

[0034] The present invention also provides a resource utilization system capable of implementing the resource utilization method of the high-mineralization mine water described above, the system comprising:

[0035] A first chemical softening unit, used for chemically softening high-mineralized mine water to obtain mine water with magnesium hardness removed;

[0036] A first reverse osmosis unit is used to perform reverse osmosis on the mine water from which magnesium hardness has been removed to obtain first reverse osmosis product water and first reverse osmosis concentrated water;

[0037] a first crystallizer, used for inducing crystallization of the first reverse osmosis concentrated water, so that sulfate radicals and calcium ions in the first reverse osmosis concentrated water are crystallized to form calcium sulfate dihydrate, and obtaining a first mother liquor;

[0038] a nanofiltration unit, used for separating the monovalent salt and the divalent salt from the first mother liquor after the filtration treatment and obtaining concentrated water rich in sodium sulfate and produced water rich in sodium chloride; the concentrated water outlet of the nanofiltration unit is connected to the first crystallizer to circulate the concentrated water rich in sodium sulfate to the first crystallizer;

[0039] A concentration unit, used for concentrating the produced water rich in sodium chloride to obtain a concentrated solution;

[0040] A post-processing unit, used for post-processing the concentrated liquid to obtain a product including sodium chloride;

[0041] Preferably, the method further comprises a second chemical softening unit disposed between the first crystallizer and the nanofiltration unit, for chemically softening the first mother liquor before entering the nanofiltration unit so as to allow calcium ions and carbonates in the first mother liquor to react.

[0042] In a preferred embodiment, it further comprises a coagulation and sedimentation unit, a first filtration unit, an ultrafiltration unit, and a second filtration unit;

[0043] The coagulation and sedimentation unit is used to treat the high-mineralization mine water to remove suspended matter and coal powder therein; the water output outlet of the coagulation and sedimentation unit is connected to the water inlet of the first chemical softening unit;

[0044] The water inlet of the first filter unit is connected to the water outlet of the first chemical softening unit, the water outlet of the first filter unit is connected to the water inlet of the ultrafiltration unit, and the water outlet of the ultrafiltration unit is connected to the water inlet of the first reverse osmosis unit;

[0045] The second filtering unit is arranged between the second chemical softening unit and the nanofiltration unit, and is used for filtering the mixed liquid obtained by the reaction in the second softening unit; preferably, the second filtering unit includes a bag microfiltration device.

[0046] In a preferred embodiment, the nanofiltration unit includes a secondary nanofiltration device; preferably, the nanofiltration unit includes a primary nanofiltration device and a secondary nanofiltration device connected in series.

[0047] In some embodiments, the concentration unit includes a second reverse osmosis unit and an evaporator, the water inlet of the second reverse osmosis unit is connected to the water production outlet of the nanofiltration unit, and the concentrated water outlet of the second reverse osmosis unit is connected to the water inlet of the evaporator;

[0048] In a preferred embodiment, the post-treatment unit includes a second crystallizer and a mother liquor purification device, the second crystallizer is connected to the concentrated liquid outlet of the concentrating unit, and is used to evaporate and crystallize the concentrated liquid to obtain sodium chloride and a second mother liquor; the mother liquor purification device is connected to the second crystallizer, and is used to treat the second mother liquor to remove organic matter and residual hardness therein and obtain a purified second mother liquor; preferably, the post-treatment unit also includes a bipolar membrane electrodialysis device for treating the purified second mother liquor to obtain acid and alkali, or includes a sodium hypochlorite generator for treating the purified second mother liquor to obtain sodium hypochlorite.

[0049] The technical solution provided by the present invention has the following beneficial effects:

[0050] The scheme of the present invention can reduce the drug consumption and energy consumption in the pretreatment process, reduce the pretreatment cost, and at the same time, can turn the miscellaneous salt into industrial salt products, which can be used as industrial raw materials in other industries, realizing the transformation of waste into treasure. Through the low-cost treatment and resource utilization of mine water, mine water can be made into the second water source for water-deficient areas in the west, alleviating the water shortage for industrial and agricultural production in the west.

[0051] The scheme of the present invention can reduce the processing cost of high-mineralization mine water and the disposal cost of mixed salts, thereby realizing the deep utilization of mine water resources. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 A schematic diagram of a system for resource utilization of high-mineralization mine water in one implementation.

[0053] Figure 2 In one embodiment, the Figure 1 Schematic diagram of the main flow changes in the system for treating high-mineralized mine water.

[0054] Figure 3 A schematic diagram of a system for resource utilization of high-mineralization mine water in another implementation manner. DETAILED DESCRIPTION

[0055] In order to facilitate the understanding of the present invention, the present invention will be further described below in conjunction with examples. It should be understood that the following examples are only for a better understanding of the present invention and do not mean that the present invention is limited to the following examples.

[0056] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which the present invention belongs. The term "and / or" as may be used herein includes any and all combinations of one or more of the related listed items. In the text, the terms "first", "second", etc. are used only for descriptive purposes and are not to be understood as indicating or implying relative importance.

[0057] Where specific experimental steps or conditions are not specified in the examples, the corresponding conventional experimental steps or conditions in the art can be used. The reagents or instruments used without specifying the manufacturer are all conventional products that can be purchased commercially.

[0058] The present invention provides a method for resource utilization of high-mineralization mine water, which mainly comprises the following steps:

[0059] 1) Sending the high-mineralization mine water to the first chemical softening unit for treatment, removing the magnesium hardness in the mine water by chemical softening, and then sending it to the first reverse osmosis unit for reverse osmosis, so that the mine water is concentrated, and the first reverse osmosis product water and the first reverse osmosis concentrated water are obtained. Among them, the first reverse osmosis product water can be used for subsequent reuse;

[0060] 2) sending the first reverse osmosis concentrated water into a first crystallizer for inducing crystallization. The first crystallizer may be a self-induced crystallizer. By inducing crystallization, sulfate radicals and calcium ions in the first reverse osmosis concentrated water are crystallized to form calcium sulfate dihydrate (i.e., dihydrate gypsum), and a first mother liquor is obtained at the same time;

[0061] 3) After filtering the first mother liquor and discharging the solid waste, the filtrate is sent to a nanofiltration unit for salt separation to separate the monovalent salt and the divalent salt to obtain concentrated water rich in sodium sulfate and produced water rich in sodium chloride;

[0062] Alternatively, the first mother liquor is sent to a second chemical softening unit for treatment, and the calcium ions in the first mother liquor react with carbonate ions through chemical softening to obtain a calcium carbonate mixed solution, and then the calcium carbonate mixed solution is filtered, and after the solid waste is discharged, the filtrate is sent to a nanofiltration unit for salt separation treatment to separate the monovalent salt and the divalent salt, and obtain concentrated water rich in sodium sulfate and produced water rich in sodium chloride;

[0063] 4) returning all the concentrated water rich in sodium sulfate in step 3) to the first crystallizer in step 2) for further treatment, i.e., sulfate radicals continue to crystallize with calcium ions to generate calcium sulfate dihydrate;

[0064] 5) sending the produced water rich in sodium chloride to a concentration unit for concentration to obtain a concentrated solution;

[0065] 6) The concentrated liquid is treated in a post-treatment unit to obtain a product including sodium chloride. Preferably, the obtained product may also include sodium hypochlorite or industrial acid or industrial alkali.

[0066] Furthermore, in step 1), when the first chemical softening unit is processing, a first softener is added into the first chemical softening unit to remove magnesium hardness in the mine water, and the first softener is preferably lime or sodium hydroxide.

[0067] Furthermore, in step 3), when the second chemical softening unit is processing, a second softener capable of providing carbonate is added to the second chemical softening unit, so that the calcium ions in the first mother liquor can be converted into calcium carbonate for removal. Preferably, the second softener is sodium carbonate.

[0068] The method of the present invention is used to treat high-mineralized mine water, first removing magnesium hardness, then concentrating through reverse osmosis, inducing crystallization to obtain calcium sulfate dihydrate, and then filtering the obtained first mother liquor and sending it to a nanofiltration unit to separate monovalent salts and divalent salts, or chemically softening and filtering the first mother liquor to further remove calcium hardness, filtering and removing calcium carbonate, and then sending it to a nanofiltration unit to separate monovalent salts and divalent salts; then, all the concentrated water rich in sodium sulfate is returned to the first crystallizer to continue to react with calcium ions. Compared with the traditional process of removing calcium ions from wastewater by double alkali softening of lime and sodium carbonate, the process of the present invention does not need to add a softening agent in the first crystallizer, which can greatly reduce the amount of softening agents used, and can greatly reduce the evaporation amount of the evaporator, reducing the evaporation energy consumption. Specifically, the present invention first removes magnesium hardness from high-mineralized mine water with a first softener, then concentrates it through reverse osmosis, crystallizes it through an inducing agent, and returns concentrated water to the subsequent nanofiltration unit, which can fully utilize the calcium ions and sulfate ions contained in the wastewater itself to generate calcium sulfate dihydrate, remove calcium hardness, and greatly reduce the amount of the second softener required for subsequent treatment, such as sodium carbonate; at the same time, the first reverse osmosis treatment is performed before entering the first crystallizer, and the second reverse osmosis treatment is performed after the nanofiltration nano-element treatment, which can greatly reduce the evaporation amount of the subsequent evaporator, reduce energy consumption, and save processing costs. The process of the present invention can remove most of the hardness while reducing the amount of softening agents used, and at the same time it is beneficial to improve the recovery rate of the nanofiltration unit (for example, it can be increased to 70%-75%), and the concentrated water rich in sodium sulfate will be greatly reduced (for example, only about 25% of the concentrated water), so that the amount of nanofiltration concentrated water returned to the front end for further treatment is reduced, which can reduce the amount of pre-treatment water and operating costs, saving investment costs.

[0069] In one embodiment of the present invention, the first mother liquor of the first crystallizer is not processed by the second chemical softening unit, but directly enters the nanofiltration unit after filtration; by adopting this embodiment, the amount of softening agent can be greatly reduced, saving agent costs. In a more preferred embodiment of the present invention, the first mother liquor of the first crystallizer enters the second chemical softening unit for treatment, and then enters the nanofiltration unit after filtration. Compared with the traditional treatment process, this embodiment can reduce the amount of softening agent used in the overall process, and the amount of concentrated water in the nanofiltration unit is greatly reduced compared with the previous embodiment, so the required processing scale of the first crystallizer is greatly reduced, which can significantly reduce the investment cost of the processing equipment and can more significantly reduce energy consumption. At the same time, compared with the previous embodiment, this preferred method can reduce membrane scaling, and the system operation stability and safety are higher.

[0070] In a preferred embodiment, in step 1), the apparent salt retention rate of the first reverse osmosis unit is preferably not less than 97%; preferably, the recovery rate of the first reverse osmosis unit is adjusted so that the calcium sulfate saturation in the second reverse osmosis concentrated water obtained by the first reverse osmosis unit does not exceed 700%.

[0071] Furthermore, in step 1), before the high-mineralized mine water is sent to the first chemical softening unit for chemical softening treatment, the high-mineralized mine water is subjected to coagulation and sedimentation treatment to remove suspended matter and coal powder therein. The coagulation and sedimentation treatment can be carried out by conventional treatment operations in the art, and flocculants (such as PAC (polyaluminium chloride)), coagulants (such as PAM (polyacrylamide)) and other agents can be added during the treatment process.

[0072] Furthermore, in step 1), after the high-mineralization mine water is sent to the first chemical softening unit to remove the magnesium hardness, it is first filtered to remove the residual suspended matter, and then ultrafiltration treatment is performed to reduce the turbidity of the mine water, for example, the turbidity of the mine water is reduced to less than 0.5NTU, and then it is sent to the first reverse osmosis unit for reverse osmosis.

[0073] Specifically, in step 2), during the induced crystallization process, an inducer is added to the first crystallizer to promote the sulfate and calcium ions in the first reverse osmosis concentrated water to crystallize into calcium sulfate dihydrate. Preferably, the inducer is added and the mass concentration of calcium sulfate dihydrate crystals in the first crystallizer is about 3-10%. The inventors have found that regulating the amount of the inducer in this way is beneficial to accelerate the reaction rate of calcium ions and sulfate ions to generate calcium sulfate on the one hand, and on the other hand, it can reduce the supersaturation of calcium sulfate in the effluent of the reaction tank, and will not cause the turbidity of the effluent of the subsequent treatment unit to increase and affect the effluent effect. Preferably, the inducer is calcium sulfate dihydrate powder. Preferably, the induced crystallization does not require additional heating; for example, the induced crystallization is carried out at 10-45°C. In the present invention, no additional softening agent is required to be added to the first crystallizer.

[0074] Preferably, in step 3), the filtration is preferably carried out in a bag microfiltration device, the solid waste is removed by filtration, and the obtained filtrate is continued for subsequent operations.

[0075] Preferably, in step 3), the nanofiltration unit includes a secondary nanofiltration device; preferably, the nanofiltration unit includes a primary nanofiltration device and a secondary nanofiltration device connected in series. Preferably, the nanofiltration product water is also sent to a weak acid cation bed for treatment after the nanofiltration unit, and the resin used in the weak acid cation bed is a weak acid cation exchange resin, such as D113. By treating with a weak acid cation bed, the calcium and magnesium ions in the nanofiltration product water can be further reduced.

[0076] Preferably, in step 3), the nanofiltration membrane used in the nanofiltration unit is a material separation membrane; preferably, the separation rates of monovalent salts and divalent salts of the nanofiltration unit are not less than 95%.

[0077] In some preferred embodiments, the concentration unit in step 5) includes a second reverse osmosis unit and an evaporator, wherein the second reverse osmosis unit is connected to the nanofiltration unit, and the sodium chloride-rich produced water output by the nanofiltration unit enters the second reverse osmosis unit for reverse osmosis to obtain second reverse osmosis produced water and second reverse osmosis concentrated water; wherein the obtained second reverse osmosis concentrated water enters the evaporator for evaporation and concentration, and the second reverse osmosis produced water can be reused as recycled water. Specifically, the evaporator can be a MED evaporator (multiple-effect evaporator). Preferably, the second reverse osmosis unit obtains a second reverse osmosis concentrated water with a TDS of about 13%-18%. Preferably, the evaporator uses steam exhaust or low-pressure steam as a heat source, and the water production ratio of the evaporator is preferably 5-12. Preferably, in step 5), the sodium chloride-rich produced water is concentrated to a TDS of about 23-30%% after being treated by the concentration unit, which is conducive to reducing the energy consumption of subsequent treatment, reducing equipment investment costs and operating costs. The reverse osmosis devices used in the first reverse osmosis unit and the second reverse osmosis unit can respectively adopt reverse osmosis membranes known in the art, such as BWRO, SWRO, HPRO and DTRO, and the reverse osmosis concentration can be multi-stage concentration.

[0078] Preferably, in step 1), the apparent salt rejection rate of the first reverse osmosis unit is preferably not less than 97%; in step 1), the recovery rate of the first reverse osmosis unit is adjusted so that the calcium sulfate saturation in the first reverse osmosis concentrated water obtained by the first reverse osmosis unit does not exceed 700%; in step 4), the separation rate of monovalent salt and divalent salt of the nanofiltration unit is not less than 95%. The adoption of this preferred scheme is conducive to the good separation of divalent salts such as sodium chloride, sodium sulfate, and calcium sulfate while concentrating the mine water, which is conducive to the deep resource recovery of the mine water and further reduces the output of impurity salts.

[0079] In a preferred embodiment, in step 6), the post-processing unit includes a second crystallizer and a mother liquor purification device; in step 6), the concentrated solution is sent to the second crystallizer for evaporation and crystallization to obtain sodium chloride (industrial salt product) and a second mother liquor, and distilled water that can be reused is also obtained. Then the second mother liquor is sent to the mother liquor purification device for treatment to remove organic matter and residual hardness therein to obtain a purified second mother liquor. The mother liquor purification device can use the corresponding device that can remove organic matter and hardness in the art, and there is no special restriction on this. For example, a high-pressure nanofiltration device and / or a chelating resin can be used to purify and separate the mother liquor. Preferably, in step 6), the post-processing unit also includes a bipolar membrane electrodialysis device or a sodium hypochlorite generator. The purified second mother liquor is passed into the bipolar membrane electrodialysis device for treatment to obtain industrial acid and industrial alkali, which can be used as a pH adjusting agent. Alternatively, the purified second mother liquor is passed into a sodium hypochlorite generator for treatment to obtain sodium hypochlorite, for example, as a disinfectant.

[0080] In step 6), the second crystallizer can be a multiple-effect evaporator or MVR device, and the industrial salt recovery rate is preferably more than 90%.

[0081] In some embodiments, the working pressure of the nanofiltration unit is 1.0-6.0 MPa, the working pressure of the first reverse osmosis unit is 1.0-3.0 MPa, and the working pressure of the second reverse osmosis unit is 5.0-7.0 MPa. Specifically, the nanofiltration unit, the first reverse osmosis unit and the second reverse osmosis unit are respectively equipped with a high-pressure pump, which is equipped to pressurize the salt water to be treated to provide the pressure required to complete the nanofiltration or reverse osmosis treatment.

[0082] By adopting the method of the present invention, the impurity salts in the mine water can be fully and deeply recovered, and calcium sulfate dihydrate and various industrial products can be obtained, wherein the industrial products specifically include sodium chloride industrial salt, industrial acid and industrial alkali. The calcium sulfate dihydrate can be further processed to obtain calcium carbonate whiskers.

[0083] In the present invention, the high-mineralization mine water mentioned is, for example, mine water with a mass salt content of 0.2%-2.0%.

[0084] The present invention also provides a resource utilization system capable of implementing the resource utilization method of the high-mineralization mine water described above, see Figure 3 The system mainly includes:

[0085] A first chemical softening unit is used to chemically soften the high-mineralization mine water to remove magnesium hardness, thereby obtaining mine water with magnesium hardness removed;

[0086] A first reverse osmosis unit is used to perform reverse osmosis on the mine water from which magnesium hardness has been removed to obtain first reverse osmosis product water and first reverse osmosis concentrated water;

[0087] A first crystallizer is used to induce crystallization of the first reverse osmosis concentrated water, so that sulfate radicals and calcium ions in the first reverse osmosis concentrated water are crystallized to form calcium sulfate dihydrate, and obtain a first mother liquor;

[0088] A nanofiltration unit is used to separate monovalent salt and divalent salt from the filtered first mother liquor, thereby obtaining concentrated water rich in sodium sulfate and produced water rich in sodium chloride; the concentrated water outlet of the nanofiltration unit is connected to the first crystallizer, so that the concentrated water rich in sodium sulfate can be circulated to the first crystallizer;

[0089] A concentration unit, used for concentrating the produced water rich in sodium chloride to obtain a concentrate;

[0090] The post-processing unit is used for post-processing the concentrated liquid to obtain a product including sodium chloride.

[0091] Preferably, see Figure 1 The system provided by the present invention also includes a second chemical softening unit arranged between the first crystallizer and the nanofiltration unit, which is used to chemically soften the first mother liquor before entering the nanofiltration unit so that the calcium ions and carbonates in the first mother liquor react. Specifically, the mixed liquor obtained in the second chemical softening unit enters the nanofiltration unit for further treatment after filtration.

[0092] The resource utilization method of the aforementioned high-mineralization mine water provided by the present invention can be implemented by the above-mentioned system provided by the present invention. If there is no special explanation about the technical content of the system of the present invention in the text, you can refer to the corresponding description of the resource utilization method in the previous text, and will not be repeated one by one.

[0093] Specifically, the first chemical softening unit includes a water inlet, a water production outlet and a mud discharge outlet. In a specific implementation, the magnesium hardness in the mine water is removed by adding a chemical softener (such as lime or sodium hydroxide) into the first chemical softening unit. The first reverse osmosis unit includes a water inlet, a first reverse osmosis water production outlet and a first reverse osmosis concentrated water outlet, and the mine water is further concentrated in the first reverse osmosis unit. The first crystallizer can be specifically a self-induced crystallizer, which is provided with a water inlet, a first mother liquor outlet and a crystallization outlet, wherein the water inlet is connected to the first reverse osmosis concentrated water outlet of the first reverse osmosis unit, and the crystallization outlet is used to discharge calcium sulfate dihydrate (dihydrate gypsum). In one embodiment, see Figure 1 The first mother liquor outlet is connected to the water inlet of the second chemical softening unit. The second chemical softening unit specifically includes a water inlet, a calcium carbonate mixed liquor outlet and a mud outlet. In a specific implementation, a chemical softener (such as sodium carbonate) is added to the second chemical softening unit to convert calcium ions in the first mother liquor into calcium carbonate. In another embodiment, see Figure 3 , there is no second chemical softening unit between the first crystallizer and the nanofiltration unit.

[0094] Furthermore, the system of the present invention also includes a coagulation sedimentation unit, a first filtration unit, an ultrafiltration unit and a second filtration unit. The coagulation sedimentation unit is used to perform coagulation sedimentation treatment on high-mineralization mine water, so as to remove suspended matter and coal powder therein. Specifically, the coagulation sedimentation unit includes a water inlet, a water outlet and a mud outlet, and the water outlet of the coagulation sedimentation unit is connected to the water inlet of the first chemical softening unit; that is, after the high-mineralization mine water is treated by the coagulation sedimentation unit, it enters the first chemical softening unit for further treatment.

[0095] Furthermore, the water inlet of the first filter unit is connected to the water outlet of the first chemical softening unit, the water outlet of the first filter unit is connected to the water inlet of the ultrafiltration unit, and the water outlet of the ultrafiltration unit is connected to the water inlet of the first reverse osmosis unit. That is, the mine water obtained in the first chemical softening unit and freed from magnesium hardness is filtered by the first filter unit to remove the residual suspended matter, and then enters the ultrafiltration unit for ultrafiltration treatment to reduce its turbidity, and then is sent to the first reverse osmosis unit for reverse osmosis.

[0096] In one embodiment, see Figure 1 The second filtering unit is disposed between the second chemical softening unit and the nanofiltration unit, and is used to filter the calcium carbonate mixture obtained by the second chemical softening unit, that is, after the calcium carbonate mixture is filtered by the second filtering unit, the filtrate obtained enters the nanofiltration unit for further processing. Alternatively, in another embodiment, see Figure 3 The second filtration unit is arranged between the first crystallizer and the nanofiltration unit to directly filter the first mother liquor. Preferably, the second filtration unit comprises a bag-type microfiltration device. The bag-type microfiltration device specifically comprises a water inlet, a water outlet and a mud discharge port, and the filtered sludge is discharged through the mud discharge port.

[0097] Preferably, the nanofiltration unit includes a secondary nanofiltration device, for example, the nanofiltration unit includes a primary nanofiltration device and a secondary nanofiltration device connected in series. Further preferably, the nanofiltration membrane used in the nanofiltration unit is a material separation membrane, and the separation rate of monovalent salt and divalent salt of the nanofiltration unit is preferably not less than 95%.

[0098] Preferably, the concentration unit includes a second reverse osmosis unit and an evaporator, wherein the water inlet of the second reverse osmosis unit is connected to the water outlet of the nanofiltration unit, the concentrated water outlet of the second reverse osmosis unit is connected to the water inlet of the evaporator, and the concentrated liquid outlet of the evaporator is connected to the water inlet of the post-processing unit. That is, the sodium chloride-rich produced water output by the nanofiltration unit first enters the second reverse osmosis unit for reverse osmosis, and then enters the evaporator for evaporation and concentration, and the obtained concentrated liquid enters the subsequent post-processing unit for further processing. Preferably, the second reverse osmosis unit adopts a high-concentration reverse osmosis device; the reverse osmosis device used in the second reverse osmosis unit can adopt reverse osmosis membranes such as BWRO, SWRO, HPRO and DTRO, and the reverse osmosis concentration can be multi-stage concentration. Preferably, the evaporator adopts a MED evaporator, which specifically includes a water inlet, a distilled water discharge port and a concentrated liquid outlet.

[0099] Preferably, the post-processing unit includes a second crystallizer and a mother liquor purification device. Specifically, the second crystallizer includes a water inlet, a distilled water outlet, a crystal salt outlet and a second mother liquor discharge port. The water inlet of the second crystallizer is connected to the concentrated liquid outlet of the concentration unit, and is used to evaporate and crystallize the concentrated liquid, so as to obtain sodium chloride industrial salt and a second mother liquor, and the sodium chloride industrial salt is discharged from the crystal salt outlet. The mother liquor purification device is connected to the second mother liquor discharge port of the second crystallizer, and is used to treat the second mother liquor to remove organic matter and residual hardness therein, thereby obtaining a purified second mother liquor, and the purified second mother liquor is discharged from the water outlet of the mother liquor purification device. Preferably, the post-processing unit also includes a bipolar membrane electrodialysis device or a sodium hypochlorite generator, wherein the bipolar membrane electrodialysis device is connected to the water outlet of the mother liquor purification device, and is used to treat the purified second mother liquor to obtain industrial acid (e.g., hydrochloric acid) and industrial alkali (e.g., sodium hydroxide), and the industrial acid and industrial alkali can be used as pH regulators. Alternatively, the sodium hypochlorite generator is connected to the water outlet of the mother liquor purification device to process the purified second mother liquor to obtain sodium hypochlorite, which can be used as a disinfectant.

[0100] The second crystallizer can be a multiple-effect evaporator or MVR device, and the industrial salt recovery rate is preferably over 90%.

[0101] Specifically, the nanofiltration unit, the first reverse osmosis unit and the second reverse osmosis unit are respectively equipped with high-pressure pumps, which are equipped to pressurize the salt water to be treated to provide the pressure required to complete the nanofiltration or reverse osmosis treatment.

[0102] Each specific processing device etc. involved in the present invention can directly adopt existing devices in the art that can realize corresponding functions, and no further description is given for this.

[0103] The following application examples are used to Figure 1The resource utilization system shown is an exemplary introduction to the resource utilization method of high-mineralized mine water.

[0104] Example 1

[0105] like Figure 2 As shown, the flow rate is 20m 3 / h, and high-mineralization mine water with a mass salt content of 1.2% first enters a coagulation and sedimentation unit (PAC (polyaluminum chloride) and PAM (polyacrylamide) are added in an amount of 30 mg / L and 0.5 mg / L, respectively) for coagulation and sedimentation treatment. After the suspended solids are removed, the water enters the first chemical softening unit for treatment. In the first chemical softening unit, the magnesium hardness in the mine water is removed by adding lime (the first softener). The magnesium hardness of the produced water obtained by the first chemical softening unit is less than 50 mg / L (in this embodiment, lime is used to remove the magnesium hardness, the magnesium ions in the wastewater are removed, and the calcium ion concentration in the mine water is further increased, which will be conducive to the reaction of calcium ions with sulfate ions in the subsequent first crystallizer to form calcium sulfate dihydrate). After the magnesium hardness is removed, the mine water is filtered through the filter of the first filtration unit to remove the residual suspended solids, and then enters the ultrafiltration unit, where ultrafiltration is performed in the ultrafiltration device to further reduce the turbidity of the mine water. The turbidity of the produced water output by the ultrafiltration unit is less than 0.5 NTU. The mine water obtained through the previous pretreatment enters the first reverse osmosis unit for desalination and concentration treatment (apparent salt retention rate is 98%), and the reverse osmosis recovery rate is controlled according to the calcium sulfate supersaturation in the mine water, and the calcium sulfate supersaturation in the first reverse osmosis concentrated water is controlled to be ≤700%. The first reverse osmosis concentrated water enters the first crystallizer for reaction, and an inducer (calcium sulfate dihydrate powder) is added during the reaction, and the mass concentration of calcium sulfate dihydrate crystals in the first crystallizer is maintained between 3-10wt%. The calcium sulfate dihydrate obtained in the first crystallizer is discharged and used to prepare calcium sulfate whiskers; the first mother liquor obtained in the first crystallizer enters the second chemical softening unit for further reaction with sodium carbonate (the second softener), and the calcium ions and carbonates in the first mother liquor react to form calcium carbonate, and the calcium carbonate mixture is filtered through the second filtration unit (bag microfiltration membrane) to remove the calcium hardness in the wastewater. The calcium hardness in the obtained filtrate is 80 mg / L (after removing the calcium hardness, the recovery rate of the subsequent first-level nanofiltration can be improved, and the reflux rate of nanofiltration concentrate can be reduced, thereby reducing the investment and operating costs of the entire pretreatment system). The filtrate of the second filtration unit enters the nanofiltration unit (including a first-stage nanofiltration device and a second-stage nanofiltration device connected in series, and the separation rates of monovalent salt and divalent salt of the nanofiltration unit are 95% and 97% respectively) for treatment, and the nanofiltration concentrated water (concentrated water rich in sodium sulfate) flows back to the first crystallizer to participate in the reaction to generate calcium sulfate dihydrate, and the nanofiltration produced water (produced water rich in sodium chloride) enters the second reverse osmosis unit for high-fold reverse osmosis concentration. The TDS of the concentrated mine water is about 13%, and it further enters the evaporator (MED evaporator) for further concentration. The TDS of the concentrated solution is between 23% and 30%. The concentrated solution enters the second crystallizer for evaporation and crystallization, and the sodium chloride industrial salt produced by the crystallization can be sold as a product.The second mother liquor discharged from the second crystallizer is sent to a mother liquor purification device (specifically a high-pressure nanofiltration device, with a working pressure of 10 MPa) to remove organic matter and residual hardness therein to obtain a purified second mother liquor. The purified second mother liquor can be processed in a bipolar membrane electrodialysis device to produce industrial acid (hydrochloric acid) and industrial alkali (sodium hydroxide), which can be used as a pH adjusting reagent or sold externally; the purified second mother liquor can also be sent to a sodium hypochlorite generator for the preparation of sodium hypochlorite, and the obtained sodium hypochlorite can be used as a disinfectant.

[0106] Example 2

[0107] like Figure 3 As shown, the flow rate is 100m 3 / h, and high-mineralization mine water with a mass salt content of 1.5% first enters a coagulation and sedimentation unit (PAC (polyaluminium chloride) and PAM (polyacrylamide) are added in an amount of 50mg / L and 0.7mg / L, respectively) for coagulation and sedimentation treatment, and after removing the suspended matter therein, enters the first chemical softening unit for treatment. In the first chemical softening unit, magnesium hardness in the mine water is removed by adding lime (first softener), and the magnesium hardness of the produced water obtained by the first chemical softening unit is less than 50mg / L (in this embodiment, lime is used to remove magnesium hardness, magnesium ions in the wastewater are removed, and the calcium ion concentration in the mine water is further increased, which will be conducive to the reaction of calcium ions with sulfate ions in the subsequent first crystallizer to form calcium sulfate dihydrate). After the magnesium hardness is removed, the mine water is filtered through the filter of the first filtration unit to remove the residual suspended matter, and then enters the ultrafiltration unit, and ultrafiltration is performed in the ultrafiltration device to further reduce the turbidity of the mine water. The turbidity of the produced water output by the ultrafiltration unit is less than 0.5NTU. The mine water obtained after the previous pretreatment enters the first reverse osmosis unit for desalination and concentration treatment (apparent salt retention rate is 98%). The reverse osmosis recovery rate is controlled according to the calcium sulfate supersaturation in the mine water, and the calcium sulfate supersaturation in the first reverse osmosis concentrated water is controlled to be ≤700%. The first reverse osmosis concentrated water enters the first crystallizer (auto-induction crystallizer) for reaction. During the reaction, an inducer (calcium sulfate dihydrate powder) is added, and the mass concentration of calcium sulfate dihydrate crystals in the first crystallizer is maintained between 3-10wt%. The dihydrate gypsum obtained in the first crystallizer is discharged and used to prepare calcium sulfate whiskers; the first mother liquor obtained in the first crystallizer enters the second filtration unit (using a bag microfiltration membrane) for filtration to remove calcium hardness in the wastewater, and the calcium sulfate supersaturation in the obtained filtrate is between 100% and 150%. The filtrate of the second filtration unit enters the nanofiltration unit (including a first-stage nanofiltration device and a second-stage nanofiltration device connected in series, the separation rates of monovalent salt and divalent salt of the nanofiltration unit are 95% and 97% respectively, the recovery rate of the nanofiltration device is controlled at about 50%, and the supersaturation of calcium sulfate in the nanofiltration concentrated water is controlled below 700%) for treatment, and the nanofiltration concentrated water (concentrated water rich in sodium sulfate) is refluxed to the first crystallizer to participate in the reaction to generate calcium sulfate dihydrate, and the nanofiltration produced water (produced water rich in sodium chloride) enters the second reverse osmosis unit for high-fold reverse osmosis concentration. The TDS of the concentrated mine water is about 13%, and it further enters the evaporator (MED evaporator) for further concentration. The TDS of the concentrated solution is between 23% and 30%. The concentrated solution enters the second crystallizer (MVR / multi-effect crystallizer) for evaporation and crystallization, and the sodium chloride industrial salt produced by crystallization can be sold as a product. The second mother liquor discharged from the second crystallizer is sent to a mother liquor purification device (specifically a high-pressure nanofiltration device, working pressure 10 MPa) to remove organic matter and residual hardness therein to obtain a purified second mother liquor.The purified second mother liquor can be processed in a bipolar membrane electrodialysis device to produce industrial acid (hydrochloric acid) and industrial alkali (sodium hydroxide), which can be used as a pH adjusting reagent or sold externally; the purified second mother liquor can also be fed into a sodium hypochlorite generator to prepare sodium hypochlorite, and the obtained sodium hypochlorite can be used as a disinfectant.

[0108] It is easy to understand that the above embodiments are only examples for clear explanation and do not mean that the present invention is limited thereto. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from this are still within the protection scope of the present invention.

Claims

1. A method for resource utilization of high-mineralization mine water, characterized in that: The method comprises the following steps: 1) sending the high-mineralization mine water to a first chemical softening unit for treatment to remove magnesium hardness, and then sending it to a first reverse osmosis unit for treatment to obtain first reverse osmosis product water and first reverse osmosis concentrated water; 2) sending the first reverse osmosis concentrated water into a first crystallizer to induce crystallization, so that sulfate and calcium ions in the first reverse osmosis concentrated water are crystallized to form calcium sulfate dihydrate, and obtaining a first mother liquor; 3) After filtering the first mother liquor, the mother liquor is sent to a nanofiltration unit for treatment to obtain concentrated water rich in sodium sulfate and produced water rich in sodium chloride; Alternatively, the first mother liquor is sent to a second chemical softening unit for treatment, so that calcium ions in the first mother liquor react with carbonate ions to obtain a calcium carbonate mixed solution, and then the calcium carbonate mixed solution is filtered and sent to a nanofiltration unit for treatment to obtain concentrated water rich in sodium sulfate and produced water rich in sodium chloride; 4) returning the concentrated water rich in sodium sulfate in step 3) to the first crystallizer in step 2) for further treatment; 5) concentrating the produced water rich in sodium chloride in a concentration unit to obtain a concentrated solution; 6) treating the concentrated solution in a post-treatment unit to obtain a product including sodium chloride.

2. The method for resource utilization of high-mineralization mine water according to claim 1, characterized in that: In step 1), a first softening agent is added into the first chemical softening unit to remove the magnesium hardness, and the first softening agent is preferably lime or sodium hydroxide; In step 3), a second softening agent capable of providing the carbonate ions is added into the second chemical softening unit. Preferably, the second softening agent is sodium carbonate.

3. The method for resource utilization of high-mineralization mine water according to claim 1, characterized in that: In step 1), the apparent salt rejection rate of the first reverse osmosis unit is preferably not less than 97%; Preferably, the recovery rate of the first reverse osmosis unit is adjusted so that the calcium sulfate saturation in the first reverse osmosis concentrated water obtained by the first reverse osmosis unit does not exceed 700%; Preferably, in step 1), before the high-mineralization mine water is fed into the first chemical softening unit, the high-mineralization mine water is subjected to coagulation and sedimentation treatment to remove suspended matter and coal powder therein; Preferably, in step 1), the high-mineralization mine water is treated by the first chemical softening unit, filtered and ultrafiltered, and then sent to the first reverse osmosis unit.

4. The method for resource utilization of high-mineralization mine water according to any one of claims 1 to 3, characterized in that: In step 2), during the induced crystallization process, an inducer is added to the first crystallizer. Preferably, the inducer is added to make the mass concentration of calcium sulfate dihydrate crystals in the first crystallizer be 3%-10%; Preferably, the inducer is calcium sulfate dihydrate powder; Preferably, the induced crystallization does not require additional heating; further preferably, the induced crystallization is carried out at 10-45°C.

5. The method for resource utilization of high-mineralization mine water according to any one of claims 1 to 3, characterized in that: In step 3), the filtration is carried out in a bag microfiltration device; And / or, in step 3), the nanofiltration unit includes a secondary nanofiltration device; preferably, the nanofiltration unit includes a primary nanofiltration device and a secondary nanofiltration device connected in series; preferably, the nanofiltration membrane used in the nanofiltration unit is a material separation membrane; preferably, the separation rate of monovalent salts and divalent salts of the nanofiltration unit is not less than 95%.

6. The method for resource utilization of high-mineralization mine water according to any one of claims 1 to 3, characterized in that: In step 5), the concentration unit includes a second reverse osmosis unit connected to the nanofiltration unit, and an evaporator connected to the second reverse osmosis unit, the second reverse osmosis unit is used to perform reverse osmosis treatment on the produced water rich in sodium chloride, and the evaporator is used to evaporate and concentrate the second reverse osmosis concentrated water obtained by the second reverse osmosis unit; Preferably, the second reverse osmosis unit obtains second reverse osmosis concentrated water with a TDS of 13%-18%; Preferably, the evaporator uses steam exhaust or low-pressure steam to provide heat energy, and the water production ratio of the evaporator is preferably 5-12; Preferably, in step 5), the sodium chloride-rich produced water is concentrated to a TDS of 23%-30% by the treatment of the concentration unit.

7. The method for resource utilization of high-mineralization mine water according to any one of claims 1 to 3, characterized in that: In step 6), the post-processing unit includes a second crystallizer and a mother liquor purification device; sending the concentrated solution into the second crystallizer for evaporation and crystallization to obtain sodium chloride and a second mother liquor; sending the second mother liquor into the mother liquor purification device for treatment to remove organic matter and residual hardness therein to obtain a purified second mother liquor; Preferably, the post-treatment unit further comprises a bipolar membrane electrodialysis device or a sodium hypochlorite generator; the purified second mother liquor is passed into the bipolar membrane electrodialysis device for treatment to obtain acid and alkali; or, the purified second mother liquor is passed into the sodium hypochlorite generator for treatment to obtain sodium hypochlorite.

8. A resource utilization system capable of implementing the resource utilization method of high-mineralization mine water according to any one of claims 1 to 7, characterized in that: The system comprises: A first chemical softening unit, used for chemically softening high-mineralized mine water to obtain mine water with magnesium hardness removed; A first reverse osmosis unit is used to perform reverse osmosis on the mine water from which magnesium hardness has been removed to obtain first reverse osmosis product water and first reverse osmosis concentrated water; a first crystallizer, used for inducing crystallization of the first reverse osmosis concentrated water, so that sulfate radicals and calcium ions in the first reverse osmosis concentrated water are crystallized to form calcium sulfate dihydrate, and obtaining a first mother liquor; a nanofiltration unit, used for separating the monovalent salt and the divalent salt from the first mother liquor after the filtration treatment and obtaining concentrated water rich in sodium sulfate and produced water rich in sodium chloride; the concentrated water outlet of the nanofiltration unit is connected to the first crystallizer to circulate the concentrated water rich in sodium sulfate to the first crystallizer; A concentration unit, used for concentrating the produced water rich in sodium chloride to obtain a concentrated solution; A post-processing unit, used for post-processing the concentrated liquid to obtain a product including sodium chloride; Preferably, the method further comprises a second chemical softening unit disposed between the first crystallizer and the nanofiltration unit, for chemically softening the first mother liquor before entering the nanofiltration unit so as to allow calcium ions and carbonates in the first mother liquor to react.

9. The resource utilization system of high-mineralization mine water according to claim 8, characterized in that: It also includes a coagulation and sedimentation unit, a first filtration unit, an ultrafiltration unit, and a second filtration unit; The coagulation and sedimentation unit is used to treat the high-mineralization mine water to remove suspended matter and coal powder therein; the water output outlet of the coagulation and sedimentation unit is connected to the water inlet of the first chemical softening unit; The water inlet of the first filter unit is connected to the water outlet of the first chemical softening unit, the water outlet of the first filter unit is connected to the water inlet of the ultrafiltration unit, and the water outlet of the ultrafiltration unit is connected to the water inlet of the first reverse osmosis unit; The second filtering unit is arranged between the second chemical softening unit and the nanofiltration unit, and is used for filtering the mixed liquid obtained by the reaction in the second softening unit; preferably, the second filtering unit includes a bag microfiltration device.

10. The resource utilization system of high-mineralization mine water according to claim 8, characterized in that: The nanofiltration unit comprises a secondary nanofiltration device; preferably, the nanofiltration unit comprises a primary nanofiltration device and a secondary nanofiltration device connected in series in sequence; And / or, the concentration unit comprises a second reverse osmosis unit and an evaporator, the water inlet of the second reverse osmosis unit is connected to the water production outlet of the nanofiltration unit, and the concentrated water outlet of the second reverse osmosis unit is connected to the water inlet of the evaporator; And / or, the post-treatment unit includes a second crystallizer and a mother liquor purification device, the second crystallizer is connected to the concentrated liquid outlet of the concentrating unit, and is used to evaporate and crystallize the concentrated liquid to obtain sodium chloride and a second mother liquor; the mother liquor purification device is connected to the second crystallizer, and is used to treat the second mother liquor to remove organic matter and residual hardness therein and obtain a purified second mother liquor; preferably, the post-treatment unit also includes a bipolar membrane electrodialysis device for treating the purified second mother liquor to obtain acid and alkali, or includes a sodium hypochlorite generator for treating the purified second mother liquor to obtain sodium hypochlorite.

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