Method and apparatus for treating wastewater

Abstract

The invention relates to a method and a device for treating wastewater. The method comprises the following steps: (1) an electrochemical membrane reactor treatment step: carrying out electrochemical membrane reactor treatment on wastewater containing soluble alkali metal chloride and soluble alkali metal sulfate and an ammonium bicarbonate solution to obtain a mixed solution containing ammonium sulfate and ammonium chloride and an alkali metal bicarbonate solution; and (2) precipitation separation: reacting the mixed solution with calcium oxide, calcium hydroxide or a combination thereof to obtain ammonia gas and a reaction mixture containing calcium sulfate and calcium chloride, carrying out solid-liquid separation on the reaction mixture, and reacting the ammonia gas in the step (2) with carbon dioxide and water to obtain the ammonium bicarbonate solution in the step (1). The apparatus comprises (1) an electrochemical membrane reactor module and (2) a precipitation separation module, the apparatus further comprising a first reaction tank for reacting ammonia gas from (2) with carbon dioxide and water to obtain an ammonium bicarbonate solution supplied to (1).

Description

Technical Field

[0001] The present invention generally relates to the technical field of wastewater treatment, and in particular to a method and a device for treating wastewater, in particular to a method and a device for treating wastewater containing soluble alkali metal chloride and soluble alkali metal sulfate. Background Art

[0002] With the development of industry, especially the rapid development of the chemical industry, a large amount of high-salt wastewater has been generated. If high-salt wastewater is not treated or poorly managed and directly discharged into the environment, it will cause soil salinization, water eutrophication, groundwater pollution and other problems.

[0003] Therefore, these industrial wastewaters need to be treated. However, in the treatment of industrial wastewater in salt chemical industry, chlor-alkali chemical industry, coal chemical industry, hydrometallurgy, pharmaceutical industry and other industries, mixed salt wastewater containing both soluble alkali metal chloride (e.g., sodium chloride) and soluble alkali metal sulfate (e.g., sodium sulfate) is often encountered. If this type of wastewater directly enters the evaporation crystallization system and is converted into mixed salt, a large amount of solid waste will be generated, the solid waste treatment cost is high, and the economic benefit is low.

[0004] Mixed salt separation is the best way to reduce the final mixed salt products. If the components of the mixed salt solution can be separated before evaporation and crystallization to obtain a single-component salt product of refined industrial salt grade, or it can be converted into other products, the cost of solid waste treatment can be greatly reduced and the economic benefits of the enterprise can be improved.

[0005] Traditional mixed salt separation processes mainly include freezing denitrification, salt and nitrate co-production, nanofiltration membrane method, etc. However, the existing mixed salt separation process is still imperfect, with shortcomings such as cumbersome steps, waste materials needing additional treatment, low economic benefits, and environmental unfriendliness. Especially for high-salinity wastewater, the existing separation technology usually requires other additional treatment of the high-salinity wastewater in advance.

[0006] Therefore, there is an urgent need to provide a method and device for treating mixed salt wastewater with a simple process and environmental friendliness, which can directly treat high-salt wastewater, separate low-value mixed salt and convert it into high-value products, and achieve a closed process loop with almost no emission of any pollutants, thereby achieving environmental benefits while generating higher economic value. Summary of the invention

[0007] The present invention is made in view of the above problems existing in the prior art.

[0008] In a first aspect, the present invention relates to a method for treating wastewater comprising the following steps:

[0009] (1) An electrochemical membrane reactor step, comprising:

[0010] - treating the first wastewater containing soluble alkali chloride and soluble alkali sulfate with an ammonium bicarbonate solution by electrochemical membrane reactor to obtain a first mixed solution containing ammonium sulfate and ammonium chloride and an alkali bicarbonate solution, respectively; and

[0011] (2) A precipitation separation step, comprising:

[0012] - mixing and reacting the first mixed solution containing ammonium sulfate and ammonium chloride obtained in step (1) with calcium oxide, calcium hydroxide or a combination thereof to obtain ammonia gas and a reaction mixture containing calcium sulfate and calcium chloride, respectively; and

[0013] - subjecting the reaction mixture to solid-liquid separation to obtain a solution containing calcium chloride and solid calcium sulfate, respectively;

[0014] At least a portion of the ammonia gas obtained in step (2) is reacted with carbon dioxide and water to obtain the ammonium bicarbonate solution used in step (1).

[0015] In a second aspect, the present invention relates to an apparatus for treating wastewater, comprising the following modules:

[0016] (1) An electrochemical membrane reactor module, comprising:

[0017] - an electrochemical membrane reactor unit, which is used to treat the first wastewater containing soluble alkali chloride and soluble alkali sulfate with an ammonium bicarbonate solution by electrochemical membrane reactor to obtain a first mixed solution containing ammonium sulfate and ammonium chloride and an alkali bicarbonate solution, respectively; and

[0018] (2) A precipitation separation module downstream of the electrochemical membrane reactor module, comprising:

[0019] - a reaction unit for mixing and reacting a first mixed solution containing ammonium sulfate and ammonium chloride obtained from an electrochemical membrane reactor unit with calcium oxide, calcium hydroxide or a combination thereof to obtain ammonia gas and a reaction mixture containing calcium sulfate and calcium chloride, respectively; and

[0020] - a solid-liquid separation unit downstream of the reaction unit, which is used to separate the reaction mixture obtained from the reaction unit into solid and liquid to obtain a solution containing calcium chloride and solid calcium sulfate, respectively,

[0021] The device further includes a first reaction box downstream of the reaction unit and connected to the electrochemical membrane reactor module, which is used to react at least a portion of the ammonia obtained from the reaction unit with carbon dioxide and water to obtain an ammonium bicarbonate solution, and the ammonium bicarbonate solution is supplied to the electrochemical membrane reactor unit.

[0022] In the above-mentioned method and apparatus according to the present invention, mixed salt wastewater containing soluble alkali chloride (e.g., sodium chloride) and soluble alkali sulfate (e.g., sodium sulfate) is first treated with an ammonium bicarbonate solution in an electrochemical membrane reactor to obtain an ammonium sulfate / ammonium chloride solution. Then, the ammonium sulfate / ammonium chloride solution is reacted with calcium oxide and / or calcium hydroxide to obtain a reaction mixture containing calcium sulfate precipitate and calcium chloride and ammonia. The obtained reaction mixture can be separated by solid-liquid separation to obtain a calcium chloride solution and a calcium sulfate solid, thereby achieving the purpose of separating mixed salts. The obtained ammonia can be reacted with carbon dioxide and water to obtain an ammonium bicarbonate solution, which can be returned to the electrochemical membrane reactor for use as a raw material.

[0023] Therefore, the present invention reuses industrial waste mixed salt solution through the above method and device, separates low-value mixed salt into high-value single salt components in a simple and efficient manner, and realizes a closed process loop, almost no pollutants are discharged, thereby generating high economic value and achieving environmental benefits. Moreover, the method and device according to the present invention can directly treat high-salt wastewater without additional treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the technical solution of the present invention, the following will briefly describe the drawings required for describing the embodiments. It should be understood that the drawings are only for the convenience of technicians to understand the present invention more easily, and are not intended to limit the scope of the present invention.

[0025] Figure 1 A schematic diagram showing an exemplary embodiment of a method for treating wastewater according to the present invention.

[0026] Figure 2 A schematic diagram showing an exemplary embodiment of an apparatus for treating wastewater according to the present invention. DETAILED DESCRIPTION

[0027] In order to make the invention purpose, technical solution and beneficial technical effect of the present application clearer, the present application will be described in detail below. It should be noted that the various aspects, features, implementation methods and advantages described in the present application may be compatible and / or may be combined together.

[0028] If not otherwise specified, the meaning of the scientific and technological terms in this specification is the same as that generally understood by those skilled in the art. In addition, unless explicitly described to the contrary, the words "comprise", "include" or "contain" will be understood to include the stated elements, but do not exclude any other elements.

[0029] It will be understood that although the terms "first", "second", "third", etc. may be used herein to describe various elements, components, process steps and / or parts, these elements, components, process steps and / or parts should not be limited by these terms. These terms are only used to distinguish one element, component, process step or part from another element, component, process step or part. Therefore, without departing from the teachings herein, the "first element", "component", "process step" or "part" discussed below may be referred to as a second element, component, process step or part.

[0030] The present invention relates to a method and an apparatus for treating wastewater.

[0031] The present invention will be described in detail below.

[0032] Methods for treating wastewater

[0033] In a first aspect, the present invention relates to a method for treating wastewater comprising the following steps:

[0034] (1) An electrochemical membrane reactor treatment step comprising:

[0035] - treating the first wastewater containing soluble alkali chloride and soluble alkali sulfate with an ammonium bicarbonate solution by electrochemical membrane reactor to obtain a first mixed solution containing ammonium sulfate and ammonium chloride and an alkali bicarbonate solution, respectively; and

[0036] (2) A precipitation separation step, comprising:

[0037] - mixing and reacting the first mixed solution containing ammonium sulfate and ammonium chloride obtained in step (1) with calcium oxide, calcium hydroxide or a combination thereof to obtain ammonia gas and a reaction mixture containing calcium sulfate and calcium chloride, respectively; and

[0038] - subjecting the reaction mixture to solid-liquid separation to obtain a solution containing calcium chloride and solid calcium sulfate, respectively;

[0039] At least a portion of the ammonia gas obtained in step (2) is reacted with carbon dioxide and water to obtain the ammonium bicarbonate solution used in step (1).

[0040] In a preferred embodiment, the method further comprises:

[0041] (3) Bipolar membrane electrodialysis step, comprising:

[0042] - subjecting a soluble alkali metal chloride and / or a soluble alkali metal sulfate solution to bipolar membrane electrodialysis to obtain a hydrochloric acid and / or sulfuric acid solution and an alkali metal hydroxide solution, respectively;

[0043] - optionally reacting the hydrochloric acid and / or sulfuric acid solution obtained from the bipolar membrane electrodialysis treatment with at least a portion of the ammonia obtained in step (2) to obtain an ammonium chloride and / or ammonium sulfate solution; and

[0044] - reacting the alkali metal hydroxide solution obtained from the bipolar membrane electrodialysis treatment with the alkali metal bicarbonate solution obtained in step (1) to obtain an alkali metal carbonate solution, and subjecting the alkali metal carbonate solution to a first treatment to obtain an alkali metal carbonate solid.

[0045] Each step is described in detail below.

[0046] Step (1)

[0047] The method according to the present invention comprises step (1), namely, an electrochemical membrane reactor step.

[0048] In step (1), the mixed salt wastewater is subjected to electrochemical membrane reactor treatment. The first wastewater containing soluble alkali metal chloride and soluble alkali metal sulfate is subjected to electrochemical membrane reactor treatment with an ammonium bicarbonate solution to obtain a first mixed solution containing ammonium sulfate and ammonium chloride and an alkali metal bicarbonate solution, respectively.

[0049] The electrochemical membrane reactor treatment described herein is also referred to as displacement electrodialysis treatment. In the electrochemical membrane reactor treatment, a plurality of cation exchange membranes and anion exchange membranes are alternately arranged between the anode and the cathode to form an ion exchange membrane array, wherein the cations are subjected to the electric field force to migrate toward the cathode side, and the anions are subjected to the electric field force to migrate toward the anode side. When the cations encounter the cation exchange membrane while traveling, the cations can pass through, and when the cations encounter the anion exchange membrane while traveling, the cations are blocked and impermeable. When the anions encounter the anion exchange membrane while traveling, the anions can pass through, and when the anions encounter the cation exchange membrane while traveling, the anions are blocked and impermeable. The electrochemical membrane reactor process utilizes this principle to achieve the redistribution of the anions and cations therein, thereby enabling the realization of some products that are not convenient for the production of the double decomposition reaction method.

[0050] The soluble alkali metal chloride can be selected from one or more of lithium chloride, sodium chloride and potassium chloride. For example, the soluble alkali metal chloride can be sodium chloride.

[0051] The soluble alkali metal sulfate may be selected from one or more of lithium sulfate, sodium sulfate and potassium sulfate. For example, the soluble alkali metal sulfate may be sodium sulfate.

[0052] In one or more embodiments, the soluble alkali metal chloride is sodium chloride and the soluble alkali metal sulfate is sodium sulfate.

[0053] The concentration of soluble alkali metal chloride in the first wastewater may be 2 wt %-20 wt %, for example, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 wt % or within the range defined by any two of the above values.

[0054] The concentration of soluble alkali metal sulfate in the first wastewater may be 3 wt %-20 wt %, for example, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 wt % or within the range defined by any two of the above values.

[0055] The total concentration of soluble alkali metal chloride and soluble alkali metal sulfate in the first wastewater can be 3% to 20% by weight, for example, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20% by weight or in the range defined by any two of the above values.

[0056] The alkali metal bicarbonate solution can be selected from one or more of a lithium bicarbonate solution, a sodium bicarbonate solution and a potassium bicarbonate solution. For example, the alkali metal bicarbonate solution can be a sodium bicarbonate solution.

[0057] Before the electrochemical membrane reactor treatment, the first wastewater containing soluble alkali chloride and soluble alkali sulfate can be pretreated to remove particulate matter with a particle size greater than 5 μm. Through this pretreatment step, the clogging phenomenon caused by these particulate matter in the subsequent electrochemical membrane reactor process can be effectively avoided. The specific method of pretreatment is not particularly limited in principle, and those skilled in the art can select a suitable pretreatment method according to actual needs. For example, the pretreatment can be selected from one or more of filtration and ion exchange. In one or more embodiments, the pretreatment can be carried out by one or more of the following equipment: a multi-media filter, a microfilter, an ultrafilter, a tubular microfilter, a tubular ultrafilter, a ceramic membrane filter, a fiber filter, a precision filter with a filter element or a filter bag installed, and an ion exchanger, etc.

[0058] Before the electrochemical membrane reactor treatment, the ammonium bicarbonate solution can be prepared into a certain concentration. Those skilled in the art can select the concentration of a suitable ammonium bicarbonate solution according to actual needs. In one or more embodiments, the concentration of the ammonium bicarbonate solution used in step (1) is 3% by weight to 20% by weight, for example, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20% by weight or within the range defined by any two of the above values.

[0059] The electrochemical membrane reactor treatment in step (1) can be carried out in a manner known to those skilled in the art. For example, the electrochemical membrane reactor treatment is carried out using a four-channel electrodialysis device as described in CN 110917882A, the contents of which are incorporated herein by reference in their entirety.

[0060] By using ammonium bicarbonate solution and mixed salt wastewater containing soluble alkali chloride and soluble alkali sulfate for electrochemical membrane reactor treatment, a first mixed solution containing ammonium sulfate and ammonium chloride and an alkali bicarbonate solution can be obtained respectively. The obtained first mixed solution containing ammonium sulfate and ammonium chloride will be subjected to precipitation separation in step (2) (i.e., precipitation separation step) to be described in detail below to obtain two separate salt components; and the obtained alkali bicarbonate solution can be treated (e.g., evaporation crystallization treatment or freezing crystallization treatment) to obtain alkali bicarbonate solid, or can be reacted with the alkali hydroxide solution obtained in step (3) (i.e., bipolar membrane electrodialysis step) to be described in detail below to obtain an alkali carbonate product with high economic value, while also being able to promote the acid-base production efficiency of the bipolar membrane electrodialysis process.

[0061] Step (2)

[0062] The method according to the present invention comprises step (2), namely a precipitation separation step.

[0063] In step (2), the first mixed solution containing ammonium sulfate and ammonium chloride obtained in step (1) is reacted with calcium oxide and / or calcium hydroxide to obtain ammonia gas and a reaction mixture containing calcium sulfate precipitate and calcium chloride, respectively. For the obtained reaction mixture containing calcium sulfate precipitate and calcium chloride, solid calcium sulfate and calcium chloride solution can be obtained by solid-liquid separation, thereby achieving separation of mixed salts and obtaining a single salt component with high economic value. For the obtained ammonia gas, at least a part or all of it can be reacted with carbon dioxide and water to obtain an ammonium bicarbonate solution, which can be returned to step (1) and used as a raw material for electrochemical membrane reactor treatment, thereby achieving a closed process loop and avoiding product emissions.

[0064] Step (2) comprises mixing and reacting the first mixed solution containing ammonium sulfate and ammonium chloride obtained in step (1) with calcium oxide, calcium hydroxide or a combination thereof to obtain ammonia gas and a reaction mixture containing calcium sulfate and calcium chloride, respectively.

[0065] In this step, those skilled in the art can select an appropriate amount according to actual needs. In one or more embodiments, the weight ratio between the calcium oxide, calcium hydroxide or a combination thereof used in step (2) and the total amount of ammonium sulfate and ammonium chloride contained in the first mixed solution is such that the molar ratio of calcium element to the total amount of sulfate and chloride ions is stoichiometrically equivalent or in excess.

[0066] In step (2), the first mixed solution containing ammonium sulfate and ammonium chloride obtained in step (1) and calcium oxide, calcium hydroxide or a combination thereof can be reacted under pH conditions of 9-14, for example, under pH conditions of 9, 10, 11, 12, 13, 14 or within a range defined by any two of the above values.

[0067] In step (2), the first mixed solution containing ammonium sulfate and ammonium chloride obtained in step (1) is reacted with calcium oxide, calcium hydroxide or a combination thereof at a temperature of 10° C. to 60° C., for example, at a pH of 10, 20, 30, 40, 50, 60 or within a range defined by any two of the above values.

[0068] When the pH condition and temperature within the above range are used, the reaction efficiency can be effectively improved.

[0069] Step (2) further comprises carrying out solid-liquid separation of the reaction mixture comprising calcium sulfate and calcium chloride to obtain a solution comprising calcium chloride and calcium sulfate solid respectively. The specific mode of solid-liquid separation is not particularly limited in principle, and those skilled in the art can select a suitable solid-liquid separation mode according to actual needs, such as solid-liquid separation can be selected from one or more of precipitation, clarification and filtration. In one or more embodiments, solid-liquid separation can be carried out by one or more of the following equipment: a high-density sedimentation tank, a mechanical stirring clarification tank, a V-type filter, a variable pore filter, a rapid filter, a tubular microfilter, a tubular ultrafilter, a ceramic membrane filter, an immersion ultrafilter, a belt filter press, a vacuum belt filter, a plate and frame filter press, a chamber filter press, and a diaphragm filter press, etc. The calcium sulfate solid can be dried. The solution comprising calcium chloride can be processed by evaporative crystallization or frozen crystallization to obtain a calcium chloride solid.

[0070] At least a portion of the ammonia obtained in step (2) is reacted with carbon dioxide and water to obtain the ammonium bicarbonate solution used in step (1). Regarding the reaction conditions and amounts of reactants of ammonia, carbon dioxide and water, those skilled in the art can select appropriate reaction conditions and amounts according to actual needs.

[0071] In a preferred embodiment, at least a portion of the ammonia gas obtained in step (2) can be reacted with the hydrochloric acid and / or sulfuric acid solution obtained in step (3) (i.e., the bipolar membrane electrodialysis step) described in detail below to produce ammonium chloride and / or ammonium sulfate solution, and the obtained solution can be treated to obtain ammonium chloride and / or ammonium sulfate solid as one of the final products, or when the obtained solution is ammonium chloride and ammonium sulfate solution, it can be subjected to the above-mentioned precipitation separation step. The economic and environmental benefits are further improved by the mutual utilization of the products between the two steps.

[0072] Step (3)

[0073] In a preferred embodiment, the method according to the present invention may further comprise step (3), namely a bipolar membrane electrodialysis step.

[0074] In step (3), a soluble alkali chloride and / or a soluble alkali sulfate solution is subjected to bipolar membrane electrodialysis. By subjecting the soluble alkali chloride and / or the soluble alkali sulfate solution to bipolar membrane electrodialysis, hydrochloric acid and / or sulfuric acid solution and an alkali metal hydroxide solution are obtained respectively. The obtained hydrochloric acid and / or sulfuric acid solution can be directly used as a final product. In addition, the obtained hydrochloric acid and / or sulfuric acid solution can also be reacted with at least a portion of the ammonia obtained in step (2) as described above to produce ammonium chloride and / or ammonium sulfate solution, and the obtained solution is processed to obtain ammonium chloride and / or ammonium sulfate solid as one of the final products. Alternatively, when the obtained solution is ammonium chloride and ammonium sulfate solution, it can be subjected to the precipitation separation step described above to obtain a calcium chloride product and a calcium sulfate product respectively. The obtained alkali metal hydroxide solution can be reacted with the alkali metal bicarbonate solution obtained in step (1) to produce an alkali metal carbonate solution, and the alkali metal carbonate solution is treated to obtain an alkali metal carbonate solid as one of the final products. Since the generated new product reduces ion back migration, the acid and alkali production efficiency of the bipolar membrane electrodialysis process can be improved.

[0075] Therefore, through the interactive utilization of products between the above steps, the discharge of products is avoided, the process closed loop is achieved, and the final product with high economic value is obtained, while the acid and alkali production efficiency of the bipolar membrane electrodialysis step is improved.

[0076] Step (3) comprises subjecting the soluble alkali metal chloride and / or soluble alkali metal sulfate solution to bipolar membrane electrodialysis to obtain hydrochloric acid and / or sulfuric acid solution and alkali metal hydroxide solution, respectively.

[0077] The soluble alkali metal chloride and the soluble alkali metal sulfate may be the same as described above with respect to step (1).

[0078] In one or more embodiments, the soluble alkali chloride and soluble alkali sulfate solution is subjected to bipolar membrane electrodialysis, the soluble alkali chloride and soluble alkali sulfate solution being derived from a second wastewater. The second wastewater may be the same as or different from the first wastewater.

[0079] The concentration of soluble alkali metal chloride in the second wastewater may be 2 wt %-20 wt %, for example, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 wt % or within a range defined by any two of the above values.

[0080] The concentration of soluble alkali metal sulfate in the second wastewater may be 3 wt%-20 wt%, for example, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 wt% or within the range defined by any two of the above values.

[0081] The total concentration of soluble alkali metal chloride and soluble alkali metal sulfate in the second wastewater may be 3 wt%-20 wt%, for example, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 wt% or within the range defined by any two of the above values.

[0082] The alkali metal hydroxide solution can be selected from one or more of a lithium hydroxide solution, a sodium hydroxide solution, and a potassium hydroxide solution. For example, the alkali metal hydroxide solution can be a sodium hydroxide solution.

[0083] Before the bipolar membrane electrodialysis treatment, the second wastewater containing soluble alkali metal chloride and soluble alkali metal sulfate can be pretreated. Through the pretreatment step, the particles with a particle size greater than 5 μm and the calcium ions and magnesium ions in the second wastewater are removed. The specific method of pretreatment is not particularly limited in principle, and those skilled in the art can select a suitable pretreatment method according to actual needs. For example, the pretreatment can be selected from one or more of filtration and ion exchange.

[0084] Before the bipolar membrane electrodialysis treatment, the second wastewater containing soluble alkali metal chloride and soluble alkali metal sulfate can be pre-formulated to obtain a certain concentration, preferably so that the concentration of soluble alkali metal chloride is 2% by weight to 20% by weight and the concentration of soluble alkali metal sulfate is 3% by weight to 20% by weight. For example, the concentration of soluble alkali metal chloride can be 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20% by weight or in the range defined by any two of the above values, and the concentration of soluble alkali metal sulfate can be 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20% by weight or in the range defined by any two of the above values.

[0085] The bipolar membrane electrodialysis treatment in step (3) can be carried out in a manner known to those skilled in the art. For example, the bipolar membrane electrodialysis treatment can be carried out using a bipolar membrane electrodialyzer as described in CN 107298450B, the contents of which are incorporated herein by reference in their entirety.

[0086] Optionally, step (3) may further comprise reacting the hydrochloric acid and / or sulfuric acid solution obtained from the bipolar membrane electrodialysis treatment with at least a portion of the ammonia obtained in step (2) to obtain ammonium chloride and / or ammonium sulfate solution.

[0087] For the reaction conditions and the amount of reactants of hydrochloric acid and / or sulfuric acid solution and ammonia, those skilled in the art can select appropriate reaction conditions and amounts according to actual needs. When the amount of ammonia is insufficient, aqueous ammonia or liquid ammonia can be added to react with the hydrochloric acid and / or sulfuric acid solution.

[0088] In one embodiment, the ammonium chloride and / or ammonium sulfate solution obtained in step (3) is subjected to a second treatment to obtain ammonium chloride and / or ammonium sulfate solid.

[0089] The specific method of the second treatment is not particularly limited in principle, as long as it can convert the second mixed solution into a solid. For example, the second treatment can be selected from evaporative crystallization and freeze crystallization.

[0090] In another embodiment, when a soluble alkali metal chloride and a soluble alkali metal sulfate solution are used for bipolar membrane electrodialysis treatment, the obtained products (ammonium chloride and ammonium sulfate solution) can be subjected to the precipitation separation step described above to obtain a calcium chloride product and a calcium sulfate product, respectively. That is, the soluble alkali metal chloride and the soluble alkali metal sulfate solution are subjected to bipolar membrane electrodialysis treatment, and step (3) further comprises reacting the hydrochloric acid and sulfuric acid solution obtained from the bipolar membrane electrodialysis treatment with at least a portion of the ammonia obtained in step (2) to obtain ammonium chloride and ammonium sulfate solution, and the ammonium chloride and ammonium sulfate solution are subjected to the precipitation separation step (2).

[0091] Step (3) may further include reacting the alkali metal hydroxide solution obtained from the bipolar membrane electrodialysis treatment with the alkali metal bicarbonate solution obtained in step (1) to obtain an alkali metal carbonate solution, and subjecting the alkali metal carbonate solution to a first treatment to obtain an alkali metal carbonate solid.

[0092] Regarding the reaction conditions and amounts of the alkali metal hydroxide solution and the alkali metal bicarbonate solution, those skilled in the art can select appropriate reaction conditions and amounts according to actual needs.

[0093] The alkali metal carbonate can be selected from one or more of lithium carbonate, sodium carbonate and potassium carbonate. For example, the alkali metal carbonate can be sodium carbonate.

[0094] The specific method of the first treatment is not particularly limited in principle as long as it can convert the alkali metal carbonate solution into a solid. For example, the first treatment can be selected from evaporative crystallization and freeze crystallization.

[0095] The following will be combined Figure 1 An exemplary embodiment of the method for treating wastewater according to the present invention is described.

[0096] like Figure 1 As shown in , firstly, the first wastewater containing sodium chloride and sodium sulfate and the ammonium bicarbonate solution are subjected to electrochemical membrane reactor treatment. Before the electrochemical membrane reactor treatment, the first wastewater may be optionally pretreated to remove particulate matter with a particle size greater than 5 μm; and the ammonium bicarbonate may be dissolved in water to prepare an ammonium bicarbonate solution of a certain concentration. Through the electrochemical membrane reactor treatment, a first mixed solution containing ammonium sulfate and ammonium chloride and a sodium bicarbonate solution are obtained respectively. The sodium bicarbonate solution can be directly evaporated and crystallized to obtain sodium bicarbonate solid, or it can be reacted with the sodium hydroxide solution obtained from the bipolar membrane electrodialysis treatment described below.

[0097] Then, slaked lime (i.e., calcium hydroxide) and / or quicklime (i.e., calcium oxide) are added to the obtained first mixed solution containing ammonium sulfate and ammonium chloride, and the two react to generate a reaction mixture containing a calcium chloride solution and a calcium sulfate precipitate. The reaction mixture is subjected to solid-liquid separation to obtain a calcium chloride solution and a calcium sulfate precipitate, respectively, to achieve the purpose of separating mixed salts, wherein the calcium chloride solution can be evaporated and crystallized to obtain a calcium chloride solid, and the calcium sulfate precipitate can be dried to obtain a calcium sulfate solid. The reaction simultaneously generates ammonia, and a part of the generated ammonia is reacted with carbon dioxide and water to generate an ammonium bicarbonate solution, which is then returned to the aforementioned electrochemical membrane reactor for use as a raw material. At the same time, another part of the generated ammonia can be reacted with a hydrochloric acid / sulfuric acid solution obtained from a bipolar membrane electrodialysis treatment to be described later to generate an ammonium chloride / ammonium sulfate solution, which can be prepared into a solid salt by evaporation and crystallization.

[0098] In addition, the sodium chloride and / or sodium sulfate solution or the first wastewater containing sodium chloride and sodium sulfate is subjected to bipolar membrane electrodialysis treatment. Before the bipolar membrane electrodialysis treatment is carried out, the sodium chloride and / or sodium sulfate solution or the first wastewater can be pre-prepared to a certain concentration. Through the bipolar membrane electrodialysis treatment, hydrochloric acid / sulfuric acid solution and sodium hydroxide solution are obtained respectively. The obtained hydrochloric acid / sulfuric acid solution can be reacted with a part of the ammonia obtained by the above-mentioned precipitation reaction (when the amount of ammonia is insufficient, ammonia water can be added to react with the hydrochloric acid / sulfuric acid solution) to generate ammonium chloride / ammonium sulfate solution, and the ammonium chloride / ammonium sulfate solution can be prepared into a solid salt as one of the final products by evaporation and crystallization. In addition, the obtained sodium hydroxide solution can be reacted with the sodium bicarbonate solution obtained by the above-mentioned electrochemical membrane reactor treatment to obtain a sodium carbonate solution, and the sodium carbonate solution can be prepared into a sodium carbonate solid salt as one of the final products by evaporation and crystallization. At the same time, since the generated new product reduces the ion back migration, the acid-base production efficiency of the bipolar membrane electrodialysis treatment is also improved, thereby further improving the process efficiency.

[0099] As can be seen from the above, the above method reuses industrial waste mixed salt solution, and through the interactive utilization of the products of each step, it separates the low-value mixed salt and converts it into high-value single salt components in a simple and efficient manner, while realizing a closed process loop and emitting almost no pollutants. In addition, it also improves the acid and alkali production efficiency of bipolar membrane electrodialysis treatment.

[0100] Devices for treating wastewater

[0101] In a second aspect, the present invention relates to an apparatus for treating wastewater, comprising the following modules:

[0102] (1) An electrochemical membrane reactor module, comprising:

[0103] - an electrochemical membrane reactor unit, which is used to treat the first wastewater containing soluble alkali chloride and soluble alkali sulfate with an ammonium bicarbonate solution by electrochemical membrane reactor to obtain a first mixed solution containing ammonium sulfate and ammonium chloride and an alkali bicarbonate solution, respectively; and

[0104] (2) A precipitation separation module downstream of the electrochemical membrane reactor module, comprising:

[0105] - a reaction unit for mixing and reacting a first mixed solution containing ammonium sulfate and ammonium chloride obtained from an electrochemical membrane reactor unit with calcium oxide, calcium hydroxide or a combination thereof to obtain ammonia gas and a reaction mixture containing calcium sulfate and calcium chloride, respectively; and

[0106] - a solid-liquid separation unit downstream of the reaction unit, which is used to separate the reaction mixture obtained from the reaction unit into solid and liquid to obtain a solution containing calcium chloride and solid calcium sulfate, respectively,

[0107] The device further includes a first reaction box downstream of the reaction unit and connected to the electrochemical membrane reactor module, which is used to react at least a portion of the ammonia obtained from the reaction unit with carbon dioxide and water to obtain an ammonium bicarbonate solution, and the ammonium bicarbonate solution is supplied to the electrochemical membrane reactor unit.

[0108] In a preferred embodiment, the device further comprises:

[0109] (3) Bipolar membrane electrodialysis module, comprising:

[0110] - a bipolar membrane electrodialysis unit, which is used to subject a solution containing a soluble alkali metal chloride and / or a soluble alkali metal sulfate to bipolar membrane electrodialysis to obtain a hydrochloric acid and / or sulfuric acid solution and an alkali metal hydroxide solution, respectively;

[0111] - a second reaction box, optionally downstream of the bipolar membrane electrodialysis unit and connected to the electrochemical membrane reactor module, for reacting the hydrochloric acid and / or sulfuric acid solution obtained from the bipolar membrane electrodialysis unit with at least part of the ammonia gas obtained from the reaction unit to obtain ammonium chloride and / or ammonium sulfate solution;

[0112] - a third reaction box downstream of the bipolar membrane electrodialysis unit and connected to the electrochemical membrane reactor module, which is used to react the alkali metal hydroxide solution obtained from the bipolar membrane electrodialysis unit with the alkali metal bicarbonate solution obtained from the electrochemical membrane reactor unit to obtain an alkali metal carbonate solution; and

[0113] - A first treatment unit downstream of the third reaction tank, which is used to subject the alkali metal carbonate solution obtained from the third reaction tank to a first treatment to obtain alkali metal carbonate solid.

[0114] In one or more embodiments, the device according to the present invention is a device for implementing the method for treating wastewater as described above.

[0115] Each module will be described in detail below.

[0116] Module(1)

[0117] The device according to the invention comprises a module (1), namely an electrochemical membrane reactor module (also called displacement electrodialysis module).

[0118] The electrochemical membrane reactor module comprises an electrochemical membrane reactor unit, which is used to perform electrochemical membrane reactor treatment on first wastewater containing soluble alkali chloride and soluble alkali sulfate and ammonium bicarbonate solution to obtain a first mixed solution containing ammonium sulfate and ammonium chloride and an alkali bicarbonate solution respectively.

[0119] The electrochemical membrane reactor unit may include an electrochemical membrane reactor device (also called a displacement electrodialysis device), such as a four-channel electrodialysis device described in CN 110917882A. The electrochemical membrane reactor device may have a structure known to those skilled in the art. The electrochemical membrane reactor device generally includes an electrochemical reaction membrane stack. The main components of the electrochemical membrane reactor device are diaphragms (anion exchange membranes and cation exchange membranes), partitions, electrode plates, foaming materials, compression plates, frames, and locking (or hydraulic locking) devices. The membrane stack may include anion exchange membranes and cation exchange membranes, wherein the anion exchange membranes and cation exchange membranes are alternately arranged and form an intermembrane chamber. In the electrochemical membrane reactor device, a plurality of cation exchange membranes and anion exchange membranes are alternately arranged between the anode and the cathode to form an ion exchange membrane array, wherein the cations migrate to the cathode side under the force of the electric field, and the anions migrate to the anode side under the force of the electric field. When the cations encounter the cation exchange membrane while traveling, the cations can pass through, and when the cations encounter the anion exchange membrane while traveling, the cations are blocked and cannot pass through. When the anions encounter the anion exchange membrane during their travel, the anions can pass through, and when the anions encounter the cation exchange membrane during their travel, the anions are blocked and cannot pass through. The first wastewater and the ammonium bicarbonate solution are subjected to ion exchange in the ion exchange membrane array.

[0120] The soluble alkali metal chloride, soluble alkali metal sulfate and alkali metal bicarbonate solutions may be the same as described above with respect to step (1).

[0121] In one or more embodiments, the electrochemical membrane reactor unit may include a raw water tank upstream of the electrochemical membrane reactor device, which is used to store the first wastewater.

[0122] The first wastewater may optionally undergo pretreatment before entering the raw water tank. In one or more embodiments, the electrochemical membrane reactor module further includes a pretreatment unit (e.g., a raw water pretreatment device) upstream of the electrochemical membrane reactor unit, which is used to pretreat the first wastewater containing soluble alkali chloride and soluble alkali sulfate before entering the electrochemical membrane reactor unit to remove particulate matter with a particle size greater than 5 μm. The pretreatment unit may be selected from one or more of a filter and an ion exchanger. In one or more embodiments, the pretreatment unit may include one or more of the following: a multi-media filter, a microfilter, an ultrafilter, a tubular microfilter, a tubular ultrafilter, a ceramic membrane filter, a fiber filter, a precision filter with a filter element or a filter bag installed, and an ion exchanger, etc. The pretreatment unit may be connected to the raw water tank via a pipeline, and the pretreated first wastewater may be supplied to the raw water tank.

[0123] In one or more embodiments, the electrochemical membrane reactor unit may include a reagent tank upstream of the electrochemical membrane reactor device for storing an ammonium bicarbonate solution. Ammonium bicarbonate may be dissolved in water in the reagent tank to prepare an ammonium bicarbonate solution having a concentration of 3 wt % to 20 wt %, such as an ammonium bicarbonate solution having a concentration of 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 wt % or within a range defined by any two of the above values.

[0124] The first wastewater stored in the raw water tank and the ammonium bicarbonate solution stored in the reagent tank can be supplied to the electrochemical membrane reactor device. Due to the unique selectivity of the electrochemical reaction membrane stack in the electrochemical membrane reactor device, the two ions of the original combination of the contained ionic compounds are separated and recombined to form a new ionic compound, that is, the alkali metal bicarbonate solution and the first mixed solution containing ammonium sulfate and ammonium chloride.

[0125] In one or more embodiments, the electrochemical membrane reactor unit may include a product tank and a byproduct tank downstream of the electrochemical membrane reactor device, wherein the product tank is used to store the alkali metal bicarbonate solution obtained from the electrochemical membrane reactor device, and the byproduct tank is used to store the first mixed solution containing ammonium sulfate and ammonium chloride obtained from the electrochemical membrane reactor device. The alkali metal bicarbonate solution stored in the product tank can be supplied to an evaporation crystallization unit or a freezing crystallization unit downstream of the electrochemical membrane reactor module, and the alkali metal bicarbonate solid is obtained by treatment in the evaporation crystallization unit or the freezing crystallization unit; or it can be supplied to module (3) (i.e., a bipolar membrane electrodialysis module), and the first mixed solution containing ammonium sulfate and ammonium chloride stored in the byproduct tank can be supplied to module (2) (i.e., a precipitation separation module).

[0126] Modules (2)

[0127] The device according to the invention comprises a module (2), namely a precipitation separation module downstream of an electrochemical membrane reactor module.

[0128] Through the precipitation separation module, the first mixed solution containing ammonium sulfate and ammonium chloride obtained from the electrochemical membrane reactor unit is separated to obtain a single salt product with high economic value. At the same time, the ammonia gas produced can be used to generate raw materials in the electrochemical membrane reactor module, forming a process closed loop.

[0129] The precipitation separation module includes a reaction unit, which is used to mix and react a first mixed solution containing ammonium sulfate and ammonium chloride obtained from an electrochemical membrane reactor unit with calcium oxide, calcium hydroxide or a combination thereof to obtain ammonia gas and a reaction mixture containing calcium sulfate and calcium chloride, respectively.

[0130] The precipitation separation module further includes a solid-liquid separation unit downstream of the reaction unit, which is used for carrying out solid-liquid separation of the reaction mixture obtained from the reaction unit to obtain a solution containing calcium chloride and a calcium sulfate solid respectively. The solid-liquid separation unit in the precipitation separation module can be selected from one or more of a sedimentation tank, a clarification tank and a filter. For example, the solid-liquid separation unit may include one or more of the following: a high-density sedimentation tank, a mechanical stirring clarification tank, a V-type filter, a variable pore filter, a fast filter, a tubular microfilter, a tubular ultrafilter, a ceramic membrane filter, an immersion ultrafilter, a belt filter press, a vacuum belt filter, a plate and frame filter press, a chamber filter press, and a diaphragm filter press, etc. The precipitation separation module may further include an evaporative crystallization unit downstream of the solid-liquid separation unit, which is used for converting a solution containing calcium chloride into a calcium chloride solid. The precipitation separation module may further include a drying unit downstream of the solid-liquid separation unit, which is used for drying the calcium sulfate solid.

[0131] The device according to the present invention further comprises a first reaction box downstream of the reaction unit and connected to the electrochemical membrane reactor module, which is used to react at least a portion of the ammonia obtained from the reaction unit with carbon dioxide and water to obtain an ammonium bicarbonate solution, and the ammonium bicarbonate solution is supplied to the electrochemical membrane reactor unit.

[0132] Modules (3)

[0133] In a preferred embodiment, the device according to the invention comprises a module (3), namely a bipolar membrane electrodialysis module.

[0134] By utilizing the product interaction between the bipolar membrane electrodialysis module and the above-mentioned electrochemical membrane reactor module and precipitation separation module, the process efficiency can be further improved, and the process closed loop can be achieved to avoid product emissions, thereby achieving environmental benefits while generating higher economic value.

[0135] The bipolar membrane electrodialysis module comprises a bipolar membrane electrodialysis unit, which is used to perform bipolar membrane electrodialysis treatment on a soluble alkali metal chloride and / or a soluble alkali metal sulfate solution to obtain a hydrochloric acid and / or sulfuric acid solution and an alkali metal hydroxide solution, respectively.

[0136] The bipolar membrane electrodialysis unit may include a bipolar membrane electrodialysis device, such as the bipolar membrane electrodialyzer described in CN 107298450B. The bipolar membrane electrodialysis device may have a structure known to those skilled in the art. The bipolar membrane electrodialysis device generally includes a bipolar membrane stack. The bipolar membrane stack is a core component of the device, generally composed of a cation exchange layer, an anion exchange layer and an interface hydrophilic layer therebetween.

[0137] In one or more embodiments, the bipolar membrane electrodialysis unit may include a bipolar membrane raw water tank upstream of the bipolar membrane electrodialysis device, which is used to store a soluble alkali chloride and / or soluble alkali sulfate solution. The soluble alkali chloride and / or soluble alkali sulfate solution may be optionally pre-formulated to obtain a certain concentration before entering the bipolar membrane raw water tank.

[0138] In one or more embodiments, when the second wastewater containing soluble alkali chloride and soluble alkali sulfate solution is subjected to bipolar membrane electrodialysis treatment, the bipolar membrane electrodialysis module further includes a pretreatment unit upstream of the bipolar membrane electrodialysis unit, which is used to pretreat the second wastewater containing soluble alkali chloride and soluble alkali sulfate before entering the electrochemical membrane reactor unit to remove particulate matter with a particle size greater than 5 μm and calcium ions and magnesium ions. The pretreatment unit can be selected from one or more of a filter and an ion exchanger.

[0139] The soluble alkali metal chloride, soluble alkali metal sulfate and alkali metal hydroxide solutions may be the same as described above with respect to step (3).

[0140] The bipolar membrane electrodialysis module may optionally further include a second reaction box downstream of the bipolar membrane electrodialysis unit and connected to the electrochemical membrane reactor module, which is used to react the hydrochloric acid and / or sulfuric acid solution obtained from the bipolar membrane electrodialysis unit with at least a portion of the ammonia gas obtained from the reaction unit to obtain ammonium chloride and / or ammonium sulfate solution.

[0141] In one embodiment, when the soluble alkali metal chloride and the soluble alkali metal sulfate solution are subjected to bipolar membrane electrodialysis treatment, the bipolar membrane electrodialysis module may further include a first pipeline connecting the second reaction box and the precipitation separation module, which is used to supply the ammonium sulfate and ammonium chloride solutions obtained from the second reaction box to the precipitation separation module.

[0142] In another embodiment, the bipolar membrane electrodialysis module may further include a second treatment unit downstream of the second reaction box, which is used to perform a second treatment on the ammonium chloride and / or ammonium sulfate solution obtained from the second reaction box to obtain ammonium chloride and / or ammonium sulfate solid. In one or more embodiments, the second treatment unit may be an evaporative crystallization unit or a frozen crystallization unit.

[0143] The bipolar membrane electrodialysis module may further include a third reaction box downstream of the bipolar membrane electrodialysis unit and connected to the electrochemical membrane reactor module, which is used to react the alkali metal hydroxide solution obtained from the bipolar membrane electrodialysis unit with the alkali metal bicarbonate solution obtained from the electrochemical membrane reactor unit to obtain an alkali metal carbonate solution.

[0144] The bipolar membrane electrodialysis module may further include a first treatment unit downstream of the third reaction tank, which is used to perform a first treatment on the alkali metal carbonate solution obtained from the third reaction tank to obtain alkali metal carbonate solid. In one or more embodiments, the first treatment unit may be an evaporative crystallization unit or a frozen crystallization unit.

[0145] The following will be combined Figure 2 An exemplary embodiment of the apparatus for treating wastewater according to the present invention is described.

[0146] like Figure 2 As shown in , the device for treating wastewater is divided into three modules: an electrochemical membrane reactor module, a precipitation separation module and a bipolar membrane electrodialysis module.

[0147] (1) Electrochemical membrane reactor module: This module is mainly composed of an electrochemical membrane reactor device. The device uses an electrochemical reaction membrane stack to construct four loops to achieve the function of separating ions in the solution and then recombining them to form new ionic compounds. In this module, there are raw water pretreatment equipment (equipment No. 1), a raw water tank (tank No. 2), a reagent tank (tank No. 3), a product tank (tank No. 4), a by-product tank (tank No. 5), an electrochemical reaction membrane stack, a pump, etc. The raw water pretreatment equipment (equipment No. 1) and the raw water tank (tank No. 2) are connected by a pipeline. After the mixed salt wastewater containing sodium chloride and sodium sulfate is pretreated in the raw water pretreatment equipment (equipment No. 1), all particles with a particle size greater than 5μm in the mixed salt wastewater are removed. Ammonium bicarbonate is added to the reagent tank and dissolved in water to obtain an ammonium bicarbonate solution of a certain concentration. The pretreated mixed salt wastewater and the ammonium bicarbonate solution are respectively transported to the raw water tank (tank No. 2) and the reagent tank (tank No. 3) by pumps. After turning on the power, the pretreated mixed salt wastewater and ammonium bicarbonate solution enter the electrochemical reaction membrane stack. Inside the electrochemical reaction membrane stack, due to the unique selectivity of the electrochemical reaction membrane stack, the ions of the original combination of the contained ion compounds are separated and recombined into new ion compounds: sodium bicarbonate solution is obtained in the product box (Box 4), and a solution containing ammonium chloride and ammonium sulfate is obtained in the by-product box (Box 5). The above process is circulated under the action of the pump. As this process proceeds, the number of ions in the solution in the raw water tank (Box 2) and the reagent box (Box 3) will gradually decrease to the minimum trigger value. At this time, the pump will continue to work and continue to input new pretreated mixed salt wastewater and ammonium bicarbonate solution into the raw water tank (Box 2) and the reagent box (Box 3). During the entire operation process, the mixed salt wastewater will be continuously fed into the raw water pretreatment equipment (equipment No. 1), and after pretreatment, it will enter the raw water tank (tank No. 2) to maintain the salt content of the raw water; at the same time, ammonium bicarbonate is continuously added to the reagent box (tank No. 3) to control the concentration of the ammonium bicarbonate solution. After the salt content of the sodium bicarbonate solution (tank No. 4) reaches a certain value, it can be supplied to the evaporation crystallization unit (not shown) for treatment to obtain a solid sodium bicarbonate salt as one of the final products. In an alternative embodiment, after the salt content of the sodium bicarbonate solution (tank No. 4) reaches a certain value, the feed liquid in the alkali liquid tank (tank No. 7) of the bipolar membrane electrodialysis module is supplied to the No. 4 tank, and a sodium carbonate solution is generated in the No. 4 tank, and the sodium carbonate solution is supplied to the evaporation crystallization unit (not shown) for treatment to obtain a solid sodium carbonate salt as one of the final products. The solution containing ammonium chloride and ammonium sulfate (tank No. 5) is transported to the precipitation separation module.

[0148] (2) Precipitation and separation module: The solution containing ammonium chloride and ammonium sulfate generated by the electrochemical membrane reactor module enters the reaction water tank A of the precipitation and separation module, and slaked lime and / or quicklime are added to the reaction water tank A, which reacts with the solution containing ammonium chloride and ammonium sulfate to generate a reaction mixture containing a calcium chloride solution and a calcium sulfate precipitate. The reaction mixture is supplied to the solid-liquid separation unit for separation to obtain a calcium chloride solution and a calcium sulfate solid, respectively, thereby achieving the purpose of separating mixed salts. The reaction simultaneously generates ammonia gas, and a portion of the generated ammonia gas is introduced into the reaction water tank B to react with water and carbon dioxide to generate an ammonium bicarbonate solution, which is then supplied to the reagent box (box 3) of the electrochemical membrane reactor unit. In addition, another portion of the generated ammonia gas can be introduced into the acid tank (box 8) of the bipolar membrane electrodialysis module to react with the hydrochloric acid / sulfuric acid solution generated from the bipolar membrane electrodialysis module to generate an ammonium chloride / ammonium sulfate solution. Since the generation of the salt product reduces the ion back migration, the acid-base production efficiency of the bipolar membrane electrodialysis module is improved, further improving the process efficiency. The ammonium chloride / ammonium sulfate solution is supplied to an evaporative crystallization unit (not shown) for treatment to prepare a solid salt. If another portion of the generated ammonia gas is reacted with the hydrochloric acid and sulfuric acid solution produced from the bipolar membrane electrodialysis module to generate ammonium chloride and ammonium sulfate solutions, the ammonium chloride and ammonium sulfate solutions can be transported to the reaction water tank A for precipitation separation.

[0149] (3) Bipolar membrane electrodialysis module: This module is mainly composed of bipolar membrane electrodialysis equipment. The bipolar membrane is composed of a cation exchange layer, an anion exchange layer and an intermediate hydrophilic interface layer. During the initial startup, mixed salt wastewater containing sodium chloride and sodium sulfate at a certain concentration enters the bipolar membrane raw water tank (tank No. 6), and the mixed salt wastewater is transported to the bipolar membrane stack via a pump. When a reverse voltage is applied to both sides of the bipolar membrane, the charged ions diffuse to the outside through the anion and cation exchange layers, respectively, causing the hydrophilic layer to form a high potential gradient and electrolyze water, generating H + and OH - Under the action of the electric field, they migrate to the peripheral solution. At the same time, the sodium ions and chloride ions / sulfate ions in the water selectively pass through the ion exchange membrane under the action of the electric field and react with the OH generated by the bipolar membrane. - and H +Sodium hydroxide solution and hydrochloric acid / sulfuric acid solution are formed respectively. The sodium hydroxide solution and hydrochloric acid / sulfuric acid solution generated by the bipolar membrane electrodialysis device are transported to the alkali liquid box (box 7) and the acid liquid box (box 8) respectively. After the sodium hydroxide solution in the alkali liquid box (box 7) reaches a certain concentration, the feed liquid is sent to the product box (box 4) of the electrochemical membrane reactor module, and reacts with the sodium bicarbonate solution obtained from the electrochemical membrane reactor module to generate sodium carbonate solution. After accumulating a certain amount of sodium carbonate solution, the solution is transported to the corresponding evaporation crystallization unit to prepare sodium carbonate salt as one of the final products. The hydrochloric acid / sulfuric acid solution in the acid liquid box (box 8) reacts with a part of the ammonia obtained from the precipitation separation module to generate ammonium chloride / ammonium sulfate solution. In the case of insufficient amount of ammonia, ammonia water can be added to react with the hydrochloric acid / sulfuric acid solution. After accumulating a certain amount of ammonium chloride / ammonium sulfate solution, the solution is transported to the corresponding evaporation crystallization unit to prepare solid salt as one of the final products. If another part of the generated ammonia gas is reacted with the hydrochloric acid and sulfuric acid solution produced from the bipolar membrane electrodialysis module to generate ammonium chloride and ammonium sulfate solution, the ammonium chloride and ammonium sulfate solution can be transported to the reaction water tank A for precipitation separation.

[0150] The above is only an exemplary embodiment of the present invention. It should be noted that, for those skilled in the art, without departing from the inventive concept of the present invention, improvements can be made to the present invention, but these all belong to the protection scope of the present invention.

Claims

1. A method for treating wastewater, comprising the following steps: (1) An electrochemical membrane reactor treatment step comprising: - treating the first wastewater containing soluble alkali chloride and soluble alkali sulfate with an ammonium bicarbonate solution by electrochemical membrane reactor to obtain a first mixed solution containing ammonium sulfate and ammonium chloride and an alkali bicarbonate solution, respectively; and (2) A precipitation separation step, comprising: - mixing and reacting the first mixed solution containing ammonium sulfate and ammonium chloride obtained in step (1) with calcium oxide, calcium hydroxide or a combination thereof to obtain ammonia gas and a reaction mixture containing calcium sulfate and calcium chloride, respectively; and - subjecting the reaction mixture to solid-liquid separation to obtain a solution containing calcium chloride and solid calcium sulfate, respectively; At least a portion of the ammonia gas obtained in step (2) is reacted with carbon dioxide and water to obtain the ammonium bicarbonate solution used in step (1).

2. The method for treating wastewater according to claim 1, wherein the method further comprises: (3) Bipolar membrane electrodialysis step, comprising: - subjecting a soluble alkali metal chloride and / or a soluble alkali metal sulfate solution to bipolar membrane electrodialysis to obtain a hydrochloric acid and / or sulfuric acid solution and an alkali metal hydroxide solution, respectively; - optionally reacting the hydrochloric acid and / or sulfuric acid solution obtained from the bipolar membrane electrodialysis treatment with at least a portion of the ammonia obtained in step (2) to obtain an ammonium chloride and / or ammonium sulfate solution; and - reacting the alkali metal hydroxide solution obtained from the bipolar membrane electrodialysis treatment with the alkali metal bicarbonate solution obtained in step (1) to obtain an alkali metal carbonate solution, and subjecting the alkali metal carbonate solution to a first treatment to obtain an alkali metal carbonate solid.

3. A method for treating wastewater as claimed in claim 1 or 2, wherein in step (2), the first mixed solution containing ammonium sulfate and ammonium chloride obtained in step (1) is reacted with calcium oxide, calcium hydroxide or a combination thereof at a pH of 9-14 and a temperature of 10°C-60°C.

4. The method for treating wastewater as claimed in claim 2, wherein the soluble alkali metal chloride and the soluble alkali metal sulfate solution are subjected to bipolar membrane electrodialysis treatment, and the soluble alkali metal chloride and the soluble alkali metal sulfate solution are derived from the second wastewater.

5. A method for treating waste water as claimed in claim 4, wherein the second waste water containing soluble alkali chloride and soluble alkali sulfate is pretreated to remove particulate matter having a particle size greater than 5 μm and calcium ions and magnesium ions before being subjected to bipolar membrane electrodialysis treatment, wherein the pretreatment is selected from one or more of filtration and ion exchange.

6. The method for treating wastewater as claimed in claim 2, wherein the ammonium chloride and / or ammonium sulfate solution obtained in step (3) is subjected to a second treatment to obtain ammonium chloride and / or ammonium sulfate solids.

7. A method for treating wastewater as claimed in claim 2, wherein the soluble alkali metal chloride and the soluble alkali metal sulfate solution are subjected to bipolar membrane electrodialysis treatment, and step (3) further comprises reacting the hydrochloric acid and sulfuric acid solution obtained from the bipolar membrane electrodialysis treatment with at least a portion of the ammonia obtained in step (2) to obtain ammonium chloride and ammonium sulfate solutions, and subjecting the ammonium chloride and ammonium sulfate solutions to the precipitation separation step (2).

8. The method for treating wastewater according to claim 1 or 2, wherein the soluble alkali metal chloride is sodium chloride, and the soluble alkali metal sulfate is sodium sulfate.

9. A method for treating wastewater as described in claim 1 or 2, wherein the first wastewater containing soluble alkali metal chloride and soluble alkali metal sulfate is pretreated to remove particulate matter with a particle size greater than 5 μm before being treated in an electrochemical membrane reactor, wherein the pretreatment is selected from one or more of filtration and ion exchange.

10. The method for treating wastewater according to claim 1 or 2, wherein the concentration of the ammonium bicarbonate solution used in step (1) is 3% to 20% by weight.

11. The method for treating wastewater according to claim 1 or 2, wherein the solid-liquid separation in step (2) is selected from one or more of precipitation, clarification and filtration.

12. The method for treating wastewater as claimed in claim 4, wherein the second wastewater containing soluble alkali chloride and soluble alkali sulfate is pre-formulated before being subjected to bipolar membrane electrodialysis treatment so that the concentration of soluble alkali chloride is 2% to 20% by weight and the concentration of soluble alkali sulfate is 3% to 20% by weight.

13. A device for treating wastewater, comprising the following modules: (1) An electrochemical membrane reactor module, comprising: - an electrochemical membrane reactor unit, which is used to treat the first wastewater containing soluble alkali chloride and soluble alkali sulfate with an ammonium bicarbonate solution by electrochemical membrane reactor to obtain a first mixed solution containing ammonium sulfate and ammonium chloride and an alkali bicarbonate solution, respectively; and (2) A precipitation separation module downstream of the electrochemical membrane reactor module, comprising: - a reaction unit for mixing and reacting a first mixed solution containing ammonium sulfate and ammonium chloride obtained from an electrochemical membrane reactor unit with calcium oxide, calcium hydroxide or a combination thereof to obtain ammonia gas and a reaction mixture containing calcium sulfate and calcium chloride, respectively; and - a solid-liquid separation unit downstream of the reaction unit, which is used to separate the reaction mixture obtained from the reaction unit into solid and liquid to obtain a solution containing calcium chloride and solid calcium sulfate, respectively, The device further includes a first reaction box downstream of the reaction unit and connected to the electrochemical membrane reactor module, which is used to react at least a portion of the ammonia obtained from the reaction unit with carbon dioxide and water to obtain an ammonium bicarbonate solution, and the ammonium bicarbonate solution is supplied to the electrochemical membrane reactor unit.

14. The device for treating wastewater according to claim 13, further comprising: (3) Bipolar membrane electrodialysis module, comprising: - a bipolar membrane electrodialysis unit, which is used to subject a soluble alkali metal chloride and / or a soluble alkali metal sulfate solution to bipolar membrane electrodialysis to obtain a hydrochloric acid and / or sulfuric acid solution and an alkali metal hydroxide solution, respectively; - a second reaction box, optionally downstream of the bipolar membrane electrodialysis unit and connected to the electrochemical membrane reactor module, for reacting the hydrochloric acid and / or sulfuric acid solution obtained from the bipolar membrane electrodialysis unit with at least part of the ammonia gas obtained from the reaction unit to obtain ammonium chloride and / or ammonium sulfate solution; - a third reaction box downstream of the bipolar membrane electrodialysis unit and connected to the electrochemical membrane reactor module, which is used to react the alkali metal hydroxide solution obtained from the bipolar membrane electrodialysis unit with the alkali metal bicarbonate solution obtained from the electrochemical membrane reactor unit to obtain an alkali metal carbonate solution; and - A first treatment unit downstream of the third reaction tank, which is used to subject the alkali metal carbonate solution obtained from the third reaction tank to a first treatment to obtain alkali metal carbonate solid.

15. A device for treating waste water as claimed in claim 14, wherein when soluble alkali chloride and soluble alkali sulfate solution are subjected to bipolar membrane electrodialysis treatment, the bipolar membrane electrodialysis module further comprises a first pipeline connecting the second reaction box and the precipitation separation module, which is used to supply the ammonium sulfate and ammonium chloride solution deriving from the second reaction box to the precipitation separation module.

16. The device for treating wastewater as claimed in claim 14, wherein the bipolar membrane electrodialysis module further comprises a second treatment unit downstream of the second reaction tank, which is used to subject the ammonium chloride and / or ammonium sulfate solution obtained from the second reaction tank to a second treatment to obtain ammonium chloride and / or ammonium sulfate solids.

17. The apparatus for treating wastewater according to claim 13 or 14, wherein the soluble alkali metal chloride is sodium chloride, and the soluble alkali metal sulfate is sodium sulfate.

18. An apparatus for treating wastewater as described in claim 13 or 14, wherein the electrochemical membrane reactor module further includes a pretreatment unit upstream of the electrochemical membrane reactor unit, which is used to pretreat the first wastewater containing soluble alkali metal chlorides and soluble alkali metal sulfates before entering the electrochemical membrane reactor unit to remove particulate matter with a particle size greater than 5 μm, wherein the pretreatment unit is selected from one or more of a filter and an ion exchanger.

19. The device for treating wastewater according to claim 13 or 14, wherein the solid-liquid separation unit in the sedimentation separation module is selected from one or more of a sedimentation tank, a clarification tank and a filter.

20. A device for treating wastewater as claimed in claim 14, wherein when the second wastewater containing soluble alkali chloride and soluble alkali sulfate is subjected to bipolar membrane electrodialysis treatment, the bipolar membrane electrodialysis module further includes a pretreatment unit upstream of the bipolar membrane electrodialysis unit, which is used to pretreat the second wastewater containing soluble alkali chloride and soluble alkali sulfate before entering the electrochemical membrane reactor unit to remove particulate matter with a particle size greater than 5 μm and calcium ions and magnesium ions, wherein the pretreatment unit is selected from one or more of a filter and an ion exchanger.

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