Method for separating anions and cations in solution and application of method

Abstract

The invention relates to a method for separating zwitterions in a solution and application thereof, and relates to enrichment, concentration and separation of zwitterions in a solution containing zwitterions, including but not limited to sewage treatment in tap water purification, seawater desalination, industry, agriculture, food processing, municipal administration and other industries. A solution flows through an electrolytic bath channel, and a part of the channel of the electrolytic bath is divided into two outlet channels, so that zwitterions which are separated from each other can respectively enter the two outlet channels. Wherein one outlet is used for collecting a solution containing more positive ions in the original solution, and the other outlet is used for collecting a solution containing more negative ions in the original solution, so that enrichment separation or partial separation of the negative ions and the positive ions in the solution is realized, and the technical barrier that the negative ions and the positive ions can be separated only by an ionic membrane in an electrodialysis technology is solved by using the flowing of the solution.

Description

Technical Field

[0001] The present invention relates to a method for separating cations and anions in a solution and its application, involving the enrichment, concentration and separation of cations and anions in a solution containing cations and anions, including but not limited to sewage treatment in industries such as tap water purification, seawater desalination, industry, agriculture, food processing, and municipal administration. Background Art

[0002] Some sewage or general water treatment, including seawater desalination and tap water purification, involves or partially involves the cations and anions contained in the solution and the separation and extraction of ions, such as the treatment of wastewater from electroplating electrolyte, metal processing and refining, titanium dioxide production process, power plant, monosodium glutamate production, coal chemical industry, paper mill, domestic sewage, medicine, food processing and other production and living processes. Current sewage treatment technologies often have high economic costs and great technical difficulties, which hinder the utilization of resources and the investment and development of production projects. In addition, current sewage treatment technologies are difficult to economically and effectively concentrate, recover and utilize valuable components in water, which are originally resource substances but become a burden on the production process and the environment. Therefore, a substantial technical breakthrough is needed in terms of economic practicality and low cost.

[0003] Technologies similar to the cation and anion separation and extraction technology of the present invention are the now basically mature electrolysis and electrodialysis technologies. However, these mature technologies familiar and mastered by those skilled in the art basically need to use cation and anion membranes or ion exchange resins, thereby increasing the operating cost and operation difficulty. Summary of the Invention

[0004] A method for separating cations and anions in a solution and its application according to the present invention is to flow a solution containing cations and anions through an electrolytic cell. Inside or at the outlet of the electrolytic cell, there are two non-connecting and electrically insulated sub-channels or sub-outlets separated by a partition. The flow direction of the solution is parallel to the electrode plate, and the separated solutions are collected from the two sub-channels or sub-outlets respectively.

[0005] In the solution collected from the sub-channel on the positive electrode side, the concentration of anions in the original solution increases, while in the solution collected from the sub-channel on the negative electrode side, the concentration of cations increases. Through the regular and restricted flow of the solution, the enrichment and separation or partial separation of cations and anions in the original solution are achieved. The traditional electrolytic separation technology is limited by the mature technical concepts over the years, mainly the limitations of the electrodialysis technical concept, and all use diaphragms or ion membranes or ion exchange resins to separate and partition the solute ions enriched on both sides of the electrodes.

[0006] Assume that the solute cations and anions in the solution are completely separated symmetrically or asymmetrically on both sides of the electrode. If the solution is separated at the boundary between the cations and anions, two solutions with completely separated cations and anions are obtained. If the solute cations and anions cannot be completely separated, the solution is separated at the position of pH 7 of the neutral solution, or at the position where the concentrations of the two ions are the same or nearly the same, or at the center line position (Note: Since the cations separated by the electrode are attracted to the hydroxide ions, and the anions are attracted to the hydrogen ions, the pH value distribution in the steady-state solution increases from low to high from the anode to the cathode).

[0007] The solution collected on one side, such as the solution on the negative electrode side, is returned to the original first electrolysis device for continuous recycling treatment. The solution collected on the other side, the positive electrode side, flows through a second electrolysis device with the same structure as above. The solution flowing out of the negative electrode side of the second electrolysis device flows back to the first electrolysis device for treatment, and the solution flowing out of the positive electrode side returns to the second electrolysis device again. Finally, two solutions with gradually increasing corresponding solute ion concentrations can be obtained until the concentration remains stable. Since the separation level of cations and anions is directly affected by the electrolysis voltage difference and the solution flow rate, the final enrichment concentration is related to the electrolysis voltage, the solution flow rate, and also related to the number of cycles of separation and recycling.

[0008] Theoretically, the salt solution can ultimately be almost separated into a single acid and base solution; while the acid or base solution can be separated into a concentrated acid or base solution and diluted water (solution); realizing the concentration of dilute acid or dilute base solutions. This method can be applied to the concentration of acid- and alkali-containing wastewater and the recycling of acids and alkalis, obtaining the required acidic or alkaline chemicals on-site. For example, sulfur dioxide in the sulfur-containing waste gas of a power plant can first be extracted by water washing to obtain a sulfurous acid solution, and then the sulfurous acid solution can be concentrated and recycled by the technology of the present invention; this method can extract metal ions, such as magnesium, from seawater during the seawater desalination and seawater pretreatment process, and concentrate to obtain a concentrated sodium hydroxide solution.

[0009] Since a polarization electromotive force is formed after the separation of cations and anions, resulting in reverse ion flow, the separation level of cations and anions in highly concentrated acid, alkali, and salt solutions is limited and can only be partially separated. However, by extracting and separating the metal ions that form carbonate precipitates in the alkaline solution or react with carbon dioxide, or the volatile ammonium ions from the solution, after multiple cycles, the metal ions that are prone to form carbonate or hydroxide precipitates and the volatile ammonium ions in the initial solution can be completely or almost completely extracted.

[0010] If there are metal ions in the wastewater or solution that can form precipitation with carbonate or bicarbonate ions, and ammonium ions that easily form volatile ammonia in an alkaline environment, the metal cations from the negative electrode solution can be aerated to form carbonate precipitation or ammonium ions with carbon dioxide in the air to volatilize, so as to achieve the net separation, extraction or removal of cations in the wastewater or solution; if the wastewater contains water-insoluble lignin and organic acid substances (including amino acids), the lignin and organic acids can be separated from the solution by filtration, or the negative ions in the solution can be separated, extracted or removed by flocculation precipitation, adsorption and other methods. In particular, this method can extract valuable metal ions from seawater and provide softened water for conventional seawater desalination; it can extract lignin products from paper mill wastewater, and the wastewater after lignin extraction can be reused in most pulping processes. Similarly, calcium chloride and calcium sulfate can be separated into acidic solutions and calcium carbonate precipitates, and iron sulfates and hydrochlorides can be separated into iron oxide or iron oxide precipitates and acidic solutions. Sodium chloride and sodium sulfate solutions can also be used to separate and produce alkali and acid solutions on site, which can be used in various processes requiring acid and alkali.

[0011] like Figure 1 As shown, in order to make the solution flow in a steady state when passing through the electrolytic cell, a buffer tank 1 is placed in front of the electrolytic cell, and the solution first enters the buffer tank 1, and the buffer tank 1 is connected to the electrolytic cell 2 through a filter screen or filter plate 3, and the electrolytic cell 2 is connected to two outlet slots 6-1, 6-2 through a filter screen or filter plate 3-1, so as to stabilize the flowing solution. The solution is separated by an insulating partition 4 between the electrodes, and the partition can separate or partially separate the two opposite electrode plates 5 in space. The path for separating anions and cations needs to bypass the end 7 of the partition 4, and some anions and cations can be directed to flow directly to the opposite electrode. In order to stabilize the flow of the solution, the part between the two electrodes but not separated by the partition 4 is separated by a porous partition or a filter plate or a filter screen 4-1, which can stabilize the flow of the solution and allow the directional diffusion and movement of anions and cations; the electrode 5 can be a point, a line, or a panel, and a filter screen or a filter plate 3-1 can be set at the outlet of the two separated solution streams to buffer and stabilize the flow of the solution. The inlet or two outlets of the solution can be controlled by three (electromagnetic) valves that are synchronized or asynchronous. The flow direction of the solution, that is, the installation direction of the electrolytic cell, can be parallel or perpendicular to or inclined at any angle to the direction of gravity. Figure 1 The arrow in the middle indicates the flow direction of the solution.

[0012] If lignin-like colloids or solids are precipitated near the anode electrode plate, or if oxides or hydroxides of metal ions or solids or colloids are precipitated near the cathode electrode plate, they can be periodically scraped out of the electrolytic cell with a scraper.

[0013] Because of the action of an electric field or voltage, as long as there are positively and negatively charged cations and anions in the solution, or as long as the solute can be separated into cations and anions, there will be an effect of separating cations and anions. That is, the solution described in the present invention is not limited to aqueous solutions, but also includes organic solutions containing cations and anions in ionic states.

[0014] One of the advantages of the present invention is that the electrodialysis technology can be realized without the participation of ion membranes and ion exchange resins, achieving the enrichment and separation of cations and anions, thereby reducing the cost of water treatment and significantly expanding the application scope of electrolytic water treatment.

[0015] A method for separating cations and anions in a solution of the present invention and its application are to flow the solution through an electrolytic cell channel. A part of the channel of the electrolytic cell is divided into two outlet channels. When the solution flows, it is preferably in a stable flow state so that the separated cations and anions can enter the two outlet channels respectively. One outlet collects the solution containing more cations in the original solution, and the other outlet collects the solution containing more anions in the original solution. Thus, the enrichment separation or partial separation of cations and anions in the solution is achieved, and the technical obstacle that the electrodialysis technology requires an ion membrane to separate cations and anions is solved by the flow of the solution. The solution described in the present invention is an aqueous solution containing cations and anions or an organic solution containing cations and anions, including but not limited to tap water, seawater, pulp and paper wastewater, electroplating, non-ferrous, rare metal smelting, titanium dioxide production wastewater or domestic sewage, and any wastewater or organic solution containing cations and anions generated in the industrial, building materials, agricultural, pharmaceutical, and food industries. In particular, aerate or charge carbon dioxide into the collected solution containing cations, so that the cations capable of forming carbonate precipitates are precipitated. The technology of the present invention can also decompose salt compounds into alkalis and acids as industrial products or products used on the production site, such as sodium chloride, sodium sulfate, calcium sulfate, sodium formate, sodium oxalate, etc. Brief Description of the Drawings

[0016] Figure 1 Shown is a schematic structural diagram of an electrolytic device for a method for separating cations and anions in a solution and its application according to the present invention. Among them, 1 is a buffer tank, 2 is an electrolytic cell with positive and negative electrodes 5 built therein, 3 and 3-1 are buffer filter plates or filter meshes, 4 is an insulating partition for dividing the electrolytic cell, 7 is the end of the partition, 4-1 is a porous partition or filter plate between the two electrodes 5, 7 and 4-1 can be connected to each other, 6-1 and 6-2 are two outlet channels, and the arrow indicates the solution flow direction. Detailed Description of the Invention

[0017] For the experimental methods without specific conditions noted in the following examples, they are usually carried out under conventional conditions. All kinds of commonly used chemical reagents or facilities used are commercially available products.

[0018] Example 1

[0019] This embodiment is to demonstrate that under the action of the positive and negative electrode voltages, anions and cations in the solution are enriched and separated to the corresponding two electrodes. The difference from a conventional electrolytic cell or ionization device (hereinafter referred to as an electrolytic cell) is that the electrolyte or solution flows through the electrolytic cell and is divided into two paths of solution by an insulating partition (glass or plastic material) at the outlet of the electrolytic cell and is separately collected, obtaining two solutions in which anions and cations are partially or fully separated. One contains more anions in the original solution; the other contains more cations in the original solution.

[0020] The distance between the electrodes is 20 mm, the electrode height is 25 mm, the width is 30 mm, the partition is at the center line of the two electrodes, the electrode extends into the electrode area by 0 mm, or 10 mm or 40 mm, and the DC voltage is adjusted between 1 V and 300 V. The distance between the buffer tank plates is 20 mm, the height is 25 mm, and the width is 40 mm. One of the outlet tanks has a width of 40 mm, and the other outlet tank has a width of 50 mm, so that the two paths of solution can be conveniently collected separately. The solution enters the buffer tank at an inflow rate of about 5 milliliters per second. The electrode material used is a 1-mm-thick pure aluminum plate, and graphite electrodes or inert electrode materials can be used in actual use. In this embodiment, both the partition or the electrolytic cell container plate are glass sheets, which are bonded and fixed by glass glue.

[0021] The following table is a report on the pH values of the two solutions obtained after various different solutions flow through the designed electrolytic device above. The electrolysis voltage is demonstrated to be 30 V. The concentrations or pH values in the table are the concentrations or pH values of the solutions. The difference or significant difference in the pH values of the two outlet solutions indicates that anions and cations in the solution have achieved enrichment and separation. After the power is turned on, it can be seen that hydrogen and oxygen bubbles are generated on the two electrodes. In actual application, hydrogen and oxygen can be collected as products, further reducing the economic cost of the technology of the present invention, or using the technology of the present invention in the process of electrolyzing water to produce hydrogen and oxygen, and at the same time for extracting beneficial resource substances in the solution.

[0022] Table 1:

[0023]

[0024]

[0025] Example 2

[0026] The mineral salt content in the tap water of some areas is high and the water quality is hard. Therefore, softening treatment is necessary. Using the device and method of Example 1 to treat tap water, precipitates can be visually observed in the water coming out from the cathode side after several hours. They should be hydroxides of metal ions such as calcium and magnesium or carbonate precipitates formed with carbon dioxide in the air. In order to accelerate the precipitation of metal ions, air aeration treatment can be used. The air for aeration can first pass through an aqueous solution to wash away the dust in the air. Obviously, this part of the tap water becomes softened tap water and can be stored for standby, while the tap water diverted from the anode side can be stored for use in daily life for cleaning and flushing toilets.

[0027] In actual use, the above device can be connected to the tap water inlet pipe, and the outlet is respectively connected to two storage tanks. When in use, water flows out from the two tanks respectively; the width of the channels used and the voltage used can be dynamically adjusted according to the requirements of the water source quality, the outlet water quality and the water volume.

[0028] Example 3

[0029] This example simulates seawater desalination or is only for extracting metal cations in seawater as resource products. Commercial sea salt is dissolved in tap water, and the weight content of sea salt is about 3%. The device and method of Example 1 are used for treatment. The pH value of the water coming out from the cathode side reaches 14, and precipitates can be visually observed after about 1 hour. They should be hydroxides of metal ions such as magnesium and calcium or carbonate precipitates formed with carbon dioxide in the air. In order to accelerate the precipitation of metal ions, air aeration treatment can be used to make carbon dioxide in the air form carbonate precipitates with metal ions such as calcium and magnesium in it. Extracting the precipitates can obtain metal ion resources in seawater, especially magnesium element resources. On the other hand, softened seawater mainly containing sodium ions is obtained. This softened seawater can be directly used in the pretreatment seawater softening process of current seawater desalination processes such as reverse osmosis.

[0030] Alternatively, this softened seawater can also be continuously treated by the method of Example 1 in a cycle, similar to treating a solution containing only sodium hydroxide, to concentrate and separate the sodium ions in it, as well as nearly fresh water containing a small amount of sodium ions.

[0031] Alternatively, the seawater mainly containing sodium ions is exchanged through a cation exchange membrane with a high-concentration ammonia water or ammonium carbonate solution, so that this part of the seawater changes from containing sodium ions to seawater containing ammonium ions. Since calcium and magnesium ions are required in drinking water, therefore, the seawater containing ammonium ions can be alkalized by adding an appropriate concentration of magnesium hydroxide and calcium hydroxide to promote the precipitation of ammonia gas, or negative pressure can be added to further promote the precipitation of ammonia gas. After the ammonia gas is precipitated, aeration is carried out to convert the calcium and magnesium ions into bicarbonates, and finally drinking water containing appropriate amounts of calcium and magnesium ions is obtained. Also, the seawater mainly containing chloride ions is subjected to anion exchange through an anion exchange membrane with a high-concentration ammonium carbonate or sodium carbonate solution, so that this part of the seawater mainly contains carbonic acid water, and carbonic acid is volatile, thus realizing the desalination of seawater. After the products sodium carbonate and ammonium chloride after the above-mentioned cation and anion exchange reactions react and are separated, ammonium carbonate and sodium chloride are obtained. The ammonium carbonate is recycled for use in the aforementioned ion exchange reaction.

[0032] Example 4

[0033] This example simulates the treatment of papermaking pulping wastewater. A small amount of alkali lignin or sodium lignosulfonate is dissolved in tap water to obtain solutions with pH values of 9 and 5 respectively. The treatment is carried out using the device and method of Example 1. The pH value of the water coming out from the cathode side reaches 14, which mainly contains a large amount of sodium ions or sodium hydroxide, or still contains some solutes in the original solution. After filtering and removing impurities from this alkaline solution, it can be recycled for use in the pulping process to dissolve and separate the lignin in the pulping raw materials.

[0034] The solution coming out from the anode side contains precipitated lignin or sulfonated lignin, and its pH value is about 3 - 4. After filtration, lignin or sulfonated lignin products, as well as an aqueous solution or an aqueous solution still containing some lignin substances are obtained. This aqueous solution can be recycled for use in the pulping process, such as in the cleaning process. One of the essences of pulping is to separate the lignin in the raw materials. The method of the present invention can not only separate the lignin, but also obtain lignin products. At present, most of the traditional pulping processes incinerate the lignin, increasing energy consumption and wasting valuable lignin resources.

[0035] Example 5

[0036] This embodiment simulates the resource utilization of the concentrated extraction of nutrients such as phosphate ions, ammonium ions, and potassium ions in municipal sewage, domestic sewage, domestic waste cleaning and treatment wastewater, rivers, and lakes. A small amount of sewage at the entrance of municipal sewage treatment is randomly taken and treated using the device and method of Embodiment 1. The pH value of the sewage solution coming out from the cathode side reaches 9 - 10, which mainly contains various metal ions or their hydroxides. After standing or aeration, the ions that can react with carbon dioxide to form carbonates precipitate to form sediments. The sediments are filtered and collected as utilizable products, or the harmful heavy metal ions in the wastewater are extracted and removed. If the wastewater contains ammonium ions, they are easily precipitated by volatilization and collected as products. When there are no harmful metal ions, heavy metal ions, and harmful anions in the wastewater, it can be safely discharged.

[0037] The sewage solution coming out from the anode side may contain various anions, such as chloride ions, nitrate ions, sulfate ions, phosphate ions, and organic acid root ions. Adding lime water for a neutralization reaction results in precipitates of calcium sulfate, calcium phosphate, and water-insoluble calcium organic acid salts.

[0038] The above process can extract some metal ions and nitrogen and phosphorus components from municipal domestic sewage, realizing the resource utilization in the sewage treatment process.

[0039] Embodiment 6

[0040] This embodiment demonstrates the treatment and resource utilization of electroplating wastewater. Electroplating, non-ferrous metals, including lithium elements, and rare earth refining wastewater have different components according to different electrolytes or different chemical reaction solutions, but all contain metal cations, such as zinc ions, iron ions, nickel ions, etc., and anions such as cyanide, sulfate, chloride, etc. Using the device and method of Embodiment 1, cations and anions will also be enriched and separated. The same aeration treatment can obtain carbonates or hydroxides precipitates of corresponding metal ions. After filtration and separation, beneficial resource materials are obtained. The wastewater on the anode side is acidic and contains concentrated various anions, which can be recycled for the cleaning, pretreatment process, or production process of electroplated parts or refining raw materials, or recycled for diluting the mother liquor to facilitate the extraction of cations and anions, especially metal cations, in the mother liquor.

[0041] In practical applications, the electrolytic cell in Embodiment 1 can be used as a part of the electroplating cell, and a partition is set at the tail of the electroplating cell to shunt and enrich and separate the solution enriched with cations and anions.

Claims

1. A method for separating cations and anions in a solution, characterized in that, The solution flows through an electrolytic cell channel, and a part of the channel of the electrolytic cell is divided into two outlet channels.

2. The method according to claim 1, wherein, One outlet collects the solution containing more cations in the original solution, and the other outlet collects the solution containing more anions in the original solution.

3. The method according to claims 1-2, wherein, The solution is an aqueous solution containing cations and anions or an organic solution containing cations and anions.

4. The method according to claim 3, wherein, The solution is tap water, seawater, pulp and paper wastewater, electroplating wastewater, non-ferrous metal smelting wastewater, rare metal smelting wastewater, titanium dioxide production wastewater or domestic sewage.

5. The method according to claim 3, wherein, The solution is any wastewater or organic solution containing cations and anions generated in the industrial, building materials production, agricultural, pharmaceutical and food industries.

6. The method according to any one of claims 1-5, wherein Aeration or carbon dioxide injection is carried out in the collected solution containing cations, so that the cations capable of forming carbonate precipitates are precipitated.

7. Application of a method for separating cations and anions in a solution, characterized in that, Using the method of claims 1-6, the cations and anions in the solution containing cations and anions are enriched and separated to realize the purification of tap water, the desalination of seawater and the separation of cations and anions in wastewater.

8. Use of the method according to claim 7, wherein, The salt compound is decomposed into an alkali and an acid as industrial products or on-site products for production.

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