Why can electrodialysis cations only pass through cations?

Wright. Ryder The semi-permeable membrane used in electrodialysis is actually an ion exchange membrane. This ion exchange membrane can be divided into two types: cation exchange membrane (cation film) and anion exchange membrane (negative film) according to the charge properties of the ions.

In the electrolyte aqueous solution, the cation film allows the cation to permeate and repel the blocking anion, and the anion allows the anion to permeate and repel the blocking cation, which is the selective permeability of the ion exchange membrane. In the electrodialysis process, the ion exchange membrane does not exchange with a certain ion in the aqueous solution like the ion exchange resin, but only selectively transmits ions with different electrical properties, that is, the ion exchange membrane does not need to be regenerated. The compartment of the electrode and membrane in the electrodialysis process is called the electrode chamber, and the electrochemical reactions that occur in it are the same as those of ordinary electrodes.

Oxidation occurs in the anode chamber, the anode water is acidic, and the anode itself is easy to corrode. The reduction reaction occurs in the cathode chamber, and the cathode water is alkaline, and the cathode is easy to scale.

Electrodialysis was first used in seawater desalination to produce drinking water and industrial water, seawater concentration to produce salt, and combination with other unit technologies to produce high-purity water, and later it was also widely used in wastewater treatment.

In wastewater treatment, there are two types of electrodialysis operations according to the characteristics of the process: one is an ordinary electrodialysis process composed of alternating positive membranes and negative membranes, which is mainly used to simply separate pollutant ions from wastewater, or separate pollutant ions and non-electrolyte pollutants in wastewater and then treat them by other methods; The other is a special electrodialysis nesting process composed of composite membrane and positive membrane, which uses the polarization reaction in the composite membrane and the electrode reaction in the polar chamber to produce H+ ions and OH- ions to produce acids and alkalis from wastewater.

Although the cation membrane repels cations, there is a cathodic attraction behind the cation membrane, and the cathode attraction to the cations must be greater than the repulsion of the cation membrane to the cations, so that electrodialysis can be achieved; The anion membrane has the opposite effect of the above; Electrodialysis is constituted due to the presence of the above.

Under the action of the direct current electric field, the dielectric ions in the water passing through the separator move directionally, and the exchange membrane is selective for the ions. Between a pair of electrodes of the electrodialyzer, the anion membrane, the positive membrane and the separator (A and B) are arranged alternately to form a dense chamber and a light chamber (that is, cations can pass through the positive film, and anions can pass through the negative membrane).The cations in the light chamber water migrate to the negative electrode and pass through the positive membrane and are intercepted by the negative membrane in the concentrated chamber. The anions in the water migrate to the positive direction of the anion and are intercepted by the positive film in the concentration chamber, so that the number of ions in the water through the light chamber gradually decreases and becomes fresh water, and in the water of the concentration chamber, due to the continuous influx of anions and cations in the concentration chamber, the concentration of dielectric ions continues to rise, and it becomes concentrated water, so as to achieve the purpose of desalination, purification, concentration or refining.

(1) The anion exchange membrane only allows anion free passage, the cation exchange membrane only allows cations to pass freely, the separator A is connected to the anode, and the anode is anion discharge, so the separator A is an anion exchange membrane, so the answer is: anion exchange;

The silver nitrate-containing waste liquid was treated, and the silver was precipitated by electrolysis of silver nitrate by electrolysis, and the chemical equation of the reaction was 4AGNO3

2 H2O electrolysis.

4ag+o2

4HNO3, so the answer is: 4AGno3

2 H2O electrolysis.

4ag+o2

4hno32）①mgcl2

It is easy to hydrolyze to form magnesium hydroxide precipitate during depyretic, and hydrolysis should be prevented at this time, so it should be in HCl atmosphere, so the answer is: in HCl atmosphere; Prevent mgCl2

Hydrolysis makes the product impure;

The melting point of MGO is much higher than that of MgCl2, so attention should be paid to saving energy, and magnesium chloride can be used instead, so the answer is: disagree; The melting point of MGO is much higher than that of MGCl2, and electrolytic melting of MGO consumes a lot of energy.

3) The amount of the substance decreases as reactants, and the amount increases as products, and the reactants are H2

s, HDO, and the product is HDS, H2

o, the chemical equation of the reaction is h2

s+hdo=hds+h2

o, the hydrogen atom in HDS can continue to react with HDO, hence H2

s is recyclable, so the answer is: h2

s+hdo=hds+h2

o；h2s．

Ion exchange resins are a class of polymer materials with ion exchange functions. In solution, it can exchange its own ions with the same number of ions in the solution. According to the different properties of exchange groups, ion exchange resins can be divided into two categories: cation exchange resins and anion exchange resins.

Most cation exchange resins contain acidic groups such as sulfonic acid groups (—SO3H), carboxyl groups (—COOH) or phenol groups (—C6H4OH), in which hydrogen ions can be exchanged with metal ions or other cations in solution. For example, the polymer of styrene and divinylbenzene is sulfonated to obtain a strong acid cation exchange resin, and its structural formula can be simply expressed as R—SO3H, where R represents the resin matrix, and its exchange principle is.

2r—so3h＋ca2＋ （r—so3）2ca＋2h+

This is also the principle of hard water softening.

Anion-exchange resins contain basic groups such as quaternary amine groups [-N(CH3)3OH], amine groups (—NH2), or imino groups (—NH2). They can generate OH- ions in water, which can be exchanged with various anions, and the exchange principle is as follows.

r—n（ch3）3oh＋cl- r—n（ch3）3cl＋oh-

Since ion exchange is reversible, used ion exchange resins are generally washed with an appropriate concentration of inorganic acids or bases, which can be restored to their original state and reused, a process called regeneration. The cation exchange resin can be washed with dilute hydrochloric acid, dilute sulfuric acid and other solutions; Anion-exchange resins can be treated with solutions such as sodium hydroxide for regeneration.

Ion exchange resins are used in a wide range of applications, mainly for separation and purification. For example, it is used for hard water softening and deionized water, metal in industrial wastewater, separation of rare metals and antibiotics, etc.

Ion exchange membrane is a thin film made of polymer materials with selective permeability to ions, and cationic membranes are usually sulfonic acid type, with fixed groups and dissociable ions such as sodium sulfonic acid type: the fixed group is a sulfonic acid group and the dissociated ion is sodium ion.

The cation exchange membrane can be regarded as a polymer electrolyte, its polymer parent is insoluble, and the sulfonic acid group attached to the parent body has a negative charge and dissociable ions are attracted to each other, and they are hydrophilic.

Because the positive film has a negative charge, although the original dissociated positive ions are dissociated into water by the action of water molecules, outside the membrane we are energized through the electric field, and the positively charged cations can pass through the positive film, while the anions cannot pass through because of same-sex repulsion, so they have selective permeability.

Simply knowing the principle is very helpful for electrodialysis or EDI equipment maintenance, and the principle of ion exchange resin is said upstairs, which is very well written, but it is off topic.

Hail accompaniment oak 1) cl2

H2 can be obtained because of the reaction that occurs at the cathode

It can collapse indiscriminately (2) to produce chlorine, hydrogen and high-concentration caustic soda, and to obtain fresh water and high-concentration brine at the same time.

1) Anode: 2cl-

2e-===cl2

Cathode: 2h+

2e-===h2

Because chlorine can react with caustic soda, it cannot be used to produce chlorine, and there is no problem with hydrogen production next to the source.

2) From the above principle, at least the electrolyte products chlorine, hydrogen and high concentration of caustic soda can be obtained, and at the same time fresh water and concentrated seawater can be used for further use.

Electrodialysis can effectively remove ionic components in water, and is mainly used for desalination of seawater and brackish water and industrial water softening. Microfiltration can separate components with a diameter in water, which is mainly used to remove bacteria, suspended solids, turbidity, etc. in the blowing water.

Reverse osmosis can separate solute molecules with a molecular weight of less than 500, so it has a high removal rate of organic matter and inorganic salts in water, which is an effective separation technology in the deep purification treatment of water and wastewater, and is widely used, including reverse osmosis devices to produce pure water. The reverse osmosis membrane uses a high pressure (1 10MPa) and a low water yield (the water ** rate is only 75% to 80%, so the operating cost is higher.

Electrodialysis uses the selective permeability of semipermeable membranes to separate different solute particles, such as ions, and is called dialysis. When dialysis is performed under the action of an electric field, the phenomenon of the migration of charged solute particles (such as ions) in the solution through the membrane is called electrodialysis.

The driving force of electrodialysis is the electric field force, which is generally used in combination with ion exchange membranes. Under the action of the applied electric field, the ions in the water move directionally in the solution, and with the help of the selective permeability of the ion exchange membrane, the concentration, desalination and purification of the solution are realized, and the pollution of the ion exchange membrane is the most critical.

Reverse osmosis, also known as reverse osmosis, is a membrane separation operation pressure that uses the pressure difference as the driving force to separate the solvent from the solution. The driving force of reverse osmosis is the pressure difference, so reverse osmosis membranes need to be resistant to high pressures.

Electrodialysis is a method that uses the selective permeability of semi-permeable membranes to separate different DU solute particles (such as ions). The phenomenon of dialysis in solution when dialysis is performed under the use of an electric field as a DAO, and the migration of charged solute particles (such as ions) in solution through the membrane is called electrodialysis.

Reverse osmosis membrane is the core element of reverse osmosis, which is an artificial semipermeable membrane made of simulated biological semi-permeable membrane with certain characteristics. It is generally made of polymer materials. Such as cellulose acetate film, aromatic polyhydrazide film, aromatic polyamide film.

Electrodialysis membranes are divided into two categories: non-selective membranes and selective membranes. Non-selective membrane is a kind of natural or artificial semi-permeable membrane such as collodion glue, blister membrane, etc., this kind of membrane can permeate ions but can not penetrate larger colloidal particles, under the action of external direct current electric field, as impurities of ions through the membrane and carried away by the water flow, and the solution (colloidal and other polymer solutions) is purified. This membrane is not selective, and both anions and cations can pass through, and the removal effect of ions in aqueous solutions is very poor.

At present, most of the widely used in industry are selective membranes, that is, ion exchange membranes. There are two types of ion exchange membranes: anion exchange membranes and cation exchange membranes.

Drammel reverse osmosis membranes.

DTRO stands for Disc Tube Reverse Osmosis Membrane Technology, which is a membrane product specially designed to treat difficult wastewater. Compared to spiral membrane, the flow channel is wider. The surface of the membrane element deflector plate is designed with bumps, which makes the material liquid appear turbulent during the flow process and enhances the anti-fouling ability of the membrane element.

Independent filter membrane element design, when the diaphragm is contaminated, part of the DTRO diaphragm and the deflector plate can be replaced according to the actual situation, reducing the cost of system consumables.

Electrodialysis is the process of separating electrolytes from water by using the permeability selectivity of ion exchange membranes under the action of a direct current electric field.

In the electrodialyzer, there are many alternating positive and negative membranes, which are divided into small water chambers. When raw water enters these chambers, the ions in the solution migrate directionally under the action of a direct current electric field. The cation film only allows cations to pass through and intercepts anions; The omentum only allows anions to pass through and the cations are retained.

As a result, part of these chambers becomes a freshwater chamber with very little ions, and the effluent is called freshwater. The chamber adjacent to the freshwater chamber becomes a concentrated water chamber where a large number of ions are gathered, and the effluent is called concentrated water. As a result, the ions are separated and concentrated, and the water is purified.

Electrodialysis membrane - an organic polymer with the same chemical structure as the ion exchange resin as the backbone. It is a resin film with a spatial network structure formed by a certain number of crosslinkers through the cross-key bridging action.

According to the different membrane structure (or according to the manufacturing process), ion exchange membranes are divided into three types: heterogeneous membranes, homogeneous membranes and semi-homogeneous membranes.

A device that uses the principle of electrodialysis to desalinate or treat wastewater is called an electrodialyzer. It consists of three parts: the membrane stack, the polar region and the pressing device.