JPH08966A - Purification by electrodialysis - Google Patents

Abstract

PURPOSE:To purify a water soln. contg. multi-valent metal ions, etc., such as a water liq. of acid cleaning of metals, to recover the water soln. and to reuse it by performing continuously and smoothly electrodialysis of the soln. without lowering its electric current efficiency. CONSTITUTION:In an electrodialysis apparatus consisting of an anode chamber, an intermediate chamber and a cathode chamber, the intermediate chamber and the anode chamber are separated with an anion exchange membrane and the intermediate chamber and the cathode chamber are separated with an cation exchange membraane and a water soln. contg. 1 or 2 acids selected from among sulfuric acid, hydrochloric acid, phosphoric acid, chloric acid, perchloric acid and chromic acid is stored in the anode chamber (a). Multi-valent metal ions and/or a multi-valent metallic acid ions-contg. water soln. is stored in the intermediate chamber (b). In addition, a water soln. contg. inorg. salts and a pH buffer agent is stored in the cathode chamber (c) as a cathode liq. and by energizing electricity, the multi-valent metals in the water soln. stored in the intermediate chamber are decreased and removed.

Description

Detailed Description of the Invention

[0001]

The present invention relates to polyvalent metal ions and / or
Alternatively, the present invention relates to a method for electrodialyzing and purifying an aqueous solution containing a polyvalent metal acid ion, in particular, by electrodialyzing the metal ion from an acid-washing waste acid containing a polyvalent metal ion generated when the metal is acid-washed. The present invention relates to an electrodialysis purification method in which an acid washing solution is recovered by removing and reducing with high current efficiency.

[0002]

2. Description of the Related Art When a metal such as steel, stainless steel, copper, zinc, aluminum, cadmium, tin, antimony or bismuth is acid-cleaned, an acid cleaning waste liquid containing metal ions is produced as a by-product. Conventionally, these acid cleaning waste liquids have been treated with a waste liquid after being treated by an alkali neutralization method in which they are mainly neutralized with an alkali. The alkali neutralization method is not economical because the basic unit of the acid for cleaning and the alkali for neutralization is poor, and when sulfuric acid or hydrofluoric acid is used as the acid, a large amount of sludge such as gypsum and calcium fluoride is by-produced. When nitric acid or phosphoric acid is used as an acid, a large amount of nitrogen or phosphorus is mixed into the wastewater, productivity is reduced due to line stoppage due to replacement of the acid solution, and a secondary process of neutralization work is performed. There was a problem that it was necessary to obtain it for processing. Therefore, an alternative method to the alkali neutralization method has been proposed. For example, there is an electrodialysis method proposed in Japanese Patent Publication No. 2-45489. This method uses an aqueous acid solution containing polyvalent metal ions as an anolyte, an inorganic carbonate, hydrogen carbonate or hydroxide or a mixture thereof as a catholyte, and an anolyte and a catholyte as cation exchange membranes. It is a method of isolation and electrodialysis.

[0003]

The electrodialysis method proposed above is advantageous in that it can be treated by circulating an aqueous solution to be treated such as an acid washing waste liquid, is simple in operation, and is excellent in industrial property. However, according to the inventors, when the acid concentration of the acid aqueous solution containing polyvalent metal ions is increased, the current efficiency of metal removal is lowered, and the liquid to be treated containing ferrous ions as polyvalent metals is reduced. In the case of, the ferrous ion is oxidized to ferric ion, and when the treatment liquid is recovered in the pickling step and pitting occurs on the steel surface, the liquid to be treated containing polyvalent metal ions is used as the anolyte. Therefore, it has been found that there are various problems such as shortening the life of the anode. The inventors of the present invention have solved the above problems and can continuously and stably purify an aqueous solution containing a polyvalent metal ion or the like such as an acid cleaning waste solution by electrodialysis, and further As a result of intensive studies for the purpose of developing a more useful electrodialysis purification technique, the present invention has been completed.

[0004]

According to the present invention, in an electrodialysis apparatus comprising an anode chamber, an intermediate chamber and a cathode chamber, the intermediate chamber and the anode chamber are anion exchange membranes, and the intermediate chamber and the cathode chamber. Is isolated by a cation exchange membrane, and (a) sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, chloric acid, perchloric acid,
An aqueous solution containing one or more chromic acids is contained as an anolyte, (b) an aqueous solution containing polyvalent metal ions and / or polyvalent metal acid ions is contained in the intermediate chamber, (c)
Provided is an electrodialysis purification method characterized in that an aqueous solution containing an inorganic salt and a pH buffer is contained in a cathode chamber as a catholyte and electricity is applied to reduce and remove polyvalent metals in the aqueous solution contained in an intermediate chamber. To be done. In the electrodialysis purification method of the present invention, the anode chamber, the intermediate chamber and the cathode chamber, after the aqueous solution contained in each chamber is extracted and made into each contained liquid, the circulation system is returned to each chamber again. In addition, water is replenished in the circulation system of the anode chamber, electrodialysis liquid is replenished in the circulation system of the intermediate chamber, and the polyvalent metal component is separated and removed in the circulation system of the cathode chamber to give a predetermined inorganic salt. And pH buffer is preferably supplemented.

[0005]

The present invention is configured as described above, and separates the cathode chamber and the intermediate chamber, in which the aqueous solution containing the predetermined inorganic salt and the pH buffer is contained, by the cation exchange membrane, and at the same time, contains the inorganic acid aqueous solution. The anode chamber and the intermediate chamber are separated by an anion exchange membrane, and the aqueous solution containing the polyvalent metal ion and / or the polyvalent metal acid ion is stored in the intermediate chamber to energize, so that the acid cleaning stored in the intermediate chamber is performed. The polyvalent metal component such as polyvalent metal ion contained in the aqueous solution such as waste liquid is adjusted to have a pH value so as to diffuse and move into the cathode chamber to generate hydroxide, and precipitates as hydroxide near the cathode. To do. Further, the hydroxide of the polyvalent metal precipitated in the cathode chamber can be extracted by the circulation system of the cathode chamber, separated and removed. Furthermore, since the composition of the aqueous solution contained in each chamber changes due to energization, a part of the aqueous solution is extracted and processed in a circulation system, adjusted to a predetermined contained liquid, returned to each chamber, and continuously electrodialyzed. be able to. Further, the circulation system of the intermediate chamber can be replenished with an electrodialysis liquid such as an acid cleaning liquid, and the polyvalent metal contained can be continuously removed to regenerate, recover and reuse the liquid. In the intermediate chamber of the present invention, the ratio of polyvalent metal ions to all ions is increased, so that the current efficiency of metal removal is increased. Further, without holding the electrode, an aqueous solution containing a polyvalent metal acid ion is stored in an intermediate chamber adjacent to the cathode chamber and the anode chamber, which is separated by a cation and anion exchange membrane, and electrodialysis is performed to collect the aqueous solution. Therefore, even if the ferrous ion is contained, the ferrous ion in the conventional anode chamber is oxidized to ferric ion and the pitting generation trouble in the pickling process does not occur, and the presence of metal ion exists. As a result, the anode life is not shortened, and electrolytic dialysis can be continuously and smoothly promoted.

Hereinafter, the present invention will be described in detail. The electrodialysis of the present invention corresponds to a so-called three-chamber method including an anode chamber, an intermediate chamber and a cathode chamber. The intermediate chamber is adjacent to the anode chamber and the cathode chamber, is separated from the anode chamber by an anion exchange membrane, and is separated from the cathode chamber by a cation exchange membrane. It is not preferable to separate the anode chamber, the cathode chamber, and the intermediate chamber from each other by a cation exchange membrane or both the cation exchange membrane and the anion exchange membrane because the current efficiency is low. The anode chamber of the present invention contains an aqueous solution containing one or more inorganic acids consisting of sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, chloric acid, perchloric acid and chromic acid as an anolyte, and the cathode chamber contains an inorganic salt. And an aqueous solution containing a pH buffer is contained as a catholyte. In the intermediate chamber, polyvalent metal ions and / or polyvalent metal acid ions (hereinafter simply referred to as polyvalent metal ions, etc.)
The polyvalent metal contained can be diffused and moved to the cathode chamber and removed by containing and energizing the aqueous solution for electrodialysis purification treatment containing the. As the aqueous solution containing polyvalent metal ions to be stored in the intermediate chamber and subjected to electrodialysis purification treatment, (1) an aqueous solution of an electroplating acid contaminated with dissolved polyvalent cations, (2) polyvalent An aqueous solution of a salt containing an anion of an acid containing a metal and a cation, (3) An aqueous solution of a salt containing an anion of an acid containing a sulfuric acid, phosphorus, halogen or carbon and a polyvalent metal cation, or (4) Can be mentioned. In particular, in the present invention,
The acid cleaning waste liquid of a metal such as a steel plate can be preferably applied.

The catholyte of the present invention contains, as inorganic salts, hydroxides, sulfates and chlorides of alkali metals and alkaline earth metals,
An aqueous solution containing one or more of nitrate, chlorate and perchlorate can be used. From these inorganic salts, the polyvalent metal species to be removed and purified, the anionic species of the anolyte and intermediate chamber liquids, the operating cost of industrial implementation, and the like can be appropriately selected and used. Preferably, the anion species of the inorganic salt and the anion species of the anolyte solution and / or the intermediate chamber solution are the same. The inorganic salt in the catholyte of the present invention can increase the electrical conductivity and reduce the voltage during electrolysis. The concentration of the inorganic salt contained in the catholyte is not particularly limited, and the higher the concentration, the higher the electric conductivity, which is desirable. However, in a saturated solution, there is a risk of salt precipitation and the like, and the concentration is usually less than the saturated solubility.

In the catholyte of the present invention, in addition to the above inorganic salt, p
An H buffer is included. Examples of the pH buffering agent include (1) alkali metal, alkaline earth metal, or ammonia sulfite or hydrogen sulfite, (2) ammonia hydroxide, sulfate, chloride, nitrate, chlorate, or perchlorine. Acid salts, (3) phosphoric acid, boric acid, acetic acid, citric acid, phthalic acid, tartaric acid, lactic acid, benzyl bilturic acid or dimethylglycine acids, (4) 2,4,6-trimethylpyridine, tris (hydroxy) Methyl) aminomethane, 2
-Aminomethyl 1,3-propanediol, ethylmorpholine, phenylhydrazine, aniline, pyridine, quinoline, hexamine or one or more selected from urea-containing nitrogen compounds can be appropriately selected and used. The pH buffer of the present invention maintains the pH value of the catholyte, especially the catholyte in the vicinity of the cathode, in a range suitable for the production of hydroxides of polyvalent metals that move from the intermediate chamber liquid to the cathode chamber, and perform electrodialysis. Can be continuously stabilized. That is, in the catholyte near the cation exchange membrane that separates the cathode chamber and the intermediate chamber, the pH tends to decrease because hydrogen ions (H ⁺ ) from the anode chamber and / or the intermediate chamber generally diffuse. . On the other hand, since hydrogen gas is generated at the cathode and hydroxide ions (OH ⁻ ) are generated along with it, the pH of the catholyte around the cathode tends to rise. For this reason, when the pH buffer is not contained, hydroxides such as polyvalent metal ions are deposited in the vicinity of the cation exchange membrane in the cathode chamber, making electrodialysis impossible. In the present invention, by containing the pH buffer agent in the catholyte, the pH of the cation exchange membrane on the cathode chamber side is maintained at an acidity such that polyvalent metal ions do not precipitate as hydroxides,
At the same time, the pH of the catholyte near the cathode can be maintained above the value at which polyvalent metal ions or the like are deposited as hydroxides. The pH value of the catholyte of the present invention varies depending on the polyvalent metal ion species, polyvalent metal ion concentration, electrolysis conditions, etc., but cannot be generally stated, but it is usually 4 to 12, preferably 6 to 10. It is preferable to adjust The type and addition amount of the pH buffer agent of the present invention are appropriately selected depending on the polyvalent metal ion species, the polyvalent metal ion concentration, the electrolysis conditions, the operating cost, and the like. Usually, when the acid concentration of the intermediate chamber liquid is high, the vicinity of the cation exchange membrane is inclined to the acidic side, so even if the pH of the catholyte is slightly high, polyvalent metal ions, etc. will precipitate as hydroxide on the cation exchange membrane. There is little to do. When the polyvalent metal ion is an amphoteric ion such as aluminum or zinc, the p of the catholyte is
It is preferable to strictly adjust and control H and set it to a low level.
If you want to lower the pH of the catholyte, add an acid type pH buffer, while if you want to raise the pH of the catholyte, add a pH buffer selected from inorganic hydroxides or organic amine compounds. Is good.

As the cation exchange membrane used in the present invention, commercially available hydrocarbon or perfluorocarbon cation exchange membranes can be used. However, since it is used under acidic conditions, a film having only a carboxylic acid as a functional group cannot be used. As the anion exchange membrane used in the present invention, commercially available hydrocarbon-based or perfluorocarbon-based anion exchange membranes can be used. The electrodialysis apparatus of the present invention is not particularly limited in the type of electrodialysis tank used. Any of so-called filter press type, box type and tank type can be used. Further, as a method of connecting the electrodes, either a monopolar type or a bipolar type can be adopted. Further, the material constituting the anode of the present invention is preferably highly durable and does not deteriorate under electrolysis conditions, and graphite, titanium or tantalum metal coated with platinum iridium alloy can be used.
The cathode material is preferably highly durable and does not deteriorate under electrolysis conditions like the anode, and stainless steel, nickel, steel plated with nickel, graphite, titanium metal coated with platinum, and the like can be used. In the electrodialysis purification of the present invention, the electrodialysis conditions are not particularly limited, and generally, the current density is 1 to 100 A / d.
Conditions with good electrolysis efficiency can be appropriately selected within the range of m ² and the temperature of the electrolytic solution of 10 to 100 ° C.

In the present invention, a part of each chamber liquid contained in each chamber of the anode chamber, the intermediate chamber and the cathode chamber is extracted, treated as necessary, and each chamber liquid is made up. It has a circulation system that returns to the chamber. In this case, extraction and supply circulation of the aqueous solution in each chamber can usually be performed using a pump. By forming this circulation system, electrodialysis purification is continuously performed, and the circulation system in the intermediate chamber is constantly replenished with an aqueous solution containing polyvalent metal ions, etc. Removed and purified,
It can be collected and reused. In the above continuous electrodialysis operation, the polyvalent metal hydroxide that has precipitated is removed in the catholyte circulation system and the electrode solution is replenished. A liquid containing a metal component, a contained ionic component, or the like is replenished, and an amount corresponding to the acid component generated in the anode chamber is partially outflowed from the anolyte circulation system to replenish predetermined water. In the anode chamber and the intermediate chamber, polyvalent metal ions are converted to hydrogen ions to generate an acid, so the anolyte and intermediate chamber liquids flowing out from the circulation system may have part of their water content evaporated by an evaporator or the like. After the evaporation treatment, it can be recovered and reused in the metal acid cleaning treatment step. Removal of polyvalent metal hydroxide from the catholyte circulation system can be performed using a filtration device, etc., and the same amount of hydroxide as that produced in the catholyte per unit time is removed from the system. It is preferably discharged. The filtration method is not particularly limited,
Belt filters, filter presses, precoat filters, etc. can be used. When the electrolytic dialysis operation is carried out in a batch system, the discharge of the polyvalent metal hydroxide can be carried out intermittently.

In the present invention, the amount of catholyte tends to increase with the progress of electrodialysis. This is because there is permeated water that accompanies the diffusion movement of cations from the intermediate chamber, and the catholyte in the cathodic chamber is gradually diluted by the permeated water. Therefore, as described above, an electrode solution comprising an inorganic salt and a pH buffer is appropriately replenished and added to the circulation system to adjust and maintain the composition of the catholyte within a predetermined range. Further, the anolyte tends to decrease with the progress of electrodialysis, and the acid concentration tends to increase. This is because acid generation and water decomposition occur at the anode. Therefore, the acid concentration of the anolyte is adjusted and maintained within a predetermined range by controlling the addition of water and the withdrawal of the anolyte from the system by the circulation system. The adjusted acid concentration of the anolyte can be appropriately selected as an optimum value depending on the life of the electrode, the electrolytic voltage, the cost of water removal by the evaporator, the water balance of the metal acid cleaning process, and the like. The conversion rate of polyvalent metal ions contained in the intermediate chamber liquid to hydrogen ions is the comprehensive evaluation of electrolytic performance such as electric power consumption, adhesion of polyvalent metal hydroxide to cation exchange membranes, acid recovery equipment, etc. Therefore, the optimum value can be appropriately selected. In the present invention, the waste liquid for washing with acid such as metal, which is preferably supplied as an intermediate chamber liquid and treated, can be pretreated prior to electrodialysis purification treatment. In general, the acid cleaning waste liquid contains hydrogen ions in addition to polyvalent metal ions. Therefore, the acid cleaning waste liquid is subjected to diffusion dialysis treatment in advance to remove only the acid content, so that the polyvalent metal ion / hydrogen ion ratio is increased. It is possible to improve the polyvalent metal recovery efficiency in electrodialysis purification by increasing the value.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the drawings. However, the present invention is not limited to the following examples. FIG. 1 is an explanatory diagram of an electrodialysis flow according to an embodiment of the present invention. The electrodialysis cell of FIG. 1 is composed of three chambers, an anode chamber 2, an intermediate chamber 11 and a cathode chamber 13, and the anode chamber 2 and the intermediate chamber 11 are formed by an anion exchange membrane.
Further, the cathode chamber 13 and the intermediate chamber 11 are separated from each other by a cation exchange membrane. A circulation system including an anolyte circulation line 4, an intermediate chamber liquid circulation line 10 and a catholyte circulation line 16 is formed in each chamber. In FIG. 1, in the anode chamber 2, hydrogen ions, oxygen gas or chlorine gas is generated in the anode 1. If a large amount of chloride ions are present in the anolyte, chlorine gas may be generated. Oxygen gas or chlorine gas generated at the anode 1 is discharged out of the system through a line 3 in the middle of the anolyte circulation line 4. On the other hand, a part of the anolyte is withdrawn as a recovered acid from the line 6 in the middle of the anolyte circulation line 4 and sent to an evaporator or a metal acid washing step. Anions move from the intermediate chamber 11 to the anode chamber through the anion exchange membrane 9. Water is supplied from the line 5 to the anolyte circulation line 4. In addition, the intermediate chamber 11
Then, the polyvalent metal ions hydrogen ions move to the cathode chamber 13 through the cation exchange membrane 12. As the intermediate chamber liquid, the metal acid cleaning waste liquid to be treated is supplied from a line 7 in the middle of the intermediate chamber liquid circulation line 10, and a part of the liquid is withdrawn from the system through a line 8 in the middle. The intermediate chamber liquid extracted from the line 8 is sent to an evaporator or a metal acid cleaning step. In the cathode chamber 13, hydrogen ions combine with electrons at the cathode 14 to generate hydrogen gas and hydroxide ions. The produced hydrogen gas is discharged from the system through the line 15 of the catholyte circulation line 16. In the cathode chamber 13, polyvalent metal ions react with hydroxide ions to produce polyvalent metal hydroxide. On the cathode side of the cation exchange membrane 12, a pH buffer is used to prevent polyvalent metal ions from generating hydroxide, and the pH value is maintained at 7-9. The polyvalent metal hydroxide produced in the cathode chamber 13 is separated by a filter 17 arranged in the middle of the catholyte circulation line 16 and discharged to the outside of the system through a line 18, and the filtrate is fed to the catholyte circulation line 16. Will be returned. Also, line 1
The inorganic catholyte and the pH buffer corresponding to the amount discharged from the catholyte circulation system to the outside of the system are replenished from 9 to maintain a predetermined catholyte composition.

Examples 1 to 3 A three-chamber electrodialysis cell similar to that shown in FIG.
Acrylic resin was used for the cell frames of the anode chamber, the intermediate chamber and the cathode chamber, and platinum-plated titanium extract band metal was used as both the anode and the cathode having an electrode size of 10 cm × 10 cm, and the cation exchange membrane was manufactured by DuPont. Nafion NE-450 manufactured by Asahi Glass Co., Ltd. was used as an anion exchange membrane. Using the three-chamber electrodialysis cell formed as described above, various acid cleaning waste solutions having the stock solution compositions shown in Table 1 were electrodialyzed for 3 days under the conditions of current density of 30 A / dm @ 2 and electrolysis temperature of 50. +-. 5.degree. The results are shown in Table 1.

[0014]

[Table 1]

Comparative Examples 1 to 3 A three-chamber electrodialysis cell formed in the same manner as in Example 1 except that the anode chamber, the intermediate chamber and the cathode chamber were all isolated by using Nafion NE-450 (trade name) manufactured by DuPont. 2N sulfuric acid was used as the anolyte, and the current density was 30 A / d.
Under conditions of m ² and electrolysis temperature of 50 ± 5 ° C., various acid / acid cleaning waste solutions having the stock solution compositions shown in Table 2 were electrodialyzed for 3 days. The results are shown in Table 2.

[0016]

[Table 2]

As is clear from the above Examples and Comparative Examples, the electrodialysis purification method of the present invention is an aqueous solution containing a polyvalent metal ion and / or a polyvalent metal acid ion such as a metal acid washing waste liquid with high current efficiency. It can be seen from the above that the polyvalent metal ion can be removed for purification.

[0018]

The electrodialysis purification method of the present invention comprises an electrodialysis cell consisting of an anode chamber, an intermediate chamber and a cathode chamber,
Using anion exchange membrane and cation exchange membrane as the diaphragm,
In addition, by using a mixed aqueous solution of an inorganic salt and a pH buffer as a catholyte, and containing an aqueous solution containing a polyvalent metal ion and / or a polyvalent metal acid ion of the aqueous solution to be purified in the intermediate chamber and performing electrodialysis. , Electric dialysis can be performed with a lower power consumption rate than the conventional method.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of an electrodialysis flow according to an embodiment of the present invention.

[Explanation of symbols]

 1 Anode 2 Anode Chamber 3, 5, 6, 7, 8, 15, 18, 19 Line 4 Anolyte Circulation Line 9 Anion Exchange Membrane 10 Intermediate Chamber Liquid Circulation Line 11 Intermediate Chamber 12 Cation Exchange Membrane 13 Cathode Chamber 14 Cathode 16 Catholyte circulation line 17 Filter

Claims (6)

[Claims] 1. An electrodialyzer comprising an anode chamber, an intermediate chamber and a cathode chamber, wherein the intermediate chamber and the anode chamber are separated by an anion exchange membrane, and the intermediate chamber and the cathode chamber are separated by a cation exchange membrane. , (A) In the anode chamber, sulfuric acid, hydrochloric acid, phosphoric acid, chloric acid,
An aqueous solution containing one or more selected from perchloric acid and chromic acid was contained as an anolyte, and (b) an aqueous solution containing polyvalent metal ions and / or polyvalent metal acid ions was contained in the intermediate chamber. And (c) Inorganic salt and pH in the cathode chamber
An electrodialysis purification method characterized in that a polyvalent metal contained in an aqueous solution contained in an intermediate chamber is reduced and removed by accommodating an aqueous solution containing a buffer as a catholyte and energizing it. 2. The electrodialysis according to claim 1, wherein each of the anode chamber, the intermediate chamber and the cathode chamber has a circulation system for returning the respective aqueous solutions stored in the respective chambers to the respective chambers. Purification method. 3. A circulating system in the anode chamber is replenished with water, a circulating system in the intermediate chamber is replenished with electrodialysate, and a circulating system in the cathode chamber separates a polyvalent metal component to a predetermined amount. 3. The electrodialysis purification method according to claim 2, wherein the inorganic salt and the pH buffer are supplemented and treated. 4. The pH value of the catholyte is adjusted by selecting the pH buffering agent so that the polyvalent metal component contained in the aqueous solution contained in the intermediate chamber precipitates as a hydroxide near the cathode. The electrodialysis purification method according to any one of claims 1 to 3, wherein 5. The pH buffer is (1) an alkali metal, an alkaline earth metal, or a sulfite or bisulfite of ammonia, (2) a hydroxide of ammonia,
Sulfate, chloride, nitrate, chlorate or perchlorate,
(3) Phosphoric acid, boric acid, acetic acid, citric acid, phthalic acid, tartaric acid, lactic acid, diethylbabirturic acid or dimethylglycine acids, and (4) 2,4,6-trimethylpyridine, tris (hydroxymethyl) Aminomethane, 2-
The electrodialysis purification according to any one of claims 1 to 4, which is one or more selected from nitrogen-containing compounds such as aminomethyl 1,3-propanediol, ethylmorpholine, phenylhydrazine, aniline, pyridine, quinoline, hexamine or urea. Law. 6. The polyvalent metal is one or more of iron, nickel, chromium, copper, zinc, aluminum, cadmium, tin, antimony and bismuth.
The electrodialysis purification method according to any one.