JPH0947638A - Acid recovery method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the water movement amount from the recovery side to the stock solution side and achieve the high acid recovery rate by keeping a stock solution feed chamber in the state of pressure higher than that of an acid recovery chamber by the specified value or more and using an anion exchange membrance of high acid impregnation speed. SOLUTION: A hollow fiber membrane 1 is fixed by a housing 7 with a potting material 6. Stock solution is fed from a stock solution feed opening 2 to the inside of the hollow fiber membrane 1, and recovered acid water solution is permeated through the hollow fiber membrane 1 and collected outside the membrane and discharged from a recovered solution outlet 5 to the outside of a module. Water is fed from a diluting water feed opening 1 to the outside of the hollow fibers to retain the recovered acid concentration constant. The stock solution from which acid is recovered is discharged out of a stock solution outlet 3. As for the operation condition, acid can be recovered efficiently by keeping a stock solution feed side chamber in the state of pressure higher than that of an acid recovery side chamber by 0.1kg/cm<2> or over. The above process is particularly effective in the case of diffusion dialysis using a separating membrane of high acid permeation speed.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an acid recovery method by diffusion dialysis.

[0002]

2. Description of the Related Art A method of recovering an acid by diffusion dialysis, that is, an operation of separating and recovering a desired acid through a diaphragm using a difference in acid concentration as a driving force for mass transfer has been widely used in recent years. The method of using an anion exchange membrane as the diaphragm is particularly preferred. That is, hydrogen ions are relatively easily permeated through the anion exchange membrane, but metal cations are not easily permeated. Therefore, by utilizing this phenomenon, an acid is selectively separated from the coexisting impurity metal salt and recovered. is there.

The acid recovery method by diffusion dialysis described above is widely used for recovering sulfuric acid from aluminum anodic oxidation bath waste liquid, recovering hydrofluoric nitric acid from stainless steel pickling waste liquid, recovering acid from various plating waste liquids, and the like. There is.

As described above, the diffusion dialysis method uses the difference in concentration as the driving force for mass transfer. Naturally, the acid and metal salt concentrations on the side of the stock solution, which is the object of recovery, are the recovery side, that is, the recovery. This is higher than the acid and metal salt concentrations on the side. Therefore, an osmotic pressure based on the concentration difference between the stock solution side and the recovery side tends to be generated, and a phenomenon occurs in which water as a solvent moves from the collection side to the stock solution side.

The moving speed of water that permeates the membrane and moves from the recovery side to the undiluted side depends on the water permeability coefficient of the membrane. In the case of an anion exchange membrane, the higher the anion exchange membrane is, the higher the water content is. It tends to have a transmission coefficient. When the amount of water transferred from the acid recovery side to the stock solution side increases, the amount of dialysis waste solution from the stock solution side also increases, and the concentration on the stock solution side decreases and the concentration difference, which is the driving force for mass transfer, decreases. The amount of acid permeation decreases. Therefore, the acid recovery rate from the stock solution is reduced.

[0006] Industrially, it is desired to improve the acid permeation rate, and if an anion exchange membrane having a high acid permeation rate is used as a diaphragm to meet the demand, the amount of water transferred to the side of the undiluted solution increases and the acid recovery rate decreases. As a result, the dialysis waste liquid increases. The current situation is that it is difficult to achieve this balance.

[0007]

DISCLOSURE OF THE INVENTION The present invention is an acid recovery method by a diffusion dialysis method, which uses an anion exchange membrane having a high acid permeation rate and reduces the amount of water transfer from the recovery side to the stock solution side. A method of achieving acid recovery is provided.

[0008]

The present invention provides a method for supplying a stock solution containing an acid to one side of a diaphragm and recovering the acid from the other side of the diaphragm by diffusion dialysis through the diaphragm. Side chamber is 0.1 kg / cm more than acid recovery side chamber
Provided is a method for recovering an acid that maintains a high pressure state of ² or more.

In the present invention, the acid in the stock solution supply side chamber is made higher than the pressure in the acid recovery side chamber to recover the acid efficiently. For example, a high acid recovery rate can be achieved when the acid is recovered from the acid waste liquid and reused. Although the mechanism of this action is not always clear, it is considered that the following factors contribute in a complex manner.

(1) The amount of water transferred from the acid recovery side to the stock solution supply side due to the difference in osmotic pressure is reduced to maintain a high concentration in the stock solution supply side chamber. As a result, the concentration difference between the stock solution supply side and the acid recovery side is maintained at a high value, so that the acid permeation amount based on the concentration difference does not decrease and the acid recovery rate can be maintained high.

(2) Acid transfer occurs from the stock solution supply side to the acid recovery side due to the pressure difference, and the acid recovery rate is improved.

(3) Water transfer from the acid recovery side to the stock solution supply side is reduced, and the post-dialysis waste solution from the stock solution supply side chamber is reduced.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The pressure difference between the stock solution supply side chamber and the acid recovery side chamber must be 0.1 kg / cm ² or more. It is more preferable that the pressure difference is 1 kg / cm ² or more. When the pressure difference exceeds 50 kg / cm ² , it is not preferable from the viewpoint of pressure resistance of the diaphragm and the device. As long as the diaphragm and the device have excellent pressure resistance, it is possible to apply a pressure difference above this value. How much the differential pressure between the stock solution supply side and the acid recovery side diaphragm is set in actual operation is appropriately determined depending on the water permeability coefficient, pressure resistance, use conditions, required performance, etc. of the used diaphragm. By making the differential pressure larger than the osmotic pressure, the direction of water movement can be changed from the stock solution side to the recovery side, and the acid concentration on the recovery side can be controlled by the amount of water movement.

In order to recover an acid by diffusion dialysis using a diaphragm, a stock solution containing an acid component is supplied to one of the diaphragms, the acid is selectively diffused in the diaphragm, and the acid is recovered from the opposite side of the diaphragm. . A fixed amount of water is preferably supplied to the acid recovery side to recover the acid as an aqueous solution having a certain concentration.

As means for providing a pressure difference between the stock solution supply side and the acid recovery side, a method in which the stock solution supply side is made airtight and a pressure is applied by air pressure or a dynamic pressure of the solution supply, and an acid recovery side is made airtight And a method of using these in combination, and the like.

The acid which can be recovered by the present invention is not particularly limited, and inorganic acids such as sulfuric acid, nitric acid, phosphoric acid, hydrochloric acid, hydrofluoric acid and chromic acid, and organic acids such as acetic acid and oxalic acid can be recovered. It can be suitably used for the recovery treatment of an acid from an acid waste liquid consisting of a solution containing these acids and various metal salts.

As the diaphragm, a mere porous membrane having no fixed ions in the membrane can be used. When an anion exchange membrane is used, a highly pure acid is selectively recovered from a solution containing a metal salt. It is preferable because it is possible.

The present invention is particularly effective in the case of diffusion dialysis using a diaphragm having a high acid permeation rate. In the case of a diaphragm having a high acid permeation rate, it is easily affected by the above-mentioned osmotic pressure. That is, a membrane having a higher acid permeation rate tends to have a higher water permeation coefficient, so that the amount of water transfer based on the osmotic pressure is large, the acid recovery rate in the diffusion dialysis operation is reduced, and the original acid permeation performance of the membrane is effectively exhibited. It is hard to be done. Therefore, the effect of osmotic pressure is reduced and a high acid recovery rate is expressed by pressurizing the stock solution supply side.

Here, the acid permeation rate is the amount of acid permeating the membrane per unit area of the membrane, per unit time, per unit difference in acid concentration through the membrane. The acid permeation rate is a physical property that depends on the type of acid. As the acid permeation rate of the diaphragm in the present invention, the sulfuric acid permeation rate is 3 mol · m ⁻² · h ⁻¹ ·
(Mol / liter) ^-1 or more is preferable. Particularly preferably, it is 10 mol · m ⁻² · h ⁻¹ · (mol / liter) ⁻¹ or more. It is preferable that the acid permeation rate is high, but in the present membrane, the upper limit is 30 mol · m ⁻² · h ⁻¹ ·
(Mol / liter) ^-1 .

The water permeability coefficient is per unit area of permeable membrane,
It is the amount of water that permeates the diaphragm per unit time and per unit pressure differential across the diaphragm. A styrene-divinylbenzene copolymer type anion exchange membrane has a sulfuric acid permeation rate of 3 to
6 mol · m ⁻² · h ⁻¹ · (mol / liter) ⁻¹ , water permeability coefficient is 0.1 to 1.0 mol · m ⁻² · h ⁻¹ · atm ⁻¹
It is a degree. The high acid permeation type anion exchange membrane has a sulfuric acid permeation rate of 10 to 20 mol · m ⁻² · h ⁻¹ · (mol / liter) ⁻¹ and a water permeation coefficient of 1.0 to 10 mol · m ⁻² · h ^−1.
・ Atm ^-1 .

In the present invention, the movement of water through the diaphragm from the acid recovery side to the stock solution supply side is suppressed by pressurizing. Specifically, the water movement amount is 10 mol.
It is preferable to operate at m ⁻² · h ⁻¹ or less. More preferably, it is 5 mol · m ⁻² · h ⁻¹ or less. The amount of water transferred in diffusion dialysis is the amount of water that permeates the permeation membrane per unit area per unit time. If the pressurization from the stock solution supply side is made sufficiently large, water will move from the stock solution supply side to the acid recovery main side, that is, the above water transfer amount will be a negative value, but this is preferable for some purposes. Is.

As the anion exchange membrane, an anion exchange membrane obtained by aminating styrene (or vinylpyridine) -divinylbenzene copolymer with amination or quaternary pyridinium can be used. In this case, the ion exchange capacity is 0.5 to 5.0.
Meq / g dry resin is preferred. Ion exchange capacity is 5.
When it exceeds 0 meq / g dry resin, the water content of the membrane becomes high, the water permeability coefficient becomes high, and further the metal cation exclusion property decreases, which is not preferable. If the ion exchange capacity is less than 0.5 meq / g dry resin, the water content of the membrane will be low and the acid permeation rate will be low, such being undesirable. It is particularly preferable when the ion exchange capacity is 1.0 to 4.0 meq / g dry resin.

The styrene-divinylbenzene copolymer-based anion exchange membrane has an acid permeation rate of not more than a medium as an anion exchange membrane, and a sulfuric acid permeation rate of 6 mo.
It is difficult to obtain a product having a viscosity of l · m ⁻² · h ⁻¹ · (mol / liter) ⁻¹ or more. When using an aromatic polysulfone-based anion exchange membrane as the anion exchange membrane, 10 mol · m ⁻² · h
It is preferable that a sulfuric acid permeation rate as high as ^-1 · (mol / liter) ⁻¹ or more can be obtained.

As the aromatic polysulfone-based anion exchange membrane, specifically, an anion exchange membrane in which a chloromethylated aromatic polysulfone-based polymer having a repeating unit represented by the general formula (1) is aminated with a monoamine is used. Or, an anion exchange membrane further crosslinked with a polyamine is preferable.

[0025]

Embedded image

The base material structure of the aromatic polysulfone-based anion exchange membrane has at least one repeating unit selected from the group consisting of polysulfone, polyethersulfone, polyarylethersulfone, polyphenylsulfone and polythioethersulfone. A copolymer is mentioned. Among them, the aromatic polysulfone-based block copolymer represented by the general formula (2) is particularly preferable.

[0027]

Embedded image

As the monoamine used for the amination, those represented by the general formula (3) are preferable, and trimethylamine is particularly preferable.

[0029]

Embedded image

As the polyamine used in carrying out the cross-linking amination, one of ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, polyethyleneimine, phenylenediamine and the like can be used.
~ Polyamine compounds consisting of secondary amines, N, N,
N ', N'-tetramethyldiaminomethane, N, N,
N ′, N′-tetramethyl-1,2-diaminoethane,
N, N, N ', N'-tetramethyl-1,3-diaminopropane, N, N, N', N'-tetramethyl-1,6
-Diaminohexane, N, N, N ', N'-tetramethylbenzidine, p, p'-tetramethyldiaminodiphenylmethane and the like. A primary or secondary aminated compound such as polyvinyl pyridine or polychloromethylstyrene can also be used.

Among them, the diamine having two amino groups represented by the general formula (4) at the molecular end is easily available and has high amination reactivity, and by changing the number (p) of methylene groups, It is a particularly preferred polyamine because the physical properties of the film can be easily controlled. Particularly, it is particularly preferable when the molecular end in the general formula (4) is a tertiary amino group.

[0032]

Embedded image

In the case of an aromatic polysulfone type anion exchange membrane, the degree of cross-linking is lower than that of the styrene or vinylpyridine-divinylbenzene type anion exchange membrane, so that it is 1.0 to 3.0 meq / g dry resin. Are preferable from the viewpoints of acid permeation rate, water permeation coefficient and metal cation exclusion.

The anion exchange membrane can be made to have a composite structure by laminating a porous membrane as a reinforcement layer, thereby increasing the membrane strength and the pressure resistance. As the porous film, a polyolefin-based porous film, particularly a polyfluoroolefin-based porous film is preferable.

Examples of the polyolefin porous film include polyethylene, polypropylene, poly-4-methylpentene and the like. Examples of the polyfluoroolefin-based porous film include polyvinylidene fluoride, polytetrafluoroethylene, hexafluoropropylene-tetrafluoroethylene copolymer, perfluoropropyl vinyl ether-tetrafluoroethylene copolymer, fluoroolefin-based monomer-olefin-based monomer. Examples thereof include polyfluoroolefins such as copolymers. Among them, tetrafluoroethylene is excellent in corrosion resistance, oxidation resistance and workability, and is a particularly preferable material for the reinforcing layer.

As the form of the membrane, a flat membrane may be used as it is, or a spiral module or a hollow fiber membrane module may be used.

A well-known technique can be adopted for the spiral module. For example, the diaphragm is rolled into a roll with a water-permeable membrane support material (for example, polyester cloth) and a spacer (for example, polypropylene mesh),
A water collecting pipe that collects the acid recovery liquid may be arranged in the center, and the water may be stored in a pressure resistant pipe.

The hollow fiber membrane module can also adopt a known technique. The hollow fiber membrane can be produced, for example, by forming an aromatic polysulfone-based anion-exchange polymer into a hollow fiber shape by melt-proofing or wet-proofing. It can also be produced by processing the above-mentioned porous membrane for a reinforcing body into a cylindrical shape, immersing it in an aromatic polysulfone-based anion exchange polymer solution, and then removing the solvent by drying. The hollow fiber membrane can be made into a hollow fiber membrane module by storing it in a pressure resistant tube and sealing the inlet and outlet of the supply liquid and the recovery liquid with a potting material.

[0039]

Example 1 An anion exchange membrane of styrene-divinylbenzene copolymer system (manufactured by Asahi Glass Co., Ltd., trade name Selemion DSV, film thickness 120 μm, ion exchange capacity 2.0 meq as a diaphragm.
/ G dry resin) was used to carry out acid recovery by diffusion dialysis. The stock solution supply side had a sealed structure, and the gas phase portion was pressurized with air to create a pressure difference between the stock solution supply side and the acid recovery side. The acid permeation rate of sulfuric acid through this anion exchange membrane is 5mo.
It was l · m ⁻² · h ⁻¹ · (mol / liter) ⁻¹ . The operating conditions are as follows.

Pressure difference 3.0 kg / cm ² , permeable membrane area 0.1 m ² , stock solution composition H ₂ SO ₄ 317 g / l, Fe 34 g / l, stock solution supply rate 86 ml / h, recovery side composition H ₂ SO ₄ 262 g / liter, Fe 1 g / liter.

Water was supplied to the acid recovery side so as to have the above composition on the acid recovery side. The amount of water transferred is 4 mol · m ⁻² · h ⁻¹ ,
The acid recovery rate was 82.5%. Here, the acid recovery rate is defined by Equation 1.

[0042]

[Equation 1]

Comparative Example 1 Acid recovery by diffusion dialysis was carried out in the same manner as in Example 1 except that the pressure difference between the stock solution supply side and the acid recovery side was 0 kg / cm ² . The amount of water transfer is 12 mol ・ m ^-2・
h ⁻¹ , the acid recovery rate was 77.6%, which was lower than that of Example 1.

Example 2 An aromatic polysulfone-based anion exchange membrane having a high acid permeation rate used as a diaphragm was prepared as follows. First, 4,4′-diphenol is reacted with dihalodiphenyl sulfone to synthesize a precursor of m = 10 composed of an aromatic polysulfone unit, and then the precursor is reacted with dihalodiphenyl sulfone and sodium sulfide (5) (m / n = 1/1, z has an intrinsic viscosity of 0.62 dl
/ G) was obtained) to obtain an aromatic polysulfone-polythioether sulfone copolymer A.

[0045]

Embedded image

The copolymer A was dissolved in 1,1,2,2-tetrachloroethane, chloromethyl ether and anhydrous tin chloride were added, and the mixture was reacted at 110 ° C. for 4 hours. A methylated copolymer B was obtained. The introduction rate of chloromethyl groups was about 1.9 per unit of aromatic polysulfone. The ion exchange capacity when the copolymer B is all reacted with trimethylamine is 2.
It was 2 meq / g dry resin.

The copolymer B was dissolved in N, N-dimethylformamide, and a 1N trimethylamine solution of N, N-dimethylformamide was added to give an ion exchange capacity of 1.2 m.
eq / g was added so as to be a dry resin to obtain an aminated solution C aminated with a monoamine. Amination solution C is cast on a polyethylene terephthalate film and heated at 50 ° C.
After being dried for 2 hours, a cast film D having a film thickness of 10 μm was obtained.

On the other hand, pore size 1 μm, porosity 80%, film thickness 1
A 40 μm porous film of polytetrafluoroethylene was impregnated with ethanol, immersed in water, further immersed in a 0.5 wt% aqueous polyvinyl alcohol solution, and dried at 60 ° C. for 30 minutes. Further, a cross-linking treatment with glutaraldehyde was performed to obtain a hydrophilic cross-linked porous membrane E.

Adhesive solution F obtained by diluting the above amination solution C to 5% by weight with a mixed solvent of N, N-dimethylformamide / 2-methoxyethanol (97: 3 by weight ratio).
Was coated on the cast film D in a liquid film thickness of 20 μm, and the hydrophilic crosslinked porous film E was quickly laminated, and then dried at 50 ° C. for 2 hours to obtain a laminated film G. The laminated film G is further immersed in an ethanol solution of 5N N, N, N ′, N′-tetramethyl-1,3-diaminopropane at 50 ° C. for 16 hours,
A polyamine crosslinked composite film H was obtained.

Using this composite membrane H, acid recovery was carried out by diffusion dialysis in the same manner as in Example 1. The acid permeation rate of sulfuric acid of the composite membrane H is 13 mol · m ⁻² · h ⁻¹ · (mol / liter) ⁻¹ . The operating conditions are as follows.

Pressure difference 5.5 kg / cm ² , permeable membrane area 0.1 m ² , stock solution composition H ₂ SO ₄ 289 g / liter, Fe 25 g / liter, stock solution supply amount 52 ml / h, recovery side composition H ₂ SO ₄ 251 g / liter, Fe 1.5 g / liter.

Water was supplied to the acid recovery side so as to have the above composition on the acid recovery side. The amount of water transferred is 5 mol · m ⁻² · h ⁻¹ ,
The acid recovery rate was 92.0%.

Comparative Example 2 The same polyamine-crosslinked composite membrane H as in Example 2 was used as a diaphragm.
Acid recovery was performed by diffusion dialysis with the pressure difference between the stock solution supply side and the acid recovery side set to 0 kg / cm ² . Water movement is 60mo
1 · m ⁻² · h ⁻¹ , the acid recovery rate was 75.0%, which was lower than that in Example 2.

Example 3 The same polyamine-crosslinked composite membrane H as in Example 2 was wound into a roll with a water-permeable support material made of polyester and a spacer mesh made of polypropylene, and a polyvinyl chloride water collecting tube was placed at the center of the winding. Then, the spiral module was stored in a cylindrical pipe made of polyvinyl chloride. In this module, the stock solution is supplied to the gap formed by the spacer mesh between the composite membranes H.
The acid aqueous solution that has permeated the composite membrane H gradually moves to the winding center through the gap formed by the water-permeable membrane support material between the composite membranes H, and finally is collected in the central water collecting pipe,
It will be taken out of the spiral module.

Using this spiral module, acid recovery was carried out by diffusion dialysis. The operating conditions are as follows. The inside of the hollow fiber membrane is pressurized by adjusting the discharge pressure of the pump for supplying the undiluted solution, and the inside of the hollow fiber (undiluted solution supply side)
And the pressure difference between the outside of the hollow fiber (acid recovery side) was adjusted.

Pressure difference 6.0 kg / cm ² , permeable membrane area 0.05 m ² , stock solution composition H ₂ SO ₄ 289 g / liter, Fe 25 g / liter, stock solution supply amount 35 ml / h, recovery side composition H ₂ SO ₄ 251 g / liter, Fe 1.5 g / liter.

Water was supplied to the acid recovery side (the water-permeable membrane support material side of the spiral tube) so that the above composition was on the acid recovery side. The amount of transferred water was 4 mol · m ⁻² · h ⁻¹ and the acid recovery rate was 94.0%.

Comparative Example 3 Using the spiral module of Example 4, the pressure difference between the stock solution supply side and the acid recovery side was adjusted to 0.05 kg / cm ² , and the acid recovery was similarly performed by diffusion dialysis. as a result,
The amount of water transferred was 58 mol · m ⁻² · h ⁻¹ and the acid recovery rate was 76.
It was 0%. When the pressure difference was less than 0.1 kg / cm ² , the pressurizing effect was hardly exhibited.

Example 4 A polyethylene porous hollow fiber membrane having a porosity of 80%, a film thickness of 100 μm and an inner diameter of 300 μm was immersed in the amination solution C used in Example 2 and then pulled up and dried at 50 ° C. for 2 hours. By doing so, an anion-exchangeable hollow fiber membrane was obtained. Using this hollow fiber membrane, the anion-exchangeable hollow fiber module shown in FIG. 1 was produced. This module has an effective membrane area of 1.2
m ² , the module inner diameter was 8 cm, and the hollow fiber effective length was 15 cm.

Acid recovery was carried out by diffusion dialysis using this hollow fiber membrane module. In FIG. 1, the hollow fiber membrane 1 is fixed in a housing 7 by a potting material 6. The stock solution is supplied from the stock solution supply port 2 into the hollow fiber membrane 1, the recovered acid aqueous solution permeates the hollow fiber membrane, is collected outside the hollow fiber membrane, and is discharged from the recovery solution outlet 5 to the outside of the module. Water is supplied from the diluting water supply port 1 to the outside of the hollow fiber so that the concentration of the recovered acid can be kept constant. The stock solution from which the acid has been recovered is discharged from the stock solution outlet 3. The operating conditions are as follows. The inside of the hollow fiber is pressurized by adjusting the discharge pressure of the pump for supplying the undiluted solution, and the inside of the hollow fiber (on the undiluted solution supply side)
And the pressure difference between the outside of the hollow fiber (acid recovery side) was adjusted.

Pressure difference 6.5 kg / cm ² , permeable membrane area 1.2 m ² , stock solution composition H ₂ SO ₄ 289 g / liter, Fe 25 g / liter, stock solution supply amount 120 ml / h, recovery side composition H ₂ SO ₄ 251 g / liter, Fe 1.5 g / liter.

Water was supplied to the acid recovery side (outside of the hollow fiber membrane) so as to have the above composition on the acid recovery side. The amount of water transfer is 2
mol · m ⁻² · h ⁻¹ , acid recovery was 95.0%.

Comparative Example 4 Using the hollow fiber membrane module of Example 4, the pressure difference between the stock solution supply side and the acid recovery side was adjusted to 0.05 kg / cm ² .
Similarly, the acid was recovered by diffusion dialysis. As a result, the amount of transferred water was 56 mol · m ⁻² · h ⁻¹ and the acid recovery rate was 75.5%.
Met. When the pressure difference was less than 0.1 kg / cm ² , the pressurizing effect was hardly exhibited.

[0064]

EFFECT OF THE INVENTION High-purity acid can be recovered by diffusion dialysis. The acid recovery rate in the present invention can be dramatically improved as compared with the prior art. It also has the effect of reducing the amount of waste liquid after dialysis.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a hollow fiber membrane module used in Example 4.

[Explanation of symbols]

 1: Hollow fiber membrane 2: Undiluted solution supply port 3: Undiluted solution outlet 4: Dilution water supply port 5: Recovered acid outlet 6: Potting material 7: Housing

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hisakataka Tanaka 1150 Hazawa-machi, Kanagawa-ku, Yokohama-shi, Kanagawa Asahi Glass Co., Ltd. Central Research Laboratory

Claims (4)

[Claims] 1. A method for supplying a stock solution containing an acid to one side of a diaphragm and recovering the acid from the other side of the diaphragm by diffusion dialysis through the diaphragm, wherein the stock solution supply side chamber is more A method for recovering an acid that maintains a high pressure of 1 kg / cm ² or more. 2. The method of recovering an acid according to claim 1, wherein the diaphragm is an anion exchange membrane. 3. The acid recovery method according to claim 1, wherein the anion exchange membrane is an aromatic polysulfone-based anion exchange membrane. 4. The sulfuric acid permeation rate of the diaphragm is 3 mol · m ⁻² · h.
⁻¹ · (mol / liter) ⁻¹ or more, The acid recovery method according to claim 1, 2 or 3.