JP2009039672A - Recovery method of acid from fluoronitric acid waste liquid - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for recovering an acid of high purity from a fluoronitric acid waste liquid by the reduced number of processes. <P>SOLUTION: A pair of anion exchange membranes A is arranged between the anode and the cathode, and a cation exchange membrane C and a monovalent selective cation exchange membrane CIMS are successively arranged between a pair of the anion exchange membranes A from the anode side. The fluoronitric acid waste liquid is supplied to the desalting and deoxidation chamber 5 formed between the anion exchange membrane A and the cation exchange membrane C and electrodialysis is performed while supplying an acid aqueous solution to a drainage chamber 7 which is adjacent to the desalting and deoxidation chamber 5 and formed between the cation exchange membrane C and the monovalent selective cation exchange membrane SC, so that nitric acid and/or fluoric acid is recovered from the acid chamber 9 adjacent to the desalting and deoxidation chamber 5 and formed between the monovalent selective cation exchange membrane SC and the anion exchange membrane A. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for recovering acid from a nitric hydrofluoric acid waste solution containing nitric acid and / or hydrofluoric acid.

  A so-called nitric hydrofluoric acid waste solution containing nitric acid and hydrofluoric acid is discharged from the pickling process of stainless steel. A large amount of such fluoric acid waste liquid is also discharged from LSI factories where etching and the like are performed. Since such nitric hydrofluoric acid waste liquid contains a large amount of valuable metals such as iron, chromium and nickel, from the viewpoint of resource saving and environmental pollution, acid and valuable metals are recovered from the waste liquid and reused. Is planned.

  In order to recover nitric acid and hydrofluoric acid from the above-mentioned nitric hydrofluoric acid waste solution, generally, after filtering this, a method of recovering acid by removing valuable metal components by diffusion dialysis using an anion exchange membrane is known. However, in this method, the recovered metal contains a considerable amount of valuable metal components, and it is difficult to recover a highly pure acid. Accordingly, various methods have been proposed for recovering high purity acid.

  As a typical method, for example, in Patent Documents 1 and 2, acid waste liquid is deoxidized by diffusion dialysis, and then neutralized by adding an aqueous solution of an alkali metal such as KOH, followed by filtration. There has been proposed an acid recovery method in which components are precipitated and separated, and the filtrate (aqueous alkaline salt solution of nitric acid or hydrofluoric acid) is treated using an electrodialyzer equipped with a bipolar membrane.

Japanese Patent Laid-Open No. 9-887 Japanese Patent Laid-Open No. 9-10557

According to said method, a valuable metal component can be removed effectively and a highly purified acid can be collect | recovered. However, prior to electrodialysis using a bipolar membrane, neutralization and filtration are necessary, the number of processes is large, and there is still room for improvement.
In addition, nitrate ions in the nitric hydrofluoric acid waste solution are difficult to separate as precipitates, and it is difficult to efficiently recover nitrate ions. In recent years, the negative influence on the environment caused by nitrogen contained in wastewater has been pointed out, and technology for recovering nitrate ions in wastewater has become increasingly important under the circumstances where nitrogen emission regulations become severe.

  Accordingly, an object of the present invention is to provide a method for recovering a high-purity acid from a nitric hydrofluoric acid waste solution with a small number of steps.

According to the present invention, at least one pair of anion exchange membranes is arranged between an anode and a cathode, and a cation exchange membrane and a monovalent selective cation exchange membrane are arranged in this order from the anode side between the pair of anion exchange membranes. And
A nitric hydrofluoric acid waste solution containing a nitrate metal salt and / or a hydrofluoric acid metal salt is supplied to a demineralization deoxidation chamber formed between the anion exchange membrane and the cation exchange membrane, and the demineralization deoxidation chamber Electrodialysis while supplying an aqueous acid solution to a drainage chamber adjacent to and formed between the cation exchange membrane and the monovalent selective cation exchange membrane,
Nitric acid hydrofluoric acid, wherein nitric acid and / or hydrofluoric acid is recovered from an acid chamber adjacent to the desalting and deoxidizing chamber and formed between a monovalent selective cation exchange membrane and an anion exchange membrane A method for recovering acid from waste liquid is provided.

  In the present invention, it is preferable to recover the desalted solution of nitric hydrofluoric acid waste solution from the desalting and deoxidizing chamber, add the acid aqueous solution to the desalted solution, and supply to the draining chamber for electrodialysis. .

  According to the present invention, by directly electrodialyzing the nitric hydrofluoric acid waste liquid without performing steps such as neutralization with alkali and filtration separation of the precipitate formed by neutralization (removal of metal components), high efficiency can be achieved. Pure acid can be recovered. That is, the greatest advantage of the present invention is that the acid can be recovered from the nitric hydrofluoric acid waste solution with a small number of steps.

  In the present invention, in FIG. 1 showing a typical structure of an electrodialysis apparatus used for electrodialysis for acid recovery, in this apparatus, a pair of anion exchange membranes A and A are arranged, Furthermore, a cation exchange membrane C and a monovalent selective cation exchange membrane SC are disposed between the pair of anion exchange membranes A and A in this order from the anode 1 side. A desalting and deoxidizing chamber 5 is formed between the cation exchange membrane C and the monovalent selective cation exchange membrane SC adjacent to the desalting and deoxidizing chamber 5. An acid chamber 9 is formed between the monovalent selective cation exchange membrane SC and the anion exchange membrane A adjacent to the cathode 3 side of the liquid chamber 7.

  Further, in the apparatus of FIG. 1, a monovalent selective cation exchange membrane SC is further provided on the outer side (anode side) of the anion exchange membrane A on the anode 1 side so as to be adjacent to the stock solution chamber 5. An acid chamber 9 is formed, and a cation exchange membrane C and a monovalent selective cation exchange membrane SC are further provided outside the anion exchange membrane A on the cathode 3 side (cathode side). A stock solution chamber 5 is also formed between the anion exchange membrane A and the cation exchange membrane C adjacent to each other, and also between the cation exchange membrane C adjacent to the stock solution chamber 5 and the monovalent selective cation exchange membrane SC. A drainage chamber 7 is formed.

  Therefore, the anode 1 and the cathode 3 are accommodated in the anode chamber 10 or the cathode chamber 11 partitioned by the monovalent selective cation exchange membrane SC.

  In the electrodialysis apparatus having the above structure, as the anion exchange membrane A and the cation exchange membrane C, membranes known per se are used. For example, it has a structure in which a woven fabric, a nonwoven fabric, a porous film or the like made of polyolefin resin, polyvinyl chloride, fluorine-based resin or the like is used as a base material and the base material is filled with an ion exchange resin.

  The above ion exchange resin is obtained by introducing an ion exchange group (anion exchange group in an anion exchange membrane or a cation exchange group in a cation exchange membrane) into a hydrocarbon-based or fluorine-based base resin. Is not particularly limited as long as it is a functional group that can be negatively or positively charged in an aqueous solution. For example, examples of the anion exchange group include primary to tertiary amino groups, quaternary ammonium groups, pyridyl groups, imidazole groups, and quaternary pyridinium groups. Generally, quaternary ammonium groups or 4 that are strongly basic groups are used. A class pyridinium group is preferred. Examples of the cation exchange group include a sulfonic acid group, a carboxylic acid group, and a phosphonic acid group. In general, a sulfonic acid group that is a strongly acidic group is preferable.

The ion exchange capacity of such anion exchange membrane A and cation exchange membrane C is generally 0.1 to 3.0 meq / g, preferably 0.5 to 2.5 meq / g. Is about 10 to 500 μm, particularly about 30 to 300 μm.
The anion exchange membrane is prone to proton leakage from the recovered acid side to the stock solution side, and an anion exchange membrane with low proton leakage is preferably used in order to improve acid recovery efficiency.

Further, the monovalent selective cation-exchange membrane SC is, H ^+, Na ^+, monovalent cations such as K ⁺ are selectively permeable, anion, of course, polyvalent cations such as polyvalent metal ions It is a cation exchange membrane with a blocking property. The monovalent cation selective permeability is, for example, a relative transport number (ion selective permeability coefficient: P ^H _Mg ) of a monovalent cation with respect to a magnesium ion of a divalent cation represented by the following formula (1) is 10 or more, preferably , 100 or more is important.
_{^{P H Mg = (t H /}} t Mg) / (C H / C Mg) (1)
t _H : Transport number of protons in the membrane t _Mg : Transport number of magnesium ions in the membrane C _H : Specified concentration of protons in the processing solution C _Mg : Specified concentration of magnesium ions in the processing solution Such monovalent selection The cationic cation exchange membrane SC is also known per se, and is specifically a composite cation exchange membrane having a structure in which an anion exchanger layer is formed on at least one surface of the cation exchange membrane.

  As the composite cation exchange membrane used as the monovalent selective cation exchange membrane SC as described above, for example, one disclosed in JP-A-62-205135, for example, on at least one surface of the cation exchange membrane, Those having a polymer layer (anion exchanger layer) formed by polymerizing a vinyl compound having a quaternary ammonium base and three or more vinylbenzyl groups select monovalent ions. It is particularly suitable from the viewpoint of blocking the polyvalent metal ions that permeate and exist in the waste liquid described later.

  In the above composite cation exchange membrane, the quaternary ammonium bases possessed by the vinyl compound include not only quaternary ammonium bases but also so-called onium bases such as quaternary pyridinium bases, sulfonium bases, and phosphonium bases. It may be. The number of quaternary ammonium bases possessed by the vinyl compound is effectively 1 or more, but if the amount is more than necessary, the monovalent selectivity is lowered, so generally 1 to 1000, especially 3 to 50 are present. preferable. In addition, the number of vinyl benzyl groups in the vinyl compound is not limited as long as it is 3 or more. However, the more vinyl benzyl groups, the denser polymer layer is formed on the surface of the cation exchange membrane. The desired effect is exhibited as a cation exchange membrane. However, when there are too many vinylbenzyl groups in such a vinyl compound, polymerization occurs easily between the molecules of the vinyl compound and within the molecule and is difficult to handle. Therefore, the number of vinylbenzyl groups possessed by the vinyl compound is generally 3 -1000, especially 3-100 are preferable.

  A vinyl compound having a quaternary ammonium base and three or more vinylbenzyl groups as described above is generally synthesized by, for example, the following method.

（式中、Ｘ^２は、式；（ＣＨ_３）_２Ｎ（ＣＨ_２）_３−で表される基である）、
で表される化合物などを例示することができる。
（４）同一分子中に３個以上のハロゲン原子を有する化合物、例えば下記式；
Ｈ−（ＣＨ_２ＣＨＸ^３）ｎ−Ｈ
（式中、Ｘ^３は、ｏ−，ｍ−またはｐ−クロロメチルフェニル基である）、
で表される化合物に、ビニルフェニルアルキルN,N−ジアルキルアミンを反応させる。 (1) Alkylating a primary amine such as methylamine or ethylamine with three vinylbenzyl chlorides.
(2) A divalent primary amine such as ethylenediamine or propylenediamine is reacted with three or more vinylbenzyl chlorides to form a quaternary ammonium base with an alkylating agent such as methyl iodide or dimethyl sulfate as necessary.
(3) A tertiary amino compound having a valence of 3 or more is reacted with at least 3 vinylbenzyl chlorides. Further, if necessary, an unreacted tertiary amino group may be converted to a quaternary amino group with another alkylating agent.
Examples of the trivalent or higher tertiary amino compounds include the following formulas:
^{_{H- (CH 2 CHX 1) n}} -H,
(In the formula, X ¹ is p-pyridyl group, m-pyridyl group, 3-methylpyridin-4-yl group, dimethylaminomethyl group, o-, m- or p- (dimethylaminomethyl) phenyl group, o- , M- or p- (dimethylaminoethyl) phenyl group, o-, m- or p- (diethylaminomethyl) phenyl group, o-, m- or p- (diethylaminoethyl) phenyl group, and n is 3 An integer greater than or equal to
_{(CH 3) 2 N (CH} 2) 3 -N (CH 3) - (CH 2) 3 N (CH 3) 2,
_{(CH 3) 2 N (CH} 2) 2 -N (CH 3) - (CH 2) 2 N (CH 3) 2,
_{(CH 3) 2 N (CH} 2) 6 -N (CH 3) - (CH 2) 6 N (CH 3) 2,

(Wherein X ² is a group represented by the formula: (CH ₃ ) ₂ N (CH ₂ ) ₃ —),
The compound etc. which are represented by these can be illustrated.
(4) A compound having 3 or more halogen atoms in the same molecule, for example, the following formula:
^{_{H- (CH 2 CHX 3) n}} -H
(Wherein X ³ is an o-, m- or p-chloromethylphenyl group),
Is reacted with vinylphenylalkyl N, N-dialkylamine.

  In such a monovalent selective cation exchange membrane SC, generally, the thickness of the polymer layer of the anion exchanger formed on the surface of the cation exchange membrane should be in the range of about 0.01 to 50 μm, In addition, the anion exchange capacity is preferably in the range of about 0.1 to 3 meq / g in order to ensure appropriate monovalent selectivity. The polymer layer of the anion exchanger may be provided on one surface of the cation exchange membrane, but can be provided on both surfaces.

  In the apparatus of FIG. 1, the monovalent selective cation exchange membrane SC is arranged so that the surface of the anion exchanger on the polymer layer side faces the anode 1 side.

  In the present invention, the acid is recovered from the nitric hydrofluoric acid waste liquid by supplying the nitric hydrofluoric acid waste liquid to the desalting and deoxidation chamber 5 of the electrodialysis apparatus described above and performing electrodialysis.

  As already mentioned, this nitric hydrofluoric acid waste liquid is discharged from the pickling process of stainless steel, or is also discharged in large quantities from places such as LSI factory where etching and plating are performed, such as filtration. The solid content has been removed through a wastewater treatment process, which contains hydrofluoric acid and nitric acid, and further contains polyvalent metal ions such as iron, chromium and nickel. Of course, this nitric hydrofluoric acid waste liquid may contain only one of nitric acid or hydrofluoric acid. Further, the polyvalent metal ion concentration may be reduced by a known treatment such as diffusion dialysis.

  In the present invention, the nitric hydrofluoric acid waste liquid is supplied to the demineralization and deoxidation chamber 5 as a stock solution, and at the same time, a dilute acid aqueous solution is supplied to the anode chamber 10 and the cathode chamber 11 as an extreme solution. Supplies a dilute acid aqueous solution or ion-exchanged water, and further supplies an acid aqueous solution as a proton replenishment source to the drainage chamber 7. In this state, a predetermined voltage is applied between the anode 1 and the cathode 3, Electrodialysis is performed at a predetermined current density.

  The acid used as the proton supply source is not particularly limited. However, since the present invention recovers hydrofluoric acid and nitric acid from a nitric hydrofluoric acid waste solution, the same kind of acid is not used. There is no meaning, and hydrochloric acid is not suitable because of problems such as corrosion of the apparatus. Therefore, sulfuric acid or phosphoric acid is generally used, and sulfuric acid is preferably used particularly in terms of cost. The dilute acid supplied to the anode chamber 10, the cathode chamber 11 or the acid chamber 9 is preferably the same acid as the acid to be recovered, that is, nitric acid or hydrofluoric acid.

When electrodialysis is performed as described above, as shown in FIG. 1, NO ₃ ⁻ and F ⁻ are separated from the anion exchange membrane from the stock solution (nitric acid hydrofluoric acid waste solution) supplied to the desalting and deoxidizing chamber 5. Move through A to the acid chamber 9. On the other hand, metal multivalent ions such as Fe ²⁺ , Cr ³⁺ , Ni ^2+, and H ⁺ move to the drainage chamber 7 through the cation exchange membrane. Further, H ⁺ in the drainage chamber 7 flows into the acid chamber 9 through the monovalent selective cation exchange membrane SC. In this case, the inflow of the metal multivalent ions into the acid chamber 5 is blocked by the monovalent selective cation exchange membrane SC.

Therefore, when the electrodialysis is continued as described above, the hydrofluoric acid and nitric acid concentrations in the acid chamber 9 increase, and when the acid chamber 9 reaches an appropriate concentration, the acid chamber 9 mixes these acids. Collect the liquid. From the drainage chamber 7, an acid aqueous solution containing metal polyvalent ions such as Fe ²⁺ , Cr ³⁺ , and Ni ²⁺ is discharged.

In the present invention described above, it is extremely important to supply the acid aqueous solution to the drainage chamber 7. That is, when electrodialysis is performed as described above, the acid radicals forming a salt with the polyvalent metal contained in the nitric hydrofluoric acid waste solution (stock solution) also pass through the anion exchange membrane A into the acid chamber 9. Transition. Accordingly, protons are insufficient in the liquid in the acid chamber 9, and when the liquid in the acid chamber 9 is recovered as it is, the acid recovery efficiency decreases due to insufficient protons. Therefore, in the present invention, in order to compensate for the lack of protons, an acid aqueous solution such as sulfuric acid is supplied to the drainage chamber 7 to compensate for the lack of protons. That is, H ⁺ derived from the acid supplied to the drainage chamber 9 moves to the acid chamber 9 through the monovalent selective cation exchange membrane SC to compensate for proton deficiency, thereby recovering the acid with high efficiency. be able to.
In the above case, the anion (for example, SO ₄ ²⁻ ) derived from the acid supplied as the proton replenishment source remains in the drainage chamber 7 as it is.

As described above, the acid supplied to the drainage chamber 9 compensates for the lack of protons derived from polyvalent metal salts of acids such as Fe (NO ₃ ) ₂ and FeF. What is necessary is just to be the same as the polyvalent metal ion contained in the nitric hydrofluoric acid waste solution (stock solution) supplied to the deoxidation chamber 5.

In the present invention, the aqueous acid solution supplied as a proton replenishment source can be supplied alone to the drainage chamber 7, but generally, as shown in FIG. It is preferable that polyvalent metals such as Fe are efficiently recovered by adding the above acid to the dilute solution that has been supplied to the solution and desalted and deacidified by electrodialysis and circulating it in the drainage chamber 7. It is.
1 shows an electrodialysis apparatus having a structure in which a pair (two) of anion exchange membranes A is used, and a cation exchange membrane C and a monovalent selective cation exchange membrane SC are disposed therebetween. However, the electrodialysis apparatus used in the present invention is not limited to such a structure. For example, a larger number of anion exchange membranes A are used, and each pair of anion exchange membranes A is used. It is of course possible to use an electrodialyzer having a structure in which the cation exchange membrane C and the monovalent selective cation exchange membrane SC are arranged.

  After completion of the electrodialysis as described above, the mixed solution of nitric acid and hydrofluoric acid or the aqueous solution of nitric acid or hydrofluoric acid is removed from the acid chamber 9 and the polyvalent metal is removed and recovered with high purity. Further, from the drain chamber 7, a liquid containing an acid and a polyvalent metal supplied as a proton supply source is taken out as a waste liquid.

  In the present invention, the acid recovered as described above is reused in a stainless steel cleaning process or the like. In addition, the waste liquid discharged from the drain chamber 7 is reused for producing stainless steel by collecting polyvalent metals as necessary.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to these Examples.

In the following experiment, an electrodialyzer (processing capacity 9 L / Hr · m ² ) having the structure shown in FIG. 1 and having the following ion exchange membrane was used.
The ion selective permeation coefficient (P ^H _Mg ) of the cation exchange membrane used was measured by the following method. An ion exchange membrane is sandwiched between two-chamber acrylic cells, and both chambers are filled with a mixed aqueous solution containing 0.25N-HCl and 0.25N-MgCl2 and stirred at 25 ° C. for 60 minutes at a current density of 10 mA / cm 2. Electrodialysis was performed, and after electrodialysis, the amount of protons and magnesium ions in both chambers was measured, and P ^H _Mg was calculated from Equation 1.
Cation exchange membrane C; Neoceptor CMX
Thickness: 180μm
Cation exchange capacity: 1.6 meq / g
P ^H _Mg: 2
Anion exchange membrane A; Neoceptor AMX
Thickness: 140 μm
Anion exchange capacity: 1.5 meq / g
Monovalent selective cation exchange membrane SC; Neoceptor CIMS
Thickness: 140 μm
P ^H _Mg: 210

<Example 1>
A stock solution having the following composition was prepared as a virtual acid waste solution.
Stock solution composition;
NO ₃ concentration: 20.4 g / L
SO ₄ concentration: 0
Fe concentration: 3.9 g / L
H ⁺ concentration: 0.12N

Moreover, the following acid aqueous solution was prepared as an acid and proton supply source for polar solutions.
Aqueous acid aqueous solution; nitric acid aqueous solution NO ₃ concentration: 7.6 g / L
H ⁺ concentration: 0.13N
Acid aqueous solution for proton supply; sulfuric acid aqueous solution SO ₄ concentration: 22.7 g / L
H ⁺ concentration: 0.51N

  1 liter of the above stock solution is supplied to the demineralization and deoxidation chamber of the electrodialysis apparatus, 200 cc of nitric acid for polar solution is supplied to the anode chamber, the cathode chamber and the acid chamber, and further, the sulfuric acid aqueous solution for proton replenishment is supplied to the drainage chamber. 1 liter was supplied, and electrodialysis was performed by energizing 2.5 A / dm 2 for 120 minutes under the following conditions.

  After electrodialysis, the composition of the recovered acid recovered from the acid chamber, the desalted liquid recovered from the demineralized deacidified chamber, and the waste liquid recovered from the drained chamber was analyzed by ion chromatography, atomic absorption, or titration. It was as follows. Nitric acid from which iron ions were sufficiently removed could be recovered.

Recovered acid (280 ml);
NO ₃ concentration: 63.2 g / L
SO ₄ concentration: 3.12 g / L
Fe concentration: 0.19 g / L
H ⁺ concentration: 1.15N
Desalted solution (910 ml);
NO ₃ concentration: 1.22 g / L
SO ₄ concentration: 0.17 g / L
Fe concentration: 0.03 g / L
H ⁺ concentration: 0.025N
Waste liquid (1000 ml);
NO ₃ concentration: 1.04 g / L
SO ₄ concentration: 21.4 g / L
Fe concentration: 3.2 g / L
H ⁺ concentration: 0.49N

<Comparative Example 1>
Electrodialysis was performed under exactly the same conditions as in Example 1, except that 1 liter of ion-exchanged water was supplied to the drain chamber of the electrodialysis apparatus instead of the sulfuric acid aqueous solution for proton replenishment. However, the electrical conductivity of the liquid in the drainage chamber was low, sufficient electricity did not flow, and electrodialysis could not be performed.

<Comparative example 2>
Except for the cation exchange membrane Neoceptor CMX in the electrodialysis machine, except that the chamber between Neoceptor AMX and Neoceptor CIMS is used as the desalting and deoxidizing chamber, and the stock solution is supplied, and the drainage chamber for supplying the sulfuric acid aqueous solution for proton supply is removed. Electrodialyzed under exactly the same conditions as in Example 1, and analyzed the composition of the recovered acid recovered from the acid chamber and the desalted solution recovered from the demineralized deoxidation chamber after electrodialysis. The results were as follows. The amount of protons in the stock solution is small compared to the amount of electricity applied, and iron ions permeate even when a monovalent cation selective permeable membrane is used. As a result, the concentration of iron ions in the recovered acid increases, A high acid could not be obtained.

Recovered acid (280 ml);
NO ₃ concentration: 54.6 g / L
SO ₄ concentration: 0 g / L
Fe concentration: 14.9 g / L
H ⁺ concentration: 0.35N
Desalted solution (920 ml);
NO ₃ concentration: 3.6 g / L
SO ₄ concentration: 0 g / L
Fe concentration: 1.0 g / L
H ⁺ concentration: 0.02N

The figure which shows the typical structure of the electrodialysis apparatus used for this invention.

Explanation of symbols

A: Anion exchange membrane C: Cation exchange membrane CS: Monovalent selective cation exchange membrane 1: Anode 3: Cathode 5: Desalination deoxidation chamber 7: Drainage chamber 9: Acid chamber

Claims (2)

Arranging at least one pair of anion exchange membranes between the anode and the cathode, and arranging a cation exchange membrane and a monovalent selective cation exchange membrane in order from the anode side between the pair of anion exchange membranes,
A nitric hydrofluoric acid waste solution containing a nitrate metal salt and / or a hydrofluoric acid metal salt is supplied to a demineralization deoxidation chamber formed between the anion exchange membrane and the cation exchange membrane, and the demineralization deoxidation chamber Electrodialysis while supplying an aqueous acid solution to a drainage chamber adjacent to and formed between the cation exchange membrane and the monovalent selective cation exchange membrane,
Nitric acid hydrofluoric acid, wherein nitric acid and / or hydrofluoric acid is recovered from an acid chamber adjacent to the desalting and deoxidizing chamber and formed between a monovalent selective cation exchange membrane and an anion exchange membrane Method for recovering acid from waste liquid.   The acid according to claim 1, wherein the desalted solution of nitric hydrofluoric acid waste solution is recovered from the desalting and deoxidizing chamber, the acid aqueous solution is added to the desalted solution, and the acid is supplied to the draining chamber for electrodialysis. Recovery method.

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