JP2007222779A - Recovery process of very pure inorganic acid - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a recovery process of a high purity inorganic aqueous solution reducing the concentration of metal ions by electrodialysis using an electrodialyser constructed of using a bipolar membrane. <P>SOLUTION: The recovery process comprises arranging the bipolar membrane B and an anion exchange membrane A between a positive electrode and a negative electrode, using the electrodialyser having a positive electrode side chamber 12 and a negative electrode side chamber 11 formed by partitioning a pair of bipolar membranes B with the anion exchange membrane A, supplying an inorganic acid waste liquid containing the metal ions to the negative electrode side chamber 11 as a treated liquid, supplying water or the high purity inorganic aqueous solution to the positive electrode side chamber 12 as a recovery medium liquid, by performing the electrodialysis in this state, selectively transferring a conjugate base from the negative electrode side chamber 11 to the positive electrode side chamber 12 to increase the concentration of the inorganic acid in the recovery medium liquid, and recovering the recovery medium liquid from the positive electrode side chamber 12 as the high purity inorganic acid aqueous solution. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for recovering a high purity inorganic acid from an inorganic acid drainage containing metal ions, and particularly to a method for recovering a high purity hydrofluoric acid aqueous solution from a low purity hydrofluoric acid aqueous solution.

  At present, hydrofluoric acid aqueous solutions are widely used in semiconductor manufacturing processes and pickling processes for metal materials. The spent hydrofluoric acid drainage used and recovered in such a process contains metal ions. Therefore, in order to reuse such used hydrofluoric acid waste liquid, it is required to reduce the concentration of metal ions to obtain a highly purified hydrofluoric acid aqueous solution.

  Conventionally, a coagulation-precipitation treatment using slaked lime or the like has generally been adopted as a method for treating a hydrofluoric acid aqueous solution, and the removal of hydrofluoric acid in waste liquid has been attempted by using a large amount of an aluminum / iron-based coagulant. However, with the recent tightening of regulations due to environmental problems and the like, a more advanced hydrofluoric acid aqueous solution treatment method is required. Moreover, from the viewpoint of reducing the amount of sludge generated in the coagulation sedimentation treatment, the actual situation is that the reuse of recovered used hydrofluoric acid is being considered without performing such coagulation sedimentation treatment.

  From the above viewpoint, a method for recovering high-purity hydrofluoric acid obtained by removing metal ions from a hydrofluoric acid waste solution containing metal ions as impurities has been studied by electrodialysis.

As a method for recovering hydrofluoric acid-containing effluent, the acid effluent containing metal ions is neutralized with alkali, the contained metal ions are precipitated, the precipitate is removed with a filter, etc., and the obtained metal ion content There has been proposed a method in which a salt solution with a small amount is supplied to an electrodialysis apparatus using a bipolar membrane, an anion exchange membrane, and a cation exchange membrane, and an acid is recovered from the salt solution. However, in the method using the electrodialyzer using the bipolar membrane, the anion exchange membrane, and the cation exchange membrane as described above, it is necessary to neutralize the low-purity acid with an alkali, and a step for separating the precipitate is necessary. It becomes. Therefore, since chemicals are consumed and the number of processing steps increases, it is difficult to say that this is an efficient high-purity acid recovery method.
7-11558

An object of the present invention is to use an electrodialyzer constructed using a bipolar membrane, and recover high-purity hydrofluoric acid aqueous solution with reduced metal ion concentration by electrodialysis using such an electrodialyzer. It is to provide a way to do.
Another object of the present invention is to provide a method for recovering a high-purity inorganic acid that can significantly reduce the metal ion concentration of not only hydrofluoric acid but also other inorganic acids.

  According to the present invention, a bipolar membrane and an anion exchange membrane are disposed between a positive electrode and a negative electrode, and the bipolar membranes formed by partitioning the bipolar membrane with an anion exchange membrane, each having a single wall, An electrodialyzer equipped with a positive electrode side chamber and a negative electrode side chamber is used, a metal ion-containing inorganic acid drainage solution is supplied to the negative electrode side chamber as a treatment liquid, and the positive electrode side chamber is made of water or a high-purity inorganic acid aqueous solution. By supplying medium liquid and performing electrodialysis in this state, the conjugate base is selectively transferred from the negative electrode side chamber to the positive electrode side chamber to increase the concentration of inorganic acid in the recovery medium liquid, and the recovery medium liquid is discharged from the positive electrode side chamber. There is provided a method for recovering a high-purity inorganic acid, which is recovered as a high-purity inorganic acid aqueous solution.

As a method of the present invention,
(1) using hydrofluoric acid as the inorganic acid,
(2) using an electrodialyzer in which bipolar membranes are partitioned by a plurality of anion exchange membranes and at least one intermediate chamber is formed between the positive electrode side chamber and the negative electrode side chamber;
(3) performing electrodialysis while maintaining the concentration of hydrofluoric acid in the treatment liquid at a concentration of 0.25 mol / L or more;
(4) performing electrodialysis while maintaining the hydrofluoric acid concentration in the range of 0.25 to 10 mol / L;
Is preferred.

  The method of the present invention uses an electrodialyzer constructed using a bipolar membrane, but a particularly important feature is not to remove metal ions contained in the inorganic acid drainage to be treated, but to treat the ions. This is in that the recovery medium liquid is recovered as a high purity inorganic acid aqueous solution by moving the conjugate base contained in the inorganic acid drainage liquid to be collected into the recovery medium liquid water or a high purity inorganic acid aqueous solution. Thus, a highly pure inorganic acid aqueous solution with reduced metal ion concentration can be recovered, and electrodialysis can be performed with high current efficiency.

That is, when high-purity inorganic acid is recovered by removing metal ions that are cations, an electrodialysis apparatus in which a cation exchange membrane is disposed between a pair of bipolar membranes is used, and the positive electrode side chamber (acid The inorganic acid drainage to be treated is supplied to the chamber), and electrodialysis is performed in this state, whereby the metal ions in the inorganic acid drainage permeate the cation exchange membrane and move to the negative electrode side chamber (base chamber). As a result, metal ions are removed from the inorganic acid drainage supplied to the positive electrode side chamber, and the purity of the inorganic acid aqueous solution is increased and recovered as a high-purity inorganic acid aqueous solution. However, in such means, since H ⁺ is present in a large amount as compared with the metal ion due to the dissociation of the inorganic acid, the current efficiency is particularly remarkable for moving the metal ion from the liquid in which the metal ion is present in a very small amount. It will be lower. For example, in Comparative Example 1, which will be described later, the current efficiency of Fe is about 0.03%, which makes it extremely difficult to efficiently reduce the metal ion concentration.

  However, in the present invention, since a high-purity inorganic acid aqueous solution is recovered by moving a conjugate base instead of metal ions to a positive electrode side chamber as a recovery chamber, a cation exchange membrane is not interposed between a pair of bipolar membranes. An electrodialyzer provided with an anion exchange membrane is used. In addition, an inorganic acid drainage solution to be treated is supplied to the negative electrode side chamber, and a water or high-purity inorganic acid aqueous solution as a recovery medium solution is supplied to the positive electrode side chamber. Electrodialysis is performed in this state, and the inorganic acid in the negative electrode side chamber is supplied. The conjugate base is moved from the aqueous solution to the positive electrode side chamber through the anion exchange membrane. Therefore, the concentration of the inorganic acid in the collection medium liquid in the positive electrode side chamber increases, the electric force that moves the metal ion from the negative electrode chamber side to the positive electrode chamber side does not act, and the movement of the metal ion is limited by the anion exchange membrane. Therefore, the increase in the metal ion concentration of the recovery medium liquid due to the movement of the metal ions from the negative electrode side chamber to the positive electrode side chamber is extremely small. As a result, the recovery medium liquid can be recovered as a high-purity inorganic acid aqueous solution.

  In the present invention, the inorganic acid is not particularly limited. In particular, an inorganic acid such as hydrofluoric acid, hydrochloric acid, nitric acid, and buffered hydrofluoric acid, and a mixed inorganic acid drainage can be used as the treatment liquid.

In the present invention, hydrofluoric acid is most preferable among the inorganic acids. That is, in an aqueous hydrofluoric acid solution, hydrofluoric acid (HF) is dissociated to produce F ^−, but a part of this F ⁻ hydrogen bonds with HF and behaves as HF ₂ ⁻ . Further, since hydrofluoric acid is a weak acid, the amount of H ⁺ that deviates into the positive electrode side chamber (acid chamber) is small, and it is difficult to leak to the negative electrode side chamber through the anion exchange membrane. For this reason, when hydrofluoric acid is used, electrodialysis can be performed with a current efficiency of F of 100% or more, particularly as high as about 200%.

The present invention will be described below in detail by way of specific examples based on the accompanying drawings.
FIG. 1 is a diagram showing a schematic structure of an electrodialysis apparatus used in the present invention,
FIG. 2 is a diagram showing a schematic structure showing another embodiment of the electrodialysis apparatus used in the present invention,
Furthermore, FIG. 3 is a schematic diagram for explaining the principle of electrodialysis performed by the electrodialysis apparatus of FIG.

  In FIG. 1, the electrodialysis apparatus used in the present invention has a bipolar membrane B and an anion exchange membrane A disposed between an anode chamber 3 having an anode 1 and a cathode chamber 7 having a cathode 5. The negative electrode side chambers 11 and the positive electrode side chambers 12 are alternately formed from the side toward the anode 1 side. In the example of FIG. 1, six bipolar membranes B and five anion exchange membranes A are alternately arranged, and five positive electrode side chambers 12 and negative electrode side chambers 11 are alternately arranged. The number n of the positive electrode side chamber 12 and the negative electrode side chamber 11 formed in this way is not limited to this, and the number n is usually in the range of about 1 to 100. Although omitted in FIG. 1, the surface of the bipolar membrane B on the anode 1 side is formed of an anion exchange membrane, and the surface of the cathode 5 side is formed of a cation exchange membrane. In FIG. 1, the membrane in contact with the positive electrode chamber 3 and the negative electrode chamber 7 is a bipolar membrane, but an anion exchange membrane or a cation exchange membrane may be used as appropriate depending on the usage form.

  In such an electrodialysis apparatus, an aqueous electrolyte solution in which an electrolyte salt such as sodium sulfate, sodium nitrate, and sodium hydroxide is dissolved is accommodated in the anode chamber 3 and the cathode chamber 7 as a polar solution, or is circulated and supplied. The present invention uses such an electrodialysis apparatus, supplies a metal ion-containing inorganic acid drainage described later as a treatment liquid to the negative electrode side chamber 11, and uses water or a high-purity inorganic acid aqueous solution as a recovery medium liquid for the positive electrode side chamber. 12, and in this state, a predetermined voltage is applied between the anode 1 and the cathode 5 to perform electrodialysis. As a result, the recovery medium liquid in the positive electrode side chamber 12 is converted into a high-purity inorganic acid. It can be recovered as an aqueous solution.

  Further, as shown in FIG. 2, the electrodialysis apparatus used in the present invention partitions between bipolar membranes B by a plurality of anion exchange membranes A, and includes at least one intermediate chamber between the positive electrode side chamber 12 and the negative electrode side chamber 11. A structure in which 13 is formed can also be adopted. With such a structure, the leakage of metal ions leaking from the negative electrode side chamber 11 can be reduced over a plurality of stages by the anion exchange membrane, which is preferable. It is preferable that the thickness of the intermediate chamber 13 is smaller than the thickness of the positive electrode side chamber 12 and the negative electrode side chamber 11 to prevent the cell voltage from rising.

  In such an electrodialysis apparatus, a metal ion-containing inorganic acid drainage solution is supplied to the negative electrode side chamber 11 as a treatment liquid, and water or a high-purity inorganic acid aqueous solution is used as a recovery medium liquid to collect the positive electrode side chamber 12, the anion exchange membrane, and the anion. It is supplied to a chamber 13 partitioned by an exchange membrane.

The principle of such electrodialysis will be briefly described below with reference to FIG.
That is, when a hydrofluoric acid drainage containing Fe ions (Fe ²⁺ ) is used as a treatment liquid and a hydrofluoric acid aqueous solution not containing Fe ions is used as a recovery medium liquid, for example, by applying a voltage, For example, bipolar membrane B takes in water (H ₂ O) in an aqueous solution, releases anions (OH ⁻ ) on the anion exchange membrane surface side, and releases protons (H ⁺ ) on the cation exchange membrane surface side of bipolar membrane B. To do. Since the bipolar membrane B is partitioned by the anion exchange membrane A, the conjugate base (F ⁻ ) in the treatment liquid in the negative electrode side chamber 11 moves from the negative electrode side chamber 11 through the anion exchange membrane A to the positive electrode side chamber 12. Become. At this time, the Fe ions remain in the negative electrode side chamber 11 as they are. Therefore, by continuously performing such electrodialysis, the hydrofluoric acid concentration in the treatment liquid in the negative electrode side chamber 11 gradually decreases, and the hydrofluoric acid concentration in the recovery medium liquid in the positive electrode side chamber 12 gradually increases. . Thus, by performing electrodialysis for a certain period of time, the recovery medium solution can be recovered as a higher-concentration, high-purity hydrofluoric acid aqueous solution.

  In the present invention, the inorganic acid aqueous solution used as the treatment liquid is a used inorganic acid aqueous solution used as an etching liquid in, for example, a semiconductor manufacturing process or an acid cleaning process of a metal material, and is transmitted through a nanofilter or the like. It is recovered by removing the solid content by processing with a microfilter, and contains various metal ions such as Fe ions. In the present invention, in principle, the kind of inorganic acid is not particularly limited as long as it is an aqueous solution of such an inorganic acid, and a high-purity inorganic acid aqueous solution with a reduced metal ion content is recovered as a recovery medium liquid. be able to.

Of the inorganic acids, hydrofluoric acid is particularly suitable. When a hydrofluoric acid drainage containing metal ions such as Fe ions is used as the treatment liquid, the most efficient high-purity hydrofluoric acid aqueous solution should be recovered. Can do. That is, hydrofluoric acid (HF) dissociates in water as shown by the following formula, and F ⁻ forms a hydrogen bond with HF to generate HF ₂ ^-1 .
HF = H ⁺ + F ⁻
(Dissociation constant K ¹ = [H ⁺ ] [F ⁻ ] / [HF] = 7.4 × 10 ⁻⁴ )
F ⁻ + HF = HF ₂ ⁻
(Dissociation constant K ² = [HF ₂ ⁻ ] / [HF] [HF ⁻ ] = 4.7)
The dissociation constants K ¹ and K ² are measured values at 25 ° C.

As can be understood from this, during the hydrofluoric acid aqueous solution, a part dissociated F ^- is HF ₂ ^- behaves as, HF ₂ ^- move from the negative electrode side chamber 11 in the form of the positive electrode side chamber 12. That is, two F elements move with respect to the movement of one anion, and the current efficiency apparently doubles. Further, HF on the positive electrode side chamber 12 side is a weak acid, and very little H + moves from the positive electrode side chamber 12 to the negative electrode side chamber 11 side. For this reason, by using hydrofluoric acid drainage as the treatment liquid, electrodialysis is performed with a current efficiency exceeding 100%, and the concentration of hydrofluoric acid in the recovery medium liquid is increased efficiently, resulting in a high-purity hydrofluoric acid aqueous solution. It is possible to recover from the positive electrode side chamber 12.

  Furthermore, in the present invention, when metal ion-containing hydrofluoric acid drainage is used as the treatment liquid, the concentration of hydrofluoric acid in the treatment liquid in the negative electrode side chamber 11 is maintained in the range of 0.25 mol / L or more, particularly 2 mol / L. It is optimal to perform electrodialysis while ensuring high current efficiency. That is, FIG. 4 shows the hydrofluoric acid concentration and current when electrodialysis was performed by supplying hydrofluoric acid aqueous solutions having various hydrofluoric acid concentrations to the negative electrode side chamber 11 as the treatment liquid (refer to Experimental Example 1 described later for detailed conditions). It is the figure which showed the relationship with efficiency. According to FIG. 4, it is understood that when the concentration of hydrofluoric acid is increased to 0.25 mol / L or more, the current efficiency rapidly increases, and when it is 2 mol / L or more, the current efficiency reaches about 200%.

Thus, the present inventors have estimated that the high current efficiency can be obtained by setting the hydrofluoric acid concentration in a certain range as follows.
That is, three types of dissociated ion species, H ⁺ , F ⁻ , and HF ₂ ⁻ are present in the hydrofluoric acid aqueous solution. In such a form, in the low concentration region where the hydrofluoric acid concentration is lower than 0.25 mol / L, the amount of HF ₂ ⁻ is small, and a state of simple dissociation between H ⁺ and F ⁻ is obtained. For this reason, most of the conjugate bases move in the form of F ⁻ and the current efficiency is about 100%. On the other hand, in a high concentration region where the hydrofluoric acid concentration is 0.25 mol / L or more, HF ₂ ⁻ is dominant, and when it is 2 mol / L or more, most of the conjugate base is HF ₂ ⁻ . For this reason, the current efficiency approaches 200% as the concentration of hydrofluoric acid increases, and reaches about 200% at 2 mol / L or more. Thus, in the present invention, a hydrofluoric acid drainage solution having a hydrofluoric acid concentration within the above range is used as a treatment solution, and when the hydrofluoric acid concentration decreases with the progress of electrodialysis, the treatment solution (or hydrofluoric acid) is appropriately used. By replenishing and continuing the electrodialysis while maintaining the hydrofluoric acid concentration in the treatment liquid within the above range, the electrodialysis can be performed with high current efficiency.

In the present invention, if the hydrofluoric acid concentration becomes higher than necessary, the current efficiency tends to decrease again. Therefore, the hydrofluoric acid concentration is preferably 10 mol / L or less at the highest. That is, as the concentration of hydrofluoric acid further increases, HF gradually becomes a strong proton donor, and in a state close to anhydrous, where a trace amount of water is present, a trace amount of water is ideally dissociated, and H ₂ F is obtained as follows. ⁺ Produces.
^{_{HF + H 2 O = H 3}} O + + F ^{over
_{HF + HF = H 2 F +}} + F ^over

  That is, when the concentration of hydrofluoric acid is higher than 10 mol / L, the current efficiency decreases again. Therefore, in the present invention, the hydrofluoric acid concentration is preferably within the above range in order to ensure high current efficiency.

  In the present invention, the metal ion concentration in the inorganic acid drainage used is not particularly limited. However, when metal ions are contained at a very high concentration, the metal ions leak into the positive electrode side chamber 12. There is a risk. Further, there is a possibility that hydroxide ions and hydroxides generated from the bipolar membrane are generated in the negative electrode side chamber 11 to block the flow path of the negative electrode side chamber. Therefore, the metal ion concentration is generally suppressed to 1000 ppm or less, preferably 100 ppm or less. That is, if the inorganic acid drainage to be treated contains metal ions at a high concentration, the metal ion concentration is reduced to the above range in advance by pretreatment with an ion exchange resin or the like. After that, it is preferable to carry out the treatment according to the invention.

  In the present invention, the recovery medium liquid supplied into the positive electrode side chamber 12 is water or an aqueous solution of the same kind of inorganic acid as that of the treatment liquid. In particular, the recovered high-purity inorganic acid aqueous solution is reused. In view of the properties, it is preferable to use an aqueous solution of the same kind of inorganic acid as the treatment liquid (that is, an unused aqueous solution of inorganic acid).

  In the electrode dialysis apparatus having the structure shown in FIG. 1 described above, a known electrode can be used as the electrode. For example, platinum, titanium / platinum, carbon, nickel, ruthenium / titanium, iridium / titanium, etc. are used as the anode 1, and iron, nickel, platinum, titanium / platinum, carbon, stainless steel, etc. are used as the cathode 5. used. Also, the structure of such an electrode may be a known structure per se, and may have an arbitrary structure such as a mesh shape or a lattice shape.

  The bipolar membrane B used in such an apparatus is not particularly limited, and a known bipolar membrane having a structure in which a cation exchange membrane and an anion exchange membrane are bonded together can be used. The cation exchange membrane surface of B faces the cathode 5 side, and the anion exchange membrane surface faces the anode 2 side.

Such a bipolar membrane B is manufactured by various known methods. For example, the following method can be mentioned as such a manufacturing method.
A method of adhering a cation exchange membrane and an anion exchange membrane with a mixture of polyethyleneimine-epichlorohydrin and curing and bonding (Japanese Patent Publication No. 32-3962), a method of adhering a cation exchange membrane and an anion exchange membrane with an ion exchange adhesive (Japanese Examined Patent Publication No. 34-3961), a method in which a cation exchange membrane and an anion exchange membrane are pressure-bonded by sandwiching a coating layer of a fine powdered ion exchange resin, or a paste-like mixture of an anion or cation exchange resin and a thermoplastic substance (special No. 35-14531), a method of applying a paste-like substance composed of vinylpyridine and an epoxy compound on the surface of a cation exchange membrane, and irradiating this with radiation (Japanese Examined Patent Publication No. 38-16633), on the surface of an anion exchange membrane A method of cross-linking by irradiating ionizing radiation after adhering sulfonic acid type polymer electrolyte and allylamines 51-4113), a method of depositing a mixture of a dispersion of an ion exchange resin having an opposite charge and a base polymer on the surface of an ion exchange membrane (Japanese Patent Laid-Open No. 53-37190), styrene, divinylbenzene on a polyethylene film A sheet-like material impregnated and polymerized is sandwiched between stainless steel frames, one side is sulfonated, the sheet is removed, the remaining part is chloromethylated, and then aminated (U.S. Pat. No. 3,562,139), a method in which specific metal ions are applied to the surfaces of an anion exchange membrane and a cation exchange membrane, and both the ion exchange membranes are stacked and pressed (Electrochemica Acter Vol. 31, 1175 to 1176) Page, 1986).

  In addition, the base material of the bipolar membrane B varies depending on the type of cation exchange membrane or anion exchange membrane to be joined, but generally heat such as polyethylene, polypropylene, polyvinyl chloride, styrene-divinylbenzene copolymer, etc. Plastic resin films, nets, knitted fabrics, woven fabrics, non-woven fabrics and the like are used.

  The cation exchange group of the cation exchange membrane constituting the bipolar membrane B is not particularly limited, and may be a known cation exchange group such as a sulfonic acid group or a carboxylic acid group. In particular, from the viewpoint of application of the bipolar membrane B in the present invention, a sulfonic acid group in which an exchange group is dissociated even under an acidic condition is preferable. Also, the anion exchange group of the anion exchange membrane constituting the bipolar membrane B is not particularly limited. For example, known anion exchange such as ammonium base, pyridinium base, primary amino group, secondary amino group, tertiary amino group, etc. It may be a group. Particularly preferred is an ammonium base in which the exchange group is dissociated even under basic conditions.

  The anion exchange membrane A used in the electrodialyzer is not particularly limited, and a known anion exchange membrane can be used. For example, anion exchange is performed on a substrate sheet (having a form of nonwoven fabric, net, porous sheet, etc.) made of polyolefin such as polyvinyl chloride, polyethylene, polypropylene, polybutene, or a copolymer or blend thereof. A resin-provided one is used, and like the anion exchange membrane of the bipolar membrane B, the anion exchange group is not limited, and known ammonium base, pyridinium base, primary amino group, secondary amino group, tertiary amino group, etc. The anion exchange group of

  In addition, the negative electrode side chamber 11 and the positive electrode side chamber 12 are provided with a spacer member having a form such as a granular material, a non-woven fabric, and a net so as to ensure appropriate liquid permeability, if necessary. It is also possible to reliably prevent contact with the anion exchange membrane A.

  In electrodialysis using the electrodialysis apparatus as described above, the treatment liquid is supplied to each negative electrode side chamber 11 using a branch pipe. In this case, the treatment can be carried out in a so-called batch system in a state where a predetermined amount of treatment liquid is supplied to the negative electrode chamber 11, but in general, electrodialysis is performed while circulating the treatment liquid in each negative electrode chamber 11. Good. In addition, when using hydrofluoric acid drainage as the treatment liquid, the treatment liquid is appropriately replenished according to the decrease in the hydrofluoric acid concentration accompanying the progress of electrodialysis, and the electrodialysis is performed while maintaining the hydrofluoric acid concentration within the predetermined range described above. It is good to do.

  Further, in the electrodialysis, the polar liquid in the anode chamber 3 and the cathode chamber 7 and the recovery medium liquid in the positive electrode side chamber 12 are preferably circulated and supplied.

The temperature of each solution during electrodialysis is usually in the range of 5 to 80 ° C., particularly 20 to 60 ° C., and the current density is not particularly limited, but is generally 0.1 to 50 A / dm ² , particularly 1 to It is about 20 A / dm ² .

  In principle, the electrodialysis described above can be carried out for a long time to move most of the conjugate base in the treatment liquid into the positive electrode side chamber 12 and recover a high-purity inorganic acid aqueous solution at a higher concentration. However, if electrodialysis is performed for an excessively long time, metal ions in the treatment liquid may leak into the positive electrode side chamber 12, and the metal ion concentration may exceed an allowable range. Therefore, when the metal ion concentration in the recovery medium liquid reaches the allowable limit, or before that, electrodialysis should be temporarily stopped, and the recovery medium liquid (high-purity inorganic acid aqueous solution) should be recovered from the positive electrode side chamber 12. .

  The high-purity inorganic acid aqueous solution recovered as described above has a remarkably low level of metal ions, so it can be reused for applications that dislike metal ions, such as semiconductor manufacturing processes and metal material acid cleaning processes. Can be used.

Hereinafter, although an example and a comparative example explain the present invention still in detail, the present invention is not limited to these examples.
In the examples and comparative examples, the specifications of the electrodialyzer 4 chamber cell used are as follows.

4-chamber cell: effective membrane area 10 cm ² / sheet bipolar membrane B; manufactured by Astom Co., Ltd., Neoceptor BP-1E
Anion exchange membrane: AHA made by Astom Co., Ltd.
Cation exchange membrane: Astom Co., Ltd., CMB

<Experimental example 1>
Using a four-chamber cell, 100 ml of a hydrofluoric acid aqueous solution (metal ion content: 0 ppm) having a hydrofluoric acid concentration shown in Table 1 below was supplied to the negative electrode side chamber 11. Also, 100 ml of the same solution was supplied to the positive electrode side chamber 12, and 1 mol / l sodium hydroxide was supplied to the anode chamber 3 and the cathode chamber 7, respectively.
In this state, electrodialysis was performed by energizing under the conditions shown in Table 1, and the current efficiency for F ⁻ was determined. The results are also shown in Table 1, and the relationship between hydrofluoric acid concentration and current efficiency is shown in FIG. The current efficiency was determined as follows.

Current efficiency:
(HF amount [meq] of 12 rooms after energization−HF amount [meq] of 12 rooms before energization) / (total coulomb amount flowed by energization))

  From the above results, it can be seen that when the hydrofluoric acid concentration is 0.25 mol / L or more, the current efficiency increases rapidly, and when it is 2.0 mol / L or more, the current efficiency reaches about 200%.

<Example 1>
A four-chamber cell was used as the electrodialyzer.
As a treatment liquid, 100 mL of a 4.82 mol / L hydrofluoric acid aqueous solution (containing 1.22 ppm Fe in the form of FeCl ₂ ) is supplied to the negative electrode side chamber 11, and the positive electrode side chamber 12 does not contain 4.82 mol of Fe. 100 mL of a hydrofluoric acid aqueous solution of / L hydrofluoric acid (that is, Fe content of 0 ppm) was supplied as a recovery medium liquid. Further, as in Experimental Example 1, sodium hydroxide was supplied to the anode chamber 3 and the cathode chamber 7. The circulating supply amounts of the treatment liquid, the recovery medium liquid, and the polar liquid were exactly the same as in Experimental Example 1.

In this state, electrodialysis was performed by applying a current of 0.5 A for 2 hours. After electrodialysis, the hydrofluoric acid concentration and Fe concentration of the treatment liquid and the recovery medium liquid were measured, and the results are shown in Table 2.
At this time, the diffusion leak rate of Fe (the rate of transfer of Fe from the treatment liquid to the recovery medium liquid) was about 6%, and the current efficiency was about 200%.

<Comparative Example 1>
As the electrodialyzer, a four-chamber cell in which a cation exchange membrane was provided between bipolar membranes was used.
As a treatment liquid, 100 mL of a 4.78 mol / L hydrofluoric acid aqueous solution (containing 1.22 ppm Fe in the form of FeCl ₂ ) is supplied to the positive electrode side chamber 12, and the negative electrode side chamber 12 has the same concentration but contains Fe. 100 mL of a non-hydrofluoric acid aqueous solution was supplied. Further, as in Experimental Example 1, sodium hydroxide was circulated and supplied to the anode chamber 3 and the cathode chamber 7. The current and energization time were exactly the same as in Experimental Example 1.

In this state, electrodialysis was performed by applying a current of 0.5 A for 2 hours, and after electrodialysis, the hydrofluoric acid concentration and Fe concentration of the treatment liquid and the circulating liquid to the negative electrode side chamber were measured. Indicated.
In addition, the current efficiency about Fe at this time was about 0.03%.

The figure which shows schematic structure of the electrodialysis apparatus used for this invention. The figure which shows schematic structure which shows the other aspect of the electrodialysis apparatus used for this invention. The schematic diagram for demonstrating the principle of the electrodialysis performed with the electrodialysis apparatus of FIG. It is a figure which shows the relationship between the hydrofluoric acid density | concentration of the hydrofluoric-acid aqueous solution used as a process liquid, and current efficiency.

Explanation of symbols

B: Bipolar membrane A: Cation exchange membrane 11: Negative electrode side chamber 12: Positive electrode side chamber 13: Intermediate chamber

Claims (5)

  A bipolar membrane and an anion exchange membrane are disposed between the positive electrode and the negative electrode, and are formed by partitioning the bipolar membrane with an anion exchange membrane. An inorganic acid drainage containing metal ions is supplied as a treatment liquid to the negative electrode side chamber, and a recovery medium liquid consisting of water or a high-purity inorganic acid aqueous solution is supplied to the positive electrode side chamber. By performing electrodialysis in this state, the conjugate base is selectively transferred from the negative electrode side chamber to the positive electrode side chamber to increase the concentration of the inorganic acid in the recovery medium liquid, and the high purity inorganic acid aqueous solution is recovered from the positive electrode side chamber. A high-purity inorganic acid recovery method, characterized in that   The method for recovering a high-purity inorganic acid according to claim 1, wherein the electrodialysis apparatus partitions the bipolar membrane with a plurality of anion exchange membranes to form at least one intermediate chamber between the positive electrode side chamber and the negative electrode side chamber.   The method for recovering a high-purity inorganic acid according to claim 1, wherein a hydrofluoric acid aqueous solution is used as the inorganic acid.   The method for recovering a high-purity inorganic acid according to claim 3, wherein electrodialysis is performed while maintaining the concentration of hydrofluoric acid in the treatment liquid at a concentration of 0.25 mol / L or more.   The method for recovering a high purity inorganic acid according to claim 4, wherein electrodialysis is performed while maintaining the hydrofluoric acid concentration in a range of 0.25 to 10 mol / L.

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