JPH05309378A - Treatment of waste fluid containing cod-donating substance - Google Patents

Abstract

PURPOSE:To efficiently, certainly and simply subject a COD-donating substance to oxidizing treatment with good handleability by electrolyzing a solution to be treated with a pH value of 5 or more prepared by dissolving salt in a waste fluid containing a COD-donating substance to form hypochlorous acid and oxidizing the COD donating substance in a liquid phase by hypochlorous acid. CONSTITUTION:Salt is dissolved in a waste fluid containing a COD donating substance such as a hypophosphorous ion, a phosphorous ion or an org. acid, typically, a waste electroless plating solution containing a hypophosphorous ion as a reducing agent to prepare a solution 2 to be treated, which is, in turn, hydrolyzed in an electrolytic cell 1 equipped with an anode 8 and a cathode 9. In this case, the pH value of the solution 2 to be treated prepared by dissolving salt in the waste fluid is adjusted to 5 or more and this solution 2 to be treated is hydrolyzed to immediately form hypochlorous acid and the COD donating substance is efficiently and certainly oxidized by hypochlorous acid.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to hypophosphite ions and phosphite ions in electroless plating solution waste solutions containing hypophosphite as a reducing agent, or COD such as organic acids or salts thereof.
It relates to a method for treating a waste liquid containing a donor substance.

[0002]

2. Description of the Related Art An electroless plating solution (typically an electroless nickel plating solution) using hypophosphite as a reducing agent is used for plating by reducing action of hypophosphite ion. The metal ion in the liquid is reduced and precipitated, and the hypophosphite ion is oxidized to the phosphite ion. Therefore,
The concentration of metal ions and hypophosphite ions in the plating solution decreases as the plating reaction progresses, which causes problems such as a decrease in the deposition rate and changes in the physical properties of the deposited film. In addition, the plating solution is continuously used by replenishing metal ions and hypophosphite ions in accordance with the consumption of hypophosphite ions.

However, as described above, in the electroless plating solution using hypophosphite as a reducing agent, phosphite ions produced by the oxidation of hypophosphite ions gradually accumulate. Accumulation of a large amount of acid ions adversely affects the plating reaction in various ways, so that it is necessary to discard the plating solution.

As a method for removing the phosphite ion in the electroless plating solution waste solution using hypophosphite as a reducing agent, the waste solution is conventionally electrolyzed at a high current, and oxygen generated at the anode at that time is electrolyzed. By electrolysis of phosphorous acid to phosphoric acid
A method has been adopted in which ₂ O ₂ is added to a waste liquid to chemically oxidize phosphorous acid into phosphoric acid, and the resulting acid is neutralized and precipitated as calcium phosphate by adding CaCl ₂ or the like.

However, this method has a problem in that it efficiently and surely removes the phosphite ion, and the hypophosphite ion remaining in the waste solution of the electroless plating solution or the electroless plating solution remains. It is difficult to effectively remove the organic acid ions contained as the complexing agent.

[0006] Therefore, a waste liquid treatment method for efficiently and surely removing not only phosphorous acid ions but also COD-donating substances such as hypophosphite ions and organic acids, to reduce COD in the waste liquid as much as possible. It was requested to be established.

[0007]

Means and Actions for Solving the Problems As a result of intensive studies to meet the above-mentioned demands, the present inventor has found that a waste liquid containing a COD-donating substance such as hypophosphite ion, phosphite ion and organic acid, Typically, salt is dissolved in an electroless plating solution waste solution containing hypophosphite as a reducing agent, and this is electrolyzed in an electrolytic cell equipped with an anode and a cathode. In this case, salt solution is dissolved in the waste solution. By performing electrolytic treatment with the pH of the treatment liquid at 5 or more, hypochlorous acid is immediately generated, and the hypochlorous acid efficiently converts COD-donating substances such as hypophosphite ion, phosphite ion, and organic acid. It has been found that the method is well and reliably oxidized, and that this method is easy to handle as a method for removing COD-donor substances by oxidation, is simple, and can be industrially advantageously adopted.

Therefore, according to the present invention, sodium chloride is dissolved in a waste liquid containing a COD-donating substance, and a liquid to be treated whose pH is adjusted to 5 or more is electrolyzed in an electrolytic cell having an anode and a cathode,
Provided is a method for treating a waste liquid containing a COD-donating substance, which comprises subjecting the COD-donating substance to liquid-phase oxidation with the hypochlorous acid thus produced.

Thus, in the method of the present invention, CO
Dissolve the salt in the waste liquid containing the D-donating substance and adjust the pH to 6
Although electrolysis is performed in the above, when the liquid to be treated is electrolyzed, the following reaction (1) occurs in the anode and the cathode.
And (2) occur.

[0010]

[Chemical 1]

In this case, chlorine generated on the anode side is dissociated in the liquid to be treated as follows.

[0012]

[Chemical 2]

Here, the reactions of the above formulas (3) and (4) depend on the pH of the liquid to be treated, and as shown in FIG. The generated chlorine is immediately dissociated into HClO or ClO ⁻ in the liquid to be treated, chlorine gas is not substantially generated, and the chlorine dioxide in the liquid to be treated is oxidized by the oxidizing action of HClO or ClO ⁻ dissolved in the liquid to be treated. Phosphate ions are oxidized to phosphite ions or phosphate ions in a liquid phase reaction. During this reaction, HClO or ClO ⁻ is reduced to Cl ^−, but this Cl ⁻ is anodized to Cl ₂ .

Therefore, if the solution to be treated in which salt is dissolved and the pH is adjusted to 5 or higher is electrolyzed, HClO or ClO ⁻ is immediately produced in the solution to be treated, and hypophosphite ions in the liquid phase, Since COD-donating substances such as phosphite ions and organic acids are oxidized by chlorine, they can be easily removed as compared with ordinary electrolytic treatment methods.

In this case, although the oxidation method of the COD-donating substance is chlorine oxidation, it is different from the method of oxidizing the COD-donating substance by adding chlorine or hypochlorite to the waste liquid which is troublesome to handle. Hypochlorous acid is generated only by adding salt and adjusting pH and electrolyzing this, and chlorine gas is not substantially generated, so that it is easy to handle. In this method, chlorine is generated from chloride ion by electrolysis, and this chlorine is immediately dissociated into HClO and ClO ⁻ by the reaction of the above formulas (3) to (4) to oxidize chlorine. Chloride ions produced by the equation (3) and the oxidation reaction are subjected to the anodic reaction of the equation (1), and since chlorine gas is not substantially generated as described above, the chloride ions are substantially consumed. For this reason, it is only necessary to dissolve the salt in the waste liquid at the time of processing, and the management is easy. Furthermore, according to this method, both a batch method and a continuous method are possible, and scale-up can be easily performed.

The present invention will be described in more detail below. In the method for treating a waste liquid containing a COD-donating substance such as hypophosphite ion, phosphite ion and organic acid according to the present invention, hypophosphite is used as a reducing agent. It is preferably used for treating a waste plating solution such as an electroless nickel plating solution.

In the treatment of such waste liquid, first, salt is added to the waste liquid to dissolve it, and the pH is adjusted to 5 or more. In this case, the amount of salt added is appropriately selected and is not particularly limited, but is usually in the range of 10 to 300 g / l, and more preferably in the range of 30 to 100 g / l. The pH may be 5 or more, and more preferably 5.5 to 8. The pH of the waste liquid was originally 5
In the above case, it is only necessary to dissolve the salt in this, but when the pH of the waste liquid is lower than 5, it is necessary to add caustic soda to make the pH of the waste liquid 5 or higher.

Next, in the present invention, the waste liquid (solution to be treated) having a pH of 5 or more in which salt is dissolved is electrolyzed in an electrolytic cell equipped with an anode and a cathode. In this case, the materials of the anode and the cathode are not particularly limited, but an insoluble anode such as graphite, platinum group metal or titanium coated with a platinum group metal oxide is preferable. Also, various materials such as nickel and stainless steel can be used as the cathode.

The electrolysis current is appropriately selected, but usually the anode current density (D _A ) is 5 to 100 _A / dm ² , particularly 20 to 5
It is preferably 0 A / dm ² . In this case, when the liquid to be treated contains metal ions, the area of the cathode is adjusted and the cathode current density is set high, that is, the current density is set equal to or higher than the limiting current density corresponding to the metal ion concentration. It is reduced to a powder form to prevent it from sticking to the cathode,
It is preferable to promote hydrogen generation and suppress the deposition of metal or hydrated oxide on the cathode. The treatment time is appropriately set according to the concentration of the COD-donating substance in the waste liquid and the like (the energizing amount is approximately proportional to the content of the COD-donating substance).

The structure of the electrolytic cell is not limited, and for example, an electrolytic cell having a partition between the anode and the cathode may be used. However, since the stirring effect of hydrogen gas generated at the cathode is effectively used, It is recommended to use a diaphragm-free electrolytic cell in which the cathode is not separated by a diaphragm. It is preferable to stir the liquid to be treated. Therefore, the electrolytic cell can be provided with a stirrer such as air stirrer or mechanical stirrer. Especially, when the anode and the cathode are separated by a diaphragm, It is preferable to attach a stirring device to the chamber side, but using a diaphragmless electrolytic cell,
When the stirring effect by the hydrogen gas as described above is expected, the stirring device may not be attached.

FIG. 1 shows an example of an apparatus for carrying out the method of the present invention. In FIG. 1, reference numeral 1 designates a relatively tall bottomed cylindrical electrolytic cell. The partition plate 3 is arranged so as to be spaced apart and below the liquid surface of the liquid to be treated 2 that is to be put into the electrolytic bath 1, whereby the inside of the electrolytic bath 1 is divided into an electrolytic chamber 4 and a flow chamber 5. Has been done. The electrolytic chamber 4 and the flow chamber 5 have a space (upper space) 6 between the partition plate 3 and the liquid surface of the liquid to be treated 2 and the partition plate 3 and the electrolytic cell wall 1.
And (interval on the lower side) 7 communicate with each other. And
Inside the electrolysis chamber 4, an anode 8 and a cathode 9 are provided on the lower side thereof, respectively, and the anode 8 and the cathode 9 are connected to a DC power source (not shown).

When the liquid to be treated 2 is electrolyzed using this apparatus, chlorine is produced at the anode as described above (oxygen is also a by-product depending on the conditions), and this chlorine is immediately converted into HClO.
And ClO ⁻ to act to oxidize the COD donor, while hydrogen gas is generated from the cathode. This hydrogen gas becomes bubbles and rises while stirring the liquid to be treated 2 and escapes from the liquid surface of the liquid to be treated 2. At this time, the liquid to be treated 2 also rises along with the hydrogen gas, and the liquid to be treated 2 from which the hydrogen gas has escaped is
The liquid to be treated 2 in the flow chamber 5 flows into the electrolytic chamber 4 through the lower space 7 through the upper space 6. Therefore, the liquid to be treated 2 in the electrolysis chamber 4 is agitated by the hydrogen gas, rises as the hydrogen gas rises and escapes, and circulates and flows in the circulation chamber 5 and the electrolysis chamber 4 by a kind of pump action. .. Therefore, it is not necessary to separately provide a stirrer, and good processing is performed.

The apparatus for carrying out the method of the present invention is, of course, not limited to that shown in FIG. Further, the treatment method of FIG. 1 is a batch method, but the treatment can be continuously performed.

In the method of the present invention, the above formula (1),
As shown in (3) and (4), the active chlorine generated by the anodic reaction of chloride ions is immediately converted to hypochlorous acid, and the COD donor is oxidized by the action of this hypochlorous acid (for example, hypochlorous acid). It oxidizes phosphate ions to phosphite ions and phosphate ions). In this case, regarding the oxidation treatment of hypophosphite ion, the treatment may be terminated in a state where the hypophosphite ion is oxidized to the hypophosphite ion, or the hypophosphite ion is converted to the hypophosphite ion. It may be oxidized and stopped in the state of being further oxidized to phosphate ions (at this time, if the waste liquid contains phosphite ions, these are also oxidized to phosphate ions). At this time, thereafter, the treatment can be performed according to a usual treatment method.

[0025]

EXAMPLES The present invention will be specifically described below by showing Examples and Comparative Examples, but the present invention is not limited to the following Examples.

[Example 1] 1 M containing 8 g / l of malic acid
-Na ₂ SO ₄ solution (pH = 6 to 7) 16 liters fully to the electrolytic cell, and electrolysis was performed at room temperature MODE U a (stone Fu metallic IrO ₂ coated titanium electrode) an anode, a SUS 304 as a cathode. In this case, the pole interval was 10 mm. As a result, the concentration of malic acid was almost unchanged even when a current of 300 Ah was applied (line B in FIG. 3). Next, add 9 to the above solution.
When 00g of salt was added (NaCl concentration of about 1M / l) and electrolysis was performed again, the concentration of malic acid decreased almost along the theoretical line (current efficiency of about 100%, straight line A in FIG. 3), 1
Although it was slightly deviated from the theoretical line at g / l or less, the malic acid concentration in the liquid after energization of 325 Ah was 0 g / l. In addition,
The overall current efficiency at this time was 95%.

Example 2 The same experiment as in Example 1 was carried out for tartaric acid, succinic acid, and citric acid. As a result, as in the case of malic acid, when no salt was contained, no oxidative decomposition was caused. In the case of containing 1 M / l, all organic acids were decomposed with a current efficiency of 90% or more.

Therefore, it was found that the organic acid and its derivative or salt, which are widely used in the field of surface treatment technology such as electroless nickel plating, can be efficiently oxidatively decomposed by this method.

[Example 3] The same experiment as in Example 1 was carried out on a solution containing 30 g / l of sodium hypophosphite. As a result, when salt was not contained, almost no oxidation occurred (line D in Fig. 4). In a solution containing 1 M / l of sodium chloride, the solution decomposed to almost 5 g / l according to the theoretical value (line C in FIG. 4), and the NaHPO ₂ concentration in the solution after energization of 650 Ah was 0 g / l.

[Example 4] The same experiment as in Example 1 was carried out on a solution containing 150 g / l of sodium phosphite. As a result, almost no oxidation was observed in the absence of sodium chloride (line F in Fig. 5). In a solution containing 1 M / l of salt, it decomposed to almost 20 g / l according to the theoretical value (straight line E in FIG. 5), and Na ₂ HPO _{3 in} the solution after energization of 550 Ah.
The concentration was 0 g / l.

Example 5 1M containing 8 g / l of malic acid
A predetermined amount of sodium chloride was added to the Na ₂ SO ₄ solution, and Example 1 was added.
An experiment was conducted in the same manner as in, and the amount of electricity until malic acid was completely oxidized and decomposed was measured to calculate the current efficiency. As a result, as shown in FIG. 6, when the salt becomes 50 g / l or less, the current efficiency slightly decreases, but at 20 g / l, 84%, 10%.
Even in g / l, it was about 75%, and it was confirmed that this almost coincided with the chlorine generation current efficiency.

Similar results were obtained with a solution containing tartaric acid, succinic acid, citric acid, hypophosphite and phosphite.

As a result of changing the current density within the range of 5 to 100 A / dm ² , the current efficiency hardly changed depending on the current density when the salt concentration was 30 g / l or more.

Example 6 A mixed solution of malic acid (about 8 g / l), sodium hypophosphite (about 30 g / l) and sodium phosphite (about 150 g / l) was prepared in the same manner as in Example 1. Although electrolysis was carried out by the method, it was found that the COD did not change at all and did not undergo electrolytic oxidation (straight line H in FIG. 7). It decreased almost linearly with the amount of electricity applied up to 1, and the reaction rate decreased a little after that.
The COD after 0 Ah energization was almost 0 g / l (straight line G (white circle) in FIG. 7). The estimated current efficiency at this time is about 6
It was 8%.

After dissolving NiSO _{4 in the} above mixed solution (concentration: about 5 g / l), NaOH was added to adjust the pH to 7
The nickel hydrate oxide precipitate produced in step (1) was separated by a static method and filtration, and 30 g / l of salt was added to perform electrolysis. As a result, almost the same result as the above experiment was obtained (in FIG.
(△ mark)).

[0036]

INDUSTRIAL APPLICABILITY According to the present invention, the COD-donating substance in the waste liquid containing the COD-donating substance such as hypophosphite ion, phosphite ion and organic acid can be efficiently and reliably oxidized. Moreover, it provides a convenient and industrially advantageous waste liquid treatment method that is easy to handle.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing an example of an apparatus used for carrying out the present invention.

FIG. 2 is a graph showing the relationship between the Cl ₂ , HClO, and ClO ⁻ concentrations in a salt solution and pH when the salt solution is electrolyzed at various pHs.

FIG. 3 is a graph showing the relationship between the amount of electricity and the concentration of residual malic acid when electrolysis is performed with or without the addition of sodium chloride to a solution containing malic acid.

FIG. 4 is an amount of electricity and residual NaH ₂ when electrolysis is performed with or without addition of sodium chloride to a solution containing NaH ₂ PO ₂ .
Is a graph showing the relationship between PO ₂ concentration.

FIG. 5 Na₂H PO₃Or add salt to the solution containing
Electricity and residual Na when electrolyzing without adding₂H
PO₃It is a graph which shows the relationship with a density.

FIG. 6 is a graph showing the relationship between the salt concentration and the current efficiency when electrolysis is performed by adding salt in various amounts to a solution containing malic acid.

FIG. 7: Malic acid, NaH₂PO₂, Na₂H PO₃including
When electrolysis is performed with or without adding salt to the solution
3 is a graph showing the relationship between the amount of electricity and the COD concentration.

[Explanation of symbols]

 1 Electrolyzer 2 Liquid to be treated 3 Partition plate 4 Electrolysis chamber 8 Anode 9 Cathode

Claims (2)

[Claims] 1. Hypochlorous acid produced by dissolving salt in a waste liquid containing a COD-donating substance and electrolyzing a liquid to be treated whose pH is adjusted to 5 or more in an electrolytic cell equipped with an anode and a cathode. A method for treating a waste liquid containing a COD-donating substance, which comprises subjecting the COD-donating substance to liquid-phase oxidation with an acid. 2. The method according to claim 1, wherein the waste liquid containing the COD-donating substance is a waste liquid of an electroless plating solution containing hypophosphite as a reducing agent.