JPH06136549A - Treatment of hypophosphoric acid ion in aged plating liquid - Google Patents

Abstract

PURPOSE:To eliminate the harmfulness of hypophosphoric acid ions as phosphoric acid ions or calcium phosphate by subjecting an aged electroless plating liquid contg. a large amt. of the hypophosphoric acid ions to an oxidation treatment. CONSTITUTION:The aged liquid of the electroless plating liquid, such as electroless Ni plating liquid, contains the hypophosphoric acid ions of a high concn. and is inadequate as waste water in terms of eutrophication and chemical oxygen consumption and, therefore, the powder of TiO2 deposited with a noble metal, such as Pt, is added as a photocatalyst to this aged liquid in the state of maintaining the liquid at a pH 1 to 4 range at a ratio of, for example, 8g/l. While air or oxygen is blown into the liquid, the liquid is irradiated with UV rays by a high-voltage mercury lamp, by which the hypophosphoric acid ions are oxidized to the phosphoric acid ions or a Ca salt is added thereto to form the calcium phosphate. Such liquid is maintained at pH 1 to 3 and is filtered, by which the TiO2 catalyst deposited with the noble metal is recovered. The remaining liquid is reused after the phosphoric acid ions are removed. The remaining liquid is otherwise easily drained as the calcium phosphate-contg. liquid.

Description

Detailed Description of the Invention

[0001]

This invention relates to a plating aging solution,
Specifically, a plating aging solution that oxidizes the persistent hypophosphite ion contained as a reducing agent in the electroless plating aging solution and recovers the phosphate ion or disposes it as calcium phosphate by adding a calcium salt. The method of treating hypophosphite ions in the inside.

[0002]

2. Description of the Related Art Electroless plating is widely used as functional plating because it can uniformly and non-conductive material. Since the electroless plating solution uses hypophosphite ions as a reducing agent, its life is short and a large amount of aging solution is generated. Since this aging liquid contains a high concentration of hypophosphite ion, it needs to be treated in terms of eutrophication and chemical oxygen consumption.

Wastewater treatment of the phosphoric acid compound in the plating waste liquid is generally performed by adding chemicals. That is,
A method of adding a calcium salt to phosphite ions or phosphate ions to form sparingly soluble calcium phosphite or calcium phosphate and subjecting it to coagulation precipitation treatment is used. However, hypophosphite ion is difficult to treat because it is difficult to form a precipitate due to calcium salt. Therefore, a method of treating a phosphorus compound containing hypophosphite ion after once oxidizing it to phosphate ion is adopted.

In this oxidation method, a solution containing hypophosphite ions is heated to 90 ° C. or higher by steam, and metal salts such as nickel ions and cobalt ions are added to the solution to make hypophosphite ions phosphorous. Oxidize to acid ions, add calcium salt to this and treat as calcium phosphite,
There is, so to speak, an oxidation treatment method by the autolysis of hypophosphite ions.

As another oxidation method, there is an electrolytic oxidation method in which a solution containing hypophosphite ions is electrolyzed and the hypophosphite ions are oxidized to phosphate ions by oxygen generated at the anode.

As another oxidation method, hydrogen peroxide is added to a solution containing hypophosphite ions and irradiated with ultraviolet rays, and hypophosphite ions are converted into active acid species produced by decomposition of hydrogen peroxide. There is a combined use of hydrogen peroxide and ultraviolet rays that oxidize to phosphate ions.

[0007]

However, the self-decomposition method has a problem that the oxidation treatment effect is poor and it is difficult to reliably control oxidation. Since the electrolytic oxidation method requires a long processing time, it has a problem of high power cost and lack of economy. The combined use of ultraviolet rays and hydrogen peroxide has problems such as a large amount of hydrogen peroxide used as an oxidizing agent.

In any case, since there are many problems in the conventional oxidation method, the hypophosphite ion treatment is not carried out, but the treatment by ocean dumping is performed.

As a method for treating a plating waste liquid containing phosphite and its salt, Japanese Patent Laid-Open No. 63-274491 is known. In this method, phosphorous acid is oxidized by utilizing the photocatalyst's ability to oxidize holes.

However, this oxidizing method has a weak oxidizing power, and in this conventional example, since the processing is carried out by an oxidizing reaction, there is a problem that the processing time becomes long. Although no mention is made of the pH range, the plating aging liquid contains a large amount of heavy metals. When these heavy metals are deposited on the photocatalyst, there is a problem in that they hinder the reaction. Further, although the used photocatalyst is not recovered, it is difficult to say that it is economical unless it is reused, and there is a problem of recovery and reuse.

On the other hand, the inventor wonders how to generate and use active oxygen species in order to effectively oxidize the hypophosphite ion in the electroless plating aging solution. It was examined to effectively oxidize.
As a result, it was found that the photocatalyst and oxygen coexist in the acidified aging liquid, and the light irradiation can efficiently oxidize in a short time.

[0012]

Means for Solving the Problems The present invention is based on these findings,

A plating aging solution containing hypophosphite ions is added
Keeping H1 to 4 and coexisting with titanium dioxide powder carrying a noble metal as a photocatalyst, irradiating light while blowing oxygen or air into the aging solution to oxidize hypophosphite ions to phosphate ions, and then to adjust pH. A method for treating hypophosphite ions in a plating aging liquid, characterized in that a titanium dioxide powder carrying a noble metal is recovered by keeping it at 1 to 3 and filtering,

[0014]

[0015]

Example The pH of the electroless plating aging solution containing hypophosphite ions is kept at 1 to 4, and titanium dioxide powder carrying a noble metal is allowed to coexist as a photocatalyst at room temperature. At the same time, while blowing oxygen or air into the aging liquid, ultraviolet rays are irradiated by a high pressure mercury lamp having a main wavelength of 365 nm to oxidize hypophosphite ions into phosphate ions. Next, the pH of the treated water containing the photocatalyst is maintained at 1 to 3 and filtered to recover the titanium dioxide powder carrying the noble metal and reuse it.

When a photocatalyst such as titanium dioxide (TiO ₂ ) in an aqueous solution is irradiated with light having energy higher than the band cap, the electrons in the valence band of titanium dioxide are excited and move to the conduction band, and the positive valence band is detected. It is divided into holes and electrons in the conduction band. Then, holes in the valence band and water generate hydroxyl radicals by an oxidation reaction. On the other hand, electrons in the conduction band and hydrogen ions generate hydrogen by a reduction reaction.

Generally, active oxygen species of hydroxyl radicals generated by the oxidation reaction of holes are used as an oxidizing agent, but the oxidizing power is small. On the other hand, in this embodiment, titanium dioxide is partially supported by a noble metal such as platinum or silver to improve charge separation, and oxygen or air is blown into the titanium dioxide to generate hydrogen peroxide in the conduction band due to oxygen reduction reaction. The active oxygen species of radicals are mainly used as an oxidizing agent to oxidize hypophosphite ions to phosphate ions.

The oxidation reaction is carried out in the pH range of 1-4. This is because the electroless plating aging solution contains a large amount of heavy metals such as nickel ions, so that when the pH increases, the heavy metals are prevented from precipitating on the surface of the photocatalyst and inhibiting the oxidation reaction.

The irradiation of light is preferably ultraviolet irradiation, and more preferably irradiation of a high pressure mercury lamp having a main wavelength of 365 nm. That is, using a low-pressure mercury lamp (13 W) having a main wavelength of 250 to 260 nm and a high-pressure mercury lamp (400 W) having a main wavelength of 365 nm, 1 g / l of titanium dioxide was added as a photocatalyst to obtain 1000 mg / l of hypophosphorous acid. When the relationship between the oxidation rate of oxidizing the acid ions to phosphate ions and the oxidation time was examined, it was found that when a high pressure mercury lamp was used,
Although it was oxidized 100% in about 110 minutes, only 5% of the oxidation reaction proceeded in 110 minutes with the low pressure mercury lamp. In a low-pressure mercury lamp, it is considered that when the amount of suspended matter increases, the light is blocked due to the short wavelength and the oxidation effect is reduced.

Air or oxygen is blown into the oxidation. That is, 300 ml of an electroless plating aging solution having a hypophosphite ion concentration of 1000 mg / l was taken and 8 g / l of titanium dioxide was used as a photocatalyst while blowing air at 3 l / min.
It was added and irradiated with a high pressure mercury lamp. As a result, it took 70 minutes to completely oxidize to 100% phosphate ion. When nitrogen was blown in instead of air, no oxidation reaction was shown.

Further, the change in the amount of air blown and the oxidation end time were determined. As a result, it was found that the oxidation time was shorter when the amount of air blown was larger. If it is 3 l / min or more, the oxidation reaction time cannot be shortened so much. This is probably because titanium dioxide could not be effectively diffused due to the structure of the experimental apparatus, and the oxidation reaction did not proceed.

Titanium dioxide is used as the photocatalyst. That is, the hypophosphite ion concentration is 1000 mg / l
300ml of electroless plating aging liquid of
The oxidation reaction time and the abundance ratios of various phosphate ions produced by the reaction were investigated in the case of irradiation with only a high-pressure mercury lamp while blowing at min, and in the case of irradiation with titanium dioxide of 8 g / l as a photocatalyst. As a result, it took 3 hours and 20 minutes to oxidize to 100% phosphate ions when only high-pressure mercury lamp irradiation was performed. On the other hand, when titanium dioxide was coexisted as a photocatalyst for irradiation, it was completely oxidized in 70 minutes.

It was also found that in the course of oxidation of hypophosphite ion to phosphate ion, phosphite ion is produced and oxidized to phosphate ion. When a high-pressure mercury lamp is irradiated in the presence of oxygen and titanium dioxide, the oxidation reaction proceeds effectively, so that hypophosphite ion is oxidized to phosphate ion.

The amount of the photocatalyst added was found out below. That is, when only titanium dioxide was used as a photocatalyst in a solution containing a hypophosphite ion concentration (pH 5.2) of 1000 mg / l, and when platinum-supported titanium dioxide was used, the addition amount and the oxidation completion time of each were determined. I investigated the relationship. In the case of titanium dioxide alone, or in the case of platinum-supported titanium dioxide, the larger the added amount, the shorter the oxidation reaction proceeds,
The optimum addition amount was 8 g / l for both. When titanium dioxide alone was used, the oxidation completion time was 70 minutes, and when platinum-supported titanium dioxide was used for 45 minutes, it was possible to perform the oxidation treatment in a shorter time using platinum-supported titanium dioxide. Both are 8
The oxidation completion time was almost constant even if g / l or more was added. It is considered that this is because titanium dioxide has a high specific gravity of 3.9, and while stirring, a part of the titanium dioxide does not disperse and precipitates at the bottom of the reactor.

After the completion of the oxidation, the treated water and the photocatalyst are separated at a pH of 3 or less by filtration to reuse the photocatalyst. When the pH is 3 or less, the photocatalyst has good cohesiveness, and separation is easy to occur. The effect is the same even if the photocatalyst is repeatedly used.

Example 1

A solution prepared by adding 82.2 mmol / 1 of nickel sulfate as a metal salt to a sodium hypophosphite solution containing 1000 mg / l of hypophosphite ion was kept at pH 3 for oxidation treatment. 300 ml of the solution was placed in an internal irradiation type photochemical reaction device for a volume of 300 ml, and 8 g / l of platinum-supported titanium dioxide powder was allowed to coexist in this, and irradiation with a high pressure mercury lamp was performed while blowing air at a rate of 31 / min. Was able to oxidize to 100% phosphate ion.

Example 2

Using a commercially available electroless nickel plating solution, a solution diluted to a hypophosphite ion concentration of 1000 mg / l was maintained at pH 2.5 for oxidation treatment. Put 300 ml of the solution into the internal irradiation type photochemical reactor for the volume of 300 ml,
Platinum-supported titanium dioxide powder was allowed to coexist therewith in an amount of 8 g / l, and irradiation with a high-pressure mercury lamp was performed while blowing air at a rate of 31 / min. As a result, it was possible to oxidize to 100% phosphate ions in 120 minutes.

Example 3

Hypophosphite ion 10.4 g / l, phosphite ion 52.8 g / l, phosphate ion 0.6 g / l,
And organic acid has an organic carbon content (TOC) of 9.1 g
PH of the actual electroless nickel plating aging liquid containing 1 / l.
It was kept at 0 and subjected to oxidation treatment. 300 ml of solution with a volume of 300 m
It was placed in an internal irradiation type photochemical reaction device for 1 l, and 8 g / l of platinum-supported titanium dioxide powder was made to coexist therein, and air was added to
As a result of irradiation with a high pressure mercury lamp while blowing at a rate of 1 / min, it was oxidized to 100% phosphate ions in 50 hours,
The TOC became 50 mg / l or less in 55 hours.

[0032]

Therefore, according to this method, the hypophosphite ion is efficiently oxidized from the plating aging solution in a short time and economically without using an oxidizing chemical, and the phosphate ion is converted into the phosphate ion. Make it easy to reuse or process as calcium phosphate. Also, the used photocatalyst is recovered and reused.

Claims (1)

[Claims] 1. A plating aging solution containing hypophosphite ions is maintained at pH 1 to 4, titanium dioxide powder carrying a noble metal is allowed to coexist as a photocatalyst, and oxygen or air is blown into the aging solution to irradiate light. A hypophosphite ion in a plating aging solution, characterized in that the phosphite ion is oxidized to a phosphate ion, and the titanium dioxide powder carrying a noble metal is recovered by filtering while maintaining the pH at 1 to 3. Processing method.