JP2012172248A - Method for treating electroless nickel plating waste solution - Google Patents

Abstract

PROBLEM TO BE SOLVED: To smoothly perform activated sludge treatment for an electroless nickel plating waste solution.SOLUTION: The amount of chemicals to be used is reduced, and the activated sludge treatment for the waste solution can be smoothly performed, by carrying out a pretreatment for the electroless nickel plating waste solution including: a stage 1 of adding calcium hydroxide to an aged solution as the electroless nickel plating waste solution to control the pH of the aged solution to 6 to 7; a stage 2 of adding sodium hydroxide to the aged solution obtained in the stage 1 to control the pH of the aged solution to ≥12 and performing solid-liquid separation to control the concentration of nickel in the aged solution to ≤20 ppm; and a stage 3 of performing activated sludge treatment with the aged solution obtained in the stage 2 as the solution to be treated.

Description

  The present invention relates to a waste liquid treatment method for electroless nickel plating.

Conventionally, electroless nickel plating has been performed to form a nickel thin film on the surface of a nonconductor such as plastic or ceramic. In electroless nickel plating, metal nickel is obtained by immersing the non-conductive object in a plating solution mainly containing a nickel salt, a reducing agent, and a chelating agent, and reducing the nickel salt with the reducing agent. It is deposited on the surface of the workpiece.
Hypophosphorous acid is mainly used as the reducing agent. However, as the plating process proceeds, the reducing agent is oxidized and the nickel salt is consumed. It is necessary to replenish.
In such an electroless nickel plating process, as the plating process proceeds, reaction residues such as oxides of the reducing agent accumulate, and the plating treatment capacity of the plating solution decreases. The plating solution needs to be renewed. The plating solution with a reduced processing capacity is discarded as a waste solution, and the waste solution (aging solution) contains a number of BOD components and COD components such as oxides of the reducing agent, residual nickel salts, chelating agents, and pH adjusting agents. In order to prevent environmental pollution, it is necessary to remove the BOD component, the COD component, etc. contained in the aging solution in order to prevent environmental pollution.
As the above-mentioned treatment methods, a Fenton oxidation treatment method, a treatment method with calcium hypochlorite, a treatment method with ozone, an electrolytic oxidation treatment method, an oxidation treatment method by light irradiation using a photocatalyst, and the like have been conventionally performed. However, the above-mentioned treatment method has a poor oxidation treatment effect, a long treatment time, a high concentration of waste liquid containing BOD component and COD component, a treatment effect is not sufficient, or a treatment operation is complicated, There were many problems such as using a large amount of chemicals.

In order to solve the above problems, in Patent Document 1, as a first step, phosphorous acid is used to remove hypophosphorous acid remaining in the waste liquid by heating to 90 to 110 ° C. while maintaining the pH of the waste liquid at 5.5 to 9. As a second step, phosphorous acid and orthophosphoric acid in the waste liquid are removed as calcium salts by adding a calcium source while maintaining the pH of the waste liquid at 11 to 12 as a second step, and a waste solution as a third step. A method is disclosed in which phosphorous acid remaining therein is oxidized to normal phosphoric acid using ozone or the like, and further, the phosphorus component in the waste liquid is precipitated and removed as a calcium salt.
In Patent Document 2, an inorganic acid is added to the waste liquid as the first step, and sodium hypophosphite-derived sodium in the waste liquid is removed as a salt as an acidic waste liquid having a pH of less than 2, and a calcium compound is added to the waste liquid as the second step. Add to adjust pH to 2-7, remove precipitates containing calcium phosphite and calcium sulfate, add alkaline agent to the waste liquid as third step to adjust pH to 9.5 or higher, nickel hydroxide A method for generating and removing the precipitate is disclosed.

JP 2001-79570 A JP-A-2005-232517

The method of Patent Document 1 requires a two-stage pH adjustment step and further an oxidation step, which makes the process complicated, makes it difficult to efficiently oxidize in the oxidation step, and requires a long time for the oxidation. In addition, two stages of precipitation removal are required.
In the method of Patent Document 2, an inorganic acid is necessary for pH adjustment in the first step, and the pH of the waste liquid is set to less than 2 in the first step. The amount of calcium compound used to adjust to 7 increases. Also, the precipitation removal process requires two steps.

In the present invention, as means for solving the above-mentioned conventional problems, treatment is performed in Step 1 and Step 1 in which the pH of the aging solution is set to 6 to 7 by adding calcium hydroxide to the aging solution which is an electroless nickel plating waste solution. Further, sodium hydroxide is added to the above-described aging solution so that the pH of the aging solution is 12 or more, and the nickel-containing component that precipitates as a solid is separated from the aging solution, and the nickel concentration of the aging solution is 20 ppm or less The present invention provides a method for treating an electroless nickel plating waste liquid comprising the steps 2 and 3, a step 3 for treating activated sludge using the aging solution obtained in the step 2 as a liquid to be treated, and the above steps.
In this case, it is desirable that the amount of calcium hydroxide and sodium hydroxide used in Step 1 and Step 2 is 1: 0.05 to 1: 0.1 molar ratio.
Furthermore, in the step 2, it is desirable that the means for separating the nickel-containing component precipitated as a solid from the aging solution is a filter press or suction filtration.

[Action]
In order to perform activated sludge treatment on the electroless nickel plating waste liquid (aging solution), it is necessary to make the nickel concentration in the aging solution 20 ppm (20 mg / l) or less. Since the aging solution contains a large amount of nickel salt and a BOD component such as a chelating agent, a pH adjuster, and a COD component, the excess nickel salt should be removed so that the nickel salt becomes 20 ppm or less prior to the activated sludge treatment. is required. In order to remove the nickel salt in the aging solution, the aging solution may be made alkaline, and the nickel salt in the aging solution may be precipitated from the liquid as nickel hydroxide. The nickel concentration in the aging solution can be 20 ppm (20 mg / l) or less.
However, when only the calcium hydroxide is added for ease of filtration and handling in order to set the pH of the aging solution to 12 or more, calcium phosphate crystals are precipitated on the surface of the calcium hydroxide undissolved particles. As a result, further reaction between the calcium hydroxide and the nickel salt in the aging solution is inhibited, so that the calcium hydroxide particles become insoluble, and the calcium hydroxide and nickel salt in the aging solution become more insoluble. A large amount of calcium hydroxide is required to promote the reaction and bring the aging solution to a predetermined pH.
On the other hand, when only sodium hydroxide is added, the precipitated nickel hydroxide becomes fine particles and is finely dispersed in the waste liquid due to the dispersion effect of the sodium hydroxide as a surfactant. And the solid-liquid separation efficiency is low.
Therefore, in the present invention, first, in step 1, calcium hydroxide is added to the aging solution to adjust the pH to 6-7. In the pH range in the above step 1, the amount of precipitated nickel hydroxide crystals is not excessive, and the insolubilization of calcium hydroxide particles is not significant. However, in Step 1, since a certain amount of nickel salt that has not yet precipitated remains in the aging solution, sodium hydroxide is further added to pH 12 or more in Step 2 without separating the precipitate. The remaining nickel salt is precipitated as nickel hydroxide so that the nickel concentration in the aging solution is 20 ppm or less.
In the step 2, the pH in the aging solution is already adjusted to 6 to 7 in the step 1, so that the amount of sodium hydroxide used for making the pH 12 or more can be reduced, and thus the aging solution is precipitated in the aging solution. The solid content containing nickel is efficiently separated, and the nickel concentration in the aging solution is easily reduced to 20 ppm or less.

Activated sludge treatment is a method generally used for removing BOD components and COD components in waste liquids such as domestic wastewater and industrial wastewater, but in the case of aging liquid treated by the above-mentioned Step 1 and Step 2. As described above, the residual nickel concentration is 20 ppm or less, and a liquid capable of being treated with activated sludge is obtained. Therefore, in the present invention, by performing the activated sludge treatment as the final step 3, it is not necessary to separate the precipitate in the step 1, and the liquid separated in the step 2 is directly treated with activated sludge to obtain phosphorus and BOD. Components, COD components and the like are efficiently removed, and the aging liquid is purified to a state where it can be drained into a river or the like.
Further, the amount of calcium hydroxide and sodium hydroxide used in the above steps 1 and 2 can be greatly reduced as described above, but the amount of calcium hydroxide and sodium hydroxide is 1: 0. When the molar ratio is from 0.05 to 1: 0.1, the nickel hydroxide formation reaction in the aging solution is efficiently performed, and the nickel in the aging solution is smoothly removed.
Furthermore, the solid-liquid separation process in step 2 can be performed more easily and efficiently by performing the solid-liquid separation using a filter press or suction filtration.

〔effect〕
According to the present invention, the treatment for removing nickel from the electroless nickel plating waste solution (aging solution) to 20 ppm or less reduces the amount of chemicals used, shortens the process, and performs the treatment operation. However, the activated sludge treatment can be smoothly performed on the aging liquid from which nickel has been removed to 20 ppm or less in this manner.

Graph of filtration rate and filtrate generation amount.

The waste liquid treatment method of the present invention will be described in detail below.
[Step 1]
In step 1 of the waste liquid treatment method of the present invention, the pH of the aging solution is adjusted to 6 to 7 by adding calcium hydroxide to the aging solution. At this point, nickel, phosphorus and the like are precipitated to some extent as a solid, but in this step, solid-liquid separation or the like is not performed.
When the pH of the aging solution adjusted in this step is less than 6, it is necessary to add a large amount of sodium hydroxide in the following step 2, and the efficiency of solid-liquid separation also deteriorates. When the pH exceeds 7, as described above, calcium phosphate crystals are precipitated on the surface of the unmelted calcium hydroxide particles, and as a result, the calcium hydroxide is likely to be insoluble. Addition amount becomes excessive.

[Step 2]
In step 2 of the waste liquid treatment method of the present invention, the pH of the aging solution is adjusted to 12 or more by adding sodium hydroxide to the aging solution whose pH is adjusted to 6 to 7 in the above step 1. In this step, by setting the pH to 12 or more, nickel remaining in the aging solution can be precipitated as a solid more than in the above step 1, and the nickel precipitated from the aging solution is solid-liquid separated as a solid content. Thus, the nickel concentration can be 20 ppm or less. In addition, in this step, phosphorus, other BOD components, and COD components can be precipitated from the aging solution as most of the salt, etc., so that the solid is separated from the aging solution as a solid. I can do it.
Here, when the pH of the aging solution is less than 12, nickel in the solution does not sufficiently precipitate, and nickel remains in the aging solution after the solid-liquid separation by 20 ppm or more.

  The solid-liquid separation means in the step 2 is not particularly limited, such as a filter press, a suction filtration method, a precipitation method, a centrifugal separation method, etc., but the use of a solid-liquid separation method by a filter press or suction filtration facilitates processing and processing speed. From the point of view is desirable.

  Here, it is desirable that the amount of calcium hydroxide and sodium hydroxide used in Step 1 and Step 2 is 1: 0.05 to 1: 0.1 molar ratio. When the ratio of calcium hydroxide is higher than 1: 0.05, the amount of calcium hydroxide is excessive with respect to sodium hydroxide, and calcium phosphate crystals are likely to precipitate on the surface of undissolved calcium hydroxide particles. When the ratio of sodium hydroxide is larger than 1: 0.1, a large amount of sodium hydroxide acts as a surfactant as described above. Minutes are easily dispersed finely in the liquid, and the filtration rate during solid-liquid separation is reduced. Also, within this molar ratio range, the amount of calcium hydroxide and sodium hydroxide used is minimized.

[Step 3]
The aging solution from which the solid content has been separated by the solid-liquid separation in the above step 2 has most of the nickel removed, and the amount of residual nickel is 20 ppm or less. However, phosphorus, BOD components, and COD components remain in the aging solution to some extent.
Therefore, in step 3 of the waste liquid treatment method of the present invention, activated sludge treatment is performed using the aging solution treated in step 2 as a liquid to be treated. In performing the activated sludge treatment, the pH of the aging solution whose pH is adjusted to 12 or more is adjusted to pH 7 to 8 using an acid such as hydrochloric acid or sulfuric acid. And since the said aging liquid (liquid to be treated) has a residual nickel amount of 20 ppm or less, the activated sludge treatment can be sufficiently performed smoothly.
In this case, as long as it is an activated sludge treatment method, a batch activated sludge method, a continuous activated sludge method, or other methods may be used. In general, the liquid to be treated is filled in an aerobic tank equipped with air blowing means in the tank, activated sludge is dispersed in the liquid to be treated, and BOD components and COD components are aerobically blown into the air. The aerobic activated sludge treatment that decomposes is applied, but the anaerobic tank in which an activated sludge is dispersed in an anaerobic tank equipped with a stirrer and agitated to decompose the BOD and COD components An activated sludge treatment may be applied. In particular, when a large amount of phosphorus remains in the liquid to be treated, when the atmosphere is changed from an oxygen-deficient state to an aerobic state in the presence of an aerobic microorganism, the microorganism ingests an excessive amount of phosphorus. Activated sludge treatment to remove phosphorus in the liquid to be treated by accumulating polyphosphoric acid in microorganisms by providing anaerobic tank and aerobic tank, or anaerobic tank, anoxic tank and aerobic tank Method is a desirable method.
The liquid to be treated that has been subjected to the above activated sludge method is biologically decomposed and removed of phosphorus, BOD components, and COD components in the liquid efficiently, and the liquid to be treated thus purified precipitates decomposition products. After separation, the quality will be satisfactory even if drained into rivers.

An embodiment of the present invention will be described below. In addition, this invention is not limited only to this Example.
[Example 1]
To 1 liter of electroless nickel plating waste liquid (nickel: 4900 mg / l) which is an aging solution, 2.4 liter of 10 mass% calcium hydroxide aqueous solution was added and stirred for 30 minutes. The pH at this time was 6.6.
Next, 132 ml of 10 mass% sodium hydroxide aqueous solution was added to precipitate nickel. The molar ratio of added calcium hydroxide to sodium hydroxide is 1: 0.055. The pH at this time was 12.0. This was filtered by suction filtration. The residual nickel concentration in the filtrate was 3.1 mg / l (20 ppm or less).

[Reference Example 1]
To 1 liter of electroless nickel plating waste liquid (nickel: 4900 mg / l) which is an aging solution, 3.08 liter of 10 mass% calcium hydroxide aqueous solution was added and stirred for 30 minutes. The pH at this time was 13.0. Although this was filtered by suction filtration, although the filterability itself was good, it was difficult to adjust the pH, and the required amount of aqueous calcium hydroxide (3.08 liters) was compared with the required amount of Example 1 (2.4 liters). And increased by 28 vol%. The residual nickel concentration in the filtrate was 1.2 mg / l (20 ppm or less).

[Reference Example 2]
To 1 liter of electroless nickel plating waste liquid (nickel: 4900 mg / l) was added 496 ml of a 10 mass% sodium hydroxide aqueous solution, and the mixture was stirred for 30 minutes. The pH at this time was 12.0. This was filtered by suction filtration. The residual nickel concentration in the filtrate was 29 mg / l, and filtration also took a long time.

FIG. 1 shows a graph of the amount of filtrate generated with respect to the filtration time when performing suction filtration in Example 1 and Reference Examples 1 and 2.
In Example 1, a good correlation was found between the filtration time and the amount of filtrate produced, and the residual nickel concentration in the filtrate was sufficiently low to enable the activated sludge treatment.
In the case where only calcium hydroxide of Reference Example 1 was added, the residual nickel concentration in the filtrate was low, but the dissolution rate of calcium hydroxide was slow and the ion dissociation of calcium hydroxide was small, so that a large amount of water was used. It was necessary to add calcium oxide, and it was difficult to control to a predetermined pH.
In the case of adding only sodium hydroxide in Reference Example 2, the residual nickel concentration in the filtrate is high and it is difficult to perform activated sludge treatment. Further, in the filtration treatment, solid components such as nickel hydroxide are liquid as fine particles. The filter medium was clogged from the beginning of filtration (the filtration time was up to 1 minute in the graph of FIG. 1), and the increase in the amount of filtrate produced worsened.

  The filtrate obtained by the waste liquid treatment performed in Example 1 was adjusted to pH 7 with dilute hydrochloric acid, and further diluted 20-fold with tap water to carry out activated sludge treatment using the liquid to be treated. Table 1 shows the nickel concentration, BOD value, COD value, and phosphorus concentration in each waste liquid before treatment, after solid-liquid separation in step 2, and after activated sludge treatment.

  As shown in Table 1, it was confirmed that the waste liquid whose nickel concentration was reduced to 20 mg or less by the treatment of Example 1 further decomposed and removed phosphorus, BOD component, and COD component efficiently by activated sludge treatment. It was.

The present invention can be used industrially because the treatment of the electroless nickel plating waste liquid (aging solution) can be easily performed with a small amount of chemicals.

Claims (3)

Step 1, in which the pH of the aging solution is adjusted to 6 to 7 by adding calcium hydroxide to the aging solution which is an electroless nickel plating waste solution;
By further adding sodium hydroxide to the aging solution treated in the above step 1, the pH of the aging solution is set to 12 or more, and the nickel-containing component precipitated as a solid is separated from the aging solution, Step 2 in which the nickel concentration is 20 ppm or less,
Step 3 for treating activated sludge using the aging solution obtained in Step 2 as a liquid to be treated,
A method for treating an electroless nickel plating waste liquid, comprising the steps described above.   The method for treating an electroless nickel plating waste liquid according to claim 1, wherein the amount of calcium hydroxide and sodium hydroxide used in Step 1 and Step 2 is 1: 0.05 to 1: 0.1 molar ratio. The method for treating an electroless nickel plating waste liquid according to claim 1 or 2, wherein in the step 2, the means for separating the nickel-containing component precipitated as a solid from the aging solution is a filter press or suction filtration.