JPH0368959B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a method for purifying nickel plating wastewater, particularly reducing total organic carbon (hereinafter abbreviated as TOC), and regenerating it as a replenishment liquid for nickel electrolytic refining. [Prior Art] This plating wastewater is concentrated plating washing water etc. generated in plating factories of small and medium-sized enterprises. Although the nickel concentration of the wastewater is accepted as relatively high, it contains a large amount of TOC and the like as impurities. Therefore, if this plating wastewater is supplied as is to the nickel electrolyte system, various problems will occur that are thought to be caused by the TOC concentration in the electrolyte. For example, the nickel electrodeposited on the Ni seed plate may peel off due to electrolysis, or the hardness of the nickel may increase. In order to avoid the above-mentioned phenomenon, it is not practical to replenish the electrolyte with the nickel-plated wastewater only in very small amounts. Another method is to add alkali to this nickel-plated wastewater to separate the nickel as hydroxide, then roast it and melt it in an electric furnace to form an anode, followed by electrolysis to form a liquid. has the drawbacks of being complicated and expensive. [Problems to be Solved by the Invention] The purpose of the present invention is to solve the above-mentioned problems, and to add a relatively large amount of the plating wastewater to the electrolytic solution of nickel electrolytic refining using a simple method. The object of the present invention is to provide a method for obtaining an aqueous nickel sulfate solution. [Means for Solving the Problems] The inventors of the present application conducted an experiment on the influence of the TOC concentration in the electrolytic solution for obtaining electrical nickel on the properties of the resulting nickel electrodeposit. Electrolyte Ni concentration 65-75g/
It was found that the TOC concentration needs to be 4 ppm or less in this case. If the TOC concentration is higher than this, the above-mentioned phenomenon will occur to a greater or lesser extent. Therefore, a nickel sulfate aqueous solution with a Ni concentration of 65 to 75 g/N obtained by regenerating nickel plating wastewater can be added at a rate of about 1/10 of the volume to the electrolyte taken out from the electrolytic tank for nickel electrolytic refining. In order to
The TOC concentration should be 40 ppm or less. That is, in the present invention, in order to obtain such a nickel sulfate aqueous solution from nickel plating wastewater, an alkaline aqueous solution with a pH of 8.0 to 9.0 is maintained at 40°C or higher and stirred, and then added to the aqueous solution while being stirred. Nickel plating wastewater and an aqueous alkali carbonate solution or an aqueous alkali hydroxide solution are added at the same time by blowing into the bottom of the aqueous solution while maintaining the pH and temperature of the aqueous solution, and the resulting precipitate is repulped with hot water, The dehydration operation to separate the washing water is performed multiple times, and after the adhering moisture is reduced to at least 35% by weight in the final dehydration operation, it is dissolved in dilute sulfuric acid and the nickel concentration is adjusted to a concentration suitable for electrolytic refining of nickel. . [Function] The reason why the reaction is carried out in the pH range of 8 to 9.0 in the method of the present invention is that when the pH is lower than this, some double salts with basic sulfate are formed, and when the pH is higher than this,
This is because TOC removal becomes insufficient. The reason why the reaction temperature is set to 40°C or higher, preferably 60°C or higher is because the filtration rate of the product is slow at higher temperatures. Next, first prepare a small amount of alkaline aqueous solution in the reaction tank, and add nickel plating wastewater and aqueous solution of alkali carbonate or alkali hydroxide to it by simultaneously blowing into it while maintaining the pH value and temperature. For example, if nickel plating wastewater at a predetermined temperature is added to a concentrated alkaline aqueous solution as in the conventional method, the reaction between the concentrated alkali and nickel proceeds locally, and normal carbonates or hydroxides are not produced. This is because the removal rate of TOC etc. is significantly reduced. The nickel precipitate as carbonate or hydroxide is separated from the mother liquor by strong suction filtration or centrifugation, and the resulting cake is repulped by adding a large amount of hot water at the same temperature as the initial process. After that, a dehydration operation to separate the washing water is performed two or more times. Apply a strong suction filtration method. At this time, in the final dehydration operation, the adhering moisture should be 35% by weight or less,
It is recommended to perform this washing and dehydration operation two or more times, as one time is not sufficient, and doing so twice or more will remove the adhering moisture in the final dehydration operation.
By setting the content to 35% by weight or less, TOC removal can be improved.
This is because when this precipitate is later dissolved in dilute sulfuric acid and the nickel concentration is adjusted to a concentration suitable for electrolytic refining of nickel, the TOC concentration can be reduced to about 40 ppm or less. [Example] Examples will be described below. Example 1 Into a beaker with a capacity of 10, add each aqueous solution at a predetermined pH and temperature of 50°C, which was adjusted by adding an aqueous sodium carbonate solution to water.
Add 500 ml of nickel, stir with a three-one motor, and add 84 g of nickel/TOC, 6.6 g/of nickel-plated waste water, and 150 g of sodium carbonate aqueous solution at room temperature using a roller pump.
Add 400 to 500 ml of wastewater per minute and 1.05 to 1.1 equivalents of alkali per minute to the bottom of the beaker at the same time. During this time, the inside of the container was kept at 50℃ with a water bath, and the pH was Using a PH controller manufactured by Hirama Rika, the addition of the sodium carbonate aqueous solution was turned ON and OFF while maintaining the specified PH value while treating each of the 5 nickel plating wastewaters.The residence time of the reaction liquid was varied and the resulting slurry was sucked out. It was filtered using a filter (Nutsche). Next, the cake obtained was 600 ml per 100 g, 50°C.
Repulp washing was carried out for 30 minutes each at a temperature of , and each time the cake was filtered using a suction filter, and in the final filtration, the cake was dehydrated by suction until the moisture content of the cake was about 30% by weight. The cake obtained in this way is
Dissolve Ni75 in 1.1 equivalent of dilute sulfuric acid and add water.
g/g/ of an aqueous solution, and its TOC was determined based on JIS standards. The results are shown in Table 1.

[Table] As is clear from Table 1, the TOC, which was initially as high as 6.6 g/mt, was reduced to the expected value of 30 ppm or less, and was clearly cleared in all cases. Example 2 Nickel plating wastewater containing 85 g/Ni and 12 g/TOC was reacted at a reaction temperature of 60°C using 200 g/Aqueous sodium hydroxide solution as an alkali.
TOC removal treatment was carried out in the same manner as in Example 1, except for the following. The results are shown in Table 2. However, in Experiment No. 9, ordinary light suction filtration was performed both times.

[Table] As can be seen from Table 2, even if the TOC concentration in the raw material was about twice as high as in Example 1, the TOC was decomposed and removed with almost the same removal rate, and the TOC concentration was about 20 ~
A low concentration of 30ppm was obtained. Above example 1
and 2 are cases where the repulp washing and dehydration operation was performed twice, and by increasing the number of repulp washing and dehydration operations, it is possible to obtain a nickel regenerated liquid with a lower TOC. In Experiment No. 9, which applied the normal filtration method, even though the washing and dehydration method and recovery were the same,
TOC removal was inadequate. By the way, in the case of sample No. 2 in Table 1 and sample No. 5 in Table 2, the cake that had been washed and dehydrated once was dissolved in sulfuric acid.
The TOC concentration when making an aqueous solution of Ni75g/
They were 220ppm and 160ppm. [Effects of the invention] As described above, TOC removal from nickel-plated wastewater is extremely difficult compared to the removal of general impurities, but when the method of the present invention is applied, more than 99.5% by weight can be removed and the resulting recycled electrolytic The TOC concentration in the solution is 65 to 75 when performing matt electrolysis.
In the case of g/Ni, the TOC can be lowered to 10 to 30 ppm. Although not specifically shown in the examples, application of the method of the present invention also provides the advantage that other impurities (those that do not precipitate due to the addition of alkali) are also removed at the same time. The yield of nickel recovered from the plating wastewater is 99.5% by weight or more. The recycled nickel aqueous solution obtained by the method of the present invention can be used without any problem by being extracted from the nickel pine electrolytic cell as it is, purified as an electrolytic waste liquid, and then combined with the electrolytic waste liquid supplied to the electrolytic cell. .

Claims (1)

[Claims] 1. Keep an alkaline aqueous solution with a pH of 8.0 to 9.0 above 40°C, and add nickel plating wastewater and an alkali carbonate aqueous solution or an alkali hydroxide aqueous solution to the aqueous solution while stirring, and adjust the pH and temperature of the aqueous solution. It is added to the bottom of the aqueous solution by blowing it into the bottom of the aqueous solution while maintaining the water content, and the precipitate formed is repulped with warm water and dehydrated from the washed material several times to reduce the adhering moisture to 35% by weight or less in the final dehydration operation. A method for regenerating nickel-plated wastewater as a replenishment liquid for electrolytic refining of nickel, characterized by dissolving it in dilute sulfuric acid and adjusting the concentration of nickel to a concentration suitable for electrolytic refining of nickel.