JPH0223236B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a method for recovering nickel from aged waste liquid of a chemical nickel plating bath, in which hypophosphite is used as a reducing agent, and citric acid, phosphoric acid, or succinic acid is used as a complexing agent. Oxalic acid is added to the aged waste liquid of a chemical nickel plating bath using an organic acid with a large complexing effect such as, and the nickel ions complexed with the organic acid are precipitated as insoluble nickel oxalate with a low phosphorus content, It is characterized by filtration and recovery. Conventionally, chemical nickel plating can be applied to nonconducting materials such as plastics and ceramics.
Moreover, it is widely used in electronic parts, precision instruments, and others because it provides a uniform plating layer with high added values such as corrosion resistance and abrasion resistance. The chemical nickel plating bath contains nickel ions, a reducing agent, a complexing agent, etc. The reducing agent is said to be essential for reducing nickel ions to nickel, but it is oxidized as nickel is deposited. concentration decreases. If the reducing agent is hypophosphite, it will be oxidized to phosphite, so in order to effectively retain the chemical nickel plating bath, it is essential to control the concentration of hypophosphite ions and nickel ions, and These are replenished to regenerate the plating solution. but,
There is a limit to this replenishment, and as the amount of phosphite ions accumulated in the solution increases, the deposition rate and precipitation condition deteriorate, and the plating solution ages and becomes unusable after 5 to 6 cycles, and is disposed of as aged waste solution. In order to reduce the concentration of nickel, phosphorus, COD, etc. to within the emission standards, various waste liquid treatments are performed before discharge. However, there is still no effective treatment technology for the aged waste liquid of chemical nickel plating baths, and nickel is also a rare metal, so it is necessary to recycle it to save resources, but nickel cannot be recovered from aged waste liquid. The phosphorus content of recovered nickel is high, making it difficult to recycle it effectively.

For example, methods for recovering nickel from the aged waste liquid of a chemical nickel plating bath consisting of nickel chloride, sodium hypophosphite, and a complexing agent during bath preparation include cathodic electrolysis or alkaline agents such as sodium hydroxide and sodium carbonate. There is a method of adding nickel hydroxide to precipitate it as nickel hydroxide, but in the former cathodic electrolysis method, the electrodeposit contains 5 to 15% phosphorus.
It has the disadvantage that it cannot be effectively reused as nickel metal. In the latter method of precipitating as nickel hydroxide, nickel ions easily precipitate as hydroxide at pH 8 to 9 when no complexing agent is included.
PH in the case of chemical nickel waste containing complexing agents
At 8 to 9, there is almost no hydroxide formation, and the high pH value
Hydroxide is produced only at pH 10 to 13, and since the hydroxide is in the form of a fine colloid, it is difficult to filter and nickel cannot be easily recovered. Therefore, in order to recover nickel with a low phosphorus content, calcium chloride and calcium hydroxide are added to the aged wastewater to form an insoluble calcium phosphite precipitate around pH 9, and the filtrate is filtered. Another option is to lower the pH to around 4 and collect it as an electrodeposit using cathode electrolysis, but
In this method, a large amount of calcium phosphite precipitate contains nickel and a complexing agent, so washing and filtration with water is required to separate them from the calcium phosphite precipitate to be discarded. Since the cathodic electrolysis method is carried out by adding the filtrate containing nickel ions to the initial filtrate, the nickel ion concentration is low, making it impossible to obtain a satisfactory electrodeposit. Furthermore, since a large amount of calcium phosphite precipitate to be discarded is washed and filtered, it is time consuming and uneconomical.

In short, in the method of recovering nickel from aging nickel plating waste liquid, it is important to make the precipitate easy to filter and to minimize the amount of phosphorus contained in the recovered nickel.

However, in the present invention, the aged waste liquid of a chemical nickel plating bath using hypophosphite as a reducing agent and an organic acid with a large complexing effect such as citric acid, malic acid, or succinic acid as a complexing agent is used. In this case, oxalic acid is added to the waste liquid to make it acidic to a pH of 1 to 3, and the nickel ions complexed with organic acids in the aged waste liquid are precipitated as insoluble nickel oxalate. Low water volume and good settling properties,
Contamination with phosphorus components is small, and the waste liquid can be filtered to easily and quickly recover nickel ions as nickel oxalate. Also, as is well known, nickel oxalate can be easily produced by heating it at about 300 to 400°C for more than 1 hour in an atmosphere of city gas, methane gas, nitrogen gas, hydrogen gas, etc. or in a vacuum (10 ^-4 torr or less). More than 90% is reduced to nickel metal. The phosphorus content in the nickel metal is 0.1% or less, which is extremely small compared to conventional methods, and can be added to steel materials to improve their quality. In addition, by heating nickel oxalate to 400℃ or higher in the atmosphere, it can be made into nickel oxide with a phosphorus content of 0.06% or less, which can be widely used by adding it to ceramic materials to improve their quality, and as a rare metal. This enables effective use as a Furthermore, the ability to recover nickel as nickel oxalate from the aging waste liquid of chemical nickel plating baths and reuse it as nickel metal and nickel oxide has a very large economic effect on the industry.

Examples of the present invention will be explained in detail below.

Example 1 Composition of aging liquid Nickel chloride 10g/(Ni ²⁺ 2400mg/) Sodium citrate
20g/(10000ppm as COD value) Sodium phosphite
40g/(5700ppm as P) a Processing conditions for nickel recovery Amount of oxalic acid added 6.7g/(1.3 times mole of Ni ²⁺ ) PH value after addition PH2.0 Processing temperature 50℃, processing time 24 hours b Nickel ion concentration in the filtered solution and phosphorus concentration contained in the filtered material (nickel oxalate) Nickel ion concentration in the filtered solution 43 mg/
The phosphorus concentration (P/Ni percentage) in nickel oxalate is 0.8% in the filtered state;
Approximately 0.1% per 1g of nickel oxalate washed with 100ml of water, approximately 0.05% for 200ml c Treatment conditions for phosphorus and COD values Calcium chloride dihydrate is added to the above filtrate (the amount added is Ca/phosphorus). acid (mole ratio) 1.2 times mole, Ca/citric acid (mole ratio) 1.8 times mole (total of 51 g/), adjust the pH to 8, and add calcium phosphite, calcium citrate, and calcium oxalate (excess oxalic acid). ) as a precipitate.

Treatment temperature: 50℃, treatment time: 24 hours Phosphorus in supernatant liquid, COD value Phosphorus: 300ppm, COD value: 700ppm Since the wastewater standard is COD value of 100ppm, the wastewater is diluted with approximately 7 to 10 times as much water and treated with an oxidizing agent. It is necessary to take a treatment method such as adding a substance to oxidize the organic substance, or oxidizing the organic substance by an anodic oxidation electrolytic method.

However, even if these treatments are applied, most of the nickel ions are removed as nickel oxalate in baths using citric acid as a complexing agent due to the use of oxalic acid. Therefore, most of the citric acid does not exist as a complex with nickel ions, so it can easily react with Ca ²⁺ ions and be removed as insoluble calcium citrate.
As a result, the concentration of citric acid is greatly reduced, and the above-mentioned wastewater treatment can be carried out easily and economically.

In the aged waste liquid of a chemical nickel plating bath that uses hypophosphite as a reducing agent and citric acid as a complexing agent, nickel is recovered by the method described above, and the filtrate is obtained by filtering nickel oxalate. Furthermore, calcium salts such as slaked lime and calcium chloride are added to the PH
The mixture is made alkaline to a pH of 7 to 10 to precipitate calcium ions, phosphorous acid, citric acid, and excess oxalic acid as insoluble calcium phosphite, calcium citrate, and calcium oxalate, and these are filtered. Since the concentration of citric acid in this filtrate is greatly reduced, the COD value can be reduced more easily and economically by oxidizing the organic acid using an oxidizing agent or an anodic oxidation electrolytic method.

Example 2 Composition of aging liquid Nickel chloride 10g/(Ni ²⁺ 2400mg/) Sodium phosphite 40g/ Malic acid 18g/ Succinic acid 16g/a Nickel recovery conditions Amount of oxalic acid added 6.7g/(Ni ²⁺ 1.3 times mole) PH value after addition PH2.0 Treatment temperature 50℃, treatment time 24 hours b Nickel ion concentration in liquid 59mg/
Washed with 100ml of water per 1g of nickel oxalate P/Ni value 0.1%

Claims (1)

[Claims] 1 Hypophosphite as a reducing agent, citric acid as a complexing agent,
Chemical nickel plating using organic acids with a large complexing effect such as malic acid and succinic acid.When recovering nickel from aging wastewater, oxalic acid is added to the wastewater to make it acidic with a pH of 1 to 3. A method for recovering nickel from the waste liquid of a chemical nickel plating bath, characterized in that nickel ions complexed with the organic acid are precipitated as insoluble nickel oxalate with a low phosphorus content and recovered by filtration.