JPH0242911B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for supplying metal ions to a plating chamber by dissolving metals with acid recovered from an anode chamber in electroplating using an anion exchange membrane diaphragm.

Conventionally, an insoluble anode or a soluble anode has been used as an anode in an electroplating method.

As for the soluble anode, for example, in the case of Zn plating, a Zn anode is used, and in the case of alloy plating, such as Zn--Ni plating, an anode system is used in which individual anodes such as a Zn anode and a Ni anode are combined. When such a soluble anode is used, the oxidation reaction in which Fe ²⁺ ions contained in the plating bath become Fe ³⁺ does not proceed, and there is an advantage that the metal ions in the plating bath can be supplied by elution from the anode itself. The main drawbacks are as follows.

(1) In Zn plating such as Zn plating, Ni-Zn plating, and Fe-Zn plating, Zn dross (Zn precipitate) is generated in the plating bath, and the dross must be recovered.

(2) In alloy plating such as Zn-Ni plating, Ni anodes, Zn anodes, etc. are installed separately in multiple electrolytic baths, but it is extremely difficult to balance the metal ions in the baths.

(3) With soluble anodes, metal ions are supplied by elution from the anode itself, so the anode gradually wears out and must be replaced with a new anode each time. Moreover, as the anode wears out, the distance between the anode and the steel plate changes. When plating various types of plating, such as Zn plating and Zn-Ni plating, on the same line, it is necessary to change the anode each time the type of plating is changed.

(4) When using an Fe anode in Fe-based plating, there are large changes in bath composition such as Fe ²⁺ ion concentration and pH, and when the current density is high, for example 40 A/dm ² or higher, the Fe anode Passivation occurs, and Fe ²⁺ ions are oxidized to Fe ³⁺ ions at the anode, which impairs plating properties.

On the other hand, even if an insoluble anode is used, there are the following problems.

(1) Elutes from the bare back surface of the steel plate to be plated.
Fe ²⁺ and Fe ²⁺ , which is a plating component in Fe-based plating baths such as Fe plating and Zn-Fe alloy plating, are
It is oxidized to Fe ³⁺ ions by electrode reactions at the anode or O ₂ gas generated at the anode. The presence of Fe ³⁺ ions in the plating bath due to this oxidation not only accelerates the corrosion of Fe on the back side of the object to be plated and conductor rolls (Ni plating, etc.), but also causes Fe
(OH) ₃ , which poses a problem in managing the plating bath.

(2) In the case of Fe-based plating that contains Fe ³⁺ in the plating bath, such as Fe-Zn alloy plating, it not only changes the composition of the plating film in which Fe ²⁺ is generated, but also causes uneven color tone and There is a problem that current efficiency decreases.

On the other hand, various methods of using ion exchange membranes have been proposed for electroplating using insoluble anodes, and one example is the method described in Japanese Patent Publication No. 51-2900 (referred to as the prior art described in the publication). be. However, even if this method is adopted, the anion exchange membrane first prevents Ni ²⁺ and Zn ²⁺ from permeating and moving from the metal bath to the anode chamber, but the anion exchange membrane Due to the performance of the diaphragm,
Regarding Fe ²⁺ , there is actually a permeation movement to the anode chamber due to the concentration gradient, which poses a problem in bath management. Secondly, the H ⁺ generated in the anode chamber should not permeate and migrate to the plating bath through the anion exchange membrane diaphragm, but due to the performance of the diaphragm, the permeation of small ions such as H ⁺ can be ignored. Especially when a concentrated acid such as 1-3N H ₂ SO ₄ is circulated in the anode chamber, the transfer number of H ⁺ reaches 30-60%, which lowers the pH of the metal bath. This also makes it difficult to manage the plating bath.

The present invention was proposed in order to solve the above-mentioned problems, and in view of the fact that using a soluble anode would have the basic problem as described above, an insoluble anode is used. However, even if an insoluble anode is used, there are unavoidable difficulties in managing the plating bath as described above, so an anion exchange membrane diaphragm is also used. Furthermore, the present invention is not limited to the combination of an insoluble anode and an anion exchange membrane diaphragm, but when considering the permeability of an anion exchange membrane diaphragm, the presence of Fe ³⁺ ions in the plating bath is In addition, as plating progresses, the acid concentration of the anode chamber solution increases, so in order to keep the acid concentration constant, it is necessary to gradually extract the acid. At that time, in order to effectively utilize the acid, if the acid is supplied as it is into the plating bath, Fe ³⁺ ions will be mixed in, which will cause deterioration of the plating properties as described above. In the process of melting metal, it is reduced to Fe ²⁺ and then supplied to the metal bath. Moreover, as will be explained in detail later, even if a metal plate is brought into contact with an acid during metal melting, the amount of metal dissolved is so small that it is not sufficient to replenish metal ions. The purpose is to smoothly replenish the metal ions needed in the plating bath by bringing the metal into contact with the metal and filling the melting tower.

That is, the present invention is an Fe-based electroplating method that is carried out by installing an insoluble anode in an anode chamber separated from the plating bath by an anion exchange membrane diaphragm, and which is performed by installing an ^insoluble anode in an anode chamber separated from the plating bath by an anion exchange membrane diaphragm. After adjusting the sulfuric acid concentration by adding water to 3N sulfuric acid, a portion is circulated to the anode chamber, and the remaining portion is brought into contact with iron or iron-containing metal powder or metal particles filled in the melter to dissolve the metal. The method is characterized in that after reducing Fe ³⁺ ions to Fe ²⁺ ions, a solution containing Fe ²⁺ ions is supplied to the plating bath.

By the way, the present invention is applicable to Fe plating, Fe-Zn plating, Fe-Ni plating, etc., since the presence of Fe ³⁺ must be avoided as much as possible in Fe-based plating.
This is particularly effective in the case of Fe-based plating.

According to the present invention, firstly, since a diaphragm is used, Fe ²⁺ hardly migrates into the anode chamber and the generation of Fe ³⁺ by O ₂ gas generated at the anode is prevented, which is preferable. Second, it is actually
Some of the Fe ²⁺ is oxidized in the anode chamber through the diaphragm.
Fe ³⁺ is produced during the metal dissolution process.
Because it can be reduced to Fe ²⁺ , it ends up in the Metsuki bathroom.
Plating can be performed in the substantial absence of Fe ³⁺ . Thirdly, the acid from the anode chamber can be recovered and used effectively as a plating replenishment solution, and fourthly, water is added to this anode chamber solution and a portion is recycled to the anode chamber, so the sulfuric acid concentration can be reduced. The pH of the plating bath can be kept constant at all times, and the metal ions that should be replenished by dissolving the metal can be replenished, so the amount of expensive FeSO ₄ and ZnSO ₄ used can be reduced or completely eliminated. It can be economical. This point is especially remarkable and unique, but the fifth
In view of the fact that whenever metal ions are replenished by dissolving metal, the amount of dissolved metal must be considerably large, so instead of simply immersing a metal plate in an acid bath, metal particles or metal powder are used. Moreover, since the solution is packed in a dissolution tower and brought into contact with an acid solution for dissolution, a high dissolution rate can be obtained with a compact device.

Next, the present invention will be explained in further detail using the case of Fe--Zn plating shown in FIG. 1 as an example.

The plating tank 1 is separated into a plating bath 3 and an anode chamber 4 by an anion exchange membrane diaphragm 2. 5
6 is an insoluble anode made of Pt or a Pb alloy, and 6 is an object to be plated as a cathode, such as a steel plate. A power source 7 is connected between these to apply a plating voltage. Also, in Metsuki Bathroom 3, for example,
It is filled with a plating liquid consisting of ZnSO ₄ .7H ₂ O, FeSO ₄ .7H ₂ O and (NH ₄ ) ₂ SO ₄ .
This plating liquid is sequentially extracted, combined with a plating replenishing liquid to be described later in a plating liquid circulation tank 8, and returned to the plating bathroom 3 by a pump 9.

On the other hand, the anode chamber liquid is sequentially extracted from the anode chamber 4 , the acid concentration is adjusted in the anode chamber liquid circulation tank 10 , and then returned to the anode chamber 4 by the pump 11 .

If we consider the case where the diaphragm 2 is not used, the following reactions (1) and (2) occur at the insoluble anode 5.

2H ₂ O→4H ⁺ ＋O ₂ ↑＋4e ^- ……(1) Fe ²⁺ Fe ³⁺ ＋e ^- ……(2) In other words, at the insoluble anode, first the anodic reaction (2)
occurs, Fe ²⁺ is oxidized to Fe ³⁺ , O ₂ gas is generated by water electrolysis, and H ⁺ is generated.
The generated O ₂ gas oxidizes Fe ²⁺ to generate Fe ³⁺ . If this happens, a phase change in the plating film, a change in the alloy structure, a decrease in current efficiency, uneven coloring of the film, etc. occur, and the desired plating film cannot be obtained. Therefore, the diaphragm 2 is used to prevent the transfer of Fe ²⁺ in the plating bath 3 to the anode chamber 4, and to prevent Fe ³⁺ from moving into the anode chamber 4.
This prevents the formation of oxides and allows the desired plating film to be obtained.

By the way, H ⁺ and SO ₄ ^2- ions freely permeate through the diaphragm 2. In addition, in the cathode 6, the current efficiency is poor with Fe-based plating, about 60 to 90%, and therefore the remaining electricity that is not used for the precipitation of Fe and Zn is is consumed in electrolysis, producing OH ^- ions and generating H ₂ gas.

2H ₂ O＋2e→2OH ^- +H ₂ ↑ ...(3) Then, at a certain instant, for the SO 4 ^2- ion transference number from the metal bath 3 to the anode chamber 4, the SO ₄ 2- ion transference number from the anode chamber 4 is H ⁺ ions permeate into the bathroom 3. Further, the SO ₄ ^2- transferred to the anode chamber 4 generates H ₂ SO ₄ in the anode chamber 4, increasing the sulfuric acid concentration in the anode chamber. When this sulfuric acid concentration changes, the transport numbers of H ⁺ ions and SO ₄ ^2- ions through the diaphragm 2 change, and as the sulfuric acid concentration increases,
The amount of H ⁺ ions transferred to the bathroom 3 increases.
However, if no alkali is added to the plating bath 3 and the amount of OH ^- ions produced at the cathode 6 is constant over time, the acid concentration of the plating solution will increase and the PH of the plating bath 3 will change. Put it away. especially
In Fe-based plating, the pH should be kept constant to stabilize the film, so changes in the pH should be avoided as much as possible. Of course, the current efficiency changes with changes in PH, so the production rate of OH ^- ions also changes, but if the problem is simply to keep the PH constant, it would be sufficient to increase the amount of current by that amount, but the current efficiency When plating is to be done in an optimal manner to keep the pH high and constant, changes in the pH in the plating bathroom 3 are unavoidable unless some measure is taken.

Therefore, in the above example, a PH meter is installed in the circulation tank 10 that forms part of the anode chamber liquid circulation system, so that H2O is supplied to the anode chamber liquid circulation tank 10 so that the sulfuric acid concentration in the anode chamber is constant. We are trying to add ₂ O and extract H ₂ SO ₄ liquid from it. By doing this, the transference numbers of SO ₄ ^2- ions and H ⁺ ions can be made constant over time, and the PH in the bathroom 3 can be made constant without changing the current efficiency. Can be done.

In the present invention, as mentioned above, the PH of the metal bath is adjusted by adjusting the acid concentration of the anode chamber solution, which has a sulfuric acid concentration of 1N to 3N and has an H ⁺ transfer number of 30 to 60%. . This is because if it exceeds 3N, the plating efficiency will decrease, and if it is less than 1N, the current density will increase and the life of the anion exchange membrane membrane will be shortened.

In order to use the H ₂ SO ₄ extracted from the circulation tank 10 as effectively as possible, it must be used in the bathroom 3.
It is to return to However, the diaphragm 2
Most of the Fe ²⁺ permeation is blocked, but a small amount moves to the anode chamber 4 due to the concentration gradient, and as described above, the anode reaction at the anode 5 (Fe ²⁺ →Fe ³⁺ +e ^- ) or water It is oxidized by the O ₂ gas generated by the electrolysis and becomes Fe ³⁺ , which is mixed into the sulfuric acid solution extracted from the circulation tank 10 . Therefore, this sulfuric acid solution containing Fe ³⁺ cannot be returned to the plating bath 3 as it is. Although Zn ²⁺ is also mixed into the sulfuric acid solution, it does not cause any major problems with the plating film, so focus should be placed on Fe ions.

To solve this problem, in this example, focusing on the fact that Fe ³⁺ is reduced to Fe ²⁺ during the metal melting process, the extracted sulfuric acid is introduced into the Fe melter 12 and Zn melter 13, which are installed in parallel. , Fe filled inside
The sulfuric acid solution is supplied to the circulation tank 8 after being brought into contact with the powder and Zn powder to dissolve them and reduce them to Fe ²⁺ . 14 and 15 are sludge removal devices, respectively.

Note that, as shown in FIG. 2, the dissolvers 12 and 13 may be provided in series. However, dissolving Zn first and then dissolving Fe is not desirable because Fe has poor solubility and must be dissolved with a concentrated acid, and Zn will precipitate on the surface where Fe is dissolved. do not have.

The present invention aims not only to utilize sulfuric acid effectively and reduce Fe ³⁺ , but also to use dissolved metal as a replenishment source for metal precipitated by plating in continuous plating. . As mentioned earlier, Fe-Zn is used to supply the metal for plating.
For alloy plating, FeSO ₄ 7H ₂ O and ZnSO ₄
It can also be added in the form of 7H ₂ O, but these are expensive and it is better to use cheaper metal powders to dissolve them.

However, in order to supply enough metal ions to keep up with the precipitation rate of plating metal, even if it is done by immersing metal plates in a sulfuric acid solution, for example, it is difficult to immerse a large number of metal plates in a long dissolution tank. However, it is impossible to obtain a high dissolution rate using a compact device.

As a solution to this problem, the inventors have developed the third
It has been found that it is sufficient to use a melting tower 50 as shown in the figure, fill the inside with metal particles 51 (or powder), and flow sulfuric acid from the recovered sulfuric acid supply port 52 at the top to bring it into contact with the metal particles 51. 53 is a metal grain supply port;
54 is a filter, and 55 is a gas vent.

Also, 60 is the sludge removal device mentioned earlier,
If dissolving Fe, cementite Fe ₃ C and fine powder of Fe are removed, and if dissolving Zn, fine powder of Zn is removed. 71 is a bypass path, and 72 is a sulfuric acid supply amount regulating valve.

When such a dissolving tower 50 is used, the surface area per unit volume of the metal particles 51 becomes extremely large, and the dissolution rate per unit volume increases accordingly. Moreover,
Hydrogen gas is generated during melting, which disturbs the flow of sulfuric acid, increases the degree of contact between unused sulfuric acid and the surface of metal particles, and causes each metal particle or its bed filled with hydrogen gas to Since it is in a fluidized state, the dissolution rate is further increased. In addition, since the passage speed of sulfuric acid between metal particles becomes faster, high solubility can be expected in this respect as well.

By the way, if the surface area per unit volume is simply increased, the particles need only be small, but according to the findings of the present inventors, it is desirable that the particles be 0.1 mm to 3 mm. The lower limit is thought to be due to the fact that sulfuric acid in the vicinity of particles is directly consumed by dissolution, but there is no diffusion effect to replace it with new sulfuric acid.

On the other hand, it is desirable to dissolve Fe at a sulfuric acid concentration of about 1N to 5N, and to dissolve Zn at a sulfuric acid concentration of 0.1N or higher. If the desired amount of dissolution cannot be obtained with just one pass of sulfuric acid contact, multiple dissolution towers of the same type may be installed, or a second dissolution tower may be installed.
The lysate may be fed back through a return path 16 as shown in the figure. Further, metal dissolution and addition of FeSO ₄ and ZnSO ₄ may be used together. The method to be adopted is determined from an economic standpoint. Furthermore, a part of the sulfuric acid extracted from the circulation tank 10 can also be taken out of the system.

Next, examples will be shown.

Example In this example, Fe--Zn alloy plating was performed using the same plating equipment as shown in Fig. 1, and the bath composition was as follows:
ZnSO ₄・7H ₂ O150g/, FeSO ₄・7H ₂ O250g/
, (NH ₄ ) ₂ SO ₄ 100g/, PH=2, as bath temperature
Anion exchange membrane diaphragm (manufactured by Tokuyama Soda) was used at 50℃.
Neosepta "AF-4T") is separated and the anode chamber is
Filled with 0.5 mol/H ₂ SO ₄ and using Pt as an anode,
Continuous plating was performed at 30A/ ^dm2 .

Note that the characteristics of the anion exchange membrane membrane in this example are that the transport number of H ⁺ is 25% and the transport number of SO ₄ ^2- is 75.
It was %. Further, the current efficiency of the Fe--Zn alloy plating in this example was 70%.

As a result, H ₂ SO ₄ equivalent to 75% of the amount of electricity supplied was generated in the anode chamber 4, and since the concentration of H ₂ SO ₄ in the anode chamber increased, ₄ minutes of the generated H ₂ SO 4 was collected.
Furthermore, at the exit of the plating bath in the plating bath 3, OH ^- ions equivalent to 5% of the amount of electricity that was supplied remained, so the pH increased to 2.1.

The recovered sulfuric acid was led to an Fe dissolver 12 and a Zn dissolver 13 to dissolve Fe and Zn.

Here, the alloy composition of Fe-Zn in this example is Fe-20
%, Zn-80%, the amount of Fe-Zn dissolved was 19%, Zn in the Fe dissolver, and the amount of sulfuric acid solution was changed to dissolve the supplied metal ions commensurate with the composition ratio.
Feed 56% to the dissolver. In the dissolvers 12 and 13, since Zn dissolves more easily than Fe, the entire amount of H ₂ SO ₄ supplied reacted with Zn. Further, Fe dissolution left H ₂ SO ₄ equivalent to 5% of the amount of electricity applied as unreacted H ₂ SO ₄ . The solution that has passed through the dissolvers 12 and 13 is removed by removal devices 14 and 15 to remove unreacted metal particles and sludge (often in the case of Fe, mainly Fe ₃ C).
After removing it, it was supplied to the plating bath circulation tank 8.

Here, in the solution supplied as the plating bath supply solution, 5% of H ⁺ was present in the amount of electricity applied.
In the Metsuki bath recovered from Metsuki Bathroom 3,
Since 5% OH ^- was present, the pH was kept constant at 2.0.

Regarding metal ions, Fe ²⁺ is always stable,
The concentration composition of Zn ²⁺ and the number of Fe ³⁺ ions
We were able to suppress it to 10ppm or less.

Therefore, even after continuous plating for 300 hours, a uniform alloy film of 20% Fe and 80% Zn was always obtained.

[Brief explanation of drawings]

Figure 1 is a schematic diagram of a configuration example of Fe-Zn alloy plating.
FIG. 2 is a schematic diagram of a different embodiment, and FIG. 3 is a schematic diagram showing an example of a dissolver. 2... Anion exchange membrane diaphragm, 3... Metsuki bathroom, 4
...anode chamber, 5...insoluble anode, 6... object to be plated, 1
2...Fe melter, 13...Zn melter, 50...metal melting tower, 51...metal particles.

Claims (1)

[Claims] 1 Fe is carried out by installing an insoluble anode in an anode chamber separated from the metal bath by an anion exchange membrane diaphragm.
system electroplating, recovered from the anode chamber.
After adjusting the sulfuric acid concentration by adding water to 1N to 3N sulfuric acid containing Fe ³⁺ ions, part of it is circulated to the anode chamber and the rest is filled in the dissolver. Iron or metal powder or metal grains containing iron. melt the metal by contacting it with
A method for supplying metal ions in electroplating, which comprises reducing Fe ³⁺ ions to Fe ²⁺ ions and then supplying a solution containing Fe ²⁺ ions to a plating bath.