JPS6152398A - Out-of-system reduction treatment of metallic ion - Google Patents

Abstract

PURPOSE:To reduce easily Fe<3+> ions and to execute satisfactory plating by conducting an Fe plating liquid to a cathode chamber having the anion exchange membrane of a reducing device separate from a plating cell and returning the liquid to the plating cell after electrolysis. CONSTITUTION:Part of the plating liquid in the slating cell 10 provided with an anode 11 consisting of a Pb alloy, etc. and a cathode 12 consisting of a steel plate, etc. is conducted to the cathode chamber 4 of the reducing device consisting of the electrolytic cell 1 separated to the cathode chamber 4 and the anode chamber 3 by the cation exchange membrane 2 in the stage of Fe plating in which plating of an Fe-Zn alloy is executed in the cell 10 by using the plating liquid contg. FeSO4, ZnSO4, Na2SO4, etc. A high concn. of H2SO4 is put as an anolyte into the chamber 3 and electricity is conducted to the cathode 6 and the anode 5 to execute electrolysis. The Fe<3+> ions in the plating liquid in the chamber 4 are thus easily and economically reduced to Fe<2+> ions and said liquid is returned as the plating liquid contg. the Fe<3+> ions at the smaller ratio to the cell 10 through a plating bath tank 20.

Description

[Detailed Description of the Invention] [Industrial Application Field] The wood powder is made of Fe, Fe-Zn or Fe-Ni.
The present invention relates to an out-of-system reduction treatment method for metal ions that reduces Fea+ ions to Fe2+ ions in system plating.

[Prior art] Generally, in Fe-based plating, Fe2+ in the plating bath
Ions are extremely unstable, and Fe2+ ions are oxidized to produce Fe3+ ions by the reaction of equation (1) due to dissolved oxygen in the plating solution, and by the reaction of equation (2) due to the electrode reaction on the anode surface. .

F e ”+1/402 +1/2 H20=Fe3
"+OH-* ・Fist (1) Fe2+ → Fe3++e ... (2) As a result, due to changes in the Fe2+ concentration in the plating bath, especially in the case of Fe-based alloy plating, the alloy composition changes and a uniform coating can be obtained. This causes problems such as a decrease in current efficiency.

Therefore, in order to deal with this problem, the following technique is available as a means for preventing Fe2+ from becoming liquefied, or as a means for reducing or removing Fe''+ ions in an amount corresponding to the amount of Fe3+ ions produced.

(1) A method using a soluble anode (Fe-based anode).

(2) A method in which the generated Fe3+ is reduced by dissolving Fe powder or Fe grains, etc. to obtain Fe2+ and supply it to the plating bath.

(3) A method of removing Fe3+ using a solvent extraction method or the like.

(4) A method of plating while installing an insoluble anode in an anode chamber separated from the plating bath by an anion exchange membrane diaphragm.

[Problems to be solved by the invention] However, in the method 1), although the electrode reaction equation (2) can be avoided, the reaction of the equation (1) cannot be avoided, and as a result, a certain amount of Fe3+ ions must be removed by adsorption with a chelate resin, and the amount of plating metal ions corresponding to the difference between anode efficiency and cathode efficiency becomes excessive, which not only makes it extremely difficult to maintain a constant bath composition, but also increases the The anode must be replaced every time it wears out, which is fatal when considering a continuous plating line, and it also requires 30 A.
Under high current density conditions of /drn' or higher, there is a drawback that the Fe anode undergoes a non-4@ state phenomenon, making operation impossible.

In method (2), the dissolution rate of Fe powder or grains is low, the reducing ability is insufficient, and the contribution of the dissolution reaction of Fe by H is large. Therefore, when reducing the required amount of Fe3+, Fe2+ ion To avoid this, a large amount of plating solution must be tracked out. Moreover, this method focuses on the reactions of formulas (3) to (5).

As an anodic reaction, Fe+Fe2++2e # a * e (
3) Competitive reactions of formulas (4) and (5) occur as cathode reactions.

F63++6. , +F62+ -* * *
(4) H+ e+1/2 Hz
`` `` fist '' (5) and (
Since the reaction of equation 5) is dominant, it is necessary to increase the reaction of equation (3) in order to reduce the required amount of Fe. As a result, Fe2+ is oversupplied in the plating bath, and the plating The bath liquid must be dragged out.

Method (3) increases the running cost and
5042+ for ferrous sulfate when supplying 2+
It cannot be used due to the balance of Fe2+, and it is difficult to dissolve with Fe powder, so there is a problem of insufficient supply of Fe2+.

On the other hand, method (4) uses an insoluble anode, which allows plating at high current density, makes it easy to control the bath composition, and, in principle, does not require replacement of the anode. There are certain advantages. In addition, the anion exchange membrane separates the anode chamber from the plating bath, preventing Fe2+ ions from moving to the anode chamber as much as possible, which can be expected to reduce the amount of Fe3+ ions produced at the anode. (1) ~(3
) method is much more practical.

However, when performing continuous coating, the distance between the poles is usually kept small in consideration of power efficiency, etc., and there is a risk of damage to the diaphragm due to deflection of the running strip. .

An object of the present invention is to provide an ex-system reduction treatment method for metal ions that can achieve good plating in Metxel even without using a diaphragm.

[Means for Solving the Problems] The present invention for solving the above-mentioned problems includes providing a reduction device separate from the Metsuki cell during Fe-based plating, and providing a cathode with an ion exchange membrane as the reduction device. Using a separate cathode chamber and an anode chamber equipped with an anode, a part of the plating solution in the Metsuki cell is taken out and guided to the cathode chamber of the reduction device, electrolysis is performed in the reduction device, and plating is carried out in the cathode chamber. This method is characterized in that after Fe3+ ions in the solution are reduced to Fe2+ ions, the plating solution containing less Fe3+ ions is returned to the Metsuki cell.

[Function] In the method of the present invention, the reduction device according to the present invention is installed separately from the Metxel, and the plating solution is extracted from the Metxel and guided to the reduction device, where the Fea+ ions in the plating solution are removed. After being reduced to Fe2+ ions, Fe3
The plating solution containing few + ions will be returned to Metsukicell. therefore.

It has enough Fe2+ ions necessary for plating, and Fe3+
Since the plating solution containing few ions can be replenished into the Metsuki Cell, the plating solution with an appropriate Fe ion concentration can be managed in the Metsuki Cell, making continuous plating possible.

In the reduction device, the cathode chamber is separated from the anode chamber by an ion exchange membrane diaphragm, and electrolysis is performed there, so that Feg+ ions can be reduced to Fe2+ ions.

[Specific examples of the invention] The present invention will be explained in more detail below.

First, the method of the present invention will be schematically explained with reference to FIG.

1 is an electrolytic cell, and 10 is a metsuki cell, which are separate bodies.

The electrolytic cell 1 is separated into an anode chamber 3 and a cathode chamber 4 by an ion exchange membrane diaphragm 2, for example an anion exchange membrane diaphragm, and an anode 5 and a cathode 6 are disposed in each of the anode chamber 3 and the cathode chamber 4, respectively. At the top of the anode chamber 3.

A gas-liquid separation chamber 7 having a 02 gas outlet is provided.

On the other hand, a cathode 11 made of a Pb alloy or the like and an anode 12 made of a steel plate or the like are arranged in the Metsuki cell.

In the present invention, a part of the plating solution is taken out from the Metsuki cell 10, guided to the cathode chamber 4 of the electrolytic cell 1, and electrolyzed in the electrolytic cell (the one containing the cathode and anode serves as a reducing device). In Step 4, Fe3+ ions are reduced to Fe2+ ions, and the plating solution is returned to the Metxcell 10 directly or via the plating bath tank 20 as a plating solution with less Fe2+ ions and more Fe2+ ions.

By the way, the redox reaction of Fe ions is expressed by equation (6).

Fe”, =:Fe3++e 0.* (6) It is generally known that the redox reaction depends on the potential.

The present inventors have investigated how potential actually acts on the oxidation-reduction reaction of the Fe plating that we are currently targeting, and what consequences will occur if the potential is outside of that range. After repeated experiments and studies, the following became clear.

That is, in equation (6), the reaction to the left, that is, F
To reduce e”+ ions to F62+ ions, the potential of the cathode is set to (+0.77+) with reference to the hydrogen electrode (mass, NHE).
A potential more base than 0.04Mog(Fe”)/(Fe2+))V, preferably as a lower limit (-fL44J1og
(Fe2”) V(7) potential, (+0.53 +0°04uog(
A potential more base than Fe”)/(Fe2+))V, preferably as a lower limit (-0,68+0.031og (F
It was found that it is sufficient to hold the potential at V.

In this case, the two-limit value varies depending on the iron ion concentration ratio r = (Fe"")/(Fe"), as shown in the formula. Normally, the concentration ratio r in a plating bath is less than 1. Therefore, the value on the front side of the potential is usually +0.77.
It needs to be lower than V (mas, NHE). For example, (Fe2+) = 50g/sentence, (Fe3+) = 5
g/ In case of statement (1), +0.73V (mass, NH
E) It needs to be made more base. If this upper limit is exceeded, the Fe 3+ + e −+ Fe 2+ reaction will not occur, resulting in no electricity flowing.

On the other hand, the lower limit also depends on the Fe2+ concentration as shown in the formula, and in a normal plating bath -0.44V (MaS.

'NHE) is more to blame. When the potential is lower than this lower limit, the reduction reaction of Fe3+ (Fe''+e+Fe2+
) In addition to hydrogen generation reaction (H” + e −+ 1/
2H2) and the electrodeposition reaction of iron (Fe2++2e+Fe)
There is a problem that occurs.

In addition, since the reduction reaction of Fe3+ is a diffusion-limited reaction,
It has also become clear that, in practice, the greater the agitation of the plating solution at the cathode, the better.

In the present invention, any suitable cathode can be used as the cathode of the reduction device, but suitable examples include those made of expanded metal or lath as the electrode base material and coated with platinum coating on titanium or platinum to iridium oxide. It is. When the electrode base material is expanded metal or lath, the diffusion of the plating solution on the electrode surface becomes large, and the above Fe3++
There is an advantage that the reduction reaction of e-+Fe2+ is promoted. Further, an iron plate or lath-like iron may be used as the cathode, but if the pH of the plating bath is low, Fe may be eluted, which is disadvantageous as it requires frequent replacement.

For the anode, 1% lead or Ag is added to a corrosion-resistant material such as titanium.
It is preferable to use a lead alloy coated with a lead alloy containing aluminum or titanium or niobium clad with platinum.The electrode shapes include expanded metal, lath,
Additionally spaced tilted electrodes are desirable to remove oxygen gas generated at the anode.

The diaphragm may be any ion exchange membrane diaphragm that can prevent the permeation of Fe2+ ions, such as Seleimio
n AMV, C3V, CMV (manufactured by Asahi Glass Co., Ltd., Ac
1plex CK-1, CA-1 (manufactured by Asahi Kasei Corporation)
, Neosepta AY-4T, CL-25T, C
H-45T and AF-4T (manufactured by Tokuyama Soda Co., Ltd.) can be used.

By the way, in Metsukicell, plating may be performed in a batch manner or continuous plating on continuously moving steel plates. In the reduction device, the potential of the cathode is maintained within a predetermined range using a known constant potential electrolyzer. In this case, the electrolytic potential is set while controlling the concentration ratio of [Fe2+] and (Fe3+). Fe at the cathode
For the reduction reaction to E+, the anode chamber is 0.1-1O
When filled with Hz SO4 at a high concentration of about N, H at the anode
The reaction 20→2H+1/202+ 2 e occurs. Therefore, it is preferable to provide a gas-liquid separator above the anode chamber to remove gas and reuse the anode chamber liquid. moreover,
The reduction apparatus according to the present invention can also adopt a multiplex system in which the anode chamber also serves as an embodiment, as will be described later.

[Examples] Next, the present invention will be explained in further detail by showing Examples and Comparative Examples.

(Example 1) As shown in FIG. 1, electroplating was carried out and reduction was also carried out using an electroplating system that combined the Metsuki cell 10 and a reduction device.

As the anode 11 of the Metsuki cell 10, a Pb alloy electrode is used. A steel plate is used as the cathode 12, and the steel plate 12 is coated with Fe-Z.
n plating was performed. As a plating bath in Metsukicel,
F e S04 ・7 H20= 300g/l, Zn
5O+ ・7HzO=150g/i, N az S04
= 7'5 g/1 (1) composition, p) (= 2.5
0″C and Fe3+ concentration of Ig/jL was used.

The current density for plating was 4OA/d. Along with plating, the Fe3+g degree in Metxel tends to increase, and at the outlet side of the plating solution, the Fe3+g degree is 2.5 g/J.
It was L.

This plating solution was introduced into the cathode chamber 4 of the electrolytic cell 1 and subjected to reduction. However, the potential of the cathode is +o, 1v (vs, 5C
E). In the reduction device, electricity with a current density of 12 A/drn' flows, and the Fe3+ concentration in the plating bath is 1.
g/l. This reduced plating solution was stored in the plating bath tank 20 and then returned to Metsukicell IO. Furthermore, a Pb porous plate was used as the anode 5 of the reduction device. In the anode chamber, HzO is electrolyzed and 02 gas is generated.
H is generated, and this H" force (5042
- In order to maintain the balance of ions, H 2 SO 4 generated in the anode chamber 3 must be returned to the plating bath 4, but in this example, a high concentration of H 2 SO 4 is used as the anode chamber solution.
Since the anode chamber solution is used, the pH of the anode chamber solution is adjusted by adding HzO in the pH adjustment tank 30, and then led to the plating bath tank 20, where Fe and Zn powder and granules are added and the metals are dissolved. After that, Metuxel 10 was introduced. In this case, the dissolution of the metal becomes a source of metal ions that are carried out of the system by plating.

In addition, for the permeation through the gap H2 of 3042-, a corresponding amount of Fe5 is added to the cathode chamber 4 or Metxcell 10.
It is also possible to supply it in the form of 0+.7H20.

(Example 2) A plating solution was reduced using the reduction apparatus shown in FIG. As the electrolytic cell, a vertical two-chamber type electrolytic cell 1 made of acrylic resin was used, which was separated into an anode chamber 3 and a cathode chamber 4 by an anion exchange membrane diaphragm 2 . A liquid weight of approximately 501 mm is placed on the back of the anode 5 and cathode 6, and supply ports for the plating solution and H2SO4 are formed at the bottom of the anode chamber 3 and cathode chamber 4, respectively, and a width of 100 mm is formed at the top of the anode chamber 3.
A gas-liquid separation chamber 7 having a height of 100 mm and a thickness of 30 mm was provided, and an oxygen gas outlet was provided in the upper part of this separation chamber 7.

The plating baths used were 300 g/l of Fe50+ 7H20 and 150 g/l of ZnSO4 7H20.
, a composition of 75 g/fL (1) of Na 2 S 04, a pH of 2, and a Fe3+ concentration of 7.5 g/L.

Thus, using a constant potential electrolyzer and a saturated calomel electrode as a reference electrode, the potential of the cathode made of a Ti-based Pt-clad expanded metal was maintained at +0.2■. As a result, Fe3+ in the plating solution is proportional to the amount of current applied.
A decrease in concentration was observed.

The current density at that time varies depending on the amount of circulation of the plating solution, that is, the diffusion conditions, but it ranges from lO to 25 A/dm'.
Met. It was also found that the greater the amount of plating solution circulated, the greater the amount of reduction. Furthermore, the Fe3+ concentration decreased to 0.5 g/m after 10 minutes, making it clear that reduction could be carried out suitably.

On the other hand, 100 g of Naz so4 was used as the anode chamber solution.
/l and pH = 2, but at the anode, Hz SO4 is generated as electricity is applied, and the pH decreases, so in order to keep the pH constant, an equivalent amount of NaOH was added. did. Here, if a high concentration of Hz SO is used as the anode chamber solution,
When using 4, H2O is added and the generated H2
An amount corresponding to S04 may be overflowed and collected.

(Comparative Example 1) Compared to Example 1, the potential was set to 10.7V (vs, 5C
I tried to reduce it by changing E). In this case, it is true that F
A reduction reaction of e3+ occurred, but a hydrogen generation reaction (H++
e −+1/2 H2) also occurs, and an iron electrodeposition reaction also occurs,
The cathode was to be plated with Fe. Although a current density of 30 A/dm' was obtained, there was a decrease in current efficiency for reducing Fe3+.

(Comparative example 2) The potential was set to +〇, 50V Cvs, 5CE).

However, reduction of Fe3+ did not occur and no current flowed.

(Example 3) The two-chamber electrolytic cell shown in FIGS. 1 and 2 was modified to prepare a three-chamber electrolytic cell 1″ shown in FIG.
, both sides are cathode chambers 4.4, and the anode chamber 3 is the left and right cathode chambers 4.
, 4 was reduced using a reduction device having a structure common to both.

The intervals between the cathode 6, the diaphragm 2, and the IIM pole 5 were the same. The plating bath used was Fe50+-7H20.
= 300 g/l, Z n S O4.7 HO
4-150g/liter, composition of Na2304 = 75g/l, pH = 2, Fe3+ concentration is 7.5g/fLO). In addition, one constant potential electrolysis device was used, and its cathode was connected in parallel to the electrodes of the left and right cathode chambers, and the anode was connected to the electrode of the intermediate anode chamber. At this time, a current was applied to the cathode located on the left using a constant potential electrolyzer under conditions that measured the potential difference between the saturated calomel electrode and the saturated calomel electrode installed in the cathode chamber using a separate voltmeter. The potential of the cathode is +〇, 2
As a result of controlling the constant potential electrolyzer so that the current density was V (MaS, 5CE), the current density varied in the range of 10 to 25 A/drn' as the flow rate of the plating solution and the Fea+ concentration varied. Under the same flow rate of the plating solution as in Example 1, after half the time, that is, 5 minutes, the same Fe
``The concentration reached 0.5 g/i.

In this example, since the anode chamber is also used, the structure is simple. Further, instead of the three-room type of this example, it is also possible to use a multiple-house type.

[Effect of the invention] As described above, according to the present invention, Fe3+ ions are converted to Fe2
It can be easily and economically reduced to + ions, and the concentration of Fea + ions in the plating solution in Metsukicell can be suppressed to achieve good plating.

[Brief explanation of drawings]

FIGS. 1 to 3 are schematic diagrams of the experimental apparatus used in Examples 1 to 3, respectively. 1, l', electrolytic cell 2, anion exchange membrane diaphragm 3, anode chamber 4, cathode chamber (plating bath) 5, anode 6. ,,, cathode i o ,
,,, Metuxel 11. ,,,Anode 12 ,,,,
Cathode diagram 1

Claims (1)

[Claims] (1) For Fe-based plating, a reduction device separate from the plating cell is provided, and as this reduction device, a cathode chamber with a cathode and an anode chamber with an anode are separated by an ion exchange membrane diaphragm. A part of the plating solution in the plating cell was taken out and led to the cathode chamber of the reduction device, where electrolysis was performed, and Fe^3^+ ions in the plating solution were reduced to Fe^2^+ ions in the cathode chamber. A method for reducing metal ions outside the system, characterized in that the plating solution containing less Fe^3^+ ions is then returned to the plating cell.