JPS5925991A - Reducing method of metallic ions - Google Patents

Abstract

PURPOSE:To reduce easily and economically Fe<3+> ions to Fe<2+> ions in Fe plating, by separating an electrolytic cell to a plating bath chamber and an anode chamber with an anion exchange membrane, and maintaining the potential of the cathode in the plating bath chamber at a specific value. CONSTITUTION:A vertical two-chamber type electrolytic cell 1 made of an acrylic resin is separated by an anion exchange membrane 2 to an anode chamber 3 and a plating bath chamber 4. An insoluble anode 5 is provided in the chamber 3, and a cathode 6 in the chamber 4. The potential of the cathode is maintained at (+0.77+0.04log[Fe<3+>]/[Fe<2+>])V-(-0.44+0.03log[Fe<2+>] at a hydrogen elec trode standard (vs.NHE) and at (+0.53+0.04log[Fe<3+>]/[Fe<2+>])V-(-0.68+0.03log [Fe<2+>])V at a saturated caromel electrode standard (vs.SCE) in the stage of electrolysis. The concn. of Fe<3+> ions in the plating soln. is thus uppressed and good plating is accomplished.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a metal ion reduction method for reducing Fe''+ ions to Fez+ ions in Fe-based plating such as Fe, Fe-Zn or Fe-Ni.
In Fe-based plating, Fe2+ ions in the plating bath are extremely unstable, and dissolved oxygen in the plating solution
With the reaction of formula (1), Fe2+ ions are oxidized and Fe3+ ions are generated by the electrode reaction on the anode surface with the reaction of formula (2).

F e"+'/402 + 1/2H2Q -+ 'f
;' e3++OR-...” (1) Fe”→Fe””
+e ” = (2) As a result, due to changes in the FeZ+ concentration in the plating bath, especially in the case of Fe-based alloy plating, the alloy composition changes, making it impossible to obtain a uniform film and causing problems such as a decrease in current efficiency. Therefore, in order to deal with this problem, we need a means to prevent the oxidation of Fe2+ or a method to prevent Fe3+ from oxidizing.
The following techniques are available as means for reducing or removing Fe3+ ions in an amount corresponding to the amount of ions produced. (1) A method using a soluble anode (Fe-based anode).

(2) A method of reducing the generated Fe3+ by dissolving Fe powder or Fe grains to obtain Fez+ and supplying 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.

However, in method 1), although the electrode reaction equation (2) can be avoided, the reaction of equation (1) cannot be avoided, and in the end, a certain amount of Fea+ ions must be removed by adsorption with a chelate resin, etc. In addition, there is an excess of plating metal ions corresponding to the difference between anode efficiency and cathode efficiency.
Not only is it extremely difficult to maintain a constant bath composition, but the anode must be replaced every time it wears out, which is fatal when considering a continuous plating line, and the 30A
Under high current density conditions of /di'' or higher, there is a drawback that passivation occurs at the Fe anode, making operation impossible.

In method (2), the dissolution rate of Fe powder or grains is low, the reducing ability is not sufficient, and the contribution of the dissolution reaction of Fe to H+ is large. Therefore, when reducing the required amount of Fe3+, To avoid an oversupply of ions, it is necessary to drag out a large amount of plating solution. Moreover, this method focuses on the reactions of formulas (3) to (5).

As an anode reaction, Fe-+Fe"+ 2e...= (3) As a cathode reaction, competitive reactions of formulas (4) and (5) occur O Fe"e-+Fe"" (4) H"76-+ 1 /2 H2” ” (5) And (
Since the reaction of formula 5) is dominant, it is necessary to increase the reaction of formula (3) in order to reduce the necessary amount of Fe3+. As a result, Fe 2 + is oversupplied in the plating bath,
The plating bath solution 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.

Furthermore, since the anion exchange membrane separates the anode chamber and the plating bath into the anode chamber and prevents Fe2+ ions from moving to the anode chamber as much as possible, it is expected that the amount of Fe a+ ions produced at the anode will be reduced. This method is much more practical than methods 1) to (3).

However, when continuous plating is performed, the distance between the electrodes is usually kept small in consideration of power efficiency, etc., and there is a risk that the running strip may sway and damage the diaphragm.

An object of the present invention is to provide a method for reducing metal ions that can achieve good plating in Metxel even without using a diaphragm.

That is, in the present invention, in reducing Fe3+ ions in the plating bath to Fe"+ ions during Fe-based plating,
An anion exchange membrane diaphragm separates the plating bath from the anode chamber, and the plating bath is equipped with a cathode and the anode chamber is equipped with an insoluble anode, and the potential of the cathode is set to the hydrogen electrode standard (VS, NH
K) Te(-1-0,77+0.04A!og[Fe3
+)/CFe”,])V~(-0,44+0.031o
g[Fe”))V, saturated calomel electrode reference (VS, 5C
E) at (+0.53+0.04nog(Fe”)/(F
e” ) ) V ~ (-0,,68+0.031og (
Electrolysis is carried out by holding the ions at V () to reduce Fea+ ions to Fe2+ ions at the cathode (however, the above [Fez+] and [Fea+] are metal ions 7 (7
For example, the method of the present invention is characterized by: installing the reducing device according to the present invention separately from the Metxel, extracting the plating solution from the Metxel and guiding it to the reducing device; After reducing Fea+ ions in the plating solution to Fe2+ ions in the reduction device,
This method is applied to a mode in which a plating solution containing few Fe3+ ions is returned to Metsuki Cell.

The redox reaction of Fe ions is expressed by equation (6)0 Fe2+ @ Fe3++ e...” (6)
It is generally known that redox reactions depend on their potential.

The present inventors have investigated how potential actually acts on the oxidation-reduction reaction of the Fe-based plating that we are currently targeting, and what the results will be if the potential is outside of that range. As a result of repeated experiments and studies, the following was clarified:
To reduce e"+ ions to Fe2+ ions, the potential of the cathode is set to (+0.770, 0411og CFe" / [F e") ) with respect to hydrogen electrode (VS, NHE).
V~(-0,44+o, o3gog[Fe''))V, (+0.53 with saturated calomel electrode reference (vs, 5CE)
+0.041og [:Fe”:]/[Fe2+))
V~(-0,68+0.031og[Fe”)])
It has been found that it is sufficient to maintain it at V. In this case, the upper limit value varies depending on the iron ion concentration ratio r=[Fe3+]/[Fe2+], as shown by the formula. Since the concentration ratio r in a normal plating bath is often less than 1, the value on the front side of the potential is usually +〇, 77V (v
s, NHE) need to be made more base. for example,〔
In the case of [Fe2+]-50g/l and [Fe3+]-5jj/l, it is necessary to make it more base than +0.73V (VS,,NHE). If such upper limit is exceeded, F
e"+ e -'p No reaction of Fe2+ occurs, 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 (vs.

NHE) becomes more noble. When the potential is less base than this lower limit, the reduction reaction of Fe3+ (Fe3+10e→Fe2+
), hydrogen generation reaction (H++e→'/2 H2)
At the same time, there is a problem that an iron electrodeposition reaction (F e''+2 e −+F6) occurs.

In addition, since the reduction reaction of Fea+ 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 material can be used as the cathode, but a suitable example is one in which the electrode base material is expanded metal or lath, and titanium is coated with platinum or a platinum to iridium oxide coating. be. When the electrode base material is expanded metal or lath, there is an advantage that diffusion of the plating solution on the electrode surface is large υ, and the above-mentioned reduction reaction of Fe''→Fe2+ is promoted. It is also possible to use iron in the form of iron as the cathode, but if the pH of the plating bath is low, the elution of Fe may occur, which is disadvantageous as it requires frequent replacement.

As the anode, it is desirable to use a corrosion-resistant material such as titanium coated with a lead alloy containing about 1% lead or Ag, or a platinum clad on titanium or niobium. The electrode shapes include expanded metal shape, lath shape,
Further spaced angled electrodes are desirable to remove oxygen gas generated at the anode.

The diaphragm may be any anion exchange membrane diaphragm that can prevent the permeation of Fe2+ ions, such as Selemio
n AMV (manufactured by Asahi Glass Co., Ltd., Ac1plex CA
-1 (manufactured by Asahi Kasei Corporation), Neosepta AV -
4T (manufactured by Tokuyama Soda Co., Ltd.) can be used.

By the way, as an example of application of the method of the present invention, there is a case where a reducing device is provided separately from Metxel as described above.

At Metsukicell, plating can be performed either batchwise or continuously 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 [Fez+] and [Fe3+]. For the reduction reaction of e3+ at the cathode, if the anode chamber is filled with H2SO4 at a high concentration of 01 to ION, H2O-)2 at the anode.
A reaction of H++ 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. Furthermore, the reduction device according to the present invention can also adopt a multiplex system in which the anode chamber also serves as an embodiment, as described later.

According to the present invention, as in the following embodiment, Fe3+ ions can be easily and economically reduced to Fe2+ ions, and the concentration of Fe"+ ions in the plating solution in Metxcell can be suppressed to achieve good plating.

Next, the present invention will be explained in further detail by showing examples and comparative examples.

Example 1 The plating solution was reduced using the reduction apparatus shown in FIG. A liquid space of approximately 501πm is provided on the back of the anode 5 and cathode 6, which are separated into an anode chamber 3 and a cathode chamber 4, and supply ports for the plating solution and H2SO4 are provided at the bottoms of the anode chamber 3 and cathode chamber 4, respectively. At the same time, a width 100 mm is formed at the top of the anode chamber 3.
A gas-liquid separation chamber 7 with a height of 100 mm and a thickness of 30 mm was provided, and an oxygen gas outlet was provided at the top of the separation chamber 7.The plating bath used was FeSO4.7H20.
00g/l, znSO4・7H20 is 150. ! i'/
J! ! .

NazSO4 is 75! With a composition of i'/l, the pH
= 2, and the Fe3+ concentration was 7.5 g/l.

Thus, the potential of the cathode made of Ti-based PT clad expanded metal was maintained at +0.2 V using a constant potential electrolyzer and a saturated calomel electrode as a reference electrode. As a result, Fe3+ in the plating solution is proportional to the amount of current applied.
The decrease in concentration was found to be 10-25 A/di. It was also found that the greater the amount of plating solution circulated, the greater the amount of reduction. Moreover, the Fe” concentration was 0.5g/10 minutes later.
On the other hand, as the anode chamber liquid, N FL 2 SO4 was reduced to 1
In 009/IJ, a solution with pH = 2 was used, but in the anode chamber, H2SO4 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. Here, if there is a high concentration of H2S in the anode chamber solution,
When using 04, H2O is added and the generated H2
An amount corresponding to S04 may be overflowed and recovered.

Comparative Example 1 Compared to Example 1, the potential was set to -0.7V (VS, 5CE
) and tried to reduce it. In this case, it is true that Fe
A reduction reaction of 3+ occurred, but a hydrogen generation reaction (H++e→
1/2 H2) also occurs, an iron electrodeposition reaction also occurs, and the cathode becomes F
It was decided that it would be e-plated.

A current density of 30 A/di” was obtained, but Fe
0 Comparative Example 2 There was a decrease in current efficiency for reducing 3+ The potential was set to +〇, 50VIVs, 5CE). However, reduction of Fe3+ did not occur and no current flowed.

Example 2 Electroplating was carried out and reduction was also carried out using an electroplating system that combined the Metsuki cell 10 shown in FIG. 2 and a reduction device similar to that shown in FIG. 1.

A PB alloy electrode is used as the anode 11 of the Metsuki cell 10, a steel plate is used as the cathode 12, and the steel plate 12 is made of Fe7Z.
n-metsuki was performed. As a plating bath in Metsukicel,
FeSO4・77H2O-300/LZnSO4・7H
The composition used was 20=150 g/l, NazSO4" 75 g/l, pH=2.50° C., and Fe3+ concentration of 1 g/l. The current density of plating was 40 A/di". Along with plating, the Fe3+ concentration within the Metxel tends to increase, and the Fe3+ concentration was 2.5 g/l on the outlet side of the plating solution.This plating solution is led to the cathode chamber 4 of the electrolytic cell 1, A reduction similar to Example 1 was carried out. However, the potential of the cathode is +0. I V (vs, ScE
), electricity with a current density of 12 A/di flows, and the Fe3+ concentration in the plating bath is 1 g/l.
It declined to . This reduced plating solution was stored in the plating bath tank 20 and then returned to the Metxel 10. Furthermore, a PB porous plate was used as the anode 5 of the reduction device. In the anode chamber, H2O is electrolyzed, 02 gas is generated, and H+ is generated. This H" reacts with SO42- passing through the diaphragm 2 to generate H2SO4. Therefore, the balance of 5042- ions is adjusted. To maintain the H2S generated in the anode chamber 3
O4 must be returned to the plating bath 4, but in this example, since high concentration HzSO4 is used as the anode chamber solution, the pH of the anode chamber solution is adjusted by adding H2O in the pH adjustment tank 3o, and then the plating is carried out. Guide it to the bath tank 2 degrees,
Therefore, powder and granules of Fe + Zn were added, and after the metals were melted, they were introduced into Metxel 10. in this case,
The dissolution of metal becomes a source of metal ions that are carried out of the system by plating.

In addition, an amount of FeS corresponding to the permeation of SO42- through the diaphragm 2 is placed in the cathode chamber 4 or within 1° of the mesh cell.
It is also possible to supply it in the form of O4.7H20.

Example 3 The two-chamber electrolytic cell shown in Fig. 1 was modified to produce the electrolytic cell shown in Fig. 3.
A chamber-type electrolytic cell 1' is prepared, and an anode chamber 3 is provided in the middle, and cathode chambers 4.4 are provided on both sides. Reduction is carried out using a reduction device having a structure in which the anode chamber 3 is shared by the left and right cathode chambers 4.4. went.

The intervals between the cathode 6, the diaphragm 2, and the anode 50 were the same.

The plating bath used was FeSO47H20=3
00g/CZn5O4H7H20”150jj/l.

Composition of NNa2S04 = 75/l, pH = 2, Fe3
+ concentration is of 7.5 g/l. 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 was +〇, 2V (vs, 5cE). As a result of controlling the constant potential electrolyzer, the current density varied in the range of 10 to 25 A/dm as the flow rate of the plating solution and the Fe3+ concentration varied. . Under the same plating solution flow rate as in Example 1, after half the time, 1.5 minutes, the Fe3+ concentration was the same as in Example, i.e. 0.59/12.
reached.

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.

[Brief explanation of drawings]

FIGS. 1 to 3 are schematic diagrams of the experimental apparatus used in Examples 1 to 3, respectively. 1.1'... Electrolytic cell 2... Anion exchange membrane diaphragm 3.
・Anode room 4...Cathode room (plating bathroom) 5...Anode
6...Cathode 1o...Metsukicell 11...Anode
12... Cathode Figure 1 Figure 3 Figure 2

Claims (1)

[Claims] (1) When reducing Fe3+ ions in the plating bath to Fe2+ ions during Fe-based plating, the plating bath and anode chamber are separated by an anion exchange membrane diaphragm, and the cathode is placed in the anode chamber in the plating bath. are each provided with an insoluble anode,
The potential of the cathode is set to (+) with reference to the hydrogen electrode (VS, NHE).
0.77-1-0.041og(Fe”)]/CFe”
))V~(-0,44-1-0,03log CF e
2+]) V, saturated calomel electrode reference (vs, SCE
) Te(+0.53+0.04Aog[:Fe3+)/
CF e”) )V~(-0,68+0.03/l
og [F e”)) to perform electrolysis and reduce Fe3+ ions to Fe2+ ions at the cathode (
However, the above [Fe2+] and [Fe3+] are gold R, t
(7) A method for reducing metal ions, characterized by: (7) indicating a concentration).