JPH0428799B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for recycling iron-based electroplating solution.

[Prior art] Fe ³⁺ ions, which are the main component of iron-based electroplating baths, are extremely unstable and are easily oxidized, for example, by dissolved oxygen in the plating bath or by electrode reactions on the anode surface. It becomes ³⁺ ion.
These reactions can be expressed as follows.

Fe ²⁺ +1/4O ₂ +1/2H ₂ O→Fe ³⁺ +OH ^- ...(1) Fe ²⁺ →Fe ³⁺ +e ...(2) The Fe ³⁺ ions generated as above are
Since it changes the plating and longitudinal composition and has an adverse effect on the plating, it is necessary to always reduce and/or remove an amount corresponding to the amount produced. The air oxidation caused by the reaction of equation (1) can be reduced to a considerable extent by improving the Metxel structure or sealing the Metxel with _N2 , but the oxidation caused by the electrode reaction of equation (2) When using
50 to 90% of the amount of current is generated. Therefore, particularly in the latter case, reduction and/or removal of Fe ³⁺ ions is an essential problem in plating operation.

Conventionally, there is a chelate resin method as a method for removing Fe ³⁺ ions generated in zinc-based plating baths (Japanese Patent Publication ^No. 57-27960). Although this chelate resin method has been applied to iron-based plating, it has the following main drawbacks and is not necessarily practically effective. That is, (1) an amount of Fe ³⁺ corresponding to the amount of Fe ³⁺ removed;
needs to be supplied to the plating bath from outside the system, (2) the cost of neutralizing the regenerated liquid in the chelate resin method column is high, (3) the cost of replacing the resin is high due to deterioration of the chelate resin, (4) the chelate resin Column systems are expensive to install and require a large amount of space.

[Problem to be solved by the invention]

Therefore, the present inventors first proposed a method for effectively and advantageously reducing Fe ³⁺ ions generated in the plating bath during iron-based electroplating, by adding and dissolving metals to be supplied to the plating bath into the plating solution. proposed a method that can reduce Fe ³⁺ and replenish the plating metal at the same time (for example, Japanese Patent Application No. 57-52565)
No. 17153)). In connection with this method, the present inventors also set the Fe ³⁺ production rate in the plating solution, the plating current efficiency, and the Fe ³⁺ reduction efficiency in the dissolution reaction as parameters, and while actually measuring these, metal We have proposed a method to control the plating bath concentration by adjusting the supply amount and plating solution waste amount.

In the case of this method, it is assumed that all the metal powder added to the dissolution reaction tank is completely dissolved, and the amount of metal constantly present in the dissolution reaction tank is
This approximately corresponds to the addition equivalent calculated stoichiometrically from the required processing load amount, which will be described later. The reaction area of the metal powder in this dissolution reactor is determined by the addition equivalent and the particle size of the metal powder and its reduction due to subsequent reactions. In this case, since there is a restriction on the reaction area, the amount of dissolution per hour in the reaction tank is limited. Therefore, there are drawbacks that the reaction time is long, the reaction tank capacity is large, and the equipment investment cost and equipment space are large.

Generally, a method for increasing the reaction surface area is to use particles of fine particle size.
However, the industrially and economically available particle size is up to several μm. In addition, in the case of zinc powder, the powder has cohesive properties, and particles with a particle size of several micrometers will cause aggregation, which will actually inhibit the reaction, so a particle size of several + micrometers is appropriate. It is. In this way, even if particles with a fine particle size are used, there is a limit to the increase in reaction area;
This is not necessarily an effective method for promoting the metal dissolution reaction in the plating bath.

Therefore, an object of the present invention is to provide a method for reducing Fe ³⁺ ions in a plating bath and replenishing the plating metal by adding and dissolving the metal to be replenished into the plating bath. The object of the present invention is to provide a method for regenerating an iron-based electroplating solution that can greatly increase the reaction surface area and improve the amount of dissolution per hour.

[Means to solve the problem]

In order to solve the above-mentioned problems and achieve the above-mentioned objects, the present invention provides a method for recycling iron-based electroplating liquid that replenishes metal, in which Fa ³⁺ -containing plating liquid and metal powder to be replenished are mixed in a stirring tank. By contact melting in the mold melting tank, when reducing Fe ³⁺ ions in the plating solution and replenishing the metal at the same time, 2 of the metal powder addition equivalent calculated stoichiometrically from the processing load required for plating solution regeneration is used. It is characterized by continuously supplying ~10 times more metal powder to the metal melting reaction.

Next, the present invention will be explained with reference to the drawings.
FIG. 1 shows an example in which the plating bath regeneration method of the present invention is applied to iron-zinc alloy electroplating. In the figure, 1 is a plating tank filled with a plating solution containing Fe ³⁺ ions and Zn ²⁺ ions as main components, 2 is an insoluble anode, 3 is a material to be plated, such as a steel strip, and 4 is a plating solution in plating tank 1. Buffer tank for replenishing
5 is the metal Fe powder to be replenished, 6 is the metal Fe stirring tank type dissolution layer in which the Fe powder is dissolved by the plating liquid extracted from the plating tank 1, and 7 is the metal Zn to be replenished.
Powder, 8 is a Zn stirred tank type dissolution layer by the plating solution extracted from the plating tank 1 in the same way as the metal Fe stirred tank type dissolution tank 6, 9 is a Zn stirred tank type dissolution layer, 9 is a sludge, for example, horn seed oxides (FeO, MnO) contained as impurities. etc.) and carbides (Fe ₃ C, etc.), and 10 is a plating liquid drain-off receiving tank.

The reactions in the metal Fe stirred tank type dissolution tank 6 and the metal Zn stirred tank type dissolution tank 8 are as follows.

Fe ³⁺ +1/2Fe →3/2Fe ²⁺ (Fe ³⁺ reduction reaction) ...(3) 2H ⁺ +Fe→Fe ²⁺ +H ₃ (acid dissolution) ...(4) Fe ³⁺ +1/2Zn →Fe ³⁺ 1/2Zn ³⁺ (Fe ³⁺ reduction reaction) ...(5) 2H ⁺ +Zn→Zn ³⁺ +H ₂ (acid dissolution) ...(6) That is, in each stirring type tank dissolution tank 6 and 8, By adding metallic Fe and metallic Zn to the plating solution and stirring them, Fe ³⁺ in the plating solution is removed.
In addition to reducing ions, the plating solution is regenerated by dissolving and replenishing metals into the plating solution.

In the present invention, in the iron-zinc alloy electroplating system as described above, when Fe powder and Zn powder are added to the stirred tank type melting tanks 6 and 8 respectively and the above reaction is carried out, a specific amount of metal is constantly stirred. It is designed to exist in a bath-type dissolution tank.

In other words, the required amount of treatment liquid is determined from the Fe ³⁺ ion concentration in the plating solution and the amount of metal powder dissolved necessary for adjusting the bath components, and the equivalent amount of metal powder to be added is calculated stoichiometrically from this required treatment load amount. However, the metal powder is added so that 2 to 10 times the equivalent amount of the metal powder added is constantly present in the stirring tank type dissolving tank. The preferred excess amount depends on the type of metal powder, specific gravity, particle size, plating bath component concentration, PH temperature, processing conditions such as Fe ³⁺ concentration, equipment attached to the equipment, etc., and the optimum amount should be determined individually in relation to these factors. is selected. In order to improve the stirring flow of the metal powder and prevent sedimentation, it is efficient to use an excess of 2 to 10 times the equivalent amount. If it exceeds 10 times, stirring becomes difficult.

Here, a method for calculating the added equivalent will be described using FIG. 1 as an example. The Fe ³⁺ concentration at the inlet of the treated solution to the stirred tank type dissolution tank is now Cin (Kmol/m ³ ), and the intended outlet Fe ³⁺ concentration of the regenerated solution after reduction treatment is Cout.
(Kmol/m ³ ), and the flow rate of the treatment liquid passing through this stirred tank type dissolution layer is Q (m ³ /hr), then the required treatment load amount of Fe ³⁺ can be determined by the following formula.

Q (Cin−Cout) ...(7) Therefore, from equations (3), (4), (5), and (6), the Fe ³⁺ reduction efficiency R in the stirred tank type dissolution tank is defined as follows. .

R = (amount of metal dissolved due to Fe ³⁺ reduction reaction) / {(amount of metal dissolved due to Fe ³⁺ reduction reaction) + (amount of metal dissolved due to reaction with H ⁺ acid)} Therefore, chemical reaction theory of metal powder Equivalent amount added
Eeq is as follows.

Eeq=Q(Cin-Cout)/R...(8) Under such conditions, the present invention adds an excess amount of metal powder of 2Eeq to 10Eeq in the stirred tank type melting tank.

〔Example〕

Next, the effects of the present invention will be illustrated by experimental examples.

Experimental example 1 Fe-based plating bath (composition: Fe ²⁺ 1kmol/m ³ ,
Zn ²⁺ 0.3kmol/m ³ , Na ₂ SO ₄ 1kmol/m ³ , PH2.0,
A temperature of 50°C and an initial Fe ³⁺ concentration of 400 mg/) were introduced into a stirred tank type dissolution tank, and a dissolution reaction was carried out in the presence of twice the equivalent of 200 meshes of Fe powder. The results are shown in FIG. As is clear from FIG. 2, compared to the case of equivalent addition, the amount of Fe ³⁺ reduction per hour and therefore the amount of metal dissolution were greatly improved.

Experimental Example 2 Using the same Fe-based plating bath as in Experimental Example 1 except that the initial Fe ³⁺ concentration was 1000 mg/
A dissolution reaction was carried out in the presence of 200 mesh Zn powder. The results are shown in Figure 3. Compared to those with equivalent addition, the Fe ³⁺ reduction rate and hence the metal dissolution rate were significantly improved.

[Brief explanation of drawings]

Figure 1 is a schematic diagram showing an example in which the present invention is applied to an iron-zinc alloy electroplating method, Figure 2 is a diagram showing a comparison between the conventional technology and the present invention in metal Fe melting, and Figure 3 is a diagram showing a comparison of the present invention in metal Zn melting. FIG. 3 is a diagram showing a comparison between the prior art and the present invention. 1... Plating tank, 2... Insoluble anode, 3... Material to be plated, 4... Buffer tank, 5... Fe powder,
6...Metal Fe stirring tank type dissolution tank, 7...Zn powder, 8
...Metallic Zn stirring tank type dissolution tank, 9...Solid-liquid separator, 10...Plating liquid drain-off receiving tank.

Claims (1)

[Claims] 1. In a method for regenerating iron-based electroplating liquid that replenishes metal, plating is carried out by contacting and dissolving Fe ³⁺ -containing plating liquid and metal powder to be replenished in a stirred tank-type dissolving tank. At the same time as reducing Fe ³⁺ ions in the liquid, replenishing the metal to be plated, add 2 to 10 times the equivalent amount of metal powder added stoichiometrically from the processing load required for plating liquid regeneration. A method for regenerating an iron-based electroplating solution, characterized in that the iron-based electroplating solution is constantly present in a stirring tank type dissolving tank.