JPS627900A - Method for supplying zinc ion to galvanizing bath - Google Patents

Abstract

PURPOSE:To facilitate the dissolution of metallic zinc by dissolving zinc in a soln. contg. tervalent iron ions and ions of a metal having a higher electric potential and a lower hydrogen overvoltage than zinc and by supplying the resulting soln. to a galvanizing bath. CONSTITUTION:When zinc ions are replenished during galvanization using an insoluble electrode, metallic zinc is dissolved in an aqueous soln. contg. 50-1,000ppm tervalent iron ions and 10-400ppm ions of a metal having a higher electric potential and a lower hydrogen overvoltage than zinc, e.g., Ni, Bi, Tl or Pb. The resulting soln. contg. zinc ions is supplied to a galvanizing bath. By the effect of the coexisting tervalent iron ions and other metallic ions, the deposition of impurities by substitution is facilitated and a hydrogen generating reaction, that is, a zinc dissolving reaction is accelerated.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a method for supplying zinc ions to a galvanizing bath, particularly for replenishing zinc ions to a galvanizing bath in an electrogalvanizing method using an insoluble electrode as an anode. regarding its supply method.

(Prior Art) In zinc-based electroplating, the following method has been conventionally used as a method for supplying zinc ions into a bath.

When using an insoluble anode: This uses lead, lead-silver, -tin, -antimony-based lead alloy, carbon, platinum, etc. as the anode.
As a source of zinc ions to the plating bath, use zinc hydroxide, zinc carbonate, or a mixture thereof with zinc oxide, which has a higher dissolution rate and solubility than metal zinc, or a mixture of these and zinc oxide p) I = 3 ~
(Example: JP-A-50-85531 and JP-A-55-152167). However, the drawback is that the zinc consumption rate is higher than that of metal zinc.

In this regard, if the operation is performed at an extremely low pH (0.1 to 0.5), metal zinc can be dissolved and supplied because it is relatively easily dissolved in such a plating bath. However, such extremely low po
In this case, corrosion of the plating bath and piping becomes a problem, and equipment costs increase because it is necessary to use expensive materials with high corrosion resistance for parts of the equipment that come into contact with the plating solution.

It has also been proposed that zinc dross, slag, etc. be treated in the presence of ferric ions to selectively elute zinc ions and use them as a supply source to the zinc plating bath (Japanese Patent Application Laid-Open No. 1983-1999)
-155131).

Using a soluble electrode: This uses metallic zinc as an anode, which is consumed and dissolved during the plating process, supplying zinc ions to the plating bath. Metallic zinc constitutes the anode, so the consumption rate is low, but it is difficult to handle when replacing the electrode.
It is also difficult to maintain a constant distance between electrodes during close electrolysis.

Thus, a constant supply of zinc ions to the galvanizing bath, which is essentially continuously depleted of zinc ions, is in any case essential and is a technically and economically superior method. It is hoped that the establishment of

(Problems to be Solved by the Invention) In the case of plating using the above-mentioned insoluble anode, the plating operating conditions are relatively easy to manage, there are few operational problems, and alloy plating can be performed at the same time. Most production lines for galvanized steel sheets use an insoluble anode.

By the way, when producing a thick zinc-grained steel sheet using such an insoluble anode, the cost is high because the zinc source is expensive, and therefore it is desired to reduce the consumption rate. In this case, it is very economically advantageous to use metallic zinc, which has a slow dissolution rate but a low basic unit, as a zinc source.

゛ Here, the present inventors have conducted various studies regarding means for promoting the dissolution of metallic zinc and methods for supplying a solution containing metallic zinc ions to a plating bath when using an insoluble electrode, and have found that the results show that After learning that it is effective to set up a dissolving tank for metallic zinc separately from the tank and dissolving metallic zinc there, we conducted further experiments.
Under conditions in which trivalent iron ions (Fe3+) and metal ions whose standard electrode potential (hereinafter simply referred to as "potential") is higher than that of zinc and whose hydrogen overpotential is lower than that of zinc coexist, their synergism increases. The present invention was completed based on the knowledge that this effect further promotes the dissolution of metallic zinc.

Here, the present invention provides trivalent iron ions 50~too, op
Metallic zinc is dissolved in a solution containing p- and 10 to 400 ppm of ions of a metal whose potential is more noble than zinc and whose hydrogen overvoltage is lower than that of zinc, and the resulting zinc ion-containing aqueous solution is used for galvanizing. This is a method for supplying zinc ions to a galvanizing bath.

The dissolution reaction of metallic zinc can be expressed by the following equation.

Zn −* Zn” + 2e−・・・・・・
■2H" + 2e--L °°°°゛■ Metallic zinc has a high hydrogen overvoltage, so the reaction in (2) becomes rate-limiting and its dissolution rate is extremely low. In the present invention, zinc ions The coexistence of two other metal ion species promotes their dissolution.

Generally, the dissolution rate of metallic zinc is extremely slow in a bath that does not contain any trace ions, but by dissolving trace ions that are more harmful than zinc, they are substituted and precipitated on the zinc surface.
It is well known that the reaction ① above is accelerated on metals that are harmful to metals.

However, according to the present invention, trivalent iron ions (Fe
) and ions of a metal whose potential is more noble than zinc and whose hydrogen overpotential is lower than that of zinc, respectively, at a concentration of 50 to 1100.
Metallic zinc is dissolved in a solution containing 0 pp and 10 to 400 ppII+, and according to the findings of the present inventors, the coexisting effect with Fe'+ is Fe''-Fe3°
Because the reaction of Zn? 1j solution reaction is half reaction. Therefore, the dissolution reaction of metallic zinc is improved synergistically, and the dissolution reaction proceeds more effectively than was previously possible.

According to the present invention, the acidic solution used to dissolve metallic zinc is not particularly limited as long as it can be supplied to the plating bath as a plating bath. However, usually pH 3~
This is an aqueous sulfuric acid solution of No. 5.

Note that metallic zinc containing such metals as impurities may be used as long as it supplies the coexisting metal ions specified in the present invention due to its properties.

(Operation) The present invention will be further described below with reference to the accompanying drawings.

FIG. 1 is a flow sheet showing the method according to the present invention, in which a zinc ion-containing solution, for example, a sulfuric acid aqueous solution, is sent from a dissolution tank 10 for dissolving metallic zinc to a storage tank 14 via a solid-liquid separation means 12 as appropriate. Then, an appropriate amount of this zinc ion-containing solution is sent to the plating tank 16 as required. Alternatively, a circulating flow may be constantly provided between the storage tank 14 and the plating bath 16, so that the plating bath composition is always kept constant. - Here, according to the invention, in the dissolution tank, 3
valent iron ions and metal ions whose potential is higher than that of zinc and whose hydrogen overvoltage is lower than that of zinc, such as Ni.
, B+, Tj! , Pb, and other ions coexist.

Figure 2 shows the temperature of each metal grain of 100 mesh at 50°C.
, when dissolved in sulfuric acid solution of PH-2.0 for 60 minutes,
This is a graph showing the amount dissolved at each time.
In the illustrated example, it can be seen that the coexistence effect of Fe'' and Ni'' is significant.

In addition, it was confirmed from a series of experimental results that similar effects can be seen for metal ions other than Ni, which are nobler than zinc and have a lower hydrogen overvoltage.

Incidentally, the larger the amount of Fe''' (trivalent iron ion), the more advantageous it is in promoting the dissolution of metallic zinc, but generally, Fe''' is used as an acid ion on the bare surface of the copper strip during single-sided plating. However, as a result of experiments on actual production lines, the inventors of the present invention confirmed that this phenomenon does not actually occur at a concentration of about 1,000 ppm or less. However, in order to improve the dissolution rate of metal zinc, which is the intended purpose of the present invention, it is necessary to add at least 50 ppm or more. Preferably it is 100 to 500 ppm. It was confirmed that the iron ion content within the above range did not adversely affect the chromate reactivity and the processing adhesion of the film.

In the present invention, at least one other coexisting element (Ni", Bi'°, Tβ order/'"
, pb""・4◆, etc.) exhibits the desired effect in an amount within the range of 10 to 400 ppm, more preferably 15 to 200 ppm. These coexisting chlorine ions have some influence on chromate reactivity and processing adhesion, but as long as they are within the above-mentioned range, their influence is small in the coexistence with Fe3°. Within this range, the lower the total concentration of coexisting ionic species is, the better; however, if it is too low, the chromate reactivity may be reduced to some extent, so it is desirable to strictly define the lower limit.

Table 1 shows Fe” ion 300.700.1l100p
When galvanizing was carried out in the coexistence of each metal ion in an aqueous solution of sulfuric acid containing p, the processing adhesion and chromate reactivity of the plated steel sheets obtained were tested under the following conditions, and the results of the tests on the surface of the steel sheet. This is a summary of the results of examining the presence or absence of acid discoloration.

Made by Sarasugi and Yu Huangyu: Steel plate to be treated: 5PCG O, 8mm thickness x 100n
+m width x 100mm length Plating bath composition: ZnSOs
・7HtO=500 (g/A'), NatS
On = 1100 (/j!) Bath temperature: 5
0 ('C) Current density: 70 (A/dmz) Plating amount:
20 (g/m") Processing adhesion test (cylindrical deep drawing): 5011IIIφ test piece, 30mmφ cylindrical deep drawing outer surface tape peeling visual evaluation in 4 stages, chromate reactivity test: Test liquid: Barker ZM352 5 seconds immersion fluorescence Table 1: 4-grade evaluation of Cr adhesion and amount of red rust generated after 5ST20 (hr) using X-rays (Continuation of Table 1) (Shige ◎: Excellent, O: Fairly good, △ : Slightly poor, ×: Poor Next, the present invention will be further explained with reference to Examples.

Example 1 According to the present invention, dissolution experiments were conducted using actual equipment at the pilot plant level. In this example, a filling tank is filled with high-purity metallic zinc (20 to 40 meshes) to form a fixed bed and a plating bath of Zn5Oa 7HzO=
500 g/1, NazSO4=100 g/41
Using a plating bath with a composition of A stainless steel filter was installed at the outlet of the melting and defilling tank, and the average amount of dissolved metal zinc and clogging of this filter were observed.
They are summarized in the table. In addition, as a comparative example, p e 2 +
The amount dissolved in the case where no metal ion is included and when only one of the ions is included is also shown.

Example 2 In this example, Example 1 was repeated except that the aqueous sulfuric acid solution was blown into the tank from the bottom to create a fluidized bed. Dissolution is promoted because the mixing effect of metal zinc powder in the liquid is large. The results are also summarized in Table 2.

(Continuation of Table 2 an) (Effects of the invention) As explained above, according to the present invention, the dissolution rate of metallic zinc is dramatically increased compared to the conventional method, and the method using an insoluble anode Profits can be used even more effectively, and the practical effects are significant.

[Brief explanation of drawings]

FIG. 1 is a conceptual block diagram of a plating apparatus using the method according to the present invention; and FIG. 2 is a graph showing the coexistence effect of each metal ion on metal zinc dissolution in the present invention.

Claims (1)

[Claims] Zinc obtained by dissolving metallic zinc in a solution containing 50 to 1000 ppm of trivalent iron ions and 10 to 400 ppm of ions of a metal whose potential is nobler than that of zinc and whose hydrogen overvoltage is lower than that of zinc. A method for supplying zinc ions to a galvanizing bath, the method comprising supplying an ion-containing aqueous solution to the galvanizing bath.