JPS613900A - Method for dissolving metallic zinc shot - Google Patents

Abstract

PURPOSE:To dissolve rapidly metallic zinc shot at a low cost by feeding an excess of metallic zinc shot to a dissolving tank for supplying zinc to a galvanizing tank and by specifying the concn. of iron ions in a used galvanizing soln. flowing in the dissolving tank. CONSTITUTION:A used galvanizing soln. is drawn from a galvanizing tank, and after dissolving zinc in a zinc dissolving tank to fill up the deficiency, the soln. is returned to the galvanizing tank. At this time, metallic zinc shot is fed to the dissolving tank by an amount >=2 times the amount of zinc to be dissolved, and the concn. of iron ions in the used galvanizing soln. flowing in the dissolving tank is regulated to 0.5-2.0g/l by adding FeSO4 or the like. The deposition of iron on zinc shot and the dissolution of zinc shot take place simultaneously, and the continuous dissolution of zinc shot is ensured.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for dissolving zinc shot for electrolytic lead metki, and particularly to a dissolving tank placed in communication with an electroplating tank in order to increase the dissolution rate of metal zinc shot. By providing more than twice the required dissolution amount of zinc shot in the melting tank and maintaining the iron ion concentration in the circulating plating solution in the dissolution tank at α5 to 2.0 g/l, iron can be deposited on the surface of the zinc grains. The method of dissolving zinc shot while precipitating it is related.

IE galvanizing is widely used to prevent corrosion of steel materials. Recently, the demand for galvanized steel sheets in the fields of automobiles, home appliances, building materials, plant materials, etc. has increased significantly, and thick galvanized steel sheets are particularly required for automobile applications.

In order to cope with this increase in demand and thicker plating, high-speed electrogalvanizing methods that use insoluble anodes and perform plating under high current density are currently attracting attention rather than conventional electrogalvanizing methods that use soluble anodes. . In the high-speed plating method using insoluble 1lIII, it is necessary to replenish the plating solution with zinc as the zinc is consumed in the plating bath. In general, a method is adopted in which a dissolving tank is installed separately from the plating tank, and the post-plating solution from the metal and metal tanks is transferred to the dissolving tank, and the plating solution in which lead is replenished and dissolved is circulated from the dissolving tank to the plating tank. . When replenishing zinc in the dissolving tank, the rate of zinc dissolution must be fast enough to continuously maintain a predetermined zinc concentration in the plating tank. When zinc carbonate is used as supplementary zinc, rapid dissolution is guaranteed, but due to the increased cost, a method of dissolving metallic zinc shot directly into the plating plate is currently being considered.

However, the solubility of metallic zinc shot is not as good. Therefore, in order to suitably implement a high-speed plating method using an insoluble anode, it is necessary to establish measures to improve the solubility of metallic zinc sheets. As a countermeasure for this, a considerable increase in cost is caused, which makes using inexpensive zinc shot useless.

Under these circumstances, the present invention aims at establishing an inexpensive method for rapidly dissolving metallic zinc stain in a dissolving bath for electrogalvanizing.

Phenomenon 4, which is related to the dissolution of zinc shot into the plating solution, still has many unresolved aspects. When a metal is dissolved in an acidic solution, it is essential that hydrogen be generated by the following reaction as a cathodic reaction.

H++ @-= '/2 Hz The potential at which this reaction occurs is greatly influenced by the electrode surface where the reaction occurs. Therefore, metals with larger hydrogen overvoltages are more difficult to dissolve. The hydrogen overvoltage of zinc is quite large, and this is thought to be the reason why the rate of dissolution of zinc shot into the plating solution is low. By the way, cathode current density = 10-” A/cW?, I N
-The overpotential of zinc under the conditions of HC1 and room temperature is α85
It is at a high level of V.

The sound of the present invention is to reduce the apparent overvoltage of zinc shots.
We came up with the idea of depositing a thin layer of iron on the surface of zinc shot, and conducted repeated studies. As a result, a small amount of F・
We succeeded in accelerating the dissolution of zinc shot by allowing ions to coexist and depositing iron on the surface of the zinc shot through a substitution reaction with zinc. Since the hydrogen overvoltage of iron is about 50% that of zinc, it is thought that the dissolution of zinc is promoted. By constantly maintaining zinc stain in the dissolution tank at least twice the required dissolution amount of metal zinc shot, precipitation and dissolution occur simultaneously and a continuous supply of zinc is ensured, allowing the specified amount of zinc to be maintained in the plating tank. Concentrated plating solution is replenished. The required iron ion concentration is α5~2. Oq/l
Deaya. Iron is eluted from the steel material to be plated into the solution after electroplating, and the concentration generally exceeds the above concentration. However, in the past, the plating solution extracted from the plating tank was purified and then sent to the dissolving tank, so that the iron ion concentration in the dissolving tank was insufficient to fall within the above range. Therefore, in practical operation, the coexistence of iron ions in the dissolution tank can be brought about by not removing too much iron ions in the purification equipment.

Thus, the present invention is a method for dissolving metallic zinc shot in a dissolving tank in which the missing zinc is dissolved in the post-plating solution extracted from the electrogalvanizing tank and circulated to the electrogalvanizing tank. Then, metal zinc shot is present in the dissolution tank at least twice the required dissolution amount, and the iron ion concentration in the post-plating solution flowing into the dissolution tank is set to αs 9/l −
Provided is a method for melting metallic zinc shot, characterized in that the amount is 2.0 g7.

The present invention will be specifically explained below based on experimental examples.

At present, the A high-speed electrogalvanizing method using an insoluble anode is ZnSO4.7H,O: 4509/l (Zn:1
02 luc) NalSO4 (anhydrous): 3ag/i
fr@e-H1SO4: 4.9 g/l is used as the basic bath composition. The pH of the solution is typically α8~&5, and the bath temperature is typically 50~60''C. Lead alloys, platinum group metals, alloys, etc. are used as the insoluble anode. Some parts were continuously extracted from
The zinc is introduced into a dissolution tank via a purification facility 3, and there, zinc corresponding to the amount consumed by plating is replenished and dissolved. A plating solution with a predetermined zinc concentration is circulated through the electroplating bath.

The post-plating solution taken out from the plating tank generally contains iron leached from the strip, etc., but until now, virtually all of these iron ions have been removed in purification equipment. In the bath, the dissolution of zinc shot was carried out at very low, if any, concentrations of iron ions.

In order to conduct a zinc shot dissolution test, a plating solution with the same composition as the above actual example and F s 804/7H105 were used.
, 0 g/l (Fe equivalent: taq 7t) was prepared. The sample zinc shot was the purest zinc shot with a particle size of 2 to 4 mm (grade Fe: 2 ppm).
, Pb: 15 ppm5Cd: 8 ppm,
Ni (10ppm) 100ml was used.

Pour 1 liter of plating solution into a microwave oven, hold it at 55-60°C on a hot plate, and add zinc to it)
1009 was added and stirred with a stirring blade at 45 Orpm, and the amount of zinc shot dissolved was examined for a test time of 3 hours. The results are shown in Figure 1. The horizontal dotted line in the figure is the maximum amount of dissolved lead calculated from chemical ffi theory. Song lIA is Fe
These are the test results for single zinc supplement without the addition of ions, and the other are the results for Shirakoma (average of 5 tests). Dissolution rate of zinc alone: 0.56 ri/5 hr・! On the other hand, the average value of the 5@ repeated test of the present invention is t 96 q/hr・! in the time period α5 to 15 hr. It can be seen that it has become very large. The Fe grade of the zinc shot after the test was 3.
Although it is about 0 to 40 ppm, the Fe concentration is very high on the surface of the shot particles, and the hydrogen overvoltage of Fe is as low as cL40v, so it is thought that the dissolution reaction was promoted.

Since the presence of F@ is also expected in the 10-line liquid,
A test was conducted by adding Fax(SO2)m instead of F02% in the basic liquid composition. It was confirmed that all F ions immediately before the start of the test were Fem+. Figure 2 shows the wt results.

The initial amount of zinc dissolved is slightly larger than that in the basic test. This can be seen from the fact that the generation of H1 bubbles was faster for 10 minutes than usual (which increases 20 minutes after the start). However, the weight reduction of the shot after the end is 4.12
g is larger than the value calculated from the free-H1SO4 concentration, but this is considered to be largely due to the contribution of the reaction according to the following equation.

Zn+2Fe"=Zn"+2Fe" The figure shows the change in Fe ion degree, but 60 minutes after the start, more than 80% of Fes+ has become Fe2+, which indicates the dissolution of zinc. Free-H amount
As shown in the figure in addition to the calculated value from 2SO46 degrees, it can be seen that the initial dissolution rate is very high. However, most of the Fe"10 quickly becomes F@"+ and its effect disappears, and the average dissolution rate for 1 to 2 hours is 13/h.
r・! and is smaller than the basic test.

Equilibrium theory shows that Fe'' cannot coexist in a system where there is an excess of zinc, and when a solution containing this ion comes into contact with Zn, most of it is reduced to Fe'' in a short time, resulting in the loss of zinc. Dissolution rate is accelerated.

It is known that the reaction temperature has a large effect on the dissolution rate, but in order to examine this effect, the reaction temperature was
Tests were conducted in the same manner as before at three levels of 0°C. The results are shown in Figure 3 and the table below.

As shown in the table, when looking at the quality of the shot after the test, the Fe quality increases at high temperatures, and in addition to the temperature dependence of the reaction rate constant, the number of active reaction points increases due to the F6 precipitation site. It is also shown that the amount of water contributes significantly to the dissolution rate.

Therefore, maintaining the liquid temperature at 55°C to 80°C is also effective when used in conjunction with the present invention as a measure to promote zinc shot dissolution.

Next, the effect of shot reuse was investigated using the same plating solution as above containing Fe''+: t 5 /l.

Test v-1: Fe” concentration = 15 l/l Other conditions are the same as before Test V-2: Inject the shot used in V-1 as is (
Reuse) Fe″10 concentration - t s g/l Test V-3: Inject the shot used in V-2 as is (
(repeated use) Fe concentration was set to -10 ri/l.

The results are shown in Figure 4. The dissolution rate of zinc in V-1 is initially much larger than in the basic test, but its slope is 2.2')/hr-1°α5~ from 0 to 10 hr.
The t5hr was 1879/hr-1, which was almost no difference from the basic test.

On the other hand, with V-2 and V-s, the initial reaction rate increases further, and at 0 to 0.5 hr, V-2 has a 4.13
ri/hr-j, ■-5 and 6.09/hr-7, which is extremely large. The reason for this is thought to be that the initial reaction stagnation (Fe precipitation time) was shortened, but it is unclear at this point because the first measurement time was 30 minutes later.

In actual operation, as described above, the plating solution discharged from the electrogalvanizing tank already contains iron ions.

In order to secure the iron ion concentration of α5~2-09/l in the dissolution tank according to the present invention, it is useful to not wash the post-plating solution as thoroughly as before, but to leave iron ions within a specified range. be. Of course, iron ions may be added to the specified range after thorough cleaning. As the plating solution is recycled, the concentration of iron ions gradually accumulates, so care must be taken.

If the iron ion concentration is lower than the lower limit α5g/l, a dissolution rate commensurate with the line speed cannot be guaranteed. On the other hand,
If the upper limit of zO/l is exceeded, zinc-iron alloy plating will be produced, which is not preferable.

Zinc shot is always present in the dissolution tank at least twice the amount required for dissolution. By doing this, the precipitation of iron onto the zinc shot and the dissolution of the zinc shot occur in a graceful manner, ensuring continuous zinc shot dissolution.

As described above, the present invention enables rapid dissolution of zinc shot, which is necessary for industrially performing high-speed electrogalvanizing using an insoluble anode, and has extremely great industrial significance. .

[Brief explanation of the drawing]

Figure 1 is a graph showing the effect of increasing the amount of zinc dissolution due to the addition of Fe''+ ions, Figure 2 is a graph showing the effect of Fe''+ ion concentration on the zinc dissolution rate, and Figure 3 is a graph showing the effect of Fe''+ ion concentration on the zinc dissolution rate.
Figure 4 is a graph showing the effect of temperature on zinc dissolution rate, and Figure 4 is a similar graph showing the effect of shot reuse. Figure 1 Dissolution time (hr) Figure 2

Claims (1)

[Scope of Claims] 1) A method of dissolving metallic zinc shot in a dissolving tank in which the missing amount of zinc is dissolved in a post-plating solution extracted from an electrogalvanizing tank and circulated to the electrogalvanizing tank, comprising: , the metal zinc shot is present in the dissolution tank at least twice the required dissolution amount, and the iron ion concentration in the post-plating solution flowing into the dissolution tank is 0.5 g/l to 2.0 g/l. Dissolving method for metallic zinc shot. 2) The method according to claim 1, wherein the liquid temperature in the dissolution tank is maintained at 55 to 80°C.