JPS5914094B2 - How to recover metallic tin from halogen bath tin plating - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for recovering metallic tin from sludge deposited in a halogen bath, and in particular, the present invention relates to a method for recovering metallic tin from sludge that settles at the bottom of a bath during the production of tin-plated steel sheets in a halogen bath. Regarding the method.

The sludge produced by the conventional halogen bath tin plating method is either treated as an auxiliary raw material during Sn refining as shown in Figure 1, or it is processed as an electrodeposited metal after electrolysis through a wet electrolytic process as shown in Figure 2. It is extracted as Sn. 5. FIG. 1 is a process diagram of the dry Sn refining method. If the sludge is used as an auxiliary raw material, other harmful components contained therein will be volatilized, making it unsuitable as a method for recovering Sn from sludge.

Furthermore, using the sludge as the main raw material in the dry method is also inappropriate as a method for recovering Sn10 for the same reason as when using the sludge as an auxiliary raw material.
FIG. 2 is a process diagram for recovering Sn using the wet electrolysis method as described above, but as can be seen from the figure, the steps up to the electrolysis are complicated and require a heavy equipment burden. The present invention is a method that eliminates and improves the drawbacks of the conventional method of recovering metal tin from halogen bath tin plating sludge. It is an object of the present invention to provide a method for recovering ku0, and the above object can be achieved by the method described in the claims.

Next, the present invention will be explained in detail.

The present invention is illustrated by a flow sheet as shown in 25 in Figure 3, which shortens the processing steps from sludge to electrolysis, and
The present invention is characterized in that the compositional form of is a compositional form that can be rationally electrolyzed.

The present invention will be explained below with reference to experimental data. First, water is added to the sludge to form a slurry.30 This slurry can be decomposed even when the dry weight of the sludge is less than 110 g, but the ratio of water to sludge is large and the temperature decreases relative to heated NaOH. The energy loss associated with this is extremely undesirable, and when it exceeds 140q, the slurry viscosity increases35 and becomes difficult to handle. This slurry is 10% water
The slurry was adjusted to contain a dry amount of 110 to 1,409 ml per 0 ml, and the slurry was heated to 50 to 800 C.
Decompose the sludge in addition to the liquid. This decomposition reaction is shown below (
The reaction is carried out according to the reaction formulas 1) and (2). Na
4SnF6+4Na0H→Sn(0H)4+6NaF(
1) Sn(0H)4+2Na0H-+Na2SnO3+
3H20(2)) That is, Sn in the sludge is Na2sn
Dissolve in NaOH solution as O3.

In this case, the concentration and temperature of NaOH, the amount of slurry added, Sn
The relationship with the elution rate was as shown in the table below. From the same table, the concentration of NaOl-1 used is 10%, and the temperature is 50%.
At ~80°C, add 8 m of slurry to ml of NaOHlOOml.
1 added f). It has been found that the best results can be obtained in the case of 11. Temperatures below 50°C are unfavorable as decomposition is poor, while temperatures above 8'C are decomposition possible but thermal energy is wasted, judging from this recovery rate. A temperature of 50 to 80°C is sufficient.

In addition, the amount of slurry added is preferably 8 ml when the temperature is 50 to 80°C, and if it exceeds 8 ml, the decomposition rate is poor, and the dry amount of sludge is 110 to 140 per 100 ml of water.
8 ml in the slurry range defined as 9 is appropriate. 8m
If it is less than 1, decomposition is possible if it is assumed to be carried out under similar decomposition conditions, but the decomposition efficiency (work efficiency) is poor due to the dilution and is not appropriate.

Fe4[Fe(CN)6]3 is decomposed as shown in the following formula (3) and precipitates as Fe(0H)3. Fe4 [Fe
(CN)6〕3+12Na0H→4Fe(0H)3+3
Na4[Fe(CN)6]3 (3) Next, the precipitated Fe(0H)3 and other heavy metal compounds are separated by filtration.

The bottom liquid obtained in this way becomes a mother liquid to be directly subjected to electrolysis.
The present inventors investigated various conditions for electrolyzing this mother liquor.
In other words, one of the important factors during electrolysis is the pH of the electrolyte, which is related to the dissociation energy of the electrolyte, and the value closest to the theoretical current efficiency will have a high recovery rate. It must be managed to suit the conditions.

As a result of various experiments, in order to efficiently recover Sn, the liquid temperature is 8.
It has been found that it is good to neutralize NaOH by adding 35 to 53 ml/t of concentrated hydrochloric acid to the mother liquor at 0°C±100C. As a guideline for neutralization, HCf. All you have to do is add. Incidentally, in order to decompose the sludge, the NaOll concentration may be as high as about 10 to 15%, but this results in an increase in the amount of HCt consumed during later neutralization.

The amount of NaOH remaining after decomposing the sludge in the slurry with NaOH varies depending on the component composition of the sludge, so the amount of HCt added for neutralization will also vary; 20TfL1/decomposition liquid 28
It is within the range of 0 m1, and it is advantageous to manage the pH to about 13 to 7. If the pH is more or less than this, the current efficiency will decrease. Figure 4 is a diagram showing the relationship between electrolytic current density, electrolytic temperature, and Sn deposition amount, and is 2.55A.
It can be seen that electrolysis can be carried out at a current density of /di. The relationship between the electrolysis time and the amount of Sn recovered when electrolysis is performed under these conditions is shown in Figure 5, and when the amount of Sn remaining in the solution is about 1% or less, the current efficiency decreases. Therefore, it is necessary to manage the liquid composition so that the Sn concentration in the electrolytic solution is 1% or more. Further, the current efficiency at 1% or more was about 82%, and the purity of the metal Sn obtained by the method of the present invention was 99.5% or more. As mentioned above, it is difficult to apply the conventional dry method to treat Sn metal slag in a halogen bath.
In addition, when using the conventional wet method, it was necessary to go through a long and complicated process before electrolysis, but according to the present invention, the sludge is decomposed in the form of a slurry using a hot alkali, and coexisting substances are also decomposed. Heavy metals that affect the purity of Sn are removed due to the adsorption effect of the generated Fe(0H)3, so these precipitates are removed, the electrolytic mother liquor is purified, and metal Sn is electrolyzed. It can be recovered, various steps required up to electrolysis by conventional methods can be omitted, and the burden on equipment can be significantly reduced.

[Brief explanation of the drawing]

Figure 1 is a diagram of the process for pyrometallurgical refining of Sn metal slag, Figure 2 is a diagram of the Sn recovery process using the conventional wet electrolysis method for Sn metal slag, Figure 3 is a diagram of the process of the method of the present invention, and Figure 4 is a diagram of the electrolyte temperature and Sn recovery process. A diagram showing the relationship between the amount of Sn adhered to the electrode and the electrode plate width of the Hull cell tester, Figure 5 shows the relationship between the amount of Sn adhered to the electrode and the Sn in the electrolyte
It is a figure which shows the relationship between amount and electrolysis time.

Claims (1)

[Claims] 1 In a method for recovering metallic tin from halogen bath tin plating sludge, the sludge is mixed with a dry weight of 1 sludge per 100 ml of water.
The slurry adjusted to contain 10 to 140 g is
8 for 100ml of 10% NaOH heated to 80℃
ml to cause a chemical reaction to occur, then add an acid to the filtrate after filtering the precipitate produced by the reaction to adjust the hydrogen ion concentration (pH) of the filtrate within the range of 7 to 13. 1. A method for recovering metallic tin from a halogen bath tin plating slurry, which comprises electrolyzing and electrodepositing tin.