JPH0438834B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for treating tin stripping solution, and more specifically, it involves recovering tin coated on copper, copper alloy, etc. after dissolving it, and regenerating the solution after recovering the tin. This invention relates to a method for treating tin stripper. [Prior Art] Traditionally, tinned materials based on copper and copper alloys have been widely used as terminals or connector members in the field of electronic equipment. These tin-plated materials are usually plated in a hoop shape and then punched into terminals, connectors, etc. in order to save labor and reduce costs. However, since the scrap generated by this punching process contains about 5 to 30 g of tin, it is difficult to handle it as copper scrap, and its uses are limited. In order to effectively utilize scrap as a resource, it is necessary to remove the tinned layer. Hitherto, the tin layer of copper and copper alloys has been removed by immersion in hot concentrated phosphoric acid or hot concentrated hydrochloric acid, or by dissolution in sodium hydroxide. However, in all of these methods, if the immersion continues even after the tin layer has been dissolved and removed, the base material of copper and copper alloy will be eroded, resulting in a poor recovery rate of the base material. Since impurities eluted from the base material are mixed in, the stripping solution is usually discarded when the solubility of the tin layer decreases. Therefore, as properties required for the stripping solution, it is desirable that the stripping solution dissolves only the tin layer and that even if the copper or copper alloy substrate is exposed in the stripping solution, the substrate will not be corroded. As a method for stripping a tin layer with such characteristics, as described in JP-A-58-087275, the tin layer is coated with a stripping solution prepared by adding copper salts to a dilute aqueous solution of a strong acid. A method has been proposed in which the tin layer is dissolved and peeled off by immersing the copper alloy that has been used in the manufacturing process to take advantage of the difference in electrochemical order between tin and copper. When copper and copper alloys coated with a tin layer are immersed in this stripping solution, the tin layer is preferentially eluted into the stripping solution and copper is precipitated due to the reaction of Cu ²⁺ + Sn → Sn ²⁺ + Cu. Since the deposited copper has a lower hydrogen overvoltage than tin, it forms an effective cathode point and further promotes the dissolution of tin, which is an anode reaction. On the other hand, the copper and copper alloy substrates from which the tin layer coated on the copper and copper alloys has been dissolved and removed are brought into contact with the dilute acid solution, but the copper and copper alloys in the dilute acid solutions do not contain strong oxidizing agents. The erosion rate is slight;
Even if the base material is immersed for a long time, it is possible to increase the recovery efficiency of the base material. Therefore, if such a stripping solution is used, the amount of impurities mixed in from the base material will be reduced, but if stripping work is continued in this state, Sn ²⁺ will be oxidized and metastannic acid (SnO ₂ XH ₂ O) will be formed. Since the tin precipitates as a metal, it is either discarded at this point or discarded after the metastannic acid has been recovered, resulting in high stripping costs and limited use of the recovered tin. [Problems to be Solved by the Invention] As explained above, the present invention was made in view of the various problems encountered when recovering a tin layer from conventional tin layer-coated copper and copper alloy substrates. As a result of intensive research and consideration by the present inventor, the tin layer is peeled off by immersing the copper and copper alloy substrate coated with the tin layer in a sulfuric acid aqueous solution containing Cu ions. At the same time, they developed a method for processing tin stripping solution that allows for efficient recovery of tin from the stripping solution, as well as recycling and repeated use of the stripping solution without having to be disposed of. [Means for Solving the Problems] The tin stripping solution treatment method according to the present invention is characterized by immersing copper and copper alloys coated with a tin layer in a sulfuric acid aqueous solution containing Cu ions. to dissolve the tin layer and reduce the Cu ion concentration in this solution to 4
The method is to electrolytically recover tin at a Sn ²⁺ ion concentration of 5 to 30 g/, and then add copper sulfate to the solution after tin recovery to adjust the Cu ion concentration to 5 to 25 g/. When recovering this tin by electrolysis, it is preferable to isolate the anode with an anion exchange membrane. The method for treating a tin stripper according to the present invention will be described in detail below. When copper and copper alloys coated with a tin layer are immersed in an aqueous sulfuric acid solution containing Cu ions, the tin preferentially elutes and the copper precipitates, so if the stripping process is continued, the Cu ion concentration will increase. and the solubility is reduced. Therefore, if Cu ions are replenished in the form of copper sulfate, the solubility will be improved again and stripping work can be continued, but if this is repeated, the concentration of tin in the solution will increase and metatin will be produced. Acid begins to precipitate. However, even if metastannic acid precipitates in the solution, it still has the ability to strip off the tin layer covering copper and copper alloys, but the reaction rate gradually slows down and the stripping solution becomes cloudy, resulting in poor workability. Therefore, the stripping solution is usually discarded in such a state, or the tin is collected as metatin and then discarded, which makes the entire stripping process quite time-consuming and uneconomical. According to the method for treating tin stripping solution according to the present invention, the tin stripping solution is recovered by electrolysis with a Cu ion concentration of 4 g/or less and a Sn ²⁺ ion concentration of 5 to 30 g/. If the Cu ion concentration exceeds 4 g/, the copper content in the electrolytic deposit will increase and the tin purity will decrease, so the Cu ion concentration should be reduced to 4 g/
below, and then the Sn ²⁺ ion concentration is 5g/
If it is less than that, the tin recovery efficiency is poor and it is uneconomical.
If the concentration exceeds 30 g/, metastannic acid is likely to be produced and efficient recovery cannot be performed, so the Sn ²⁺ ion concentration is set at 5 to 30 g/. Furthermore, if the Cu ion concentration of the solution after electrolytic recovery of tin is less than 5 g/, the peeling rate of the tin layer decreases, and if the concentration exceeds 25 g/, excessive Cu
Since ions do not contribute to improving the peeling rate of the tin layer and are uneconomical, the Cu ion concentration is set to 5 to 25 g/. In addition, in the method for treating a tin stripper according to the present invention, after producing a new stripper, Cu ions within the scope of the method for treating a tin stripper according to the present invention are used two to three times.
If the concentration of Sn ²⁺ ions is high, a high recovery rate similar to that of the electrolysis method using an anion exchange membrane can be obtained, but the Sn ²⁺ ions in the stripping solution are destroyed by oxygen gas generated from the anode during electrolysis. As the tin is heated and oxidized, the tin recovery rate gradually decreases. When the stripping solution is disposed of without being regenerated, there is no need to use a diaphragm when recovering tin, but when the stripping solution is recycled, it can be recovered by performing an electrolytic recovery method that separates the anode with an anion exchange membrane. Increased efficiency. Furthermore, in order to prevent air oxidation in the stripping solution, the production of metastannic acid can be significantly reduced by blowing a small amount of inert gas such as N ₂ or Ar during stripping work or during pauses. [Example] Examples of the method for treating tin stripping liquid according to the present invention will be described. Example 1 Test conditions Electrolysis conditions Cathode current density 1.0A/dm ² Electrolysis time 5 hours Anode diaphragm None Electrolyte Stirred solution Temperature 15-40℃ Table 1 shows the Cu ion concentration obtained under the above electrolysis conditions during electrolytic recovery, Indicates Sn ²⁺ ion concentration. Furthermore, the tin recovery rate and the Cu content in the deposits are shown.

[Table] As is clear from Table 1, if the Cu ion and Sn ion concentrations in the solution are specified in the tin stripping solution treatment method according to the present invention, tin recovery is high and the Although the copper content in the precipitates is also low,
Comparative examples have problems in that the tin recovery rate is low and the copper content in the deposits is high (No. 7 to 10), and the copper content with a high recovery rate is also high (No. 6). Example 2 Test conditions (1) Test material Copper alloy coated with a tin layer (tin coating amount approx.
(5μ) (2) Stripping conditions Liquid temperature: 50°C Immersion time: 5 minutes Table 2 shows the Cu ion concentration of the solution (regenerated solution) and the solubility of the tin layer after tin electrodeposition under these test conditions.

【table】

[Table] It is clear from Table 2 that by using the Cu ion concentration specified in the stripping solution treatment method according to the present invention, the tin recovery rate is 99% or more, and below this specified range, the tin recovery rate is The recovery rate is poor, and above that the recovery rate is good, but there is no further improvement.
It is uneconomical. Example 3 Test conditions Stripping solution Sn ²⁺ ion 30g / Electrolysis conditions Cathode current density 1.0A/dm ² Cathode area 4 dm ² Anode diaphragm Anion exchange membrane (e.g. Selemion manufactured by Asahi Glass) Electrolyte Stirring solution Temperature 15-40℃ Under these conditions, FIG. 1 shows the relationship between the electrolysis time and the tin recovery rate when a diaphragm is used and when a diaphragm is not used in the tin stripping solution treatment method according to the present invention. In FIG. 1, 1 is the case where the treatment method using the new stripping solution according to the present invention is used, and 2 is the case where the Cu ion concentration of the solution after tin stripping is repeatedly adjusted by the treatment method using the tin stripping solution according to the present invention ( 3 is a treatment method in which a new stripping solution is used without using a diaphragm, and 4 is a treatment method in which a diaphragm is not used and the Cu ion concentration of the solution after tin stripping is repeatedly adjusted (20 times). It can be seen that the tin recovery rate is significantly improved by using the diaphragm. [Effects of the Invention] As explained above, since the tin stripping solution treatment method according to the present invention has the above configuration, tin can be efficiently recovered from tin-coated copper and copper alloys at a high recovery rate. Furthermore, it has the excellent effect that the solution after tin recovery can be recycled without being discarded and used to dissolve tin from tin-coated copper and copper alloys. .

[Brief explanation of drawings]

FIG. 1 is a diagram showing the relationship between electrolysis time and tin recovery rate.

Claims (1)

[Claims] 1 Copper and copper alloys coated with a tin layer are
The tin layer is dissolved by immersion in a sulfuric acid aqueous solution containing ions, and the tin is electrolytically recovered by setting the Cu ion concentration in this solution to 4 g/or less and the Sn ²⁺ ion concentration to 5 to 30 g/. A method for treating a tin stripping solution, which comprises adding copper sulfate to the solution to adjust the Cu ion concentration to 5 to 25 g/.