JPH037760B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for reducing and regenerating plating baths and aluminum electrolytic coloring solutions containing tin salts. Therefore, it relates to a method for reducing and regenerating stannous ions.

Generally, as the electrolytic solution containing tin ions, a tin salt aqueous solution containing stannous ions (Sh ²⁺ ) is used. However, this aqueous solution containing stannous ions is very unstable and is easily oxidized by oxygen in the atmosphere or oxygen generated during electrolysis to become stannous ions (Sn ⁴⁺ ). When such stannous ions are generated in the electrolyte, the concentration of stannous ions in the electrolyte decreases and the current efficiency decreases.At the same time, the stannous ions become insoluble substances such as stannic acid, and moreover, they become colloids. This poses a troublesome problem in that it is difficult to remove by filtration due to its oxidative nature. Furthermore, there is a problem that this insoluble substance adheres to the surface of the product and causes pitting. Therefore, it can be seen that controlling the stannic ion concentration in the electrolyte is essential for producing stable products.

Therefore, conventionally, chelating agents were added to the electrolyte.
A method of dissolving Sn ⁴⁺ or an electrolytic reduction method (Japanese Patent Publication No. 53-19856) has been proposed. However, in these methods, it is necessary to dispose of the aqueous solution with increased concentration of stannic ions, and the method also requires an extremely long time and requires high equipment and operating costs. . In contrast, the present inventors previously proposed a method for regenerating tin ions in an electrolytic solution containing tin salt by reducing them to stannous ions, in which the electrolytic solution was adjusted to an acidic region, and then metal tin was added to the electrolytic solution. A method of reductive regeneration by adding and heating to a temperature of 80℃ to boiling temperature without applying pressure or
Publication No. 42720 and Japanese Patent Application No. 110047/1983).
In these inventions, it is possible to perform reduction regeneration very efficiently, but because the reaction is carried out at high temperatures in a strongly acidic region, there are limitations on the reaction vessel and the equipment cost is extremely high. .

Therefore, the present inventors further conducted intensive research on reduction regeneration methods, and as a result, completed the present invention.

That is, the present invention provides a method for reducing and regenerating stannic ions in an electrolytic solution containing a tin salt to stannous ions, in which metallic tin is added to the electrolytic solution and an inert gas and an inert gas are added in an acidic region. The present invention provides a method for reductive regeneration of an electrolytic solution containing a tin salt, characterized by heating the electrolytic solution to a temperature of 40 to 80°C in a reducing gas atmosphere.

The electrolytic solution in the present invention is not particularly limited as long as it contains a tin salt. Initially, this electrolyte contains mostly tin ions and almost no tin ions, but as the electrolysis progresses, the tin ions increase and the tin ions relatively decrease. I'll come. The method of the present invention is applied to an electrolytic solution in which stannic ions have increased to some extent.

In the method of the present invention, the operation is performed with the electrolytic solution adjusted to an acidic range. Adjustment at this time is not necessarily necessary if the PH of the electrolyte is already in a predetermined range, but it is necessary to lower the PH if the electrolyte is from weakly acidic to alkaline. Usually, an electrolyte contains a chelating agent to keep the stannous ions and stannous ions in a dissolved state, and the pH is adjusted from weakly acidic to alkaline to exhibit the chelating effect. Therefore, in many cases it is necessary to lower the pH. In this case, pH adjustment is generally carried out using an acid, such as sulfuric acid, hydrochloric acid,
Acids containing the same anion species as those present in the target electrolytic solution, such as phosphoric acid, nitric acid, pyrophosphoric acid, or various organic acids, are used alone or in a mixture of two or more. Among these acids, sulfuric acid is particularly effective in the method of the present invention. Further, in the method of the present invention, metal tin may be added after adjusting the pH of the electrolytic solution to an acidic range, or it may be adjusted to an acidic range after or while adding metal tin.

When adjusting the pH of this electrolyte, the pH is usually 4.
Hereinafter, it is particularly preferable to adjust the pH to a range of 0.5 to 2. If the pH is too low, the metal tin will dissolve quickly, but the reduction rate will slow down somewhat.
Conversely, when the pH exceeds 4, the dissolution of metal tin decreases and the reaction does not proceed quickly.

On the other hand, in the method of the present invention, metal tin is added to the electrolytic solution and heated. In this case, the metal tin is preferably one with high reactivity, such as a form with a large specific surface area such as fine powder or thin foil. is preferred. The amount of metallic tin to be added may be determined as appropriate depending on the concentration of stannic ions in the electrolytic solution, the concentration of required stannous ions, etc., and is not particularly limited, but in general, 1 of the required amount of reduction is required. It should be about 10 times the molar amount. Note that even if metallic tin is added in excess, unreacted metallic tin will only be deposited at the bottom of the reaction tank, and there will be no particular problem, and it can be reused.

In the present invention, as described above, it is necessary to allow the reduction reaction of the electrolytic solution to which metallic tin is added to proceed in an inert gas and/or reducing gas atmosphere.

Here, the inert gas is not particularly limited as long as it is inert to the electrolytic solution containing tin salt. Specifically, nitrogen, carbon dioxide, argon, etc. are mentioned, and nitrogen is preferably used in view of economic efficiency.
Furthermore, hydrogen gas or sulfur dioxide gas is used as the reducing gas. These inert gases and reducing gases may be used singly or in combination of two or more.

In the method of the present invention, the heating temperature is 40°C to 80°C.
For processing tin salt-containing solutions at relatively low temperatures of °C,
The invention proposed earlier (Japanese Patent Publication No. 57-42720,
The processing will take a longer time than in the case of Japanese Patent Application No. 110047/1983). Therefore, if it is carried out in a normal air atmosphere, an oxidation reaction with oxygen will occur, resulting in a decrease in the reductive regeneration ability. Therefore, the processing system is placed under an inert gas and/or reducing gas atmosphere to prevent the oxidation reaction from proceeding by shielding it from air. Furthermore, when a reducing gas is used, an effect of promoting reduction can be expected.

In the method of the present invention, metallic tin is added to the electrolytic solution as described above, and the reaction that occurs due to the addition of metallic tin is an oxidation-reduction reaction expressed as Sn+Sn ⁴⁺ →2Sn ²⁺ . tin and second
This is a reaction in which tin ions react and are both converted into stannous ions. This reaction proceeds rapidly by heating. The present invention is characterized in that the reaction temperature is relatively low, specifically 40 to 80°C. Although the above reaction progresses more easily at higher temperatures, it can proceed satisfactorily even at the reaction temperature of the present invention, and is extremely satisfactory in terms of equipment costs, working conditions, etc.

In the method of the invention proposed above, the reaction temperature was set at 80° C. to boiling temperature with or without pressurization. Although the process proceeds in a short time with this method, it requires the consumption of a large amount of thermal energy in a short time because the process is carried out at high temperatures, and it requires a special reaction that can withstand conditions such as high temperature and pressure in an acidic region. A container is required, and equipment costs are very expensive. In addition, working conditions deteriorated. In the present invention, the treatment conditions are mild, and although it takes some time to process, it is possible to carry out reduction regeneration treatment at a relatively low temperature while preventing oxidation reactions, and the equipment is inexpensive as there is no need for a special reaction vessel. The working conditions are also good.

Therefore, the present invention can be effectively utilized as an industrially very advantageous method for electrolytic coloring of aluminum or aluminum alloys.

Next, the present invention will be explained in detail with reference to examples.

Example 1 5 g/l of stannous ions and 13 stannous ions
40 g/l of sulfuric acid and 75 g/l of fine metal tin were added to an electrolytic solution containing 18 g/l of sulfuric acid, heated to 70°C while shielding the liquid interface with nitrogen gas, and heated to 18°C with stirring.
Allowed time to react.

As a result, the tin ion concentrations in the electrolytic solution were 22 g/l of stannous ions and 6 g/l of stannous ions.

Comparative Example A reaction was carried out under the same conditions as in Example 1, except that shielding with nitrogen gas was not performed.

As a result, the tin ion concentration in the electrolytic solution was 17 g/l of stannous ion and 10 g/l of stannous ion.

Example 2 6 g/l of stannous ions and 12 g/l of stannous ions
30 g/l of sulfuric acid and 75 g/l of fine metal tin were added to an electrolytic solution containing g/l, heated to 60°C while shielding the liquid interface with carbon dioxide, and reacted for 18 hours with stirring. Ta.

Example 3 6 g/l of stannous ions and 12 g/l of stannous ions
40 g/l of sulfuric acid and 75 g/l of fine metal tin were added to the electrolytic solution containing g/l, heated to 70° C. while feeding hydrogen gas into the solution, and reacted for 10 hours.

As a result, the tin ion concentration in the electrolyte was 22 g/l of stannous ions and 7 g/l of stannous ions.

Claims (1)

[Claims] 1. In a method of reducing and regenerating stannic ions in an electrolytic solution containing tin salts to stannous ions, metallic tin is added to the electrolytic solution and inactivated in an acidic region. Under gas and/or reducing gas atmosphere, temperature 40~
A method for reductive regeneration of an electrolytic solution containing tin salt, characterized by heating it to 80°C. 2. The reductive regeneration method according to claim 1, wherein the inert gas is nitrogen gas, carbon dioxide, or argon gas. 3. The reductive regeneration method according to claim 1, wherein the reducing gas is hydrogen gas or sulfur dioxide gas.