JP7589586B2 - How to recover tin - Google Patents

Description

The present invention relates to a method for recovering tin, and more particularly to a method for efficiently separating and recovering tin from a tin-containing material that contains tin together with copper and lead .

Conventionally, a method for recovering tin from tin-containing materials has been known in which the raw material obtained by separating lead from dross generated in the lead smelting process is melted and reduced to obtain a tin-containing material (mainly containing tin and copper), which is oxidized in a NaOH solution to leach tin, and tin is recovered from this tin leachate by electrolytic winning (Patent Document 1: Patent No. 5188768). However, if the tin-containing material contains lead, lead will leach out along with the tin, and since this lead is a more noble element than tin, it will precipitate in preference to tin during electrolytic winning, making it impossible to separate tin and lead. Another problem is the high cost of chemicals due to the use of NaOH for leaching.

On the other hand, when copper or lead is contained in the tin leachate before electrowinning, a method is known in which metallic tin powder is added to the leachate to reduce copper and lead, which are elements more noble than tin, and then the copper and lead are removed from the liquid by substitution precipitation (cementation) (Patent Document 2: JP-A-11-217634). However, when the copper or lead concentration in the raw material is high, the metallic tin used in cementation becomes expensive.

Unlike the above-mentioned method of recovering tin after leaching by electrowinning, a method is known in which copper smelting dust is leached using hydrochloric acid or nitric acid, preferentially dissolving copper and lead while concentrating and recovering tin in the leaching residue (Patent Document 3: JP 2019-151862 A, Patent Document 4: JP 2019-151863 A). This method has the advantage that tin exists as a solid after leaching, making it easy to recover tin by solid-liquid separation, but has the problem that the tin content of the resulting tin recovery product is low, since many elements are not leached together with the tin.

Patent No. 5188768 Japanese Patent Application Publication No. 11-217634 JP 2019-151862 A JP 2019-151863 A

The present invention solves the above problems in conventional tin recovery methods, and provides a method for efficiently recovering tin from tin-containing materials that contain tin as well as either copper or lead or both. It also provides a tin recovery method that can obtain a tin product with a higher tin content than the above hydrochloric acid leaching or nitric acid leaching.

The present invention provides a tin recovery method that solves the above problems by the following configuration.
[1] A method for separating and recovering tin from a tin-containing material which contains copper and lead together with tin, comprising a sulfuric acid oxidative leaching step in a sulfuric acid acidic solution in the presence of an oxidizing agent to oxidatively leach tin while leaving copper in the tin-containing material and precipitate lead, and a neutralization step in which a post-leaching solution containing tin and a leaching residue containing copper and lead are separated into solid and liquid, and this post-leaching solution is neutralized to produce and recover a tin-containing precipitate, characterized in that the tin recovery method separates and recovers the tin from the copper and lead .
[2] The method for recovering tin described in the above item [1], wherein an acidic solution having a sulfuric acid concentration of 100 g/L or more and 400 g/L or less is used in the sulfuric acid oxidative leaching step.
[3] The method for recovering tin described in [1] or [2] above, wherein chloride ions are added to the acidic solution in the sulfuric acid oxidation leaching step.
[4] A method for recovering tin according to any one of [1] to [3] above, wherein the pH of the liquid is adjusted to 3.5 or more and 4.5 or less in the neutralization step.

[Specific explanation]
The present invention will be specifically described below.
The method of the present invention is a method for separating and recovering tin from a tin-containing material containing copper and lead together with tin, and includes a sulfuric acid oxidative leaching step in which, in a sulfuric acid acidic solution and in the presence of an oxidizing agent, tin is oxidatively leached while leaving copper in the tin-containing material and lead is precipitated, and a neutralization step in which a post-leaching solution containing tin and a leaching residue containing copper and lead are solid-liquid separated, and the post-leaching solution is neutralized to generate and recover a tin-containing precipitate, and the tin recovery method is characterized in that the tin is separated from the copper and lead and recovered . An example of the process of the tin recovery method of the present invention is shown in Figure 1.

The tin recovery method of the present invention is a method for recovering tin from a tin-containing material that contains tin, copper, and lead together with tin. Examples of the tin-containing material that contains tin, copper, and lead together with tin include crushed electronic substrates (crushed substrates), scraps such as solder chips, selected products of various scraps, and various intermediate products of smelting.

[Sulfuric acid oxidation leaching]
Tin-containing materials (crushed substrates, etc.) are subjected to oxidative leaching (called sulfuric acid oxidative leaching) in an acidic solution mainly composed of sulfuric acid (called sulfuric acidic solution) to leach tin. Most of the tin contained in the crushed substrates is oxidized and leached into the solution in the form of tin sulfate or sulfate complex ions, etc., and the remaining tin is transferred to the leaching residue.

The sulfuric acid concentration for sulfuric acid oxidation leaching is preferably 100 g/L or more and 400 g/L or less. If the sulfuric acid concentration is less than 100 g/L, the leaching rate of tin drops significantly. On the other hand, if the sulfuric acid concentration exceeds 400 g/L, the leaching rate of copper increases, which leads to poor separation of tin and copper, and tin forms a stable sulfate complex ion, making it difficult for tin to precipitate during the neutralization process.

This sulfuric acid oxidation leaching is preferably carried out by blowing in air or other oxidizing agents. Using oxygen gas instead of air increases the dissolved oxygen concentration, which increases the copper leaching rate, so it is preferable to use air or other gases.

Since tin and lead are less noble metals than copper, tin and lead are preferentially oxidized over copper during sulfuric acid oxidation leaching. The oxidized lead then reacts with sulfate ions in the solution to form stable lead sulfate, which precipitates. Meanwhile, the tin oxidized by leaching remains in the solution, so most of the copper and lead can be separated as leaching residue. As a result, it is possible to significantly reduce the contamination of the tin-containing precipitate produced in the subsequent neutralization process with copper and lead.

In sulfuric acid oxidation leaching, the addition of chloride ions to the sulfuric acid solution promotes the leaching of tin, and can increase the tin transfer rate to the recovered tin. Specifically, as shown in the examples (Nos. A2 to A5), when 50 g of crushed substrate (raw material) containing 2.5% tin by mass is leached using 1 L of sulfuric acid with a concentration of 100 g/L, the addition of 1 g to 10 g of NaCl (approximately 1 to 10 times the amount of tin in the raw material) as a chloride ion additive can increase the tin transfer rate to the recovered tin by 45% to 83% compared to when NaCl is not added. Examples of the chloride ion additive that can be used include salts such as NaCl and KCl, aqueous solutions of these salts, and hydrochloric acid.

[Separation of post-leaching solution and leaching residue]
The leachate after the sulfuric acid oxidation leaching is separated from the leach residue into solid and liquid. The leachate mainly contains tin, and the leach residue contains most of the copper and lead.

[Neutralization: Formation of tin-containing precipitate]
The separated leaching solution is neutralized by adding an alkaline solution to produce a precipitate that mainly contains tin (called a tin-containing precipitate). The leaching solution containing tin is strongly acidic, and NaOH is added to it. When an alkaline solution such as tin is added to neutralize the liquid to a pH of 3.5 or higher and 4.5 or lower, a tin-containing precipitate is formed. As shown in Figure 2, the tin concentration in the liquid increases with increasing pH. If the pH exceeds 3.5 and the solution is neutralized, almost all of the tin can be precipitated. On the other hand, if some of the copper has been leached in the sulfuric acid oxidation leaching process, the pH exceeds 4.5. When the solution is neutralized, copper precipitates and becomes mixed into the tin-containing precipitate. Therefore, it is preferable to control the pH in the neutralization step to 3.5 or more and 4.5 or less. The tin is recovered by solid-liquid separation to obtain a recovered tin product.

According to the tin recovery method of the present invention, by performing sulfuric acid oxidation leaching on a tin-containing material that contains copper and lead together with tin, tin can be preferentially leached and most of the copper and lead can be transferred to the leaching residue. Therefore, a leaching solution having a high tin concentration and low copper and lead concentrations can be obtained, and a tin recovered product with a high tin quality can be obtained by neutralizing the resulting leaching solution. According to the tin recovery method of the present invention, a tin recovered product with a higher tin quality can be obtained than the tin-containing leaching residue obtained by hydrochloric acid leaching or nitric acid leaching.

The tin recovered by the method of the present invention can be used as a raw material in the tin smelting process. In addition, the copper concentration of this tin recovered is significantly lower than that of conventional methods, and it contains almost no lead, so it can be economically processed into tin bullion by processing it in a general tin smelting process.

FIG. 1 is a process diagram showing an example of a tin recovery method of the present invention. Graph showing the relationship between tin concentration and pH of a post-leaching solution.

Examples of the present invention will be described below. The percentages of concentrations are by mass.
[Example]
2 kg of waste electronic circuit boards were crushed with a biaxial crusher, and then classified with a sieve with a mesh size of 3.35 mm, and the crushed circuit boards that fell under the sieve were collected. 50 g of the crushed circuit boards were immersed in 1 L of an acidic solution with a sulfuric acid concentration of 50 to 500 g/L maintained at 60°C, and the solution was stirred for 6 hours while air was blown in at a rate of 0.5 L/min, to carry out sulfuric acid oxidation leaching. For some samples, 1 g to 10 g of NaCl was added to the sulfuric acid solution to carry out sulfuric acid oxidation leaching. Then, solid-liquid separation was carried out using a suction filtration device, and a post-leaching liquid and a leaching residue were obtained. A 48% NaOH solution was added to the obtained post-leaching liquid, and the pH was neutralized to 3.0 to 5.0. After the neutralization treatment, solid-liquid separation was carried out using a suction filtration device, and a post-neutralization liquid and a tin recovery product were obtained. The obtained tin recovery product was dried in a dryer at 105°C for 12 hours.
The contents of tin, copper, and lead contained in the crushed substrate as raw material are shown in Table 1. The treatment conditions for sulfuric acid oxidation leaching, the pH during neutralization, and the concentrations and transfer rates of tin, copper, and lead in the tin recovered product are shown in Table 2. Furthermore, for each Example and Comparative Example, the transfer rates of tin, copper, and lead in the leaching residue and the neutralized solution are shown in Table 3. These concentrations were measured by ICP-AES. The transfer rates were calculated using the following formula [3].
Transfer rate (%) = [amount of metal in recovered material] / [amount of metal in raw material] x 100 ... [3]

As shown in Tables 2 and 3, in the sulfuric acid concentration range of 100 to 400 g/L, approximately 45 to 62% of the tin in the crushed substrate was leached, and almost all of the leached tin was transferred to the tin recovery material (No. A1, A5 to A9). In addition, the addition of chloride ions increased the tin recovery rate from approximately 42% to approximately 83%, confirming the effect of adding chloride ions (No. A2 to A4). On the other hand, at a sulfuric acid concentration of 50 g/L, only approximately 5% of the tin was leached (No. B1), and at a sulfuric acid concentration of 500 g/L, the leached tin stably formed sulfate complex ions, so that not all of the tin precipitated even when neutralized to pH 4, and approximately 20% of the total tin was transferred to the neutralized solution. Furthermore, the high sulfuric acid concentration increased the copper leaching rate, and the copper transfer rate to the neutralized solution and the tin recovery material increased (No. B2). Copper has a negative effect on the tin smelting process, so tin recovered material that contains a lot of copper is not suitable as a raw material for tin smelting. In addition, when the solution was only neutralized to pH 3.0, the entire amount of tin did not precipitate regardless of the sulfuric acid concentration during leaching, and approximately 4.1% of the tin transferred to the neutralized solution (No. B3). On the other hand, when the solution was neutralized to pH 5.0, most of the leached copper precipitated, and the quality of the tin recovered material decreased (No. B4).

Claims (4)

This method for separating and recovering tin from a tin-containing material which contains copper and lead together with tin comprises a sulfuric acid oxidative leaching step in which, in a sulfuric acid acidic solution and in the presence of an oxidizing agent, tin is oxidatively leached from the tin-containing material, leaving copper behind, and lead is precipitated, and a neutralization step in which a post-leaching solution containing tin and a leaching residue containing copper and lead are separated into solid and liquid, and this post-leaching solution is neutralized to produce and recover a tin-containing precipitate, characterized in that the tin recovery method separates and recovers the tin from the copper and lead . The tin recovery method according to claim 1, in which an acidic solution having a sulfuric acid concentration of 100 g/L or more and 400 g/L or less is used in the sulfuric acid oxidation leaching process. A method for recovering tin as described in claim 1 or claim 2, in which chloride ions are added to the acidic solution in the sulfuric acid oxidation leaching process. The method for recovering tin according to any one of claims 1 to 3, wherein in the neutralization step, the pH of the liquid is adjusted to 3.5 or more and 4.5 or less.

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