Method for purifying gold in gold-tin eutectic alloy waste

Abstract

The invention discloses a gold purification method for gold-tin eutectic alloy waste. The method comprises the following steps: S1, dissolving; s2, first-time tin removal, wherein free tin elements are removed; s3, second-time tin removal is conducted, specifically, complex-state tin elements and impurity elements are removed; s4, tin is removed for the third time, and a trace amount of residual tin element is removed; and S5, gold reduction and purification. According to the method, tin elements in different forms (free state-complex state-trace residue) are removed in stages, copper powder replacement, hydrochloric acid boiling and washing and hydrolysis tin removal methods are combined, deep removal of tin in the gold dissolving solution is achieved, the purpose of efficiently separating and purifying high-purity gold from the gold-tin eutectic alloy waste is achieved, operation is easy, and complex equipment is not needed.

Description

Technical Field

[0001] The present invention relates to the technical field of metal recovery and purification, and in particular to a method for purifying gold from gold-tin eutectic alloy waste. Background Art

[0002] Gold-tin eutectic alloy, an advanced lead-free solder, demonstrates irreplaceable application value in high-tech fields due to its unique physical and chemical properties. Its high thermal conductivity ensures efficient heat dissipation from electronic components, while its good electrical conductivity ensures stable and fast signal transmission. Its low liquidus expansion coefficient and low melting point make the alloy excellent in precision electronic packaging, effectively reducing thermal stress damage to the package structure. Furthermore, its excellent wettability promotes a close bond between the solder and the substrate, further enhancing package reliability. Consequently, gold-tin eutectic alloy has found widespread application in high-end technologies such as microelectronics packaging, aerospace component interconnection, and high-power electronic device manufacturing.

[0003] With the rapid advancement of technology, the application scope of gold-tin eutectic alloys continues to expand, but this also brings with it the problem of the large amount of waste containing this alloy. This waste mainly comes from the dismantling of discarded products, defective products generated during the production process, and scraps. Due to the high gold content in gold-tin eutectic alloys and the extremely high economic value of gold as a precious metal, how to effectively separate and purify the gold from this waste has become a critical issue that needs to be addressed.

[0004] Chinese patent CN104017994A proposes a preliminary separation of gold and tin by mixing a gold-tin alloy with an oxidizing sodium (potassium) salt and calcining it at high temperature. This method uses a chemical reaction to convert tin into a soluble salt, while the gold remains as an insoluble slag. Subsequent acid dissolution, precipitation, and reduction steps yield high-purity tin product and sponge gold, respectively. This method faces challenges such as high energy consumption and reagent cost control, and further optimization is needed to reduce production costs.

[0005] Chinese patent CN111020197B proposes to effectively separate gold and tin by adding tin to gold-tin alloy waste to form a high-tin alloy, and then using acid dissolution and precipitation separation technology. This method cleverly utilizes the difference in the solubility of gold-tin alloy under different conditions. By adjusting the process parameters, tin is preferentially dissolved in acid, while gold is retained as an insoluble substance. Subsequently, a high-purity gold product is obtained through steps such as aqua regia dissolution, alkaline precipitation to remove tin, and reduction to obtain gold. This method requires the alloy waste to be remelted with tin and granulated. The entire recycling process and material transfer are time-consuming, and actual mass production has certain limitations.

[0006] Chinese patent CN107557585A describes a method for recycling gold-tin alloy waste based on hydrogenation and vacuum separation technology. This method uses a hydrogenating agent to react with the tin in the gold-tin alloy to produce a volatile stannous compound. This compound is then volatilized by aeration under vacuum conditions, thereby separating the gold from the tin. This method requires high equipment requirements and strict control of reaction conditions to ensure the smooth progress of the hydrogenation reaction and the effective volatilization of the stannous compound.

[0007] These methods generally struggle to completely remove various forms of tin (e.g., free, complexed, and trace residuals) through a single displacement or acid wash, resulting in high tin residues and limited gold purity. They also present energy and cost challenges: high temperatures or vacuum processes increase energy consumption, while complex reagent systems drive up costs. Summary of the Invention

[0008] In view of the shortcomings of the prior art, the object of the present invention is to provide a method for purifying gold from gold-tin eutectic alloy waste, which can deeply remove the tin element. The method has the advantages of simple operation, low cost, high purification efficiency, and high purity of the purified gold.

[0009] The technical solution of the present invention is a method for purifying gold from gold-tin eutectic alloy scrap, comprising S1. dissolution; S2. a first tin removal step to remove free tin; S3. a second tin removal step to remove complexed tin and impurity elements; S4. a third tin removal step to remove trace residual tin; and S5. gold reduction purification. Specifically, the following steps are included: S1. Dissolution Add aqua regia to the gold-tin eutectic alloy waste, heat and boil until the waste is completely dissolved, concentrate, remove nitrate, and remove precipitation to obtain a waste solution; S2. First detinning to remove free tin elements Add copper powder to the waste solution while slowly stirring until no more sponge gold appears, let it stand, separate the layers, and remove the filtrate containing a large amount of tin from the copper-tin compound to obtain a precipitate containing sponge gold; S3. Second detinning to remove complex tin and impurity elements Add concentrated hydrochloric acid to the precipitate containing sponge gold, boil and wash until the supernatant is colorless, remove the complexed tin element and impurity elements, and obtain alloy powder precipitate, add aqua regia, boil, concentrate, remove nitrate, and remove acid to obtain a gold-containing solution; The boiling and washing method is as follows: adding concentrated hydrochloric acid to the precipitate containing sponge gold, heating to boiling and keeping boiling for 30 to 60 minutes, stirring 1 to 3 times, stopping heating and letting it stand, and pouring off the supernatant; repeating the above operation until the supernatant is colorless.

[0010] The acid-removing method is to heat the gold-containing solution and evaporate and concentrate it, reducing the volume of the solution to 1 / 3 to 1 / 5 of the original volume, thereby removing excess free acid in the solution.

[0011] S4. The third detinning to remove the residual tin element Sodium hydroxide is added to the gold-containing solution to adjust the solution pH to 2.5-3, and the solution is boiled, allowed to stand, cooled, and filtered to obtain a gold-containing solution; S5. Gold reduction and purification The crude gold solution is heated to a boil, sodium sulfite powder is added, and stirred until the solution is clear to obtain gold powder precipitate. After purification, high-purity gold with a purity of more than 99.99% is obtained.

[0012] The purification method in step S6 is to boil and wash the gold powder precipitate with hydrochloric acid, and then add barium chloride solution dropwise to the washing liquid until no white precipitate is produced.

[0013] The method described in this invention achieves thorough tin removal from the gold solution by removing different forms of tin in stages (free, complexed, and trace residual forms), combined with copper powder replacement, hydrochloric acid washing, and hydrolysis to remove tin. This method efficiently separates and purifies high-purity gold from gold-tin eutectic alloy waste. Compared with existing technologies, the method for separating and purifying gold from gold-tin eutectic alloy waste described in this invention offers the advantages of simple operation, low cost, high purification efficiency, and high purity. Using this method, the purity of the gold recovered from the gold-tin eutectic alloy waste reaches over 99.99%, with a gold recovery rate exceeding 99%, providing an effective solution for the recycling of precious metal resources. DETAILED DESCRIPTION

[0014] To help those skilled in the art understand the features and effects of this application, the following provides a general description and definition of the terms and expressions used in the specification and claims. Unless otherwise indicated, all technical and scientific terms used herein have the ordinary meanings understood by those skilled in the art in connection with this application. In the event of any conflict, the definitions in this specification shall prevail.

[0015] The aqua regia described in the present invention is a concentrated hydrochloric acid-concentrated nitric acid solution, wherein the ratio of HCl:HNO3 is 3-4:1, the concentration of the hydrochloric acid is 36wt%, and the concentration of the nitric acid is 68wt%.

[0016] The method for removing nitrate of the present invention comprises the following steps: adding hydrochloric acid to the concentrated solution and heating the solution until no brown smoke is produced.

[0017] Unless otherwise specified, the methods, reagents and conditions used in this example are conventional methods, reagents and conditions in the art. Example 1

[0018] Taking the recovery and purification of gold from 500 grams of gold-tin eutectic alloy scrap (gold content 80.2%) as an example, the following steps are included: S1. Dissolution: Add aqua regia to the gold-tin eutectic alloy scrap and heat it to a slight boil (95-100°C) on an electric furnace to ensure that the alloy scrap is completely dissolved and a uniform solution is obtained. Add 200ml of hydrochloric acid solution in four portions, concentrate, remove nitrate, and remove precipitates to obtain a scrap solution.

[0019] S2. First detinning to remove free tin elements Copper powder was added to the waste solution while slowly stirring at a rate of 50 rpm until no more sponge gold appeared. The solution was allowed to stand for about 2 hours, separated into layers, and the filtrate containing a large amount of tin element and copper-tin compound was removed. The tin content in the filtrate was 80% to 90% of the gold-tin eutectic alloy waste to obtain a precipitate containing sponge gold.

[0020] S3. Second detinning to remove complex tin and impurity elements Add concentrated hydrochloric acid to the precipitate containing sponge gold, boil and wash until the supernatant is colorless, remove the supernatant, the tin content in the supernatant is 0.01% to 10% of the gold-tin eutectic alloy waste, obtain alloy powder precipitate, add aqua regia, boil, concentrate, remove nitrate, remove acid, and obtain a gold-containing solution; S4. The third detinning to remove the residual tin element adding sodium hydroxide solution to the gold-containing solution while slowly stirring, adjusting the pH value of the gold-containing solution to about 2.5, boiling, standing, cooling, filtering, and removing precipitate, wherein the tin content of the precipitate is less than 0.01% of the gold-tin eutectic alloy waste, to obtain a gold-containing solution; S5. Gold reduction and purification The gold-containing solution is heated to a boil, and powder is added while stirring until the solution becomes clear. Gold powder is precipitated and purified to obtain high-purity gold with a purity of more than 99.99%.

[0021] The purification method is as follows: the gold powder precipitate is boiled and washed with hydrochloric acid, barium chloride solution is added dropwise to the washing liquid until no white precipitate is produced, and excess sodium sulfite and impurities are removed.

[0022] Experimental results: 397.7 g of gold was purified using the method of the present invention. Purity test (ICP-MS) showed Au ≥ 99.992%, impurities < 80 ppm, and the recovery rate was calculated as (397.7 g / (500 g × 80.2%)) × 100% = 99.18%.

[0023] Experimental verification shows that the purity of the gold obtained is above 99.99%, and the recovery rate reaches 99.18%, realizing the efficient separation and purification of gold from gold-tin eutectic alloy waste. Example 2

[0024] Taking the recovery and purification of gold from 1000 grams of gold-tin eutectic alloy scrap (gold content 79.8%) as an example, the following steps are included: Except that the stirring rate of copper powder addition in step S2 was changed to 100 rpm, other steps were the same as those in Example 1.

[0025] Experimental results: 793.1 g of gold was purified using the method of the present invention. Purity test (ICP-MS) showed Au ≥ 99.993%, impurities < 70 ppm, and recovery was calculated as (793.1 g / (1000 g × 79.8%)) × 100% = 99.39%.

[0026] Experimental verification shows that the purity of the gold obtained is above 99.99%, and the recovery rate reaches 99.39%, realizing the efficient separation and purification of gold from gold-tin eutectic alloy waste. Example 3

[0027] Taking the recovery and purification of gold from 1000 grams of gold-tin eutectic alloy scrap (gold content 80.8%) as an example, the following steps are included: Except for adding sodium hydroxide solution in step S4 to adjust the pH value of the gold-containing solution to about 3.0, the rest is the same as in Example 1.

[0028] Experimental results: 800.2 g of gold was purified using the method of the present invention. Purity test (ICP-MS) showed Au ≥ 99.991%, impurities < 90 ppm, and the recovery rate was calculated as (800.2 g / (1000 g × 80.8%)) × 100% = 99.03%.

[0029] Experimental verification shows that the purity of the gold obtained is above 99.99%, and the recovery rate reaches 99.03%, realizing the efficient separation and purification of gold from gold-tin eutectic alloy waste.

Claims

1. A method for purifying gold from gold-tin eutectic alloy waste, characterized by: The following steps are involved: S1. Dissolution Add aqua regia to the gold-tin eutectic alloy waste, heat and boil until the waste is completely dissolved, concentrate, remove nitrate, and remove precipitation to obtain a waste solution; S2. First detinning Add copper powder to the waste solution while slowly stirring until no more sponge gold appears, let it stand, separate the layers, and remove the filtrate containing a large amount of tin from the copper-tin compound to obtain a precipitate containing sponge gold; S3. Second detinning Add concentrated hydrochloric acid to the precipitate containing sponge gold, boil and wash until the supernatant is colorless to obtain alloy powder precipitate, add aqua regia, boil, concentrate, remove nitrate and acid to obtain a gold-containing solution; S4. Third detinning Sodium hydroxide is added to the gold-containing solution to adjust the solution pH to 2.5-3, and the solution is boiled, allowed to stand, cooled, and filtered to obtain a gold-containing solution; S5. Gold reduction and purification The crude gold solution is heated to a boil, sodium sulfite powder is added, and stirred until the solution is clear to obtain gold powder precipitate. After purification, high-purity gold with a purity of more than 99.99% is obtained.

2. The purification method according to claim 1, wherein: The slow stirring rate in step S2 is 50-100 rpm.

3. The purification method according to claim 1, wherein: The boiling and washing method in step S3 is as follows: adding concentrated hydrochloric acid to the precipitate containing sponge gold, heating to boiling and maintaining boiling for 30 to 60 minutes, stirring 1 to 3 times, stopping heating and letting it stand, and pouring off the supernatant; repeating the above operation until the supernatant is colorless.

4. The purification method according to claim 1, wherein: The standing time in steps S2 and S4 is 1 to 2 hours.

5. The purification method according to claim 1, wherein: The method for removing the nitrate in steps S1 and S3 is to add hydrochloric acid to the concentrated solution and heat it until no brown smoke is produced.

6. The purification method according to claim 1, wherein: The method of removing acid in step S3 is to heat the gold-containing solution and evaporate and concentrate it, reducing the volume of the solution to 1 / 3 to 1 / 5 of the original volume, thereby removing excess free acid in the solution.

7. The purification method according to claim 1, wherein: The purification method in step S6 is to boil and wash the gold powder precipitate with hydrochloric acid, and then add barium chloride solution dropwise to the washing liquid until no white precipitate is produced.