Extraction process of gold, silver and copper from electronic waste

Abstract

The application provides an extraction process of gold, silver and copper in electronic waste, wherein the electronic waste to be detected is ground to a particle size less than 100 mesh to obtain a powder, water is added to the powder for stirring to obtain slurry with a preset concentration; then a mixed leaching agent is added to the slurry, so that the mixed leaching agent reaches a preset concentration; the mixed leaching agent is a compound of glutamic acid and cystine; then the slurry is heated to a preset temperature for stirring for 2 hours, and a pH regulator and a leaching synergist are sequentially added, and after being reduced to room temperature, the slurry is stirred for 6-72 hours to extract gold, silver and copper in the electronic waste. Through the synergistic effect of the compound mixed leaching agent and the leaching synergist, a stable chelate structure is formed with metal ions, efficient leaching of the metal ions is realized, and the process is green and environmentally friendly; the type of the environmentally-friendly leaching agent is expanded, and a thought and a screening direction are provided for subsequent search for a new type of leaching agent which can be industrialized and used on a large scale.

Description

Extraction processes for gold, silver, and copper from electronic waste Technical Field

[0001] This invention relates to the field of metal recycling technology, and in particular to a process for extracting gold, silver and copper from electronic waste. Background Technology

[0002] Traditional domestic processes for handling electronic waste mainly involve mechanical dismantling and incineration. This method not only fails to achieve efficient recycling of precious metals, but also results in high costs, high energy consumption, and serious environmental pollution.

[0003] Initially, the extraction of metal resources from ores primarily employed inorganic acids or cyanides. However, due to the high toxicity of cyanides, novel amino acid systems have garnered significant attention. On one hand, the unique structure and composition of e-waste mean that existing environmentally friendly processes suitable for extracting natural resources cannot be fully replicated in the e-waste recycling sector to achieve optimal results. On the other hand, e-waste recycling companies are typically located in suburban areas, while metal extraction companies from ores are situated in remote regions. Applying leaching processes used for natural resource treatment to e-waste recycling companies increases the uncertainty of the surrounding environment.

[0004] In order to recycle precious metals from electronic waste, in 2023, CPBroeksma pointed out (Evaluating glycine as an alternative lixiviant for copper recovery from waste printed circuit boards. Waste Management 163 (2023) 96-107) that when glycine leaching agent is used alone to treat electronic waste, such as at 60°C and under 1M glycine conditions, the leaching rate of copper is 81.2% and the leaching rate of gold is 1.3%, which is a poor extraction effect.

[0005] In view of this, it is necessary to design an improved extraction process for gold, silver and copper from electronic waste in order to solve the above problems. Summary of the Invention

[0006] The purpose of this invention is to provide a process for extracting gold, silver, and copper from electronic waste. It utilizes the synergistic effect of a compounded leaching agent and a leaching enhancer to form a stable chelate structure with metal ions, thereby achieving efficient leaching of metal ions in a green and environmentally friendly manner.

[0007] To achieve the above-mentioned objectives, this invention provides a process for extracting gold, silver, and copper from electronic waste, comprising the following steps:

[0008] S1. Grind the electronic waste to be tested to obtain powder with a particle size of less than 100 mesh, add water to the powder and stir to obtain a slurry of a preset concentration;

[0009] S2. Add a mixed leaching agent to the slurry to achieve a preset concentration; the mixed leaching agent is a compound of glutamic acid and cystine;

[0010] S3. Next, heat the slurry to the preset temperature and stir for 2 hours; then add the pH adjuster and leaching enhancer in sequence, cool to room temperature and stir for 6-72 hours to extract gold, silver and copper from electronic waste.

[0011] As a further improvement of the present invention, in step S2, the preset concentration of glutamic acid in the mixed leachate is 0.5-4 mol / L, and the preset concentration of cystine is 0.5-4 mol / L.

[0012] As a further improvement of the present invention, in step S3, the leaching enhancer is one of 3,3-dithiodipropionic acid and bis(2-hydroxyethyl) disulfide.

[0013] As a further improvement of the present invention, the mass ratio of glutamic acid to cystine in the mixed leachate is 1:0.8-1.2.

[0014] As a further improvement of the present invention, the concentration of the leaching enhancer is 0.01-0.1 mmol / L.

[0015] As a further improvement of the present invention, in step S1, the portion of the powder with a particle size of less than 100 mesh accounts for 90% of the total mass of the powder; the mass concentration of the slurry is 5%-20%.

[0016] As a further improvement of the present invention, in step S3, the slurry is heated to 40-80°C.

[0017] As a further improvement of the present invention, in step S3, a pH adjuster is added to adjust the pH of the slurry to 8-10.

[0018] As a further improvement of the present invention, the pH adjuster is one of sodium hydroxide, sodium carbonate, and sodium bicarbonate.

[0019] As a further improvement of the present invention, the leaching rate of gold in the electronic waste is as high as 87%, and the leaching rates of silver and copper are both higher than 90%.

[0020] The beneficial effects of this invention are:

[0021] (1) This invention provides a process for extracting gold, silver and copper from electronic waste. First, a glutamic acid-cysteine ​​complex is added to the slurry. Glutamic acid makes the slurry acidic. Under acidic conditions and the catalytic action of active metals (zinc, nickel, etc.) in electronic waste, cysteine ​​is partially reduced to cysteine. The conversion between cysteine ​​anions and cysteine ​​anions is in a dynamic chemical equilibrium state. Then, sodium hydroxide is added to adjust the slurry to a suitable alkalinity so that glutamic acid and cysteine ​​exist in anionic form. The oxidation of cysteine ​​anions oxidizes the target metal element into metal ions. Then, through the synergistic effect of the carboxyl and amino groups in the molecular structure of the two amino acids in the system and the sulfur-sulfur bonds, hydroxyl groups or carboxyl groups in the leaching enhancer, they form a stable chelate structure with the metal ions, thereby achieving efficient leaching of metal ions.

[0022] (2) The synergistic effect of the compounded leaching agent and leaching synergist of this invention overcomes the problem of poor leaching effect when using a single amino acid alone. At the same time, amino acid compounds play a major role in the leaching system, breaking the traditional amino acid-cyanide salt synergistic system. This leaching system is green and environmentally friendly, expanding the types of environmentally friendly leaching agents and providing ideas and screening directions for the subsequent search for new leaching agents that can be industrialized and used on a large scale. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0024] It should also be noted that, in order to avoid obscuring the present invention with unnecessary details, only the structures and / or processing steps closely related to the present invention are shown in the accompanying drawings, while other details that are not closely related to the present invention are omitted.

[0025] Additionally, it should be noted that the terms “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0026] This invention provides a process for extracting gold, silver, and copper from electronic waste, comprising the following steps:

[0027] S1. Preparation of slurry:

[0028] The electronic waste to be tested is ground to a particle size of less than 100 mesh to obtain powder. Water is added to the powder and stirred to obtain a slurry of a preset concentration. The portion of the powder with a particle size of less than 100 mesh accounts for 90% of the total mass of the powder; the mass concentration of the slurry is 5%-20%.

[0029] Electronic waste is a secondary mineral resource. The accumulation of electronic waste not only wastes resources but also pollutes the environment and occupies a large amount of space. The extraction process described in this application can efficiently extract heavy metals from electronic waste, making rational use of resources while protecting the environment, and thus has significant practical value.

[0030] By controlling the portion of the powder with a particle size smaller than 2 mm to 90% of the total powder mass, the powder in the prepared slurry is kept at a certain fineness, which is more conducive to the leaching of gold, silver and copper from the powder and improves the leaching rate.

[0031] S2. Add mixed leaching agent:

[0032] Add a mixed leaching agent to the slurry to achieve a preset concentration. The mixed leaching agent is a compound of glutamic acid and cystine, with preset concentrations of glutamic acid and cystine of 0.5-4 mol / L. That is, 0.5-4 mol of glutamic acid and 0.5-4 mol of cystine need to be added to every 1 L of slurry.

[0033] Furthermore, the mass ratio of glutamic acid to cystine in the mixed leachate is 1:0.8-1.2, preferably 1:1.

[0034] In this process, glutamic acid first makes the slurry acidic. Then, under acidic conditions and catalysis by active metals (such as zinc and nickel) in electronic waste, cystine is partially reduced to cysteine. The conversion between cysteine ​​anions and cysteine ​​anions is in a dynamic chemical equilibrium state. The oxidation of cysteine ​​anions is conducive to oxidizing the target metal element into metal ions.

[0035] S3. Extraction of gold, silver, and copper:

[0036] Next, heat the slurry to 40-80℃ and continue stirring for 2 hours; then add a pH adjuster to adjust the pH of the slurry to 8-10, add a leaching enhancer, cool to room temperature and stir for 6-72 hours to extract gold, silver and copper from electronic waste.

[0037] The pH adjuster is one of sodium hydroxide, sodium carbonate, and sodium bicarbonate, preferably sodium hydroxide.

[0038] The leaching enhancer is one of 3,3-dithiodipropionic acid and bis(2-hydroxyethyl) disulfide; the concentration of the leaching enhancer is 0.01-0.1 mmol / L, that is, 0.01-0.1 mmol of leaching enhancer needs to be added to every 1L of slurry.

[0039] In this process, sodium hydroxide is added to adjust the slurry to a suitable alkalinity, so that glutamic acid and cysteine ​​exist in anionic form. The interaction between the carboxyl and amino groups in the molecular structure of the two amino acids, as well as the sulfur-sulfur bonds, hydroxyl groups or carboxyl groups in the leaching enhancer, can form a stable chelate structure with metal ions.

[0040] Throughout the process, glutamic acid hydrolysis promotes cystine decomposition, and cystine decomposes into cysteine, which plays an oxidizing role. Then, under the synergistic effect of the mixed leaching agent and leaching enhancer, the valuable target metal is leached efficiently.

[0041] The leaching rate of gold in electronic waste is as high as 87%, while the leaching rates of silver and copper are both higher than 90%.

[0042] The present invention will be described in detail below through specific embodiments. In the following embodiments, waste circuit boards containing metal resources (a type of electronic waste) are selected. The main components of these waste circuit boards are shown in Table 1. The units for Au, Ag, Pt, and Pd are g / t.

[0043] Table 1 Main components of waste circuit boards

[0044]

[0045] Example 1

[0046] A process for extracting gold, silver, and copper from electronic waste includes the following steps:

[0047] S1. Preparation of slurry:

[0048] The electronic waste to be tested was ground to a particle size of less than 100 mesh to obtain powder. Water was added to the powder and stirred to obtain a slurry of a preset concentration. The portion of the powder with a particle size of less than 100 mesh accounted for 90% of the total mass of the powder; the mass concentration of the slurry was 5%.

[0049] S2. Add mixed leaching agent:

[0050] A mixed leaching agent is added to the slurry to reach a preset concentration. The mixed leaching agent is a compound of glutamic acid and cystine, with a preset concentration of 1 mol / L for both glutamic acid and cystine, meaning the mass ratio of glutamic acid to cystine in the mixed leaching agent is 1:1.

[0051] S3. Extraction of gold, silver, and copper:

[0052] Next, the slurry was heated to 50°C and stirred for 2 hours. Then, sodium hydroxide was added to adjust the pH of the slurry to 10, and a leaching enhancer was added. After cooling to room temperature, the slurry was stirred for 72 hours at a stirring speed of 100 r / min to extract gold, silver and copper from electronic waste.

[0053] The leaching enhancer was bis(2-hydroxyethyl) disulfide; the concentration of the leaching enhancer was 0.01 mmol / L.

[0054] Examples 2-3 and Comparative Example 1

[0055] An extraction process for gold, silver, and copper from electronic waste differs from Example 1 in that the concentration of the mixed leaching agent added in step S2 is different. Otherwise, it is largely the same as Example 1 and will not be described again here.

[0056] The leaching rates of gold, copper, and silver in Examples 1-3 and Comparative Example 1 are shown in Table 2:

[0057] Table 2 shows the leaching rates of gold, copper, and silver in Examples 1-3 and Comparative Example 1.

[0058]

[0059] Table 2 shows that, within a certain range, increasing the concentration of the mixed leaching agent is beneficial to improving the leaching effect of gold, silver, and copper. However, when the concentration of the mixed leaching agent is ≥5 mol / L, the leaching effect of gold, silver, and copper decreases significantly. This is because when the concentration of the mixed leaching agent is too high, some of it will adhere to the surface of the electronic waste slurry, affecting its leaching effect. When the concentration of the mixed leaching agent is ≤0.5 mol / L, its concentration is too low and has virtually no effect.

[0060] Comparative Examples 2-10

[0061] The extraction process for gold, silver and copper from electronic waste differs from Example 1 in that the type of mixed leaching agent added in step S2 is different. Otherwise, it is largely the same as Example 1 and will not be described again here.

[0062] The leaching rates of gold, copper, and silver in Comparative Examples 2-10 are shown in Table 3:

[0063] Table 3 shows the leaching rates of gold, copper, and silver in Comparative Examples 2-10.

[0064]

[0065] The "--" indicates that the concentration of metal ions in the leaching solution is below the instrument's detection limit, meaning that their content is very low and can be basically ignored.

[0066] As shown in Table 3, when the glutamic acid-cysteine ​​combination is replaced with other combinations of two amino acids or a single amino acid is used, the effect is significantly worse, especially the leaching effect on precious metals gold and silver, indicating the synergistic effect of glutamic acid-cysteine.

[0067] Examples 4-5 and Comparative Examples 11-12

[0068] An extraction process for gold, silver, and copper from electronic waste differs from Example 1 in that the concentration of the leaching enhancer is different in step S3. Otherwise, it is largely the same as Example 1 and will not be described again here.

[0069] The leaching rates of gold, copper, and silver in Examples 4-5 and Comparative Examples 11-12 are shown in Table 4:

[0070] Table 4 shows the leaching rates of gold, copper, and silver in Examples 4-5 and Comparative Examples 11-12.

[0071]

[0072] As shown in Table 4, with the continuous increase of the leaching enhancer concentration, the leaching rates of gold, silver, and copper initially increased significantly before decreasing. When the concentration of the leaching enhancer was too high (≥0.2 mmol / L), the leaching rates of gold, silver, and copper were significantly lower. This was mainly because the leaching enhancer underwent a series of side reactions, consuming the mixed leaching agent, and forming flocculent precipitates that adhered to the surface of electronic waste, thus affecting the leaching rates of gold, silver, and copper.

[0073] When no leaching synergist was added, the leaching rates of gold, silver, and copper all decreased, indicating that there is a synergistic effect between the leaching synergist and the mixed leaching agent.

[0074] Example 6 and Comparative Examples 13-14

[0075] The extraction process for gold, silver and copper from electronic waste differs from Example 1 in that the type of leaching enhancer in step S3 is different. The other steps are largely the same as in Example 1 and will not be described in detail here.

[0076] The leaching rates of gold, copper, and silver in Example 6 and Comparative Examples 13-15 are shown in Table 5:

[0077] Table 5 shows the leaching rates of gold, copper, and silver in Example 6 and Comparative Examples 13-15.

[0078]

[0079] As shown in Table 5, the leaching enhancers used in Examples 1 and 6 can synergistically improve the leaching effect of gold, silver, and copper in electronic waste with glutamic acid-cysteine. However, the enhancers used in Comparative Examples 13-15 generate sulfides or elemental sulfur during the leaching process, which adhere to the mineral surface and hinder the further progress of the leaching reaction.

[0080] (The effect of the leaching enhancer used in Example 6 on the leaching rate of gold, silver, and copper varies with its concentration, similar to that in Example 1.)

[0081] Examples 7-8 and Comparative Example 16

[0082] The extraction process for gold, silver, and copper from electronic waste differs from Example 6 in that the concentration of the mixed leaching agent added in step S2 is different. Otherwise, it is largely the same as Example 6 and will not be described again here.

[0083] The leaching rates of gold, copper, and silver in Examples 6-8 and Comparative Example 16 are shown in Table 6:

[0084] Table 6 shows the leaching rates of gold, copper, and silver in Examples 6-8 and Comparative Example 16.

[0085]

[0086] Table 6 shows that increasing the concentration of the mixed leaching agent is beneficial to improving the leaching effect of gold, silver, and copper. When the concentration of the leaching agent is ≥4 mol / L, the leaching effect of gold, silver, and copper tends to be stable. When the concentration of the leaching agent is ≤0.5 mol / L, the amount of leaching agent is insufficient, which affects the leaching effect.

[0087] Example 9 and Comparative Example 17

[0088] A process for extracting gold, silver, and copper from electronic waste differs from Example 1 in that the slurry concentration is different in step S1. Otherwise, it is largely the same as Example 1 and will not be described again here.

[0089] The leaching rates of gold, copper, and silver in Example 9 and Comparative Example 17 are shown in Table 7:

[0090] Table 7. Leaching rates of gold, copper, and silver in Example 9 and Comparative Example 17.

[0091]

[0092] As shown in Table 7, the leaching rates of gold, copper, and silver gradually decreased with increasing slurry concentration. This may be because, on the one hand, increasing slurry concentration affects the mass transfer between the reacting liquid and solid during the leaching process; on the other hand, it affects the relative molar ratio of the mixed leaching agent and leaching enhancer to the leached metals in the minerals. When the slurry concentration is higher than 20%, the amount of reagent used is relatively insufficient, and the metal resources in the electronic waste cannot be effectively leached. In addition, because the copper content in the selected electronic waste is relatively high, excessively high slurry concentration causes the copper-complexes originally leached by the leaching reagent to precipitate out of the solution system.

[0093] When the slurry concentration is too low (<5%), it is not conducive to industrial production. For example, it wastes water resources and generates a large amount of wastewater. In order to achieve environmentally friendly wastewater discharge, it will further increase the environmental protection costs of enterprises.

[0094] The leaching enhancer in Example 6 had a similar effect on the leaching rates of gold, silver, and copper depending on the slurry concentration.

[0095] Examples 10-11 and Comparative Examples 18-19

[0096] A process for extracting gold, silver, and copper from electronic waste differs from Example 1 in that the pH value of the slurry is adjusted using sodium hydroxide in step S3. Otherwise, the process is largely the same as in Example 1 and will not be repeated here.

[0097] The leaching rates of gold, copper, and silver in Examples 10-11 and Comparative Examples 18-19 are shown in Table 8.

[0098] Table 8. Leaching rates of gold, copper, and silver in Examples 10-11 and Comparative Examples 18-19

[0099]

[0100] Table 8 shows that the leaching effect of each substance is poor when the pH of the leaching system is ≤7. Under neutral conditions, gold is basically unable to be leached. This is mainly because the carboxyl groups in the mixed leaching agent exist in the form of electrically neutral molecules and cannot effectively complex with gold, resulting in the inability to leach gold. At the same time, the leaching rates of copper and silver are low. As the pH of the leaching system increases, the carboxyl groups in the mixed leaching agent hydrolyze into anionic forms. The increase in pH of the leaching system is beneficial to the leaching effect of metals. When the pH of the slurry is >10, the leaching effect of gold, silver, and copper decreases. This can be attributed to the fact that under highly alkaline conditions, the mixed leaching agent is decomposed, thereby affecting the leaching effect of the above metals.

[0101] The leaching enhancer in Example 6 had a similar effect on the leaching rates of gold, silver, and copper depending on the pH value.

[0102] In summary, this invention provides an extraction process for gold, silver, and copper from electronic waste. It utilizes a compounded leaching agent and a synergistic leaching enhancer to form a stable chelate structure with metal ions, achieving efficient and environmentally friendly leaching of metal ions. This process expands the range of environmentally friendly leaching agents and provides ideas and screening directions for the subsequent search for novel leaching agents suitable for industrial-scale application.

[0103] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A process for extracting gold, silver, and copper from electronic waste, characterized in that, The process includes the following steps: S1. Grind the electronic waste to be tested into powder with a particle size of less than 100 mesh, add water to the powder and stir to obtain a slurry of a preset concentration; the mass concentration of the slurry is 5%-20%; S2. Add a mixed leaching agent to the slurry to achieve a preset concentration; the mixed leaching agent is a compound of glutamic acid and cystine; the preset concentration of glutamic acid in the mixed leaching agent is 0.5-4 mol / L, and the preset concentration of cystine is 0.5-4 mol / L; S3. Then heat the slurry to a preset temperature and stir for 2 hours; then add a pH adjuster and a leaching enhancer in sequence, cool to room temperature and stir for 6-72 hours to extract gold, silver and copper from the electronic waste; the leaching enhancer is one of 3,3-dithiodipropionic acid and bis(2-hydroxyethyl) disulfide; the concentration of the leaching enhancer is 0.01-0.1 mmol / L; add a pH adjuster to adjust the pH of the slurry to 8-10.

2. The extraction process for gold, silver, and copper from electronic waste according to claim 1, characterized in that, The mass ratio of glutamic acid to cystine in the mixed leachate is 1:0.8-1.

2.

3. The extraction process for gold, silver, and copper from electronic waste according to claim 1, characterized in that, In step S1, the portion of the powder with a particle size smaller than 100 mesh accounts for 90% of the total mass of the powder.

4. The extraction process for gold, silver, and copper from electronic waste according to claim 1, characterized in that, In step S3, the slurry is heated to 40-80℃.

5. The extraction process for gold, silver, and copper from electronic waste according to claim 4, characterized in that, The pH adjuster is one of sodium hydroxide, sodium carbonate, and sodium bicarbonate.

6. The extraction process for gold, silver, and copper from electronic waste according to claim 1, characterized in that, The leaching rate of gold in the electronic waste was as high as 87%, while the leaching rates of silver and copper were both higher than 90%.

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