Cyanide-free leaching agent and process for treating tin, lead, copper and gold in electronic waste

Abstract

The application provides a cyanide-free leaching agent and a process for treating tin, lead, copper and gold in electronic waste, the cyanide-free leaching agent introduces functional functional groups with imidazole as a molecular skeleton, on the basis of ensuring the solubility of the agent in water, the agent is modified, functional functional groups are introduced into the structure, and a series of derivatives are prepared. In the process of leaching metal, the concentration of electronic waste powder and ore pulp is controlled within a reasonable range, the cyanide-free leaching agent, a pH regulator and different oxidizing agents are sequentially added, the leaching conditions are strictly controlled, different oxidizing environments are used for step-by-step oxidation of different metals and the cyanide-free leaching agent, and through strict control of the types of heterocyclic structures, the types, quantities and position relationships of the introduced functional groups in the molecular structure of the cyanide-free leaching agent, efficient leaching of tin, lead, copper and gold in electronic waste is realized; the use of cyanide is avoided in the leaching process, and the process flow is simple and easy to operate.

Description

Technical Field

[0001] This invention relates to the field of hydrometallurgical technology, and in particular to a cyanide-free leaching agent and its process for treating tin, lead, copper and gold in electronic waste. Background Technology

[0002] Printed circuit boards (PCBs) typically consist of electronic components (ECs), screen printing, soldering masks, interconnect materials, metal coatings, and polymer substrates. Waste printed circuit boards (WPCBs), commonly known as e-waste, contain up to 60 elements, including more than 40 metallic elements, such as base metals (e.g., Cu, Fe, Al, Sn) and precious metals (e.g., Ag, Au, Pd, Pt). Directly discarding e-waste not only wastes metal resources but also pollutes the environment. The unique structure and complex composition of e-waste make it significantly different from natural minerals, thus the recovery of metals from e-waste has become one of the most challenging research areas in metallurgy.

[0003] Currently, the main process for processing electronic waste is pyrometallurgy, which involves melting metals through high-temperature heating for recycling. However, this process generates large amounts of heavy metal vapors, posing significant health risks to workers and severely polluting the environment.

[0004] To address these issues, hydrometallurgical processes have been continuously studied. For example, in 2020, Oraby and Eksteen (Extraction of copper and the co-leaching behavior of other metals from waste printed circuit boards using alkaline glycine solutions. Resour. Conserv. Recycl. 154, 104624.) investigated the co-leaching behavior of extracting copper and other metals from waste printed circuit boards using alkaline glycine solutions. This method achieved a high leaching rate for copper but a low leaching rate for other metals, especially gold. To improve the leaching rate of precious metals, in 2022, Li et al. (Development of an integrated glycine-based process for base and precious metals recovery from waste printed circuit boards. Resour. Conserv. Recycl. 187, 106631) proposed a three-stage glycine leaching process. First, Cu is efficiently leached using an ammonia-glycine system, resulting in almost complete Cu leaching. The residue is then leached with Cu and Au using a low-concentration cyanide-glycine synergistic system, achieving leaching rates of 51.4% and 82.0% for Cu and Au, respectively. Next, the residue is leached with an acidic system to remove Sn, Pb, and Au, achieving leaching rates of 36.0%, 2.0%, and 71.0% for Sn, Pb, and Au, respectively. While this method improves the leaching rate of Au to some extent, the leaching rates of Sn and Pb are relatively low. Furthermore, this process requires the use of highly toxic cyanide and has a long process flow.

[0005] In view of this, it is necessary to design an improved cyanide-free leaching agent and its process for treating tin, lead, copper and gold in electronic waste in order to solve the above problems. Summary of the Invention

[0006] The purpose of this invention is to provide a cyanide-free leaching agent and a process for treating tin, lead, copper, and gold in electronic waste. The cyanide-free leaching agent uses imidazole as its molecular backbone and introduces functional groups. While ensuring the agent's solubility in water, it is modified by introducing functional groups into its structure to prepare a series of derivatives. During the metal leaching process, by strictly controlling the leaching conditions, selective leaching of tin, lead, copper, and gold from electronic waste is efficiently achieved through gradient oxidation, the synergistic effect of the molecular spatial structure of the cyanide-free leaching agent with a specific oxidation structure, and the interaction between different functional groups.

[0007] To achieve the above-mentioned objectives, this invention provides a cyanide-free leaching agent, wherein the cyanide-free leaching agent is based on imidazole as a molecular backbone with introduced functional groups, and its general structural formula is as follows:

[0008]

[0009] Where R represents hydrogen, methyl, ethyl, or propyl.

[0010] This invention also provides a process for treating tin, lead, copper, and gold in electronic waste using a cyanide-free leaching agent. The process involves using the aforementioned cyanide-free leaching agent to leach tin, lead, copper, and gold from the electronic waste, and includes the following steps:

[0011] S1. Crush the electronic waste to be processed to a particle size of less than 50 mesh to obtain material, add water to the material and stir to obtain a slurry of a preset concentration;

[0012] S2. Add one or more of the cyanide-free leaching agents to the slurry to bring the cyanide-free leaching agent to a preset concentration;

[0013] S3. Add sodium hydroxide to adjust the pH of the slurry to 10-14, stir for the preset time, and leach tin and lead;

[0014] S4. Add hydrogen peroxide, stir for the preset time, and leach out the copper;

[0015] S5. Add potassium permanganate, stir for the preset time, and leach out the gold.

[0016] As a further improvement of the present invention, in step S2, the preset concentration of the cyanide-free leaching agent in the slurry is 0.1-1 mol / L.

[0017] As a further improvement of the present invention, in step S4, the concentration of hydrogen peroxide in the slurry is 5-20 mL / L.

[0018] As a further improvement of the present invention, in step S5, the concentration of potassium permanganate in the slurry is 0.1-1 g / L.

[0019] As a further improvement of the present invention, in step S1, the portion of the material with a particle size of less than 50 mesh accounts for 90% of the total mass of the mineral powder; the mass concentration of the slurry is 5%-30%.

[0020] As a further improvement of the present invention, in step S3, the temperature of the slurry during stirring is 20℃-80℃, and the stirring time is 0.5-6h.

[0021] As a further improvement of the present invention, in step S4, the temperature of the slurry during stirring is 20℃-80℃; the stirring time is 6-24h.

[0022] As a further improvement of the present invention, in step S5, the temperature of the slurry during stirring is 20℃-80℃; the stirring time is 6-48h.

[0023] As a further improvement of the present invention, in steps S1, S3, S4 and S5, the stirring speed is 100-300 r / min.

[0024] The beneficial effects of this invention are:

[0025] (1) The cyanide-free leaching agent provided by this invention introduces functional groups into the molecular skeleton of imidazole. While ensuring the agent's solubility in water, it is modified by introducing functional groups into its structure to prepare a series of derivatives. During the metal leaching process, the concentration of electronic waste powder and slurry is controlled within a reasonable range. A cyanide-free leaching agent, pH adjuster, and different oxidants are added sequentially to efficiently convert tin, lead, copper, and gold in electronic waste into metal ions. By strictly controlling the leaching conditions, different metals and the cyanide-free leaching agent are gradually oxidized using different oxidation environments. Simultaneously, by strictly controlling the type of heterocyclic structure in the molecular structure of the cyanide-free leaching agent, the type, quantity, and positional relationship of the introduced functional groups, efficient leaching of tin, lead, copper, and gold from electronic waste is achieved. That is, selective leaching of tin, lead, copper, and gold from electronic waste is efficiently achieved through gradient-based gradual oxidation and the synergistic effect between the molecular spatial structure of the cyanide-free leaching agent with a specific oxidation structure and different functional groups.

[0026] (2) This invention expands the types of traditional leaching agents and provides ideas and screening directions for the subsequent search for new leaching agents that can be industrialized and used on a large scale.

[0027] (3) The process for treating tin, lead, copper and gold in electronic waste with cyanide-free leaching agent provided by the present invention uses cyanide-free leaching agent to treat electronic waste, avoiding the use of cyanide; at the same time, the process is simple and easy to operate; it solves the problems of cyanide use, complex process and cumbersome process faced by the current hydrometallurgical process for treating tin, lead, copper and gold in electronic waste. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the tin and lead leaching process of the cyanide-free leaching agent used in the present invention for treating tin, lead, copper and gold in electronic waste.

[0029] Figure 2 This is a schematic diagram of the copper leaching process in the process of treating tin, lead, copper, and gold in electronic waste using the cyanide-free leaching agent of the present invention.

[0030] Figure 3 This is a schematic diagram illustrating the mechanism of the gold leaching process in which the cyanide-free leaching agent of the present invention is used to treat tin, lead, copper and gold in electronic waste.

[0031] Figure 4 This is a flowchart of the preparation process for drug A. Detailed Implementation

[0032] 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.

[0033] 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.

[0034] 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.

[0035] This invention provides a cyanide-free leaching agent, which is based on imidazole as a molecular backbone and incorporates functionalized functional groups. Its general structural formula is as follows:

[0036]

[0037] Where R represents hydrogen, methyl, ethyl, or propyl.

[0038] Specifically, when R is hydrogen, the cyanide-free leaching agent is named Agent-A, with the following structural formula:

[0039]

[0040] When R is methyl, the cyanide-free leaching agent is named Agent-B, with the following structural formula:

[0041]

[0042] When R is ethyl, the cyanide-free leaching agent is named Agent-C, with the following structural formula:

[0043]

[0044] When R is propyl, the cyanide-free leaching agent is named Agent-D, with the following structural formula:

[0045]

[0046] This invention also provides a process for treating tin, lead, copper, and gold in electronic waste using a cyanide-free leaching agent. The process involves using the aforementioned cyanide-free leaching agent to leach tin, lead, copper, and gold from the electronic waste, and includes the following steps:

[0047] S1. Preparation of slurry:

[0048] The electronic waste to be processed is crushed to a particle size of less than 50 mesh to obtain the material. Water is added to the material and stirred evenly at a stirring speed of 100-300 r / min to obtain a slurry with a mass concentration of 5%-30%.

[0049] The portion of the material with a particle size of less than 50 mesh accounts for 90% of the total mass of the mineral powder. This ensures that the material in the prepared slurry is controlled to a certain fineness, which is more conducive to leaching tin, lead, copper and gold from the material and improving the leaching rate.

[0050] S2. Add cyanide-free leaching agent:

[0051] One or more cyanide-free leaching agents are added to the ore slurry to make the concentration of the cyanide-free leaching agent in the ore slurry 0.1-1 mol / L.

[0052] S3. Leaching of tin and lead:

[0053] Add sodium hydroxide to adjust the pH of the slurry to 10-14, and stir at a stirring speed of 100-300 r / min for 0.5-6 hours in an environment with a slurry temperature of 20℃-80℃ to leach tin and lead.

[0054] In this process, tin and lead first undergo a redox reaction with oxygen in the air to form metal ions. These metal ions then undergo a complexation reaction with a cyanide-free leaching agent, entering the solution phase to leach tin and lead from electronic waste. Specifically, agent C will be used as an example for explanation. Figure 1 As shown, one molecule of tin ion and one molecule of lead ion coordinate with the carboxyl group in two molecules of cyanide-free leaching agent to form a stable chelate structure.

[0055] S4. Leached copper:

[0056] After leaching tin and lead, hydrogen peroxide is added, and copper is leached by stirring at 100-300 r / min for 6-24 hours in an environment with a slurry temperature of 20℃-80℃. The concentration of hydrogen peroxide in the slurry is 5-20 mL / L (i.e., 5-20 mL of hydrogen peroxide is added per liter of slurry).

[0057] In this process, the presence of hydrogen peroxide serves two purposes: firstly, it oxidizes copper into copper ions; secondly, as... Figure 2As shown in Figure a, taking reagent C as an example, the cyanide-free leaching reagent undergoes oxidative ring-opening to generate a terminal amino group. Simultaneously, the imide group formed after ring-opening undergoes electron transfer, leading to further structural isomerization and the generation of functionalized functional groups with copper leaching effects. The lone pair electrons of the oxygen atoms in the isomerized structural fragment of the terminal amino group and the imide group work synergistically to form stable cyclic chelates with copper ions (e.g., ...). Figure 2 (As shown in b), it enters the solution phase, ultimately achieving the leaching of copper from electronic waste.

[0058] S5. Leaching gold:

[0059] After copper leaching is complete, potassium permanganate is added, and gold is leached by stirring at a speed of 100-300 r / min for 6-48 hours in an environment with a slurry temperature of 20℃-80℃. The concentration of potassium permanganate in the slurry is 0.1-1 g / L (i.e., 0.1-1 g of potassium permanganate is added per liter of slurry).

[0060] During this process, with the addition of the strong oxidizing agent potassium permanganate, gold is rapidly oxidized into gold ions on the one hand; on the other hand, as... Figure 3 As shown in Figure a, taking reagent C as an example, potassium permanganate further oxidizes the cyanide-free leaching agent that has been oxidized by hydrogen peroxide in step S4, oxidizing the hydroxyl group into a carboxyl group, thereby achieving a further change in the structure of the cyanide-free leaching agent. The specific spatial position of the newly generated carboxyl group and the synergistic effect of the imide interact with the gold ions to form a stable six-membered ring chelate, which enters the solution phase, ultimately achieving the leaching of gold from electronic waste.

[0061] The present invention will be described below through specific embodiments. In the following embodiments, waste printed circuit boards (a type of electronic waste) containing metal resources are selected. The main components of the waste printed circuit boards are shown in Table 1. Among them, the units of Au, Ag, Pt and Pd are g / t.

[0062] Table 1 Main Components of Waste Printed Circuit Boards

[0063]

[0064]

[0065] Example 1

[0066] A process for treating tin, lead, copper, and gold in electronic waste using a cyanide-free leaching agent, comprising the following steps:

[0067] S1. Preparation of slurry:

[0068] Waste printed circuit boards (electronic waste) are crushed, screened, mixed, and reduced to a particle size of less than 50 mesh to obtain material. Ensure that the portion of the material with a particle size of less than 50 mesh accounts for 90% of the total mass of mineral powder. Add water to the material and stir evenly at a stirring speed of 100 r / min to obtain a mineral slurry with a mass concentration of 10%.

[0069] S2. Add cyanide-free leaching agent:

[0070] Add reagent-A to the slurry prepared in step S1 to make the concentration of reagent-A in the slurry 0.5 mol / L.

[0071] S3. Leaching of tin and lead:

[0072] Sodium hydroxide was added to the slurry in step S2 to adjust the pH value of the slurry to 13. After returning to room temperature, the slurry was stirred at a stirring speed of 100 r / min for 3 hours in an environment with a slurry temperature of 30°C to leach tin and lead.

[0073] S4. Leached copper:

[0074] After the leaching of tin and lead is completed, hydrogen peroxide is added to the slurry in step S3 until the concentration of hydrogen peroxide in the slurry is 10 mL / L. After returning to room temperature, copper is leached by stirring at 100 r / min for 12 h in an environment with a slurry temperature of 30°C.

[0075] S5. Leaching gold:

[0076] After copper leaching is completed, potassium permanganate is added to the slurry from step S4 until the concentration of potassium permanganate in the slurry is 0.5 g / L. After the slurry is brought back to room temperature, gold is leached by stirring at 100 r / min for 48 h in an environment with a slurry temperature of 30°C.

[0077] Examples 2-4

[0078] A process for treating tin, lead, copper and gold in electronic waste with a cyanide-free leaching agent is different from that in Example 1, except that the type of cyanide-free leaching agent added in step S2 is different. The rest is roughly the same as in Example 1 and will not be described again here.

[0079] The leaching rates of tin, lead, copper, and gold in Examples 1-4 are shown in Table 2:

[0080] Table 2 shows the leaching rates of tin, lead, copper, and gold in Examples 1-4.

[0081]

[0082] As shown in Table 2, the cyanide-free leaching agents provided in Examples 1-4 all have good leaching effects on tin, lead, copper, and gold.

[0083] Examples 5-6 and Comparative Examples 1-2

[0084] A process for treating tin, lead, copper and gold in electronic waste with a cyanide-free leaching agent differs from Example 3 in that the slurry concentration is different in step S1. Otherwise, it is largely the same as Example 3 and will not be described again here.

[0085] The leaching rates of tin, lead, copper, and gold in Examples 5-6 and Comparative Examples 1-2 are shown in Table 3.

[0086] Table 3 shows the leaching rates of tin, lead, copper, and gold in Examples 5-6 and Comparative Examples 1-2.

[0087]

[0088] As shown in Table 3, within a certain range, the leaching rates of various metals fluctuate within a certain range as the slurry concentration increases. However, when the slurry concentration is too high, the leaching rates of all metals decrease. This is because as the slurry concentration increases, the mass transfer between the reaction liquid and the solid is affected during the leaching process. When the slurry concentration reaches 40%, the mass transfer between the target metal in the material and the leaching agent in the solution is severely affected, resulting in a low leaching rate of the target metal. In addition, 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.

[0089] The effects of other cyanide-free leaching agents on the leaching rates of tin, lead, copper, and gold vary depending on the pulp concentration.

[0090] Examples 7-8 and Comparative Examples 3-4

[0091] A process for treating tin, lead, copper and gold in electronic waste with a cyanide-free leaching agent is disclosed. The difference between this process and Example 3 is that the concentration of the cyanide-free leaching agent is different in step S2. Otherwise, the process is largely the same as Example 3 and will not be repeated here.

[0092] The leaching rates of tin, lead, copper, and gold in Examples 7-8 and Comparative Examples 3-4 are shown in Table 4.

[0093] Table 4 shows the leaching rates of tin, lead, copper, and gold in Examples 7-8 and Comparative Examples 3-4.

[0094]

[0095]

[0096] Table 4 shows that, within a certain range, the leaching rates of tin, lead, copper, and gold gradually increase with the increase of the concentration of the cyanide-free leaching agent (from 0.1 mol / L to 1 mol / L). With further increases in the concentration of the cyanide-free leaching agent (≥1 mol / L), the leaching effect of tin, lead, copper, and gold basically stabilizes. When the concentration of the cyanide-free leaching agent is too low (≤0.05 mol / L), the leaching rates of copper and gold decrease significantly, indicating that the cyanide-free leaching agent has a good promoting effect on the dissolution and leaching of tin, lead, copper, and gold in electronic waste.

[0097] Other cyanide-free leaching agents have similar effects on the leaching rates of tin, lead, copper, and gold, depending on their concentration.

[0098] Examples 9-10 and Comparative Example 5

[0099] A process for treating tin, lead, copper and gold in electronic waste with a cyanide-free leaching agent differs from Example 3 in that the slurry temperature is different in steps S3, S4 and S5 (the slurry temperature remains the same in steps S3, S4 and S5). The other processes are largely the same as in Example 3 and will not be described in detail here.

[0100] The leaching rates of tin, lead, copper, and gold in Examples 9-10 and Comparative Example 5 are shown in Table 5.

[0101] Table 5 shows the leaching rates of tin, lead, copper, and gold in Examples 9-10 and Comparative Example 5.

[0102]

[0103] Table 5 shows that increasing slurry temperature is beneficial for the leaching of tin, lead, copper, and gold. However, when the temperature is too high (≥90℃), the leaching rate of copper decreases and the leaching rate of gold decreases significantly. The main reason for this is that at excessively high temperatures, potassium permanganate will... Figure 3 Based on reaction α, the agent with the dicarboxyl structure obtained is further oxidized to break the carboxyl group. After excessive oxidation, the original functional groups are destroyed, making it impossible for the leaching agent to effectively chelate with gold, thus affecting the gold leaching rate.

[0104] The effects of other cyanide-free leaching agents on the leaching rates of tin, lead, copper, and gold are similar depending on the pulp temperature.

[0105] Examples 11-12 and Comparative Examples 6-8

[0106] A process for treating tin, lead, copper and gold in electronic waste with a cyanide-free leaching agent differs from Example 3 in that the concentration of hydrogen peroxide is different in step S4. Otherwise, it is largely the same as Example 3 and will not be described again here.

[0107] The leaching rates of tin, lead, copper, and gold in Examples 11-12 and Comparative Examples 6-8 are shown in Table 6:

[0108] Table 6 shows the leaching rates of tin, lead, copper, and gold in Examples 11-12 and Comparative Examples 6-8.

[0109]

[0110] As shown in Table 6, the leaching rates of tin and lead tend to stabilize with increasing hydrogen peroxide concentration, while the leaching rates of copper and gold significantly increase. However, without the addition of hydrogen peroxide, the leaching of gold is significantly inhibited. This is mainly because if potassium permanganate is introduced directly (i.e., step S5 is performed directly without step S4), the different oxidation effects of the two oxidants result in differences in the types of functionalized functional groups in the cyanide-free leaching agent, thus affecting the chelation with the target metal and consequently the leaching rate. This illustrates the necessity of gradient oxidation. With further increases in hydrogen peroxide concentration (>20 mL / L), the leaching rates of copper and gold remain relatively stable, achieving efficient leaching.

[0111] The effects of different hydrogen peroxide concentrations on the leaching rates of tin, lead, copper, and gold by other cyanide-free leaching agents are similar.

[0112] Examples 13-14 and Comparative Examples 9-11

[0113] A process for treating tin, lead, copper and gold in electronic waste with a cyanide-free leaching agent differs from Example 3 in that the concentration of potassium permanganate is different in step S5. Otherwise, it is largely the same as Example 3 and will not be described again here.

[0114] The leaching rates of tin, lead, copper, and gold in Examples 13-14 and Comparative Examples 9-11 are shown in Table 7.

[0115] Table 7. Leaching rates of tin, lead, copper, and gold in Examples 13-14 and Comparative Examples 9-11.

[0116]

[0117] As shown in Table 7, within a certain range, the leaching rates of tin, lead, and copper tend to stabilize with increasing potassium permanganate concentration, while the leaching effect of gold significantly improves. When step S5 is not performed, i.e., potassium permanganate is not introduced, the gold leaching effect is only 7%. This may be because, on the one hand, hydrogen peroxide has a relatively mild oxidizing ability and cannot efficiently oxidize gold; on the other hand, the cyanide-free leaching agent that has undergone hydrogen peroxide oxidation has factors such as the number, type, and position of functional groups in its molecular structure, which prevent it from effectively chelating with gold ions to form stable chelates, ultimately resulting in poor gold leaching effect. With further increases in potassium permanganate concentration (3 g / L), the leaching effects of tin and lead remained relatively stable, while the leaching effects of copper and gold deteriorated. The main reason for this is likely that after oxidizing the cyanide-free leaching agent, excessive potassium permanganate further oxidizes the copper chelate, destroying its stable structure and transforming it into copper hydroxide. Copper hydroxide has poor solubility and precipitates from the solution phase, ultimately leading to a decrease in the copper leaching rate. At the same time, the product of potassium permanganate oxidation under alkaline conditions is manganese dioxide. Manganese dioxide cannot dissolve in the liquid phase but adheres to the surface of the material, hindering the contact between the target metal (gold) and the leaching agent.

[0118] The effects of other cyanide-free leaching agents on the leaching rates of tin, lead, copper, and gold are similar, depending on the concentration of potassium permanganate.

[0119] Comparative Examples 12-17

[0120] A process for treating tin, lead, copper and gold in electronic waste with a cyanide-free leaching agent is different from that in Example 3, except that the type of cyanide-free leaching agent added in step S2 is different. The rest is roughly the same as in Example 3 and will not be described again here.

[0121] Table 8 shows the leaching rates of tin, lead, copper, and gold in Comparative Examples 12-17.

[0122]

[0123]

[0124] As can be seen from the data in Comparative Example 12 in Table 8, the leaching rates of tin, lead, and copper all decreased significantly with the further increase of carbon chain length, and gold could not be leached. This is mainly because the further increase of carbon chain length affects the water solubility of the cyanide-free leaching agent on the one hand, and the chelation between the target metal and the cyanide-free leaching agent on the other hand.

[0125] The data from Comparative Example 13 show that changing the positions of the hydroxyl and carboxyl groups significantly reduced the leaching rates of tin, lead, and copper, and prevented the leaching of gold. This indicates that the specific positional relationship between the hydroxyl and carboxyl groups can effectively achieve the leaching of the target metal.

[0126] The data from Comparative Examples 14-17 show that altering the aromatic structure in cyanide-free leaching agents can severely affect the leaching effect of the target metal.

[0127] This demonstrates that the types and positions of aromatic rings and functional groups in the molecular structure of cyanide-free leaching agents collectively determine the chelating effect of cyanide-free leaching agents on target metals (tin, lead, copper, gold), thereby achieving selective and efficient leaching.

[0128] The following is a method for preparing drug A, with the specific steps as follows (the preparation process is as follows). Figure 4 As shown):

[0129] S1. First, add 100g of raw material A to a three-necked flask, add 500mL of methanol, and dropwise add 5mL of 50% sulfuric acid. After returning to room temperature, heat under reflux for 4 hours, filter while hot, and collect the solid. Wash with water 5-8 times to obtain product B, with a yield of 95-98%.

[0130] S2. At -72℃, product B, hydrogen bromide, and sodium nitrite (molar equivalent ratio 1:2.5:1.2) were added to 500 mL of acetone solution, respectively. After the addition was complete, the reaction temperature was raised to -30℃ and maintained for 1 h, then raised to 0-5℃ and reacted for 3 h. After the reaction was completed, water was added at low temperature (around 0℃), followed by extraction with a large amount of ethyl acetate. The extract was dried over anhydrous sodium sulfate and rotary evaporated to obtain product C, with a yield of 61-64%.

[0131] S3. Add product C to an ethanol solution, and add potassium ferricyanide dropwise at low temperature (-36℃) (molar equivalent ratio of product C to potassium ferricyanide 1:1.2), reacting for 1 h. After the reaction is complete, filter, collect the liquid, add a large amount of ethyl acetate for extraction, dry the extract with anhydrous sodium sulfate, and rotary evaporate to obtain product D, with a yield of 68-71%.

[0132] S4. Add product D to an ethanol solution and hydrolyze for 8 hours under alkaline conditions (pH 12-13). Collect the solid product E by filtration, and dry it; the yield is 71-75%.

[0133] S5. Add product E to anhydrous tetrahydrofuran solution. Under a nitrogen atmosphere and ice bath, add a tetrahydrofuran suspension of sodium borohydride dropwise. The molar ratio of product E to sodium borohydride is 1:0.25. React for 4 hours, then slowly restore to room temperature and react for another 4 hours. After the reaction is complete, quench with a mixture of tetrahydrofuran and deionized water (volume ratio 3:1), then filter, collect the liquid, dry with a large amount of anhydrous sodium sulfate, and rotary evaporate to obtain crude product F. Separate by gradient elution on a chromatography column (using ethyl acetate and petroleum ether as eluents, volume ratio 1:1-1:5) to obtain product F in a yield of 42-47%.

[0134] S6. Add product F to a sodium hydroxide solution with pH 10, heat and reflux for 4 hours, then filter, collect the solid, wash three times with dilute hydrochloric acid to obtain product G (i.e. reagent-A), with a yield of 92-96%.

[0135] The preparation of reagent-C is achieved by replacing the hydrogen at the corresponding position in raw material A with an ethyl group.

[0136] In summary, this invention provides a cyanide-free leaching agent and a process for treating tin, lead, copper, and gold in electronic waste. The cyanide-free leaching agent uses imidazole as its molecular backbone and introduces functional groups. While ensuring the agent's solubility in water, it is modified by introducing functional groups into its structure to prepare a series of derivatives. During the metal leaching process, by strictly controlling the leaching conditions, selective leaching of tin, lead, copper, and gold from electronic waste is efficiently achieved through gradient oxidation, the synergistic effect of the molecular spatial structure of the cyanide-free leaching agent with a specific oxidation structure, and the interaction between different functional groups. Using the cyanide-free leaching agent of this invention to treat electronic waste avoids the use of cyanide; at the same time, the process is simple and easy to operate.

[0137] 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 treating tin, lead, copper, and gold in electronic waste using a cyanide-free leaching agent, characterized in that, The steps include the following: S1. Crush the electronic waste to be processed to a particle size of less than 50 mesh to obtain material, add water to the material and stir to obtain a slurry of a preset concentration; S2. Add one or more of the cyanide-free leaching agents to the slurry to bring the cyanide-free leaching agent to a preset concentration; S3. Add sodium hydroxide to adjust the pH of the slurry to 10-14, stir for the preset time, and leach tin and lead; S4. Add hydrogen peroxide, stir for the preset time, and leach out the copper; S5. Add potassium permanganate, stir for the preset time, and leach out the gold; The cyanide-free leaching agent is a functionalized reagent with imidazole as the molecular backbone, and its general structural formula is as follows: ； Where R represents hydrogen, methyl, ethyl, or propyl.

2. The process for treating tin, lead, copper, and gold in electronic waste using the cyanide-free leaching agent according to claim 1, characterized in that, In step S2, the preset concentration of the cyanide-free leaching agent in the slurry is 0.1-1 mol / L.

3. The process for treating tin, lead, copper, and gold in electronic waste using the cyanide-free leaching agent according to claim 1, characterized in that, In step S4, the concentration of hydrogen peroxide in the slurry is 5-20 mL / L.

4. The process for treating tin, lead, copper, and gold in electronic waste using the cyanide-free leaching agent according to claim 1, characterized in that, In step S5, the concentration of potassium permanganate in the slurry is 0.1-1 g / L.

5. The process for treating tin, lead, copper, and gold in electronic waste using the cyanide-free leaching agent according to claim 1, characterized in that, In step S1, the portion of the material with a particle size smaller than 50 mesh accounts for 90% of the total mass of the mineral powder; the mass concentration of the slurry is 5%-30%.

6. The process for treating tin, lead, copper, and gold in electronic waste using the cyanide-free leaching agent according to claim 1, characterized in that, In step S3, the temperature of the slurry during stirring is 20℃-80℃, and the stirring time is 0.5-6h.

7. The process for treating tin, lead, copper, and gold in electronic waste using the cyanide-free leaching agent according to claim 1, characterized in that, In step S4, the slurry temperature is 20℃-80℃ during stirring; the stirring time is 6-24h.

8. The process for treating tin, lead, copper, and gold in electronic waste using the cyanide-free leaching agent according to claim 1, characterized in that, In step S5, the slurry temperature is 20℃-80℃ during stirring; the stirring time is 6-48h.

9. The process for treating tin, lead, copper, and gold in electronic waste using the cyanide-free leaching agent according to claim 1, characterized in that, In steps S1, S3, S4 and S5, the stirring speed is 100-300 r / min.

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