Environmentally friendly cyanide-free gold leaching agent and process for extracting gold from electronic waste

Abstract

The present application provides an environmentally friendly cyanide-free gold leaching agent and a process for extracting gold from electronic waste, which belongs to the field of hydrometallurgy technology. The present invention designs an environmentally friendly cyanide-free gold leaching agent, uses non-toxic and renewable biomass resources as raw materials, optimizes its molecular structure through a series of derivatization methods, introduces specific functionalized molecular groups, and prepares a series of environmentally friendly cyanide-free gold leaching agents to solve the problem that existing cyanide-free leaching agents are difficult to process electronic waste. Under the premise of meeting technical feasibility, the balance between economy and environment is achieved to the greatest extent, and the gold leaching process is simple, easy to operate, and conforms to the original facilities of existing enterprises, without the need for additional investment in equipment upgrade costs.

Description

Technical Field

[0001] The invention relates to the technical field of hydrometallurgy, and in particular to an environmentally friendly cyanide-free gold leaching agent and a process for extracting gold from electronic waste. Background Art

[0002] Gold isn't naturally a currency, but gold is naturally a currency. As a precious metal, gold has the ability to regulate national economic issues. Therefore, gold reserves play a crucial role in stabilizing a country's economy. In recent years, as gold's safe-haven function, liquidity, and value-preserving properties have strengthened, its value has become increasingly evident.

[0003] Electronic waste is rich in precious metals such as gold, silver, and palladium. The gold content in electronic waste is higher than that in ore resources. According to statistics, when producing the same quality of gold, the process cost of extracting gold from electronic waste is only 1 / 7 of the cost of traditional mining and smelting. It is worth mentioning that 1 / 10 of the world's gold consumption can be met by extracting gold from electronic waste. It is estimated that the final profit of China's electronic waste processing companies for recycling metals from 1 ton of electronic waste is about 1.56×10 5 ~1.75×10 5 The economic value of electronic waste is immeasurable.

[0004] However, existing gold extraction processes often use cyanide extraction. Because cyanide is a highly toxic chemical and its use raises safety concerns, its application to e-waste processing must balance environmental and social factors alongside economic viability. For example, unlike mining and metallurgical operations in remote areas, e-waste processing facilities are often located in suburban areas to reduce transportation costs. In most countries, the use of cyanide in urban areas is prohibited.

[0005] Currently, there are many gold extraction processes that do not use cyanide, including the thiosulfate method, halogen method, thiourea method, glycine method, lime sulfur method, etc. While achieving environmental protection and cyanide-free, there are still certain limitations.

[0006] In the prior art, patent publication number CN119307734A provides an environmentally friendly gold leaching agent and its application method. The environmentally friendly gold leaching agent is composed of a mixture of a halide, a thiosulfate, and a strengthening agent. The application method of the environmentally friendly gold leaching agent includes the following steps: crushing and grinding the gold ore, adjusting the slurry concentration to 30%-50%, then adding 0.2wt%-5wt% of the gold leaching agent, adjusting the slurry pH to 6-12, and stirring and leaching for 8-36 hours at room temperature and pressure. The environmentally friendly gold leaching agent provided by this invention is composed of a mixture of common chemical reagents. The method is simple, has a high gold leaching rate, high reagent stability, and can achieve gold leaching under neutral to alkaline conditions. However, during the gold leaching process, if a large amount of impurity metals in the raw material undergoes a series of complex reactions with the byproducts of the decomposition of thiosulfate, it will interfere with the leaching of gold. Patent publication number CN110484724A provides an ionic liquid-based gold leaching agent and method. The ionic liquid-based gold leaching agent is prepared by mixing 1-methyl-3-(4-diacetoxyiodobenzyl)imidazolium tetrafluoroborate, an ionic liquid, and water in a molar ratio of 1:1-20:20-140. The ionic liquid is an ionic liquid containing a halogen anion or a dinitrile amide ion. The invention provides an ionic liquid-based gold leaching method, comprising: 1) preparing the ionic liquid-based gold leaching agent; 2) adding a sample containing a precious metal to the gold leaching agent obtained in step 1) and stirring thoroughly to leach the precious metal. However, this method also reacts with other impurity metals during the gold leaching process, preventing selective leaching of gold. Summary of the Invention

[0007] In view of the technical problems existing in the background technology, the present application provides an environmentally friendly cyanide-free gold leaching agent and a process for extracting gold from electronic waste, aiming to solve the problem that existing gold leaching agents cannot selectively leach gold from electronic waste.

[0008] In the first aspect, the present application provides an environmentally friendly cyanide-free gold leaching agent, which includes at least one of B-1, B-2, B-3, and B-4. The structural formula of B-1 is

[0009] ; The structural formula of the B-2 is ; The structural formula of the B-3 is ; The structural formula of the B-4 is .

[0010] The technical solutions of the embodiments of this application design environmentally friendly, cyanide-free gold leaching agents. Using non-toxic, renewable biomass resources as raw materials, these agents are optimized at the molecular level through a series of derivatization methods, introducing specific functional molecular groups to prepare a series of environmentally friendly, cyanide-free gold leaching agents. This addresses the problem that existing cyanide-free leaching agents have difficulty selectively leaching gold from electronic waste.

[0011] In a second aspect, the present application provides a process for extracting gold from electronic waste using an environmentally friendly, cyanide-free gold leaching agent, comprising the following steps:

[0012] S1. Grind the electronic waste into fine powder;

[0013] S2. Add water to the finely ground sample and stir to obtain a slurry of a preset concentration;

[0014] S3. Add the environmentally friendly cyanide-free gold leaching agent to the slurry, adjust the pH value of the slurry, and stir to obtain a gold-containing precious liquid and a solid residue.

[0015] In the technical solution of the embodiment of the present application, a process for extracting gold from electronic waste is designed by using the prepared gold leaching agent. The gold leaching agent prepared above is used to extract gold from electronic waste. The gold leaching process is simple and easy to operate, conforms to the original facilities of existing enterprises, and does not require additional investment in equipment upgrade costs.

[0016] In some embodiments, in step S1, the electronic waste includes at least one of discarded circuit boards, integrated chips, and discarded electrodes.

[0017] In this embodiment, the prepared gold leaching agent can selectively leach gold from electronic waste containing mixed metals, such as discarded circuit boards, integrated chips, and discarded electrodes.

[0018] In some embodiments, in step S1, the fineness of the fine grinding is less than 100 mesh and the content is 88.0-92.0%.

[0019] In this embodiment, the electronic waste is finely ground to a specific fineness to facilitate subsequent gold leaching.

[0020] In some embodiments, in step S2, the mass concentration of the ore pulp is 20% to 30%; the mass concentration of the environmentally friendly cyanide-free gold leaching agent in the ore pulp is 20 to 60 g / L.

[0021] In this embodiment, a certain amount of gold leaching agent is added to the ore pulp of a specific concentration, so that the gold in the ore pulp can be leached better.

[0022] In some embodiments, in step S3, the pH value of the slurry is adjusted by adding a pH adjuster; the pH adjuster is sodium hydroxide; and the pH value is adjusted to 8-14.

[0023] In this embodiment, by adjusting the pH value of the gold immersion system to alkaline, the activation sites of the functional groups of the agent are released, thereby achieving efficient chelation with gold ions.

[0024] In some embodiments, in step S3, the stirring temperature is 25-60° C.; and the stirring time is 7-8 h.

[0025] In this embodiment, by stirring the gold leaching system at a specific temperature for a certain period of time, the reagent can fully react with the gold, thereby obtaining a higher gold leaching rate.

[0026] The above description is only an overview of the technical solution of the present application. In order to more clearly understand the technical means of the present application, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] To more clearly illustrate the technical solution of this application, the following is a brief introduction to the drawings used in this application. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be derived from these drawings without inventive effort.

[0028] Figure 1 Schematic diagram of the structural formula of each gold leaching agent in the examples of this application;

[0029] Figure 2 Schematic diagram of the reaction formula of each gold leaching agent in the examples of this application;

[0030] Figure 3 This is the nuclear magnetic resonance hydrogen spectrum of the gold leaching agent B-1 in the examples of this application. DETAILED DESCRIPTION

[0031] The following embodiments of the technical solution of the present application are described in detail. The following embodiments are only used to more clearly illustrate the technical solution of the present application and are therefore only used as examples and are not intended to limit the scope of protection of the present application.

[0032] References herein to "embodiments" mean that a particular feature, structure, or characteristic described in connection with the embodiments may be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0033] In the description of the embodiments of this application, the term "and / or" is simply a description of the association relationship between associated objects, indicating that three relationships can exist. For example, A and / or B can represent the following three situations: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " in this document generally indicates that the associated objects are in an "or" relationship.

[0034] To address the difficulty of existing cyanide-free leaching agents in selectively leaching gold from electronic waste, this application provides an environmentally friendly cyanide-free gold leaching agent and a process for extracting gold from electronic waste. By designing environmentally friendly cyanide-free gold leaching agents using non-toxic, renewable biomass resources as raw materials, and optimizing their molecular structure through a series of derivatization methods and introducing specific functional molecular groups, a series of environmentally friendly cyanide-free gold leaching agents were prepared. First, the agent molecules possess a unique aliphatic molecular backbone. The imino and carboxyl groups within the molecular backbone impart significant hydrophilicity, making them suitable for mass transfer reactions in polar environments and providing a foundation for the agent's leaching of target metals. Furthermore, the core functional group within the agent molecules obtained after the raw material derivatization reaction consists of two sulfur atoms (S) and an imino group (-NH) connected by a carbon atom, forming a "hemithiourea" structural fragment. This "hemithiourea" fragment plays a key role in the molecule. The low electronegativity of the sulfur atom in the (C=S) structure of the "hemithiourea" fragment results in a significantly weaker polarity of the thiocarbonyl group (C=S) than the carbonyl group (C=O), favoring the activation of (-CS-). The lone pair of electrons on the sulfide ion in (-CS-) forms a stronger coordination bond with the metal ion than the sulfide ions in traditional reagents. This ultimately results in a very high affinity of the sulfur atom for soft acid metal Au, enabling the "hemithiourea" fragment to effectively chelate the gold ion. The synergistic effect between the carboxyl group and the "hemithiourea" fragment further enhances the molecule's selective binding ability for the target metal ion. This synergistic effect reduces nonspecific binding with non-target impurity ions, effectively preventing interference from impurities and achieving selective chelation of the target metal. This gold leaching agent addresses the difficulty of existing cyanide-free leaching agents in treating electronic waste.

[0035] In the first aspect, the present application provides an environmentally friendly cyanide-free gold leaching agent, which includes at least one of B-1, B-2, B-3, and B-4. The structural formula of B-1 is

[0036] ; The structural formula of the B-2 is ; The structural formula of the B-3 is ; The structural formula of the B-4 is .

[0037] The technical solutions of the embodiments of this application design environmentally friendly, cyanide-free gold leaching agents. Using non-toxic, renewable biomass resources as raw materials, these agents are optimized at the molecular level through a series of derivatization methods, introducing specific functional molecular groups to prepare a series of environmentally friendly, cyanide-free gold leaching agents. This addresses the problem that existing cyanide-free leaching agents have difficulty selectively leaching gold from electronic waste.

[0038] In a second aspect, the present application provides a process for extracting gold from electronic waste using an environmentally friendly, cyanide-free gold leaching agent, comprising the following steps:

[0039] S1. Grind the electronic waste into fine powder;

[0040] S2. Add water to the finely ground sample and stir to obtain a slurry of a preset concentration;

[0041] S3. Add the environmentally friendly cyanide-free gold leaching agent to the slurry, adjust the pH value of the slurry, and stir to obtain a gold-containing precious liquid and a solid residue.

[0042] In the technical solution of the embodiment of the present application, a process for extracting gold from electronic waste is designed by using the prepared gold leaching agent. The gold leaching agent prepared above is used to extract gold from electronic waste. The gold leaching process is simple and easy to operate, conforms to the original facilities of existing enterprises, and does not require additional investment in equipment upgrade costs.

[0043] Furthermore, in some embodiments, in step S1, the electronic waste includes at least one of discarded circuit boards, integrated chips, and discarded electrodes.

[0044] In the technical solution of the embodiment of the present application, the prepared gold leaching agent can selectively leach gold from electronic waste containing mixed metals such as discarded circuit boards, integrated chips and discarded electrodes.

[0045] Furthermore, in some embodiments, in step S1, the fineness of the fine grinding is less than 100 mesh and the content is 88.0-92.0%.

[0046] In the technical solution of the embodiment of the present application, the electronic waste is finely ground to a specific fineness to facilitate subsequent gold leaching.

[0047] Furthermore, in some embodiments, in step S2, the mass concentration of the ore pulp is 20% to 30%; the mass concentration of the environmentally friendly cyanide-free gold leaching agent in the ore pulp is 20 to 60 g / L.

[0048] In the technical solution of the embodiment of the present application, by adding a certain amount of gold leaching agent to the ore pulp of a specific concentration, a relatively good leaching effect is achieved on the gold in the ore pulp.

[0049] Furthermore, in some embodiments, in step S3, the pH value of the slurry is adjusted by adding a pH adjuster; the pH adjuster is sodium hydroxide; and the pH value is adjusted to 8-14.

[0050] In the technical solution of the embodiment of the present application, by adjusting the pH value of the gold immersion system to alkaline, the activation sites of the functional groups of the agent are released, thereby achieving efficient chelation with gold ions.

[0051] Furthermore, in some embodiments, in step S3, the stirring temperature is 25-60° C.; and the stirring time is 7-8 h.

[0052] In the technical solution of the embodiment of the present application, by stirring the gold leaching system at a specific temperature for a certain period of time, the reagent can fully react with the gold, thereby obtaining a higher gold leaching rate.

[0053] Some specific examples are listed below. It should be noted that the examples described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. Where specific techniques or conditions are not specified in the examples, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used without manufacturer's indication are all commercially available conventional products.

[0054] Examples 1 to 4

[0055] Examples 1 to 4 provide an environmentally friendly cyanide-free gold leaching agent and a process for extracting gold from electronic waste. The environmentally friendly gold leaching agents are B-1, B-2, B-3 and B-4, respectively. The specific structural formulas are as follows: Figure 1 shown.

[0056] The preparation method of gold leaching agent B-1 is as follows: add 1 mol of glycine to 1 L of sodium hydroxide solution with a mass concentration of 80 g / L, then add 1.5 mol of carbon sulfide, stir evenly, then heat to reflux at 40°C, react for 24 hours, and after the reaction is completed, distill the solution under reduced pressure to remove excess carbon sulfide to obtain gold leaching agent B-1 containing sodium hydroxide.

[0057] The raw materials used in gold leaching agents B-2, B-3 and B-4 are cysteine, proline and glutathione respectively. The specific preparation methods are similar to those of B-1 and will not be described here. The specific reaction formulas of B-1, B-2, B-3 and B-4 are as follows: Figure 2 shown.

[0058] The nuclear magnetic resonance hydrogen spectrum of gold leaching agent B-1 is as follows Figure 3 As shown. Figure 3 It can be seen that the molecular composition of the substances in the solution changed before and after the reaction, and glycine was converted into a glycine derivative, namely B-1.

[0059] The gold leaching agents B-1, B-2, B-3 and B-4 prepared above were used to extract gold from electronic waste, specifically comprising the following steps:

[0060] (1) Grind the waste circuit boards to a particle size of less than 100 mesh and a content of 90%;

[0061] (2) Add water to the finely ground sample and stir to obtain a slurry with a concentration of 25%;

[0062] (3) The gold leaching agents B-1, B-2, B-3 and B-4 prepared above were added to the ore pulp at a mass concentration of 50 g / L, and then sodium hydroxide was added to adjust the pH of the ore pulp to 10. The mixture was stirred at 30°C for 8 h to obtain a precious gold solution and a solid residue.

[0063] The sources and performance parameters of the raw materials are as follows:

[0064] Waste circuit boards containing precious metal resources after processing low-value metals (copper, lead, zinc, tin, nickel, etc.) are selected. The main components of the waste circuit boards are shown in Table 1.

[0065] Table 1 Main components of precious metals in waste circuit boards

[0066]

[0067] The content of each precious metal in the solid residues in Examples 1 to 4 was tested by fire assay method. The test and analysis method was based on GB / T 7739 "Chemical Analysis Methods for Gold Concentrates". The leaching rate η of each precious metal was

[0068]

[0069] Among them, η represents the leaching rate of each precious metal, in units of %; m1 represents the mass of the original material, in units of g; β1 represents the grade of the original material, in units of g / t; m2 represents the mass of the solid residue after leaching, in units of g; β2 represents the grade of the solid residue after leaching, in units of g / t.

[0070] The concentrations of each precious metal in the gold-containing solutions of Examples 1-4 were then measured using ICP-OES. The results from the two methods were compared, and valid data were considered when the deviation between the two methods was less than 1%. The final leaching rates of each precious metal in Examples 1-4 are shown in Table 2.

[0071] Table 2 Leaching rate of precious metals from waste circuit boards in Examples 1 to 4

[0072]

[0073] From the leaching rates of the precious metals in Examples 1 to 4, it can be seen that the four gold leaching agents all have a high leaching rate for gold in waste circuit boards and have a selective leaching effect on gold.

[0074] Examples 5-6 and Comparative Examples 1-2

[0075] Examples 5-6 and Comparative Examples 1-2 respectively provide a process for extracting gold from electronic waste using an environmentally friendly, cyanide-free gold leaching agent. Compared with Example 1, the difference lies in the different concentrations of the gold leaching agent in step (3). The concentrations of the gold leaching agent corresponding to each Example and Comparative Example are shown in Table 3. The other steps are substantially the same as those in Example 1 and are not described in detail here.

[0076] Table 3 Concentration of gold leaching agent in Examples 5-6 and Comparative Examples 1-2

[0077]

[0078] The gold leaching rates of Examples 5-6 and Comparative Examples 1-2 were analyzed according to the method in Example 1, and the results are shown in Table 4.

[0079] Table 4 Gold leaching rate in Examples 5-6 and Comparative Examples 1-2

[0080]

[0081] The gold leaching rates in Examples 5-6 and Comparative Examples 1-2 show that a suitable concentration of environmentally friendly, cyanide-free gold leaching agent can achieve efficient leaching of gold from electronic waste. When the agent concentration is 20 g / L, the gold leaching rate is 90%. With this as the cutoff point, when the agent concentration is less than 20 g / L, the gold leaching effect is difficult to achieve efficient. As the agent concentration increases, when the agent concentration reaches 60 g / L, a stable point appears, at which the gold leaching rate is 98%. Subsequently, the gold leaching rate is no longer affected by further increases in the agent concentration. Considering factors such as actual on-site operation and economic factors, a more reasonable range of agent concentrations is 20-60 g / L, with a gold leaching rate of ≥90%.

[0082] Examples 7-8 and Comparative Example 3

[0083] Examples 7 to 8 and Comparative Example 3 respectively provide a process for extracting gold from electronic waste using an environmentally friendly cyanide-free gold leaching agent. Compared with Example 1, the difference lies in the different pH values in step (3). The pH values corresponding to each example and comparative example are shown in Table 5. The other steps are substantially the same as those in Example 1 and will not be described in detail here.

[0084] Table 5 pH values in Examples 7-8 and Comparative Example 3

[0085]

[0086] The gold leaching rates of Examples 7-8 and Comparative Example 3 were analyzed according to the method in Example 1, and the results are shown in Table 6.

[0087] Table 6 Gold leaching rate in Examples 7-8 and Comparative Example 3

[0088]

[0089] The gold leaching rates in Examples 7-8 and Comparative Example 3 demonstrate that an appropriate slurry pH is a prerequisite for efficient gold leaching from electronic waste. Under neutral acidic conditions, the reagent cannot exist as an anionic species in the solution system, and the functional group activation sites are protonated, making them unable to chelate with gold ions. Only under alkaline conditions are the activated sites of the reagent functional groups released, allowing efficient chelation with gold ions. Furthermore, under strongly alkaline conditions (pH ≥ 12), the gold leaching rate was not affected, demonstrating that the side reaction reagent can remain stable in a strongly alkaline environment.

[0090] In summary, the present application provides an environmentally friendly cyanide-free gold leaching agent and a process for extracting gold from electronic waste. By designing an environmentally friendly cyanide-free gold leaching agent, using non-toxic and renewable biomass resources as raw materials, optimizing the molecular structure through a series of derivatization methods, and introducing specific functionalized molecular groups, a series of environmentally friendly cyanide-free gold leaching agents are prepared. This solves the problem that existing cyanide-free leaching agents are difficult to process electronic waste. Under the premise of meeting technical feasibility, the balance between economy and environment is achieved to the greatest extent. In addition, the gold leaching process is simple and easy to operate, and is compatible with the existing facilities of existing enterprises, without the need for additional investment in equipment upgrades.

[0091] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A process for extracting gold from electronic waste using an environmentally friendly, cyanide-free gold leaching agent, characterized in that: The steps include: S1. Grind the electronic waste into fine powder; S2. Add water to the finely ground sample and stir to obtain a slurry of a preset concentration; S3. Adding an environmentally friendly cyanide-free gold leaching agent to the slurry, adjusting the pH value of the slurry, stirring, and obtaining a precious gold-containing liquid and a solid residue; The environmentally friendly cyanide-free gold leaching agent includes at least one of B-1, B-2, B-3, and B-4, and the structural formula of B-1 is ; The structural formula of the B-2 is ; The structural formula of the B-3 is ; The structural formula of the B-4 is .

2. The process for extracting gold from electronic waste using an environmentally friendly cyanide-free gold leaching agent according to claim 1, characterized in that: In step S1, the electronic waste includes at least one of discarded circuit boards, integrated chips and discarded electrodes.

3. The process for extracting gold from electronic waste using an environmentally friendly cyanide-free gold leaching agent according to claim 1, characterized in that: In step S1, the fineness of the fine grinding is less than 100 mesh and the content is 88.0-92.0%.

4. The process for extracting gold from electronic waste using an environmentally friendly cyanide-free gold leaching agent according to claim 1, characterized in that: In step S2, the mass concentration of the ore pulp is 20% to 30%.

5. The process for extracting gold from electronic waste using an environmentally friendly cyanide-free gold leaching agent according to claim 1, characterized in that: In step S3, the mass concentration of the environmentally friendly cyanide-free gold leaching agent in the ore pulp is 20-60 g / L.

6. The process for extracting gold from electronic waste using an environmentally friendly cyanide-free gold leaching agent according to claim 1, characterized in that: In step S3, the pH value of the slurry is adjusted by adding a pH regulator; the pH regulator is sodium hydroxide.

7. The process for extracting gold from electronic waste using an environmentally friendly cyanide-free gold leaching agent according to claim 1, characterized in that: In step S3, the pH value is adjusted to 8-14.

8. The process for extracting gold from electronic waste using an environmentally friendly cyanide-free gold leaching agent according to claim 1, characterized in that: In step S3, the stirring temperature is 25-60°C.

9. The process for extracting gold from electronic waste using an environmentally friendly cyanide-free gold leaching agent according to claim 1, characterized in that: In step S3, the stirring time is 7 to 8 hours.

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