Gold immersion pharmaceutical system and method for recovering gold from waste printed circuit boards

Abstract

The application provides a gold leaching agent system and a method for recovering gold from waste printed circuit boards, and belongs to the technical field of hydrometallurgy. The application constructs a high-efficiency gold leaching system with multi-component synergistic effect, combines a gold leaching electrolysis system, and realizes in-situ cyanide production through acetoamide electrolysis, thereby fundamentally eliminating the storage and transportation of highly toxic cyanide and realizing safety. Meanwhile, a multifunctional synergistic system composed of propylene glycol, DMSO and sodium anthraquinone-2-sulfonate is introduced. The system effectively overcomes the three technical bottlenecks of "difficult entry of leaching solution", "difficult contact of target" and "slow oxidation of reaction" through the synergistic effect of penetration enhancement (propylene glycol), package destruction (DMSO swelling resin) and catalytic oxidation (anthraquinone cycle), thereby significantly improving the gold leaching rate and recovery rate under the premise of ensuring process safety and environmental protection, and simultaneously having the outstanding advantages of process integration and economic efficiency.

Description

Technical Field

[0001] This invention relates to the field of hydrometallurgical technology, specifically to an immersion gold reagent system and a method for recovering gold from waste printed circuit boards. Background Technology

[0002] Cyanide leaching, a traditional gold immersion process, uses sodium or potassium cyanide solutions and is a mature technology. However, this process has a fatal flaw: the transportation, storage, and use of highly toxic cyanide pose extremely high safety risks and environmental pressures. Furthermore, the complex structure of circuit boards often encapsulates the gold within hydrophobic epoxy resin or other substrates, forming "invisible gold," resulting in low leaching efficiency and long processing times for traditional cyanide leaching methods.

[0003] To address the safety concerns surrounding cyanide, researchers have explored non-cyanide gold leaching systems, such as the thiosulfate method and the thiourea method. However, these methods suffer from drawbacks including high reagent consumption, system instability, and high costs. On the other hand, physical crushing and pyrolysis methods have been used as pretreatment to improve leaching efficiency, but these methods are energy-intensive and prone to causing secondary pollution.

[0004] Acetamide electrolysis in-situ cyanide generation technology offers a new approach to green leaching gold, avoiding the direct use of sodium cyanide and reducing safety risks at the source. However, this technology still faces two major challenges when applied to circuit boards with complex structures: first, the penetration problem, specifically the difficulty for the electrolyte to effectively wet and penetrate into the micropores and cracks of the epoxy resin substrate; second, the contact problem, specifically the inability of gold particles tightly coated by epoxy resin to effectively contact the leaching agent. These bottlenecks severely restrict the leaching rate and recovery rate of this technology, limiting its industrial application.

[0005] Therefore, developing an in-situ electrolytic cyanide leaching gold method that can balance safety, efficiency, and specificity is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] In view of the technical problems existing in the background art, this application provides a gold leaching agent system and a method for recovering gold from waste printed circuit boards, aiming to solve the problems of safety risks and low leaching efficiency in existing cyanide gold leaching.

[0007] In a first aspect, this application provides a gold immersion reagent system comprising acetamide, sodium anthraquinone-2-sulfonate, propylene glycol, and dimethyl sulfoxide.

[0008] Secondly, this application provides a method for recovering gold from waste printed circuit boards using an immersion gold reagent system, characterized in that the process employs the aforementioned immersion gold reagent system and includes the following steps:

[0009] S1. Grind the printed circuit board to obtain a ground sample;

[0010] S2. Add water to the ground sample to prepare a slurry, and then adjust the slurry to a specific pH value to obtain a pretreated slurry;

[0011] S3. Add acetamide and sodium anthraquinone-2-sulfonate to water to prepare an electrolyte, then add propylene diamine and dimethyl sulfoxide. Using a three-electrode system, electrolyze the treated slurry under stirring to obtain a gold-containing solution and solid residue.

[0012] In some embodiments, in step S2, the specific pH value is 12-14.

[0013] In some embodiments, in step S3, the concentration of acetamide in the electrolyte is 0.5~2 mol / L.

[0014] In some embodiments, in step S3, the concentration of sodium anthraquinone-2-sulfonate in the electrolyte is 0.05~0.5 mol / L.

[0015] In some embodiments, in step S3, the volume of propylene glycol is 5-10% of the electrolyte volume.

[0016] In some embodiments, in step S3, the volume of the dimethyl sulfoxide is 1 to 5% of the electrolyte volume.

[0017] In some embodiments, in step S3, the constant potential during electrolysis is 10~30V, and the electrolysis time is 3~6h.

[0018] In some embodiments, in step S3, the three-electrode system consists of an anode: a graphite electrode, a cathode: a titanium-based platinum-plated mesh counter electrode, and a dual salt bridge reference electrode.

[0019] In some embodiments, in step S2, the concentration of the slurry is 10-15%.

[0020] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0021] To more clearly illustrate the technical solutions of this application, the accompanying drawings used in this application will be briefly described below. Obviously, the drawings described below are merely some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without any creative effort.

[0022] Figure 1 This is a SEM image of the sample after grinding in an embodiment of this application.

[0023] Figure 2 Images of the ore after grinding before and after DMSO treatment in the embodiments of this application are shown; wherein, (a) is a physical image, (b) is a SEM image, and (c) is a scanning electron microscope and energy dispersive spectroscopy (EDS) image of the ore after grinding after DMSO treatment.

[0024] Figure 3 This is an XRD pattern of the solid residue in the embodiments of this application. Detailed Implementation

[0025] The embodiments of the technical solution of this application are described in detail below. The following embodiments are only used to illustrate the technical solution of this application more clearly, and are therefore only examples, and should not be used to limit the scope of protection of this application.

[0026] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0027] To address the safety risks and low leaching efficiency of existing cyanide leaching gold processes, this application provides a gold leaching reagent system and a method for recovering gold from waste printed circuit boards. By constructing a multi-component synergistic high-efficiency gold leaching system, combined with an electrolytic gold leaching system, the key lies in the in-situ generation and precise supply of cyanide: using acetamide as a precursor, oxidation occurs at the anolyte interface under electrolytic conditions (2CH3CONH2-8e). - →(CN)2↑+4H2↑), decarboxylation reaction ((CN)2+2OH) - →CN - +CNO - The process of reacting cyanide with hydrogen ions (+H₂O) allows for the controlled release of free cyanide ions. This enables in-situ synthesis and immediate utilization of cyanide ions at the reaction interface, avoiding the large-scale storage of highly toxic cyanide in the system and laying a safety foundation from the source. Furthermore, impurity metals present in printed circuit boards (such as copper and iron) have a strong affinity for cyanide ions; they compete with gold for cyanide ions, forming stable cyanide complexes (such as [Cu(CN)₄)₄). 3- This process results in a significant consumption of cyanide ions. The generated byproduct, isocyanate ions, forms more stable complexes with these impurity metal ions, thereby locking in the impurity metals and reducing their consumption of cyanide ions. This allows more cyanide ions to be used for gold leaching.

[0028] To further accelerate the gold dissolution kinetics, this application designs an electrochemical catalytic cycle based on a redox mediator, using sodium anthraquinone-2-sulfonate as a synergistic oxidant to construct a highly efficient catalytic cycle. Specifically, on the cathode surface, sodium anthraquinone-2-sulfonate is reduced to hydroquinone (AQ + H₂O + 2e⁻). - →AHQ (AQ represents sodium anthraquinone-2-sulfonate, AHQ represents reduced hydroquinone)), hydroquinone diffuses into the bulk solution, efficiently reducing dissolved oxygen to hydrogen peroxide, and regenerating itself back to sodium anthraquinone-2-sulfonate. This cycle not only transforms cathode side reactions (such as hydrogen evolution) into a valuable oxidant production process, but also constructs a continuous and efficient oxidation environment on the gold surface, greatly promoting the reaction rate of gold complexation with cyanide (2Au + 4CN). - +H₂O₂→2[Au(CN)₂] - +2OH - This resulted in a doubling of the immersion gold efficiency.

[0029] This application introduces a synergistic mechanism of physical penetration and chemical swelling, solving a key bottleneck in drug delivery and target contact. Propylene glycol significantly enhances the wetting and capillary penetration capabilities of the drug solution onto the hydrophobic epoxy resin substrate by reducing the surface tension of the solution, thus opening delivery channels for the active component. Simultaneously, dimethyl sulfoxide (DMSO), as a highly polar solvent, can effectively penetrate into the interior of the epoxy resin polymer network, causing molecular chain relaxation and increased spacing, resulting in a "swelling effect." This breaks down the resin's confinement of the encapsulated gold, fully exposing it and allowing it to contact the leaching agent.

[0030] This application utilizes acetamide electrolysis in-situ cyanide production technology to fundamentally eliminate the storage and transportation of highly toxic cyanide, ensuring safety. Simultaneously, it introduces a multifunctional synergistic system composed of propylene glycol, DMSO, and sodium anthraquinone-2-sulfonate. This system effectively overcomes three major technical bottlenecks—difficulty in liquid entry, difficulty in target contact, and slow oxidation—through the synergistic effects of enhanced penetration (propylene glycol), disruption of encapsulation (DMSO swelling resin), and catalytic oxidation (anthraquinone cycle). Thus, while ensuring process safety and environmental protection, it significantly improves the gold leaching rate and recovery rate, while also possessing outstanding advantages in process integration and economic efficiency.

[0031] In a first aspect, this application provides a gold immersion reagent system comprising acetamide, sodium anthraquinone-2-sulfonate, propylene glycol, and dimethyl sulfoxide.

[0032] Secondly, this application provides a method for recovering gold from waste printed circuit boards using an immersion gold reagent system, characterized in that the process employs the aforementioned immersion gold reagent system and includes the following steps:

[0033] S1. Grind the printed circuit board to obtain a ground sample;

[0034] S2. Add water to the ground sample to prepare a slurry, and then adjust the slurry to a specific pH value to obtain a pretreated slurry;

[0035] S3. Add acetamide and sodium anthraquinone-2-sulfonate to water to prepare an electrolyte, then add propylene diamine and dimethyl sulfoxide. Using a three-electrode system, electrolyze the treated slurry under stirring to obtain a gold-containing solution and solid residue.

[0036] Furthermore, in some embodiments, in step S12, the particle size of the ground sample is not less than 95% less than 100 mesh.

[0037] Furthermore, in some embodiments, in step S2, the specific pH value is 12-14.

[0038] Furthermore, in some embodiments, in step S3, the concentration of acetamide in the electrolyte is 0.5~2 mol / L.

[0039] Furthermore, in some embodiments, in step S3, the concentration of sodium anthraquinone-2-sulfonate in the electrolyte is 0.05~0.5 mol / L.

[0040] Furthermore, in some embodiments, in step S3, the volume of propylene glycol is 5-10% of the electrolyte volume.

[0041] Furthermore, in some embodiments, in step S3, the volume of the dimethyl sulfoxide is 1 to 5% of the electrolyte volume.

[0042] Furthermore, in some embodiments, in step S3, the constant potential during electrolysis is 10~30V, and the electrolysis time is 3~6h.

[0043] Furthermore, in some embodiments, in step S3, the three-electrode system consists of an anode: a graphite electrode, a cathode: a titanium-based platinum-plated mesh counter electrode, and a dual salt bridge reference electrode.

[0044] Furthermore, in some embodiments, in step S3, the stirring rate is 500 rpm.

[0045] Furthermore, in some embodiments, in step S2, the concentration of the slurry is 10-15%.

[0046] The following are some specific embodiments. It should be noted that the embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0047] Example 1

[0048] Example 1 provides a method for recovering gold from waste printed circuit boards using an immersion gold reagent system, specifically including the following steps:

[0049] (1) Grind the printed circuit board until 95% of the particles are smaller than 100 mesh to obtain the ground sample;

[0050] (2) Add water to the ground sample and stir to obtain a slurry with a concentration of 10%. Then add sodium hydroxide to adjust the pH value to 12 to obtain a pretreated slurry.

[0051] (3) Add 7.5% of the electrolyte volume of propylenediamine and 2.5% of the electrolyte volume of dimethyl sulfoxide to an electrolyte containing 1 mol / L acetamide and 0.25 mol / L sodium anthraquinone-2-sulfonate. Use a graphite electrode as the anode, a titanium-based platinum-plated mesh counter electrode and a double salt bridge reference electrode to form a three-electrode system. Electrolyze the pretreated slurry for 4 hours under mechanical stirring at 500 rpm and a working potential of 20 V to obtain a precious metal solution and solid residue.

[0052] The gold content in the solid residues of each embodiment and comparative example was determined by fire assay, and the testing and analysis methods were in accordance with GB / T 7739 "Chemical Analysis Methods for Gold Concentrates". Therefore, the gold leaching rate η was...

[0053]

[0054] Where η represents the gold leaching rate, in %; m1 represents the mass of the printed circuit board, in g; β1 represents the grade of the printed circuit board, in g / t; m2 represents the mass of the solid residue after leaching the printed circuit board, in g; and β2 represents the grade of the solid residue after leaching the printed circuit board, in g / t.

[0055] The gold concentration in the gold-containing solutions of each embodiment and comparative example was then detected by ICP-OES. The gold leaching rate test results of the two methods were compared, and data with a deviation of less than 1% between the two methods were considered valid. Finally, the gold leaching rate in each embodiment and comparative example was determined.

[0056] Examples 2-3 and Comparative Examples 1-2

[0057] Examples 2-3 and Comparative Examples 1-2 each provide a method for recovering gold from waste printed circuit boards using a gold leaching agent system. The difference between Example 1 and Example 2 is that the pH value of the slurry is different, as shown in Table 1. The other steps are roughly the same as in Example 1 and will not be repeated here.

[0058] Table 1. pH value and gold leaching rate of the slurry in Examples 1-3 and Comparative Examples 1-2.

[0059]

[0060] As shown in Table 1, the slurry pH has a decisive influence on the efficiency of this gold leaching system: when the pH value is maintained in the strongly alkaline range of 12 to 14 (Examples 1-3), the gold leaching rate is consistently above 96%; while when the pH value drops to 11 and 10 (Comparative Examples 1-2), the leaching rate decreases significantly to 81% and 52%, respectively; due to the chemical equilibrium of the cyanide system, under the condition of hydrogen cyanide pKa≈9.2, the key active component cyanide ions (CN-C) generated in situ in the system... - This will be converted into volatile hydrogen cyanide (HCN), which not only causes ineffective loss of the cyanide source but also poses serious safety hazards. Therefore, no comparative test was conducted with pH < 10. In summary, strictly controlling the slurry pH above 12 is a key and necessary condition to ensure that this technology simultaneously achieves high leaching rates (>96%) and safe operation.

[0061] Examples 4-5 and Comparative Examples 3-4

[0062] Examples 4-5 and Comparative Examples 3-4 respectively provide a method for recovering gold from waste printed circuit boards using a gold immersion agent system. The difference from Example 1 is that the amount of acetamide added is different, as shown in Table 2. The other steps are roughly the same as in Example 1, and will not be repeated here.

[0063] Table 2 shows the concentration of acetamide and the gold leaching rate in Examples 1, 4-5, and Comparative Examples 3-4.

[0064]

[0065] As shown in Table 2, acetamide concentration is a key factor controlling gold leaching efficiency. When the concentration is below 0.50 mol / L (as in Comparative Example 3), the gold leaching rate drops sharply to 59%. This phenomenon reveals the severe impact of a dual consumption mechanism on free cyanide ions—not only due to insufficient precursors leading to cyanide (CN) leaching efficiency. - The total amount of ) generated is relatively low, especially due to its oxidation derivative isocyanate (CNO) -When the concentration of acetamide is insufficient, the selective complexation barrier of acetamide against impurity metals such as copper and iron fails. Under this critical state, a large number of unbound impurity metal ions directly compete with gold for the already insufficient concentration of free cyanide ions, resulting in the ineffective dissipation of the target cyanide ions. However, when the concentration of acetamide is increased to 0.50 mol / L or above, the system can simultaneously provide sufficient cyanide ions and isocyanate ions with protective functions, thereby effectively overcoming impurity interference and stabilizing the gold leaching rate at over 92%. Further increasing the concentration of acetamide does not change the gold leaching rate, thus clarifying the concentration threshold for the effective action of acetamide in this technical system.

[0066] Examples 6-7 and Comparative Examples 5-7

[0067] Examples 6-7 and Comparative Examples 5-7 respectively provide a method for recovering gold from waste printed circuit boards using a gold immersion agent system. The difference between Example 1 and Example 2 is that the amount of sodium anthraquinone-2-sulfonate added is different, as shown in Table 3. The other steps are roughly the same as in Example 1 and will not be described again here.

[0068] Table 3 shows the concentration of sodium teranthraquinone-2-sulfonate and the gold leaching rate in Examples 1, 6-7, and Comparative Examples 5-7.

[0069]

[0070] As shown in Table 3, sodium anthraquinone-2-sulfonate acts as a synergistic oxidant, and its concentration has a clear optimal window for gold leaching rate. When the concentration is 0 (Comparative Example 7), the leaching rate is only 64%, indicating that the catalytic cycle lacking this oxidant results in severely insufficient kinetics for gold oxidation and dissolution. As the concentration increases from 0.05 mol / L to 0.50 mol / L, the leaching rate increases from 90% and stabilizes at a high level of 96-97%, proving that it effectively constructs a highly efficient "redox" cycle, continuously generating oxidant and significantly increasing the reaction rate. However, when the concentration exceeds 0.50 mol / L, the leaching rate decreases instead of increasing. This is mainly because excessive sodium anthraquinone-2-sulfonate is over-adsorbed on the cathode and the surface of gold particles. On the one hand, it hinders the electron transfer process at the cathode, inhibits its own reduction and regeneration into active hydroquinone, and disrupts the catalytic cycle. On the other hand, it also physically shields the active reaction sites on the gold surface, hindering the contact between cyanide and oxidant with gold. Therefore, controlling the concentration of sodium anthraquinone-2-sulfonate within the range of 0.05~0.50 mol / L is crucial for achieving and maintaining its catalytic function and avoiding negative shielding effects.

[0071] Examples 8-9 and Comparative Examples 8-10

[0072] Examples 8-9 and Comparative Examples 8-10 respectively provide a method for recovering gold from waste printed circuit boards using a gold immersion agent system. The difference from Example 1 is that the volume of propylene glycol added is different, as shown in Table 4. The other steps are roughly the same as in Example 1 and will not be repeated here.

[0073] Table 4 shows the volume fraction of propylene glycol and the gold leaching rate in Examples 1, 8-9, and Comparative Examples 8-10.

[0074]

[0075] As shown in Table 4, the addition of propylene glycol has a crucial impact on the efficiency of this immersion gold system. When no propylene glycol is added, the gold leaching rate is only 83%, indicating a lack of wetting and penetration, making it difficult for the solution to effectively contact the "invisible gold" encapsulated by epoxy resin. As the volume fraction of propylene glycol increases to 4%, the leaching rate improves to 90%. When it reaches 5-7.5%, the leaching rate stabilizes at a high level of 96-97%. It is noteworthy that even with further increases in volume fraction, the leaching rate, while remaining high, does not increase significantly, indicating that its penetration effect tends to saturate after reaching a threshold of approximately 5%. Therefore, controlling the volume fraction of propylene glycol within the range of 5-10% ensures sufficient wetting and penetration of the circuit board substrate, effectively exposing the target metal, while avoiding excessive reagent use, making it an economical and optimized choice for achieving efficient leaching.

[0076] Examples 10-11 and Comparative Examples 11-13

[0077] Examples 10-11 and Comparative Examples 11-13 respectively provide a method for recovering gold from waste printed circuit boards using a gold immersion agent system. The difference from Example 1 is that the volume of dimethyl sulfoxide added is different, as shown in Table 5. The other steps are roughly the same as in Example 1 and will not be described again here.

[0078] Table 5. Volume fraction of dimethyl sulfoxide and leaching rate of gold in Examples 1, 10-11 and Comparative Examples 11-13.

[0079]

[0080] As shown in Table 5, the amount of dimethyl sulfoxide added is crucial to the leaching efficiency of gold. Figure 1As shown, a layer of organic conductive material adhered to the surface of some gold in the printed circuit board powder sample. When no DMSO was added to the system, the gold leaching rate was only 83%, proving that the epoxy resin encapsulation of the metal was the key bottleneck restricting the recovery rate. Without the swelling effect of DMSO, a large amount of "invisible gold" could not come into contact with the leaching agent. Even with the addition of a small amount of DMSO (Comparative Example 12, 0.5%), the leaching rate only increased to 87%, indicating that the swelling effect was insufficient. When the volume fraction of DMSO reached 1% (Example 8), the leaching rate significantly increased to 93%, indicating that the resin encapsulation could be effectively broken. When the volume fraction was increased to 5% (Example 9), the leaching rate reached a peak of 98%. It is worth noting that when the DMSO was further increased to 6% (Comparative Example 13), the leaching rate remained at 98% without further improvement, indicating that its swelling effect tended to saturate after reaching about 5%. Therefore, controlling the volume fraction of DMSO within the range of 1% to 5% is the best choice to achieve efficient resin dissociation, ensure sufficient gold exposure, and achieve optimal leaching effect.

[0081] Figure 2 These are scanning electron microscope (SEM) images of waste printed circuit board powder samples before and after DMSO treatment. By comparing the images before and after treatment, the swelling of organic matter (epoxy resin) in the circuit board powder samples can be observed, as well as the exposure of some interlayer metals (Ni, Cu, Fe, Zn).

[0082] Examples 12-13 and Comparative Examples 14-15

[0083] Examples 12-13 and Comparative Examples 14-15 respectively provide a method for recovering gold from waste printed circuit boards using a gold immersion agent system. The difference between these methods and Example 1 is that the constant potential is different, as shown in Table 6. The other steps are roughly the same as in Example 1 and will not be repeated here.

[0084] Table 6. Constant potential and gold leaching rate in Examples 1, 12-13 and Comparative Examples 14-15

[0085]

[0086] As shown in Table 6, the electrolysis potential is a key parameter driving the oxidation of acetamide to cyanide and affecting the stable operation of the system. When the potential is too low (5 V), the overpotential of the acetamide oxidation reaction cannot be overcome, resulting in ineffective cyanide formation and zero gold leaching rate. When the potential is increased to the range of 10 V to 30 V, the system can stably produce sufficient cyanide and maintain a highly efficient catalytic cycle, with the gold leaching rate stabilizing at a peak plateau of 95% to 96%. However, when the potential is too high, reaching 40 V, the gold leaching rate drops significantly to 72%, mainly due to two side effects: firstly, excessively high potential exacerbates the oxygen evolution reaction of water, competing with acetamide oxidation and reducing current efficiency; secondly, a strong oxidizing environment accelerates the formation of cyanide (CN). - It is over-oxidized into isocyanate (CNO3), which has no gold immersion capability. - This results in the ineffective loss of the cyanide source and may also compromise the stability of the synergistic oxidant. Therefore, controlling the electrolysis potential within the range of 10 V to 30 V is the best choice for achieving efficient and stable operation of this technology.

[0087] Examples 14-15 and Comparative Examples 16-17

[0088] Examples 14-15 and Comparative Examples 16-17 respectively provide a method for recovering gold from waste printed circuit boards using an immersion gold reagent system. The difference from Example 1 is that the electrolysis time is different, as shown in Table 7. The other steps are roughly the same as in Example 1 and will not be described again here.

[0089] Table 7 shows the electrolysis time and gold leaching rate in Examples 1, 14-15, and Comparative Examples 16-17.

[0090]

[0091] As shown in Table 7, electrolysis time is the key parameter determining the gold leaching rate, and its influence shows a clear trend of first increasing and then decreasing. When the electrolysis time is too short (2.5 h), the acetamide conversion and cyanide formation are insufficient, and the penetration of the solution into the circuit board and the swelling effect of the resin are not balanced, resulting in a gold leaching rate of only 63%. As the time is extended to 3-6 h, the reactions in the system (cyanide formation, resin swelling, catalytic oxidation) tend to be sufficient, and the leaching rate steadily increases to a peak of 94-98%. XRD analysis of the residual solids after the electrolytic leaching in Example 1, such as... Figure 3As shown, valuable metals such as gold and copper in the printed circuit board were completely leached. However, when the leaching time was further extended to 6.5 hours, the leaching rate decreased to 79%, mainly due to the aggravated side reactions caused by excessively long electrolysis: on the one hand, the gold-cyanide complexes that had already dissolved in the system may undergo re-dissolution / degradation at the anode; on the other hand, continuous electrolysis would over-oxidize cyanide ions to generate ineffective isocyanates, and exacerbate the continuous dissolution of impurity metals, jointly leading to the redeposition or secondary encapsulation of the leachable gold. Therefore, controlling the electrolysis time within the range of 4 to 6 hours is the optimal balance point for achieving efficient gold leaching and avoiding excessive reactions that lead to a decrease in recovery rate.

[0092] In summary, this application provides an immersion gold reagent system and a method for recovering gold from waste printed circuit boards. By constructing a highly efficient immersion gold system with multi-component synergistic effects, combined with an immersion gold electrolysis system, the key lies first in the in-situ generation and precise supply of cyanide: using acetamide as a precursor, oxidation occurs at the anode interface under electrolysis conditions (2CH3CONH2-8e). - →(CN)2↑+4H2↑), decarboxylation reaction ((CN)2+2OH) - →CN - +CNO - The process of reacting cyanide with hydrogen ions (+H₂O) allows for the controlled release of free cyanide ions. This enables in-situ synthesis and immediate utilization of cyanide ions at the reaction interface, avoiding the large-scale storage of highly toxic cyanide in the system and laying a safety foundation from the source. Furthermore, impurity metals present in printed circuit boards (such as copper and iron) have a strong affinity for cyanide ions; they compete with gold for cyanide ions, forming stable cyanide complexes (such as [Cu(CN)₄)₄). 3- This process results in a significant consumption of cyanide ions. The generated byproduct, isocyanate ions, forms more stable complexes with these impurity metal ions, thereby locking in the impurity metals and reducing their consumption of cyanide ions. This allows more cyanide ions to be used for gold leaching.

[0093] To further accelerate the gold dissolution kinetics, this application designs an electrochemical catalytic cycle based on a redox mediator, using sodium anthraquinone-2-sulfonate as a synergistic oxidant to construct a highly efficient catalytic cycle. Specifically, on the cathode surface, sodium anthraquinone-2-sulfonate is reduced to hydroquinone (AQ + H₂O + 2e⁻). - →AHQ (AQ represents sodium anthraquinone-2-sulfonate, AHQ represents reduced hydroquinone)), hydroquinone diffuses into the bulk solution, efficiently reducing dissolved oxygen to hydrogen peroxide, and regenerating itself back to sodium anthraquinone-2-sulfonate. This cycle not only transforms cathode side reactions (such as hydrogen evolution) into a valuable oxidant production process, but also constructs a continuous and efficient oxidation environment on the gold surface, greatly promoting the reaction rate of gold complexation with cyanide (2Au + 4CN). -+H₂O₂→2[Au(CN)₂] - +2OH - This resulted in a doubling of the immersion gold efficiency.

[0094] This application introduces a synergistic mechanism of physical penetration and chemical swelling, solving a key bottleneck in drug delivery and target contact. Propylene glycol significantly enhances the wetting and capillary penetration capabilities of the drug solution onto the hydrophobic epoxy resin substrate by reducing the surface tension of the solution, thus opening delivery channels for the active component. Simultaneously, dimethyl sulfoxide (DMSO), as a highly polar solvent, can effectively penetrate into the interior of the epoxy resin polymer network, causing molecular chain relaxation and increased spacing, resulting in a "swelling effect." This breaks down the resin's confinement of the encapsulated gold, fully exposing it and allowing it to contact the leaching agent.

[0095] This application utilizes acetamide electrolysis in-situ cyanide production technology to fundamentally eliminate the storage and transportation of highly toxic cyanide, ensuring safety. Simultaneously, it introduces a multifunctional synergistic system composed of propylene glycol, DMSO, and sodium anthraquinone-2-sulfonate. This system effectively overcomes three major technical bottlenecks—difficulty in liquid entry, difficulty in target contact, and slow oxidation—through the synergistic effects of enhanced penetration (propylene glycol), disruption of encapsulation (DMSO swelling resin), and catalytic oxidation (anthraquinone cycle). Thus, while ensuring process safety and environmental protection, it significantly improves the gold leaching rate and recovery rate, while also possessing outstanding advantages in process integration and economic efficiency.

[0096] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A gold immersion reagent system, characterized in that, The gold immersion reagent system consists of acetamide, sodium anthraquinone-2-sulfonate, propylene glycol, and dimethyl sulfoxide; The gold immersion agent system comprises an electrolyte consisting of acetamide at a concentration of 0.5-2 mol / L and sodium anthraquinone-2-sulfonate at a concentration of 0.05-0.5 mol / L, with propylene glycol accounting for 5-10% of the electrolyte volume and dimethyl sulfoxide accounting for 1-5% of the electrolyte volume.

2. A method for recovering gold from waste printed circuit boards using an immersion gold reagent system, characterized in that, The treatment using the gold immersion reagent system described in claim 1 includes the following steps: S1. Grind the printed circuit board to obtain a ground sample; S2. Add water to the ground sample to prepare a slurry, and then adjust the slurry to a specific pH value to obtain a pretreated slurry; S3. Add acetamide and sodium anthraquinone-2-sulfonate to water to prepare an electrolyte, then add propylene glycol and dimethyl sulfoxide, and electrolyze the pretreated slurry using a three-electrode system under stirring to obtain a precious metal-containing solution and solid residue. The specific pH value is 12-14; During the electrolysis, the constant potential is 10~30V, and the electrolysis time is 3~6h.

3. The method for recovering gold from waste printed circuit boards using the gold immersion reagent system according to claim 2, characterized in that, In step S3, the three-electrode system consists of an anode: a graphite electrode, a cathode: a titanium-based platinum-plated mesh counter electrode, and a dual salt bridge reference electrode.

4. The method for recovering gold from waste printed circuit boards using the gold immersion reagent system according to claim 2, characterized in that, In step S2, the concentration of the slurry is 10-15%.

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