Bromine-based leaching reagent system and method for recovering precious metals from waste circuit boards

Abstract

The application provides a bromine-based leaching reagent system and a method for recycling precious metals from waste circuit boards, and belongs to the technical field of hydrometallurgy. The application takes stable bromine-based strong oxidant, sodium bromide and sodium iodide as the leaching reagent system, controls the bromine volatilization loss to be below 5% through the slow-release bromine mechanism, reduces the bromine consumption by more than 15% compared with the traditional liquid bromine leaching process, simultaneously introduces sodium iodide as a catalytic additive, and significantly reduces the sodium bromide consumption. The weak acid leaching environment is adopted, the leaching efficiency is ensured, and the equipment corrosion problem is effectively reduced. The developed "distillation-precipitation" coupling process realizes efficient recovery of silver and synchronous regeneration of bromine reagent, so that the bromine recycling rate is more than 80%. Through the construction of a gold selective reduction-silver distillation precipitation-palladium solvent extraction hierarchical separation system, efficient recovery of precious metals is realized. The application greatly reduces the processing cost through the recycling of bromine reagent, has significant industrial application value and broad market prospect.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of hydrometallurgy, and particularly relates to a bromine-based leaching reagent system and a method for recovering precious metals from waste circuit boards. BACKGROUND

[0002] Metal recovery of waste printed circuit boards mainly relies on pyrometallurgy and hydrometallurgy. Although pyrometallurgy can extract metals through high-temperature smelting, it has the disadvantages of high energy consumption, high cost, easy production of toxic waste gas, and the like, and needs to be equipped with a strict tail gas treatment system, which has high environmental and economic costs. In comparison, hydrometallurgy is more promising as a recovery method due to its advantages of less investment, controllable pollution, and high metal recovery rate, and is particularly suitable for small and medium-sized recycling enterprises.

[0003] In the hydrometallurgical process, the waste printed circuit boards usually need to be first manually or mechanically disassembled to remove the main components, and then crushed and ground, and the obtained powder is separated into copper, lead, zinc and other heavy metals through acid leaching or alkali leaching process. The residue after leaching needs to be further extracted by cyanidation, halogenation and the like to extract precious metals. However, the traditional cyanidation leaching process has the problems of high toxicity, long leaching period, and low recovery rate, and in comparison, the halogenation gold extraction technology is increasingly concerned due to its high efficiency.

[0004] At present, the commonly used halogen leaching agents include hydrochloric acid, chlorine, hypochlorous acid, sodium hypochlorite, iodine and liquid bromine, etc. However, halogen has active chemical properties, is easy to volatilize and produce irritating gas, and usually reacts under strong acidic conditions, which has strong corrosion to equipment, increases the process complexity and operating cost. Therefore, developing a green, efficient and low-toxicity precious metal (gold, silver, platinum, palladium) recovery process for waste printed circuit boards has important social significance for improving resource utilization and promoting the development of circular economy. SUMMARY

[0005] In view of the technical problems in the background art, the present application provides a bromine-based leaching reagent system and a method for recovering precious metals from waste circuit boards, which aims to solve the problems of low leaching efficiency, high cost, strong corrosion to equipment and easy production of harmful gas of the existing leaching reagent system for precious metals.

[0006] In a first aspect, the present application provides a bromine-based leaching reagent system, which comprises a bromine-based strong oxidizing agent, sodium bromide and sodium iodide.

[0007] In the technical scheme of the embodiment of the application, the bromine-based strong oxidant is slowly released by using bromine-based strong oxidant, sodium bromide and sodium iodide as the leaching reagent system, and the bromine-based strong oxidant can slowly release bromine monomer and compounds with strong oxidizing property. The slow release process maintains the effective bromine concentration in the gold leaching system at an optimal level, and avoids the low efficiency and loss of leaching reagent caused by the rapid volatilization and decomposition of Br2. The bromine volatilization loss is controlled below 5% by the slow release bromine mechanism, and the bromine consumption is reduced by more than 15% compared with the traditional liquid bromine leaching process. Meanwhile, sodium iodide is introduced as a catalyst additive to form a stable complex with the noble metal oxidized to a positive valence, thereby significantly reducing the consumption of sodium bromide. The reagent system can be used for leaching in a weak acid environment, which effectively reduces the equipment corrosion problem while ensuring the leaching efficiency.

[0008] In some embodiments, the stable bromine-based strong oxidant is one or more of dibromodimethylhydantoin, bromochlorodimethylhydantoin and monobromodimethylhydantoin.

[0009] In the embodiment, the stable bromine-based strong oxidant can slowly release bromine monomer and compounds with strong oxidizing property, and the system can maintain the optimal bromine concentration required for gold leaching. By slow oxidation and conversion of the noble metal into soluble ions, high-efficiency complex dissolution of the noble metal from the waste circuit board is achieved.

[0010] In some embodiments, the molar concentrations of the stable bromine-based strong oxidant, sodium bromide and sodium iodide in the bromine-based leaching reagent system are 0.04-0.2 mol / L, 0.2-1.2 mol / L and 0.02-0.04 mol / L, respectively.

[0011] In the embodiment, the appropriate proportioning of the reagents can achieve better leaching effect.

[0012] In a second aspect, the application provides a method for recovering noble metals from waste circuit boards by using the above-mentioned stable bromine-based leaching reagent system, which comprises the following steps:

[0013] S1. The waste circuit board is crushed and ground, and then a mixed solution of sulfuric acid and strong oxidant is added for leaching to obtain a noble metal-enriched leaching residue;

[0014] S2. The bromine-based leaching reagent system is added to the noble metal-enriched leaching residue, and the pH value is adjusted, followed by stirring leaching and solid-liquid separation to obtain a noble metal separation stock solution;

[0015] S3. Ferrous sulfate is added to the noble metal separation stock solution, and the redox reaction potential is detected. After the redox reaction is completed, gold powder and filtrate are obtained by pressure filtration;

[0016] S4. The filtrate is subjected to vacuum distillation, and then centrifugal separation, to obtain AgBr precipitate, gaseous bromine and distillate, the AgBr precipitate is electrolytically purified to obtain silver powder, and the gaseous bromine is condensed to obtain liquid bromine for regeneration of the bromine-based oxidizing agent;

[0017] S5. The distillate is mixed with an extractant to perform extraction, and a loaded organic phase is obtained, the loaded organic phase is mixed with a back-extractant to perform back-extraction, and palladium is separated out.

[0018] In the technical scheme of the embodiment, through construction of a gold selective reduction-silver distillation precipitation-palladium solvent extraction cascade separation system, combined with the above-mentioned stable bromine-based leaching reagent system, efficient recovery of the noble metal is realized. Meanwhile, a distillation-precipitation coupling process is developed, efficient recovery of silver and synchronous regeneration of the bromine reagent are realized, and the bromine recycling rate is more than 80%. Through recycling of the bromine reagent, the treatment cost is greatly reduced, and the application has significant industrial application value and broad market prospect.

[0019] In some embodiments, in step S2, the mass-volume ratio of the noble metal-enriched leaching residue and the bromine-based leaching reagent system is 1:2-1:4.

[0020] In the embodiment, the specific ratio of the noble metal-enriched leaching residue and the bromine-based leaching reagent system can make the leaching effect better.

[0021] In some embodiments, in step S2, the pH value in the pH value adjustment is 3.0-4.5.

[0022] In the embodiment, the process adopts a medium-weak acidic leaching environment with a pH value of 3.0-4.5, the slow-release bromine-based strong oxidizing agent can keep the redox potential of the leaching system above 0.8V, which effectively reduces the equipment corrosion problem while ensuring the leaching efficiency.

[0023] In some embodiments, in step S2, the temperature of the stirring leaching is 25-30℃, and the time of the stirring leaching is 14-24h.

[0024] In the embodiment, efficient leaching of the noble metal can be realized at a lower temperature, the volatilization of bromine can be reduced, and effective leaching is ensured.

[0025] In some embodiments, in step S4, the temperature of the vacuum distillation is 60-75℃, and the temperature of the condensation is 0-10℃.

[0026] In the embodiment, through vacuum distillation, bromine is volatilized in a gaseous form, and silver ions are precipitated out in the form of AgBr, and then through condensation, the gaseous bromine can be condensed into liquid bromine.

[0027] In some embodiments, in step S3, 4.5-6 moles of ferrous sulfate are added per mole of gold ions in the noble metal separation stock solution, the temperature of the redox reaction is 20-60°C, the reaction time is 20-60 min, and the redox potential is <200 mV.

[0028] In this embodiment, the gold ions in the solution undergo a redox reaction with ferrous sulfate, the ferrous ions are oxidized to ferric ions, and the gold-bromine complex ions are reduced to gold.

[0029] In some embodiments, in step S5, the extractant is β-hydroxy oxime or triisobutyl phosphine sulfide, the volume ratio of the distillate and the extractant is 2:1, the stripping agent is a thiourea solution or ammonia water, the molar concentration of the thiourea solution is 0.8-1.2 mol / L, the mass concentration of the ammonia water is 3-8%, and the volume ratio of the loaded organic phase and the stripping agent is 1:1.

[0030] In this embodiment, the extractant is added to the distillate, the palladium ions form stable chelates with the extractant to obtain a loaded organic phase, and then the stripping agent is added to strip the palladium ions from the organic phase to the inorganic phase to recover the palladium.

[0031] The above description is only a summary of the technical solutions of the present application. In order to more clearly understand the technical means of the present application, the following specific embodiments of the present application can be implemented according to the content of the description, and in order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the following specific embodiments of the present application are described. BRIEF DESCRIPTION OF DRAWINGS

[0032] In order to more clearly illustrate the technical solutions of the present application, the following will briefly introduce the drawings used in the present application. Obviously, the drawings described below are only some embodiments of the present application, and those skilled in the art can also obtain other drawings according to these drawings without creating any creative labor.

[0033] Figure 1 The flow chart of the bromine-based leaching reagent system for treating waste printed circuit boards in the embodiments of the present application. DETAILED DESCRIPTION

[0034] The embodiments of the technical solutions of the present application will be described in detail below. The following embodiments are only used to more clearly illustrate the technical solutions of the present application, and therefore only serve as examples, but cannot limit the protection scope of the present application.

[0035] 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.

[0036] To address the problems of low leaching efficiency, high cost, strong corrosiveness to equipment, and easy generation of harmful gases in existing leaching agent systems for precious metals, this application provides a bromine-based leaching agent system and a method for recovering precious metals from waste circuit boards. The leaching agent system uses a stable bromine-based strong oxidant, sodium bromide, and sodium iodide. The stable bromine-based strong oxidant can slowly release bromine and its compounds, which have strong oxidizing properties. This slow release process maintains the effective bromine concentration in the leaching system at an optimal level, avoiding inefficiency and leaching agent loss caused by excessively rapid Br2 volatilization and decomposition. By controlling bromine volatilization loss to below 5% through a slow-release bromine mechanism, the amount of bromine used is reduced by more than 15% compared to traditional liquid bromine leaching processes. Simultaneously, sodium iodide is introduced as a catalyst to form stable complexes with the precious metals oxidized to positive valence, significantly reducing the amount of sodium bromide used. A weakly acidic leaching environment is used, effectively mitigating equipment corrosion while ensuring leaching efficiency. A specially developed "distillation-precipitation" coupled process achieves efficient silver recovery and simultaneous regeneration of bromine reagent, resulting in a bromine recycling rate of over 80%. By constructing a tiered separation system of gold selective reduction-silver distillation precipitation-palladium solvent extraction, efficient recovery of precious metals is achieved. This application significantly reduces processing costs through the recycling of bromine reagent, demonstrating significant industrial application value and broad market prospects.

[0037] In a first aspect, this application provides a bromine-based leaching agent system, which comprises a bromine-based strong oxidant, sodium bromide, and sodium iodide.

[0038] In the technical solution of this application embodiment, a leaching agent system is used, consisting of a bromine-based strong oxidant, sodium bromide, and sodium iodide. This system stabilizes the bromine-based strong oxidant and allows for the slow release of bromine and its compounds, which possess strong oxidizing properties. This slow release process maintains the effective bromine concentration in the gold leaching system at an optimal level, avoiding inefficiency and leaching agent loss caused by excessively rapid Br2 volatilization and decomposition. By controlling bromine volatilization loss to below 5% through a slow-release bromine mechanism, the amount of bromine used is reduced by more than 15% compared to traditional liquid bromine leaching processes. Simultaneously, sodium iodide is introduced as a catalyst, forming stable complexes with the noble metals oxidized to positive valence, significantly reducing the amount of sodium bromide used. This agent system can leach in a weakly acidic environment, effectively mitigating equipment corrosion while ensuring leaching efficiency.

[0039] Furthermore, in some embodiments, the stable bromine-based strong oxidant is one or more of dibromodimethylhydantoin, bromochlorodimethylhydantoin, and monobromodimethylhydantoin.

[0040] In the technical solution of this application embodiment, a stable bromine-based strong oxidant can slowly release bromine elemental and compounds with strong oxidizing properties. This system can maintain the optimal bromine concentration required for immersion gold, and achieve efficient complexation and dissolution of precious metals from waste circuit boards by slowly oxidizing and converting precious metals into soluble ions.

[0041] Furthermore, in some embodiments, the molar concentrations of the stable bromine-based strong oxidant, sodium bromide, and sodium iodide in the bromine-based leaching agent system are 0.04~0.2 mol / L, 0.2~1.2 mol / L, and 0.02~0.04 mol / L, respectively.

[0042] In the technical solution of this application embodiment, the leaching effect can be better by using appropriate ratios of various agents.

[0043] Secondly, this application provides a method for recovering precious metals from waste circuit boards using a bromine-based leaching agent system. The method employs the aforementioned stable bromine-based leaching agent system and includes the following steps:

[0044] S1. The waste circuit boards are crushed and ground, then a mixed solution of sulfuric acid and strong oxidant is added and leached to obtain precious metal-enriched leaching residue.

[0045] S2. Add a bromine-based leaching agent system to the precious metal enrichment leaching residue, adjust the pH value, then stir and leach, and separate the solid and liquid to obtain the precious metal separation raw solution;

[0046] S3. Add ferrous sulfate to the precious metal separation solution, monitor and control the potential of the redox reaction, and after the redox reaction is completed, filter by pressure to obtain gold powder and filtrate;

[0047] S4. The filtrate is subjected to vacuum distillation and then centrifuged to obtain AgBr precipitate, gaseous bromine and distillate. The AgBr precipitate is purified by electrolysis to obtain silver powder, and the gaseous bromine is condensed to obtain liquid bromine for regenerating bromine-based oxidants.

[0048] S5. The distillate is mixed with an extractant and extracted to obtain a loaded organic phase. The loaded organic phase is then mixed with a back-extractant and back-extracted to separate palladium.

[0049] In the technical solution of this application, a stepped separation system of gold selective reduction-silver distillation precipitation-palladium solvent extraction is constructed, combined with the aforementioned stable bromine-based leaching reagent system, to achieve efficient recovery of precious metals. Simultaneously, a "distillation-precipitation" coupled process is developed, enabling efficient silver recovery and simultaneous regeneration of the bromine reagent, resulting in a bromine recycling rate of over 80%. This application significantly reduces processing costs through the recycling of the bromine reagent, demonstrating significant industrial application value and broad market prospects.

[0050] Furthermore, in some embodiments, in step S2, the mass-to-volume ratio of the precious metal enrichment leaching residue and the bromine-based leaching agent system is 1:2 to 1:4.

[0051] In the technical solution of this application embodiment, a specific ratio of precious metal enrichment leaching residue and bromine-based leaching agent system can improve the leaching effect.

[0052] Furthermore, in some embodiments, in step S2, the pH value in the pH adjustment is 3.0 to 4.5.

[0053] In the technical solution of this application embodiment, the process adopts a weakly acidic leaching environment with a pH of 3.0~4.5. The slow-release bromine-based strong oxidant can maintain the redox potential of the leaching system above 0.8V, effectively reducing equipment corrosion problems while ensuring leaching efficiency.

[0054] Furthermore, in some embodiments, in step S2, the temperature of the stirring leaching is 25~30°C, and the stirring leaching time is 14~24h.

[0055] In the technical solution of this application embodiment, efficient leaching of precious metals can be achieved at a lower temperature, which can reduce the volatilization of bromine while ensuring effective leaching.

[0056] Furthermore, in some embodiments, in step S4, the temperature of the vacuum distillation is 60~75°C, and the temperature of the condensation is 0~10°C.

[0057] In the technical solution of this application embodiment, bromine is volatilized in gaseous form by vacuum distillation, while silver ions are precipitated as AgBr. After condensation, the gaseous bromine can be condensed into liquid bromine.

[0058] Furthermore, in some embodiments, in step S3, 4.5-6 mol of ferrous sulfate is added to each mole of gold ions in the precious metal separation solution, the temperature of the redox reaction is 20-60°C, the reaction time is 20-60 min, and the redox potential is <200 mV.

[0059] In the technical solution of this application embodiment, gold ions in the solution undergo a redox reaction with ferrous sulfate, whereby the ferrous ions are oxidized to ferric ions and the gold-bromine complex ions are reduced to elemental gold.

[0060] Further, in some embodiments, in step S5, the extractant is β-hydroxyoxime or triisobutylphosphine sulfide, and the volume ratio of the distillate to the extractant is 2:1; the back-extraction agent is thiourea solution or ammonia, the molar concentration of the thiourea solution is 0.8~1.2 mol / L, the mass concentration of the ammonia is 3~8%, and the volume ratio of the supported organic phase to the back-extraction agent is 1:1.

[0061] In the technical solution of this application embodiment, an extractant is added to the distillate, and palladium ions form a stable chelate with the extractant to obtain a loaded organic phase. Then, a back-extractant is added to back-extract the palladium ions from the organic phase to the inorganic phase, and palladium is recovered.

[0062] Further, in some embodiments, step S4, the step of regenerating the bromine-based oxidant includes: dissolving 5,5-dimethylhydantoin in a 5-10% NaOH solution, then adding it to the liquid bromine, wherein the molar ratio of Br2 to 5,5-dimethylhydantoin is 2:1, adjusting the pH value to 8-12, and reacting at 10°C to obtain the bromine-based oxidant.

[0063] In the technical solution of this application embodiment, the method can realize the recovery and utilization of bromine in the leaching agent system.

[0064] Furthermore, in some embodiments, in step S1, the fineness of the grinding is such that 80% of the material is less than 120 mesh.

[0065] In the technical solution of this application embodiment, electronic waste is ground to a certain particle size to facilitate subsequent leaching.

[0066] Furthermore, in some embodiments, in step S1, the concentration of sulfuric acid is 1~2 mol / L, the strong oxidant is hydrogen peroxide or sodium hypochlorite, and the mass concentration of the strong oxidant is 3~7%; the solid-liquid ratio in the leaching system is 1:3~1:5, the leaching temperature is 50~70℃, and the leaching time is 4~6h.

[0067] In the technical solution of this application embodiment, under these conditions, valuable metals such as copper, zinc, tin, and lead can be selectively removed to obtain precious metal-enriched leaching residue.

[0068] 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.

[0069] Example 1

[0070] Example 1 provides a bromine-based leaching agent system comprising 0.06 mol / L dibromodimethylhydantoin, 0.4 mol / L sodium bromide, and 0.04 mol / L sodium iodide.

[0071] Waste printed circuit boards were treated using the above-mentioned bromine-based leaching agent system, such as... Figure 1 As shown, the specific steps include the following:

[0072] (1) The waste printed circuit board was mechanically crushed and ground into powder with a particle size of less than 120 mesh accounting for 80%. 2 mol / L sulfuric acid and 5% hydrogen peroxide were mixed to obtain a mixed solution. The solution was then leached for 6 hours at a solid-liquid ratio of 1:3 and a leaching temperature of 70℃ to obtain precious metal enriched leaching residue.

[0073] (2) The above precious metal enrichment leaching residue and bromine-based leaching agent system are mixed at a solid-liquid ratio of 1:3, the pH value is adjusted to 4, and the mixture is stirred and leached at 25°C for 16 hours. After leaching, the mixture is separated by pressure filtration to obtain the precious metal separation solution.

[0074] (3) Add ferrous sulfate to the original solution of precious metal separation, wherein 6 mol of ferrous sulfate is added for every mole of gold ions, and react at 40°C for 60 min. The potential of the redox reaction is controlled to be <200 mV. After the reaction is completed, the solution is filtered by pressure to obtain gold powder and filtrate.

[0075] (4) The above filtrate was distilled under reduced pressure at 70°C to obtain bromine gas, and then the bromine gas was condensed at 5°C to obtain liquid bromine. The slurry after distillation was separated by centrifugation to obtain AgBr precipitate.

[0076] (5) The distillate was mixed with triisobutylphosphine sulfide at a volume ratio of 2:1 and extracted to obtain a loaded organic phase. The loaded organic phase was then mixed with 1.2 mol / L thiourea solution at a volume ratio of 1:1 and extracted again to recover palladium.

[0077] (6) Dissolve 5,5-dimethylhydantoin in 9% NaOH solution and add it to the above liquid bromine. The molar ratio of Br2 to 5,5-dimethylhydantoin is 2:1. Adjust the pH value to 10 and react at 10℃ to obtain bromine-based oxidant.

[0078] The performance parameters of the raw materials are shown in Table 1.

[0079] Table 1 Chemical composition of waste printed circuit boards

[0080]

[0081] Comparative Example 1

[0082] Comparative Example 1 provides a method for recovering precious metals from waste circuit boards using a leaching agent system. The difference from Example 1 is that the leaching agent in step (2) is 0.06 mol / L liquid bromine, and the pH value is adjusted to 0.8. The other steps are roughly the same as in Example 1, and will not be repeated here.

[0083] Comparative Example 2

[0084] Comparative Example 2 provides a method for recovering precious metals from waste circuit boards using a leaching agent system. The difference from Example 1 is that the leaching agent system in step (2) does not contain sodium iodide. The other steps are roughly the same as in Example 1 and will not be repeated here.

[0085] The leaching rates of gold, silver, and palladium in step (2) and the recovery rate of bromine in step (4) of the above examples and comparative examples were measured respectively. The test results are shown in Table 2.

[0086] Table 2 shows the leaching rates of gold, silver, and palladium in step (2) of Example 1, and the bromine recovery rate in step (4).

[0087]

[0088] As shown in Table 2, the comparison results between Example 1 and Comparative Example 1 indicate that when using the traditional liquid bromine leaching process, the leachate needs to be maintained under strongly acidic conditions (pH < 1), and the bromine recovery rate is greatly reduced, with bromine volatilization loss reaching as high as 30%, resulting in a significant increase in reagent consumption. The comparison results between Example 1 and Comparative Example 2 confirm that adding sodium iodide as a catalyst to the leaching system not only greatly improves the leaching rate of precious metals, but also increases the bromine recovery rate, and reduces the amount of sodium bromide used by about 10%.

[0089] Examples 2-6 and Comparative Examples 3-8

[0090] Examples 2-6 and Comparative Examples 3-8 respectively provide a method for recovering precious metals from waste circuit boards using a bromine-based leaching agent system. The difference from Example 1 is that the concentrations of each component in the leaching agent system are different, as shown in Table 3. The other steps are roughly the same as in Example 1 and will not be repeated here.

[0091] Table 3 shows the concentrations of each component in the leaching agent systems of Examples 2-6 and Comparative Examples 3-8.

[0092]

[0093] The leaching rates of gold, silver, and palladium in step (2) of Examples 1-6 and Comparative Examples 3-8, and the recovery rate of bromine in step (4) were measured respectively. The test results are shown in Table 4.

[0094] Table 4 shows the leaching rates of gold, silver, and palladium in step (2) of Examples 1-6 and Comparative Examples 3-8, and the bromine recovery rate in step (4).

[0095]

[0096] Table 4 shows that the leaching efficiency of gold, silver, and palladium mainly depends on the concentrations of the stable bromine-based oxidant, sodium bromide, and sodium iodide. The key is to maintain a sufficient oxidation potential to oxidize the noble metals and to promote the formation of stable complexes between Br⁻ and I⁻ and the oxidized metal ions. However, excessive addition of reagents not only reduces the recovery efficiency and increases production costs but also affects overall economic viability. Furthermore, the bromine recovery rate is highly dependent on the control effectiveness of subsequent processes.

[0097] In summary, this application provides a bromine-based leaching agent system and a method for recovering precious metals from waste circuit boards. Using a stable bromine-based strong oxidant, sodium bromide, and sodium iodide as the leaching agent system, the stable bromine-based strong oxidant can slowly release elemental bromine and its compounds, which have strong oxidizing properties. This slow release process maintains the effective bromine concentration in the leaching system at an optimal level, avoiding inefficiency and leaching agent loss caused by excessively rapid Br2 volatilization and decomposition. By controlling bromine volatilization loss to below 5% through a slow-release bromine mechanism, the amount of bromine used is reduced by more than 15% compared to traditional liquid bromine leaching processes. Simultaneously, sodium iodide is introduced as a catalyst to form stable complexes with the precious metals oxidized to positive valence, significantly reducing the amount of sodium bromide used. A weakly acidic leaching environment is used, effectively mitigating equipment corrosion while ensuring leaching efficiency. A specially developed "distillation-precipitation" coupling process achieves efficient silver recovery and simultaneous regeneration of the bromine reagent, resulting in a bromine recycling rate of over 80%. By constructing a stepped separation system of gold selective reduction-silver distillation precipitation-palladium solvent extraction, efficient recovery of precious metals was achieved. This application significantly reduces processing costs through the recycling of bromine reagents, demonstrating significant industrial application value and broad market prospects.

[0098] 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 method for recovering precious metals from waste printed circuit boards using a bromine-based leaching reagent system, characterized by, The method comprises the following steps: S1. crushing, grinding, adding a mixed solution of sulfuric acid and strong oxidizing agent, leaching, and obtaining a precious metal enriched leaching residue; S2. adding a bromine-based leaching reagent system to the precious metal enriched leaching residue, adjusting the pH value, then stirring and leaching, and performing solid-liquid separation to obtain a precious metal separation stock solution; S3. adding ferrous sulfate to the precious metal separation stock solution, detecting the redox reaction potential, and after the redox reaction is completed, performing pressure filtration to obtain gold powder and a filtrate; S4. performing vacuum distillation on the filtrate, then performing centrifugal separation to obtain AgBr precipitate, gaseous bromine, and a distillate, electrolytically purifying the AgBr precipitate to obtain silver powder, and condensing the gaseous bromine to obtain liquid bromine for regenerating the bromine-based oxidizing agent; S5. mixing the distillate with an extractant, performing extraction to obtain a loaded organic phase, mixing the loaded organic phase with a stripping agent, and performing stripping to separate out palladium. The bromine-based leaching reagent system comprises stable bromine-based strong oxidizing agent, sodium bromide, and sodium iodide. The stable bromine-based strong oxidizing agent is one or more of dibromodimethylhydantoin, bromochlorodimethylhydantoin, and monobromodimethylhydantoin.

2. The process for recovery of precious metals from waste printed circuit boards by bromine based leaching reagent system as claimed in claim 1 wherein, The molar concentrations of the stable bromine-based strong oxidizing agent, sodium bromide, and sodium iodide in the bromine-based leaching reagent system are 0.04-0.2 mol / L, 0.2-1.2 mol / L, and 0.02-0.04 mol / L, respectively.

3. The process for recovery of precious metals from waste printed circuit boards by bromine based leaching reagent system as claimed in claim 1 wherein, In step S2, the mass-to-volume ratio of the precious metal enriched leaching residue to the bromine-based leaching reagent system is 1:2-1:

4.

4. The process for recovery of precious metals from waste printed circuit boards by bromine based leaching reagent system as claimed in claim 1 wherein, In step S2, the pH value in the pH value adjustment is 3.0-4.

5.

5. The process for recovery of precious metals from waste printed circuit boards by bromine based leaching reagent system as claimed in claim 1 wherein, In step S2, the temperature of the stirring and leaching is 25-30℃, and the time of the stirring and leaching is 14-24 h.

6. The process for recovery of precious metals from waste printed circuit boards by bromine based leaching reagent system as claimed in claim 1 wherein, In step S4, the temperature of the vacuum distillation is 60-75℃, and the temperature of the condensation is 0-10℃.

7. The method of recovering precious metals from waste circuit boards by using a bromine-based leaching reagent system according to claim 1, characterized in that, In step S3, 4.5-6 mol of ferrous sulfate is added per mol of gold ions in the precious metal separation stock solution, the temperature of the redox reaction is 20-60℃, the reaction time is 20-60 min, and the redox potential is <200 mV.

8. The method of recovering precious metals from waste circuit boards by using a bromine-based leaching reagent system according to claim 1, characterized in that, In step S5, the extractant is β-hydroxy oxime or triisobutyl phosphine sulfide, the volume ratio of the distillate to the extractant is 2:1, the stripping agent is a thiourea solution or ammonia water, the molar concentration of the thiourea solution is 0.8-1.2 mol / L, the mass concentration of the ammonia water is 3-8%, and the volume ratio of the loaded organic phase to the stripping agent is 1:1.

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