Centrifugal extraction method of noble metal in waste circuit board

Abstract

The application discloses a centrifugal extraction method of noble metals in waste circuit boards, and relates to the technical field of metal resource recovery.The application modifies pretreated inorganic porous materials by using a silane coupling agent containing a mercapto group to obtain modified inorganic porous materials, and then the modified inorganic porous materials are put into waste circuit board leaching liquor to produce adsorption and coordination combination with noble metal ions in the waste circuit board leaching liquor, and then the noble metals are efficiently recovered through centrifugation and extraction and the like.The method is simple, efficient, energy-saving and environment-friendly, and can realize resourceization and harmless treatment of waste circuit boards.

Description

Technical Field

[0001] This application relates to the field of metal resource recycling technology, and in particular to a centrifugal extraction method for precious metals from waste circuit boards. Background Technology

[0002] With the rapid iteration of the electronics and information industry, the amount of electronic waste generated continues to grow. Among these, waste circuit boards (PCBs), a core component of electronic waste, contain precious metals such as gold, silver, and palladium, with grades far exceeding those of natural ores, making them highly valuable for recycling. Existing methods for recycling precious metals from waste PCBs suffer from low efficiency, high losses, poor environmental performance, and low purity of the recovered precious metals. Therefore, it is necessary to develop a centrifugal extraction method for precious metals adapted to the waste PCB system to overcome existing technological limitations and meet the industry's urgent need for efficient and environmentally friendly precious metal recycling. Summary of the Invention

[0003] To address the shortcomings of existing technologies, this application provides a centrifugal extraction method for precious metals from waste circuit boards. This application modifies a pretreated inorganic porous material using a silane coupling agent containing mercapto groups to obtain a modified inorganic porous material. This modified inorganic porous material is then added to the leachate of the waste circuit boards, where it adsorbs and coordinates with the precious metal ions. The precious metals are then efficiently recovered through centrifugation and extraction.

[0004] To achieve the above objectives, this application provides a centrifugal extraction method for precious metals from waste circuit boards, comprising the following steps:

[0005] S1. The waste circuit board is crushed and separated to obtain non-metallic powder and metallic powder. The metallic powder is put into the leaching agent for leaching treatment to obtain a preliminary leachate.

[0006] S2. The preliminary leachate is filtered to remove impurities and then heated to obtain waste circuit board leachate, and its pH is adjusted.

[0007] S3. The inorganic porous material is calcined in a muffle furnace, cooled to room temperature, added to hydrochloric acid and boiled under reflux, then washed with water until neutral and vacuum dried to obtain the pretreated inorganic porous material.

[0008] S4. Disperse the pretreated inorganic porous material in an ethanol-water mixed solvent, adjust the pH of the system, then add a silane coupling agent containing mercapto groups, react under preset conditions, then filter and vacuum dry to obtain the modified inorganic porous material.

[0009] S5. The modified inorganic porous material is added to the leaching solution of waste circuit boards and stirred to obtain a complex mixture. Then, it is centrifuged to separate the complex solid phase and liquid phase.

[0010] S6. Add the coordination solid phase to the desorbent, centrifuge again after desorption treatment to obtain the desorbed liquid and the regenerated modified inorganic porous material, add the extractant to the desorbed liquid, let it stand and separate to obtain the extract, add the reducing agent to the extract, reduce and separate to obtain the precious metal powder.

[0011] The centrifugal extraction method for precious metals in waste circuit boards provided in this application achieves efficient leaching, adsorption, separation, and purification of precious metals by using specific thiol-modified inorganic porous materials in conjunction with an optimized centrifugal extraction process. This method is low-cost, environmentally friendly, and easily scaled up, making it suitable for industrial-scale processing of waste circuit boards.

[0012] In step S1, the waste circuit board is first crushed and separated into non-metallic powder and metallic powder. This process removes non-metallic components such as glass fiber and resin that do not participate in the subsequent leaching reaction, avoiding the adsorption and consumption of the leaching agent by non-metallic components and reducing potential interference with precious metal recovery. Simultaneously, the crushing process increases the specific surface area of ​​the metallic components, allowing the leaching agent to fully contact the precious metals, thus improving leaching efficiency from the source.

[0013] In step S2, the preliminary leachate is filtered to remove unreacted solid impurities, preventing them from clogging the pores of the inorganic porous material to be used later. Heating promotes the removal of volatile substances (such as hydrogen chloride gas) generated during leaching from the leachate, further reducing interference from impurities in precious metal recovery. Subsequent pH adjustment provides a stable chemical environment for the coordination adsorption of the thiol-modified material.

[0014] In step S3, muffle furnace calcination removes adsorbed organic matter, moisture, and volatile impurities from the pores of inorganic porous materials, opens up blocked pore channels, and significantly increases the specific surface area and pore volume of the material. Boiling and refluxing with hydrochloric acid can etch the surface of inorganic porous materials through acid etching, further enriching their pore structure, while exposing more active silanol groups (Si-OH) on their surface. This provides sufficient reaction sites for the subsequent grafting reaction of thiol-containing silane coupling agents, thereby improving the modification grafting rate and ensuring the functional group loading.

[0015] In step S4, the thiol-containing silane coupling agent undergoes hydrolysis in an ethanol-water mixed solvent, and then undergoes a dehydration condensation reaction with the silanol groups on the surface of the pretreated inorganic porous material to form stable Si-O-Si covalent bonds, firmly grafting the thiol groups (-SH) onto the surface and inner walls of the porous material. Since noble metal ions are soft acids and the sulfur atoms in the thiol groups possess lone pairs of electrons, making them soft bases, the two can form stable noble metal-thiol complexes through coordination bonds, achieving highly specific adsorption and enrichment of noble metal ions in the leachate.

[0016] In step S5, centrifugal separation is adopted after adsorption is completed. Centrifugation enhances the density difference between the solid and liquid phases, thereby achieving rapid and efficient separation between the coordinated solid phase (inorganic porous material that adsorbs and enriches precious metals) and the liquid phase (leaching residue containing other impurities). The efficiency is much higher than that of traditional plate and frame filtration, vacuum filtration and other methods.

[0017] In step S6, a desorbent is used to elute the noble metal from the coordination solid phase, thereby achieving the secondary removal of the noble metal.

[0018] Secondary enrichment simultaneously regenerates the thiol functional groups of the modified porous material, allowing it to be recycled for leaching and adsorption processes, significantly reducing material costs. Moreover, the concentration of noble metal ions in the desorption solution is much higher than that in the original leachate. At this point, further extraction and purification can significantly reduce the amount of extractant used, improve extraction and separation efficiency, and reduce secondary pollution caused by the volatilization of the organic phase. Finally, the noble metal ions are reduced to elemental form by a reducing agent, and high-purity noble metal powder is obtained through separation.

[0019] In one feasible implementation, in step S1, the leaching agent is a mixed solution of hydrochloric acid and sodium hypochlorite solution; the volume ratio of hydrochloric acid to sodium hypochlorite solution is (5-10):1; the concentration of hydrochloric acid is 5-8 mol / L; the mass fraction of sodium hypochlorite solution is 10-20%; the mass ratio of leaching agent to metal powder is (10-15):1; and the leaching conditions include: a leaching temperature of 45-60℃ and a leaching time of 6-8 hours.

[0020] Sodium hypochlorite decomposes under acidic conditions to generate chlorine gas and hypochlorous acid, which have strong oxidizing properties, oxidizing elemental noble metals into high-valence metal ions. At the same time, hydrochloric acid provides a high concentration of chloride ions, which can form stable soluble chloride complexes with the noble metal ions generated by oxidation. With optimized leaching conditions, efficient dissolution and leaching of noble metals can be achieved.

[0021] In one feasible implementation, in step S2, the initial leaching solution is heated at a temperature of 50-70°C for 1-2 hours; the pH of the waste circuit board leaching solution is 1-3.

[0022] Heating at 50-70℃ decomposes residual oxidizing substances in the initial leachate, eliminating their oxidative damage to subsequently introduced thiol functional groups; it also promotes the removal of volatile substances generated during leaching from the leachate, reducing potential interference from impurities in precious metal recovery. Furthermore, a strongly acidic environment with a pH of 1-3 inhibits the coordination of non-precious metal ions with thiol groups, further enhancing the adsorption selectivity of thiol groups for precious metal ions.

[0023] In one feasible implementation, in step S3, the inorganic porous material includes any one of diatomaceous earth, expanded perlite, and zeolite molecular sieve; the calcination conditions include: a calcination temperature of 500-600℃ and a calcination time of 2-4 hours; a hydrochloric acid concentration of 0.5-2 mol / L; a reflux time of 1-2 hours; and a mass ratio of the inorganic porous material to hydrochloric acid of 1:(10-15).

[0024] In one feasible implementation, in step S4, the mass ratio of the pretreated inorganic porous material to the ethanol-water mixed solvent is 1:(8-12); the mass ratio of ethanol to water in the ethanol-water mixed solvent is (70-80):(20-30); the pH is 3-5; and the mercapto-containing silane coupling agent includes any one of 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, and 3-mercaptopropylmethyldimethoxysilane.

[0025] The mass ratio of the mercapto-containing silane coupling agent to the pretreated inorganic porous material is (5-15):(85-95).

[0026] In one feasible implementation, the reaction conditions in S4 include: nitrogen protection, a reaction temperature of 60-80°C, a stirring rate of 300-500 rpm, and a reaction time of 5-8 h.

[0027] Nitrogen protection can isolate oxygen in the system, prevent thiol groups from being oxidized during the reaction, ensure that the grafted thiol functional groups have coordination activity, and retain the adsorption performance of the prepared modified inorganic porous material to the greatest extent.

[0028] In one feasible implementation, in step S5, the mass ratio of the modified inorganic porous material to the waste circuit board leachate is 1:(50-100), the stirring rate is 400-600 rpm, and the stirring time is 3-5 h.

[0029] In one feasible implementation, in S5, the centrifugal separation speed is 4000-6000 rpm, and the centrifugal separation time is 10-20 min.

[0030] By optimizing the process parameters, noble metal ions can be more fully enriched and adsorbed onto the modified inorganic porous material; efficient separation of the modified inorganic porous material loaded with noble metals from the liquid phase containing non-noble metal impurities is achieved, avoiding excessive loss of noble metals, while significantly shortening the separation time and improving production efficiency.

[0031] In one feasible implementation, in step S6, the desorbent is a 0.1-2 mol / L thiourea solution; the pH of the thiourea solution is 1-2; the desorption conditions include: a desorption temperature of 40-60℃ and a desorption time of 2-4 h; a centrifugation speed of 8000-10000 rpm and a centrifugation time of 5-15 min.

[0032] Thiourea has a strong coordination ability for noble metal ions. Under acidic conditions, the sulfur atoms in the thiourea molecule can form a more stable soluble noble metal-thiourea complex with noble metal ions than the mercapto-noble metal complex. Through coordination competition, the noble metal ions are desorbed from the mercapto groups on the surface of the modified inorganic porous material and enter the liquid phase to form a desorption liquid. At the same time, the mercapto functional groups on the surface of the modified inorganic porous material are reactivated, thus realizing the regeneration of the adsorption material.

[0033] In one feasible implementation, in step S6, the extractant includes either dibutylcarbidol or trioctylphosphine oxide; the reducing agent is formic acid; and the conditions for the reduction treatment include a reduction treatment temperature of 70-90°C and a reduction treatment time of 3-5 hours.

[0034] The extractant used in this application can form a stable extract with the noble metal-thiourea complex in the desorption solution through solvation, thus entering the organic phase. Other metal impurity ions, not noble metals, remain in the aqueous phase, achieving deep separation of noble metal ions from other impurities. This yields a solution containing high-purity noble metal ions.

[0035] This provides a foundation for the subsequent reduction and preparation of high-purity precious metal powders.

[0036] Moreover, the reducing agent used in this application can reduce noble metal ions from a high valence state to an elemental state. Under optimized process parameters, the reduction reaction is stable, without violent side reactions, and will not introduce difficult-to-remove impurity ions. The noble metal powder obtained by reduction has high purity.

[0037] In one feasible implementation, in step S6, the mass ratio of the desorbent to the coordinating solid phase is (5-20):1; the volume ratio of the extractant to the desorption liquid is 1:(1-10); and the mass ratio of the reducing agent to the extractant is...

[0038] (0.05-0.1): 1.

[0039] Beneficial technical effects:

[0040] This application utilizes high-temperature calcination of inorganic porous materials to remove adsorbed organic matter, moisture, and volatile impurities from their pores, thereby opening up blocked pore channels and significantly increasing their specific surface area and pore volume. Furthermore, the hydrochloric acid reflux pretreatment activation process further etches the surface of the inorganic porous material through acid etching, enriching its pore structure and exposing more active silanol groups (Si-OH) on the surface. This provides sufficient reaction sites for the subsequent grafting reaction of thiol-containing silane coupling agents, thereby increasing the modification and grafting rate, ensuring the loading of thiol functional groups, and firmly grafting thiol groups onto the surface and pore walls of the inorganic porous material. These thiol groups can then form stable noble metal-thiol complexes with noble metal ions through coordination bonds, achieving highly specific adsorption and enrichment of noble metal ions in the leachate. Subsequent desorption via thiourea removes the noble metal ions from the thiol groups on the surface of the modified inorganic porous material, forming a desorption solution in the liquid phase. Simultaneously, the thiol functional groups on the surface of the modified inorganic porous material are reactivated, achieving regeneration of the adsorbent material. Finally, a stable extractant is formed by the extractant and the noble metal-thiourea complex in the desorption solution, which then enters the organic phase. Other non-noble metal impurities remain in the aqueous phase, achieving deep separation of noble metal ions from other impurities and ultimately yielding high-purity noble metal powder. This method achieves efficient leaching, adsorption, separation, and purification of noble metals from waste circuit boards. The process is simple, efficient, energy-saving, and environmentally friendly, enabling the resource-based and harmless treatment of waste circuit boards, and is worthy of widespread application. Attached Figure Description

[0041] Figure 1 is a process flow diagram of a centrifugal extraction method for precious metals from waste circuit boards provided in this application. Detailed Implementation

[0042] To facilitate understanding of the content described in this application, the technical solutions described herein are further explained below with reference to specific embodiments; however, this application is not limited thereto. All equivalent transformations or simple substitutions made based on the substantive content of this application should fall within the protection scope of this application.

[0043] The singular forms of "for," "or," "a," and "any one" used in this application are...

[0044] The word “the” is intended to include the majority form unless the context clearly indicates otherwise.

[0045] The following will describe in detail, with reference to different embodiments, a centrifugal extraction method for precious metals in waste circuit boards provided in this application.

[0046] Example 1

[0047] A centrifugal extraction method for precious metals from waste circuit boards, as shown in Figure 1, includes the following steps:

[0048] S1. The waste circuit board is crushed and separated to obtain non-metallic powder and metallic powder. The metallic powder is put into a mixed solution of 5 mol / L hydrochloric acid and 10% sodium hypochlorite solution (the volume ratio of hydrochloric acid to sodium hypochlorite solution is 5:1, and the mass of the mixed solution is 10 times that of the metallic powder) for leaching treatment. The leaching temperature is 45℃ and the leaching time is 6 hours to obtain a preliminary leachate.

[0049] S2. The preliminary leachate is filtered to remove impurities and then heated at 50°C for 1 hour to obtain waste circuit board leachate. The pH of the leachate is then adjusted to 1 using 1 mol / L NaOH solution.

[0050] S3. The diatomaceous earth is calcined in a muffle furnace at a temperature of 500℃ for 2 hours. After cooling to room temperature, it is added to 0.5 mol / L hydrochloric acid and boiled under reflux for 1 hour. Then it is washed with water until neutral and vacuum dried to obtain pretreated diatomaceous earth. The mass ratio of diatomaceous earth to hydrochloric acid is 1:10.

[0051] S4. The pretreated diatomaceous earth was dispersed in an ethanol-water mixed solvent (the mass ratio of ethanol to water was 70:30). The pH of the system was adjusted to 3 using 0.5 mol / L hydrochloric acid. Then, 3-mercaptopropyltrimethoxysilane was added, and the reaction was carried out for 5 hours under nitrogen protection, at a temperature of 60℃ and a stirring speed of 300 rpm. The mixture was then filtered and vacuum dried to obtain modified diatomaceous earth. The mass ratio of 3-mercaptopropyltrimethoxysilane to pretreated diatomaceous earth was 5:95, and the mass ratio of pretreated diatomaceous earth to the ethanol-water mixed solvent was 1:8.

[0052] S5. Add the modified diatomaceous earth to the waste circuit board leaching solution and stir at 400 rpm for 3 hours to obtain a coordination mixture. Then centrifuge it at 4000 rpm for 10 minutes to separate the coordination solid phase and liquid phase. The mass ratio of the modified diatomaceous earth to the waste circuit board leaching solution is 1:50.

[0053] S6. The coordinated solid phase was added to a 0.1 mol / L thiourea solution with pH 1 (adjusted using 2 mol / L sulfuric acid). Desorption was carried out at 40℃ for 2 h, followed by centrifugation at 8000 rpm for 5 min to obtain the desorbed solution and regenerated modified diatomaceous earth. Dibutylcarbitol was added to the desorbed solution, and after standing separation, the extract was obtained. Formic acid was added to the extract, and reduction was carried out at 70℃ for 3 h. After filtration separation, the noble metal powder was obtained. The mass ratio of thiourea solution to coordinated solid phase was 5:1; the volume ratio of dibutylcarbitol to desorbed solution was 1:1; and the mass ratio of formic acid to extract was 0.05:1.

[0054] A centrifugal extraction method for precious metals from waste circuit boards, as shown in Figure 1, includes the following steps:

[0055] S1. The waste circuit board is crushed and separated to obtain non-metallic powder and metallic powder. The metallic powder is put into a mixed solution of hydrochloric acid with a concentration of 8 mol / L and sodium hypochlorite solution with a mass fraction of 20% (the volume ratio of hydrochloric acid to sodium hypochlorite solution is 10:1, and the mass of the mixed solution is 15 times that of the metallic powder) for leaching treatment. The leaching temperature is 60℃ and the leaching time is 8h to obtain a preliminary leachate.

[0056] S2. The preliminary leachate is filtered to remove impurities and then heated at 70℃ for 2 hours to obtain waste circuit board leachate. The pH of the leachate is then adjusted to 3 using 1 mol / L NaOH solution.

[0057] S3. The expanded perlite was calcined in a muffle furnace at a temperature of 600℃ for 4 hours. After cooling to room temperature, it was added to 2 mol / L hydrochloric acid and boiled under reflux for 2 hours. Then it was washed with water until neutral and vacuum dried to obtain pretreated expanded perlite. The mass ratio of expanded perlite to hydrochloric acid was 1:15.

[0058] S4. Disperse the pretreated expanded perlite in an ethanol-water mixed solvent (ethanol to water mass ratio of 80:20), adjust the pH of the system to 5 using 0.5 mol / L hydrochloric acid, then add 3-mercaptopropyltriethoxysilane, and react for 8 hours under nitrogen protection, at 80℃ and a stirring speed of 500 rpm. Afterward, filter and vacuum dry to obtain modified expanded perlite; wherein the mass ratio of 3-mercaptopropyltriethoxysilane to pretreated expanded perlite is 15:85; the mass ratio of pretreated expanded perlite to ethanol-water mixed solvent is...

[0059] The ratio is 1:12;

[0060] S5. Add the modified expanded perlite to the waste circuit board leaching solution and stir at 600 rpm for 5 hours to obtain a coordination mixture. Then centrifuge it at 6000 rpm for 20 minutes to separate the coordination solid phase and liquid phase. The mass ratio of the modified expanded perlite to the waste circuit board leaching solution is 1:100.

[0061] S6. The coordinated solid phase was added to a 2 mol / L thiourea solution with a pH of 2 (adjusted using 2 mol / L sulfuric acid). Desorption was carried out at 60°C for 4 h, followed by centrifugation at 10000 rpm for 15 min to obtain the desorbed solution and regenerated modified expanded perlite. Dibutylcarbitol was added to the desorbed solution, and after standing separation, the extract was obtained. Formic acid was then added to the extract, and reduction was carried out at 90°C for 5 h, followed by separation to obtain the noble metal powder. The mass ratio of thiourea solution to coordinated solid phase was 20:1; the volume ratio of dibutylcarbitol to desorbed solution was 1:10; and the mass ratio of formic acid to extract was 0.1:1.

[0062] Example 3

[0063] A centrifugal extraction method for precious metals from waste circuit boards, as shown in Figure 1, includes the following steps:

[0064] S1. The waste circuit board is crushed and separated to obtain non-metallic powder and metallic powder. The metallic powder is then added to a mixed solution of 6.5 mol / L hydrochloric acid and 15% sodium hypochlorite solution (hydrochloric acid and sodium hypochlorite solution).

[0065] A leaching treatment was carried out using a sodium chlorate solution with a volume ratio of 7:1 and a mixed solution with a mass of 12 times that of the metal powder. The leaching temperature was 50℃ and the leaching time was 7h to obtain a preliminary leachate.

[0066] S2. The preliminary leachate is filtered to remove impurities and then heated at 60℃ for 1.5 hours to obtain waste circuit board leachate. The pH of the leachate is then adjusted to 2 using 1 mol / L NaOH solution.

[0067] S3. The zeolite molecular sieve was calcined in a muffle furnace at a temperature of 550℃ for 3 hours. After cooling to room temperature, it was added to 1.2 mol / L hydrochloric acid and boiled under reflux for 1.5 hours. Then, it was washed with water until neutral and vacuum dried to obtain the pretreated zeolite molecular sieve. The mass ratio of the zeolite molecular sieve to hydrochloric acid was 1:12.

[0068] S4. The pretreated zeolite molecular sieve was dispersed in an ethanol-water mixed solvent (the mass ratio of ethanol to water was 75:25). The pH of the system was adjusted to 4 using 0.5 mol / L hydrochloric acid. Then, 3-mercaptopropylmethyldimethoxysilane was added, and the reaction was carried out for 6.5 h under nitrogen protection, at 70 °C and a stirring speed of 400 rpm. After filtration and vacuum drying, the modified zeolite molecular sieve was obtained. The mass ratio of 3-mercaptopropylmethyldimethoxysilane to the pretreated zeolite molecular sieve was 10:90. The pretreated zeolite molecular sieve and the ethanol-water mixed solvent...

[0069] The mass ratio of the agents is 1:10;

[0070] S5. The modified zeolite molecular sieve was added to the waste circuit board leaching solution and stirred at 500 rpm for 4 hours to obtain a coordination mixture. Then, it was centrifuged at 5000 rpm for 15 minutes to separate the coordination solid phase and liquid phase. The mass ratio of the modified zeolite molecular sieve to the waste circuit board leaching solution was 1:75.

[0071] S6. The coordinated solid phase was added to a 1 mol / L thiourea solution with a pH of 1.5 (adjusted with 2 mol / L sulfuric acid), and desorbed at 50 °C for 3 h. Then, it was centrifuged again at 9000 rpm for 10 min to obtain the desorbed solution and the regenerated modified zeolite molecular sieve. Trioctylphosphine oxide was added to the desorbed solution, and after standing separation, the extract was obtained. Formic acid was added to the extract, and the mixture was reduced at 80 °C for 4 h and then separated to obtain the noble metal powder. The mass ratio of thiourea solution to coordinated solid phase was 12.5:1; the volume ratio of trioctylphosphine oxide to desorbed solution was 1:5; and the mass ratio of formic acid to extract was 0.08:1.

[0072] Example 4

[0073] A centrifugal extraction method for precious metals from waste circuit boards, as shown in Figure 1, includes the following steps:

[0074] S1. The waste circuit board is crushed and separated to obtain non-metallic powder and metallic powder. The metallic powder is put into a mixed solution of hydrochloric acid with a concentration of 8 mol / L and sodium hypochlorite solution with a mass fraction of 10% (the volume ratio of hydrochloric acid to sodium hypochlorite solution is 6:1, and the mass of the mixed solution is 13 times that of the metallic powder) for leaching treatment. The leaching temperature is 45℃ and the leaching time is 8h to obtain a preliminary leachate.

[0075] S2. Filter the preliminary leachate to remove impurities and heat it to 70℃ for [heating time].

[0076] The process takes 1 hour to obtain the leachate from the waste circuit board, and its pH is adjusted to 1 using a 1 mol / L NaOH solution.

[0077] S3. The diatomaceous earth is calcined in a muffle furnace at a temperature of 600℃ for 2 hours. After cooling to room temperature, it is added to hydrochloric acid with a concentration of 2 mol / L and boiled under reflux for 1 hour. Then it is washed with water until neutral and vacuum dried to obtain pretreated diatomaceous earth. The mass ratio of diatomaceous earth to hydrochloric acid is 1:14.

[0078] S4. The pretreated diatomaceous earth was dispersed in an ethanol-water mixed solvent (the mass ratio of ethanol to water was 80:20). The pH of the system was adjusted to 3 using 0.5 mol / L hydrochloric acid. Then, 3-mercaptopropyltriethoxysilane was added, and the reaction was carried out for 5 hours under nitrogen protection, at 80℃ and a stirring speed of 300 rpm. The mixture was then filtered and vacuum dried to obtain modified diatomaceous earth. The mass ratio of 3-mercaptopropyltriethoxysilane to pretreated diatomaceous earth was 15:85, and the mass ratio of pretreated diatomaceous earth to the ethanol-water mixed solvent was 1:11.

[0079] S5. Add the modified diatomaceous earth to the waste circuit board leaching solution and stir at 600 rpm for 3 hours to obtain a coordination mixture. Then centrifuge it at 6000 rpm for 10 minutes to separate the coordination solid phase and liquid phase. The mass ratio of the modified diatomaceous earth to the waste circuit board leaching solution is 1:50.

[0080] S6. The coordinated solid phase was added to a 0.5 mol / L thiourea solution with a pH of 2 (adjusted using 2 mol / L sulfuric acid). Desorption was carried out at 55 °C for 2 h, followed by centrifugation at 9500 rpm for 5 min to obtain the desorbed solution and regenerated modified diatomaceous earth. Dibutylcarbitol was added to the desorbed solution, and after standing separation, the extract was obtained. Formic acid was then added to the extract, and reduction was carried out at 90 °C for 3 h, followed by separation to obtain the noble metal powder. The mass ratio of thiourea solution to coordinated solid phase was 20:1; the volume ratio of dibutylcarbitol to desorbed solution was 1:3; and the mass ratio of formic acid to extract was 0.06:1.

[0081] Example 5

[0082] A centrifugal extraction method for precious metals from waste circuit boards, as shown in Figure 1, includes the following steps:

[0083] S1. The waste circuit board is crushed and separated to obtain non-metallic powder and metallic powder. The metallic powder is put into a mixed solution of hydrochloric acid with a concentration of 5 mol / L and sodium hypochlorite solution with a mass fraction of 16% (the volume ratio of hydrochloric acid to sodium hypochlorite solution is 8:1, and the mass of the mixed solution is 11 times that of the metallic powder) for leaching treatment. The leaching temperature is 55℃ and the leaching time is 6h to obtain a preliminary leachate.

[0084] S2. The initial leachate is filtered to remove impurities and then heated at 55℃ for 2 hours to obtain waste circuit board leachate. The pH of the leachate is then adjusted to 2 using 1 mol / L NaOH solution.

[0085] S3. The expanded perlite was calcined in a muffle furnace at a temperature of 580℃ for 4 hours. After cooling to room temperature, it was added to 0.5 mol / L hydrochloric acid and boiled under reflux for 2 hours. It was then washed with water until neutral and vacuum dried to obtain pretreated expanded perlite. The mass ratio of expanded perlite to hydrochloric acid was 1:13.

[0086] S4. Disperse the pretreated expanded perlite in an ethanol-water mixed solvent (ethanol to water mass ratio of 76:24), adjust the pH of the system to 4.5 using 0.5 mol / L hydrochloric acid, then add 3-mercaptopropylmethyldimethoxysilane, and react for 7.5 h under nitrogen protection, at 65℃ and a stirring speed of 450 rpm. Afterward, filter and vacuum dry to obtain modified expanded perlite; wherein the mass ratio of 3-mercaptopropylmethyldimethoxysilane to pretreated expanded perlite is 12:88; the pretreated expanded perlite and ethanol-water mixture...

[0087] The mass ratio of the mixed solvents is 1:9;

[0088] S5. Add the modified expanded perlite to the waste circuit board leaching solution and stir at 450 rpm for 5 hours to obtain a coordination mixture. Then centrifuge it at 4500 rpm for 16 minutes to separate the coordination solid phase and liquid phase. The mass ratio of the modified expanded perlite to the waste circuit board leaching solution is 1:60.

[0089] S6. The coordinated solid phase was added to a 1.5 mol / L thiourea solution with pH 1 (adjusted with 2 mol / L sulfuric acid), and desorbed at 45 °C for 3.5 h. Then, it was centrifuged again at 8500 rpm for 12 min to obtain the desorbed solution and the regenerated modified expanded perlite. Trioctylphosphine oxide was added to the desorbed solution, and after standing separation, the extract was obtained. Formic acid was added to the extract, and the solution was reduced at 70 °C for 5 h and then separated to obtain the noble metal powder. The mass ratio of thiourea solution to coordinated solid phase was 12:1; the volume ratio of trioctylphosphine oxide to desorbed solution was 1:8; and the mass ratio of formic acid to extract was 0.07:1.

[0090] Example 6

[0091] A centrifugal extraction method for precious metals from waste circuit boards, as shown in Figure 1, includes the following steps:

[0092] S1. The waste circuit board is crushed and separated to obtain non-metallic powder and metallic powder. The metallic powder is put into a mixed solution of hydrochloric acid with a concentration of 7 mol / L and sodium hypochlorite solution with a mass fraction of 14% (the volume ratio of hydrochloric acid to sodium hypochlorite solution is 9:1, and the mass of the mixed solution is 14 times that of the metallic powder) for leaching treatment. The leaching temperature is 55℃ and the leaching time is 6.5h to obtain a preliminary leachate.

[0093] S2. The preliminary leachate is filtered to remove impurities and then heated at 65℃ for 1.2 hours to obtain waste circuit board leachate. The pH of the leachate is then adjusted to 2.5 using 1 mol / L NaOH solution.

[0094] S3. The zeolite molecular sieve was calcined in a muffle furnace at a temperature of 580℃ for 2.5 h. After cooling to room temperature, it was added to 1.5 mol / L hydrochloric acid and boiled under reflux for 1.8 h. Then, it was washed with water until neutral and vacuum dried to obtain the pretreated zeolite molecular sieve. The mass ratio of the zeolite molecular sieve to hydrochloric acid was 1:15.

[0095] S4. The pretreated zeolite molecular sieve was dispersed in an ethanol-water mixed solvent (the mass ratio of ethanol to water was 78:22). The pH of the system was adjusted to 4.5 using 0.5 mol / L hydrochloric acid. Then, 3-mercaptopropyltrimethoxysilane was added, and the reaction was carried out for 7 hours under nitrogen protection, at a temperature of 75℃ and a stirring speed of 450 rpm.

[0096] After filtration and vacuum drying, modified zeolite molecular sieves were obtained; the mass ratio of 3-mercaptopropyltrimethoxysilane to the pretreated zeolite molecular sieve was 8:92; the mass ratio of the pretreated zeolite molecular sieve to the ethanol-water mixed solvent was [missing information].

[0097] The ratio is 1:12;

[0098] S5. The modified zeolite molecular sieve was added to the waste circuit board leaching solution and stirred at 550 rpm for 3.5 h to obtain a coordination mixture. Then, it was centrifuged at 5500 rpm for 12 min to separate the coordination solid phase and liquid phase. The mass ratio of the modified zeolite molecular sieve to the waste circuit board leaching solution was 1:80.

[0099] S6. The coordinated solid phase was added to a 1.5 mol / L thiourea solution with a pH of 2 (adjusted using 2 mol / L sulfuric acid). Desorption was carried out at 55 °C for 2.5 h, followed by centrifugation at 9000 rpm for 8 min to obtain the desorbed solution and the regenerated modified zeolite molecular sieve. Trioctylphosphine oxide was added to the desorbed solution, and after standing separation, the extract was obtained. Formic acid was added to the extract, and reduction was carried out at 85 °C for 3.5 h, followed by separation to obtain the noble metal powder. The mass ratio of thiourea solution to coordinated solid phase was 15:1; the volume ratio of trioctylphosphine oxide to desorbed solution was 1:6; and the mass ratio of formic acid to extract was 0.08:1.

[0100] Comparative Example 1

[0101] This comparative example provides a centrifugal extraction method for precious metals from waste circuit boards. The difference between this method and Example 3 is that the pretreated inorganic porous material was not modified with 3-mercaptopropylmethyldimethoxysilane. Other process parameters and operating steps are exactly the same as in Example 3.

[0102] Comparative Example 2

[0103] This comparative example provides a centrifugal extraction method for precious metals from waste circuit boards. The difference from Example 3 is that centrifugation is not used in steps S5 and S6; instead, ordinary filtration is used. Other process parameters and operating steps are exactly the same as in Example 3.

[0104] Comparative Example 3

[0105] This comparative example provides a centrifugal extraction method for precious metals from waste circuit boards. The difference between this method and Example 3 is that the inorganic porous material was not subjected to muffle furnace roasting and hydrochloric acid boiling reflux. Other process parameters and operating steps are exactly the same as in Example 3.

[0106] The effectiveness of the centrifugal extraction method for precious metals from waste circuit boards provided in this application is demonstrated by separating gold from the precious metal powders obtained in each embodiment and each comparative example, and testing their purity and recovery rate. The test results of the purity and recovery rate of gold in the precious metal powders obtained in each embodiment and comparative example are statistically shown in Table 1.

[0107] Table 1. Test results of the precious metal powders prepared in the examples and comparative examples.

[0108]

[0109] As shown in Table 1, the purity and recovery rate of the precious metal powders prepared in Examples 1 to 6 are better than those prepared in Comparative Examples 1 to 3.

[0110] The main reason is that in Examples 1 to 6, the inorganic porous material was calcined at high temperature to remove the organic matter, moisture, and volatile impurities adsorbed in its pores, thus opening up the blocked pore channels and significantly increasing its specific surface area and pore volume. Moreover, the hydrochloric acid reflux pretreatment activation process further etched the surface of the inorganic porous material through acid etching, enriching its pore structure and exposing more active silanol groups (Si-OH) on its surface. This provides sufficient reaction sites for the subsequent grafting reaction of thiol-containing silane coupling agents, thereby increasing the modification grafting rate, ensuring the loading of thiol functional groups, and firmly grafting thiol groups onto the surface and pore walls of the inorganic porous material. In this way, stable noble metal-thiol complexes can be formed with noble metal ions through coordination bonds, achieving highly specific adsorption and enrichment of noble metal ions in the leachate. Subsequently, through thiourea desorption, noble metal ions are desorbed from the thiol groups on the surface of the modified inorganic porous material and enter the liquid phase to form a desorption solution. Simultaneously, the thiol functional groups on the surface of the modified inorganic porous material are reactivated, achieving regeneration of the adsorbent material. Finally, a stable extractant is formed by the extractant and the noble metal-thiourea complex in the desorption solution, entering the organic phase. Other non-noble metal impurity ions remain in the aqueous phase, achieving deep separation of noble metal ions from other impurities, ultimately yielding high-purity noble metal powder.

[0111] In contrast, the pretreated inorganic porous material in Comparative Example 1 was not modified with 3-mercaptopropylmethyldimethoxysilane, and therefore could not form a stable noble metal-thiol complex with noble metal ions through coordination bonds, thus failing to achieve highly specific adsorption and enrichment of noble metal ions in the leachate, resulting in a different noble metal powder.

[0112] The recovery rate and purity of gold in the body were the lowest.

[0113] In Comparative Example 2, centrifugation was not used for separation. Ordinary filtration methods suffer from filter cake entrainment and filter loss, resulting in a decrease in the gold recovery rate and purity of the final precious metal powder.

[0114] In Comparative Example 3, the inorganic porous material zeolite molecular sieve was not calcined in a muffle furnace and boiled and refluxed in hydrochloric acid. Therefore, it was impossible to etch the surface of the inorganic porous material through acid etching to enrich its pore structure. At the same time, it was also impossible to expose more active silanol groups (Si-OH) on its surface, making it difficult to provide sufficient reaction sites for the subsequent grafting reaction of mercapto-containing silane coupling agents. As a result, the recovery rate and purity of gold in the final precious metal powder were significantly reduced.

[0115] The above results demonstrate and describe the basic principles and main features of this application, as well as its advantages.

[0116] Those skilled in the art should understand that this application is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of this application. Various changes and modifications can be made to this application without departing from the spirit and scope thereof, and all such changes and modifications fall within the scope of this application as claimed. The scope of protection of this application is defined by the equivalents of the appended claims.

Claims

1. A method for centrifugal extraction of precious metals from waste circuit boards, characterized in that, Includes the following steps: S1. The waste circuit board is crushed and separated to obtain non-metallic powder and metallic powder. The metallic powder is put into the leaching agent for leaching treatment to obtain a preliminary leachate. S2. The preliminary leachate is filtered to remove impurities and then heated to obtain waste circuit board leachate, and its pH is adjusted. S3. The inorganic porous material is calcined, cooled to room temperature, added to hydrochloric acid and boiled under reflux, then washed with water until neutral and vacuum dried to obtain the pretreated inorganic porous material. S4. Disperse the pretreated inorganic porous material in an ethanol-water mixed solvent, adjust the pH of the system, then add a silane coupling agent containing mercapto groups, react under preset conditions, then filter and vacuum dry to obtain the modified inorganic porous material. S5. The modified inorganic porous material is added to the leaching solution of waste circuit boards and stirred to obtain a complex mixture. Then, it is centrifuged to separate the complex solid phase and liquid phase. S6. Add the coordination solid phase to the desorbent, centrifuge again after desorption treatment to obtain the desorbed liquid and the regenerated modified inorganic porous material, add the extractant to the desorbed liquid, let it stand and separate to obtain the extract, add the reducing agent to the extract, reduce and separate to obtain the precious metal powder.

2. The centrifugal extraction method for precious metals from waste circuit boards according to claim 1, characterized in that, In step S1, the leaching agent is a mixed solution of hydrochloric acid and sodium hypochlorite solution; the volume ratio of hydrochloric acid to sodium hypochlorite solution is (5-10):1; the concentration of hydrochloric acid is 5-8 mol / L; the mass fraction of sodium hypochlorite solution is 10-20%; the mass ratio of leaching agent to metal powder is (10-15):1; the leaching conditions include: a leaching temperature of 45-60℃ and a leaching time of 6-8 h.

3. The centrifugal extraction method for precious metals from waste circuit boards according to claim 1, characterized in that, In step S2, the initial leaching solution is heated at a temperature of 50-70°C for 1-2 hours; the pH of the waste circuit board leaching solution is 1-3.

4. The centrifugal extraction method for precious metals from waste circuit boards according to claim 1, characterized in that, In step S3, the inorganic porous material includes any one of diatomaceous earth, expanded perlite, and zeolite molecular sieve; the calcination conditions include: a calcination temperature of 500-600℃ and a calcination time of 2-4 hours; and the concentration of hydrochloric acid is 0.5-2 mol / L. The reflux time is 1-2 hours; the mass ratio of the inorganic porous material to hydrochloric acid is 1:(10-15).

5. The centrifugal extraction method for precious metals from waste circuit boards according to claim 1, characterized in that, In step S4, the mass ratio of the pretreated inorganic porous material to the ethanol-water mixed solvent is 1:(8-12); the mass ratio of ethanol to water in the ethanol-water mixed solvent is (70-80):(20-30); the pH is 3-5; the mercapto-containing silane coupling agent includes any one of 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, and 3-mercaptopropylmethyldimethoxysilane; the mass ratio of the mercapto-containing silane coupling agent to the pretreated inorganic porous material is (5-15):(85-95).

6. The centrifugal extraction method for precious metals from waste circuit boards according to claim 1, characterized in that, In step S4, the reaction conditions include: nitrogen protection, a reaction temperature of 60-80℃, a stirring rate of 300-500 rpm, and a reaction time of 5-8 h.

7. The centrifugal extraction method for precious metals from waste circuit boards according to claim 1, characterized in that, In step S5, the mass ratio of the modified inorganic porous material to the waste circuit board leachate is 1:(50-100), the stirring speed is 400-600 rpm, and the stirring time is 3-5 h.

8. The centrifugal extraction method for precious metals from waste circuit boards according to claim 1, characterized in that, In step S5, the centrifugal separation speed is 4000-6000 rpm, and the centrifugal separation time is 10-20 min.

9. The centrifugal extraction method for precious metals from waste circuit boards according to claim 1, characterized in that, In S6, the desorbent is a 0.1-2 mol / L thiourea solution; The pH of the thiourea solution is 1-2; the desorption treatment conditions include: a desorption treatment temperature of 40-60℃ and a desorption treatment time of 2-4 hours. The centrifugation speed is 8000-10000 rpm, and the centrifugation time is 5-15 min.

10. The centrifugal extraction method for precious metals from waste circuit boards according to claim 1, characterized in that, In step S6, the extractant includes either dibutylcarbidol or trioctylphosphine oxide; the reducing agent is formic acid; and the conditions for the reduction treatment include a reduction treatment temperature of 70-90℃ and a reduction treatment time of 3-5h.

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