Multilayer modified magnetic nanoparticles, preparation method thereof and method for extracting precious metal from electronic waste

Abstract

The invention discloses a multi-layer modified magnetic nanoparticle, a preparation method thereof and a method for extracting precious metal from electronic waste, and belongs to the technical field of precious metal extraction.The multi-layer modified magnetic nanoparticle comprises the following structures that a core layer is composed of iron oxide nanoparticles and provides magnetism; the inner layer is composed of silicon dioxide and coats the surface of the core layer, so that the chemical stability and the biocompatibility of the particles are improved; the outer layer is composed of polyethylene glycol-sulfydryl, coats the surface of the inner layer, provides specific adsorption sites and is used for adsorbing precious metal nanoparticles. According to the method, the precious metal can be effectively extracted, interference of other metal ions on extraction of the precious metal is avoided in the extraction process, and gold, silver nanoparticles and platinum nanoparticles can be independently separated.

Description

Technical Field

[0001] This invention relates to the field of precious metal extraction technology, specifically to a multilayer modified magnetic nanoparticle and its preparation method, and a method for extracting precious metals from electronic waste. Background Technology

[0002] There are several methods for extracting precious metals from electronic waste, including physical methods: Mechanical separation: This involves separating the metallic and non-metallic components of electronic waste using physical methods such as crushing, screening, and magnetic separation. For example, a magnetic separator can separate iron-containing metals. Gravity separation: This method utilizes the difference in settling velocity of materials with different densities in a gravitational field, separating precious metals using gravity separation equipment (such as shaking tables and spiral chutes). This method is particularly effective for high-density metals such as gold and silver. However, it is less effective at separating fine particles, making it difficult to completely separate precious metals and accurately separate specific precious metals, potentially resulting in the contamination of other high-density non-precious metals. Chemical leaching: This method uses chemical reagents (such as aqua regia and cyanide) to dissolve precious metals from electronic waste. For example, aqua regia can dissolve gold and platinum, while cyanide can dissolve gold. The leached solution can then be used to recover precious metals through ion exchange, precipitation, or other methods. Electrochemical methods: This method separates precious metals from electronic waste through electrochemical reactions. For example, electrolysis can deposit gold from a gold-containing solution. Bioleaching: This method uses the metabolic activity of microorganisms (such as thiobacilli) to dissolve metals from electronic waste. It is environmentally friendly and relatively inexpensive, but slower and suitable for processing low-grade electronic waste.

[0003] Traditional chemical leaching methods (such as using aqua regia or cyanide) are typically non-selective, dissolving multiple metals and resulting in low extraction efficiency for precious metals, requiring complex subsequent separation steps. Aqua regia is a strong oxidizing acid composed of concentrated hydrochloric acid and concentrated nitric acid in a 3:1 volume ratio. Dissolution mechanism: The nitric acid in aqua regia has strong oxidizing properties, oxidizing precious metals into soluble salts, while the hydrochloric acid provides chloride ions, forming soluble coordination compounds with the precious metal ions. For example, gold is oxidized to Au in aqua regia. 3+Then, it reacts with chloride ions to form soluble tetrachloroauric acid. Non-selective: Aqua regia can dissolve not only precious metals (such as gold and platinum) but also many other metals (such as copper and silver). This is because the strong oxidizing and acidic properties of aqua regia allow it to react with various metals to form soluble salts. Result: When treating electronic waste, aqua regia dissolves multiple metals simultaneously, resulting in a diverse range of metal ions in the solution, increasing the difficulty of subsequent separation. Separation methods used include precipitation, ion exchange, and solvent extraction. Each method has its applicable scope and advantages and disadvantages, requiring selection based on specific circumstances. Precipitation: Specific metal ions are precipitated by adding a precipitant, but this method has poor selectivity and easily introduces impurities. Ion exchange: Utilizing the selective adsorption of different metal ions by ion exchange resins, but the selection and regeneration of the resin require precise operation. Studies have shown that introducing thiol groups onto the surface of magnetic nanoparticles can adsorb silver ions, but the adsorption capacity is limited. Furthermore, the adsorption of silver ions is also affected by competition from other ions in the solution. Summary of the Invention

[0004] In order to overcome the shortcomings of the prior art, one of the objectives of the present invention is to provide a multilayer modified magnetic nanoparticle that has chemical stability and can adsorb noble metal ions or noble metal nanoparticles.

[0005] The second objective of this invention is to provide a method for preparing multilayer modified magnetic nanoparticles, which has simple steps.

[0006] The third objective of this invention is to provide a method for extracting precious metals from electronic waste. This method can effectively extract precious metals and avoids interference from other metal ions during the extraction process. It can also separate gold and silver nanoparticles and platinum nanoparticles separately.

[0007] One of the objectives of this invention is achieved through the following technical solution:

[0008] A multilayer modified magnetic nanoparticle comprising the following structure:

[0009] Core layer: composed of iron oxide nanoparticles, providing magnetism;

[0010] Inner layer: Composed of silicon dioxide, it coats the surface of the core layer to improve the chemical stability and biocompatibility of the particles;

[0011] Outer layer: Composed of polyethylene glycol-thiol groups, it coats the surface of the inner layer and provides specific adsorption sites for adsorbing noble metal nanoparticles.

[0012] Furthermore, the thickness of the inner layer is 1-10 nm; the thickness of the outer layer is 1-5 nm.

[0013] The second objective of this invention is achieved by the following technical solution:

[0014] A method for preparing multilayer modified magnetic nanoparticles includes the following steps:

[0015] S1. Preparation of the core layer: The iron oxide nanoparticles were synthesized by a co-precipitation method;

[0016] S2, Inner Coating Layer: The iron oxide nanoparticles are dispersed in a mixed solution of ethanol and water, and tetraethyl orthosilicate (TEOS) and ammonia are added dropwise. The mixture is stirred and reacted for several hours to form a silica coating layer, thus obtaining silica-coated iron oxide nanoparticles.

[0017] S3. Introducing amino functional groups: The silicon dioxide-coated iron oxide nanoparticles are dispersed in ethanol, and 3-aminopropyltriethoxysilane (APTES) is added dropwise. The mixture is stirred for several hours to form amino functional groups, thus obtaining iron oxide nanoparticles with amino functional groups.

[0018] S4. Coating the outer layer: The iron oxide nanoparticles with amino functional groups are dispersed in ethanol, and polyethylene glycol-thiol is added dropwise. The mixture is stirred and reacted for several hours to form a thiol-modified outer layer.

[0019] S5. Centrifugation and washing: Remove unreacted reagents by centrifugation and washing. Centrifuge at 5,000-10,000 rpm for 10-30 minutes to obtain the multilayer modified magnetic nanoparticles.

[0020] The third objective of this invention is achieved by the following technical solution:

[0021] A method for extracting precious metals from electronic waste includes the following steps:

[0022] S1. Pre-processing steps: Remove large pieces of plastic and metal casing, and crush and screen the electronic waste;

[0023] S1. Magnetic field-assisted leaching step: Under the action of an intermittent magnetic field, chemical reagents are used to leach electronic waste, so that precious metals dissolve into the solution to obtain precious metal leachate.

[0024] S2, S21, Phase transfer catalyst addition step: Add mercaptoacetic acid (HSCH2COOH) or mercaptopropionic acid (HSCH2CH2COOH) to the noble metal leachate as a phase transfer catalyst;

[0025] S22, Organic solvent addition step: Add an appropriate amount of toluene to the above mixed solution in step S21 to provide an organic phase environment for the noble metal salt;

[0026] S23. Phase transfer step: By stirring or ultrasonic treatment, the precious metal salts containing gold and silver are transferred from the aqueous phase to the toluene phase, while the precious metal salts containing platinum remain in the aqueous phase.

[0027] S24. Organic phase separation step: Separate the organic phase (toluene phase) from the aqueous phase using a separatory funnel to form a toluene solution containing gold and silver precious metal salts and an aqueous solution containing platinum.

[0028] S25. Reduction reaction step: Mix the toluene solution of the gold and silver precious metal salts with the aqueous solution of sodium hydride (NaH) and stir thoroughly. Thioalkane or aminoalkane is present at the same time. Sodium hydride reduces the gold and silver precious metal salts to gold and silver nanoparticles. The thioalkane or aminoalkane is adsorbed on the surface of the gold and silver nanoparticles to prevent aggregation.

[0029] S26. Add trioctylamine (TOA) as an extractant to the aqueous solution containing platinum;

[0030] S27. Phase transfer step: The platinum complex is transferred from the aqueous phase to the toluene phase by stirring or ultrasonic treatment;

[0031] S28. Organic phase separation step: Separate the organic phase (toluene phase) from the aqueous phase using a separatory funnel to form a toluene solution containing platinum nanoparticles.

[0032] S29. Reduction reaction step: Mix a toluene solution containing platinum with an aqueous solution of sodium hydride (NaH) and stir thoroughly. Thioalkane or aminoalkane is present at the same time. Sodium hydride reduces the platinum complex to platinum nanoparticles. The thioalkane or aminoalkane is adsorbed on the surface of the platinum nanoparticles to prevent aggregation.

[0033] S3, Magnetic nanoparticle processing steps: Magnetic nanoparticles with specific thiol ligands on their surface are added to the toluene phase containing gold and silver nanoparticles in step S25 and the toluene phase containing platinum nanoparticles in step S29, respectively, and the magnetic nanoparticles are separated from the toluene phase by an external magnetic field.

[0034] S4. Precious Metal Recovery Steps: After separation, desorption and surface regeneration treatment are performed to recover gold and silver nanoparticles, platinum nanoparticles, and magnetic nanoparticles from the magnetic nanoparticles. Further, the pore size of the special functional layer is between 0.1 and 1.0 nanometers.

[0035] Furthermore, the chemical reagent is aqua regia, cyanide, or a combination thereof.

[0036] Furthermore, the frequency range of the intermittent magnetic field is from 10 Hz to 100 Hz.

[0037] Furthermore, in the magnetic field-assisted leaching step, the intensity of the intermittent magnetic field ranges from 100 mT to 1 T.

[0038] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0039] (1) The present invention provides a multilayer modified magnetic nanoparticle, wherein the inner layer is composed of silicon dioxide and is coated on the surface of the core layer to improve the chemical stability and biocompatibility of the particle; the outer layer is composed of polyethylene glycol-thiol and is coated on the surface of the inner layer to provide specific adsorption sites for adsorbing noble metal nanoparticles. It has chemical stability and can adsorb noble metal ions or noble metal nanoparticles.

[0040] (2) The present invention provides a method for extracting precious metals from electronic waste. Magnetic nanoparticles modified with specific thiol ligands can specifically adsorb precious metal nanoparticles, resulting in a more stable and rapid adsorption process. This significantly improves the adsorption performance. The precious metal leachate is treated in step S2 to convert the precious metal ion state into a nanoparticle state, avoiding interference from other metal ions and allowing for the separate separation of gold, silver, and platinum nanoparticles. Detailed Implementation

[0041] The present invention will now be further described in conjunction with specific embodiments. It should be noted that, without conflict, the embodiments or technical features described below can be arbitrarily combined to form new embodiments.

[0042] Example

[0043] This embodiment provides a multilayer modified magnetic nanoparticle, comprising the following structure:

[0044] Core layer: composed of iron oxide nanoparticles, providing magnetism;

[0045] Inner layer: Composed of silicon dioxide, it coats the surface of the core layer to improve the chemical stability and biocompatibility of the particles. The thickness of the inner layer is 1-10 nm.

[0046] Outer layer: Composed of polyethylene glycol-thiol groups, it coats the surface of the inner layer and provides specific adsorption sites for adsorbing noble metal nanoparticles. The thickness of the outer layer is 1-5 nm.

[0047] This embodiment provides a method for preparing multilayer modified magnetic nanoparticles, including the following steps:

[0048] S1. Preparation of the core layer: Iron oxide nanoparticles were synthesized by co-precipitation method;

[0049] S2, Inner Coating Layer: Iron oxide nanoparticles are dispersed in a mixed solution of ethanol and water, and tetraethyl orthosilicate (TEOS) and ammonia are added dropwise. The mixture is stirred and reacted for several hours to form a silica coating layer, thus obtaining silica-coated iron oxide nanoparticles.

[0050] S3. Introduction of amino functional groups: Disperse silica-coated iron oxide nanoparticles in ethanol, add 3-aminopropyltriethoxysilane (APTES) dropwise, stir for several hours to form amino functional groups, and obtain iron oxide nanoparticles with amino functional groups.

[0051] S4. Coating the outer layer: Disperse iron oxide nanoparticles with amino functional groups in ethanol, add polyethylene glycol-thiol dropwise, stir and react for several hours to form a thiol-modified outer layer;

[0052] S5. Centrifugation and washing: Remove unreacted reagents by centrifugation and washing. Centrifuge at 5,000-10,000 rpm for 10-30 minutes to obtain multilayer modified magnetic nanoparticles.

[0053] In this embodiment, the inner layer (silicon dioxide) enhances the chemical stability and biocompatibility of the magnetic nanoparticles, preventing them from being oxidized or corroded in complex environments.

[0054] Outer layer (thiol-modified polymer): provides specific adsorption sites, enhances the adsorption capacity for noble metal ions or nanoparticles, and reduces interference from other ions.

[0055] Highly efficient adsorption: Thiol-modified polymers provide abundant adsorption sites, which can effectively adsorb noble metal ions or nanoparticles.

[0056] Rapid separation: Magnetic nanoparticles are superparamagnetic and can be rapidly separated from the solution under the action of an external magnetic field, greatly shortening the separation time.

[0057] Both gold (Au) and silver (Ag) react with sulfur, especially bulk silver, which often undergoes a "tanning" phenomenon due to the formation of an Ag₂S surface layer. For organothiols, attaching them to the surface of nanoparticles is particularly effective because there is an "o" type bond, where sulfur provides the electron density and the metal atom is the acceptor, and an "n" type bond, where metal electrons are partially delocalized in the molecular orbitals formed by the filling d atoms of the metal and the vacant d atoms of sulfur.

[0058] This embodiment also provides a method for extracting precious metals from electronic waste, including the following steps:

[0059] S1. Pre-processing steps: Remove large pieces of plastic and metal casing, and crush and screen the electronic waste;

[0060] S1. Magnetic field-assisted leaching step: Under the action of an intermittent magnetic field, aqua regia is used to leach electronic waste, so that precious metals are dissolved in the solution to obtain a precious metal leachate; the frequency range of the intermittent magnetic field is 10Hz to 100Hz, and the intensity range of the intermittent magnetic field in the magnetic field-assisted leaching step is 100mT to 1T.

[0061] S2, S21, Phase transfer catalyst addition steps: Add mercaptoacetic acid (HSCH2COOH) or mercaptopropionic acid (HSCH2CH2COOH) to the noble metal leaching solution as a phase transfer catalyst;

[0062] S22, Organic solvent addition step: Add an appropriate amount of toluene to the above mixed solution in step S21 to provide an organic phase environment for the noble metal salt;

[0063] S23. Phase transfer step: By stirring or ultrasonic treatment, the precious metal salts containing gold and silver are transferred from the aqueous phase to the toluene phase, while the precious metal salts containing platinum remain in the aqueous phase.

[0064] S24. Organic phase separation step: Separate the organic phase (toluene phase) from the aqueous phase using a separatory funnel to form a toluene solution containing gold and silver precious metal salts and an aqueous solution containing platinum.

[0065] S25. Reduction reaction steps: Mix the toluene solution of gold and silver precious metal salts with the aqueous solution of sodium hydride (NaH) and stir thoroughly. Thioalkane or aminoalkane is present at the same time. Sodium hydride reduces the gold and silver precious metal salts to gold and silver nanoparticles. Thioalkane or aminoalkane is adsorbed on the surface of gold and silver nanoparticles to prevent aggregation.

[0066] S26. Add trioctylamine (TOA) as an extractant to an aqueous solution containing platinum;

[0067] S27. Phase transfer step: The platinum complex is transferred from the aqueous phase to the toluene phase by stirring or ultrasonic treatment;

[0068] S28. Organic phase separation step: Separate the organic phase (toluene phase) from the aqueous phase using a separatory funnel to form a toluene solution containing platinum nanoparticles.

[0069] S29. Reduction reaction steps: Mix a toluene solution containing platinum with an aqueous solution of sodium hydride (NaH) and stir thoroughly. Thioalkane or aminoalkane is also present. Sodium hydride reduces the platinum complex to platinum nanoparticles. Thioalkane or aminoalkane is adsorbed on the surface of platinum nanoparticles to prevent aggregation.

[0070] S3, Magnetic nanoparticle processing steps: Magnetic nanoparticles with specific thiol ligands on their surface are added to the toluene phase containing gold and silver nanoparticles in step S25 and the toluene phase containing platinum nanoparticles in step S29, respectively, and the magnetic nanoparticles are separated from the toluene phase by an external magnetic field.

[0071] S4. Precious Metal Recovery Steps: After separation, desorption and surface regeneration treatment are performed to recover gold and silver nanoparticles, platinum nanoparticles, and magnetic nanoparticles from the magnetic nanoparticles. Furthermore, the pore size of the special functional layer is between 0.1 and 1.0 nanometers.

[0072] Intermittent magnetic fields enhance leaching efficiency: In chemical leaching processes, the use of intermittent magnetic fields can enhance solution mixing and mass transfer efficiency, thereby increasing leaching rate and efficiency. For example, by setting an intermittent magnetic field in the leaching reactor, the dissolution of precious metals can be promoted.

[0073] Selection of magnetic materials: Choose suitable magnetic materials, such as superparamagnetic iron oxide nanoparticles (SPIONs). These materials can quickly align under the influence of an external magnetic field and are not prone to aggregation.

[0074] Reusable

[0075] Regeneration capability: Through simple chemical treatment, adsorbed metal ions or nanoparticles can be removed, restoring the adsorption capacity of magnetic nanoparticles and enabling multiple cycles of use.

[0076] Trioctylamine, mercaptoacetic acid, and mercaptopropionic acid act as a bridge between the aqueous and organic phases, helping noble metal salts to transfer from the aqueous phase to the organic phase. Stirring or ultrasonic treatment helps to accelerate the phase transfer process and ensure that the noble metal salts are fully transferred to the toluene phase.

[0077] When a toluene solution is mixed with an aqueous solution of sodium hydride and stirred thoroughly, thioalkane or aminoalkane are present. These ligands will adsorb onto the surface of the metal nanoparticles, playing a stabilizing role and preventing them from agglomerating.

[0078] Sodium hydride (NaH): A strong reducing agent used to reduce metal salts. Sodium hydride reduces metal salts to metal nanoparticles.

[0079] Thiol: An organic molecule containing a thiol group (-SH), used to stabilize noble metal nanoparticles. Amine: An organic molecule containing an amino group (-NH2), also used to stabilize metal nanoparticles.

[0080] 1. Trioctylamine (TOA)

[0081] Chemical formula: (C8H) 17 )3N

[0082] Structure: TOA is a tertiary amine extractant consisting of a hydrophobic tail composed of three octyl groups and a hydrophilic head composed of a nitrogen atom.

[0083] Function: TOA extracts chloride anions of metals through anion exchange mechanism, exhibiting high selectivity for platinum (Pt).

[0084] Applications: TOA is commonly used to extract platinum chloride anions (such as PtCl6). 2 Extraction was performed under acidic conditions (e.g., 2-4 mol / L HCl), and the platinum extract was N(C8H) 17 )3H2PtCl6

[0085] 2. Thioglycolic acid (HSCH2COOH)

[0086] Chemical formula: HSCH2COOH Structure: Thioacetic acid is an organic acid containing thiol (-SH) and carboxyl (-COOH) groups.

[0087] Function: Thioglycolic acid can form stable complexes with metal ions (such as gold and silver). The thiol group (-SH) has a strong binding ability with metal ions, which can effectively stabilize metal nanoparticles.

[0088] Applications: In the synthesis of metal nanoparticles, mercaptoacetic acid is commonly used as a stabilizer to prevent the aggregation of metal nanoparticles. It can also act as a reducing agent to help reduce metal ions into metal nanoparticles.

[0089] 3. Mercaptopropionic acid (HSCH2CH2COOH) Chemical formula: HSCH2CH2COOH Structure: Mercaptopropionic acid is an organic acid containing a mercapto group (-SH) and a carboxyl group (-COOH), similar to mercaptoacetic acid, but with an additional methylene group (-CH2-).

[0090] Function: Mercaptopropionic acid can also form stable complexes with metal ions, exhibiting a stabilizing effect similar to that of mercaptoacetic acid.

[0091] Applications: In the synthesis of metal nanoparticles, mercaptopropionic acid is also commonly used as a stabilizer to prevent the aggregation of metal nanoparticles. It can also act as a reducing agent to help reduce metal ions into metal nanoparticles.

[0092] Phase transfer: In the phase transfer step, copper ions (Cu) 2+ It typically does not form stable complexes with mercaptoacetic acid or mercaptopropionic acid, and therefore does not transfer into the organic phase.

[0093] Extraction: In the platinum extraction step, copper ions (Cu) 2+It does not form a stable extractable with trioctylamine (TOA) and therefore will not be extracted into the organic phase.

[0094] The difference between gold ions and gold nanoparticles

[0095] Adsorption capacity

[0096] Gold ions: Thiol-modified magnetic nanoparticles have a strong adsorption capacity for gold ions, but the reaction conditions need to be optimized to improve the adsorption efficiency.

[0097] Gold nanoparticles: Thiol-modified magnetic nanoparticles also have a strong adsorption capacity for gold nanoparticles, and the adsorption process is more stable.

[0098] Adsorption kinetics

[0099] Gold ions: The adsorption process of gold ions is usually relatively fast, but it is greatly affected by competition from other ions in the solution.

[0100] Gold nanoparticles: The adsorption process of gold nanoparticles is usually fast and less affected by competition from other ions in the solution.

[0101] Adsorption stability

[0102] Gold ions: Gold ions have high adsorption stability, but surface modification and reaction conditions need to be optimized to maintain adsorption capacity.

[0103] Gold nanoparticles: Gold nanoparticles have high adsorption stability, and thiol-modified magnetic nanoparticles can effectively prevent the aggregation of gold nanoparticles.

[0104] The above embodiments are merely preferred embodiments of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention shall fall within the scope of protection claimed by the present invention.

Claims

1. A multilayered decorated magnetic nanoparticle, characterized in that, The core layer is composed of iron oxide nanoparticles; The inner layer is composed of silicon dioxide, coated on the surface of the core layer; The outer layer is composed of polyethylene glycol-thiol, coated on the surface of the inner layer. The thickness of the inner layer is 1-10 nm; the thickness of the outer layer is 1-5 nm.

2. The multi-layered decorated magnetic nanoparticle of claim 1, wherein, The steps include:

3. A method of preparing a multilayered decorated magnetic nanoparticle, characterized in that, S1, preparing the core layer: synthesizing the iron oxide nanoparticles by co-precipitation method; S2, coating the inner layer: dispersing the iron oxide nanoparticles in a mixed solution of ethanol and water, adding tetraethyl orthosilicate (TEOS) and ammonia water drop by drop, stirring for several hours to form a silicon dioxide coating layer, and obtaining silicon dioxide-coated iron oxide nanoparticles; S3, introducing amino functional groups: dispersing the silicon dioxide-coated iron oxide nanoparticles in ethanol, adding 3-aminopropyl triethoxysilane (APTES) drop by drop, stirring for several hours to form amino functional groups, and obtaining iron oxide nanoparticles with amino functional groups; S4, coating the outer layer: dispersing the iron oxide nanoparticles with amino functional groups in ethanol, adding polyethylene glycol-thiol drop by drop, stirring for several hours to form a thiol-modified outer layer; S5, centrifugation and washing: removing unreacted reagents by centrifugation and washing steps, the centrifugation speed is 5,000-10,000 rpm, and the centrifugation time is 10-30 minutes, to obtain the multi-layer modified magnetic nanoparticles. The steps include:

4. A method of extracting precious metals from electronic waste, characterized in that, S1, pretreatment step: removing large pieces of plastic and metal shell, crushing and screening electronic waste; S1, magnetic field assisted leaching step: using chemical reagents to leach electronic waste under the action of intermittent magnetic field, so that noble metals are dissolved into the solution to obtain noble metal leaching solution; S2, S21, phase transfer catalyst addition step: adding mercaptoacetic acid (HSCH2COOH) or mercaptopropionic acid (HSCH2CH2COOH) as a phase transfer catalyst to the noble metal leaching solution; S22, organic solvent addition step: adding an appropriate amount of toluene to the above mixed solution of step S21 to provide an organic phase environment for noble metal salts; S23, phase transfer step: by stirring or ultrasonic treatment, the noble metal salts containing gold and silver are transferred from the aqueous phase to the toluene phase, and the noble metal salt containing platinum remains in the aqueous phase; S24, organic phase separation step: by separating funnel, the organic phase (toluene phase) is separated from the aqueous phase to form a toluene solution containing noble metal salts of gold and silver and an aqueous solution containing platinum; S25, reduction reaction step: mixing the toluene solution of noble metal salts of gold and silver with an aqueous solution of sodium hydride (NaH) and stirring thoroughly, while sulfur alkane or amino alkane is present, sodium hydride reduces the noble metal salts of gold and silver to gold and silver nanoparticles, and the sulfur alkane or amino alkane is adsorbed on the surface of the gold and silver nanoparticles to prevent aggregation; S26, adding trioctylamine (TOA) as an extractant to the aqueous solution containing platinum; S27, phase transfer step: by stirring or ultrasonic treatment, the platinum complex is transferred from the aqueous phase to the toluene phase; ​ S28, organic phase separation step: the organic phase (toluene phase) is separated from the aqueous phase by a separatory funnel to form a toluene solution containing platinum nanoparticles; S29, reduction reaction step: the toluene solution containing platinum is mixed with an aqueous solution of sodium hydride (NaH) and stirred thoroughly in the presence of a thioalkane or aminoalkane, the sodium hydride reduces the platinum complex to platinum nanoparticles, and the thioalkane or aminoalkane is adsorbed on the surface of the platinum nanoparticles to prevent aggregation; S3, magnetic nanoparticle treatment step: magnetic nanoparticles modified with specific mercapto ligands are added to the toluene phase containing gold and silver nanoparticles in step S25 and to the toluene phase containing platinum nanoparticles in step S29, respectively, and the magnetic nanoparticles are separated from the toluene phase by an external magnetic field; S4, noble metal recovery step: after separation, desorption, and surface regeneration treatment, gold and silver nanoparticles, platinum nanoparticles, and magnetic nanoparticles are recovered from the magnetic nanoparticles.

5. A method of extracting precious metals from electronic waste as claimed in claim 4 wherein, The chemical reagent is aqua regia, cyanide, or a combination thereof.

6. A method of extracting precious metals from electronic waste as claimed in claim 4 wherein, The frequency of the intermittent magnetic field ranges from 10 Hz to 100 Hz.

7. A method of extracting precious metals from electronic waste as claimed in claim 4 wherein, In the magnetic field assisted leaching step, the strength of the intermittent magnetic field ranges from 100 mT to 1 T. In the magnetic field assisted leaching step, the strength of the intermittent magnetic field ranges from 100 mT to 1 T.