Microwave pyrolysis recovery method of waste circuit board
By combining microwave pyrolysis with modified microwave absorbers, the problems of dust pollution and toxic gas generation in waste circuit board recycling have been solved, achieving efficient and environmentally friendly metal recycling and resource utilization.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- WUZHOU SHENGFA ENVIRONMENTAL PROTECTION TECHNOLOGY CO LTD
- Filing Date
- 2026-01-29
- Publication Date
- 2026-05-19
AI Technical Summary
Existing technologies for recycling waste circuit boards suffer from severe dust pollution, high energy consumption, and low efficiency, especially during mechanical crushing and metal separation, which can easily generate toxic and harmful gases.
Microwave pyrolysis is used to separate organic non-metallic components from waste circuit boards. Microwave absorbers are used to selectively heat the non-metallic components and pyrolyze them under a protective atmosphere to separate the metallic components. Porous carbon-based microwave absorbers are used to improve absorption efficiency and durability through surface silanization and nano-oxide modification.
It effectively reduces dust pollution, decreases the generation of toxic and harmful gases, improves metal recovery rate and resource utilization, and inhibits the generation of toxic gases such as dioxins, thus improving recycling efficiency and environmental friendliness.
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Abstract
Description
Technical Field
[0001] This invention relates to the field of waste recycling technology, and in particular to a microwave pyrolysis recycling method for waste circuit boards. Background Technology
[0002] With the rapid pace of electronic product upgrades, the number of discarded circuit boards among obsolete electronic products is also gradually increasing. These discarded circuit boards possess both resource and environmental attributes, with a total metal content as high as 30%-50%, a copper content of around 20%, and a grade of precious metals such as gold and silver that is 30-50 times higher than that of primary ores, earning them the reputation of "urban mines." In addition, discarded circuit boards also contain toxic and harmful substances such as lead, mercury, and polybrominated biphenyls. If they are directly landfilled or incinerated, heavy metals will seep into the soil and water bodies, and pollutants such as dioxins may also be generated during the incineration process.
[0003] Currently, the recycling of metal components from waste circuit boards typically involves separating the metal and non-metal components first. This can be done by mechanically crushing the circuit boards and then using methods such as gravity separation, electrostatic separation, or airflow separation to separate the metal and non-metal components. However, mechanical crushing of waste circuit boards easily generates dust pollution and is energy-intensive and inefficient. Therefore, there is an urgent need to provide a solution to address these issues. Summary of the Invention
[0004] The purpose of this invention is to provide a microwave pyrolysis recycling method for waste circuit boards. The method utilizes microwave pyrolysis to separate the organic non-metallic components in the waste circuit boards, thereby rapidly enriching the metallic components. This method is beneficial for reducing dust pollution and inhibiting the generation and emission of toxic pollutants.
[0005] The present invention provides a microwave pyrolysis recycling method for waste circuit boards, comprising: peeling off electronic components from the waste circuit board and crushing it to obtain recycled powder; mixing the recycled powder with a microwave absorber to obtain mixed powder; pyrolyzing the mixed powder at a temperature of 400℃-600℃, a microwave power of 600W-800W, and a protective atmosphere to separate metal-enriched material; grinding the metal-enriched material and separating the metal components under the action of a leaching agent.
[0006] Optionally, the preparation method of the microwave absorber includes: surface silane activation of porous carbon to obtain an active matrix; wetting and adsorbing the active matrix in a mixed solution containing iron salt and tetraethyl orthosilicate, stirring and reacting in an alkaline environment and separating to obtain a composite matrix; calcining the composite matrix under an inert atmosphere and then cooling to obtain a composite intermediate; mixing the composite intermediate with nano zinc oxide and nano calcium oxide, ball milling and granulating to obtain the microwave absorber.
[0007] Optionally, porous carbon is mixed in an ethanol solution containing 3-aminopropyltriethoxysilane, and then stirred and refluxed in a water bath at 70°C-80°C for 2-4 hours before being separated and dried to obtain the active matrix.
[0008] Optionally, the mass ratio of the porous carbon to the 3-aminopropyltriethoxysilane is 1:(0.1-0.2).
[0009] Optionally, the porous carbon is preheated at 100℃-120℃ for 1-2 hours.
[0010] Optionally, the specific surface area of the porous carbon is 1500 m². 2 / g-2000m 2 / g.
[0011] Optionally, the mass ratio of the active matrix to the iron ions in the mixed solution is 1:(0.1-0.4).
[0012] Optionally, the mass ratio of the active matrix to the tetraethyl orthosilicate is 1:(0.3-0.6).
[0013] Optionally, the solid-liquid ratio of the active matrix to the mixed solution is 0.06 g / mL to 0.1 g / mL.
[0014] Optionally, ammonia water is added dropwise to the mixed solution containing the active matrix and the mixture is stirred to react.
[0015] Optionally, the active matrix may be ultrasonically impregnated in the mixed solution for 10-30 minutes.
[0016] Optionally, the inert gas in the inert atmosphere may include one of nitrogen, argon, and helium.
[0017] Optionally, the pressure of the inert atmosphere is 0.1 MPa-0.2 MPa.
[0018] Optionally, the composite matrix is calcined at 700℃-850℃.
[0019] Optionally, the flow rate of the inert gas in the inert atmosphere is 200 mL / min to 500 mL / min.
[0020] Optionally, the composite matrix may be calcined for 1.5-2.5 hours.
[0021] Optionally, the mass ratio of the composite intermediate to the nano zinc oxide is (10-20):1.
[0022] Optionally, the mass ratio of the composite intermediate to the nano-calcium oxide is (20-30):1.
[0023] Optionally, the average particle size of the nano zinc oxide and the nano calcium oxide is independently between 30 nm and 100 nm.
[0024] Optionally, 3mm-10mm zirconia balls are used as grinding balls during mixed ball milling, with a ball-to-material ratio of (3-5):1, and ball milling for 2-4 hours.
[0025] Optionally, the microwave absorbent is pre-irradiated in a protective atmosphere with a microwave power of 300W-400W before being mixed with the recycled powder to obtain a mixed powder.
[0026] Optionally, the average particle size of the recycled powder and the microwave absorber are independently 0.1 mm to 1 mm.
[0027] Optionally, the mass ratio of the recycled powder to the microwave absorber is 1:(0.1-0.25).
[0028] Optionally, the electronic components can be stripped after the waste circuit board is preheated at 200℃-250℃.
[0029] Optionally, the electronic components can be stripped and recycled.
[0030] Optionally, the electronic components are stripped from the waste circuit board, then sheared, crushed, and cryogenically pulverized.
[0031] Optionally, the leaching agent is a sulfuric acid-ferric chloride mixture, wherein the mixture comprises 1.5 mol / L-3 mol / L of sulfuric acid and 0.2 mol / L-2 mol / L of ferric chloride.
[0032] Optionally, the mass-to-volume ratio of the mixed powder to the microwave pyrolysis chamber during microwave pyrolysis is 0.1 g / mL to 0.4 g / mL. Detailed Implementation
[0033] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0034] This invention provides a microwave pyrolysis recycling method for waste circuit boards, comprising the following steps: S1. After peeling off the electronic components from the waste circuit board, crush it to obtain recycled powder. S2. Mix the recycled powder with the microwave absorber to obtain a mixed powder; S3. The mixed powder is microwave pyrolyzed at a temperature of 400℃-600℃, a microwave power of 600W-800W, and a protective atmosphere to separate the metal-enriched material. S4. After grinding the metal-enriched material, the metal components are separated under the action of a leaching agent.
[0035] In fact, by first increasing the specific surface area of waste circuit board particles through physical crushing and then mixing the recycled powder with microwave absorbers, the problem of uneven microwave absorption of the waste circuit boards can be improved. During microwave pyrolysis, the non-metallic components in the microwave absorbers and recycled powder are selectively and rapidly heated, thereby decomposing into volatile oil and gas in a protective atmosphere, while the metallic components in the recycled powder remain in a solid state, thus achieving the dissociation of metallic and non-metallic components. The metallic components are then obtained by leaching the metal-enriched material.
[0036] In fact, the microwave pyrolysis recovery method provided by this invention rapidly pyrolyzes the non-metallic components (organic matter) in the recovered powder through microwave selective heating, which can recover combustible gases, thus improving the recovery rate and resource utilization rate of waste circuit boards. At the same time, the dissociation in a protective atmosphere can effectively suppress the generation of toxic and harmful gases such as dioxins and furans, and fix the bromine in the waste circuit boards in the dissociated residual tar or coke and mix it in the metal enrichment material.
[0037] In some embodiments, the method for preparing the microwave absorber includes: Z1. Surface silane activation of porous carbon yields an active matrix; Z2. After the active matrix is immersed and adsorbed in a mixed solution containing iron salt and tetraethyl orthosilicate, it is stirred and reacted in an alkaline environment and then separated to obtain the composite matrix. Z3. The composite matrix is calcined under an inert atmosphere and then cooled to obtain a composite intermediate. Z4. The composite intermediate is mixed with nano zinc oxide and nano calcium oxide, ball-milled and granulated to obtain a microwave absorber.
[0038] In fact, by surface silanizing porous carbon, bonding sites can be constructed on the porous carbon framework, thereby promoting the uniform co-precipitation of iron salts and tetraethyl orthosilicate on the surface of the active matrix framework. Calcination under an inert atmosphere promotes the in-situ generation of nano-iron oxide and silicon carbide on the surface of the composite matrix, thereby improving the absorption efficiency and thermal conversion capacity of the absorbent during microwave pyrolysis. At the same time, the introduction of nano-zinc oxide and nano-calcium oxide on the surface of the composite intermediate not only improves the durability of the microwave absorbent but also degrades the generation of toxic and harmful gases such as dioxins during pyrolysis.
[0039] In some embodiments, in step Z1, porous carbon can be mixed in an ethanol solution containing dissolved 3-aminopropyltriethoxysilane, and then stirred and refluxed in a water bath at 70°C-80°C for 2-4 hours before separation and drying to obtain the active matrix. In fact, surface treatment of porous carbon in a silane solution can improve the reactivity of the porous carbon surface, thereby promoting the uniform bonding of iron salts and tetraethyl orthosilicate on the surface and improving the bonding stability.
[0040] In some embodiments, during the surface silane treatment of porous carbon in step Z1, the mass ratio of porous carbon to 3-aminopropyltriethoxysilane in the silane solution is 1:(0.1-0.2). Alternatively, porous carbon can be added to a silane solution (an ethanol solution dissolving 3-aminopropyltriethoxysilane) at a solid-liquid ratio of 0.06 g / mL-0.1 g / mL and subjected to ultrasonic treatment to promote the full penetration of the silane solution into the porous carbon, thereby achieving uniform silane treatment on the surface of the porous carbon framework.
[0041] In some embodiments, before performing surface silane treatment on the porous carbon in step Z1, the porous carbon can be pre-treated at 100℃-120℃ for 1-2 hours. In fact, heat treatment of porous carbon can effectively improve its dryness, thereby facilitating the full wetting of the porous carbon by the silane solution. Simultaneously, the heat treatment process can further increase the porosity of the porous carbon, thus increasing its specific surface area. Specifically, the specific surface area of the porous carbon used can be 1500 m². 2 / g-2000m 2 / g.
[0042] In some embodiments, the mass ratio of the active matrix to the iron ions and tetraethyl orthosilicate in the mixed solution in step Z2 can be 1:(0.1-0.4):(0.3-0.6). In fact, by controlling the amount of iron ions and tetraethyl orthosilicate in the mixed solution, the loading of iron oxide and silicon carbide on the porous carbon surface can be adjusted. Specifically, the solid-liquid ratio of the active matrix to the mixed solution can be 0.06 g / mL-0.1 g / mL, and the active matrix can be dispersed in the mixed solution and immersed for 10-30 minutes under ultrasonic conditions to eliminate microbubbles and pores attached to the porous carbon.
[0043] In some embodiments, in step Z2, ammonia solution can be added dropwise to the mixed solution containing the active matrix while stirring. In practice, the dropwise addition of ammonia solution alters the liquid environment to alkaline, and in this alkaline environment, iron ions and silicon-containing compounds co-precipitate, thereby forming a composite precipitate on the surface of the active matrix. Specifically, the dropwise addition rate of ammonia solution can be controlled at 50 drops / min-60 drops / min. By slowly adding ammonia solution and stirring during the addition process, the pH of the mixed solution changes uniformly, thereby improving the uniformity of the co-precipitation.
[0044] In some embodiments, the inert gas used in step Z3 includes one of nitrogen, argon, and helium, and the pressure of the inert atmosphere can be 0.1 MPa-0.2 MPa, and the flow rate of the inert gas can be 200 mL / min-500 mL / min. In practice, the composite matrix can be calcined at 700℃-850℃ for 1.5 h-2.5 h. Specifically, calcination in an inert atmosphere can improve the stability of the composite precipitation on the porous carbon surface.
[0045] In some embodiments, the mass ratio of the composite intermediate to nano-zinc oxide in step Z4 is (10-20):1, and the mass ratio of the composite intermediate to nano-calcium oxide is (20-30):1. Furthermore, the average particle size of the nano-zinc oxide and nano-calcium oxide used is independently 30nm-100nm. Mechanical ball milling promotes the uniform adhesion of nano-zinc oxide and nano-calcium oxide to the surface of the composite intermediate, forming a stable protective layer to improve the structural stability of the microwave absorber. Further, during the mixing and ball milling, 3mm-10mm zirconium oxide balls can be used as milling balls, and ball milling is performed for 2-4 hours in a ball mill jar with a ball-to-material ratio of (3-5):1.
[0046] In some embodiments, before performing step S2, the microwave absorbent can be pretreated in a protective atmosphere with a microwave power of 300W-400W before being mixed with the recycled powder to obtain a mixed powder. In practice, when the microwave absorbent completes a microwave pyrolysis operation on a waste circuit board, the zinc oxide on the surface of the microwave absorbent reacts with the bromine produced during the pyrolysis to form zinc bromide. Therefore, the microwave absorbent that has completed one microwave pyrolysis operation can be reduced in a water vapor environment at 400℃-600℃, thereby recycling the microwave absorbent and improving its overall service life.
[0047] In some embodiments, during step S2, the average particle size of the recovered powder and the microwave absorber are independently 0.1 mm to 1 mm, and the mass ratio of the recovered powder to the microwave absorber is 1:(0.1-0.25). This facilitates uniform mixing of the recovered powder and the microwave absorber, thereby contributing to more efficient pyrolysis of non-metallic components in waste circuit boards.
[0048] In some embodiments, the waste circuit board can be preheated at 200°C-250°C before the electronic components are peeled off during step S1. In fact, the high temperature melts the metal solder between the waste circuit board and the electronic components, facilitating the peeling off of the electronic components. Furthermore, high-value and intact electronic components can be recovered after peeling. Specifically, in step S1, the waste circuit board can be subjected to vibration or mechanical scraping to peel off the electronic components from its surface.
[0049] In some embodiments, the waste circuit boards from which electronic components are removed in step S1 are sheared, crushed, and cryogenically pulverized. In practice, shearing and crushing the waste circuit boards initially reduces their size, and then, during cryogenic pulverization, the brittle change between metallic and non-metallic components is utilized to pulverize the non-metallic components and separate them from the metallic components. Simultaneously, cryogenic pulverization avoids the pyrolysis of non-metallic components during high-temperature processes, preventing the generation of toxic and harmful gases.
[0050] In some embodiments, during step S3, the mixed powder can be filled into the pyrolysis chamber of the microwave reactor at a mass-to-volume ratio of 0.1 g / mL to 0.4 g / mL. Furthermore, the leaching agent used in step S4 is a sulfuric acid-ferric chloride mixture, comprising 1.5 mol / L to 3 mol / L of sulfuric acid and 0.2 mol / L to 2 mol / L of ferric chloride.
[0051] Preparation Example 1 Example 1 provides a method for preparing a microwave absorber, comprising the following steps: Z1. Porous carbon (purchased from Jiangsu Chengyang Activated Carbon Co., Ltd., CY-P03, specific surface area greater than 1500 m²) 2 / g) was added to an ethanol solution containing 3-aminopropyltriethoxysilane (KH550, the mass ratio of porous carbon to 3-aminopropyltriethoxysilane is 1:0.2) at a solid-liquid ratio of 0.08 g / mL and ultrasonically dispersed for 15 min to obtain a dispersion. The dispersion was stirred and refluxed in a water bath at 70°C for 3 h, then filtered and dried with hot air to obtain the active matrix. Z2. The active matrix was added to a mixed solution containing ferric nitrate and tetraethyl orthosilicate at a solid-liquid ratio of 0.08 g / mL and ultrasonically dispersed for 15 min. Then, 15% ammonia solution was added dropwise at a rate of 60 drops / min and stirred to react. The mixture was then filtered, separated, and dried to obtain the composite matrix. Z3. The composite matrix was transferred into the furnace chamber of an atmosphere furnace. After the atmosphere furnace was purged three times with argon, the temperature was increased to 800℃ at a heating rate of 10℃ / min and held for calcination for 2 hours. After cooling to room temperature with the furnace, the composite intermediate was obtained. The flow rate of argon in the atmosphere furnace was controlled to be 300mL / min and the pressure was 0.1MPa. Z4. The composite intermediate, nano zinc oxide, and nano calcium oxide were added into a ball mill jar at a mass ratio of 20:20:1. Zirconia balls of 5 mm were used as milling balls, and the ball-to-material ratio was controlled at 5:1. The mixture was milled for 3 hours and then granulated in a granulator to obtain a microwave absorber with an average particle size of 0.5 mm.
[0052] Preparation Example 2 Example 2 of this preparation provides a method for preparing a microwave absorber, including the following steps: Z1. Porous carbon (purchased from Jiangsu Chengyang Activated Carbon Co., Ltd., CY-P03, specific surface area greater than 1500 m²) 2 / g) was added to an ethanol solution containing 3-aminopropyltriethoxysilane (KH550, the mass ratio of porous carbon to 3-aminopropyltriethoxysilane is 1:0.2) at a solid-liquid ratio of 0.08 g / mL and ultrasonically dispersed for 15 min to obtain a dispersion. The dispersion was stirred and refluxed in a water bath at 70°C for 3 h, then filtered and dried with hot air to obtain the active matrix. Z2. The active matrix was added to a mixed solution containing tetraethyl orthosilicate at a solid-liquid ratio of 0.08 g / mL (mass ratio of active matrix to tetraethyl orthosilicate is 1:0.5) and ultrasonically dispersed for 15 min. Then, 15% ammonia water was added dropwise at a rate of 60 drops / min and stirred to react. The mixture was then filtered and dried to obtain the composite matrix. Z3. The composite matrix was transferred into the furnace chamber of an atmosphere furnace. After the atmosphere furnace was purged three times with argon, the temperature was increased to 800℃ at a heating rate of 10℃ / min and held for calcination for 2 hours. After cooling to room temperature with the furnace, the composite intermediate was obtained. The flow rate of argon in the atmosphere furnace was controlled to be 300mL / min and the pressure was 0.1MPa. Z4. The composite intermediate, nano zinc oxide, and nano calcium oxide were added into a ball mill jar at a mass ratio of 20:20:1. Zirconia balls of 5 mm were used as milling balls, and the ball-to-material ratio was controlled at 5:1. The mixture was milled for 3 hours and then granulated in a granulator to obtain a microwave absorber with an average particle size of 0.5 mm.
[0053] Preparation Example 3 Example 3 of this preparation provides a method for preparing a microwave absorber, including the following steps: Z1. Porous carbon (purchased from Jiangsu Chengyang Activated Carbon Co., Ltd., CY-P03, specific surface area greater than 1500 m²) 2 / g) was added to an ethanol solution containing 3-aminopropyltriethoxysilane (KH550, the mass ratio of porous carbon to 3-aminopropyltriethoxysilane is 1:0.2) at a solid-liquid ratio of 0.08 g / mL and ultrasonically dispersed for 15 min to obtain a dispersion. The dispersion was stirred and refluxed in a water bath at 70°C for 3 h, then filtered and dried with hot air to obtain the active matrix. Z2. The active matrix was added to a mixed solution containing ferric nitrate at a solid-liquid ratio of 0.08 g / mL (mass ratio of active matrix to iron ions of 1:0.3) and ultrasonically dispersed for 15 min. Then, 15% ammonia water was added dropwise at a rate of 60 drops / min and stirred to react. The mixture was then filtered and dried to obtain the composite matrix. Z3. The composite matrix was transferred into the furnace chamber of an atmosphere furnace. After the atmosphere furnace was purged three times with argon, the temperature was increased to 800℃ at a heating rate of 10℃ / min and held for calcination for 2 hours. After cooling to room temperature with the furnace, the composite intermediate was obtained. The flow rate of argon in the atmosphere furnace was controlled to be 300mL / min and the pressure was 0.1MPa. Z4. The composite intermediate, nano zinc oxide, and nano calcium oxide were added into a ball mill jar at a mass ratio of 20:20:1. Zirconia balls of 5 mm were used as milling balls, and the ball-to-material ratio was controlled at 5:1. The mixture was milled for 3 hours and then granulated in a granulator to obtain a microwave absorber with an average particle size of 0.5 mm.
[0054] Preparation Example 4 Example 4 of this preparation provides a method for preparing a microwave absorber, comprising the following steps: Z1. Porous carbon (purchased from Jiangsu Chengyang Activated Carbon Co., Ltd., CY-P03, specific surface area greater than 1500 m²) 2 / g) was added to an ethanol solution containing 3-aminopropyltriethoxysilane (KH550, the mass ratio of porous carbon to 3-aminopropyltriethoxysilane is 1:0.2) at a solid-liquid ratio of 0.08 g / mL and ultrasonically dispersed for 15 min to obtain a dispersion. The dispersion was stirred and refluxed in a water bath at 70°C for 3 h, then filtered and dried with hot air to obtain the active matrix. Z2. The active matrix was added to a mixed solution containing ferric nitrate and tetraethyl orthosilicate at a solid-liquid ratio of 0.08 g / mL and ultrasonically dispersed for 15 min. Then, 15% ammonia solution was added dropwise at a rate of 60 drops / min and stirred to react. The mixture was then filtered, separated, and dried to obtain the composite matrix. Z3. The composite matrix is transferred to the furnace chamber of the atmosphere furnace. After the atmosphere furnace is purged three times with argon, the temperature of the atmosphere furnace is increased to 800℃ at a heating rate of 10℃ / min and held for calcination for 2 hours. After cooling to room temperature with the furnace, the microwave absorber is granulated in a granulator to obtain a microwave absorber with an average particle size of 0.5mm. The flow rate of argon in the atmosphere furnace is controlled to be 300mL / min and the pressure is 0.1MPa. Example 1
[0055] This embodiment 1 provides a microwave pyrolysis recycling method for waste circuit boards, including the following steps: S1. After pre-cleaning the surface of the waste circuit board, it is preheated at 230℃ for 30 minutes, and the surface electronic components are peeled off and recycled. The waste circuit board with the surface electronic components peeled off is mechanically crushed by a shearing crusher, then transferred to a liquid nitrogen environment to be frozen and ground into powder, which is then passed through a 1mm sieve to obtain recycled powder. S2. The microwave absorber from Preparation Example 1 is transferred to the chamber of the microwave reactor and microwaved at 400W for 5 minutes in an argon atmosphere. Then, the microwave absorber and the recovered powder are mixed uniformly at a mass ratio of 0.2:1 to obtain a mixed powder. S3. The mixed powder was filled into the pyrolysis chamber of the microwave reactor at a mass-volume ratio of 0.3 g / mL. Under an argon atmosphere, the mixed powder was microwave pyrolyzed at a microwave power of 700 W and a reaction temperature of 500 °C for 10 min, and then the metal-enriched material was sorted out. S4. The metal components in the waste circuit board were collected after leaching the metal-rich material at 70°C for 30 minutes using a leaching agent containing 2 mol / L sulfuric acid and 1 mol / L ferric chloride.
[0056] Comparative Example 1 Comparative Example 1 provides a microwave pyrolysis recycling method for waste circuit boards, including the following steps: D1. After pre-cleaning the surface of the waste circuit board, preheat it at 230℃ for 30 minutes, then peel off and recycle the surface electronic components. After mechanically crushing the waste circuit board with the surface electronic components peeled off using a shearing crusher, transfer it to a liquid nitrogen environment to freeze and grind it into powder, and then pass it through a 1mm sieve to obtain recycled powder. D2. The microwave absorber from Preparation Example 2 was transferred to the chamber of the microwave reactor and microwaved at 400W for 5 minutes in an argon atmosphere. Then, the microwave absorber and the recovered powder were mixed uniformly at a mass ratio of 0.2:1 to obtain a mixed powder. D3. The mixed powder was filled into the pyrolysis chamber of the microwave reactor at a mass-volume ratio of 0.3 g / mL. Under an argon atmosphere, the microwave reactor was used to microwave pyrolyze the mixed powder at a microwave power of 700 W and a reaction temperature of 500 °C for 10 min, and then the metal-enriched material was sorted out. D4. The metal components in the waste circuit board were collected after leaching the metal-rich material at 70°C for 30 minutes using a leaching agent containing 2 mol / L sulfuric acid and 1 mol / L ferric chloride.
[0057] Comparative Example 2 Comparative Example 2 provides a microwave pyrolysis recycling method for waste circuit boards, including the following steps: D1. After pre-cleaning the surface of the waste circuit board, preheat it at 230℃ for 30 minutes, then peel off and recycle the surface electronic components. After mechanically crushing the waste circuit board with the surface electronic components peeled off using a shearing crusher, transfer it to a liquid nitrogen environment to freeze and grind it into powder, and then pass it through a 1mm sieve to obtain recycled powder. D2. The microwave absorber from Preparation Example 3 was transferred to the chamber of the microwave reactor and microwaved at 400W for 5 minutes in an argon atmosphere. Then, the microwave absorber and the recovered powder were mixed uniformly at a mass ratio of 0.2:1 to obtain a mixed powder. D3. The mixed powder was filled into the pyrolysis chamber of the microwave reactor at a mass-volume ratio of 0.3 g / mL. Under an argon atmosphere, the microwave reactor was used to microwave pyrolyze the mixed powder at a microwave power of 700 W and a reaction temperature of 500 °C for 10 min, and then the metal-enriched material was sorted out. D4. The metal components in the waste circuit board were collected after leaching the metal-rich material at 70°C for 30 minutes using a leaching agent containing 2 mol / L sulfuric acid and 1 mol / L ferric chloride.
[0058] Comparative Example 3 Comparative Example 3 provides a microwave pyrolysis recycling method for waste circuit boards, including the following steps: D1. After pre-cleaning the surface of the waste circuit board, preheat it at 230℃ for 30 minutes, then peel off and recycle the surface electronic components. After mechanically crushing the waste circuit board with the surface electronic components peeled off using a shearing crusher, transfer it to a liquid nitrogen environment to freeze and grind it into powder, and then pass it through a 1mm sieve to obtain recycled powder. D2. The microwave absorber from Preparation Example 4 was transferred to the chamber of the microwave reactor and microwaved at 400W for 5 minutes in an argon atmosphere. Then, the microwave absorber and the recovered powder were mixed uniformly at a mass ratio of 0.2:1 to obtain a mixed powder. D3. The mixed powder was filled into the pyrolysis chamber of the microwave reactor at a mass-volume ratio of 0.3 g / mL. Under an argon atmosphere, the microwave reactor was used to microwave pyrolyze the mixed powder at a microwave power of 700 W and a reaction temperature of 500 °C for 10 min, and then the metal-enriched material was sorted out. D4. The metal components in the waste circuit board were collected after leaching the metal-rich material at 70°C for 30 minutes using a leaching agent containing 2 mol / L sulfuric acid and 1 mol / L ferric chloride.
[0059] Performance testing During microwave pyrolysis recovery of Examples 1 and Comparative Examples 1 to 3, the bromine concentration in the pyrolysis recovery tail gas was tested, and the pyrolysis weight loss rate was calculated (pyrolysis weight loss rate = solid mass after pyrolysis / solid mass before pyrolysis × 100%; using the pyrolysis weight loss rate in Example 1 as a benchmark, the relative weight loss rate of Comparative Examples 1 to 3 was calculated, relative weight loss rate = comparative example weight loss rate - example weight loss rate), and the results are shown in Table 1 below; The microwave absorbents that completed one operation in Examples 1 and Comparative Examples 1 to 2 were heat-treated in a water vapor environment at 500°C for 15 minutes, then transferred to an argon atmosphere for cooling and drying for recovery. The recovered microwave absorbents were repeatedly subjected to microwave pyrolysis recovery. The number of times the microwave absorbent was used when the bromine concentration in the recovered tail gas was 5 times that of the initial state was recorded as the current service life of the microwave absorbent. The percentage of the microwave absorbents in Comparative Examples 1 to 2 compared to the baseline was calculated as the service life change rate. The results are shown in Table 1 below.
[0060] Table 1 Performance Test Data
[0061] While embodiments of the present invention have been described in detail above, it will be apparent to those skilled in the art that various modifications and variations can be made to these embodiments. However, it should be understood that such modifications and variations fall within the scope and spirit of the invention as set forth in the claims. Furthermore, the invention described herein may have other embodiments and can be implemented or carried out in various ways.
Claims
1. A microwave pyrolysis method for recycling waste circuit boards, characterized in that, include: After stripping electronic components from waste circuit boards, the components are crushed to obtain recycled powder. The recycled powder is mixed with a microwave absorber to obtain a mixed powder. The mixed powder is then microwave pyrolyzed at a temperature of 400℃-600℃, a microwave power of 600W-800W, and a protective atmosphere to obtain a metal-enriched material. The metal-enriched material is then ground and separated into metal components under the action of a leaching agent.
2. The microwave pyrolysis recovery method according to claim 1, characterized in that: The preparation method of the microwave absorber includes: surface silane activation of porous carbon to obtain an active matrix; wetting and adsorbing the active matrix in a mixed solution containing iron salt and tetraethyl orthosilicate, stirring and reacting in an alkaline environment and separating to obtain a composite matrix; calcining the composite matrix under an inert atmosphere and cooling to obtain a composite intermediate; mixing the composite intermediate with nano zinc oxide and nano calcium oxide, ball milling and granulating to obtain the microwave absorber.
3. The microwave pyrolysis recovery method according to claim 2, characterized in that: Porous carbon is mixed in an ethanol solution containing 3-aminopropyltriethoxysilane, and then stirred and refluxed in a water bath at 70℃-80℃ for 2-4 hours, followed by separation and drying to obtain the active matrix; wherein: the mass ratio of the porous carbon to the 3-aminopropyltriethoxysilane is 1:(0.1-0.2); and / or, the porous carbon is pre-heat-treated at 100℃-120℃ for 1-2 hours; and / or, the specific surface area of the porous carbon is 1500 m². 2 / g-2000m 2 / g.
4. The microwave pyrolysis recovery method according to claim 2, characterized in that: The mass ratio of the active matrix to the iron ions in the mixed solution is 1:(0.1-0.4); and / or, the mass ratio of the active matrix to the tetraethyl orthosilicate is 1:(0.3-0.6); and / or, the solid-liquid ratio of the active matrix to the mixed solution is 0.06 g / mL-0.1 g / mL; and / or, ammonia is added dropwise to the mixed solution containing the active matrix and stirred to react; and / or, the active matrix is ultrasonically impregnated in the mixed solution for 10 min-30 min.
5. The microwave pyrolysis recovery method according to claim 2, characterized in that: The inert gas in the inert atmosphere includes one of nitrogen, argon, and helium; and / or, the pressure of the inert atmosphere is 0.1 MPa-0.2 MPa; and / or, the composite matrix is calcined at 700℃-850℃; and / or, the flow rate of the inert gas in the inert atmosphere is 200 mL / min-500 mL / min; and / or, the composite matrix is calcined for 1.5 h-2.5 h.
6. The microwave pyrolysis recovery method according to claim 2, characterized in that: The mass ratio of the composite intermediate to the nano zinc oxide is (10-20):1; and / or, the mass ratio of the composite intermediate to the nano calcium oxide is (20-30):1; and / or, the average particle size of the nano zinc oxide and the nano calcium oxide is independently 30nm-100nm; and / or, during ball milling, 3mm-10mm zirconium oxide is used as the milling ball, the ball-to-material ratio is (3-5):1, and the milling time is 2h-4h.
7. The microwave pyrolysis recovery method according to claim 1 or 2, characterized in that: The microwave absorber is pre-irradiated in a protective atmosphere with a microwave power of 300W-400W, and then mixed with recycled powder to obtain a mixed powder; and / or, the average particle size of the recycled powder and the microwave absorber are independently 0.1mm-1mm; and / or, the mass ratio of the recycled powder to the microwave absorber is 1:(0.1-0.25).
8. The microwave pyrolysis recovery method according to claim 1, characterized in that: The electronic components are stripped off after the waste circuit board is preheated at 200℃-250℃; and / or, the electronic components are stripped off and recycled; and / or, the electronic components are stripped off, sheared, crushed, and pulverized at low temperature; and / or, the leaching agent is a sulfuric acid-ferric chloride mixture, and the mixture includes 1.5mol / L-3mol / L sulfuric acid and 0.2mol / L-2mol / L ferric chloride; and / or, the mass-to-volume ratio of the mixed powder to the microwave pyrolysis chamber is 0.1g / mL-0.4g / mL during microwave pyrolysis.