Method for extracting copper from waste circuit board by microwave corona coupling thermal shock and green solvent

Abstract

The present application relates to the technical field of electronic waste resource utilization, and discloses a method for extracting copper from waste circuit board by microwave corona coupling thermal shock and green solvent, which comprises the following steps: mixing waste printed circuit board powder and silicon carbide particles, pyrolyzing under inert atmosphere, using large particle silicon carbide to initiate deep pyrolysis of brominated resin in the microwave field, then without natural cooling, directly putting high-temperature materials into 0-5 DEG C medium for in-situ thermal shock quenching, using thermal stress mismatch to induce a large number of micro cracks in the material, after screening and recycling silicon carbide, using deep eutectic solvent (DES) for efficient leaching of the residue, finally, purifying cathode copper by electro-deposition, in-situ regeneration of deep eutectic solvent and high-value utilization of non-metallic residue. The present application realizes high copper leaching rate, 100% solvent recycling and zero solid waste discharge.

Description

Technical Field

[0001] This invention relates to the field of electronic waste resource utilization technology, specifically a method for extracting copper from waste circuit boards using microwave corona coupling thermal shock and green solvents. Background Technology

[0002] With the rapid development of the electronics and information industry, the generation of waste printed circuit boards (WPCBs) is increasing exponentially. These boards are rich in valuable metals such as copper, gold, and silver, and also contain approximately 30% cross-linked epoxy resin (usually with added brominated flame retardants) and 30% glass fiber. Currently, metal recycling technologies for WPCBs face the following insurmountable technical bottlenecks: The challenges of leaching resistance in traditional hydrometallurgical processes include hazardous waste liquids and difficulties in leaching: conventional leaching uses strong acid (such as sulfuric acid / nitric acid) and strong oxidant systems, which not only consumes a large amount of highly corrosive reagents but also generates a massive amount of hazardous acidic waste liquids containing heavy metals that are difficult to treat; in addition, the metals in WPCBs are encapsulated by highly cross-linked dense resins, making it extremely difficult for acidic solutions at room temperature to penetrate, resulting in extremely slow leaching kinetics.

[0003] The challenges of conventional pyrolysis include highly toxic exhaust gases and carbon residue encapsulation: In order to break the resin encapsulation, pyrolysis pretreatment is often introduced. However, existing microwave pyrolysis technology lacks precise control over the particle size of the microwave absorber and the microscopic electromagnetic response of the interface. The pyrolysis temperature field is uneven, making it difficult to completely destroy the C-Br bonds of bromides, which easily generates highly toxic polybrominated dioxins / furans (PBDD / Fs). In addition, fine powdered microwave absorbers are very easy to agglomerate with carbon residue and are difficult to recover. Moreover, the dense carbon residue layer formed after pyrolysis still adheres to the surface of the copper foil, forming a "hydrophobic protective shell" for the subsequent leaching agent.

[0004] The high viscosity penetration bottleneck of advanced eutectic solvents (DES): Eutectic solvents (DES) have advantages such as zero vapor pressure and complete degradability. However, eutectic solvents have extremely high viscosity at room temperature and medium and low temperatures. Faced with dense WPCBs residues, the viscous eutectic solvents simply cannot overcome the surface tension to enter the material and contact the metal, resulting in extremely low leaching efficiency.

[0005] The lack of a closed-loop thinking of "zero solid waste from all components": existing processes only focus on extracting metals, and the remaining non-metallic residues (containing organic carbon residues and glass fibers) of more than 60% can only be landfilled as hazardous solid waste, resulting in resource waste and high environmental disposal costs. Summary of the Invention

[0006] To address the aforementioned technical challenges, this invention provides a method for extracting copper from waste circuit boards using microwave corona coupling thermal shock and green solvents. Breaking away from traditional linear metallurgical thinking, it ingeniously constructs a synergistic response mechanism of "microwave corona in-situ dehalogenation—extreme thermal shock physical hole expansion—high-efficiency impregnation with eutectic solvent—liquid-solid two-phase closed loop," achieving green, short-process, and full-component resource utilization of waste printed circuit boards. The specific steps of this invention are as follows: (1) The waste printed circuit board powder and silicon carbide particles are mixed evenly to obtain the reaction material. The reaction material is subjected to microwave pyrolysis. After the pyrolysis is completed, the reaction material under high temperature is quenched immediately.

[0007] (2) After quenching, solid-liquid separation is carried out. First, the solid material is dried, and then it is physically screened through a 16-mesh sieve to separate and recover the silicon carbide particles.

[0008] (3) The copper-rich porous residue obtained in step (2) is placed in a eutectic solvent containing hydrogen peroxide, heated and stirred for leaching, and then subjected to solid-liquid separation to obtain copper-rich leachate and non-metallic porous residue.

[0009] (4) Electrodeposition is performed directly on the copper-rich leachate obtained in step (3) to extract cathode copper. The eutectic solvent after copper removal is returned to step (3) for recycling.

[0010] (5) After washing and drying the non-metallic porous residue obtained in step 5, it can be directly used as electromagnetic shielding filler or modified aggregate for high-value application.

[0011] Preferably, the mass ratio of waste printed circuit board powder to silicon carbide particles in step (1) is 1:1 to 1.5.

[0012] Preferably, the particle size of the silicon carbide particles in step (1) is 16 mesh.

[0013] Preferably, the microwave pyrolysis conditions in step (1) are: heating to 400℃~450℃ at a heating rate of 10℃ / min~20℃ / min under an inert atmosphere and then holding at that temperature for 15~30 minutes.

[0014] Preferably, the quenching method in step (1) is water quenching, and the water quenching temperature is 0℃~5℃.

[0015] Preferably, the amount of copper-rich porous residue added to the eutectic solvent containing hydrogen peroxide is 10 g / L to 50 g / L.

[0016] Preferably, the eutectic solvent in step (3) is obtained by mixing choline chloride and a hydrogen bond donor in a molar ratio of 1:2, wherein the hydrogen bond donor is one of urea, ethylene glycol or lactic acid.

[0017] Preferably, the volume of hydrogen peroxide in step (3) is 5 to 10% of the volume of the eutectic solvent.

[0018] Compared with the prior art, the present invention has the following beneficial effects: (1) This invention first discovered and utilized the space charge polarization effect of 16-mesh large-particle silicon carbide, which generates corona discharge that releases high-energy electrons, precisely breaks C-Br bonds, eliminates the risk of dioxin generation from the source, and avoids the strong tip corona discharge caused by the agglomeration of silicon carbide in the microwave field caused by fine powder microwave absorber. Combined with microwave heating to form micro plasma hot spots, it deeply decomposes the brominated epoxy resin wrapped on the surface of copper foil, realizes in-situ harmless dehalogenation, and blocks the generation of highly toxic exhaust gas.

[0019] (2) The material heated by high temperature microwave is instantly immersed in a liquid quenching medium with a temperature of 0℃~5℃. By utilizing the thermal stress mismatch caused by the extreme temperature difference and the huge difference in the thermal expansion coefficients of the multiphase materials (copper, glass fiber, and residual carbon), micron / nano-scale cracks are torn open during the rapid cooling, completely breaking the "dead angle" of the residual carbon. The three-dimensional interconnected microcracks are like "micro capillary pumps", instantly drawing in the extremely viscous eutectic solvent, solving the industry bottleneck of the difficulty of eutectic solvent penetration, and making a qualitative leap in leaching kinetics. Furthermore, by adding the green oxidant hydrogen peroxide to the eutectic solvent, elemental copper is oxidized into copper ions, which are then complexed by chloride ions in the eutectic solvent to form CuCl4. 2- This process achieves efficient leaching, and since its decomposition products are water, it does not introduce impurities, which is beneficial for extracting metallic copper from the residue.

[0020] (3) The non-metallic porous residue prepared in this application is mainly composed of micro-nano-scale porous amorphous carbon (derived from deep carbonization of resin) and interwoven glass fiber skeleton (SiO2 and a small amount of alumina). This unique 'conductive carbon network-insulating glass fiber' composite structure is a natural high-quality electromagnetic wave absorber skeleton: the porous conductive carbon residue provides a good dielectric loss and conduction loss network, while the interwoven glass fiber not only provides mechanical strength, but also acts as a wave-transparent skeleton to adjust the overall impedance matching; the massive micropores generated by in-situ thermal shock introduce a rich solid-gas interface, which greatly enhances the interface polarization reflection and multiple scattering loss of electromagnetic waves. Therefore, after washing and drying, the non-metallic porous residue can be directly incorporated into resin or cement aggregate as a wave-absorbing filler without complex secondary modification to prepare high-performance electromagnetic shielding materials, realizing the high-value closed loop of waste residue.

[0021] (4) This invention achieves efficient copper recovery on the basis of zero secondary solid waste discharge throughout the entire process, with a copper leaching rate exceeding 98%, and completely eliminates strong acid pollution and highly toxic waste gas. The DES solvent is completely biodegradable and free of acid mist. Microwave corona discharge achieves in-situ dehalogenation and blocks highly toxic exhaust gas. It is truly zero solid waste throughout the entire life cycle: the physical sieving recovery rate of silicon carbide is >95%; 100% in-situ regeneration after liquid phase solvent electrowinning; traditional non-metallic waste residue is transformed into high-value electromagnetic shielding material due to thermal shock pore formation, and the entire process has zero secondary solid waste discharge. Attached Figure Description

[0022] Figure 1 The process flow diagram of the closed-loop process of all components in this invention. Detailed Implementation

[0023] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0024] Example 1 A method for extracting copper from waste circuit boards using microwave corona coupling thermal shock and green solvents, the specific steps of which are as follows: (1) The waste printed circuit board powder and silicon carbide particles are mixed evenly in a quartz boat at a mass ratio of 1:1 to obtain the reaction material. The quartz boat containing the reaction material is placed in a microwave oven and heated to 400°C at 15°C / min and kept at the temperature for 20 minutes for pyrolysis (using the tip corona discharge induced by large silicon carbide particles to deeply decompose the brominated epoxy resin wrapped on the surface of copper foil). After the pyrolysis is completed, the reaction material at high temperature is immediately poured into a mixture of ice and water at 0°C for quenching (using the thermal shock effect to induce a large number of micro cracks at the interface of residual carbon, glass fiber and metallic copper to achieve physical hole expansion).

[0025] (2) After quenching, solid-liquid separation is carried out. First, the solid material is dried and then passed through a 16-mesh sieve. The material under the sieve is copper-rich porous residue, and the material over the sieve is silicon carbide particles. There is no tar adhering to the surface of the silicon carbide, and the recovery rate is 96%.

[0026] (3) The copper-rich residue that was sieved was added to a eutectic solvent of choline chloride and urea (molar ratio of choline chloride to urea 1:2) containing hydrogen peroxide, and the mixture was stirred at 60°C for 1.5 hours. The solid and liquid were separated to obtain a copper-rich leachate and a non-metallic porous residue with a copper leaching rate of 98.6%.

[0027] (4) The copper-rich leaching solution uses a high-purity graphite plate as the anode and a pure copper-titanium thin plate as the cathode. High-purity cathode copper is extracted by electrodeposition at a voltage of 2.0V for 3 hours. The copper-free leaching solution is recycled as a eutectic solvent.

[0028] (5) The non-metallic porous residue is washed and dried. Its main components are micro-nano-scale porous amorphous carbon (derived from deep carbonization of resin) and interwoven glass fiber skeleton (SiO2 and a small amount of alumina), which can be directly used as porous electromagnetic shielding filler or modified aggregate for high-value utilization.

[0029] Example 2 (1) The waste printed circuit board powder and silicon carbide particles are mixed evenly in a quartz boat at a mass ratio of 1:1.5 to obtain the reaction material. The quartz boat containing the reaction material is placed in a microwave oven and heated to 450°C at 10°C / min and kept at the temperature for 15 minutes for pyrolysis. After the pyrolysis is completed, the reaction material in the high temperature state is immediately poured into a 5°C ice-water mixture for quenching.

[0030] (2) After quenching, solid-liquid separation is carried out. First, the solid material is dried and then passed through a 16-mesh sieve. The material under the sieve is copper-rich porous residue, and the material over the sieve is silicon carbide particles. There is no tar adhering to the surface of the silicon carbide, and the recovery rate is 95.5%.

[0031] (3) The copper-rich residue that was sieved was added to a eutectic solvent of choline chloride and ethylene glycol (molar ratio of choline chloride to ethylene glycol 1:2) (containing hydrogen peroxide, with hydrogen peroxide accounting for 5% of the volume of the eutectic solvent), and stirred at 50°C for 2 hours. The solid and liquid were separated to obtain a copper-rich leachate and a non-metallic porous residue with a copper leaching rate of 97.8%.

[0032] (4) The copper-rich leaching solution uses a titanium-based ruthenium-iridium coated electrode (DSA) as the anode and a pure copper plate as the cathode. High-purity cathode copper is extracted by electrodeposition at 2.5V for 3 hours. The copper-removed leaching solution is recycled as a eutectic solvent.

[0033] (5) The non-metallic porous residue is washed and dried, and then used directly as a porous electromagnetic shielding filler or modified aggregate for high-value utilization.

[0034] Example 3 (1) The waste printed circuit board powder and silicon carbide particles are mixed evenly in a quartz boat at a mass ratio of 1:1.5 to obtain the reaction material. The quartz boat containing the reaction material is placed in a microwave oven and heated to 450°C at 20°C / min and kept at that temperature for 30 minutes for pyrolysis. After the pyrolysis is completed, the reaction material at high temperature is immediately poured into a 5°C ice-water mixture for quenching.

[0035] (2) After quenching, solid-liquid separation is carried out. First, the solid material is dried and then passed through a 16-mesh sieve. The material under the sieve is copper-rich porous residue, and the material over the sieve is silicon carbide particles. There is no tar adhering to the surface of the silicon carbide, and the recovery rate is 96.5%.

[0036] (3) The copper-rich residue that is sieved is added to a eutectic solvent of choline chloride and lactic acid (molar ratio of choline chloride to lactic acid 1:2) (containing hydrogen peroxide, with hydrogen peroxide accounting for 10% of the volume of the eutectic solvent), and stirred at 70°C for 1 hour. The solid and liquid are separated to obtain copper-rich leachate and non-metallic porous residue, with a copper leaching rate of 99.2%.

[0037] (4) The copper-rich leaching solution uses a high-purity graphite plate as the anode and a pure copper plate as the cathode. High-purity cathode copper is extracted by electrodeposition at 2.5V for 2 hours. The copper-depleted leaching solution is recycled as a eutectic solvent.

[0038] (5) The non-metallic porous residue is washed and dried, and then used directly as a porous electromagnetic shielding filler or modified aggregate for high-value utilization.

[0039] Comparative Example 1 As a comparison, this comparative example differs from Example 1 in that, after microwave pyrolysis, it is naturally cooled to room temperature in argon gas (without quenching). The specific steps are as follows: (1) Waste printed circuit board powder and silicon carbide particles were mixed evenly in a quartz boat at a mass ratio of 1:1 to obtain the reaction material. The quartz boat containing the reaction material was placed in a microwave oven and heated to 400°C at 15°C / min and kept at the temperature for 20 minutes for pyrolysis. After pyrolysis, it was naturally cooled to room temperature in argon gas and then passed through a 16-mesh sieve. The material under the sieve was copper-rich porous residue, and the material over the sieve was silicon carbide particles. There was no tar adhering to the surface of the silicon carbide, and the recovery rate reached 96%.

[0040] (3) The copper-rich residue that was sieved was added to a eutectic solvent of choline chloride and urea (molar ratio of choline chloride to urea 1:2) (containing hydrogen peroxide, with hydrogen peroxide accounting for 8% of the volume of the eutectic solvent). The mixture was stirred at 60°C for 1.5 hours. The solid and liquid were separated to obtain a copper-rich leachate and a non-metallic porous residue. The copper leaching rate reached 62.4%.

[0041] (4) High-purity cathode copper is extracted by electrodeposition of copper-rich leaching solution at 2.0V, and copper-removed leaching solution is recycled as a eutectic solvent.

[0042] (5) The non-metallic porous residue is washed and dried, and then used directly as a porous electromagnetic shielding filler or modified aggregate for high-value utilization.

[0043] Due to the lack of thermal shock microcracks, high-viscosity DES penetration is extremely difficult, with a copper leaching rate of only 62.4%. This strongly demonstrates that thermal shock quenching is a necessary prerequisite for efficient leaching of the DES system.

[0044] Comparative Example 2 In comparison, this comparative example differs from Example 1 in that it uses 100-mesh (approximately 150 μm) fine silicon carbide instead of 16-mesh silicon carbide, while the other conditions are the same as in Example 1.

[0045] Results: No obvious corona discharge was observed in the microwave field, and local dehalogenation was incomplete. When sieved after quenching, fine silicon carbide powder and residual carbon severely agglomerated, and the silicon carbide recovery rate plummeted to 42%. The subsequent copper leaching rate was only 76.5%, indicating that 16-mesh SiC can achieve a higher copper leaching rate. The effect of SiC particle size on pyrolysis efficiency is different in mechanism. 16-mesh SiC particles cover the particle surface and absorb microwaves to suppress microwave metal discharge, while larger SiC particles directly absorb microwaves and transfer energy to improve pyrolysis efficiency.

[0046] Comparative Example 3 As a comparison, this comparative example differs from Example 1 in that the eutectic solvent is replaced with 2 mol / L sulfuric acid (containing hydrogen peroxide, with the hydrogen peroxide content being 10% of the sulfuric acid volume), while the other conditions are the same as in Example 1.

[0047] Results: The copper leaching rate was 95.2%. However, the leaching process was accompanied by irritating acid mist, generating difficult-to-treat strong acid waste liquid and calcium sulfate residue, thus negating the environmental advantages of closed-loop zero emission.

[0048] Comparative Example 4 In comparison, this comparative example differs from Example 1 in that it does not use silicon carbide, but is otherwise the same as Example 1.

[0049] Results: The reactants heated up extremely slowly, and no corona discharge effect was generated in the microwave field. Toxic polybrominated dibenzodioxins / furans (PBDD / Fs) were detected in the pyrolysis tail gas; the copper leaching rate subsequently dropped sharply to 32.5%.

[0050] Analysis: The epoxy resin and glass fiber in the waste circuit boards are microwave-transmitting materials with extremely poor microwave absorption. The absence of silicon carbide prevents the materials from absorbing microwave energy for effective heating. More importantly, the lack of the "corona discharge" effect caused by large silicon carbide particles in a microwave field prevents the generation of high-energy electrons to precisely break the C-Br bonds in the resin, leading to the production of highly toxic exhaust gases. Simultaneously, the dense resin that has not been deeply pyrolyzed still tightly encapsulates the copper foil, completely blocking the subsequent penetration of DES solvent, resulting in an extremely low leaching rate.

[0051] Comparative Example 5 In contrast, this comparative example differs from Example 1 in that it uses a conventional tube furnace for heating instead of microwave heating.

[0052] Results: After pyrolysis, a large amount of tar and dense carbon residue were found on the surface of silicon carbide particles during sieving, and the physical recovery rate of silicon carbide dropped to 72.4%; a small amount of bromine toxic gas was still present in the pyrolysis tail gas; and the copper leaching rate under the same conditions was only 55.3%.

[0053] Analysis: Conventional tube furnaces rely on heat conduction from the outside in for heating, resulting in a severe temperature gradient that easily produces tar and causes severe agglomeration of residual carbon and silicon carbide. Furthermore, conventional thermal fields cannot generate "micro-plasma hotspots" and "corona discharges" on the surface of silicon carbide particles like microwave electromagnetic fields, making it impossible to achieve thorough in-situ dehalogenation. The dense layer of residual carbon coating on the copper foil acts as a "hydrophobic protective shell," and even after subsequent quenching, the high-viscosity eutectic solvent (DES) still struggles to overcome surface tension and penetrate deep into the residue, severely hindering leaching kinetics.

[0054] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for extracting copper from waste circuit boards using microwave corona coupling thermal shock and green solvents, characterized in that: The specific steps are as follows: (1) The waste printed circuit board powder and silicon carbide particles are mixed evenly to obtain the reaction material. The reaction material is subjected to microwave pyrolysis. After the pyrolysis is completed, the reaction material under high temperature is quenched immediately. (2) After quenching, solid-liquid separation is carried out. First, the solid material is dried and then physically screened through a 16-mesh sieve. The material under the sieve is copper-rich porous residue, and the material over the sieve is silicon carbide particles. (3) The copper-rich porous residue obtained in step (2) is placed in a eutectic solvent containing hydrogen peroxide, heated and stirred for leaching, and then subjected to solid-liquid separation to obtain copper-rich leachate and non-metallic porous residue. (4) Electrodeposition is performed directly on the copper-rich leachate obtained in step (3) to extract cathode copper, and the eutectic solvent after copper removal is returned to step (3) for recycling. (5) The non-metallic porous residue obtained in step (3) is washed, dried and used directly.

2. The method for extracting copper from waste circuit boards using microwave corona coupling thermal shock and green solvents according to claim 1, characterized in that: In step (1), the mass ratio of waste printed circuit board powder to silicon carbide particles is 1:1 to 1.

5.

3. The method for extracting copper from waste circuit boards using microwave corona coupling thermal shock and green solvents according to claim 1, characterized in that: In step (1), the particle size of the silicon carbide particles is 16 mesh.

4. The method for extracting copper from waste circuit boards using microwave corona coupling thermal shock and green solvents according to claim 1, characterized in that: In step (1), the microwave pyrolysis conditions are: heating to 400℃~450℃ at a heating rate of 10℃ / min~20℃ / min under an inert atmosphere and then holding at that temperature for 15~30 minutes.

5. The method for extracting copper from waste circuit boards using microwave corona coupling thermal shock and green solvents according to claim 1, characterized in that: In step (1), the quenching method is water quenching, and the water quenching temperature is 0℃~5℃.

6. The method for extracting copper from waste circuit boards using microwave corona coupling thermal shock and green solvents according to claim 1, characterized in that: In step (3), the amount of copper-rich porous residue added to the eutectic solvent containing hydrogen peroxide is 10 g / L to 50 g / L.

7. The method for extracting copper from waste circuit boards using microwave corona coupling thermal shock and green solvents according to claim 1, characterized in that: The eutectic solvent mentioned in step (3) is obtained by mixing choline chloride and a hydrogen bond donor in a molar ratio of 1:2, wherein the hydrogen bond donor is one of urea, ethylene glycol or lactic acid.

8. The method for extracting copper from waste circuit boards using microwave corona coupling thermal shock and green solvents according to claim 1, characterized in that: In step (3), the volume of hydrogen peroxide is 5% to 10% of the volume of the eutectic solvent.

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