A harmless treatment method of waste printed circuit board

Abstract

The application belongs to the technical field of comprehensive utilization of solid waste, and particularly relates to a harmless treatment method of waste printed circuit boards. 4+ The Ce-Zr solid solution releases active oxygen through reversible valence change of Ce 3+ and Ce under anoxic pyrolysis environment, oxidizes and cracks bromine intermediate, and solidifies bromine in situ, thereby inhibiting the generation of dioxins from the source; the nano-magnesium oxide strengthens the solidification of bromine and inhibits the excessive cracking and polycondensation of organic components; the nitrogen-doped porous carbon realizes the efficient dispersion of active components, and promotes the formation of loose porous structure of pyrolysis products to facilitate the leaching of valuable metals. The efficient leaching of gold, silver and copper valuable metals is completed by adopting a thiourea-sulfuric acid-hydrogen peroxide system, and the leaching residue can be harmlessly landfilled after being gelled and solidified, thereby effectively improving the valuable metal recovery rate and overall resource utilization rate, and having outstanding environmental and economic benefits.

Description

Technical Field

[0001] This invention relates to the field of comprehensive utilization technology of solid waste, and in particular to a method for the harmless treatment of waste printed circuit boards. Background Technology

[0002] With the rapid development of the electronics and information industry and the continuous shortening of product upgrade cycles, electronic waste has become one of the fastest-growing solid wastes globally. Waste printed circuit boards (PCBs), as core components of electronic and electrical products, present particularly prominent challenges in their disposal: on the one hand, the content of metals such as copper, gold, and silver in PCBs is significantly higher than in natural ores, giving them extremely high resource recycling value; on the other hand, their substrate contains a large amount of brominated flame retardants and heavy metal components such as lead and tin. Improper handling, such as high-temperature incineration or improper storage, can lead to the formation of persistent organic pollutants such as brominated dioxins and the leaching and migration of heavy metals, posing a serious threat to the ecological environment and human health.

[0003] Currently, the main technologies for disposing of waste printed circuit boards (PCBs) are mechanical sorting, pyrolysis, wet leaching, and combined technologies. Among these, the combined pyrolysis and wet leaching technology has become the mainstream approach due to its ability to synergistically decompose organic components and extract valuable metals. The pyrolysis process uses deep thermal cracking at high temperatures to convert most of the organic components in the PCBs into pyrolysis gas and oil, achieving initial separation of the metal and organic phases. The wet leaching process uses chemical agents to dissolve and extract valuable metals from the metal phase, completing the high-value transformation of resources. However, the pyrolysis process generally faces problems such as high energy consumption, difficulty in precisely controlling the generation of toxic and harmful pollutants, and the tendency for products to clump together, affecting the efficiency of subsequent metal separation. The wet leaching process suffers from high reagent consumption, limited leaching efficiency, and the potential for secondary pollution, making it difficult to simultaneously achieve resource recovery and harmless disposal of waste PCBs throughout the entire process, and failing to meet the industrial disposal requirements of high efficiency, low consumption, and environmental protection. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a method for the harmless treatment of waste printed circuit boards. This method involves preparing a cerium-zirconium solid solution-nano magnesium oxide-nitrogen-doped porous carbon composite catalyst. The cerium-zirconium solid solution undergoes pyrolysis under an oxygen-deficient environment via Ce... 4+ With Ce 3+The reversible valence state transformation releases active oxygen, oxidizing and cracking brominated intermediates and fixing bromine in situ, thus inhibiting the formation of dioxins from the source. Nano-sized magnesium oxide enhances bromine fixation and inhibits excessive cracking and agglomeration of organic components. Nitrogen-doped porous carbon achieves efficient dispersion of active components and promotes the formation of a loose porous structure in pyrolysis products to facilitate the leaching of valuable metals. The efficient leaching of gold, silver, and copper using a thiourea-sulfuric acid-hydrogen peroxide system allows the leaching residue to be safely landfilled after gelation and solidification, effectively improving the recovery rate of valuable metals and the overall resource utilization rate, demonstrating both outstanding environmental and economic benefits.

[0005] To achieve the above objectives, the present invention provides a method for the harmless treatment of waste printed circuit boards, comprising the following steps:

[0006] S1. Prepare cerium-zirconium solid solution and nitrogen-doped porous carbon. Mix the cerium-zirconium solid solution, nano-magnesium oxide, and nitrogen-doped porous carbon, add deionized water to obtain a uniform slurry, and then vacuum dry, calcine, pulverize and sieve to obtain a composite catalyst.

[0007] S2. Pre-treat the waste printed circuit boards to obtain pre-treated material; mix the pre-treated material with the composite catalyst, place it in a tubular pyrolysis furnace, introduce nitrogen gas, heat up and pyrolyze, and the generated waste gas is rapidly cooled to room temperature, alkali washed, and adsorbed before being discharged in compliance with standards to obtain pyrolysis products.

[0008] S3. The pyrolysis products are crushed, sieved, magnetically separated, and electrostatically separated to obtain ferromagnetic impurities, metal-rich powder and resin-rich powder; a leaching mixture is prepared, the metal-rich powder is added to the leaching mixture, hydrogen peroxide is added dropwise for constant temperature leaching, and the leaching solution and leaching residue are separated by vacuum filtration.

[0009] S4. The leachate is adsorbed through resin to obtain a copper-containing liquid phase; the resin is eluted with sulfuric acid to obtain an eluent containing gold and silver; sulfuric acid is added to the eluent to adjust the pH, sodium sulfite is added, the reaction is carried out, and the mixture is vacuum filtered and dried to obtain gold and silver powder; the copper-containing liquid phase is extracted and back-extracted to obtain a copper sulfate enriched solution, which is concentrated by vacuum evaporation, cooled and crystallized, and centrifuged to obtain copper sulfate; the leaching residue, silicate curing agent, silicate cement and deionized water are mixed and cured to obtain a solidified block.

[0010] In one feasible implementation, the step of preparing the cerium-zirconium solid solution in S1 is as follows: cerium ammonium nitrate, zirconium oxychloride, and deionized water are mixed in a mass-volume ratio of (22-25) g: (9.5-11) g: (180-220) mL. At a temperature of 55-65℃, ammonia water with a mass fraction of 25% is added dropwise at a rate of 1-2 mL / min to adjust the pH to 9.0-9.5. The mixture is then stirred and aged at 180-220 r / min for 1.5-2.5 h. After washing with deionized water until the pH reaches 6.5-7.5, the mixture is dried at 75-85℃ for 10-14 h, calcined at a rate of 4-6℃ / min to 580-620℃ for 3.5-4.5 h, and finally ground to obtain the cerium-zirconium solid solution.

[0011] The cerium-zirconium solid solution was prepared from cerium ammonium nitrate and zirconium oxychloride through co-precipitation, washing, drying, and high-temperature calcination. In this process, cerium ions and zirconium ions undergo hydrolysis and co-precipitation to form Ce during calcination. 0.5 Zr 0.5 The stable crystal structure of O2, and the introduction of zirconium ions into the cerium oxide lattice, generate a large number of structural oxygen vacancies, which is why Ce2 ​​can occur. 4+ With Ce 3+ The core material basis of reversible valence state transition; this valence state transition requires a reducing agent to be triggered in an oxygen-deficient or inert atmosphere. Reducing agents such as CO and small organic molecules produced during pyrolysis will convert to Ce. 4+ Providing electrons, prompting Ce 4+ The electron is reduced to Ce 3+ Simultaneously, lattice oxygen in the cerium-zirconium solid solution lattice is released, forming highly oxidizing reactive oxygen species, while Ce... 3+ The re-oxidation depends on the following pathways: Firstly, the endogenous oxygen-containing small molecules such as CO2, H2O, aldehydes, and ketones continuously released from the pyrolysis of epoxy resin in the circuit board matrix can fill the oxygen vacancies on the catalyst surface through oxygen transfer reactions, thereby transferring Ce... 3+ Re-oxidized to Ce 4+ This allows for localized reversible valence state cycling. On the other hand, the structural oxygen vacancies in the cerium-zirconium solid solution significantly reduce the lattice oxygen migration barrier, allowing lattice oxygen deep in the bulk phase to rapidly diffuse to the surface through oxygen vacancies, continuously replenishing the active oxygen consumed on the surface. Together, these two factors ensure the stable release of active oxygen throughout the entire pyrolysis cycle. Ultimately, this component blocks the formation pathway of brominated dioxins from the source and achieves in-situ fixation of bromine through the continuous release of active oxygen, making it the core catalytic component for controlling pollution at the source of pyrolysis in this scheme.

[0012] Meanwhile, this valence transition is also strictly controlled by temperature. Within the low-temperature pyrolysis range suitable for this scheme, the lattice energy is moderate, and the oxygen vacancy migration rate and electron transfer efficiency are at optimal levels. 4+ With Ce3+ The reversible valence transition can occur efficiently and continuously, stably releasing active oxygen. However, if the temperature is too high, it will cause severe lattice distortion and grain sintering and agglomeration in the cerium-zirconium solid solution, resulting in the annihilation of a large number of oxygen vacancies and the destruction of the structural basis for valence transition, ultimately leading to the loss of the ability to reversibly transition valence states. If the temperature is too low, the lattice activity is insufficient, the migration rate of oxygen vacancies and the rate of electron transfer are extremely slow, and the efficiency of valence transition is extremely low, which cannot meet the catalytic requirements. In the subsequent pyrolysis of waste printed circuit boards, the active oxygen continuously released by the cerium-zirconium solid solution through the above-mentioned reversible valence transition can, on the one hand, efficiently oxidize and crack the brominated intermediates such as bromophenol produced by the pyrolysis of brominated flame retardants, blocking their further condensation and cyclization to form brominated dioxins. On the other hand, it can oxidize the bromine free radicals generated simultaneously by pyrolysis into stable cerium bromide, realizing the in-situ fixation of bromine, and inhibiting the formation of dioxin-like substances and the release of bromine pollution from the source. This is the core catalytic component for source pollution control in this scheme.

[0013] In one feasible implementation, the step of preparing nitrogen-doped porous carbon in S1 is as follows: glucose, urea, calcium chloride and deionized water are mixed in a mass-volume ratio of (18-22) g: (9-11) g: (4.5-5.5) g: (180-220) mL, and hydrothermally reacted at 170-190℃ for 10-14 h to obtain a black carbon precursor. The precursor is washed with deionized water, dried at 75-85℃ for 10-14 h, calcined at 680-720℃ at a rate of 4-6℃ / min for 2.5-3.5 h, and ground through a 200-mesh sieve to obtain nitrogen-doped porous carbon.

[0014] Nitrogen-doped porous carbon was prepared by hydrothermal reaction and high-temperature calcination using glucose as the carbon source, urea as the nitrogen source, and calcium chloride as the template agent. During the hydrothermal process, Ca2+ dissociated from calcium chloride... 2+ The salting-out effect promotes rapid supersaturation and nucleation of the carbonized mesophase generated by glucose dehydration, while Ca... 2+ Calcium chloride can adsorb onto the surface of carbon nuclei, creating a steric hindrance effect that guides the formation of a network-like carbon framework. Calcium chloride itself fills the gaps in the framework as ionic clusters, forming a pore template. Nitrogen released from urea decomposition simultaneously embeds into the carbon framework, completing the initial doping. After the hydrothermal reaction, taking advantage of calcium chloride's water solubility, most of the free calcium chloride is removed through repeated washing with deionized water. Subsequent high-temperature inert calcination achieves deep carbonization of the carbon precursor and stabilization of the nitrogen-doped structure, ultimately forming nitrogen-doped porous carbon with a large specific surface area and a continuous porous structure. The outermost layer of the doped nitrogen atoms contains lone pairs of electrons that do not participate in bonding, while the Ce in the cerium-zirconium solid solution... 4+ Ce 3+ Zr 4 + And Mg in nano magnesium oxide 2+The outermost layer of each of these atoms has empty orbitals. The lone pair electrons of nitrogen atoms can fill the empty orbitals of these metal ions to form stable coordination bonds, anchoring the two active components on the surface and in the pores of nitrogen-doped porous carbon, achieving efficient and uniform dispersion, and ensuring that the valence state transformation of cerium-zirconium solid solution and the bromine fixation and neutralization effects of nano-magnesium oxide can be performed efficiently and stably.

[0015] The interconnected porous structure of nitrogen-doped porous carbon also has multiple auxiliary functions: First, it provides physical support, offering a stable loading platform for cerium-zirconium solid solution and nano-magnesium oxide, preventing structural collapse during the reaction process. Second, it constructs gas diffusion channels, allowing small molecule gases (such as hydrogen bromide and small organic molecules) generated during the subsequent pyrolysis of waste printed circuit boards to diffuse rapidly through the porous channels. This reduces gas retention within the system, preventing the aggregation and condensation of brominated intermediates to form dioxins, and also allows nano-magnesium oxide to contact hydrogen bromide more fully, enhancing the bromine fixation effect. Third, it optimizes the structure of pyrolysis products. The smooth escape of gas can form numerous pores in the pyrolysis products, promoting a loose and porous morphology, breaking the resin's encapsulation of valuable metals, and providing a good structural basis for the subsequent sorting of pyrolysis products and the leaching of valuable metals. Simultaneously, its ultra-large specific surface area can adsorb some trace pollutants and heavy metal ions generated during pyrolysis, assisting in the pre-stabilization of heavy metals and further improving the overall harmless treatment effect.

[0016] In one feasible implementation, in S1, the mass-to-volume ratio of the cerium-zirconium solid solution, nano-magnesium oxide, nitrogen-doped porous carbon, and deionized water is (42-48) g: (28-32) g: (22-28) g: (180-220) mL; the vacuum drying temperature is 75-85℃, and the vacuum drying time is 10-14 h; the calcination step is: placing it in a muffle furnace under a nitrogen atmosphere with a flow rate of 40-60 mL / min, and calcining at a temperature rise rate of 4-6℃ / min to 530-570℃ for 2.5-3.5 h; the pulverization and sieving mesh size is 100-200 mesh.

[0017] A cerium-zirconium solid solution, nitrogen-doped porous carbon, and nano-magnesium oxide are mixed in a specific ratio and stirred at high speed to form a homogeneous slurry. Vacuum drying removes moisture to prevent structural collapse during subsequent calcination. High-temperature calcination under a nitrogen atmosphere strengthens the bonding between the components, ultimately forming a structurally stable and functionally synergistic composite catalyst. Nano-magnesium oxide, with its strong alkalinity and high reactivity, reacts with hydrogen bromide produced during pyrolysis to generate magnesium bromide, enhancing bromine fixation. Simultaneously, it neutralizes acidic substances produced during epoxy resin pyrolysis, eliminating the catalytic effect of the acidic environment on the pyrolysis of organic components and inhibiting excessive cracking and agglomeration. The three components in the composite catalyst work synergistically: the cerium-zirconium solid solution provides core catalysis and in-situ bromine fixation; the nitrogen-doped porous carbon disperses active components and regulates the structure of pyrolysis products; and the nano-magnesium oxide assists in bromine fixation and regulates the pyrolysis reaction. Together, they achieve multiple functions including catalytic pyrolysis, dioxin inhibition, bromine fixation, heavy metal pre-stabilization, and optimization of the pyrolysis product structure, providing core support for the low-temperature pyrolysis of waste printed circuit boards, efficient recovery of valuable metals, and harmless treatment throughout the entire process.

[0018] In one feasible implementation, in step S2, the pretreatment step includes: manually removing surface batteries, capacitors, connectors, and other components; removing surface oil and dust; coarsely crushing at a speed of 180-220 r / min; and vibrating and sieving for 8-12 min to obtain particulate material with a particle size of 5 mm-20 mm; the mass ratio of the pretreated material to the composite catalyst is (900-1100):(8-12); the flow rate of nitrogen gas is 40-60 mL / min; the temperature of the pyrolysis is 300-340℃; the pyrolysis time is 50-70 min; the rapid cooling step involves rapidly cooling the waste gas to below 200℃ within 0.5 s using a rapid cooler; the alkaline washing reagent is 1000 mL of 10% sodium hydroxide solution; and the adsorption medium is a packed activated carbon adsorption device.

[0019] The core function of the pretreatment process is to remove interfering factors and optimize the characteristics of pyrolysis materials: manually removing non-target components such as batteries and capacitors is to prevent these components from exploding, releasing harmful gases, or generating impurities during pyrolysis, which would affect the purity and reaction stability of the pyrolysis products; removing surface oil and dust can eliminate the inhibitory effect of oil on catalyst activity and prevent dust from forming inert impurities during pyrolysis, thus reducing pyrolysis efficiency; crushing the circuit board to a uniform particle size and sieving it improves the uniformity of subsequent mixing with the composite catalyst, increases the specific surface area of ​​the material, accelerates the pyrolysis reaction rate, and ensures that the pyrolysis process is uniform and controllable. During pyrolysis, the components of the composite catalyst work synergistically: the active oxygen released from the cerium-zirconium solid solution oxidizes and cracks the brominated intermediates produced by the bromine-based flame retardant, blocking the pathway of condensation and cyclization to form brominated dioxins, while simultaneously converting bromine free radicals into stable cerium bromide to achieve in-situ bromine fixation; nano-magnesium oxide reacts with hydrogen bromide produced by pyrolysis to generate magnesium bromide, further enhancing the bromine fixation effect, while neutralizing the acidic substances produced by epoxy resin pyrolysis, eliminating the catalytic effect of the acidic environment on the pyrolysis of organic components, and inhibiting their excessive cracking and condensation; the through-pore structure of nitrogen-doped porous carbon provides diffusion channels for pyrolysis gases, promotes the escape of small molecule gases, and causes the pyrolysis products to form a loose and porous structure, breaking the resin's encapsulation of valuable metals and creating conditions for subsequent sorting and leaching.

[0020] The gas produced by pyrolysis is first rapidly cooled by a quencher. Since dioxins are prone to secondary formation in the 200℃-400℃ range, rapidly cooling the gas to below 200℃ within 0.5 seconds can quickly block the secondary synthesis pathway of dioxins, reducing dioxin emissions at the end. Subsequently, it is cooled to room temperature by a condenser. Utilizing the difference in condensation points between tar, oil mist, and gas, the tar and oil mist are liquefied and separated, which reduces the subsequent purification load and allows for the recovery of tar for resource utilization. The condensed gas is then passed through a sodium hydroxide solution for alkaline washing. Through acid-base neutralization, acidic gases such as hydrogen bromide and hydrogen chloride are removed from the gas, preventing air pollution caused by acidic gas emissions. Finally, it undergoes deep purification by a packed activated carbon adsorption device. Relying on the ultra-large specific surface area and adsorption performance of activated carbon, residual small organic molecules, trace amounts of dioxins, and particulate matter in the gas are adsorbed, ensuring that the exhaust gas meets emission standards and avoiding secondary pollution to the environment caused by pyrolysis exhaust gas.

[0021] In one feasible implementation, in step S3, the particle size of the crushed material is 1mm-4mm; the screening conditions are: rotation speed 180-220r / min, screening time 8-12min; the magnetic separation conditions are: magnetic field strength 0.25-0.35T, magnetic separation time 4-6min; and the electrostatic separation conditions are: working voltage 18-22kV, separation time 8-12min.

[0022] Based on the differences in the physical properties of different components, separation is carried out: pyrolysis products are crushed and sieved to a suitable particle size to remove large particles of impurities that were not completely pyrolyzed, ensuring the accuracy of subsequent separation; the magnetic separation process utilizes the difference in magnetic properties between ferromagnetic impurities (such as fragments of iron components) and other components, separating the ferromagnetic impurities under the action of a magnetic field, while metal-rich powders and resin-rich powders are non-magnetic, thus achieving efficient separation; the electrostatic separation process relies on the difference in conductivity of the materials. Since metal-rich powders (containing metals such as copper, gold, and silver) have high conductivity and resin-rich powders have low conductivity, the two materials will acquire different charges in a high-voltage electrostatic field and be subjected to different electric field forces, thus achieving separation. Through magnetic separation and electrostatic separation, not only can pyrolysis products be accurately separated into ferromagnetic impurities, metal-rich powders, and resin-rich powders, improving the purity and efficiency of subsequent metal leaching, but also the resin-rich powders and ferromagnetic impurities can be utilized separately as resources, achieving full-component recovery of pyrolysis products and avoiding resource waste.

[0023] In one feasible implementation, in step S3, the step of preparing the leaching mixture is as follows: 65-72g of thiourea is mixed with 1700-1900mL of deionized water, and 35-40mL of 98% concentrated sulfuric acid is added dropwise at a rate of 1-2mL / min. After cooling to room temperature, deionized water is added to bring the solution to a final volume of 1900-2100mL to obtain the leaching mixture; the mass-volume ratio of the metal-rich powder, the leaching mixture, and hydrogen peroxide is (180-220)g:(1900-2100)mL:(28-32)mL; the mass fraction of hydrogen peroxide is 30%, and the rate of hydrogen peroxide addition is 1-2mL / min; the temperature of the constant-temperature leaching is 32-38℃, and the time of the constant-temperature leaching is 80-100min; the pressure of the vacuum filtration is -0.07~-0.09MPa.

[0024] The leaching process uses thiourea-sulfuric acid-hydrogen peroxide as its core system. Sulfuric acid provides a stable, weakly acidic environment for the leaching system, which on the one hand inhibits the hydrolysis and inactivation of thiourea, and on the other hand activates the metal sites on the surface of the metal-rich powder, breaking the oxide film on the metal surface and creating conditions for subsequent oxidation and coordination reactions. Hydrogen peroxide provides a mild and controllable oxidation environment with moderate oxidizing power, which can oxidize zero-valent gold, silver, and copper in the metal-rich powder into ionic states (Au). 0 →Au + Ag 0 →Ag + Cu 0 →Cu 2 +This process avoids the oxidation and inactivation of thiourea caused by strong oxidants, while ensuring that the metal is fully oxidized into a coordinable ionic form. Thiourea, acting as a ligand, provides lone pairs of electrons from its amino and sulfur atoms, forming stable, soluble complexes with oxidized gold, silver, and copper ions. This process removes metal ions from the metal-rich powder and dissolves them in the leachate. Simultaneously, the loose, porous structure formed by the composite catalyst in the pyrolysis products increases the contact area between the metal-rich powder and the leachate, accelerating the diffusion rate of the leachate and allowing the metal ions to fully react with the ligands, significantly improving leaching efficiency. Compared to traditional cyanide leaching, this cyanide-free leaching process avoids the high toxicity of cyanide, fundamentally reducing the environmental risks of the leaching process and meeting the requirements for harmless treatment.

[0025] In one feasible implementation, in step S4, the resin adsorption step is as follows: passing the leachate through an adsorption column packed with 45-55 mL of macroporous weakly acidic cation exchange resin at a flow rate of 1 BV / h; the sulfuric acid elution step is as follows: eluting the resin with 90-110 mL of a 0.4-0.6 mol / L sulfuric acid solution at a flow rate of 1 BV / h; the concentration of the sulfuric acid added to the eluent is 0.5-1.0 mol / L; the pH adjustment range is 1.0-1.5; the amount of sodium sulfite used is 2.5-3.5 g; the reaction temperature is 52-58℃; the reaction time is 25-35 min; the vacuum filtration pressure is -0.07~-0.09 MPa; the drying temperature is 55-65℃; and the drying time is 10-14 h.

[0026] The leachate is a thiourea-sulfuric acidic system, in which gold and silver exist in stable thiourea complex cations. Under these acidic conditions, the macroporous weakly acidic cation exchange resin has a low degree of carboxyl dissociation, and the adsorption process is mainly based on hydrophobic physical adsorption of the macroporous framework. With the help of the mesoporous structure and organic polymer framework, the thiourea complexed gold and silver components are retained through hydrophobic interactions and van der Waals forces. At the same time, the protonated carboxyl groups can form hydrogen bonds with the amino groups of the thiourea molecules through hydroxyl hydrogen, further strengthening the adsorption binding force and achieving effective retention of gold and silver components.

[0027] Copper also forms complexes with thiourea in the leaching solution, but the stability constant of these complexes is significantly lower than that of gold and silver. Some complexes may exist in a neutral or weakly charged form, readily undergoing ligand protonation and structural dissociation under acidic conditions. After dissociation, the hydrophilicity increases significantly, making it difficult for the resin framework to adsorb and retain them. These compounds then elute with the liquid phase, resulting in a copper-containing liquid phase free of gold and silver, achieving the initial separation of precious metals from copper. After adsorption, the resin is eluted with sulfuric acid solution and high-concentration H₂O. +The protonable carboxyl groups weaken hydrogen bonding and disrupt the micro-ion exchange equilibrium, causing gold and silver thiourea complex ions to desorb from the resin, resulting in a high-concentration eluent containing gold and silver. The pH of the eluent is adjusted and sodium sulfite is added for reduction. Under this acidic condition, sodium sulfite undergoes protonation to convert into sulfurous acid, some of which exists in dissolved form as the core reducing species. Its reducing power is sufficient to reduce the gold and silver thiourea complex ions to elemental metals and release free thiourea. The use of excess sodium sulfite is designed to ensure complete reduction of the precious metals.

[0028] In one feasible implementation, in step S4, the extraction step is as follows: M5640 extractant and sulfonated kerosene are mixed at a volume ratio of 1:4 to obtain an M5640 extractant organic phase with a volume fraction of 20%; the copper-containing liquid phase is mixed with the extractant organic phase at a volume ratio of 1:1, and a two-stage countercurrent solvent extraction is performed. Each stage of extraction is stirred at a speed of 180-220 r / min for 4-6 min, and allowed to stand for 8-12 min until the two phases are completely separated, thus obtaining a copper-loaded organic phase; the back-extraction step is as follows: 1.8-2.2 mol / L sulfuric acid solution is used as the back-extraction agent and mixed with the copper-loaded organic phase at a volume ratio of 1:1, stirred at a speed of 180-220 r / min for 4-6 min, and allowed to stand for 8-12 min until the two phases are completely separated, thus obtaining a copper sulfate enriched solution.

[0029] The recovery of copper-containing liquid phase utilizes the selective separation effect of solvent extraction and back-extraction. The M5640 extractant can form a stable complex with copper ions without combining with other impurity ions, thus extracting copper ions from the aqueous phase to the organic phase and achieving the separation of copper ions. Subsequently, sulfuric acid solution is used as the back-extraction agent. The sulfuric acid can destroy the complexation between the extractant and copper ions, causing the copper ions to be back-extracted from the organic phase to the aqueous phase, resulting in a high-concentration copper sulfate enriched solution.

[0030] In one feasible implementation, in step S4, the conditions for vacuum evaporation concentration are: vacuum degree -0.07~-0.09MPa, temperature 60-80℃; the cooling crystallization is natural cooling crystallization, and the cooling crystallization time is 2-4h; the centrifugation speed is 3200-3800r / min, and the centrifugation time is 6-10min; the mass-volume ratio of the leaching residue, silicate curing agent, silicate cement and deionized water is (90-110)g:(10-14)g:(6-10)g:(25-35)mL; and the curing conditions are: room temperature, relative humidity 60%-70%, and curing time 28d.

[0031] The heavy metals remaining in the leaching residue have been pre-stabilized by a composite catalyst during the pyrolysis stage, reducing their leaching activity and laying a good foundation for subsequent solidification. The leaching residue is mixed with silicate curing agent, silicate cement, and deionized water. The cement and curing agent undergo a gelation reaction, gradually forming a dense, network-like solidified structure during curing. This structure, through a combination of physical encapsulation and chemical bonding, firmly seals the remaining heavy metals and harmful components within the solid, preventing contact with external water and soil, thus significantly reducing the risk of heavy metal migration and leaching. The solidified block formed after curing meets the heavy metal leaching concentration limits for hazardous waste landfill in GB18598-2019, enabling harmless landfill disposal. This solves the environmental disposal problem of leaching residue and achieves secondary resource utilization of solid waste, ultimately completing the entire process of harmless and high-value treatment of waste printed circuit boards.

[0032] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0033] This method achieves the harmless and high-value recycling of waste printed circuit boards by preparing a cerium-zirconium solid solution-nano magnesium oxide-nitrogen-doped porous carbon composite catalyst, combined with low-temperature pyrolysis and cyanide-free leaching processes. Cerium-zirconium solid solution (Ce) 0.5 Zr 0.5 O2 can undergo Ce2 reaction under anaerobic pyrolysis conditions. 4+ With Ce 3+ The spontaneous and reversible valence state transition between the two processes releases active oxygen, which, on the one hand, oxidizes and decomposes the brominated intermediates produced by the pyrolysis of brominated flame retardants through strong oxidizing properties, blocking the pathway of further condensation and cyclization to form brominated dioxins; on the other hand, it converts the simultaneously generated bromine free radicals into cerium bromide, achieving in-situ bromine fixation and inhibiting the formation of dioxin-like substances from the source. Simultaneously, nano-magnesium oxide reacts with hydrogen bromide released by the pyrolysis of brominated flame retardants to generate magnesium bromide, further strengthening bromine fixation. This also neutralizes the acidic substances produced by the pyrolysis of epoxy resin, eliminating the catalytic effect of the acidic environment on the pyrolysis of epoxy resin and inhibiting its excessive decomposition and condensation. Nitrogen-doped porous carbon, relying on its high specific surface area and the coordination of nitrogen atom lone pair electrons, holds Ce... 0.5 Zr 0.5 O2 and nano-magnesium oxide are anchored on the carbon surface to achieve efficient dispersion. Their through-hole porous structure forms physical support and gas diffusion channels during pyrolysis, promotes the escape of small molecule gases to form pores, and causes the pyrolysis products to form a loose and porous structure, providing a structural basis for the efficient leaching of valuable metals.

[0034] The cyanide-free leaching process employs a thiourea-sulfuric acid-hydrogen peroxide system. Sulfuric acid provides a stable, weakly acidic environment to inhibit thiourea hydrolysis and activate the metal surface, while hydrogen peroxide provides a mild and controllable oxidizing environment to oxidize zero-valent metals into ionic states. Thiourea, acting as a ligand, forms soluble complexes with gold, silver, and copper ions, thus achieving highly efficient leaching. Furthermore, the composite catalyst pre-stabilizes residual heavy metals during the pyrolysis stage, reducing their leaching migration activity. The leaching residue is then cemented and solidified with a curing agent, encapsulating residual heavy metals and harmful components within a solid structure, allowing for harmless landfill disposal. This process reduces pyrolysis energy consumption and environmental risks while increasing the recovery rate of valuable metals and overall resource utilization, demonstrating significant environmental and economic benefits. Attached Figure Description

[0035] Figure 1 This is a schematic flowchart of a method for harmlessly treating waste printed circuit boards according to the present invention. Detailed Implementation

[0036] To make the technical problems, technical solutions, and beneficial effects to be solved by this application clearer, the application will be further described in detail below with reference to embodiments. However, this should not be construed as limiting the scope of this application to the following examples. All other embodiments obtained by those skilled in the art without creative effort without departing from the above-described methodological spirit of this application are within the scope of protection of this application.

[0037] The singular forms “for,” “or,” “a,” “any,” and “described” used in this application are intended to include the plural forms unless the context clearly indicates otherwise. Furthermore, the terms “first” and “second” are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0038] Example 1

[0039] like Figure 1 As shown, a method for the harmless treatment of waste printed circuit boards includes the following steps:

[0040] S1. Mix 23.6g of cerium ammonium nitrate, 10.2g of zirconium oxychloride, and 200mL of deionized water. Stir at 300r / min at room temperature until completely dissolved to obtain a mixed salt solution. Place the solution in a constant temperature water bath at 60℃. While stirring at 200r / min, add 25% ammonia solution dropwise at a rate of 1.5mL / min to adjust the pH to 9.2, forming a hydroxide coprecipitate. Continue stirring at 200r / min and aging for 2h. Wash the precipitate with deionized water until the pH reaches 7.0. Dry at 80℃ for 12h. Place the precipitate in a muffle furnace and calcine at 600℃ for 4h at a heating rate of 5℃ / min. After natural cooling, grind and pulverize to obtain cerium-zirconium solid solution Ce. 0.5 Zr 0.5 O2; 20g glucose, 10g urea, 5g calcium chloride and 200mL deionized water were mixed and stirred at 300r / min at room temperature until completely dissolved to obtain a mixed solution. The solution was transferred to a hydrothermal reactor and hydrothermally reacted at 180℃ for 12h. After naturally cooling to room temperature, a black carbon precursor was obtained. It was washed three times with deionized water and then dried at 80℃ for 12h. It was then placed in a muffle furnace under a nitrogen atmosphere at a flow rate of 50mL / min and calcined at 700℃ for 3h at a heating rate of 5℃ / min. After naturally cooling to room temperature, it was ground and passed through a 200-mesh sieve to obtain nitrogen-doped porous carbon; 45g cerium-zirconium solid solution Ce 0.5 Zr 0.5 O2, 30g of nano-magnesium oxide, and 25g of nitrogen-doped porous carbon were added to a high-speed mixer, along with 200mL of deionized water. The mixture was stirred at 3000r / min for 30min to obtain a uniform slurry. The slurry was then vacuum dried at 80℃ for 12h and placed in a muffle furnace under a nitrogen atmosphere at a flow rate of 50mL / min. The temperature was increased to 550℃ at a rate of 5℃ / min and calcined for 3h. After natural cooling, the slurry was pulverized and passed through a 150-mesh sieve to obtain the composite catalyst.

[0041] S2. Take discarded printed circuit boards from small household appliances (rice cookers / induction cookers / microwave ovens, etc.), manually remove the batteries, capacitors, connectors, and other components from the surface, clean off surface oil and dust, and put them into a jaw crusher for coarse crushing. Vibrate and screen at 200 r / min for 10 min to obtain granular material with a particle size of 5 mm-20 mm, which is the pretreated material. Add 10 g of composite catalyst to 1000 g of pretreated material, stir at 200 r / min for 10 min to mix evenly, and then put it into a tubular pyrolysis furnace. Introduce nitrogen gas into the furnace at a flow rate of 50 mL / min. After replacing the air in the furnace for 30 minutes, the furnace temperature is raised to 320℃ at a heating rate of 5℃ / min, and pyrolyzed at a constant temperature for 60 minutes. The gas produced by pyrolysis is first rapidly cooled to below 200℃ within 0.5 seconds by a quencher, and then cooled to room temperature by a condenser, so that the tar and oil mist are condensed, liquefied and separated and removed. Subsequently, the gas is passed into 1000mL of 10% sodium hydroxide solution for alkaline washing to remove acidic gases. Finally, it is deeply adsorbed and purified by a packed activated carbon adsorption device before being discharged in compliance with standards. After pyrolysis is completed, nitrogen gas is continuously purged for protection, and the gas is naturally cooled to room temperature to obtain the pyrolysis products.

[0042] S3. Transfer the pyrolysis products to an impact crusher and crush them to a particle size of 1mm–4mm. Vibrate and screen at 200r / min for 10min to remove large particles. Pass the medium-crushed material through a magnetic separator with a magnetic field strength of 0.3T for 5min to separate ferromagnetic impurities. Send the remaining material to an electrostatic separator with a working voltage of 20kV for 10min to separate metal-rich powder and resin-rich powder. Collect the separated resin-rich powder and ferromagnetic impurities for subsequent resource utilization. Mix 68.5g of thiourea with 1800mL of deionized water and stir at 300r / min until completely dissolved. 38 mL of 98% concentrated sulfuric acid was added dropwise at a rate of 1.5 mL / min with continuous stirring. After cooling to room temperature, deionized water was added to bring the solution to a final volume of 2000 mL, yielding a leaching mixture. 200 g of metal-rich powder was placed in a reactor, and 2000 mL of the leaching mixture was added. The mixture was stirred at 200 r / min, and the system temperature was controlled at 35 °C. Constant-temperature leaching was then initiated. During the leaching process, 30 mL of 30% hydrogen peroxide was added dropwise at a rate of 1.5 mL / min. The entire process was carried out at a constant temperature for 90 min. After leaching, the mixture was vacuum filtered at a pressure of -0.08 MPa to separate the leaching solution and the leaching residue.

[0043] S4. The leachate was passed through an adsorption column packed with 50 mL of macroporous weakly acidic cation exchange resin at a flow rate of 1 BV / h. Gold and silver ions in the leachate were selectively adsorbed and retained by the resin, resulting in a copper-containing liquid phase after gold and silver removal. After adsorption, the resin was eluted with 100 mL of 0.5 mol / L sulfuric acid solution at a flow rate of 1 BV / h to obtain an eluent containing gold and silver. The pH of the eluent was adjusted to 1.2 by adding 0.7 mol / L sulfuric acid, and the mixture was stirred at 200 r / min for 5 min. Then, 3 g of sodium sulfite was added, the temperature was raised to 55 °C, and the mixture was stirred at 300 r / min for 30 min. The mixture was then vacuum filtered at a pressure of -0.08 MPa. The filter cake was washed with deionized water at 200 r / min for 10 min with stirring, and the washing was repeated 3 times. The mixture was then dried at 60 °C for 12 h to obtain gold powder and silver powder. M5640 extractant and sulfonated kerosene were mixed at a volume ratio of 1:4 to obtain an M5640 extractable organic phase with a volume fraction of 20%. The copper-containing liquid phase was mixed with the extractable organic phase at a volume ratio of 1:1 and subjected to two-stage countercurrent solvent extraction. Each extraction stage was stirred at 200 r / min for 5 min and allowed to stand for 10 min until the two phases were completely separated, thus obtaining the copper-loaded organic phase. After extraction, 2 mol / L sulfuric acid solution was used as the back-extraction agent and mixed with the copper-loaded organic phase at a volume ratio of 1:1. The mixture was stirred at 200 r / min for 5 min and allowed to stand for 10 min until the two phases were completely separated, thus obtaining the copper sulfate enriched solution. The copper sulfate enriched solution was concentrated by vacuum evaporation at -0.08 MPa and 70 °C until a crystalline film appeared on the solution surface. Evaporation was stopped, and the solution was allowed to cool and crystallize naturally for 3 h. Finally, it was centrifuged at 3500 r / min for 8 min to obtain the copper sulfate product. Add 12g of silicate curing agent, 8g of ordinary silicate cement and 30mL of deionized water to 100g of leaching residue. Stir at 300r / min for 10min. Pour into a mold and cure for 28 days at room temperature and 65% relative humidity to obtain a solidified block. Perform heavy metal leaching toxicity testing on the solidified block. If it meets the standards, it can be landfilled harmlessly.

[0044] Example 2

[0045] like Figure 1 As shown, a method for the harmless treatment of waste printed circuit boards includes the following steps:

[0046] S1. Mix 22g of cerium ammonium nitrate, 9.5g of zirconium oxychloride, and 180mL of deionized water. Stir at 300r / min at room temperature until completely dissolved to obtain a mixed salt solution. Place the solution in a constant temperature water bath at 55℃. While stirring at 200r / min, add 25% ammonia solution dropwise at a rate of 1mL / min to adjust the pH to 9.0, forming a hydroxide coprecipitate. Continue stirring at 180r / min and age for 1.5h. Wash the precipitate with deionized water until the pH reaches 6.5. Dry at 75℃ for 10h. Place the precipitate in a muffle furnace and calcine at 580℃ for 3.5h at a heating rate of 4℃ / min. After natural cooling, grind and pulverize to obtain cerium-zirconium solid solution Ce. 0.5 Zr 0.5 O2; 18g glucose, 9g urea, 4.5g calcium chloride and 180mL deionized water were mixed and stirred at 300r / min at room temperature until completely dissolved to obtain a mixed solution. The solution was transferred to a hydrothermal reactor and hydrothermally reacted at 170℃ for 10h. After naturally cooling to room temperature, a black carbon precursor was obtained. It was washed three times with deionized water, then dried at 75℃ for 10h. It was then placed in a muffle furnace under a nitrogen atmosphere at a flow rate of 50mL / min and calcined at 680℃ for 2.5h at a heating rate of 4℃ / min. After naturally cooling to room temperature, it was ground and passed through a 200-mesh sieve to obtain nitrogen-doped porous carbon; 42g cerium-zirconium solid solution Ce 0.5 Zr 0.5 O2, 28g of nano-magnesium oxide, and 22g of nitrogen-doped porous carbon were added to a high-speed mixer, along with 180mL of deionized water. The mixture was stirred at 3000r / min for 30min to obtain a uniform slurry. The slurry was then vacuum dried at 75℃ for 10h and placed in a muffle furnace under a nitrogen atmosphere at a flow rate of 40mL / min. The slurry was then heated to 530℃ at a heating rate of 4℃ / min for 2.5h. After natural cooling, the slurry was pulverized and passed through a 100-mesh sieve to obtain the composite catalyst.

[0047] S2. Take discarded printed circuit boards from small household appliances (rice cookers / induction cookers / microwave ovens, etc.), manually remove the batteries, capacitors, connectors, and other components from the surface, clean off surface oil and dust, and put them into a jaw crusher for coarse crushing. Vibrate and screen at 180 r / min for 8 minutes to obtain granular material with a particle size of 5 mm-20 mm, which is the pretreated material. Add 8 g of composite catalyst to 900 g of pretreated material, stir at 200 r / min for 10 minutes to mix evenly, and then put it into a tubular pyrolysis furnace. Pour nitrogen gas at a flow rate of 40 mL / min into the furnace to replace the pyrolysis material. After 30 minutes of air in the furnace, the furnace temperature is raised to 300℃ at a heating rate of 5℃ / min, and pyrolysis is carried out at a constant temperature for 50 minutes. The gas produced by pyrolysis is first rapidly cooled to below 200℃ within 0.5 seconds by a quencher, and then cooled to room temperature by a condenser to condense and liquefy the tar and oil mist and remove them. Subsequently, the gas is passed into 1000mL of 10% sodium hydroxide solution for alkaline washing to remove acidic gases. Finally, it is purified by deep adsorption by a packed activated carbon adsorption device before being discharged in compliance with standards. After pyrolysis is completed, nitrogen gas is continuously purged for protection, and the gas is naturally cooled to room temperature to obtain the pyrolysis products.

[0048] S3. Transfer the pyrolysis products to an impact crusher and crush them to a particle size of 1mm–4mm. Vibrate and screen at 180r / min for 8 minutes to remove large particles. Pass the medium-crushed material through a magnetic separator with a magnetic field strength of 0.25T for 4 minutes to separate ferromagnetic impurities. Send the remaining material to an electrostatic separator with a working voltage of 18kV for 8 minutes to separate metal-rich powder and resin-rich powder. Collect the separated resin-rich powder and ferromagnetic impurities for subsequent resource utilization. Mix 65g of thiourea with 1700mL of deionized water and stir at 300r / min until completely dissolved. 35 mL of 98% concentrated sulfuric acid was added dropwise at a rate of 1 mL / min with continuous stirring. After cooling to room temperature, deionized water was added to bring the solution to a final volume of 1900 mL, yielding a leaching mixture. 180 g of metal-rich powder was placed in a reactor, and 1900 mL of the leaching mixture was added. The mixture was stirred at 200 r / min, and the system temperature was controlled at 32 °C. Constant-temperature leaching was then initiated. During the leaching process, 28 mL of 30% hydrogen peroxide was added dropwise at a rate of 1 mL / min. The entire process was carried out under constant-temperature leaching for 80 min. After leaching, the mixture was vacuum filtered at a pressure of -0.07 MPa to separate the leaching solution and the leaching residue.

[0049] S4. The leachate was passed through an adsorption column packed with 45 mL of macroporous weakly acidic cation exchange resin at a flow rate of 1 BV / h. Gold and silver ions in the leachate were selectively adsorbed and retained by the resin, resulting in a copper-containing liquid phase after gold and silver removal. After adsorption, the resin was eluted with 90 mL of 0.4 mol / L sulfuric acid solution at a flow rate of 1 BV / h to obtain an eluent containing gold and silver. The pH of the eluent was adjusted to 1.0 by adding 0.5 mol / L sulfuric acid, and the mixture was stirred at 200 r / min for 5 min. Then, 2.5 g of sodium sulfite was added, the temperature was raised to 52 °C, and the mixture was stirred at 300 r / min for 25 min. The mixture was then vacuum filtered at a pressure of -0.07 MPa. The filter cake was washed with deionized water at 200 r / min for 10 min with stirring, and the washing was repeated 3 times. The mixture was then dried at 55 °C for 10 h to obtain gold powder and silver powder. M5640 extractant and sulfonated kerosene were mixed at a volume ratio of 1:4 to obtain an M5640 extractable organic phase with a volume fraction of 20%. The copper-containing liquid phase was mixed with the extractable organic phase at a volume ratio of 1:1 and subjected to two-stage countercurrent solvent extraction. Each extraction stage was stirred at 180 r / min for 4 min and allowed to stand for 8 min until the two phases were completely separated, resulting in a copper-loaded organic phase. After extraction, 1.8 mol / L sulfuric acid solution was used as a back-extraction agent and mixed with the copper-loaded organic phase at a volume ratio of 1:1. The mixture was stirred at 180 r / min for 4 min and allowed to stand for 8 min until the two phases were completely separated, resulting in a copper sulfate enriched solution. The copper sulfate enriched solution was concentrated by vacuum evaporation at -0.07 MPa and 60 °C until a crystalline film appeared on the solution surface. Evaporation was stopped, and the solution was allowed to cool and crystallize naturally for 2 h. Finally, it was centrifuged at 3200 r / min for 6 min to obtain the copper sulfate product. Add 90g of leaching residue, 10g of silicate curing agent, 6g of ordinary silicate cement and 25mL of deionized water, stir at 300r / min for 10min, pour into a mold, and cure for 28 days at room temperature and 60% relative humidity to obtain a solidified block. Perform heavy metal leaching toxicity testing on the solidified block. If it meets the standards, it can be disposed of in a harmless landfill.

[0050] Example 3

[0051] like Figure 1 As shown, a method for the harmless treatment of waste printed circuit boards includes the following steps:

[0052] S1. Mix 25g of cerium ammonium nitrate, 11g of zirconium oxychloride, and 220mL of deionized water. Stir at 300r / min at room temperature until completely dissolved to obtain a mixed salt solution. Place the solution in a constant temperature water bath at 65℃. While stirring at 200r / min, add 25% ammonia solution dropwise at a rate of 2mL / min to adjust the pH to 9.5, forming a hydroxide coprecipitate. Continue stirring at 220r / min and aging for 2.5h. Wash the precipitate with deionized water until the pH reaches 7.5. Dry at 85℃ for 14h. Place the precipitate in a muffle furnace and calcine at 6℃ / min to 620℃ for 4.5h. After natural cooling, grind and pulverize to obtain cerium-zirconium solid solution Ce. 0.5 Zr 0.5 O2; 22g glucose, 11g urea, 5.5g calcium chloride and 220mL deionized water were mixed and stirred at 300r / min at room temperature until completely dissolved to obtain a mixed solution. The solution was transferred to a hydrothermal reactor and hydrothermally reacted at 190℃ for 14h. After naturally cooling to room temperature, a black carbonaceous precursor was obtained. It was washed three times with deionized water, then dried at 85℃ for 14h, and placed in a muffle furnace under a nitrogen atmosphere at a flow rate of 50mL / min. The temperature was increased to 720℃ at a rate of 6℃ / min and calcined for 3.5h. After naturally cooling to room temperature, it was ground and passed through a 200-mesh sieve to obtain nitrogen-doped porous carbon; 48g cerium-zirconium solid solution Ce 0.5 Zr 0.5 O2, 32g of nano-magnesium oxide, and 28g of nitrogen-doped porous carbon were added to a high-speed mixer, along with 220mL of deionized water. The mixture was stirred at 3000r / min for 30min to obtain a uniform slurry. The slurry was then vacuum dried at 85℃ for 14h and placed in a muffle furnace under a nitrogen atmosphere at a flow rate of 60mL / min. The slurry was then heated to 570℃ at a heating rate of 6℃ / min for 3.5h. After natural cooling, the slurry was pulverized and passed through a 200-mesh sieve to obtain the composite catalyst.

[0053] S2. Take discarded printed circuit boards from small household appliances (rice cookers / induction cookers / microwave ovens, etc.), manually remove the batteries, capacitors, connectors, and other components from the surface, clean off surface oil and dust, and put them into a jaw crusher for coarse crushing. Vibrate and screen at 220 r / min for 12 min to obtain granular material with a particle size of 5 mm-20 mm, which is the pretreated material. Add 12 g of composite catalyst to 1100 g of pretreated material, stir at 200 r / min for 10 min to mix evenly, and then put it into a tubular pyrolysis furnace. Introduce nitrogen gas into the furnace at a flow rate of 60 mL / min. After replacing the air in the furnace for 30 minutes, the furnace temperature was raised to 340℃ at a heating rate of 5℃ / min and pyrolyzed at a constant temperature for 70 minutes. The gas produced by pyrolysis was first rapidly cooled to below 200℃ in 0.5 seconds by a quencher, and then cooled to room temperature by a condenser to condense and liquefy the tar and oil mist and remove them. Subsequently, the gas was passed into 1000mL of 10% sodium hydroxide solution for alkaline washing to remove acidic gases. Finally, it was deeply adsorbed and purified by a packed activated carbon adsorption device before being discharged in compliance with standards. After pyrolysis was completed, nitrogen protection was continued, and the gas was naturally cooled to room temperature to obtain the pyrolysis products.

[0054] S3. Transfer the pyrolysis products to an impact crusher and crush them to a particle size of 1mm–4mm. Vibrate and screen at 220r / min for 12min to remove large particles. Pass the medium-crushed material through a magnetic separator with a magnetic field strength of 0.35T for 6min to separate ferromagnetic impurities. Send the remaining material to an electrostatic separator with a working voltage of 22kV for 12min to separate metal-rich powder and resin-rich powder. Collect the separated resin-rich powder and ferromagnetic impurities for subsequent resource utilization. Mix 72g of thiourea with 1900mL of deionized water and stir at 300r / min until completely dissolved. Add 40 mL of 98% concentrated sulfuric acid at a rate of 2 mL / min while stirring continuously. After cooling to room temperature, add deionized water to bring the solution to a final volume of 2100 mL to obtain a leaching mixture. Place 220 g of metal-rich powder in a reactor, add 2100 mL of the leaching mixture, and stir at 200 r / min. Control the system temperature at 38 °C and begin constant-temperature leaching. During the leaching process, add 32 mL of 30% hydrogen peroxide at a rate of 2 mL / min. Leach at a constant temperature for 100 min. After leaching, filter under vacuum at a pressure of -0.09 MPa to separate the leaching solution and leaching residue.

[0055] S4. The leachate was passed through an adsorption column packed with 55 mL of macroporous weakly acidic cation exchange resin at a flow rate of 1 BV / h. Gold and silver ions in the leachate were selectively adsorbed and retained by the resin, resulting in a copper-containing liquid phase after gold and silver removal. After adsorption, the resin was eluted with 110 mL of 0.6 mol / L sulfuric acid solution at a flow rate of 1 BV / h to obtain an eluent containing gold and silver. The pH of the eluent was adjusted to 1.5 by adding 1.0 mol / L sulfuric acid, and the mixture was stirred at 200 r / min for 5 min. Then, 3.5 g of sodium sulfite was added, the temperature was raised to 58 °C, and the mixture was stirred at 300 r / min for 35 min. The mixture was then vacuum filtered at a pressure of -0.09 MPa. The filter cake was washed with deionized water at 200 r / min for 10 min with stirring, and the washing was repeated 3 times. The mixture was then dried at 65 °C for 14 h to obtain gold powder and silver powder. M5640 extractant and sulfonated kerosene were mixed at a volume ratio of 1:4 to obtain an M5640 extractable organic phase with a volume fraction of 20%. The copper-containing liquid phase was mixed with the extractable organic phase at a volume ratio of 1:1 and subjected to two-stage countercurrent solvent extraction. Each extraction stage was stirred at 220 r / min for 6 min and allowed to stand for 12 min until the two phases were completely separated, thus obtaining the copper-loaded organic phase. After extraction, 2.2 mol / L sulfuric acid solution was used as the back-extraction agent and mixed with the copper-loaded organic phase at a volume ratio of 1:1. The mixture was stirred at 220 r / min for 6 min and allowed to stand for 12 min until the two phases were completely separated, thus obtaining a copper sulfate enriched solution. The copper sulfate enriched solution was concentrated by vacuum evaporation at -0.09 MPa and 80 °C until a crystalline film appeared on the solution surface. Evaporation was stopped, and the solution was allowed to cool and crystallize naturally for 4 h. Finally, it was centrifuged at 3800 r / min for 10 min to obtain the copper sulfate product. Add 14g of silicate curing agent, 10g of ordinary silicate cement and 35mL of deionized water to 110g of leaching residue. Stir at 300r / min for 10min. Pour into a mold and cure for 28 days at room temperature and 70% relative humidity to obtain a solidified block. Perform heavy metal leaching toxicity testing on the solidified block. If it meets the standards, it can be landfilled harmlessly.

[0056] Comparative Example 1

[0057] A method for harmlessly treating waste printed circuit boards differs from Example 1 in that a composite catalyst is not prepared in step S1, while the remaining steps and parameters are the same.

[0058] Comparative Example 2

[0059] A method for the harmless treatment of waste printed circuit boards differs from Example 1 in that only cerium-zirconium solid solution is prepared in step S1, i.e. only a single catalyst of cerium-zirconium solid solution is used. The remaining steps and parameters are the same.

[0060] Comparative Example 3

[0061] A method for harmlessly treating waste printed circuit boards differs from Example 1 in that the pyrolysis temperature in step S2 is 500℃, which is a conventional high-temperature pyrolysis temperature. The remaining steps and parameters are the same.

[0062] Performance testing:

[0063] Dioxin-like substance inhibition rate test: 100 mL of gas samples from the pyrolysis tail gas obtained in Examples 1-3 and Comparative Examples 1-3 before purification were passed into an absorption bottle containing 100 mL of n-hexane and absorbed for 30 min. After dehydration with anhydrous sodium sulfate and purification with a silica gel column, the absorbent was quantitatively detected using high-resolution gas chromatography-high-resolution mass spectrometry. A DB-5MS capillary column (30 m × 0.25 mm × 0.25 μm) was used, and the column temperature program was set to an initial temperature of 80 °C and a maintenance temperature of 100 °C. Hold for 2 min, increase the temperature to 200℃ at 5℃ / min, hold for 5 min, then increase the temperature to 280℃ at 2℃ / min, hold for 10 min, with an injection port temperature of 250℃, an injection volume of 1 μL, and a mass spectrometry resolution ≥10000. Using the dioxin formation amount of the pyrolysis system of Comparative Example 1 (without composite catalyst) as a blank baseline, calculate the dioxin inhibition rate (%) = (dioxin formation amount of blank baseline - dioxin formation amount of the test sample) / dioxin formation amount of blank baseline × 100%.

[0064] Bromine fixation efficiency test: 10g of pretreated material and 5g of pyrolysis product from Examples 1-3 and Comparative Examples 1-3 were respectively placed in polytetrafluoroethylene digestion vessels, and 20mL of nitric acid-perchloric acid mixture was added, wherein the volume ratio of nitric acid to perchloric acid in the nitric acid-perchloric acid mixture was 3:1. The vessels were placed in a microwave digester, and the digestion program was set as follows: heat to 120℃ and hold for 5min, heat to 180℃ and hold for 15min. After digestion, the mixture was cooled to room temperature, filtered to remove insoluble matter, and the filtrate was settled. The volume was increased to 50 mL. The total bromine content of the pretreated material and pyrolysis products was quantitatively determined using an ion chromatograph. An anion exchange column was used, and the mobile phase was a sodium carbonate-sodium bicarbonate mixed solution with a sodium carbonate concentration of 20 mmol / L and a sodium bicarbonate concentration of 10 mmol / L. The flow rate was 1.0 mL / min, and the detection wavelength was 210 nm. The bromine fixation efficiency (%) was calculated as: bromine content in pyrolysis products / bromine content in pretreated material × 100%.

[0065] Gold, silver, and copper leaching rate tests: Take 0.5g of the metal-rich powder from Examples 1-3 and Comparative Examples 1-3 respectively, place the metal-rich powder in a polytetrafluoroethylene beaker, add 10mL of a nitric acid-hydrochloric acid mixture (the volume ratio of nitric acid to hydrochloric acid in the mixture is 1:3), heat to 80℃ to digest until the solution is clear, cool to room temperature, and then dilute to 50mL to obtain the digestion solution, which is used as the initial metal content detection solution; simultaneously, take 10mL of the leaching solution from Examples 1-3 and Comparative Examples 1-3 respectively, add 2mL of nitric acid for acidification, and dilute to 50mL to obtain the leaching solution metal content detection solution. ICP-OES was used to quantitatively detect the concentrations of gold, silver, and copper ions in two solutions. The instrument parameters were set as follows: radio frequency power 1300W, nebulizing gas flow rate 0.8L / min, auxiliary gas flow rate 0.2L / min, observation height 15mm, and detection wavelengths of gold 242.795nm, silver 328.068nm, and copper 324.754nm. The leaching rate of gold, silver, and copper was calculated according to the formula: metal leaching rate (%) = (metal concentration in leaching solution × leaching solution volume) / (initial metal concentration in digestion solution × digestion solution volume) × 100%.

[0066] Table 1. Performance test results of the products from the harmless treatment of waste printed circuit boards in Examples 1-3 and Comparative Examples 1-3.

[0067]

[0068] Heavy metal leaching toxicity test of solidified blocks: Concentrated sulfuric acid and concentrated nitric acid were mixed at a volume ratio of 2:1, diluted thoroughly with deionized water, and the pH was adjusted to 3.2±0.2 to obtain the leaching agent. 10.00g of solidified block samples from Examples 1-3 and Comparative Examples 1-3 were taken respectively, pulverized, and passed through a 100-mesh sieve. The samples were placed in 250mL Erlenmeyer flasks, and the leaching agent was added at a liquid-to-solid ratio of 10:1. The flasks were placed in a constant temperature shaking incubator with a shaking frequency of 110r / min, a shaking temperature of 25℃, and a shaking time of 18h. After shaking, the samples were filtered through medium-speed quantitative filter paper and then through a 0.45μm filter membrane. The concentrations of copper, lead, zinc, and cadmium heavy metal ions in the filtered leachate were quantitatively detected using ICP-OES. The detection parameters were consistent with those used in the metal leaching rate test. The concentrations of Cr were determined using the diphenylcarbazide spectrophotometric method. 6+ The concentration was tested, and the test results were compared with the heavy metal leaching limits in GB18598-2019 "Standard for Pollution Control of Hazardous Waste Landfill" to determine whether the solidified block met the harmlessness standard.

[0069] Post-purification exhaust gas emission compliance testing: The final exhaust gases from Examples 1-3 and Comparative Examples 1-3, after rapid cooling, tar removal by condensation, sodium hydroxide alkaline washing, and deep purification by activated carbon adsorption, were collected. A stationary pollution source exhaust gas sampling system was used to collect exhaust gas samples at a flow rate of 1.0 L / min for 30 minutes. Dioxins, acidic gases (hydrogen bromide, hydrogen chloride), non-methane total hydrocarbons, and particulate matter were simultaneously detected in the samples. Dioxins were detected using high-resolution gas chromatography-high-resolution mass spectrometry (GC-MS), with chromatographic and mass spectrometric parameters identical to those used in the dioxin inhibition rate test. Hydrogen bromide and hydrogen chloride were detected using ion chromatography with an anion exchange column. The mobile phase was a sodium carbonate-sodium bicarbonate mixed solution, with a sodium carbonate concentration of 20 mmol / L and a sodium bicarbonate concentration of 10 mmol / L, at a flow rate of 1.0 mL / min. The detection wavelength was 210 nm. Non-methane total hydrocarbons were detected by gas chromatography, with the instrument equipped with a dual-column dual-flame ionization detector. Both the total hydrocarbon analysis column and the methane separation column were kept at a constant temperature of 105℃, the injection port temperature was 150℃, the detector temperature was 200℃, and the injection volume was 1 mL. The non-methane total hydrocarbon content was calculated by subtracting the methane concentration from the total hydrocarbon concentration. Particulate matter was detected by gravimetric method. The sample was filtered through a quartz fiber filter membrane, dried to constant weight, and then weighed to calculate the particulate matter concentration. The results of each test were compared with the corresponding national standard limits to determine whether the purified exhaust gas met the compliance emission requirements (the emission concentration limits for dioxins, hydrogen bromide, hydrogen chloride, and particulate matter refer to GB18484-2020 "Standard for Pollution Control of Hazardous Waste Incineration", and the emission limit for non-methane total hydrocarbons refer to GB16297-1996 "Integrated Emission Standard for Air Pollutants").

[0070] Table 2. Performance tests of the products from Examples 1-3 and Comparative Examples 1-3 for the harmless treatment of waste printed circuit boards.

[0071]

[0072] As shown in Tables 1 and 2, the dioxin inhibition rate, bromine fixation efficiency, and gold, silver, and copper leaching efficiency of the products from the harmless treatment of waste printed circuit boards in Examples 1-3 are higher than those in Comparative Examples 1-3. Furthermore, the concentrations of copper, lead, zinc, cadmium, and Cr in the solidified blocks are significantly lower. 6+ The leaching concentrations of dioxins, hydrogen bromide, hydrogen chloride, non-methane total hydrocarbons, and particulate matter in the waste gas were lower than those of Comparative Examples 1-3. This indicates that Examples 1-3 exhibit better performance in dioxin inhibition, bromine fixation, valuable metal leaching, heavy metal stability, and waste gas purification than Comparative Examples 1-3 for the harmless treatment products of waste printed circuit boards.

[0073] In Comparative Example 1, due to the lack of a composite catalyst, the pyrolysis process of the waste printed circuit board was in a natural reaction state without the participation of a catalyst. The large amount of bromine free radicals generated by the thermal decomposition of the brominated flame retardant could not be captured and fixed. This resulted in a large amount of bromine escaping in the form of hydrogen bromide, significantly reducing the bromine fixation efficiency, and also promoted the large-scale generation of brominated dioxins, leading to a low dioxin inhibition rate. Simultaneously, the decomposition of organic components such as epoxy resin and phenolic resin in the circuit board was limited, and metals such as copper, gold, and silver were encapsulated by incompletely decomposed resin, making it difficult for the leaching agent to fully contact and react with the metals. This directly leads to a significant decrease in the leaching rates of gold, silver, and copper. The heavy metals in the pyrolysis slag are chemically reactive, and subsequent solidification treatment can only achieve physical encapsulation, failing to form a stable chemical bond. This results in an increased leaching concentration of heavy metals in the solidified block, with some indicators exceeding national standard limits. Furthermore, the generation of pollutants such as acidic gases, non-methane hydrocarbons, and particulate matter from natural pyrolysis is higher. Even with the same waste gas purification process, efficient removal cannot be achieved, leading to a significant deterioration in both overall resource recovery and harmlessness. This fully demonstrates that composite catalysts are the core key to improving the treatment effect of waste printed circuit boards.

[0074] Comparative Example 2 used only a cerium-zirconium solid solution catalyst. The absence of nano-magnesium oxide meant that bromine free radicals generated during the decomposition of brominated flame retardants during pyrolysis could not be effectively fixed, resulting in a large amount of bromine entering the waste gas as hydrogen bromide gas, directly reducing the bromine fixation efficiency. The lack of nitrogen-doped porous carbon prevented the adsorption and enrichment of dioxin precursors and small organic molecules generated during pyrolysis, and also hindered the degradation of brominated dioxins. Relying solely on the catalytic effect of the cerium-zirconium solid solution was insufficient to effectively inhibit the formation of dioxins, leading to a significant decrease in the dioxin inhibition rate. Simultaneously, the single cerium-zirconium solid solution also affected the organic components in the circuit board. The decomposition effect of the resin is limited, and the metals are still partially coated by the undecomposed resin, thus reducing the leaching efficiency of gold, silver, and copper. In terms of heavy metal stabilization, the lack of the auxiliary effect of nano-magnesium oxide and nitrogen-doped porous carbon weakens the stabilization effect of heavy metals in the pyrolysis slag, and increases the leaching concentration of heavy metals in the solidified block. Meanwhile, the emission concentrations of pollutants such as hydrogen bromide generated due to insufficient bromine fixation and non-methane total hydrocarbons generated due to insufficient decomposition of organic components in the exhaust gas also increase accordingly. This further proves that only the synergistic effect of nano-magnesium oxide, nitrogen-doped porous carbon, and cerium-zirconium solid solution can achieve comprehensive optimization of bromine fixation, dioxin suppression, metal recovery, heavy metal stabilization, and exhaust gas purification.

[0075] Comparative Example 3 employed conventional high-temperature pyrolysis at 500℃. This temperature condition directly contradicts the core design of the low-temperature catalytic pyrolysis scheme presented in this study. It not only significantly increases pyrolysis energy consumption but also leads to substantial degradation of various performance characteristics: the 500℃ high temperature destroys the stable structure and active sites of the composite catalyst, weakens the reactive oxygen release capacity of the cerium-zirconium solid solution, the bromine fixation efficiency of nano-magnesium oxide, and the adsorption and dispersion effect of nitrogen-doped porous carbon. This prevents the effective capture and fixation of bromine free radicals generated by the decomposition of bromine-based flame retardants, resulting in a significant decrease in bromine fixation efficiency and the formation of large quantities of brominated dioxins, significantly reducing the dioxin inhibition rate. Simultaneously, the high temperature... High temperatures cause excessive cracking and condensation of organic components in circuit boards, resulting in a dense structure of pyrolysis products that blocks the contact channels between the leaching agent and valuable metals, leading to a significant reduction in the leaching efficiency of gold, silver, and copper. In addition, high temperatures alter the occurrence form of heavy metals in the pyrolysis slag, reducing the pre-stabilizing effect of the catalyst on heavy metals, which increases the leaching concentration of heavy metals in the subsequent solidified block. Furthermore, the emissions of pollutants such as acidic gases and non-methane hydrocarbons generated by high-temperature pyrolysis increase significantly, resulting in a deterioration in the exhaust gas purification effect. This fully demonstrates the core design of low-temperature pyrolysis, which effectively reduces pyrolysis energy consumption while ensuring the full performance of the composite catalyst.

[0076] Comparative Examples 1-3, due to the lack of composite catalysts and low-temperature pyrolysis processes, resulted in a decrease in the inhibition rate of dioxins, a decrease in bromine fixation efficiency, a decrease in the leaching rate of valuable metals, a deterioration in the stabilization effect of heavy metals, and an increase in the concentration of pollutants in the exhaust gas. These combined to manifest as varying degrees of deterioration in dioxin inhibition performance, bromine fixation performance, valuable metal leaching performance, heavy metal stabilization performance, and exhaust gas purification performance.

[0077] The above results demonstrate and describe the basic principles and main features of this application, as well as its advantages.

[0078] The embodiments of the present invention have been described above with reference to the accompanying drawings. However, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of the present invention without departing from the spirit and scope of the claims. All of these forms are within the protection scope of the present invention.

Claims

1. A method for the harmless treatment of waste printed circuit boards, characterized in that, Includes the following steps: S1. Prepare cerium-zirconium solid solution and nitrogen-doped porous carbon. Mix the cerium-zirconium solid solution, nano-magnesium oxide, and nitrogen-doped porous carbon, add deionized water to obtain a uniform slurry, and then vacuum dry, calcine, pulverize and sieve to obtain a composite catalyst. S2. Pre-treat the waste printed circuit boards to obtain pre-treated material; The pretreated material is mixed with the composite catalyst, nitrogen gas is introduced, and the mixture is heated to pyrolyze to obtain the pyrolysis product. S3. The pyrolysis products are crushed, sieved, magnetically separated, and electrostatically separated to obtain ferromagnetic impurities, metal-rich powder, and resin-rich powder. Prepare a leaching mixture by adding the metal-rich powder to the leaching mixture, adding hydrogen peroxide dropwise for constant temperature leaching, and then separating the leaching solution and leaching residue by vacuum filtration. S4. The leachate is adsorbed by resin to obtain a copper-containing liquid phase; the resin is eluted with sulfuric acid to obtain an eluent containing gold and silver; sulfuric acid is added to the eluent to adjust the pH, sodium sulfite is added, the reaction is carried out, and the mixture is vacuum filtered and dried to obtain gold powder and silver powder; the copper-containing liquid phase is extracted and back-extracted to obtain a copper sulfate enriched solution, which is concentrated by vacuum evaporation, cooled and crystallized, and centrifuged to obtain copper sulfate; the leaching residue, silicate curing agent, silicate cement and deionized water are mixed and cured to obtain a solidified block.

2. The method for harmlessly treating waste printed circuit boards according to claim 1, characterized in that, In step S1, the preparation of the cerium-zirconium solid solution is as follows: cerium ammonium nitrate, zirconium oxychloride, and deionized water are mixed in a mass-volume ratio of (22-25) g:(9.5-11) g:(180-220) mL. At a temperature of 55-65℃, 25% ammonia water is added dropwise at a rate of 1-2 mL / min to adjust the pH to 9.0-9.

5. The mixture is then stirred and aged at 180-220 r / min for 1.5-2.5 h. After washing with deionized water until the pH reaches 6.5-7.5, the mixture is dried at 75-85℃ for 10-14 h, calcined at a rate of 4-6℃ / min to 580-620℃ for 3.5-4.5 h, and finally ground to obtain the cerium-zirconium solid solution.

3. The method for harmlessly treating waste printed circuit boards according to claim 1, characterized in that, In step S1, the step of preparing nitrogen-doped porous carbon is as follows: glucose, urea, calcium chloride and deionized water are mixed in a mass-volume ratio of (18-22) g: (9-11) g: (4.5-5.5) g: (180-220) mL, and hydrothermally reacted at 170-190℃ for 10-14 h to obtain a black carbon precursor. The precursor is washed with deionized water, dried at 75-85℃ for 10-14 h, calcined at 680-720℃ for 2.5-3.5 h at a rate of 4-6℃ / min, and ground through a 200-mesh sieve to obtain nitrogen-doped porous carbon.

4. The method for harmlessly treating waste printed circuit boards according to claim 1, characterized in that, In S1, the mass-to-volume ratio of the cerium-zirconium solid solution, nano-magnesium oxide, nitrogen-doped porous carbon, and deionized water is (42-48) g: (28-32) g: (22-28) g: (180-220) mL; the vacuum drying temperature is 75-85℃, and the vacuum drying time is 10-14 h; the calcination step is: placing it in a muffle furnace under a nitrogen atmosphere with a flow rate of 40-60 mL / min, and calcining it at a temperature increase rate of 4-6℃ / min to 530-570℃ for 2.5-3.5 h; the pulverization and sieving mesh size is 100-200 mesh.

5. The method for harmlessly treating waste printed circuit boards according to claim 1, characterized in that, In step S2, the pretreatment step includes: manually removing surface batteries, capacitors, connectors, and other components; removing surface oil and dust; coarsely crushing at a speed of 180-220 r / min; and vibrating and sieving for 8-12 min to obtain particulate material with a particle size of 5 mm-20 mm; the mass ratio of the pretreated material to the composite catalyst is (900-1100):(8-12); the flow rate of nitrogen gas is 40-60 mL / min; the temperature of the pyrolysis is 300-340℃; and the pyrolysis time is 50-70 min.

6. The method for harmlessly treating waste printed circuit boards according to claim 1, characterized in that, In step S3, the particle size of the crushed material is 1mm-4mm; the screening conditions are: rotation speed 180-220r / min, screening time 8-12min; the magnetic separation conditions are: magnetic field strength 0.25-0.35T, magnetic separation time 4-6min; and the electrostatic separation conditions are: working voltage 18-22kV, separation time 8-12min.

7. The method for harmlessly treating waste printed circuit boards according to claim 1, characterized in that, In step S3, the step of preparing the leaching mixture is as follows: 65-72g of thiourea is mixed with 1700-1900mL of deionized water, and 35-40mL of 98% concentrated sulfuric acid is added dropwise at a rate of 1-2mL / min. After cooling to room temperature, deionized water is added to bring the solution to a final volume of 1900-2100mL to obtain the leaching mixture. The mass-volume ratio of the metal-rich powder, the leaching mixture, and hydrogen peroxide is (180-220)g:(1900-2100)mL:(28-32)mL. The mass fraction of hydrogen peroxide is 30%, and the rate of hydrogen peroxide addition is 1-2mL / min. The temperature of the constant-temperature leaching is 32-38℃, and the time of the constant-temperature leaching is 80-100min. The pressure of the vacuum filtration is -0.07~-0.09MPa.

8. A method for harmlessly treating waste printed circuit boards according to claim 1, characterized in that, In step S4, the resin adsorption step is as follows: the leachate is passed through an adsorption column packed with 45-55 mL of macroporous weakly acidic cation exchange resin at a flow rate of 1 BV / h; the sulfuric acid elution step is as follows: the resin is eluted with 90-110 mL of sulfuric acid solution with a concentration of 0.4-0.6 mol / L at a flow rate of 1 BV / h; the concentration of the sulfuric acid added to the eluent is 0.5-1.0 mol / L; the pH adjustment range is 1.0-1.5; the amount of sodium sulfite used is 2.5-3.5 g; the reaction temperature is 52-58℃; the reaction time is 25-35 min; the vacuum filtration pressure is -0.07~-0.09 MPa; the drying temperature is 55-65℃; and the drying time is 10-14 h.

9. A method for harmlessly treating waste printed circuit boards according to claim 1, characterized in that, In step S4, the extraction step is as follows: M5640 extractant and sulfonated kerosene are mixed at a volume ratio of 1:4 to obtain the M5640 extractant organic phase; the copper-containing liquid phase is mixed with the extractant organic phase at a volume ratio of 1:1, and two-stage countercurrent solvent extraction is performed. Each stage of extraction is stirred at a speed of 180-220 r / min for 4-6 min, and allowed to stand for 8-12 min until the two phases are completely separated, and the copper-loaded organic phase is obtained. The back-extraction step is as follows: 1.8-2.2 mol / L sulfuric acid solution is used as the back-extraction agent and mixed with the copper-loaded organic phase at a volume ratio of 1:

1. The mixture is stirred at a speed of 180-220 r / min for 4-6 min, and allowed to stand for 8-12 min until the two phases are completely separated, and the copper sulfate enriched solution is obtained.

10. A method for harmlessly treating waste printed circuit boards according to claim 1, characterized in that, In step S4, the conditions for vacuum evaporation concentration are: vacuum degree -0.07~-0.09MPa, temperature 60-80℃; the cooling crystallization is natural cooling crystallization, and the cooling crystallization time is 2-4h; the centrifugation speed is 3200-3800r / min, and the centrifugation time is 6-10min; the mass-volume ratio of the leaching residue, silicate curing agent, silicate cement and deionized water is (90-110)g:(10-14)g:(6-10)g:(25-35)mL; the curing conditions are: room temperature, relative humidity 60%-70%, and curing time 28d.

Images