Low-temperature pyrolysis method for recovering copper in circuit board

Abstract

The embodiment of the invention provides a low-temperature pyrolysis method for recycling copper in a circuit board, and belongs to the technical field of waste metal resource recycling. The low-temperature pyrolysis method comprises the steps that 2-12 cm < 2 > circuit board fragments are continuously heated for 40-120 min at the pyrolysis temperature of 120-270 DEG C in a pyrolysis device, so that metal and nonmetal in the circuit board fragments are dissociated, the glue connection state of copper in the metal and the circuit board is broken through pyrolysis and then falls off from the circuit board to be recycled, and the recovery rate of the copper is larger than or equal to 90%. According to the low-temperature pyrolysis method, circuit board fragments are fully mixed, do accelerated motion and collide with one another in the pyrolysis process through pyrolysis devices such as a rotary furnace, and copper separation and recovery are achieved at the low-temperature pyrolysis temperature.

Description

Technical Field

[0001] The invention belongs to the technical field of recycling waste metal resources, and in particular relates to a low-temperature pyrolysis method for recycling copper in circuit boards. Background Art

[0002] As the life cycle of technology products shortens, electronic waste has increased significantly, and it is expected to exceed 75 million tons in 2030, of which various waste circuit boards account for 10%. PCB circuit boards contain a variety of resins, flame retardants, reinforcing materials, colloids and copper metal. Recycling the copper metal resources in PCB circuit boards has a positive impact on environmental resource protection and sustainable development, and also has significant economic value.

[0003] Physical methods, high-pressure crushing methods, organic solvent swelling methods or high-temperature heat treatment methods are usually used to separate metals and non-metals in PCB circuit boards for classified recycling. High-pressure crushing methods and organic solvent swelling methods are limited to laboratory research. Industrial large-scale metal recycling generally uses physical methods, which usually require core process flows such as circuit board crushing, eddy current separation, magnetic separation, gravity separation, and graded screening. On the one hand, the physical method requires complicated process steps and each process requires corresponding special processing equipment, which makes the processing cost very high. On the other hand, the circuit board will produce more broken fine particles after crushing, which is very easy to cause over-crushing agglomeration, resulting in a loss of 10-40% of the metal before being recycled, which seriously reduces the metal recovery rate.

[0004] The high-temperature heat treatment method generally uses a fixed bed to heat treat the PCB circuit board at 300-600°C to achieve partial dissociation of the metal, and then crushes or manually peels off to achieve metal separation and recovery, and the recovery rate is generally less than 80%. On the one hand, it is difficult to further improve the metal recovery rate. On the other hand, since the reaction temperature exceeds 280°C or even higher, the halogen flame retardant in the PCB circuit board gradually decomposes. Among them, the persistent organic pollutants (POPs) such as brominated diphenyl ethers (PBDEs) produced as the reaction temperature increases will increase, causing serious and irreversible ecological pollution.

[0005] In view of this, a new low-temperature pyrolysis method for recovering copper in circuit boards is needed to fully or partially solve the above problems. Summary of the invention

[0006] In order to solve at least one aspect of the above problems and defects in the prior art, the embodiment of the present invention provides a low-temperature pyrolysis method for recovering copper in circuit boards. The circuit board fragments are pyrolyzed under low-temperature conditions by using a pyrolysis device such as a rotary kiln, so that the circuit board fragments are fully mixed, accelerated and collided with each other during the pyrolysis process to obtain higher fluidity and heat transfer. The dissociation of copper and other non-metals can be achieved at a low-temperature pyrolysis temperature of 120 to 270°C to achieve a copper recovery rate of more than 90%. The technical solution is as follows:

[0007] According to one aspect of an embodiment of the present invention, a low-temperature pyrolysis method for recovering copper in a circuit board is provided. The low-temperature pyrolysis method comprises:

[0008] In the pyrolysis device, 2 to 12 cm 2 The circuit board fragments are heated at a pyrolysis temperature of 120 to 270° C. for 40 to 120 minutes, so that the metal and non-metal in the circuit board fragments are dissociated and the copper in the metal and the circuit board are bonded in a form that is broken by pyrolysis and then falls off the circuit board to be recovered, and the recovery rate of copper is greater than or equal to 90%.

[0009] In some embodiments, specifically, the pyrolysis device includes a pyrolysis reaction chamber, a rotating component and a promoting component; the rotating component drives the pyrolysis reaction chamber to rotate at a preset speed to drive the circuit board fragments inside it to rotate; the promoting component is arranged inside the pyrolysis reaction chamber to promote the circuit board fragments to rotate, move, and collide with each other.

[0010] In some embodiments, further, the promoting component includes a blade structure, a blocking structure, or a combination of a blade structure and a blocking structure; the blade structure causes the circuit board fragments to rotate and obtain acceleration through blade rotation; the blocking structure promotes contact between the circuit board fragments to increase the probability of collision between the circuit board fragments.

[0011] In some embodiments, alternatively, the pyrolysis device is any one of a rotary furnace, a rotary kiln, a rotary tube furnace, and a rotary reaction furnace.

[0012] In some embodiments, alternatively, the circuit board fragments are waste copper clad circuit boards that have been shredded, and the waste copper clad circuit boards include any one of waste copper clad circuit boards made of paper-based materials, waste paper laminated copper clad circuit boards, scraps of paper laminated copper clad circuit boards, and glass fiber material circuit boards, or any combination thereof.

[0013] In some embodiments, specifically, 2 to 12 cm 2 The shape of the circuit board fragments is a square, a rectangle, a parallelogram, a quadrilateral or a rhombus, and the aspect ratio of the circuit board fragments is in the range of 1 to 2.5:1.

[0014] In some embodiments, specifically, the circuit board fragments are fed into the pyrolysis device in batches with a preset loading amount, and each batch of circuit board fragments is fed into the pyrolysis device after pyrolysis is completed; the preset loading amount ranges from 20 to 60 g / L.

[0015] In some embodiments, specifically, the pyrolysis atmosphere in the pyrolysis device is a nitrogen atmosphere, a helium atmosphere, an air atmosphere or a vacuum. When a nitrogen atmosphere, a helium atmosphere or an air atmosphere is used, the gas flow rate ranges from 50 to 200 mL / min; the preset rotation speed ranges from 2 to 20 r / min; the heating rate of the pyrolysis process ranges from 2 to 8°C / min; and a three-phase product is obtained after pyrolysis, wherein copper is in the solid phase product and the separation rate of copper is greater than or equal to 95%.

[0016] In some embodiments, preferably, the circuit board fragments are 5 to 10 cm 2 The invention is a rectangular product with a length-to-width ratio of 2:1; the preset filling amount of each batch is 25-35 g / L; the pyrolysis device is a rotary kiln, and the pyrolysis atmosphere in the rotary kiln is a nitrogen atmosphere with a nitrogen flow rate of 80-120 mL / min; the preset rotation speed of the rotating parts of the rotary kiln is 2-3 r / min; the heating rate of the pyrolysis process is 3-7°C / min; the pyrolysis temperature is 130-170°C; the continuous pyrolysis time at the pyrolysis temperature is 40-80 min; and the copper separation rate is 98%.

[0017] In some embodiments, the copper separated from the circuit board scraps by low temperature pyrolysis may alternatively be recovered by a vibrating screen device or a shaking table.

[0018] The low-temperature pyrolysis method for recovering copper in circuit boards provided by the embodiments of the present invention has at least one or part of the following advantages:

[0019] (1) The low-temperature pyrolysis method for recovering copper from circuit boards provided in an embodiment of the present invention utilizes a pyrolysis device such as a rotary kiln to pyrolyze circuit board fragments, so that the circuit board fragments are fully mixed, accelerated, and collide with each other during the pyrolysis process to obtain higher fluidity and heat transfer properties. The effective dissociation of copper from other metals and non-metals can be achieved at a low-temperature pyrolysis temperature of 120 to 270° C., achieving a copper separation rate of more than 90%;

[0020] (2) The low-temperature pyrolysis method for recovering copper from circuit boards provided in the embodiments of the present invention can use common industrial heat treatment equipment as a pyrolysis device, such as a rotary kiln and other heat treatment reaction furnaces with rotating blades, baffles or guide plates, etc., which has high industrial popularity and strong process adaptability;

[0021] (3) The pyrolysis temperature of the low-temperature pyrolysis method for recovering copper from circuit boards provided by the embodiment of the present invention is lower than 280° C., or even lower than 200° C., which ensures a copper separation rate and copper recovery rate of more than 90%, while effectively avoiding the decomposition of pollutants such as halogen flame retardants, and its liquid phase product does not contain halogen components, is pollution-free to the environment, and realizes clean production;

[0022] (4) The low-temperature pyrolysis method for recovering copper from circuit boards provided by the embodiment of the present invention is pyrolyzed at low temperature by a pyrolysis device such as a rotary furnace, and the adhesive state between copper and the circuit board is destroyed, so that the copper is separated from the circuit board by itself, and the separation rate exceeds 90%;

[0023] (5) The low-temperature pyrolysis method for recovering copper from circuit boards provided in the embodiment of the present invention can effectively dissociate other metals and non-metals except copper by fully mixing, accelerating movement and mutual collision of circuit board fragments in a rotary kiln, thereby facilitating the recovery and reuse of other metals or non-metals;

[0024] (6) The low-temperature pyrolysis method for recovering copper from circuit boards provided in an embodiment of the present invention crushes the circuit boards to obtain circuit board fragments of a specific size without crushing, thereby avoiding the phenomenon of over-crushing and agglomeration caused by crushing, thereby reducing the loss of metallic copper;

[0025] (7) The low-temperature pyrolysis method for recovering copper from circuit boards provided in the embodiment of the present invention is applicable to the case where a small amount of copper is recovered using a small pyrolysis device by feeding in batches according to a preset loading amount, and can also be applicable to the case where a large amount of copper is recovered by batch processing. The pyrolysis parameters do not need to be adjusted and have good industrial production adaptability;

[0026] (8) The low-temperature pyrolysis method for recovering copper from circuit boards provided in an embodiment of the present invention achieves a copper separation rate of greater than 95% after low-temperature pyrolysis in a rotary furnace, and then the separated copper can be effectively recovered using common simple screening equipment (vibrating screen, shaking table, etc.). BRIEF DESCRIPTION OF THE DRAWINGS

[0027] These and / or other aspects and advantages of the present invention will become apparent and readily understood from the following description of the preferred embodiments in conjunction with the accompanying drawings, in which:

[0028] Figure 1 A flowchart of a low-temperature pyrolysis method for recovering copper from a circuit board according to one embodiment of the present invention;

[0029] Figure 2 According to an embodiment of the present invention, the Figure 1 A schematic diagram of a circuit board structure using a low-temperature pyrolysis method;

[0030] Figure 3According to an embodiment of the present invention, the Figure 1 A schematic diagram of a pyrolysis device of a low-temperature pyrolysis method;

[0031] Figure 4 It is a comparison chart of the types and relative contents of liquid products obtained by gas chromatography-mass spectrometry (GC-MS) after pyrolysis reaction according to Examples 1 to 3 of the present invention and Comparative Example 1. DETAILED DESCRIPTION

[0032] The technical solution of the present invention is further specifically described below by examples and in conjunction with the accompanying drawings. In the specification, the same or similar reference numerals indicate the same or similar components. The following description of the embodiments of the present invention with reference to the accompanying drawings is intended to explain the overall inventive concept of the present invention and should not be construed as a limitation of the present invention.

[0033] The current industrial-level copper recycling method for circuit boards is usually fixed-bed high-temperature pyrolysis. If you want the copper separation rate or effective recovery rate to exceed 80%, the pyrolysis temperature usually needs to be at least 300°C, or even around 400°C. If you want the copper separation rate or effective recovery rate to further exceed 90%, there are usually two directions of optimization. One direction is to continue to increase the pyrolysis temperature, and the other direction is to further reduce the circuit board fragments.

[0034] However, materials such as circuit boards have very complex superimposed components, and some metals have complex physical and chemical relationships with circuit boards through bonding. As the pyrolysis temperature continues to rise, more and more substances will be dissociated from the circuit boards and may further decompose. It is worth noting that circuit boards contain flame retardants, which generally contain halogen components. When the pyrolysis temperature exceeds 280°C, the flame retardants will automatically decompose, and the decomposition process will produce halogens, which will cause serious and irreversible pollution to the environment.

[0035] At the same time, theoretically, if the degree of circuit board fragmentation can be increased, the finer the circuit board fragments, the more helpful it is to make copper fall off the circuit board during pyrolysis. But in fact, the finer the circuit board fragments, the more helpful it is to separate copper. Fine circuit board fragments or broken circuit board particles are prone to over-crushing and agglomeration during the pyrolysis process, resulting in the loss of metal substances (such as copper) before they are recycled, and the lost copper cannot be recycled.

[0036] Therefore, the embodiment of the present invention proposes a novel low-temperature pyrolysis method for recovering copper from circuit boards. The low-temperature pyrolysis method can complete pyrolysis under low temperature conditions, and on the other hand, it does not need to excessively fragment or granulate the circuit board, avoiding halogen decomposition while achieving a copper separation rate of more than 90%. The core step of the low-temperature pyrolysis method is to heat 2 to 12 cm thick copper in a pyrolysis device. 2 The circuit board fragments are heated at a pyrolysis temperature of 120 to 270° C. for 40 to 120 minutes, so that the metal and non-metal in the circuit board fragments are dissociated and the copper in the metal and the circuit board are bonded in a state of being broken by pyrolysis and then fall off the circuit board for recovery.

[0037] See also Figure 1 , showing the process flow and processing steps of the low temperature pyrolysis method, specifically including:

[0038] Step S100: crushing the circuit board to obtain circuit board fragments with a preset size;

[0039] Step S200: placing the circuit board fragments in a pyrolysis device according to a preset loading amount, and starting the pyrolysis device;

[0040] Step S300: controlling the mechanical power parameters of the pyrolysis device so that the circuit board fragments therein can fully move and collide, and controlling the pyrolysis parameters so that the circuit board fragments therein can be fully pyrolyzed;

[0041] Step S400: detecting decomposition products of the circuit board fragments during and after the pyrolysis process;

[0042] Step S500: After the pyrolysis is completed, copper in the circuit board fragments is recovered through screening.

[0043] In one example, the low-temperature pyrolysis method mainly involves the screening, determination and regulation of the following five parameters, including: the preset size of the circuit board fragments (including the shape and size of the fragments), the preset loading amount of the circuit board fragments, the structure of the pyrolysis device, the mechanical and dynamic parameters of the pyrolysis device and the pyrolysis parameters (heating rate, pyrolysis temperature, pyrolysis duration, etc.). When these parameters are optimized and combined to form the preferred parameter conditions, a copper separation rate of more than 90%, or even more than 95%, can be obtained.

[0044] In one example, alternatively, the type of waste copper-clad circuit boards that can be used in the low-temperature pyrolysis method is generally any one of paper-based waste copper-clad boards, paper-laminated copper-clad board waste, paper-laminated copper-clad board scraps, and glass fiber material circuit boards, or any combination thereof. Preferably, PCB circuit boards with single-sided or double-sided copper foils using paper as a reinforcement material can obtain a copper recovery rate of more than 90% through the low-temperature pyrolysis method.

[0045] See also Figure 2 , shows the basic structure of a type of paper-based waste copper-clad circuit board. Usually, the substrate of this type of circuit board usually includes a superimposed structure of multiple layers of reinforcing materials and multiple layers of resin, and the outermost layer of the superimposed structure is coated with metal copper by gluing. Due to the final processing and molding process, the superimposed structure of the circuit board substrate and its copper cladding undergo a series of physical and chemical reactions to form larger molecular chains. Figure 2 It can be seen that the larger molecular chains also carry halogen elements such as those in flame retardants, and the halogen elements are located at the edge of the molecular chains where they are easy to fall off. If the pyrolysis conditions are not set properly, for example, the pyrolysis temperature exceeds 270°C, they will decompose and fall off to form pollutants. Therefore, on the one hand, it is necessary to focus on selecting the structure of the pyrolysis device and its mechanical and dynamic parameters to promote the full pyrolysis of circuit board fragments, and on the other hand, it is necessary to focus on controlling the pyrolysis parameters, especially the pyrolysis temperature, to avoid the decomposition of harmful substances and achieve clean separation.

[0046] In one example, through a large number of experiments, it is verified that, specifically, when the circuit board uses the above-mentioned paper-based reinforced material waste copper-clad circuit board, the shape of the circuit board fragments can maintain a basic square structure, such as but not limited to square, rectangle, parallelogram, quadrilateral, rhombus, etc. At the same time, it is necessary to ensure that the single piece area of ​​the circuit board fragments is in the range of 2 to 12 cm 2 , and the aspect ratio of the square structure is generally in the range of 1 to 2.5:1.

[0047] In one example, in order to allow the circuit board fragments to be fully pyrolyzed in the pyrolysis device only under low temperature conditions (120-270°C) so that the copper can be fully separated, it is necessary to select an appropriate pyrolysis device. Preferably, the pyrolysis device suitable for the low-temperature pyrolysis method needs to have a controllable rotating reactor. Alternatively, such a controllable rotating reactor can use a rotary kiln, a rotary kiln, a rotary tube furnace, a rotary reactor, etc., which are very common in existing industrial applications.

[0048] Furthermore, after a specific pyrolysis device is selected, such as a small rotary kiln, the mechanical structure of the small rotary kiln and its mechanical power parameters can be determined. For example, a small rotary kiln is usually provided with a rotating part that drives its rotation, and some small rotary kilns themselves are provided with a disturbance device inside the furnace, such as a rotating blade, a stirring device, a guide plate, etc. Of course, those skilled in the art will understand that the pyrolysis device belongs to commonly used heat treatment equipment, and suitable existing heat treatment equipment can be selected according to the actual requirements of circuit board copper separation, or the existing heat treatment equipment can be modified or customized, such as optimizing the internal structure of the equipment (rotating blades, stirring devices, guide plates, etc.) according to the movement of circuit board fragments inside the equipment during the actual pyrolysis separation process. This example is only an illustrative example, and those skilled in the art should not be understood as a limitation of the present invention.

[0049] See also Figure 3 , showing a basic structural schematic diagram of a pyrolysis device. Exemplarily, the pyrolysis device 100 includes the following basic structures: a pyrolysis reaction chamber 10, a rotating component 20 and a promoting component 30. Among them, the rotating component 20 drives the pyrolysis reaction chamber 10 to rotate at a preset speed to drive the circuit board fragments 200 inside it to rotate. The promoting component 30 is arranged inside the pyrolysis reaction chamber 10 to promote the rotation, movement and mutual collision of the circuit board fragments 200. In theory, as long as the furnace body can be rotated as a whole and the promoting component 30 such as a disturbance structure and a diversion structure can be arranged inside the furnace body, the reactor can be selected as a pyrolysis carrier suitable for the low-temperature pyrolysis method. At the same time, those skilled in the art can also optimize the specific structure of the pyrolysis device and its mechanical and dynamic parameters according to actual needs.

[0050] In one example, further, the promotion component 30 includes a blade structure 31, a blocking structure 32, or a combination of the blade structure 31 and the blocking structure 32. The blade structure 31 causes the circuit board fragments 200 to rotate and obtain acceleration through blade rotation. The blocking structure 32 promotes contact between the circuit board fragments 200 to increase the probability of collision between the circuit board fragments 200.

[0051] In one example, preferably, a rotary kiln is used as the pyrolysis device 100 . In this case, the rotary kiln 100 has a rotating component 20 because it needs to be rotated in a controlled manner during operation. At the same time, the furnace of the rotary kiln 100 is the pyrolysis reaction chamber 10 .

[0052] Further preferably, a blade structure 31 is provided in the rotary kiln (pyrolysis device 100). When the rotary kiln 100 rotates under the drive of the rotating part 20, and the blade structure 31 also rotates in the pyrolysis reaction chamber 10, the numerous circuit board fragments 200 inside the pyrolysis reaction chamber 10 will move along with the rotation of the inner wall surface of the rotary kiln 100 driven by the rotation of both sides, and the numerous circuit board fragments 200 will gradually rise from the bottom of the rotary kiln 100 to the highest point of its inner wall and then fall back to its bottom along the inner wall surface. The numerous circuit board fragments 200 continuously rotate inside the pyrolysis chamber 10, and increase the probability of collision with each other when falling back. At the same time, the accelerated movement of the circuit board fragments 200 and the probability of collision with each other are further enhanced due to the blade rotation cutting or slapping the circuit board fragments 200 at the position close to the blade structure 31.

[0053] Further preferably, a blocking structure 32 is provided in the rotary furnace (pyrolysis device 100). The blocking structure 32 is provided at different positions of the pyrolysis reaction chamber 10 in different shapes (e.g., plate-shaped, strip-shaped, etc.), so as to guide or disturb the flow direction of the circuit board fragments 200 in motion, effectively increase the probability of collision between the circuit board fragments 200 in motion, and effectively increase the residence time of the circuit board fragments 200 in the pyrolysis reaction chamber 10, especially the probability of repeated cyclic movement at a specific position, so that the circuit board fragments 200 are evenly heated and evenly stressed, thereby promoting the full progress of the pyrolysis process and also helping to reduce the pyrolysis temperature.

[0054] By using the rotary kiln 100 and arranging the blade structure 31 and the blocking structure 32 inside the rotary kiln 100, the circuit board fragments 200 therein are constantly and fully moved in all directions, and the circuit board fragments 200 are violently and repeatedly collided with each other. In this case, the fluidity and heat transfer of the circuit board fragments 200 are significantly enhanced. On the one hand, the circuit board fragments 200 are fully mixed and collided, and on the other hand, the circuit board fragments are constantly changed in the direction and acceleration of movement, so that the residence time and effective pyrolysis time in the pyrolysis reaction chamber 10 are prolonged. The combination of the two aspects makes the efficiency of copper separation from the circuit board higher during the pyrolysis process, and the pyrolysis is more fully carried out so that the pyrolysis temperature can be appropriately reduced.

[0055] In one example, in order to ensure sufficient pyrolysis of the circuit board fragments, it is also necessary to adjust the loading amount in the pyrolysis device. When the processing volume of the pyrolysis device is fixed, too little or too much loading amount will affect the pyrolysis effect of the circuit board fragments. For example, when the loading amount is very small, especially when the loading amount is less than 1 / 3 of the processing volume, there are not enough circuit board fragments inside the pyrolysis device to collide with each other at a high frequency each time the pyrolysis reaction is carried out, which is not conducive to the full pyrolysis. For another example, when the loading amount is very large, especially when the loading amount is greater than 2 / 3 of the processing volume, since the pyrolysis device is full of circuit board fragments, these circuit board fragments do not have enough space to move, which is also not conducive to the full pyrolysis.

[0056] In one example, in order to ensure a suitable loading amount and to perform batch copper separation operations, preferably, the circuit board fragments are fed into the pyrolysis device in batches with a preset loading amount, and each batch of circuit board fragments is fed into the pyrolysis device after the pyrolysis is completed in the pyrolysis device. The preset loading amount ranges from 20 to 60 g / L, that is, 20 to 60 g of circuit board fragments are loaded into each liter of processing volume of the pyrolysis device.

[0057] At the same time, it has been confirmed through experiments that the actual volume of the pyrolysis device does not affect the structural size and loading amount of the circuit board fragments. In other words, whether it is a small pyrolysis device (a rotary kiln with less than 50g) or a medium or large pyrolysis device (a medium or large rotary kiln with more than 100g), the size of 2 to 12cm can be batched according to the preset loading amount. 2 The printed circuit board fragments are sent to the pyrolysis device for copper separation without adjusting the cutting of the printed circuit board fragments.

[0058] In one example, the pyrolysis reaction usually needs to be carried out in a certain pyrolysis atmosphere. Alternatively, the pyrolysis atmosphere in the pyrolysis device is a nitrogen atmosphere, a helium atmosphere, an air atmosphere or a vacuum. When a nitrogen atmosphere, a helium atmosphere or an air atmosphere is used, the gas flow rate is controlled in the range of 50 to 200 mL / min; the preset speed of the rotating part is controlled in the range of 2 to 20 r / min. At this time, the heating rate of the pyrolysis process is set in the range of 2 to 8 ° C / min; when the pyrolysis temperature rises to a certain appropriate pyrolysis temperature (a temperature in the range of 120 to 270 ° C), the pyrolysis temperature is maintained and continuously heated for 40 to 120 minutes so that the circuit board fragments are fully pyrolyzed and the copper thereon is fully separated. Usually, after pyrolysis, gas-liquid-solid three-phase products with different compositions are obtained respectively, among which copper is in the solid phase product and the separation rate of copper under the above conditions is greater than or equal to 95%.

[0059] In one example, the copper that is detached from the circuit board fragments by pyrolysis can be collected from the outlet of the pyrolysis device. Of course, the collected copper will also contain other metal components, non-metal components, etc. that are detached from the circuit board fragments. Alternatively, the collected solid mixture can be screened by using a vibrating screen device or a shaking table. Among them, the screening parameters of the vibrating screen device or the shaking table can be designed or adjusted according to actual conditions. For example, when using a vibrating screen device, multiple layers of screens can be set, each layer of the screen has sieve holes of different mesh sizes, and the copper can be screened out layer by layer. This example is only an illustrative example, and those skilled in the art should not be understood as a limitation of the present invention.

[0060] Further, based on the description of the above low-temperature pyrolysis method, in order to maximize the copper separation rate, the present invention finds a set of optimal parameters suitable for the low-temperature pyrolysis method through Examples 1 to 3, under which a copper separation rate of 98% can be achieved. The experimental conditions and pyrolysis reaction parameters of Examples 1 to 3 are shown in Table 1.

[0061] Table 1 Experimental conditions and pyrolysis reaction parameters of Examples 1 to 3

[0062]

[0063] Examples 1 to 3 all use the same rotary kiln as the pyrolysis device, wherein the rotary kiln has a self-rotating function and a promotion component is also provided inside the rotary kiln. At the same time, the circuit board fragments are all 4×2 cm 2 The rectangular fragments are filled with 31g / L (a certain error is allowed, such as ±5g / L). The pyrolysis atmosphere in the rotary kiln is preferably a nitrogen atmosphere. Due to the complex superposition structure of the circuit board, if an oxygen atmosphere is used, it is easy to cause the flame retardant to decompose and produce dioxins. Therefore, choosing an inert atmosphere will make the pyrolysis process cleaner.

[0064] After 60 minutes of pyrolysis process, the copper on the circuit board fragments has been separated from the circuit board by itself. The subsequent screening using a shaking table has achieved a copper separation rate of more than 98%, that is, a copper recovery rate of more than 98%. From Examples 1 to 3, Example 3 with the lowest pyrolysis temperature is selected as a set of optimal control parameters for the low-temperature pyrolysis method, specifically:

[0065] The default size of the circuit board fragments is 4×2cm 2The invention relates to a rectangular shape; the preset filling amount of each batch is 25-35 g / L; the pyrolysis device is a rotary furnace (with a rotating part and a promoting part), the pyrolysis atmosphere in the rotary furnace is a nitrogen atmosphere, and the nitrogen flow rate is 100 mL / min; the preset rotation speed of the rotating part of the rotary furnace is 2.44 r / min; the heating rate of the pyrolysis process is 5°C / min; the pyrolysis temperature is 150°C; the continuous pyrolysis time at this pyrolysis temperature is 60 min; the separation rate of copper obtained is greater than or equal to 98%.

[0066] Further, on the basis of Examples 1 to 3, comparative experiments were also conducted when the pyrolysis temperature reached 350°C (other conditions remained unchanged) through Comparative Example 1. After the pyrolysis reaction was fully carried out, the pyrolysis separation product was recovered, and the composition of the pyrolysis separation product, especially the liquid product therein, was detected using a gas chromatography-mass spectrometry (GC-MS) method. At the same time, the separation ratio of the gas-liquid-solid three-phase products in the pyrolysis separation product can also be preliminarily obtained through GC-MS detection, that is, the liquid phase product accounts for about 15-25%, the gas phase product accounts for about 25-35%, and the solid phase product accounts for about 40-60%. The copper separated from the circuit board fragments is in the solid phase product.

[0067] See also Figure 4 , showing the comparison of the components of the liquid phase separation products of Examples 1 to 3 and Comparative Example 1. Figure 4 From the specific component contents of each embodiment and comparative example, it can be seen that when the pyrolysis temperature is lower than 250°C, no halogen substances are decomposed in the decomposed liquid phase product. When the pyrolysis temperature is increased to 250°C or higher, more and more halogen substances are decomposed in the decomposed liquid phase product.

[0068] Furthermore, at the pyrolysis temperature of 150° C. in Example 3, the liquid phase separation products were only phenol and o-cresol, and the halogen substances were not decomposed. While obtaining a copper separation rate of more than 98%, clean and pollution-free separation was also achieved.

[0069] In one example, the rotation speed of the rotary kiln was increased based on Example 3. During the pyrolysis process, it was found that the high rotation speed of the rotary kiln helped to increase the average speed of the circuit board fragments in the rotary kiln, and also helped to produce more intense collisions between the circuit board fragments, which could shorten the pyrolysis time to a certain extent. For example, the rotation speed of the rotary kiln was increased from 2.44r / min to 18.81r / min, and other conditions remained unchanged as in Example 3. While obtaining a copper separation rate of more than 98%, the pyrolysis time was shortened from 60min to 40min.

[0070] Furthermore, the experiment also found that increasing the nitrogen gas flow rate can also help increase the movement speed of the circuit board fragments in the rotary kiln and the probability of collision between them. However, it should also be noted that increasing the rotation speed of the rotary kiln and increasing the nitrogen flow rate will also be accompanied by an increase in overall energy consumption. In the actual circuit board copper separation process, the rotary kiln speed and / or gas flow rate can be appropriately increased according to the energy consumption output ratio to promote the full pyrolysis reaction, thereby further reducing the pyrolysis temperature and shortening the pyrolysis time, and improving the economic efficiency of copper recovery.

[0071] In one example, when the loading amount of the circuit board fragments was further increased to more than 2 / 3 of the processing volume of the rotary kiln, the low-temperature pyrolysis method was continued to be used for copper separation under the conditions of Example 3, the pyrolysis temperature was controlled at 150°C, and the pyrolysis time lasted for 60 minutes. The copper separation rate decreased from 98% to 75%. The main reason for the decrease in the copper separation rate is that the excessive loading amount reduces the movable space of the circuit board fragments inside the rotary kiln, which in turn hinders the full pyrolysis.

[0072] In one example, in order to compare the effect of the pyrolysis device on the low-temperature pyrolysis method, Comparative Example 2 was designed based on Example 3. In Comparative Example 2, the operating conditions of Example 3 were kept unchanged, and only the rotary kiln was changed to a fixed reactor, such as a fixed bed reactor. This type of fixed reactor usually has no rotating parts, so the reactor does not rotate during the pyrolysis process. At the same time, no promoting components are set inside the reactor. Thus, under the pyrolysis conditions of Example 3, that is, the pyrolysis temperature is controlled at 150°C, and the pyrolysis time lasts for 60 minutes, the separation rate of copper is only 16.70%. It is further verified that the use of a pyrolysis device with controllable motion and the provision of a promoting component inside the pyrolysis device to promote the movement and collision of circuit board fragments can effectively improve the full reaction of low-temperature pyrolysis and improve the separation rate of copper under low-temperature pyrolysis conditions.

[0073] The low-temperature pyrolysis method for recovering copper in circuit boards provided by the embodiments of the present invention has at least one or part of the following advantages:

[0074] (1) The low-temperature pyrolysis method for recovering copper from circuit boards provided in an embodiment of the present invention utilizes a pyrolysis device such as a rotary kiln to pyrolyze circuit board fragments, so that the circuit board fragments are fully mixed, accelerated, and collide with each other during the pyrolysis process to obtain higher fluidity and heat transfer properties. The effective dissociation of copper from other metals and non-metals can be achieved at a low-temperature pyrolysis temperature of 120 to 270° C., achieving a copper separation rate of more than 90%;

[0075] (2) The low-temperature pyrolysis method for recovering copper from circuit boards provided in the embodiments of the present invention can use common industrial heat treatment equipment as a pyrolysis device, such as a rotary kiln and other heat treatment reaction furnaces with rotating blades, baffles or guide plates, etc., which has high industrial popularity and strong process adaptability;

[0076] (3) The pyrolysis temperature of the low-temperature pyrolysis method for recovering copper from circuit boards provided by the embodiment of the present invention is lower than 280° C., or even lower than 200° C., which ensures a copper separation rate and copper recovery rate of more than 90%, while effectively avoiding the decomposition of pollutants such as halogen flame retardants, and its liquid phase product does not contain halogen components, is pollution-free to the environment, and realizes clean production;

[0077] (4) The low-temperature pyrolysis method for recovering copper from circuit boards provided by the embodiment of the present invention is pyrolyzed at low temperature by a pyrolysis device such as a rotary furnace, and the adhesive state between copper and the circuit board is destroyed, so that the copper is separated from the circuit board by itself, and the separation rate exceeds 90%;

[0078] (5) The low-temperature pyrolysis method for recovering copper from circuit boards provided in the embodiment of the present invention can effectively dissociate other metals and non-metals except copper by fully mixing, accelerating movement and mutual collision of circuit board fragments in a rotary kiln, thereby facilitating the recovery and reuse of other metals or non-metals;

[0079] (6) The low-temperature pyrolysis method for recovering copper from circuit boards provided in an embodiment of the present invention crushes the circuit boards to obtain circuit board fragments of a specific size without crushing, thereby avoiding the phenomenon of over-crushing and agglomeration caused by crushing, thereby reducing the loss of metallic copper;

[0080] (7) The low-temperature pyrolysis method for recovering copper from circuit boards provided in the embodiment of the present invention is applicable to the case where a small amount of copper is recovered using a small pyrolysis device by feeding in batches according to a preset loading amount, and can also be applicable to the case where a large amount of copper is recovered by batch processing. The pyrolysis parameters do not need to be adjusted and have good industrial production adaptability;

[0081] (8) The low-temperature pyrolysis method for recovering copper from circuit boards provided in an embodiment of the present invention achieves a copper separation rate of greater than 95% after low-temperature pyrolysis in a rotary furnace, and then the separated copper can be effectively recovered using common simple screening equipment (vibrating screen, shaking table, etc.).

[0082] Although some embodiments of the present general inventive concept have been shown and described, it will be appreciated by those skilled in the art that changes may be made to these embodiments without departing from the principles and spirit of the present general inventive concept, the scope of which is defined by the claims and their equivalents.

Claims

1. A low-temperature pyrolysis method for recovering copper from circuit boards, characterized in that: The low-temperature pyrolysis method comprises: In the pyrolysis device, 2 to 12 cm 2 The circuit board fragments are heated at a pyrolysis temperature of 120 to 270° C. for 40 to 120 minutes, so that the metal and non-metal in the circuit board fragments are dissociated and the copper in the metal and the circuit board are bonded in a form that is broken by pyrolysis and then falls off the circuit board to be recovered, and the recovery rate of copper is greater than or equal to 90%.

2. The low-temperature pyrolysis method according to claim 1, characterized in that: The pyrolysis device comprises a pyrolysis reaction chamber, a rotating component and a promoting component; The rotating component drives the pyrolysis reaction chamber to rotate at a preset speed so as to drive the circuit board fragments inside the chamber to rotate; The promoting component is arranged inside the pyrolysis reaction chamber to promote the circuit board fragments to rotate, move, and collide with each other.

3. The low-temperature pyrolysis method according to claim 2, characterized in that: The promoting component includes a blade structure, a blocking structure or a combination of a blade structure and a blocking structure; The blade structure causes the circuit board fragments to rotate and obtain acceleration through the rotation of the blades; The blocking structure promotes contact between the circuit board fragments to increase the probability of collision between the circuit board fragments.

4. The low-temperature pyrolysis method according to claim 3, characterized in that: The pyrolysis device is any one of a rotary furnace, a rotary kiln, a rotary tube furnace, and a rotary reaction furnace.

5. The low-temperature pyrolysis method according to any one of claims 1 to 4, characterized in that: The circuit board fragments are waste copper-clad circuit boards that have been crushed, and the waste copper-clad circuit boards include any one of waste copper-clad boards made of paper-based materials, waste paper-laminated copper-clad boards, scraps of paper-laminated copper-clad boards, and circuit boards made of glass fiber materials, or any combination thereof.

6. The low-temperature pyrolysis method according to claim 5, characterized in that: 2~12cm 2 The shape of the circuit board fragments is a square, a rectangle, a parallelogram, a quadrilateral or a rhombus, and the aspect ratio of the circuit board fragments is in the range of 1 to 2.5:

1.

7. The low-temperature pyrolysis method according to claim 6, characterized in that: The circuit board fragments are fed into the pyrolysis device in batches with a preset loading amount, and each batch of circuit board fragments is fed into the pyrolysis device after the pyrolysis is completed; The preset filling amount ranges from 20 to 60 g / L.

8. The low-temperature pyrolysis method according to claim 7, characterized in that: The pyrolysis atmosphere in the pyrolysis device is a nitrogen atmosphere, a helium atmosphere, an air atmosphere or a vacuum. When a nitrogen atmosphere, a helium atmosphere or an air atmosphere is used, the gas flow rate ranges from 50 to 200 mL / min. The preset speed range of the rotating component is 2 to 20 r / min; The heating rate of the pyrolysis process ranges from 2 to 8 °C / min; After pyrolysis, a three-phase product is obtained, wherein copper is in the solid phase product and the separation rate of copper is greater than or equal to 95%.

9. The low-temperature pyrolysis method according to claim 8, characterized in that: The circuit board fragments are 5 to 10 cm 2 A rectangle with a length-to-width ratio of 2:1; The preset filling volume for each batch is 25-35 g / L; The pyrolysis device is a rotary kiln, The pyrolysis atmosphere in the rotary furnace is a nitrogen atmosphere, and the nitrogen flow rate is 80-120 mL / min; The preset speed of the rotating parts of the rotary kiln is 2-3 r / min; The heating rate of the pyrolysis process is 3-7°C / min; The pyrolysis temperature is 130-170°C; The pyrolysis time at the pyrolysis temperature is 40 to 80 minutes; The separation rate of copper was 98%.

10. The low-temperature pyrolysis method according to claim 8, characterized in that: The copper separated from the circuit board fragments by low-temperature pyrolysis is recovered by a vibrating screen device or a shaking table.

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