Method for disposing of dust collected from waste circuit boards

Abstract

To provide a method for treating collected dust obtained by recovering a fine powder generated when pulverizing a waste circuit board by a pulverizer so that. similarly to a pulverized waste circuit board obtained by the pulverizer, the collected dust can be subjected to a roasting treatment by a roasting furnace.SOLUTION: The method includes: a molding step of kneading a collected dust which is obtained by recovering with a dust collector a fine powder occurred when pulverizing a waste circuit board by a pulverizer, together with a binder, followed by compression and molding; and a roasting step of carrying out a roasting treatment by loading an obtained molded body together with the waste circuit board after being pulverized by the pulverizer.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for treating dust collected from waste substrates.

Background Art

[0002] Printed circuit boards containing trace amounts of valuable metals such as gold, silver, copper, palladium, and platinum are used in various electronic devices such as home appliances, personal computers, smartphones, and network devices. From these electronic devices that have been used and discarded, used printed circuit boards are discarded in large quantities as waste substrates (also referred to as waste electronic substrates). As this waste substrate is called "urban mine", it often has a higher grade of precious metals and rare metals (hereinafter, these are collectively referred to as precious metals unless otherwise specified) than ores mined from mines. Therefore, processes for recovering precious metals from waste substrates are being carried out by performing various treatments.

[0003] Most of the above waste substrates are derived from printed circuit boards in which electronic components such as IC chips and memories are soldered to a printed wiring board mainly made of an insulator such as a glass epoxy substrate. Therefore, in addition to metal components, they contain hydrocarbons typified by epoxy resin derived from the glass epoxy substrate, and organic bromine compounds derived from flame retardants. Therefore, it is necessary to remove these hydrocarbons and bromine compounds by pretreatment.

[0004] For example, in Patent Document 1, before performing magnetic separation and gravity separation on the crushed material of a waste substrate to separate it into magnetic substances, weight non-magnetic substances, and lightweight non-magnetic substances, as a pretreatment, it is cut into about 1 to 10 cm squares and then finely crushed using a ball impact type crusher, and the obtained crushed material is baked at 300 to 1000 °C for a molded body of a predetermined shape formed by press molding to gasify and remove the organic substances and bromine compounds contained in the waste substrate. A technique is disclosed.

Prior Art Documents

Patent Documents

[0005] [Patent Document 1] Japanese Patent Publication No. 2001-259603 [Overview of the project] [Problems that the invention aims to solve]

[0006] As disclosed in Patent Document 1 above, bromine compounds and hydrocarbons can be removed by pre-treatment, which involves crushing the waste circuit board and then charging it into a general roasting furnace such as a kiln and roasting it at an appropriate temperature. However, in the above pre-treatment, fine powder is generated when the waste circuit board is crushed by the crusher. Furthermore, due to the non-uniformity of the waste circuit board, when accurately analyzing the quality of the metal to be recovered contained in the waste circuit board, a sampling method is employed in which the waste circuit board is repeatedly crushed and reduced in size by a crusher, and fine powder is generated during this crushing process.

[0007] As described above, the fine powder generated in the crusher is collected as dust (also called collected dust) in a dust collector equipped in the crusher. Since precious metals are also contained in this collected dust, it is preferable to recover them by subjecting them to roasting treatment, but the collected dust derived from waste circuit boards is in the form of a fine powder, making it difficult to handle. Even if one tries to improve handling by molding it, its low bulk density makes it bulky, making it difficult to mold as is. Furthermore, even if the molded form is charged into a roasting furnace such as a kiln, the molded form quickly breaks down, is blown up by the airflow inside the furnace, and is expelled by suction from the exhaust port along with the airflow, resulting in loss, and thus the recovery rate of precious metals could not be increased.

[0008] The present invention has been made in view of the above circumstances, and aims to provide a method for processing dust collected by collecting fine powder generated when crushing waste circuit boards with a crusher using a dust collector, so that the collected dust can be roasted in a roasting furnace in the same way as the crushed waste circuit boards obtained by the crusher. [Means for solving the problem]

[0009] To achieve the above objective, the method for processing dust powder derived from waste circuit boards according to the present invention is obtained by collecting the fine powder generated when waste circuit boards are crushed by a crusher using a dust collector. Bulk density 0.5~0.6 kg / m 3 of Dust collection powder 2.5 to 16.0 parts by mass per 100 parts by mass binder And add 2.5 to 5.0 parts by mass of water, and further The invention is characterized by including a molding step of kneading and then compressing the material, and a roasting step of loading the resulting molded body together with the waste substrate that has been crushed in the crusher into a roasting furnace for roasting treatment. [Effects of the Invention]

[0010] According to the present invention, the recovery rate of precious metals contained in waste circuit boards can be increased. [Brief explanation of the drawing]

[0011] [Figure 1] This is a block flow diagram illustrating an embodiment of the dust collection method of the present invention. [Modes for carrying out the invention]

[0012] A common method for recovering precious metals from waste circuit boards is to first crush the boards using a crusher, as shown in Figure 1. While there are no particular limitations on the crusher, a ball mill, which crushes the material to be crushed by rotating a cylindrical container with a crushing medium such as steel balls around its central axis, and a high-speed rotary crusher, which crushes the material by impact and shear by rotating hammers, blades, pins, etc., at high speed within a casing, are preferably used. Before crushing with a crusher, the material may be crushed using a jaw crusher, shredder, or other crushing machine.

[0013] Next, the pulverized waste circuit board material is placed in a roasting furnace and roasted at a temperature of approximately 600-700°C to remove smelting-averse elements such as bromine and hydrocarbons. After this roasting process, the material is separated by magnetic separation, specific gravity separation, classification, etc., and then charged as recycled raw material into, for example, the self-smelting furnace or converter of a copper smelting plant according to its particle size. This allows the precious metals contained in the waste circuit board to be distributed to the matte side, making it possible to recover these precious metals in the form of electrolytic copper or sediment (anode slime) in the subsequent copper electrolysis process.

[0014] The fine powder generated during the crushing of waste circuit boards by the aforementioned crusher is collected as dust powder derived from waste circuit boards by being sucked into a dust collector such as a cyclone or bag filter attached to the crusher. Since this dust powder also contains precious metals derived from waste circuit boards, if it can be molded or solidified so that it can be charged as a recycled material into a roasting furnace such as a rotary kiln, which is commonly used for roasting waste circuit boards, the recovery rate of precious metals contained in the waste circuit boards can be increased.

[0015] However, the dust collected from waste circuit boards has a bulk density of 0.5-0.6 kg / m³. 3 The dust powder is of a certain degree and is significantly lower than that of crushed waste substrates, making it difficult to handle and therefore unsuitable for efficient molding as is. Therefore, the method for processing dust powder derived from waste substrates according to an embodiment of the present invention includes a molding step in which a binder is added to dust powder obtained by collecting fine powder generated when waste substrates are crushed to a size of, for example, 30 to 50 mm using a crusher, and water is added as needed, after which the mixture is kneaded and then compressed and molded; and a roasting step in which the resulting molded body is charged into a roasting furnace together with the waste substrates that have been crushed by the crusher and subjected to roasting treatment.

[0016] To explain each process in detail, first, in the molding process, a binder is added to 100 parts by mass of dust powder derived from waste substrates, preferably in an amount of 2.5 to 16.0 parts by mass, more preferably 3.0 to 7.5 parts by mass. Then, if necessary, water is added, preferably 2.5 to 12.5 parts by mass, more preferably 2.5 to 5.0 parts by mass, and the mixture is then kneaded in a kneader. There are no particular limitations on the type of kneader, and examples include a maller-type kneader that kneads the material to be kneaded by crushing it by rotating a pair of rollers around the central axis of a cylindrical container, and a horizontal-axis type kneader that kneads by rotating one or more stirring shafts that extend horizontally within a casing.

[0017] The reason for limiting the amount of water added as described above is that dust collected from waste circuit boards can expand when it absorbs moisture. If the amount of water exceeds 5.0 parts by mass per 100 parts by mass of dust collected powder, it may not be possible to obtain a molded body with sufficient strength even after compression molding. Conversely, if the amount of water is less than 2.5 parts by mass, the effect of adding water may not be obtained depending on the binder used. Furthermore, if the amount of binder added per 100 parts by mass of dust collected powder is less than 3.0 parts by mass, it may not be possible to secure sufficient strength even after compression molding in the next process. Conversely, exceeding 7.5 parts by mass will not contribute to further strength improvement and will be uneconomical.

[0018] It is preferable to use water glass No. 1 or bentonite as the binder added to the above dust collection powder. Water glass is a viscous alkaline liquid also called sodium silicate or sodium orthosilicate, and due to its properties, it is used in various applications such as binders and adhesives. Water glass is a mixture of three components: silicon dioxide (SiO2), sodium oxide (Na2O), and water (H2O), and is generally represented by the composition formula Na2O·nSiO2·mH2O. In JIS K1408, water glass is classified into water glass No. 1 to No. 3 according to the coefficient n representing the molar ratio of SiO2 / Na2O. In the order of No. 1, No. 2, and No. 3, the value of the molar ratio n increases as 2, 2.5, and 3, and the moisture content increases approximately as 43%, 49%, and 60%. Among these, water glass No. 1 is defined such that the content of silicon dioxide is 35 to 38% by mass, the content of sodium oxide is 17 to 19% by mass, the content of iron is 0.03% by mass or less, and the water-insoluble content is 0.2% by mass or less.

[0019] On the other hand, bentonite is a substance composed of a weakly alkaline clay rock mainly composed of the clay mineral montmorillonite, and contains quartz, cristobalite, feldspar, zeolite, mica, calcite, etc. as other components. Montmorillonite, the main component of bentonite, is composed of one tetrahedral sheet in which tetrahedrons composed of Si (silicon) and O (oxygen) are connected in a sheet-like form, and two octahedral sheets in which octahedrons composed of Al (aluminum) and OH (hydroxyl group) are connected in a sheet-like form sandwiching this from both sides. Mineral particles are formed by stacking several unit crystal layers. Since part of the Al constituting this octahedral sheet is substituted by Mg, the unit crystal layer has a negative charge, and cations such as Na + 、K + 、Ca 2+ etc. are incorporated. Since the cations between these crystal layers hydrate with water molecules, the crystal layer spacing expands, so bentonite has properties such as swelling and thickening.

[0020] There are no particular limitations on the type of molding machine for compression-molding the mixture kneaded by the above kneader, but it is preferable to use a briquette machine in which a pair of rotating rolls provided with the mold of the molded body on the outer peripheral surface are arranged in proximity such that their rotation axes are parallel to each other on the same horizontal plane. By supplying the above mixture from above to the proximity portion while rotating these pair of rotating rolls in opposite directions to each other, compression molding can be continuously performed. There are no particular limitations on the shape of the molded body molded by the above molding machine, and various molded bodies such as an oval shape, a pillow shape, an almond shape, a lens shape, a columnar shape, and a substantially spherical shape can be cited. The size of the molded body is preferably about 20 to 40 mm.

[0021] Next, the molded body obtained in the above molding step is charged into a roasting furnace together with the pulverized waste substrate in a roasting step and subjected to roasting treatment. Physical impacts such as dropping from a height of several tens of centimeters to 1 meter, such as charging and cutting out into a raw material hopper and transferring between a plurality of transfer conveyors, are applied to the molded body discharged from the compression molding machine in order to efficiently convey it to the roasting furnace on an industrial scale. Further, during the roasting treatment, a thermal shock is applied, and when a rotary kiln that rotates a horizontally placed cylindrical furnace body to heat-treat the roasted object while stirring is used as the roasting furnace, the molded body charged inside is subjected to physical impacts due to dropping and stirring along with the rotation of this furnace body. Thus, physical impacts such as dropping and thermal shocks are applied to the molded body, but the molded body formed through the above-described molding step has a strength that can sufficiently withstand these physical impacts and thermal shocks.

[0022] The pulverized product of the waste substrate and the molded body roasted in the above roasting furnace are pulverized as necessary, and then sorted by magnetic separation, gravity separation, etc., so that the target metal to be recovered is further concentrated. By charging this as recycled metal into, for example, a blast furnace or a converter of a copper smelting plant, precious metals can be recovered in the form of electrolytic copper or anode slime of electrolytic smelting.

Example

[0023] After shredding the waste circuit boards into approximately 2-3 cm squares using a shredder, the dust generated during the pulverization process to approximately 300-500 μm using a ball mill was collected with a dust collector. The collected dust was sampled, and its particle size was measured using laser diffraction scattering. The average particle size D50 (volume integrated) was 120 μm. This dust was divided into nine smaller portions, and various binders and water were added to each portion. These mixtures of dust, binders, and water were kneaded using a batch-type mixer (MSG-0L) manufactured by Shinto Kogyo Co., Ltd. The mixture was then supplied between a pair of rotating rolls in a briquette machine (BGSIIIN), also manufactured by Shinto Kogyo Co., Ltd., and compressed into roughly egg-shaped molded bodies with a maximum length of approximately 30 mm.

[0024] Each of the molded bodies from samples 1 to 9 prepared in this manner was sieved using a hand sieve with a mesh size of 10 mm. The "moldability" was evaluated based on the percentage of molded material remaining on the sieve: 70% or more was considered excellent, 60-69% was good, and 50-59% was acceptable. In addition, the "post-molding strength" was evaluated by subjecting the molded bodies to five free drops from a height of 2 m onto a concrete floor. The percentage of remaining chunks of 5 mm or larger was considered excellent if it was 60% or more, good if it was 50-59%, acceptable if it was 40-49%, and unacceptable if it was 39% or less.

[0025] Furthermore, when mixing samples 1 to 9 to produce each molded body, "handling ease" was evaluated as follows: good if there were no handling problems, acceptable if there were problems such as dust scattering, and unacceptable if the mixing itself was difficult or required a long time, hindering equipment management and maintenance. In addition, when the amount of binder was adjusted to be roughly equivalent to the cost when using the starch, referencing the list prices of the binder and starch used, "cost" was evaluated from the perspective of the additional cost that would be incurred if additional binder were required based on the results of the aforementioned evaluation items.

[0026] The molded bodies of samples 1 to 9 described above were each placed in a rotary kiln, which served as a roasting furnace, along with the pulverized waste circuit boards that had been crushed using the aforementioned ball mill, and roasted at 600°C. The molded bodies were placed in the roasting furnace at a ratio of 20 parts by mass to 100 parts by mass of pulverized waste circuit boards. After the roasting process, samples of each of samples 1 to 9 were sampled, and a portion of each was inspected by measuring the loss on heat. The "roasting performance" was evaluated as follows: good if the loss was 5% or less, acceptable if it was between 5% and 10%, and unacceptable if it was over 10%.

[0027] Furthermore, the remaining sample was subjected to five free drops from a height of 2m onto a concrete floor. The "post-roasting strength" was evaluated based on the percentage of remaining lumps of 5mm or larger: excellent if 60% or more remained, good if 50-59%, acceptable if 40-49%, and unacceptable if 39% or less remained. The evaluation results for the molded bodies of samples 1 to 9 are shown in Table 1 below, along with the type of binder used, its addition ratio, and the addition ratio of water. Note that the addition ratios for binder and water are in parts by mass added per 100 parts by mass of collected dust.

[0028] [Table 1]

[0029] As can be seen from Table 1 above, samples 2, 3, 5, and 6, which used water glass No. 1 or bentonite as a binder, received higher overall evaluations compared to samples 1, 4, 8, and 9, which used starch, water glass No. 2, molasses, or asphalt as binders, and sample 7, which used a large amount of cement in addition to bentonite as a binder. Furthermore, as can be seen from samples 2 and 3, when using water glass No. 1 as a binder, increasing its addition ratio from 3.4 parts by mass to 5.5 parts by mass improved moldability, post-molding strength, and post-roasting strength. In addition, as can be seen from samples 5 and 6, when using bentonite as a binder, reducing the addition ratio of water improved moldability and post-molding strength.

Claims

1. A method for processing dust powder derived from waste circuit boards, comprising: a molding step of adding 2.5 to 16.0 parts by mass of a binder and 2.5 to 5.0 parts by mass of water to 100 parts by mass of dust powder with a bulk density of 0.5 to 0.6 kg / m³ obtained by collecting the fine powder generated when waste circuit boards are crushed by a crusher using a dust collector, and further kneading and then compressing the mixture; and a roasting step of charging the resulting molded body together with the waste circuit boards that have been crushed by the crusher into a roasting furnace and roasting it.

2. A method for processing dust powder derived from waste substrates according to claim 1, characterized in that the binder is water glass No. 1 or bentonite.

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