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Based on years of experience, PCB Quick shares in this article specific methods for recycling used PCBs to improve the reuse rate of electronic components.
With the acceleration of the update speed of electronic products, the number of discarded printed circuit boards (PCB), the main component of electronic waste, is also increasing. The environmental pollution caused by used PCBs has also aroused the attention of various countries.
In used PCBs, heavy metals such as lead, mercury, and hexavalent chromium, as well as toxic chemicals such as polybrominated biphenyls (PBB) and polybrominated diphenyl ethers (PBDE), which are used as flame retardant components, are contained in the natural environment. This will cause huge pollution for groundwater and soil. The following method of recycling printed circuit boards can solve the problem of environmental pollution caused by waste printed circuit boards.
The physical method is a method that uses mechanical means and the difference in PCB physical properties to achieve recycling.
The purpose of crushing is to dissociate the metal in the waste circuit board from the organic matter as much as possible to improve the separation efficiency. The study found that when the metal is broken at 0.6 mm, the metal can basically reach 100% dissociation, but the choice of the crushing method and the number of stages depends on the subsequent process.
Separation is achieved by using differences in physical properties such as material density, particle size, conductivity, magnetic permeability, and surface characteristics. Currently widely used are wind shaker technology, flotation separation technology, cyclone separation technology, float-sink separation and eddy current separation technology.
Supercritical fluid extraction technology refers to a purification method that uses the influence of pressure and temperature on the solubility of supercritical fluids to perform extraction and separation without changing the chemical composition.
Compared with traditional extraction methods, the supercritical CO2 extraction process has the advantages of environmental friendliness, convenient separation, low toxicity, little or no residue, and can be operated at room temperature.
Chemical treatment technology is a process of extraction using the difference in chemical stability of various components in PCB.
(1) Heat treatment method
The heat treatment method is mainly a method of separating organic matter and metal by means of high temperature. It mainly includes the incineration method, vacuum cracking method, microwave method, and so on.
(2) Incineration method
The incineration method is to crush electronic waste to a certain particle size and send it to a primary incinerator for incineration, decompose the organic components in it, and separate the gas from the solid. The residue after incineration is the bare metal or its oxide and glass fiber, which can be recovered by physical and chemical methods after being crushed.
The gas containing organic components enters the secondary incinerator for combustion treatment and is discharged. The disadvantage of this method is that it produces a lot of waste gas and toxic substances.
(3) Cracking method
Pyrolysis is also called dry distillation in industry. It is to heat the electronic waste in a container under the condition of isolating air, control the temperature and pressure so that the organic matter in it is decomposed and converted into oil and gas, which can be recovered after condensation and collection.
Different from the incineration treatment of electronic waste, the vacuum pyrolysis process is carried out under oxygen-free conditions, the amount of waste gas generated is small, and the environmental pollution is small.
Microwave processing technology
The microwave recycling method is to first crush the electronic waste, and then use microwave heating to decompose the organic matter by heating. Heating to about 1400℃ melts glass fiber and metal to form a vitrified substance.
After this substance is cooled, gold, silver, and other metals are separated in the form of beads, and the remaining glass substance can be recycled for use as building materials. This method is significantly different from traditional heating methods and has significant advantages such as high efficiency, rapidity, high resource recovery and utilization, and low energy consumption.
Hydrometallurgy technology mainly uses the characteristics of metals that can be dissolved in acid solutions such as nitric acid, sulfuric acid, and aqua regia to remove metals from electronic waste and recover them from the liquid phase. It is currently the most widely used method for processing electronic waste.
Compared with pyrometallurgy, hydrometallurgy has the advantages of less exhaust gas emissions, easy disposal of residues after metal extraction, significant economic benefits, and simple process flow.
Correct recycling of printed circuit boards can not only effectively reduce the pollution caused by electronic components, but also improve the utilization rate of recycled resources. If you want to know more about printed circuit boards after reading the above, please refer to our previous news.
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