PCB Technical - ​Study the disposal methods of discarded PCB circuit boards

As the renewal of electronic products accelerates, the amount of printed circuit board (PCB) waste is also increasing. The pollution of waste PCBs to the environment has also aroused the attention of countries all over the world. Waste PCB contains heavy metals such as lead, mercury, and hexavalent chromium, as well as flame retardants such as brominated biphenyl (PBB) and brominated diphenyl ether (PBDE). These substances will cause great pollution to groundwater and soil in the natural environment, and cause great harm to people's lives and physical and mental health. The old PCB contains nearly 20 kinds of non-ferrous metals and rare metals, which have high recycling value and economic value.

A physical method.

The physical method is a recycling method that uses mechanical means and the physical properties of PCBs are different.

It broke 1.1.

The purpose of crushing is to separate the metal and organic matter in the waste circuit board as much as possible to improve the selection efficiency. The study found that when crushed at 0.6 mm, the metal can basically reach 100% dissociation, but the choice of crushing method and grade depends on the subsequent process.

Separation is to use the density, particle size, conductivity, magnetic permeability and surface characteristics of the material to separate. At present, wind shaker technology, flotation separation technology, cyclone separation technology, float-sink separation technology, etc. are used.

2 kinds of supercritical technology processing methods.

Supercritical fluid is a method of extraction and separation using the influence of pressure and temperature on the solubility of supercritical fluid without changing the chemical composition. Compared with traditional extraction methods, the supercritical CO2 extraction process has the advantages of separation environment, convenience, low toxicity, and no residue.

There are two main research directions for supercritical fluid treatment of waste PCBs. First, the supercritical CO2 fluid extracts resin and brominated flame retardant in the printed circuit board. When the resin adhesive material in the printed circuit board is removed by the supercritical CO2 fluid, the copper foil and glass fiber layer in the printed circuit board are easily separated. It provides the possibility of efficient recycling of materials in printed circuit boards. Second, directly use supercritical fluid to extract metals from waste PCBs. Wai and other reports claim that lithium carbamate (fluorinated diethyl disulfide) is a complex. Extract CD2CU2Zn2Pb2PD2AS3Au3Ga3 and SB3 from simulated cellulose filter paper or sand. The extraction efficiency is above 90%.

Supercritical processing technology also has many shortcomings, such as: high selectivity of extraction, need to add entrainer to harm the environment; extraction pressure is higher than equipment requirements. High temperature should be used in the extraction process, so energy consumption is high.

Three chemical methods.

Chemical treatment technology is an extraction process using the chemical stability of various components in PCB.

3.1 Heat treatment method.

The heat treatment method mainly uses high temperature methods to separate organics and metals. Mainly include incineration method, vacuum cracking method, microwave method, etc.

3.1.1 Incineration method.

The incineration method is to crush the electronic waste into a certain particle size and place it in an incinerator to decompose the organic components and separate the gas from the solid. The incineration residue is bare metal or oxide and glass fiber, which can be recycled by physical and chemical methods. The organic gas is discharged after entering the secondary incinerator for combustion. The disadvantage of this method is that it produces a large amount of exhaust gas and toxic substances.

3.1.2 Crack method.

Industrial cracking, also known as dry distillation, is to place electronic waste in a container, heat and control the temperature and pressure under the condition of isolating the air, thereby decomposing organic matter into oil and gas. After condensate collection, it can be recycled. Different from the incineration of electronic waste, the vacuum pyrolysis process is carried out under anaerobic conditions, which can prevent the two evil furans from producing less waste gas pollution.

The microwave processing technology is 3.1.3.

The microwave recycling method is to first break down the electronic waste, and then heat the organic matter in the microwave. Heat to about 1400°C to melt glass fiber and metal into glass material. After cooling, metals such as gold and silver are separated in the form of balls. The remaining glass materials can be recycled as building materials. This method is obviously different from traditional heating methods, and has the advantages of high efficiency, high resource recovery rate, and low energy consumption.

3.2 Hydrometallurgy.

Hydrometallurgy technology mainly utilizes the dissolution of metals in acid solutions such as nitric acid, sulfuric acid, aqua regia, etc., to remove metals from electronic waste, and to recycle them from the liquid phase. At present, it has been widely used in electronic waste treatment. Compared with pyrometallurgy, hydrometallurgy has the advantages of low exhaust gas emissions, easy disposal of metal residues, and obvious economic benefits.

4 kinds of biotechnology.

Biotechnology is the use of microbial adsorption and microbial oxidation to solve the problem of metal recovery. Microbial adsorption can be divided into two types: metal ions and microbes directly fix metal ions. The former is fixed with hydrogen sulfide produced by bacteria, and when the bacteria surface adsorbs ions to reach saturation, flocs are formed to settle. The latter uses the oxidation of ferric ions to oxidize precious metals such as gold into solubles, and expose and recycle the precious metals. Precious metals such as biotech extracts have the advantages of simple process, low cost, and convenient operation, but the long-term infiltration rate is low.

The conclusion is.

E-waste is a valuable resource for strengthening e-waste metal recycling technology. From an economic and environmental point of view, e-waste is an important research and application. Due to the complex and diverse characteristics of e-waste, the development trend of e-waste technology lies in the industrialization of processing forms. Resource recovery maximizes the scientific technology. In short, studying the resources of discarded PCBs can not only protect the environment from pollution, but also facilitate the recycling of resources and save a lot of energy. It promotes sustainable economic and social development.