Physical methods for PCB recycling and processing

　　The physical method involves recycling based on differences in physical properties such as material density, conductivity, magnetism, and surface wettability. The main processes include disassembly, crushing, sorting, recovery of precious metals, and treatment of harmful substances.

　　(1) The general order of selective dismantling of electronic waste is to select reusable parts. Disassemble harmful components and classify parts of various materials. The disassembly methods include manual disassembly, mechanical disassembly, and automatic disassembly. The automatic disassembly of PCBs uses methods such as bath washing or hot air heating to dissolve solder, and then uses vacuum clamps or robots to remove surface components of PCBs.

　　(2) Broken. The crushing of PCB includes impact crushing, extrusion crushing, and shear crushing. The most successful application currently is the ultra-low temperature freezing crushing technology, which can crush tough materials to 0.074mm after being brittle at low temperatures, allowing metals and non-metals to completely dissociate. Two stage crushing technology is commonly used in China, which involves using a shear crusher for coarse crushing, and then using a dry or wet crusher to finely crush PCB particles to the specified particle size, achieving complete separation of metals and non-metals.

　　(3) Sorting involves sorting the crushed material based on the differences in density, particle size, magnetic conductivity, and other characteristics of each component. There are usually dry and wet sorting methods. Dry separation includes dry screening, magnetic separation, electrostatic, density, and eddy current separation. Wet separation includes hydraulic cyclone classification, flotation, hydraulic shaker, etc. Wet separation has a high recovery rate, but the cost is also high. The reagents used pollute the environment, and the sorted waste residue and waste liquid cause secondary pollution to the environment. Dry sorting is relatively low-cost and less polluting, with the main drawback being a lower sorting rate for fine particles.