What is the best way to recycle PCB?

With the industrialization and scale of PCB processing and the wide application of electronic products, more and more electronic wastes are generated and manufactured in the production and living activities of human society.

Waste PCBs contain heavy metals such as lead, mercury, and hexavalent chromium. If they are discarded at will, PCBs also contain toxic chemicals such as polybrominated biphenyls (PBB) and polybrominated diphenyl ethers (PBDE) as flame retardant components. Not only will it pollute the environmental soil and water resources, potentially endanger human health, but also cause wasted resources, which are difficult to recycle. There are nearly 20 kinds of non-ferrous metals and rare metals on scrap PCBs, which have high economic value for recycling.

Therefore, it is particularly important to properly dispose of waste PCB circuit boards.

Today we talk about several ways to deal with electronic waste:

1 Physical method

According to the different physical properties of PCB, physical and mechanical means are used for recycling.

1.1 Broken

Mechanically crush the PCB to disintegrate and separate its metal and organic matter, improving the separation efficiency. When the crushed particles reach 0.6mm, the metal can basically achieve 100% dissociation, but the selection of the crushing method and the number of stages depends on the subsequent process.

1.2 Sorting

According to the differences in their physical properties such as density, particle size, electrical conductivity, magnetic permeability and surface characteristics, the crushed materials can be processed by wind shaker technology, flotation separation technology, cyclone separation technology, floating-sink separation and eddy current separation technology, etc. sorting.

2 Supercritical technology treatment method

This method will not change the chemical composition of the PCB material. Through pressure and temperature, the supercritical fluid is dissolved separately, and then extracted, separated and purified. Compared with traditional extraction methods, supercritical CO2 extraction is more environmentally friendly, easy to separate, low toxicity, less or even no residue, and has the advantages of normal temperature operation.

Supercritical processing technology is not without its flaws. For example, the entrainer used in the extraction is harmful to the environment; the high-pressure and high-temperature extraction method requires high equipment and high energy consumption.

3 chemical method

Chemical treatment technology is the process of extracting by using the different stability of various chemical components in PCB.

3.1 Heat treatment method

The heat treatment method uses high temperature to separate organic matter and metal. Heat treatment methods include vacuum cracking method, incineration method, microwave method and so on.

3.1.1 Incineration method

The electronic waste is physically broken into tiny particles, and then sent to an incinerator to decompose the organic components. The residue after incineration is composed of bare metal, metal oxide and glass fiber, which are recovered by physical and chemical methods after crushing. The disadvantage of this method is that a large amount of exhaust gas and toxic substances will be generated.

3.1.2 Lysis method

Cracking method, also known as dry distillation.

The waste PCB board is heated under the condition of isolating the air, and the pressure and temperature are controlled, so that the organic matter is decomposed and converted into oil gas, which is condensed and collected for recycling. Different from the incineration method, the vacuum pyrolysis process is carried out under anaerobic conditions, which can inhibit the production of furans and dioxins and reduce environmental pollution.

3.1.3 Microwave processing technology

Microwaves are used to heat electronic waste. When heated to about 1400 ℃, the heated glass fibers and metals will be vitrified. After cooling, gold, silver and other metals will be automatically separated in the form of small beads. Recycling the remaining glass objects can be used as building materials. Compared with traditional methods, it has the advantages of high efficiency, rapidity, high resource recovery and utilization rate, and low energy consumption.

3.2 Hydrometallurgy

Hydrometallurgy technology, placing PCBs in acid solutions such as nitric acid, sulfuric acid, and aqua regia, to remove metals from electronic waste and then recycle them. It is currently the most widely used method for dealing with electronic waste. Compared with pyrometallurgy, hydrometallurgy has the advantages of less waste gas emission, easy treatment of residues after metal extraction, significant economic benefits, and simple process flow.

4 Biotechnology

Utilize the adsorption of microorganisms on the surface of minerals and the oxidation of microorganisms to oxidize and recover metals. There are mainly two methods:

1. Microbial adsorption can be divided into using microbial metabolites to fix metal ions

Using the hydrogen sulfide produced by bacteria to fix, when the surface of the bacteria is saturated with ions, it can form flocs and settle down;

2. Using microorganisms to directly immobilize metal ions

Utilize the oxidizing properties of ferric ions to oxidize gold and other metals in precious metal alloys into soluble matter and dissolve them in the solution so that precious metals can be exposed and recovered.

The biotechnology extraction process is simple, low in cost, and easy to operate, but the leaching time is long and the yield is low, so it has not yet been put into use.

Conclusion E-waste has complex and diverse characteristics, and it is difficult to recycle it completely by a single recycling technology. The e-waste treatment technology needs to be continuously optimized to maximize resource recovery, scientific and industrialized treatment technology. In short, the processing and recycling of waste PCBs can not only protect the environment and prevent pollution, but also facilitate the recycling of resources and promote sustainable social and economic development. As a professional e-waste recycling equipment solution provider, SUNY GROUP has rich experience and first-class technical equipment in e-waste, especially circuit board recycling. If you want to know relevant information or have needs, please feel free to contact us for consultation.