Electronics has dominated our daily lives nowadays. The increase of consumer demands for electronic devices has also led to the increase of production for businesses. Due to the heightened demand and production, the amount of commercial electronic waste, or e-waste, has also increased tremendously. If not managed properly, e-waste can have fatal effects on the environment and all living beings.
To combat the increase in e-waste, countries all over the world had developed techniques for electronic recycling. The recovered metallic materials are reused for other commercial purposes. For non-metallics, they usually end up in a landfill with correct treatment.
Pyrolysis is a chemical decomposition technique that is commonly used in plastic waste. This method involves changing the chemical composition of materials and is completely irreversible. In e-recycling, printed circuit boards are heated up to a specific temperature, usually between 500 and 800 C, in an inert atmosphere. The heat melts down the solder that binds the electronic components to the board. Once pyrolysis is complete, a blackish metal substance is left behind. This substance produces good yield of copper. Other metallic materials such as iron, nickel, calcium, zinc and aluminum could also be recovered from the substance. This method is desired due to the substance that contains a lot of metals. However, the metals recovered still need to undergo processing to make them usable for other purposes.
The hydrometallurgical method is another method that uses chemicals to e-recycle. E-wastes are dissolved into strong acids and alkalis such as aqua regia, sulfuric acid, cyanide solutions and nitric acid. This technique is flexible, energy saving and cost effective. It is widely used by e-recycling service providers. Upon dissolving, metals will eventually come out of the resulting solution. Pure metals are recovered from the solution, making it viable for the market without further processing. For non-metals, they still need to be thermally treated before reusing or dumped in landfills. However, its disadvantage is solely focused on the poisonous and corrosive nature of the resulting solution.
In air classification method, the separation of dispersed solid particles happens depending on the particle size and density. When the particles are suspended in gas, they move in all sorts of directions depending on the force applied. This is where the separation takes place. It is extremely crucial and the machine that executes the separation is complicated. After the separation, there are more processes to make the recovered materials usable.
All of the e-recycling methods mentioned above deal with the chemical composition of the electronic wastes. However, most e-waste recycling service providers do not have the equipment and tools needed. To compensate, they physically disassemble the parts and separate them into categories. Then, they cut the parts into specific sizes. The pieces undergo milling processes that turn them into pulverized PCB powder. The powder goes through eddy current separators that separate the particles depending on their eddy current characteristics. They are also separated depending on their density and particle size. This method is tedious and relies on human intervention, unlike the other techniques.
There are a lot of techniques that can be used to recycle electronic waste. There are more methods that are being tested to make the process faster and more efficient such as biometallurgical separation method and other methods that focuses on non-metallics.
