New Method for Recycling PCB Waste

All over the world, gadgets contain Printed Circuit Boards or PCBs as a means of mounting and interconnecting the several electronic components they use. When the life of the gadget comes to an end, nearly all components are recycled. Although the recycling process is streamlined in some countries, it is still a growing industry in most developing countries. It is especially difficult to recycle the PCB and its components, since it often produced significant waste streams. Researchers in China have developed an innovative method to salvage the materials found in waste PCBs.

Every year, e-waste produced around the globe reaches nearly 50-million tons, most of which ends up in the developing countries such as China and India. Now, there is a friendly method for salvaging materials from waste PCBs. Using the solvent Dimethyl Sulfoxide or DMSO, Chinese researchers claim to have developed an environmentally friendly method that can simplify the process of recycling e-waste, especially waste PCBs.

Traditional methods of recovering precious metals from waste PCBs include using pyrolysis along with hydrometallurgical processes. The process uses aqueous solvents such as strong alkalis and acids. However, these processes are not environmentally friendly. They contaminate the environment with toxic heavy metals including persistent organic pollutants. They also generate a huge quantity of spend acids and alkalis that is difficult or impossible to recover.

At the Zhejiang Gongshang University in Hangzhou, researchers Ping Zhu and colleagues have developed a simple process of separation. They claim this process can recover valuable materials from waste PCBs at much lower recycling costs. At the same time, their method does not create the environmental pollution that other methods do.

Traditional methods decompose the polymer resins of waste PCBs to separate them. This process generates polybrominated dibenzofurans and deibenzodioxins, which are highly toxic. The new method is simple and easy as it swells the polymer resins, but does not allow it to decompose into the solution. Therefore, the process does not cause secondary pollution and the solvent can be reused.

According to the team, the process begins with stripping the waste PCBs of all electronic components. Next, the bare boards are shredded into fragments of approximately 1-3cm2. Then, the fragments are heated with DMSO – under an atmosphere of nitrogen. As the DMSO swells the brominated epoxy resin that holds the PCB layers together, they separate from one another. After abstracting and filtering the solution, it is evaporated under vacuum to regenerate the used DMSO. That leaves behind the separated polymer resin and the circuit board components.

At present, the size of the PCB fragments can be an issue in scaling the process up to industrial scales. At Ecyclex, an e-waste management company in the UAE, Saeed Nusri, a chemical engineer feels that this process could be remarkable. In his opinion, the process can solve many issues related to process complexity and solvent recovery that are typically faced in hydrometallurgical recycling of PCBs. Since only 2% of DMSO is lost in every run, there is a lot of savings in raw materials.