India produces about 4 million tonnes of e-waste, behind only China and the US. This waste generation will only increase with economic progress. Disposing of waste printed circuit boards (WPCB) is not easy, as they are a complex mixture of polymers, metals and ceramics. On the other hand, they can be used to mine valuable metals.
There are many recycling techniques — electrostatic separation, magnetic separation, and pyrometallurgical and hydrometallurgical methods. These methods, unfortunately, ignore polymers and other compounds. Most recyclers abandon the low-value non-metallic parts.
Pyrolysis, or heating in the absence of oxygen, is one method that is often used. The metal parts turn into char and the plastic (polymer) components turn into gas and liquid. However, pyrolysis is not a one-size-fits-all method; different parameters of heating produce different results.
Two researchers from IIT-Guwahati, Bibari Boro and Pankaj Tiwari, have used a statistical technique called ‘response surface methodology’ to determine the best conditions for a desired outcome.
They found ‘temperature’ to be the most significant parameter. They conducted further experiments with varying temperatures, keeping the heat rate and hold time constant and characterised the obtained products.
They concluded that at the optimum temperature, pyrolysis of e-waste could produce liquids rich in aromatics with high calorific value, of about 35 MJ per kg, as well as hydrogen and methane.
“This study provides a comprehensive approach, integrating both qualitative and quantitative analyses, to optimise WPCB pyrolysis for enhanced resource recovery,” say Boro and Tiwari in a paper published in Energy.