E-waste, one of the most hazardous solid waste is becoming a serious issue due to its high rate of generation and low recycling rate. Due to its high built-in value, mining industries and researchers are finding a lot of attraction to develop an eco-friendly technology for recycling and reuse of valuable components. According to a study done by United Nations University (UNU), e-waste is growing at an alarming rate of 3-5%, and globally 54 million tons of e-waste is generated in 2019. Only 20% of the e-waste generated is reported to be recycled informal sector and the rest is either recycled in the informal sector or landfilled illegally. Therefore, a challenge lies ahead for researchers to achieve a closed-loop system for manufacture-use-recycle at the end of life electronic equipment; surprisingly, limited research has been done as far as treatment of e-waste. Waste printed circuit boards (WPCBs) are one of the most essential components in waste electrical and electronic equipment. WPCBs are heterogeneous waste consisting of various components connected with conductive pathways on a non-conductive epoxy resin laminated on copper sheet and they roughly consist of 40% metals, 30% organics, and 30% refractory oxides. Herein, we developed an environment-friendly novel process for recovery of metals from waste WPCBs using ammonium chloride roasting, which operates in a low-temperature range compared to conventional pyrometallurgy processes. In this study, WPCBs are initially pyrolyzed at 400 °C to convert polymers into combustible gases and oil. The leftover of the pyrolysis process, which is rich in metal was mixed uniformly with ammonium chloride. The mixture was then roasted in the temperature range of 200 – 325 °C for conversion of metals into water-soluble metal chlorides. Being an excellent solid chlorinating agent NH4Cl decomposes at higher temperature to generate HCl and NH3, among which HCl react with metals to form metal chlorides. Water was used at 60 °C for 30 min under stirring conditions for extraction of metal chlorides. Parameters such as roasting temperature, time, and ammonium chloride dosages were varied to optimize the process. Around 91% of copper, 100 % nickel, 100% zinc, 100% of lead were recovered at optimum roasting conditions of 300 °C, 3 h with NH4Cl dosage of 3 g/g. Furthermore, cementation using aluminum was used for the separation of Cu (99% pure) from leached solution.

Environment-friendly recovery of metals from waste printed circuit boards using ammonium chloride roasting – water leaching

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.