Resources Recovery from Electronic Waste

Abstract

Printed Circuit Boards in electronic scrap are richest source of base and precious metals, promoting economic drive for metal recovery. Recovery of these metals is a difficult exercise due to complex nature of electronic waste. India is one of the leading electronic waste processing hubs where more than 95% recyclers are unorganised/non-formal, lacking such a recovery facility. An efficient metal recovery protocol with lesser environmental impact remains unavailable to unorganised recyclers. In current study, an attempt has been made to combine various hydrometallurgical methods to achieve efficient metal recovery from Printed Circuit Boards. Mimicking mineral processing protocols for metal recovery from electronic waste has been a key feature of presented research. Printed Circuit Boards of personal computers were reduced to a size ≤ 2.5 mm and were used as sample for metal recovery. Copper and silver were extracted by selective leaching using Nitric Acid. Maximum extraction efficiency of 96.8% and 99.9% were achieved for copper and silver respectively. Nitric Acid was extracted using solvent extraction method to minimize the environmental damage of remaining waste as well as for reuse in next leaching cycle. Electrodeposition of copper was done on copper cathode with stainless steel and lead anodes with a maximum recovery efficiency of 89.6%. For extraction and recovery of gold and silver, various techniques used in mineral processing were applied in this research. Thiosulfate leaching was chosen for gold extraction due to its proven environment friendly properties. Maximum gold extraction efficiency of 74.3% has been achieved in this work. To recover gold from pregnant solution, zinc cementation approach was used. Up to 85.9% gold was recovered with zinc cementation. Success of thiosulfate leaching and cementation confirms the validity of mineral processing techniques in metal recovery from electronic waste. Research in this study can serve as a backbone for potential environmentally sound technology towards efficient metal recovery from electronic waste for small and medium scale recyclers.