Development of an integrated glycine-based process for base and precious metals recovery from waste printed circuit boards

The present study developed an integrated glycine-based process to recover metals from waste printed circuit boards at high solid contents (10-15%). A novel glycine-ammonia leaching was used to selectively extract >99% copper, >85% zinc and around 50% lead at room temperature. Ammonia played a key role, increasing the copper solubility in solution (>40 g/L), shortening leaching time from 72 to 24 h, and also acting as a pH modifier. The 2nd leaching step utilised cyanide-starved glycine where extractions of 70-90% for gold and silver, and >50% for palladium were obtained. The remaining metals from the previous steps were removed by ferric sulfuric acid leaching, with/without thiourea. In the presence of thiourea, 70-95% of remaining base and precious metals were removed. Overall, the metals with major economic value were all extracted at >99% for copper, >80% for gold, >90% for silver and >85% for palladium.