The Recovery of Precious and Base Metals

Increasing volumes of waste printed circuit boards from obsolete electronic equipment posed escalating environmental risks and resource losses due to landfilling and primitive recycling practices. This study aimed to quantify recoverable precious and base metal contents in printed circuit boards and to evaluate recovery efficiencies, kinetics, and process intensities of mechanical, pyrometallurgical, hydrometallurgical, and emerging electrowinning and biometallurgical routes. The methodology consisted of a structured review of experimental and industrial-scale studies reporting metal grades, leaching efficiencies, electrowinning purities, and process conditions for copper, gold, silver, and palladium extraction from computer and mobile phone circuit boards. Typical printed circuit boards contained about 20 wt% copper, 0.04 wt% gold, 0.15 wt% silver, and 0.01 wt% palladium, with reported gold recoveries up to 95% from contactors using combined mechanical and chemical treatment, and copper leaching degrees up to 98% under optimized sulphuric acid conditions. Electrolytic recovery using EMEW electrowinning achieved metal purities up to 99.99%, while selective and eco-friendly lixiviants such as thiosulfate and thiourea provided competitive gold leaching efficiencies with reduced cyanide consumption, and physical pre-concentration lowered energy and reagent use compared with direct pyrometallurgical treatment. The review indicates that integrated flowsheets combining mechanical upgrading, optimized hydrometallurgy, and high-purity electrowinning can recover more than 95% of contained precious metals and over 90% of copper from printed circuit boards, thereby substantially decreasing hazardous emissions and diverting high-grade secondary resources from landfills.