Gold Recovery from Waste Printed Circuit Boards by Advanced Hydrometallurgical Processing

The scope of this study was to improve the hydrometallurgical processes involving iodine-iodide leaching and precipitation for recovery of gold from waste printed circuit boards. Firstly, the influence of different precipitating agents, namely ascorbic acid, trisodium citrate and sodium hydroxide on the recovery of gold from gold-iodide leach liquor were investigated in order to define the most effective precipitating agent. The leach liquor was prepared by dissolving pure gold chips in 1:6 molar ratio of iodine-iodide solution at 40 degrees C, 550 rpm for 12 h. The variables, which affect the efficiency of gold precipitation from the leach liquor, were the molar ratio of precipitating agents to gold, pH and redox potential of the solutions. The attained high gold precipitation efficiency from the leach liquor was more than 99% under the highly acidic (pH < 1.6) and alkaline conditions (pH > 13) induced by 0.1 M ascorbic acid and 0.1 M sodium hydroxide respectively, but 64.5% of gold at a weak alkaline condition (pH 8) with 0.1 M trisodium citrate. Secondly, physico-chemical properties of resultant colloidal solutions and prepared gold particles were examined. Finally, recycling of waste printed circuit boards (WPCBs) via iodine-iodide leaching followed by the ascorbic acid reduction was discussed. Results indicate that over 95% of gold extracted from WPCBs by two-step iodine-iodide leaching under the defined conditions, while the dissolution efficiencies of other precious metals (Ag, Pd) and metal impurities (Cu, Al, Fe, Ni, Pb and Zn) were less than 1% and 3%, respectively. The vast majority of Au (99.8%), Cu (95.6%) and Ag (76.8%) were precipitated from the pregnant leach solution by ascorbic acid reduction at ambient conditions.