Silver Extraction from Printed Circuit Boards using a Hybrid Supercritical Water and Carbon Dioxide Extraction process; Experimental Design and Optimization of the Process

Abstract

Abstract Electronic waste (E-waste) and its accumulation in recent years is turned in to a global issue and the management and technologies for recycling of this waste are aggressively growing. The main aim of this study is to increase the extraction efficiency of silver metal using supercritical carbon dioxide from computer printed circuit boards (PCBs) waste. Supercritical water pretreatment was used to more reachability of the silver within the PCBs structure and using ethanol co-solvent and organic ligands of Cyanex 302 ligand, Kelex and EDTA helped the efficiency enhancement of the process. The response surface method (RSM) and thermodynamic modeling was used in order to experimental design and optimization of the process. The optimized conditions for supercritical water pretreatment was determined to be 275 bar pressure, 431 ℃ temperature and 30 min residence time and for supercritical carbon dioxide extraction step it was calculated to be at the temperature of 50 ℃, dynamic residence time of 90.00 min and pressure of 300.00 bar with the response of 72.07% of efficiency for silver extraction. According to results of this study, it would be available to design and manufacture of a larger scale extraction unit to reach valuable amounts of precious silver metal from e-waste.