Weekly Seminar - Hiwa Salimi

Date:  Friday, October 14, 2016

Time:  4 p.m.

Place:  Thorvaldson 159

Modern gold extraction processes from both primary and secondary sources have changed little over the past centauries and yet easily accessible gold has become increasingly scarcer over time resulting in ever increasing energy costs, waste and pollution. Cyanide is the preferred leach reagent used in 90% of gold mines worldwide, while aqua regia remains an unmatched gold leaching reagent for secondary sources for more than a millennium. However their continued use presents significant environmental risks. Here we report two new gold extraction systems including (i) simultaneous leaching and solvent extraction and (ii) gold leaching in acidified water-miscible organic solvents. During the simultaneous process, dithiobiuret-based ligands were applied during the solvent extraction of gold simultaneously with leaching step under mild conditions. This new technique resulted to selective extraction of gold from ore samples and a significant decrease in the leaching time. In the second process, a comprehensive set of water-miscible organic solvents including small amounts of HCl, CaCl₂ and some oxidizing reagents were used as new leaching systems for gold. Among all studied solvents, acetic acid provided the highest gold dissolution rates reported to date. Along with an unmatched gold dissolution rate, this new leaching system was also highly selective for gold over base metals such that in the case of electronic scraps, more than 99% of gold was extracted from printed circuit boards (PCBs) in less than 20 seconds (which is the fastest known gold recycling process from e-waste ever reported) while less than 1.5% of nickel, 0.3% of copper, and 0.05% of all of the other base and heavy metals were leached during the same contact time. This new discovery promises to replace highly hazardous chemicals commonly used for gold recovery and opens new opportunities into the field of gold extraction for future studies.