Simple and near-zero-waste processing for recycling gold at a high purity level from waste printed circuit boards

This work proposes an efficient and simple hydrometallurgical process based on a chlorination step followed by an ion-exchange step for recycling gold (Au) from a waste printed circuit boards (WPCBs) enriched in Au resulting from a first leaching step under mild oxidizing conditions for extracting Cu and other base metals. Under optimized [3.5 mol/L HCl and 0.46 mol/L NaClO, with a liquid/solid (L/S) ratio of 40, at 40 °C for 3 h with agitation] leaching conditions, 95% Au was extracted from the residue originating a multi-metal solution containing 1.0% Au. Subsequently, Au (initial concentration: 38 µmol/L) present in the multimetal-leached solution was purified in continuous mode using two strong anionic exchange resins: DOW™ XZ-91419.00 and Purogold™ A194. Both resins were suitable in purifying Au from the multimetal-leaching solution, with at least 70% of Au recovered relative to the initial residue. When the DOW™ XZ-91419.00 resin was used, a solution containing 1.7 mmol/L Au with a purity grade of 94% was obtained, with Pb and Sn being the major contaminants (3.3 and 2.4%, respectively). For Purogold™ A194 resin, a solution containing 0.73 mmol/L Au with a purity grade of 92% was achieved; Ag, Pb and Pd were the major contaminants (1.4, 3.6 and 1.8%, respectively). In conclusion, this work demonstrates a novel hydrometallurgical strategy for recycling Au with a high grade from WPCBs, minimizing the number of leaching and purification steps and the amount of waste created.