Importance of chemical pretreatment for base metals remotion and its effect on the selective extraction of gold from Printed Circuits Boards (PCBs)

Printed Circuit Boards (PCBs) are constituted of multiple materials, which contributes to the complexity of the metal extraction process. In this work, a methodology for removing base metals and selectively extracting gold from a PCB sample was proposed; the sample tested contained ~200 g Au per ton. Two pretreatment stages were introduced (Na3C6H5O7-(NH4)3PO4-H2O2 and H2SO4-H2O2 systems), removing >90% of Cu, Ni, Zn, Fe, and Al. Subsequently, in the precious metal leaching stage, the thiourea-hydrogen peroxide-oxalic acid system (CS(NH2)2-H2O2-C2H2O4), was employed. To achieve elevated gold extraction, the oxalate ion (C2O4-2, Ox) was used as a masking agent, forming stable species with remaining base metals in the leach liquors. Furthermore, this also contributed to H2O2 and CS(NH2)2 stability, permitting a gold dissolution of 92%.

Keywords: Selective leaching of gold, Chemical pretreatment, Base metal removal.

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