Au and Ag distribution in alloys produced from the smelting of printed circuit boards - an assessment using SEM-EDS, EPMA, and LA-ICP-MS analysis

Electronic waste such as printed circuit boards (PCBs) often contains important concentrations of precious metals such as Au and Ag, which are typically recovered using pyrometallurgical methods as a first step.Understanding the phase chemistry and distribution of precious metals in alloys is of value to the pyrometallurgist, as this gives information on phase partitioning in the furnace.In the present study we aimed at determining the contributions of different phases to the Au and Ag contained in the alloy, using a combination of mineralogical techniques.Three alloy samples were first subjected to scanning electron microscopy (SEM) to distinguish the phases present.Electron probe microanalysis (EPMA) was then performed to determine the compositions of the different phases.Modal phase abundance was obtained, and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) was then used to quantify Au and Ag in the identified phases.The Au and Ag deportments were derived from these inputs.The results show that Au and Ag partition into all identified alloy phases, but principally into Cu and Pb alloy phases.Cu-rich phases containing Sn are the major hosts of Au and Ag, with the Pb phase in one sample also being a major host.The study demonstrates the success of a combined mineralogical approach incorporating LA-ICP-MS as a method of choice for detecting low concentrations of precious metals in alloy phases, and contributes to our understanding of precious metal partitioning during smelting of waste PCBs.