Proposition of electronic waste as a reference material – part 1: sample preparation, characterization and chemometric evaluation

Abstract

Electronic waste (e-waste) is attracting increasing interest in industry, politics, academic centers, and initiatives worldwide. Because of its complex composition of precious and hazardous substances, new technologies are often required to process e-waste in order to maximize resource recovery and minimize possible harm to humans and the environment. Printed circuit boards (PCBs) are present in most electronic products and currently comprise a significant fraction of e-waste. In this study, a reference material (RM) for inorganic constituents in PCB samples was prepared and leaching procedures for its characterization were developed. Full factorial design and principal component analysis (PCA) were applied to evaluate five different types of acidic solvents (aqua regia, inverted aqua regia, aqua regia 50% v/v, 7 mol L⁻¹ HNO₃ + H₂O₂, and 14 mol L⁻¹ HNO₃) in sample leaching by microwave radiation and inductively coupled plasma optical emission spectrometry (ICP OES) for the determination of Ag, Al, As, Au, Ba, Cr, Cu, Fe, Ni, Pb, Sb, Si, Sn, and Zn. Diluted aqua regia provided high leaching efficiency and the best results for these elements. The optimal conditions for further experiments were fixed for 0.1 g of sample and 10 mL of acid mixture. The PCB material was also submitted to nondestructive testing by instrumental neutron activation analysis (INAA) and a paired t-test was applied to compare the results obtained by microwave radiation and INAA. A minimum mass study was carried out and 100 mg was established as the minimum sample mass for further studies in agreement with the optimal conditions fixed for the sample mass after optimization.