Sustainable Recovery of Critical Metals from E-Waste—Low Energy Wet Media Milling for Selective Extraction of Cu, Ni and Au from Printed Circuit Boards

Electronic waste (e-waste) management remains a persistent and escalating environmental challenge due to its growing volume and hazardous nature. E-waste contains critical metals such as Cu, Ni, and Au, which are of increasing importance and value. Traditional processes in e-waste treatment, such as high-energy shredding and pyrolysis, are highly energy-intensive, dilute the feedstock, and produce toxic gases. At the same time, the treatment and refining of Au often involve the use of aqua regia or cyanide, which also imposes environmental hazards on aquatic systems and human health. This study addresses these issues by investigating low-energy media milling and sequential chemical etching to directly recover Cu, Ni, and Au from printed circuit boards (PCBs). We provide a detailed characterization of the chemical and mechanical properties of the Au fingers on the PCBs, using techniques such as nanoindentation and focused ion beam etching to probe its layered structure. We then examined the effects of sulfuric acid and hydrogen peroxide concentration on the extent and selectivity of Cu and Ni recovery. We also explore the impact of in-situ wet grinding conditions and look at how using different milling materials (borosilicate, ceramic, zirconia) and shapes (spheres, rods, prisms) affect the kinetics of Cu and Ni leaching and Au delamination. Our findings demonstrate that this novel process achieves quantitative recovery of Au in its solid form, with concomitant selective extraction of Cu and Ni, offering an efficient approach to e-waste management that does not include high-temperature smelting or shredding.