Ammonia-salt-assisted green hydrometallurgy for CuO nanosynthesis from waste PCBs

The escalating accumulation of electronic waste (e-waste), currently estimated at approximately 45 million tons annually worldwide, causes serious environmental and resource recovery challenges. Printed circuit boards (PCBs), key components of most electronic devices, are particularly valuable due to the presence of precious metals (Au, Ag, Pt, Pd, and Cu), the recovery of which is hindered by the combination of ceramics, polymers, and metals. Metal fraction makes up 25%–30% of total PCB mass, while among all metal elements, copper is present in the highest proportion—most often 60%–70% compared to the metal fraction mass. Copper has recently been designated as a critical raw material by the European Commission. Simultaneously, increasing global demand for copper, alongside limited mining capacity, has led to a growing supply gap. This research responds to both environmental and economic needs by recovering copper from discarded PCBs and converting it into copper oxide (CuO) nanoparticles, a material of high technological relevance—especially in industrial organic synthesis. Mechanical methods were applied to separate polymeric layers from metal-rich components, followed by chemical extraction using ammonium-based salts. Analysis of these extracts showed that copper extraction was more efficient if the polymer/ceramics fraction of PCB is removed by grinding. The present study can report that the PCB types (denoted PCB3) as the coarse fraction leached by (NH 4 ) 2 C 6 H 6 O 7 and obtaining 29.93 wt% Cu compared to the starting waste mass corresponds to ≈99.8% effective extraction when referenced to a Cu-rich 30 wt% feed. This result is the highest of the published data of ammoniacal-e-waste leaching. Purified extracts were used for CuO nanoparticle synthesis by means of microemulsion synthesis. Characterization by X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM) confirmed the successful synthesis of CuO nanoparticles. These results point to a practical and eco-friendly hydrometallurgical strategy for copper recovery from electronic waste, followed by CuO nanoparticle production. The method addresses both e-waste pollution and the growing copper shortfall, supporting urban mining initiatives, promoting circular resource use, and complementing green transition goals.