Advances in Recovering Noble Metals from Waste Printed Circuit Boards (WPCBs)

An extensive investigation on the NMs content in different classes of WPCBs (Random Access Memories, RAMs; Network Interface Controllers, NICs; motherboards; TV, DVD/CD player, hard-drive and mobile phone PCBs) has been performed to define the most appropriate case study and provide a robust database useful for workers in the waste valorisation field. Following accurate selection, mechanical comminution, representative sampling, quantitative digestion and analytical characterization (ICP-AES), RAMs and mobile phone PCBs confirmed to be the “richest” source, while TV PCBs the “poorest” one in term of NM content. Accordingly the RAMs case study has been employed for the application of a new Noble Metals (NMs) recovery method, previously set-up on finely comminuted WEEE underwent materials enrichment by mechanical separation. Despite the very large amount of vitreous-plastic and metallic materials present in the mixture, satisfactory NMs recovery yields (Cu 70%, Ag 92%, Au 64%) with limited by-products formation have been obtained using safe and recyclable reagents in mild conditions: citric acid for base metal leaching; ammonia in oxidizing environment for Cu and Ag separation and recovery; triiodide aqueous solution for gold recovery; room pressure; 25-100°C. The reported results provide useful quantitative parameters for assessing the profitability of an industrial scale-up of the new sustainable NMs recovery method.