Recovery opportunities of valuable and critical elements from WEEE treatment residues by hydrometallurgical processes

Due to the increasing demand of metals by industry and the limited availability of natural resources, the secondary supply of these elements from discarded products, such as waste electrical and electronic equipment (WEEE), is an important strategy for pursuing a sustainable development. Nevertheless, the complex and heterogeneous composition of this waste stream stands as one of the main drawbacks in the definition of innovative recovery processes. This study investigated the recovery potential of a multi-step leaching process to extract the strategic metals, namely precious metals and rare earth elements (REEs), from the dust produced during the industrial shredding treatment of WEEE. Using a first double-oxidative step with sulfuric acid, most rare earth elements contained in the dust were dissolved at high percentages. Moreover, around 50% of gold was extracted in a second leaching step using 0.25 M thiourea, in a solid to liquid ratio of 0.2 g/70 mL, at 600 rpm. In this regard, the optimum operating conditions were studied by a 2³ full factorial design. Experimental results address the definition of a novel approach, pursuing the recovery of resources of great industrial interest from the residues originating from WEEE mechanical treatments typically performed at large scale. As this dust fraction is not sent for recovery but currently disposed, the proposed recycling strategy promotes the diversion of waste from landfill while reducing the need for virgin materials via lower-impact metallurgical processes.