Waste electrical and electronic equipment (WEEE) is one of the fastest growing solid waste streams worldwide and, if not treated properly, presents serious health and environmental issues as well as extensive loss of strategic metals. The dramatic increase in the consumption of raw materials over recent decades to meet consumer demand has led to an imbalance in supply and demand, and a potential threat to the continued supply of critical metals. WEEE is a resource-rich source with many of the metals embedded in its composition listed as critical by the European Commission; extraction of these metals from WEEE, to mitigate their threat to supply, is imperative.
Using end-of-life mobile phones (EoL-MPs), fast-moving consumer electronics, representative of the value embedded in WEEE, as a case study, a full characterisation of metallic and non-metallic fractions within a mobile phone confirms the presence of up to 71 elements, with many of the strategic and critical metals found in higher concentrations than in their natural ores. Exploiting the unique properties of ionic liquids (ILs), chosen for their selectivity as potential extractants, [Bmim]HSO4 for copper, Cyphos 101 for gold, Cyphos 101 and Aliquat 336 for indium, and [Hbet][Tf2N] for REEs, processes were developed using model test systems to determine optimal parameters to achieve recovery. These developed processes were then applied to treat as-received multigenerational EoL-MP components (printed circuit boards, screens, speakers, etc.), with metals of almost 99% purity recovered, for conversion to products of commercial value. Moreover, the benefit of recycling the ILs as extractants multiple times, without impacting their integrity or efficiency, is realised.
This research demonstrates the potential to unlock value from this waste stream that can be exploited in other WEEE streams, as a step towards balancing the criticality of supply and demand of metals that are under threat.