In the framework of e-waste management regulations, synergistic green chemistry & engineering are powerful in addressing a sustainable circular economy.

An effective and sustainable method for the selective leaching of metals from the non-ferrous metal fraction of Waste Electric and Electronic Equipment (WEEE) is described here. This method consists of a sequence of steps which involve the selective leaching of the different metals from the shredded sample by using environmentally friendly lixiviants in water. In particular: (1) a refluxing citric acid (3 M) solution which dissolves Sn, Zn, Pb, Ni, and other base metals; (2) NH₃ in combination with an IO₃ ⁻/I⁻ mixture which allows one to oxidize Cu and Ag, and to separate them by selective AgI precipitation; (3) an I⁻/I₂ mixture (5.3 : 1 molar ratio) which is capable of leaching quantitatively Au metal from the solid residue. Each step is followed by a further treatment for: (i) high-rate metal and reagent recovery, in the case of NMs; (ii) inertization, in the case of heavy metals. The “chameleon” behaviour of iodine, which shows versatile redox/complexing/precipitating capabilities, allows one to achieve, on the one hand, a selective noble-metal (NM) leaching and, on the other hand, a simple and effective reagent and metal recovery. The comparison of the above described method with a similarly effective one previously patented by some of the same authors, allows one to point out that a significant improvement in sustainability is achieved in terms of lixiviant employment, which is of low cost, easily available and recyclable, and able to work in water solutions, while maintaining or improving its environmentally friendly character.

The direct use in catalysis of precious metal recovery products from industrial and consumer waste is a very promising recent area of investigation. It represents a more sustainable, environmentally benign, and profitable way of managing the low abundance of precious metals, as well as encouraging new ways of exploiting their catalytic properties. This review demonstrates the feasibility and sustainability of this innovative approach, inspired by circular economy models, and aims to stimulate further research and industrial processes based on the valorisation of secondary resources of these raw materials. The overview of the use of recovered gold and palladium in catalytic processes will be complemented by critical appraisal of the recovery and reuse approaches that have been proposed.

The successful production of a nanostructured and highly dispersed Pd-TiO₂ photo-catalyst, using [Pd(Me₂dazdt)₂](I₃)₂ (Me₂dazdt = N,N′-dimethyl-perhydrodiazepine-2,3-dithione) salt, obtained through the selective and safe recovery of palladium from model exhaust three-way catalysts (TWCs), is reported here. The photo-catalyst prepared by the impregnation/photo-reduction of palladium on the support showed improved performance in H₂ production from methanol and in glycerol photo-reforming compared to reference photo-catalysts obtained from conventional Pd-salts. The reported results represent a case of successful palladium “recovery and re-employment” and thus constitute an example of green chemistry by providing, in one route, the environmentally friendly recovery of a critical metal and its employment in the renewable energy field.