Recovery of precious metals from electronic waste and spent catalysts: A review

This review examines current technologies for recovering precious metals (PMs) from electronic waste (e-waste) and spent catalysts, which together account for over 90% of industrial PM consumption. Against the backdrop of limited natural reserves, geographically concentrated primary production, and rapidly increasing end-of-life products, the paper frames e-waste and spent catalysts as critical “urban mines” for gold, silver, and platinum group metals. The review systematically describes mechanical pretreatment, pyrometallurgical, and hydrometallurgical routes for e-waste processing, emphasizing dismantling, size reduction, and physical separation as essential steps to enrich metal fractions and remove hazardous components. Industrial-scale smelting operations, such as black copper smelting in advanced furnaces, are highlighted for their high recovery efficiencies, while the transition from traditional lixiviants (aqua regia, cyanide, chlorine) to less-polluting leaching agents reflects a growing focus on environmentally benign processes. For spent catalysts, the paper discusses the complexity introduced by diverse carrier materials and variable PM contents, which complicate recovery. Across both waste streams, the review evaluates the advantages, limitations, and environmental impacts of existing technologies, noting persistent challenges including incomplete recovery, loss of valuable metals during mechanical processing, and residual pollution. The authors conclude by identifying key considerations for future research and industrial practice aimed at developing environmentally friendly, sustainable recycling systems capable of achieving high PM recovery rates with minimal ecological and human health risks.