secondary metal supply routes. The functional unit is defined as 1 kg of refined metal (Au, Ag, Cu), expressed in t CO₂eq/kg metal. This unit enables normalization across heterogeneous material inputs and highlights differences in carbon intensity driven by process efficiency and metal concentration. 3.2. Scenarios and system boundaries Energy consumption across all systems was quantified for electricity and direct fuel use, and greenhouse gas emissions were calculated using emission factors consistent with the GHG Protocol. Electricity emission factors reflect the geographical context of each process stage, while fuel emission factors are based on standardized values reported in the literature. By combining primary operational data, real transport tracking, and established emission factors, this methodology enables a transparent and robust comparison between conventional mining and internationally integrated urban mining systems from a carbon footprint perspective. Three scenarios were evaluated: • BAU: Primary extraction and processing of gold, silver, and copper. Inventory data were obtained exclusively from secondary sources, including peer-reviewed literature and publicly available sustainability and operational reports from mining companies operating in Peru. The system includes extraction, concentration, and refining stages. • R&R: Urban mining pathway based on primary data, covering collection, dismantling, pre-treatment, international transport, and metallurgical recovery of metals from electronic boards. Data were obtained through direct collaboration with a Peruvian e-waste operator (collection, dismantling, export) and a European metallurgical recycler (pyro-hydrometallurgical treatment). • R&R-MP: Extrapolated scenario if the exported material consisted exclusively of mobile phone printed circuit boards (PCBs). Metal yields were adjusted using literature-based concentration factors, while all logistical and treatment parameters remained unchanged. All scenarios are modeled under consistent cradle-to-gate boundaries. 3.3. Scenarios and system boundaries The R&R analysis is based on a real industrial case involving 20.39 tons of electronic boards exported from Peru to Western Europe in 2024. Pre-treatment energy consumption data were collected directly from the Peruvian operator (Comimtel), who confirmed that the shipment consisted exclusively of segregated printed circuit boards (PCBs) dismantled prior to export. Maritime transport from the Port of Callao to the Port
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