702 Figure 2 – Total combined emissions associated with the recovery of 1 kg of gold, silver, and copper under the BAU, R&R, and R&R-MP models 4.3. Effect Of Metal Concentration On Carbon Footprint The differences observed in greenhouse gas (GHG) emissions across the evaluated models are primarily driven by the concentration of metals in the processed materials, as metal grade determines how process-related emissions are allocated to the recovered products in the carbon footprint calculation. For the recovery and reuse of mobile phone electronic boards (R&R-MP), metal concentrations were determined through chemical assays performed on a representative batch of 20.39 tons of electronic boards exported from Peru for pyro-hydrometallurgical treatment in Europe. This batch yielded total recoveries of approximately 23.86 kg of gold, 53.83 kg of silver, and 4,626.13 kg of copper, corresponding to concentrations of 1.17 kg/t for gold, 2.64 kg/t for silver, and 226.85 kg/t for copper. A comparison between urban mining feedstocks and primary ores reveals substantial differences in metal grades across all analyzed metals. Gold concentrations in the R&R feedstock reach 164 g/t, compared to approximately 3.73 g/t in typical primary gold ores, resulting in a concentration ratio greater than 40:1. Silver exhibits a similar pattern, with concentrations of 888.01 g/t in electronic boards versus 120.8 g/t in primary ores. For copper, electronic boards show concentrations of approximately 250.21 kg/t, which is about five times higher than the 50 kg/t commonly reported for conventional copper ores. These significant concentration differentials lead to lower energy use and GHG emissions per kilogram of recovered metal, as collection, transport, and processing emissions are allocated over a larger recovered output. Consequently, emissions per unit of metal are highly sensitive to metal grade, a characteristic that clearly differentiates waste treatment–based recovery systems from conventional mining operations. The carbon footprint values reported in this study reflect the simultaneous recovery of gold, silver, and copper, with gold acting as the main driver of system efficiency due to its high concentration and economic value, enabling the co-recovery of other metals with lower marginal emissions. The relationship between metal concentration and the resulting carbon footprint is illustrated in Figure 3.
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