Conventional mining (Business as Usual – BAU) exhibits the highest greenhouse gas emissions among the evaluated metal supply models. When considering the combined recovery of 1 kg of gold, 1 kg of silver, and 1 kg of copper, total emissions exceed 29.59 tCO₂eq. These values are primarily driven by the low concentration of target metals in primary ores, which results in energy-intensive extraction, beneficiation, and refining processes. Urban mining pathways show markedly improved environmental performance. The recovery and reuse of mixed electronic boards (R&R) reduce the carbon footprint associated with the joint recovery of the three metals to approximately 10.17 tCO₂eq, representing a reduction of nearly 66% relative to the BAU model. The most pronounced improvement is observed for the recovery and reuse of mobile phone electronic boards (R&R-MP), where emissions decrease to approximately 1.75 tCO₂eq for the same combined metal output. This corresponds to a reduction of up to 94% compared to conventional mining. These results highlight that, if the objective is to supply 1 kg of gold, 1 kg of silver, and 1 kg of copper, conventional mining generates substantially higher greenhouse gas emissions than urban mining pathways based on electronic waste. The magnitude of these differences across the evaluated models is illustrated in Figure 2. 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
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