Carbon dioxide emissions from acid mine drainage neutralization are a major component of metal mining carbon footprints

Achieving the transition to net zero human greenhouse gas emissions requires a large increase in metal production by mining. Acid mine drainage (AMD) neutralization is a potentially important but poorly quantified source of mining industry CO₂ emissions. Here, we show that AMD neutralization-related CO₂ emissions can be a major component of metal production carbon footprints. Data from the rivers and estuarine system draining the central and eastern Iberian Pyrite Belt show that AMD neutralization emits 32 ± 11 kt CO₂/yr. Normalized to historic copper production rates, AMD-associated emissions (0.3–4.2 t CO₂ per t Cu) are of similar magnitude as conventional copper production carbon footprints (1–9 t CO₂ per t Cu). However, continual oxidative weathering of waste sulfide minerals will increase AMD-related CO₂ emission budgets into the future. Complete oxidative weathering of waste sulfide minerals extracted from this region will yield AMD-related CO₂ emissions (7–165 t CO₂ per t Cu) that exceed conventional Cu production carbon footprints by more than 1 order of magnitude. These findings highlight the need to account for AMD-related CO₂ emissions from metal mining to support the transition toward net zero greenhouse gas emissions.