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.