Metal mining carbon footprint 10 times larger than thought due to acid mine drainage, study finds

A new study published in Environmental Science and Technology reveals that the carbon footprint of metal mining could be up to 10 times greater than conventional estimates. Researchers at the University of St Andrews found that acid mine drainage, a common byproduct of mining sulfide ores, releases significant amounts of CO2 when acidic water reacts with rocks or seawater. This emission source had not been formally quantified before, meaning the true climate impact of mining for metals like copper is much higher than previously accounted for. The study focused on the Iberian Pyrite Belt in Spain and showed that acid mine drainage since the 19th century has produced as much CO2 as all known mining emissions combined. Even after a mine closes, sulfide minerals can continue generating emissions for hundreds to thousands of years. The researchers estimate emissions of 7 to 165 tons of CO2 per ton of copper produced, with the midpoint roughly 10 times current estimates. The team is testing whether olivine, a fast-dissolving mineral, could neutralize acidic runoff without releasing carbon. The findings highlight that decarbonizing the mining industry requires addressing these overlooked emission sources to achieve net zero goals.