Metal mining carbon footprint may be 10 times larger due to acid mine drainage, study finds

A new study in Environmental Science and Technology reveals that metal mining's carbon footprint could be up to ten times larger than previously estimated. Researchers from the University of St Andrews found that acid mine drainage, a common side effect of mining, releases significant CO2 when sulfide minerals react with water and rocks. This emission source had not been formally quantified before, meaning the true climate cost of extracting metals for wind turbines, EVs, and grid upgrades is much higher than current accounting suggests. The study focused on the Iberian Pyrite Belt in Spain, a major copper mining region. It found that acid mine drainage since the 19th century has produced as much CO2 as all known mining emissions combined, effectively doubling the historical footprint. Worse, these reactions can continue for hundreds to thousands of years after mining stops, creating a long-term liability. The researchers estimate emissions of 7 to 165 tons of CO2 per ton of copper, depending on ore sulfide content and local geology. Mitigation may be possible. The team is testing olivine, a fast-dissolving mineral, to neutralize acidic runoff without releasing CO2. Identifying high-risk mining regions is the next step. Without addressing this hidden source, achieving net zero in the mining sector will be impossible. The study underscores the need for tailored decarbonization strategies that account for all emission pathways, not just diesel and equipment.