Summary:
A poorly accounted source of carbon dioxide (CO₂) could substantially increase estimates of copper production emissions in a major Spanish mining region, according to research from the University of St Andrews. The study examined 82 active and historic mines in south-eastern Spain, where acidic, metal-rich drainage occurs at exceptionally high rates.
Researchers analysed river chemistry to quantify this drainage and estimate the CO₂ released as its acidity was neutralised. They also assessed emissions produced when affected river water entered an estuary and mixed with alkaline seawater, supported by laboratory experiments that reproduced the mixing process.
The analysis indicates that neutralisation has already released an amount of CO₂ comparable to the estimated conventional carbon footprint of copper production in the region. Exposed metal sulphide minerals can continue generating acidic drainage for centuries or millennia after mining ends, meaning the full emission budget could eventually exceed that conventional estimate by more than tenfold.
Published in Environmental Science & Technology, the study indicates that these long-term emissions should be included in mining carbon assessments and considered when developing remediation methods.
— Press Release —
Carbon footprint of metal production could be more than 10 times higher than estimated
New research from the University of St Andrews has discovered that metal production carbon footprints could be more than 10 times higher than previously estimated, with serious implications for the ambition to reach net zero.
Published today in Environmental Science and Technology, this groundbreaking work is the first comprehensive quantification of CO₂ emissions from acid mine drainage neutralization for metal mining in academic peer reviewed literature.
Acid mine drainage is a common and well known side effect of mining, occurring when waters that drain mining areas become acidic and full of toxic metals . It occurs when mining digs up a certain type of mineral (metal sulphides) that then react with oxygen rich surface waters. The subsequent interaction of these acidic waters with the surrounding environment can lead to chemical reactions that release CO₂. Efforts to remediate this pollution issue often also involve reacting acid mine drainage with minerals in engineered settings, again releasing CO₂. This chemistry is already known, but to date, no one had quantified the size of this CO₂ emission source in detail.
Researchers studied an area of 82 historic or currently working mines in South East Spain that is considered to generate the highest rates of acid mine drainage in the world. They measured the chemistry of rivers draining this region to quantify the amount of acid mine drainage generated and how it is neutralized, which in turn allows estimation of the CO₂ flux. Researchers also measured how the chemistry of these rivers changes as they mix with alkaline seawater in the downstream estuary, again leading to CO₂ emissions. This was further backed up with laboratory experiments simulating river water/seawater mixing.
Results showed that when all this was considered, Acid mine drainage neutralization to date has emitted a similar amount of CO₂ as estimated for conventional copper production carbon footprints from this region
However, the problem is further compounded as acid mine drainage emissions continue to occur for a very long time after the mining activity is finished. This is because the metal sulfide minerals dug up during mining can take centuries to millennia to fully react with oxygen rich surface waters, continuing to make acid mine drainage for a long time into the future.
The senior author of the project Dr Luke Brigstock from the School of Earth and Environmental Science , said: “This is a shocking result. We estimate that the full emission budget for acid mine drainage by the time all the extracted sulfides have ‘weathered’ to produce acid mine drainage – will be more than 10 times higher than conventional carbon footprints for copper production. This presents a challenge for reaching net zero greenhouse gas emissions given the need for increased metal production to supply green technologies. It’s essential that we now look at changing how acid mine drainage is remediated to reduce these emissions”
Read also: Rethinking energy security in a net-zero world
This poorly accounted for emission source will dominate the total carbon footprint of copper production in this region in the long run. While it is likely that the size of this emission source will be lower in other mining regions, these results highlight the importance of accounting for this emission source across the metal mining sector.
Metal mining is set to rise in the future to support the green transition. Given the role of metal production in supply ‘green technologies’ – solar, wind, boosting electrification of the grid etc – decarbonizing the metal production sector is a key part of strategies to get to net zero. This wider context gives added motivation to quantifying this poorly known metal mining emission source.
Journal Reference:
Stanisław Kołodziejski, Eva E. Stüeken, Laura Sánchez López, Jose Miguel Nieto, Carlos R. Cánovas, Rafael Pérez-López, and Luke Bridgestock, ‘Carbon Dioxide Emissions from Acid Mine Drainage Neutralization Are a Major Component of Metal Mining Carbon Footprints’, Environmental Science & Technology online ver. (2026). DOI: 10.1021/acs.est.6c05684
Article Source:
Press Release/Material by University of St. Andrews
Featured image credit: Luke Brigstock | University of St. Andrews
