Waste Slag From Mining Operations Could Help Store Carbon Emissions

A new Concordia-led study suggests that iron-rich slag, one of mining’s biggest waste products could help store carbon dioxide (CO₂) emissions.

The researchers examined whether slag, a waste material generated from metal processing, can trap the greenhouse gas under realistic conditions. While scientists have long known slag can store CO₂ by forming solid minerals, most studies focus on systems that are heavily dependent on water.

This study, published in Chemical Engineering Journal, looks at what happens in conditions that are more realistic, with low-to-moderate moisture. Using slag from a Quebec smelter, the researchers placed samples in sealed containers, injected CO₂ gas and varied moisture levels, then tracked how much CO₂ remained in the air after 24 hours. They also analyzed the solids and liquids using imaging and chemical tests to identify how the carbon was stored.

The slag removed up to 99.5 per cent of CO₂ in lab tests. More notably, most of the carbon was not stored as minerals but instead attached to the slag’s surface - a process known as adsorption.

The results reveal that mineral formation need not be the only avenue for CO₂ storage, while at the same time offering a better understanding of how these materials interact in more realistic environments.

The researchers believe that the approach could be integrated directly into mining operations, where large volumes of slag are already stored on-site. Captured CO₂ from nearby industrial processes could be injected into these waste piles with minimal processing, even in remote locations, turning a liability into a passive, low-maintenance carbon sink.

Reference: Wilcox SM, Mulligan CN, Neculita CM. Evaluation of carbon sequestration by iron-rich slag materials. Chem Eng J. 2026;533:174903. doi: 10.1016/j.cej.2026.174903

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