The 2023 IPCC Climate Report makes it clear that cutting greenhouse gas emissions alone is not enough: large-scale CO₂ removal (CDR) from the atmosphere is also needed. One promising approach involves speeding up natural processes where certain crushed rocks react with CO₂. Known as enhanced weathering (or mineral carbonation when stable carbonates are formed), this process captures CO₂ and stores it in alkalinity solution, or in solid, long-lasting minerals.

To be scalable, these methods must be cost-effective and measurable. A key factor is access to suitable magnesium- and calcium-rich rocks, such as mafic and ultramafic rocks. These are often mined for metals such as nickel, platinum, copper and chromium, leaving behind large volumes of waste rock and tailings. Though typically unused, materials still contain minerals that can react with CO₂.

Since ore grades are usually below 1%, mining generates vast amounts of crushed waste. In this study, we analysed global data on tailings from metal and diamond mines to estimate their CDR potential, based on composition, production and reaction rates. We found that tailings rich in olivine, serpentine and diopside could remove tens to hundreds of millions of tonnes of CO₂ annually, offering a scalable, durable path for industrial CDR.