Carbon Capture through Enhanced Weathering of Indian Industrial and Mine Waste Materials

Society’s persistent dependence on fossil fuels has resulted in significantly increased atmospheric CO₂ concentration that contribute to severe global warming. It is now essential to remove excess CO₂ from the atmosphere to mitigate climate change. Enhanced weathering offers a promising solution by accelerating natural chemical weathering processes in which atmospheric CO₂ dissolves in rainwater, reacts with rocks, and is converted into alkalinity–effectively storing CO₂ securely over decades. Modelling indicates that increased weathering rates by selecting highly reactive rocks and expanding reactive surface area could remove up to 2 Gt of CO₂ annually [1]. The mining industry, extracts and processes huge tonnages of ore-bearing and overburden rocks, generating large amounts of freshly exposed, reactive surface area which can enable enhanced weathering. Substantial amounts of annual mine tailing and industrial waste production and higher reaction rates due to its relatively hot climate make India one of the most favourable places to implement enhanced weathering research. In India, many ore deposits are hosted by silicate rocks with high proportions of Mg- and Ca-bearing minerals.

Here we report the results of an investigation into the reactivity of Indian mine waste, including chromite mine tailings and peridotite, serpentinite, pyroxenite, and ultrabasic host rock samples from the Sukinda chromite mine in India. We also explore the potential of carbon capture of industrial waste, such as steel slag from the iron and steel industries and coal fly ash from coal-based thermal power plants.  A series of laboratory experiments were conducted whereby crushed rock, slag, and coal fly ash samples were reacted with CO₂-enriched water at room temperature and atmospheric pressure (100% CO₂). XRD, XRF and thin section studies have been conducted on the rock samples and ICP-MS, IC used for chemical analysis of the reaction liquids. Surface area normalized dissolution rates were measured across various grain sizes, mineral compositions, and solution chemistries. Among the mine waste samples, peridotite shows high reactivity with the CO₂-saturated water and reflects the significant potential to sequestrate carbon dioxide (63kg CO₂/tonne rock) in comparison to other host rocks (<5kg CO₂/tonne rock). Additionally, basic oxygen furnace (BOF) slag demonstrated promising future possibilities as an effective carbon capture medium (70kg CO₂/tonne rock) within the human timescale.

[1] Kelemen, P. B., McQueen, N., Wilcox, J., Renforth, P., Dipple, G., & Vankeuren, A. P. (2020). Engineered carbon mineralization in ultramafic rocks for CO2 removal from air: Review and new insights. Chemical Geology, 550, 119628.