Kinetics-informed global assessment of mine tailings for CO removal.

Chemically reactive mine tailings are a potential resource for drawing down carbon dioxide out of the atmosphere in mineral weathering schemes. Such carbon dioxide removal (CDR) systems, applied on a large scale, could help to meet internationally agreed targets for minimising climate change, but crucially we need to identify what materials could react fast enough to provide CDR at relevant climate change mitigation timescales. This study focuses on a range of silicate-dominated tailings, calculating their CDR potential from their chemical composition (specific capacity), estimated global production rates, and the speed of weathering under different reaction conditions. Tailings containing high abundances of olivine, serpentine and diopside show the highest CDR potential due to their favourable kinetics. We conclude that the most suitable tailings for CDR purposes are those associated with olivine dunites, diamond kimberlites, asbestos and talc serpentinites, Ni sulphides, and PGM layered mafic intrusions. We estimate the average annual global CDR potential of tailings weathered over the 70-year period 2030-2100 to be ~93 (unimproved conditions) to 465 (improved conditions) Mt/year. Results indicate that at least 30 countries possess tailings materials that, under improved conditions, may offer a route for CDR which is not currently utilised within the mining industry. By 2100, the total cumulative CDR could reach some 33 GtCO, of which more than 60% is contributed by PGM tailings produced in Southern Africa, Russia, and North America. The global CDR potential could be increased by utilization of historic tailings and implementing measures to further enhance chemical reaction rates. If practical considerations can be addressed and enhanced weathering rates can be achieved, then CDR from suitable tailings could contribute significantly to national offset goals and global targets. More research is needed to establish the potential and practicality of this technology, including measurements of the mineral weathering kinetics under various conditions.