Reducing energy-related CO 2 emissions using accelerated weathering of limestone

Abstract

The use and impacts of accelerated weathering of limestone (AWL; reaction: CO 2 +H 2 O+CaCO 3 →Ca 2+ +2(HCO 3 - ) is explored as a CO 2 capture and sequestration method. It is shown that significant limestone resources are relatively close to a majority of CO 2 -emitting power plants along the coastal US, a favored siting location for AWL. Waste fines, representing more than 20% of current US crushed limestone production (>10 9 tonnes/yr), could provide an inexpensive or free source of AWL carbonate. With limestone transportation then as the dominant cost variable, CO 2 mitigation costs of $3-$4/tonne appear to be possible in certain locations. Perhaps 10–20% of US point–source CO 2 emissions could be mitigated in this fashion. It is experimentally shown that CO 2 sequestration rates of 10 -6 to 10 -5 moles/sec per m 2 of limestone surface area are achievable, with reaction densities on the order of 10 -2 tonnes CO 2 m -3 day -1 , highly dependent on limestone particle size, solution turbulence and flow, and CO 2 concentration. Modeling shows that AWL would allow carbon storage in the ocean with significantly reduced impacts to seawater pH relative to direct CO 2 disposal into the atmosphere or sea. The addition of AWL-derived alkalinity to the ocean may itself be beneficial for marine biota.