The rate of natural carbonation of tectonically exposed mantle peridotite during weathering and low-temperature alteration can be enhanced to develop a significant sink for atmospheric CO 2. Natural carbonation of peridotite in the Samail ophiolite, an uplifted slice of oceanic crust and upper mantle in the Sultanate of Oman, is surprisingly rapid. Carbonate veins in mantle peridotite in Oman have an average 14 C age of Ϸ26,000 years, and are not 30 -95 million years old as previously believed. These data and reconnaissance mapping show that Ϸ10 4 to 10 5 tons per year of atmospheric CO 2 are converted to solid carbonate minerals via peridotite weathering in Oman. Peridotite carbonation can be accelerated via drilling, hydraulic fracture, input of purified CO 2 at elevated pressure, and, in particular, increased temperature at depth. After an initial heating step, CO 2 pumped at 25 or 30°C can be heated by exothermic carbonation reactions that sustain high temperature and rapid reaction rates at depth with little expenditure of energy. In situ carbonation of peridotite could consume >1 billion tons of CO 2 per year in Oman alone, affording a low-cost, safe, and permanent method to capture and store atmospheric CO 2.alteration and weathering ͉ carbon capture ͉ exothermic ͉ carbon sequestration ͉ mineral R ecognition that anthropogenic CO 2 input to the atmosphere has substantially increased atmospheric CO 2 concentration, and that increased CO 2 may drive rapid global warming, has focused attention on carbon capture and storage (1). One storage option is conversion of CO 2 gas to stable, solid carbonate minerals such as calcite (CaCO 3 ) and magnesite (MgCO 3 ) (2). Natural carbonation of peridotite by weathering and lowtemperature alteration is common. Enhanced natural processes in situ may provide an important, hitherto neglected alternative to ex situ mineral carbonation ''at the smokestack.'' In this article, we evaluate the rate of natural carbonation of mantle peridotite in the Samail ophiolite, Sultanate of Oman, and then show that under certain circumstances exothermic peridotite alteration (serpentinization, carbonation) can sustain high temperature and rapid reaction with carbonation up to 1 million times faster than natural rates, potentially consuming billions of tons of atmospheric CO 2 per year. In situ mineral carbonation for CO 2 storage should be evaluated as an alternative to ex situ methods, because it exploits the chemical potential energy inherent in tectonic exposure of mantle peridotite at the Earth's surface, does not require extensive transport and treatment of solid reactants, and requires less energy for maintaining optimal temperature and pressure.Tectonically exposed peridotite from the Earth's upper mantle, and its hydrous alteration product serpentinite, have been considered promising reactants for conversion of atmospheric CO 2 to solid carbonate (3). However, engineered techniques for ex situ mineral carbonation have many challenges. Kinetics is slow unless olivine and serpentine ...

No abstract

CO 2 capture and storage (CCS) has the potential to develop into an important tool to address climate change. Given society’s present reliance on fossil fuels, widespread adoption of CCS appears indispensable for meeting stringent climate targets. We argue that for conventional CCS to become a successful climate mitigation technology—which by necessity has to operate on a large scale—it may need to be complemented with air capture, removing CO 2 directly from the atmosphere. Air capture of CO 2 could act as insurance against CO 2 leaking from storage and furthermore may provide an option for dealing with emissions from mobile dispersed sources such as automobiles and airplanes.