Assessment of carbon dioxide sequestration potential of ultramafic rocks in the greenstone belts of southern India

Abstract

The growing universal concern about anthropogenically induced climate change is resulting in the development of strategies that can reduce or at least slow down the build-up of greenhouse gases in the atmosphere. Disposing of the excess carbon dioxide (CO2) by capturing it from industrial sources, separating it from flue gases and storing into potential geological reservoirs is emerging as a new technology for mitigating the detrimental effects of emissions and is referred to as carbon sequestration. An effective geochemical trapping system for storing the CO2 underground is mineral carbonation. It is based on the weathering/alternation processes occurring in nature, wherein CO2 reacts with Ca, Mg and/or Fe-bearing silicate-rich rocks such as ultramafics and mafics to form the respective carbonates. Under controlled experimental conditions with optimized reaction kinetics, mineral carbonation has considerable potential for the safe disposal of CO2 in the form of environmentally benign carbonates. India has about twenty-five major greenstone belts with maximum thickness up to 10 km and lithologies containing Ca, Fe and Mg silicaterich minerals such as olivine (Mg, FeSiO4), serpentine (Mg3Si2O 5(OH)4), pyroxene (Mg, FeSiO3), etc. In this article, the mineral carbonation potential of ultramafic rocks of the greenstone belts of the southern Indian Peninsula is considered. The alkaline silicates exist in abundance in the greenstone belts and may act as possible sinks to sequester CO2 in the form of magnesium, iron or calcium carbonates. The distribution of ultramafic rocks in southern India is noted and the approximate amounts of CO2 that can be sequestered in the two greenstone belts of the southern Indian Peninsula, namely Kolar and Chitradurga is estimated. The areal extent of the Kolar belt is about 320 sq. km with an average width of ∼6 km, while that of Chitradurga belt is 6000 sq. km and maximum depth determined is up to 10 km. Estimates show that an ultramafic portion of 1 km3 in the Kolar belt can store ∼2.94 million tonnes (mt) of CO2 and that in the Chitradurga belt ∼4.7 mt, which accounts for about 0.6% of annual CO2 production in India.