Carbon sequestration by enhanced weathering of basalt and its applicability

Abstract

Several physical and chemical geoengineering pathways have been proposed to tackle the Anthropocene rise in atmospheric CO₂ and hence, global warming. Among these, enhanced weathering of mafic and ultramafic rocks has been proposed as a carbon sequestration method to mitigate climate change. This mechanism is motivated by carbonic acid-mediated weathering of silicate minerals, which serves as the natural sink for CO₂ over million-year timescales. This work is an attempt to study the efficiency of enhanced weathering of basalt, particularly subalkaline tholeiitic basalt, as it is the major rock type of the Deccan Trap, one of the most voluminous large igneous provinces. Towards this, a lab-controlled experiment involving the interaction of basalt powder (grain size: < 150 μm) with deionized water (pH ≈ 5.8 ± 0.2) for different time intervals (1 hour, 6 hours, 12 hours, 24 hours, and 48 hours) was carried out to accurately quantify the carbon sequestration potential of powdered basalt without any background interferences. Notably, a progressive increment of total alkalinity, silica, and major cations (Na⁺, Ca²⁺, Mg²⁺) in the reacting medium was observed with time. Results from the experiment suggest that 1 g of basalt powder has the potential to sequester 0.280 ± 0.085 mg of CO₂ within 24 hours, and the relative mobility of elements is Na⁺ > Ca²⁺ > Mg²⁺ during this short-term (hourly-scale) weathering interaction. It demonstrates that basalt dust significantly increases the weathering rate of silicate minerals and hence may facilitate sequestration of atmospheric CO₂ by increasing the alkalinity of water, which is stable for approximately one million years in the hydrological cycle.