Laboratory carbonation of artificial silicate gels enhanced by citrate: Implications for engineered pedogenic carbonate formation

Carbon dioxide sequestration through carbonation of calcium or magnesium-rich silicate materials is a geoengineering technology that could mitigate a substantial proportion of anthropogenic emissions. Contemporary mineral carbonation research considers optimising this process to overcome energy requirements for mineral pre-treatment and reactor operation. This paper compliments previous studies in this area by demonstrating enhanced weathering through the action of organic acids including those exuded by plant roots. Batch weathering experiments, conducted as part of this study, with hydrated cement gels have shown that up to 80–85% of calcium is leached from the material in 5 h when exposed to solutions containing citrate anions, at an approximate log weathering rate between −8.26 and −6.86 molCa cm−2 s−1, which is much more rapid than observed carbonate precipitation rates in previous studies for urban soils that contain cement-derived minerals. Thus Ca availability is not rate limiting. Coupled silicate-dissolution/carbonate precipitation reactions provide a carbon sequestration function that can be designed into soils specifically engineered to facilitate carbon capture.

► Cement minerals lose 80–85% of Ca when exposed to citrate in 5 h weathering experiments.
► Weathering rates in urban soils (−8.26 to −6.86 log molCa cm−2 s−1) exceed precipitation.
► Silicate-dissolution/carbonate precipitation reactions sequester atmospheric CO2.
► Designed addition of Ca silicates to soils facilitates carbon capture.