Natural Carbonation of Alkaline Industrial Wastes: A Large-Scale, Unaccounted Sink for CO2

Abstract Achieving international climate goals will likely require large-scale removal of carbon dioxide from the atmosphere 1. A promising means of carbon dioxide removal (CDR) is by enhanced weathering and carbonation of various alkaline industrial wastes such as slags and ash 2,3. Although global potential of such enhanced weathering of alkaline industrial wastes has been estimated 4–7, the magnitude of carbon uptake by natural carbonation of these wastes worldwide remains uncertain. Here, using the results of more than a decade of carbonation experiments and an extensive dataset of global industrial activity and waste disposal, we show that annual global carbon uptake by natural carbonation of alkaline industrial wastes is 0.43 Gt CO2 (95% CI: 0.33–0.53 Gt CO2) in 2020, and has been increasing at an annual average rate of 2% per year for the past decade. Between 1930 and 2020, we estimate that alkaline industrial wastes have absorbed 14.0 Gt of CO2 (95% CI: 11.2–25.2 Gt CO2) by natural carbonation. Our results reveal the extent to which alkaline industrial wastes represent an unaccounted sink in the global carbon cycle, and also highlight opportunities for enhancing carbon uptake in the future.