A preliminary study of calcite saturation states with varying pH and salinity

Abstract The present work explores accelerated weathering of limestone (AWL) as an option to combat the climate change problem posed by the still growing carbon footprint. AWL is a promising low-technology solution that sequesters CO₂ through the dissolution of calcium carbonate (CaCO₃) in water to form calcium bicarbonate. One aspect of the feasibility of its application is whether the newly formed bicarbonate will remain in solution for the long term. This paper examines the carbonate equilibria for various water bodies by combining Bjerrum plots with the calcite saturation value, omega. The hydrochemistry software, aqion, was used to simulate a range of water compositions with different salinities at various conditions. The study compares saturation states of rainwater, limestone quarry water, seawater, and reverse osmosis concentrate, with their respective dissolved inorganic carbon (DIC) concentrations, across the full range of pH values. The areas of stability and instability can be observed from the generated plots in order to be able to design effective AWL processes. A key issue for successful implementation of AWL is operating within the CaCO₃ saturation limit and ensuring dissolved material does not subsequently reprecipitate.