Effects of amine, amine salt and amide on the behaviour of carbon dioxide absorption into calcium hydroxide suspension to precipitate calcium carbonate

Abstract The amount of carbon dioxide (CO 2 ) absorption and calcium ion (Ca 2+ ) concentration besides the pH of aqueous solution were observed during the CO 2 absorption to precipitate calcium carbonate (CaCO 3 ) from calcium hydroxide (Ca(OH) 2 ). A reaction rate-limiting effect of an amount of CO 2 absorption without any organic additives in the early stage of the precipitation was observed, which was attributed to an interruption effect of bicarbonate ion (HCO − 3 ) on the precipitation of CaCO 3 . The improvement for the reaction rate was achieved not only by amine additives but also by neutral additives such as e-caprolactam or amine salt. When the hexamethylene diamine was dissolved in the solution, successive change of crystal forms of CaCO 3 aragonite to calcite in aqueous suspensions, confirmed by Ca 2+ concentration change and X-ray diffraction, was concluded that a local environment around the amine group in aqueous solution and an interaction of the diamine with precipitated CaCO 3 particles were important factors for these reactions.