Fixation of carbon dioxide by carbonation with chemical precipitation

A method permitting a selected production of calcium carbonate and magnesium carbonate precipitates is developed for the fixation of carbon dioxide by chemical precipitation. Colloidal magnesium hydroxide and calcium carbonate precipitates were produced by the addition of sodium carbonate and sodium hydroxide to sea water, and then about three fourths of the supernatant sea water was removed from the resulting sea water after about 4 h of settling. Subsequently, calcium carbonate precipitates could be exclusively separated from the suspended sea water by 0.45 mum membrane filtration, owing to the injection of sufficient amounts of carbon dioxide that resulted in the re-dissolution of magnesium hydroxides precipitates. Magnesium carbonate precipitates, however, were produced by complete dryness of the filtrate sea water, followed by washing with de-ionized water and drying. Characterization of the precipitates by X-ray diffraction spectrometry was presented, it showed that calcite would be the main constituent of calcium carbonate precipitates and magnesium carbonate precipitates were considered to be the mixed compounds of hydromagnesite and dypingite. The median diameters of calcium carbonate and magnesium carbonate precipitates were 3.85 mum and 6.50 mum, respectively.