抄録
A micro bubble technique which can uniformly supply a source of objective ions into liquid phase has been applied for reactive crystallization of calcium carbonate (CaCO3), and effects of feed condition of CO2/NH3 micro bubbles on reactive crystallization of CaCO3 were investigated. CO2 was utilized as the gas feed source of carbonate ion. NH3 was supplied for the adjustment of solution pH, and N2 was used for the controlling of feed molar fraction. CaCO3 was produced by semi-batch type reaction in which CO2/NH3 micro bubbles are continuously supplied into Ca(NO3)2 aqueous solution. The solution temperature was kept constant at 298K. CO2/NH3 molar ratio and CO2 feed rate were varied as operating parameters. After CO2 feeding was employed at a specified time, the precipitated particles were filtrated, and dried at 343K for 60 minutes under reduced pressure. To clarify the progress of reactive crystallization, various physicochemical measurements were carried out with regard to solution properties (pH, electric conductivity) and solid product characteristics (total weight, shape observation by scanning electron microscope, size distribution, and identification by X-ray diffraction). Consequently, the following results were obtained by varying CO2/NH3 molar ratio and CO2 feed rate: 1) the selectivity of vaterite was high when solution pH was adjusted from 6.8 to 9.0, 2) the production of aragonite was observed in the higher pH range of 9.0 - 10.0, 3) induction period for nucleation was decreased with an increase in solution pH owing to the increasing of CO32- concentration, 4) a smaller size of spherical vaterite crystal (2.4 µm) was obtained, which seems to be the interaction effect owing to the minimization of bubbles.
