Preparation of Calcium Carbonate by Three-Stage Bubbling Carbonation in CaCl2-NH4Cl-NH3-H2O SYSTEM

To prepare calcium carbonate with reduced particle size and single vaterite phase based on the mineral carbonation technology of steel slag, preparation of calcium carbonate in system was studied by using two and three-stage bubbling carbonation under different reaction pH values and stirring conditions in the presence of ultrasound in this paper. The results show that the calcium carbonate has already gathered and the particles are small and clearly defined when the first aging pH value is 9.0. With the decrease of pH value, the particle size of calcium carbonate increases significantly with more than one peak in the particle size distribution curve, the particle surface tends to be smooth, and the calcite content increases gradually. However, the two-stage bubbling carbonation process can reduce the particle size significantly and is applicable to the system. Different stirring conditions have no significant influence on calcium content, pH value, or phase, which is mainly composed of vaterite and calcite in twostage carbonation, while the stirring in the aging stage will increase the particle size of calcium carbonate. Base on the results of the two-stage carbonization reaction, the three-stage bubbling carbonation is proposed and the calcium carbonate prepared is all single vaterite type, and its size and the agglomeration between the particles are also significantly reduced, and the stirring also has no significant influence. The formation mechanism of two and three stage bubbling carbonation reaction was also discussed.