Abstract
Japan is poor in natural resources, so it would be very beneficial if components dissolved in seawater can be used as resources. In our laboratory, reactive crystallization processes with components dissolved in seawater have been investigated by the absorption of CO2 gas that causes the greenhouse effect. In this study, Ca ion was selected as a component of seawater to produce calcium carbonate particles by means of the gas-liquid reactive crystallization. Additionally, a multistage column crystallizer was used, which is a column crystallizer partitioned with perforated plates. From an economical viewpoint, the multistage column crystallizer has been developed to overcome the redundancy of equipment due to the duplication of mixers and hardware in the cascade of MSMPR crystallizers. The aims of this study are to control the particle size of calcium carbonate and to evaluate the characteristics of the multistage column crystallizer. The staging effects of the multistage column crystallizer and the effects of operating parameters on the particle size and the conversion of Ca ion were experimentally investigated using the three-stage column crystallizer.
The following conclusions were obtained:
1. The particle size distribution of calcium carbonate obtained in the multistage column crystallizer becomes sharp compared to that obtained in the standard column crystallizer.
2. By increasing the initial concentration of calcium hydroxide, the particle size decreases and the particles are agglomerated easily.
3. From high-supersaturated solution, large particles can be obtained due to the strong effect of the agglomeration.
