SIZE-DEPENDENT GROWTH AND CONTACT NUCLEATION OF CALCITE CRYSTALS

The growth kinetics and contact nucleation of calcite crystals were studied in a pH-stat crystallizer. Large seed crystals up to 230 mum were successfully prepared by the gel growth technique. The crystal growth data over a wide range of crystal sizes were evaluated from titration curves by an initial slope method and then analyzed by the two-step model. The mass-transfer and surface integration rates were found to be functions of crystal size with the exception of mass-transfer rates of small crystals less than 10 mum. The controlling step of crystal growth process was tested using the effectiveness factor concept. Large seed crystals of calcite induced contact nucleation when a stainless-steel impeller was used for agitation. The important features of contact nucleation for calcite crystals were explored and compared with those of soluble substances.