Aragonite–calcite–vaterite: A temperature influenced sequential polymorphic transformation of CaCO3 in the presence of DTPA

Highlights: ► Crystallization of CaCO3 between 60 and 230 °C in the presence of DTPA. ► Formation of exclusive and individual polymorphs at different temperatures. ► Violation of second law of thermodynamics/Ostwald rule of stages has been observed. - Abstract: Calcium carbonate was precipitated from calcium chloride using sodium carbonate in the presence of diethylenetriaminepentaacetic acid (DTPA) between 60 and 230 °C. The samples were characterized by FTIR, Raman, XRD and SEM techniques. CaCO3 with different crystal morphologies such as spherolite/datura pod, dumbbell, peanut, were obtained depending on the experimental conditions. The results showed that pure aragonite, calcite and vaterite were formed at low, moderate and high temperatures respectively. A binary mixture of calcite and vaterite was resulted between 150 and 200 °C. The data suggested an unusual conversion of stable calcite to meta stable vaterite at higher temperature in presence of DTPA. The study revealed a novel methodology for the exclusive/individual preparation of different crystalline polymorphs of CaCO3. Formation of pure vaterite above 200 °C divulged the possibility of DTPA as a potential scale inhibitor and boiler sludge conditioner at elevated temperatures