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

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.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► 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.