Polymorphism in CaCO3 — Effect of temperature under the influence of EDTA (di sodium salt)

Abstract

Crystallization behavior and polymorphism of CaCO3 were studied at different temperatures (from 60 to 240°C) under the influence of ethylenediaminetetraacetic acid (EDTA). The samples were characterized using powder X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), Scanning electron microscope (SEM) and field emission scanning electron microscopy (FESEM). In the absence of EDTA, a calcite–aragonite binary mixture was resulted between 60 and 170°C above which calcite alone was formed. The presence of EDTA significantly influenced the crystallization behavior and composition of different polymorphs of CaCO3 varied with temperature. Formation of a binary calcite–aragonite mixture at 60°C, ternary calcite–vaterite–aragonite mixture at 100°C, a binary aragonite–vaterite mixture at 130°C, a binary calcite–aragonite mixture at 170°C, purely aragonite at 200°C and vaterite with very little aragonite at 230°C confirmed that temperature affects the crystallization process in the presence of EDTA. Rhomboidal calcite, needle/rod like aragonite and flower like vaterite were obtained under different conditions. At 230°C, a unique flower like morphology was observed for vaterite. The efficacy of EDTA on CaCO3 scale inhibition between 60 and 230°C is discussed.