Polymorphic Phase Change of Calcium Carbonate with Glutamic Acid as an Additive

Abstract

The calcium carbonate (CaCO3) crystals were successfully synthesized in the presence ofglutamic acid used as an additive at 30 °C and at a pH of 8.5. The synthesized product was characterized indetail by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and scanning electronmicroscopy (SEM) to identify the structure and habit of the crystals. Moreover, the size and surface chargeof the crystals were measured by particle size and zeta potential analyzer. XRD and FTIR results showed thatboth calcite and vaterite in forms of apparently CaCO3 crystals were obtained in the presence of 50 ppmadditive concentration at t=30 min. When increasing the glutamic acid concentration in the suspension, theformed CaCO3 were only in the vaterite form. The SEM analysis results pointed out that the addition of theglutamic acid significantly changed the shape of the CaCO3. At t=30 min the resulting product sample wasfound to contain two types of polymorphs; larger cubic shaped calcite crystals and smaller spherical-likevaterite crystals. Further addition of high concentrations of the additive enhanced the adsorption of theglutamic acid, resulting in the smaller spherical-like ellipsoidal vaterite crystals. Investigation of the zetapotential analysis indicated that higher additive concentration (100 ppm) resulted in a positive surfacecharge of the crystals, whereas lower concentration (50 ppm) gave negative electrical charge. Moreover,filtration analysis pointed out that adding glutamic acid additive resulted in a less specific cake resistancevalue (5.01 × 1011 m/kg) than that in pure media, which was 1.03 × 1012 m/kg.