The calcium carbonate (CaCO3) crystals were successfully synthesized in the presence of glutamic acid used as an additive at 30 °C and at a pH of 8.5. The synthesized product was characterized in detailed by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectrometry and scanning electron microscopy (SEM) to identify the structure and habit of the crystals. Moreover, the size and surface charge of the crystals were measured by particle size and zeta potential analyzer. XRD and FTIR results showed that both calcite and vaterite in forms of apparently CaCO3 crystals were obtained in the presence of 50 ppm additive concentration at t=30 min. When increasing the glutamic acid concentration in the suspension, the formed CaCO3 were only in the vaterite form. The SEM analysis results pointed out that the addition of the glutamic acid significantly changed the shape of the CaCO3. At t=30 min the resulting product sample was found to contain two types of polymorphs; larger cubic shaped calcite crystals and smaller spherical-like vaterite crystals. Further addition of high concentrations of the additive enhanced the adsorption of the glutamic acid, resulting in the smaller spherical-like ellipsoidal vaterite crystals. Investigation of the zeta potential analysis indicated that higher additive concentration (100 ppm) resulted in a positive surface charge 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 resistance value (5.01 × 1011 m/kg) than that in pure media, which was 1.03 × 1012 m/kg.
Calcium carbonate, polymorphism, crystal morphology, additive