Formation and Stabilization of Vaterite Calcium Carbonate by Using Natural Polysaccharide

摘要

This paper aimed to study the effects of natural polysaccharide (gum arabic, GA) on the formation of vaterite calcium carbonate and its stability in aqueous solution. Gum arabic is a macromolecule that has a high molecular weight and is amphoteric in character. A 0, 2.5, 5 or 10 ml of GA solution (30%) was added to the calcium chloride solution with various initial concentrations to prepare the vaterite calcium carbonate. The calcium carbonate particles were characterized using FTIR, XRD, SEM, TEM and DSC-TG as well as calculation of phase contents. The results of XRD and FTIR analysis were showing that the presence of GA during the precipitation changes the behavior of calcium carbonate to form vaterite until at lower dose used. In addition, the molar content of vaterite increased at the expense of content of calcite with increasing the GA dose. There are slightly improvements in the vaterite content by increasing the initial concentration. The formed vaterite calcium carbonates composed of aggregates as broccoli-like or spherical shape and with particle size 1.6 - 2.5 μm in diameter. TEM images showed that these aggregates composed of the sub spherical unit with diameter 15 - 30 nm. The thermal behavior of prepared vaterite was conformed the mineral composition of these phases. The prepared calcium carbonate, which is formed in the presence of different doses of gum, has a stability in the aqueous solutions at different temperatures, as the analyzes indicated that a very small percentage of the vaterite were converted to calcite. The gum arabic prevented or depressed the transformation of vaterite to calcite through capped the surface of particles, i.e. it is more effective in stabilizing the vaterite phase with increasing in initial concentration and time.