EFFECTS OF POLYMERIC ADDITIVES ON THE MORPHOLOGY AND THE STRUCTURE OF CALCIUM CARBONATE MATERIAL

摘要

In this work, we investigate the crystallization of calcium carbonate (CaCO_3) from supersaturated solutions and in the presence of polymeric additives such as an anionic polyelectrolyte (polystyrene sulfonate) and a non-ionic copolymer (polystyrene-polyethylene oxide). Depending on the nature and concentration of the additive used, we obtain various calcium carbonate particles having different sizes, crystalline structures, and morphologies. Thus, in the presence of the non-ionic copolymer alone, the mineral crystallization gives birth to CaCO_3 agglomerates of primary particles. The size of the primary particles, which present mostly rhombohedral morphologies, is about 4 μm and the aggregate size is the range 10-20 μm. On the other hand, in the presence of the anionic polyelectrolyte alone, we obtain CaCO_3 crystals having smooth spherical shape and size about 2 μm. However, in the presence of copolymer-polyelectrolyte mixture, the calcium carbonate crystallization gives birth to modified CaCO3 crystals morphologies. Such morphologies are function of the ratio I,I = C_(copolymer)/C_(polyelectrolyte). The C_(copolymer) and C_(copolymer), are respectively, the copolymer and the polyelectrolyte concentrations used. Hence, at value of 1=2.9, the calcium carbonate crystallization gives rough CaCO_3 spherical having size about 2 μm, while at values of 1=3.1 and 1=18.6, we observe elongated CaCO3 particles having size (maximum crystal length) in the range 3.4-4.3 μm. The CaCO_3 crystal structures obtained by the X-ray analyses were pure calcite when the additive is the non-ionic copolymer and pure vaterite in the presence of the anionic polyelectrolyte. The data obtained indicate that the pure polyelectrolyte alone inhibits the crystal growth in all direction and lead to homogenous CaCO_3 spherical particles. However in the presence of the copolymer-polyelectrolyte mixture, the crystal growth seems to be inhibited in preferential directions. This study shows that the morphology and structure of the CaCO_3 crystals can be controlled by the use of either pure or mixture polymer additives. Finally, the effects of the polyelectrolyte and non-ionic copolymer on the precipitation of the CaCO_3 are explained in term of two main mechanisms involving ion exchange and/or ion complexation and preferential adsorption.