Zeta Potential of Calcium Carbonate Precipitated in the Presence of Sodium Polyacrylates

Sodium polyacrylates (NaPA) series, having weight average molecular weights (M-w) ranging from 2500 to 10 000 g . mol(-1), were used as additives in the precipitation medium of calcium carbonate (CaCO3). Analytical methods such as Scanning Electronic Microscopy, X-ray diffraction and microelectrophoresis were then performed to determine the morphologies, polymorphs, the zeta potentials, and the sizes of the final CaCO3 particles. The X-Ray Diffraction data indicate that the final CaCO3 particles have two coexisting polymorphs: calcite and vaterite. The vaterite fraction (f(v)) is found to vary with the NaPA concentration (C-poly) and Mw. The microelectrophoresis data indicate that the magnitude of CaCO3 particles zeta potential (xi) increases when Cpoly increases from 0.024 to 0.04 g . L-1, leading to wettability transition of the mineral, respectively, from hydrophobic to hydrophilic. Further, at a given value of Cpoly, the zeta potential reaches its maximum value (xi(max)) at an optimum polymer molecular weight of M-w = 5870 g . mol(-1). Such modification CaCO3 particles surface charge by NaPA polymer is related to the calcium surface density and the rate of adsorption of the polymer onto the growing CaCO3 crystal. The mechanism by which the NaPA modifies the CaCO3 surface properties involves the formation of CaPA complexes, i.e., the formation of ions pairs between the calcium ions and carboxylate groups of the anionic PA-backbone, followed by CaPA adsorption from water onto the growing CaCO3 faces. The overall effect of polymer leads to growth inhibition and zeta potential modification of CaCO3 particles.