Study On The Precipitation Process Of Calcium Carbonate Compended By Polyaspartic Acid And Magnesium Ion

Special morphology and particle size are the principal elements that influence industrial properties of calcium carbonate material. Biomimetic synthesis is an effective way to prepare novel materials of calcium carbonate. Vaterite was formed effectively via regulating by Polyaspartic acid（PASP）, and magnesium is the classic revulsant of aragonite. PASP and magnesium ions are harmless and environmental friendly regulating agent. In this paper, the biomimetic mineralization process of calcium carbonate was studied by useing PASP and Mg²⁺ as composite system. The optimum conditions of PASP and Mg²⁺system were determined. The structure and characterization of particles were analyzed by using FT-IR, XRD and SEM. The influence of reaction conditions on polymorphs, morphology and size of calcium carbonate were researched. The synthetic methods of the small size calcite sphere and aragonite sphere calcium carbonate were obtained. The formation and growth mechanisms of the crystal were analyzed based on the principles of biominerallization.（1） The vaterite content of calcium carbonate reached 90.52% when concentration of PASP was 2.5 mg/m L. In the system which concentration of PASP was 2.5 mg/m L,since the mole concentration ratio of calcium and magnesium ions(Mg²⁺/Ca²⁺) enlarged from 0.01 to 0.09, calcite content increased from 4.38% to 45.41%. As Mg²⁺ /Ca²⁺enlarged from 0.1 to 2.2, calcite crystallinity decreased, and the morphology transformed from cubic rhombohedron with edges and corners adsorbed by tiny particles to sphere,diameter from 6.5 microns reduced to 1 micron. Elevating temperature was beneficial to the formation of calcite, morphology transformed from the round-likely roundness to sphere. Reaction time extended from 10 min to 40 min,morphology of calcium carbonate transformed from cubic rhombohedron with steps to regular sphere.（2） When Mg²⁺ /Ca²⁺ reached 2, crystal content reached 91.20%, needle-like aragonite morphology was gained. In system which Mg²⁺/Ca²⁺=2, crystal content reduced to 96.74% from 26.67%, morphology from the needle to ellipsoid（radiate）,particle size decreased to 1 micron as PASP concentration increased from 0.01 to0.20mol/L. Ca²⁺ concentration increased in the range from 0.01 to 0.15mol/L, crystal content reduced, the gathering of needle-like morphology get weak. As the increasing of reaction temperature, crystal content increased to 90.12%, class ellipsoid by needle reunion transformed to sphere morphology.（3） Controllable synthesis of spherical calcite calcium carbonate with 1 micron on the condition that 75 ℃, Mg²⁺ /Ca²⁺=2, 40 min. And controllable synthesis of spherical aragonite calcium carbonate with 1 micron which surface was arranged in order by about 50 nm fine acicular on the condition that 75 ℃, 2.5 mg/m L PASP, concentration of Ca²⁺was 0.02mol/L.（4） The Ca²⁺was placed by Mg²⁺ which could enter into the surface of calcite crystal lattice in the process of growth of calcite, leading to lattice distortion.The-COOgroups of PASP adsorbed on specific surface of calcite at the same time, eventually forming spherical calcium carbonate. PASP adsorbed on specific surface of aragonite as aragonite grows by splitting. PASP inhibit the growth of needle grain by splitting, thus controlling the precipitation of calcium carbonate particle to be smaller and the sphere（radiate）.