Calcium Carbonate Crystallization Controlled By Biological Polysaccharides

More than 60 kinds of minerals have been observed in organisms, most of which are calcium minerals. For example, the exoskeleton for invertebrates is mainly composed of calcium carbonate (CaCO3), and the skeleton and teeth are mainly composed of calcium phosphate (Ca3(PO4)2). There are small amount of organic compounds in the biominerals. The organic compounds, on the one hand, influence the morphologies, spatial arrangement, crystal orientation and polymorphs, on the other hand, endow the biominerals some properties that superior to ordinary minerals. The CaCO3 exits widely in nature and is extensively applied in industry, therefore, many investigations focus on the crystallization of CaCO3 under the influence of varied additives.With the increase in environmental protection consciousness, the environment-friendly materials are paid more attention. Biological polysaccharides have been gotten more and more concern for their excellent properties, such as biocompatibility and non-toxicity. However, the extensive application of chitosan in the field of Pharmaceuticals, food, cosmetic, textile, environmental protection, agriculture, et al. is limited for its water-insolubility. In the present dissertation, several kinds of water-soluble chitosan derivates, such as O-carboxymethyl chitosan (CMCS), (2-hydroxypropyl-3-butoxy) propyl-succinyl-chitosan (HBP-SCCHS), O-(hydroxy isopropyl) chitosan (HPCHS) and xanthan gum (XC) were used to modulate the crystallization of CaCO3. The CaCO3 particles with various morphologies and polymorphs were crystallized. The results obtained will not only provide good insight into the CaCO3 crystallization in the presence of biological polysaccharides, but also offer theoretical guidance in the selection of scale inhibitors. The present dissertation includes five topics.TopicⅠ. Progress on the crystallization of CaCO3 controlled by organic compoundsThe crystallization of CaCO3 controlled by organic compounds is progressed, and the significance and the purpose of the dissertation are elucidated. TopicⅡ. The influence of CMCS on the crystallization of CaCO3CaCO3 particles are crystallized in the aqueous solution of CMCS by an open-wided vapor diffusion method. The influences of CMCS and Ca2+ concentrations, aging time, temperature and [Mg2+]/[Ca2+] ratios on the crystallization of CaCO3 are investigated. The CaCO3 particles are characterized by scanning electron microscopy (SEM), energy dispersion spectroscopy (EDS), power X-ray diffraction (XRD) patterns, Fourier transform infrared (FTIR) spectroscopic, thermogravimetric analysis (TGA) and N2 adsorption-desorption methods. The morphologies, polymorphs, content of CMCS and specific surface area are obtained. The results indicate that the CMCS/Ca2+ complexes play a key role in the heterogeneous nucleation, growth and aggregation of CaCO3. The CMCS/Ca2+ complexes are formed under the electrostatic interaction between CMCS and Ca2+ ions. During the heterogeneous nucleation of CaCO3, the Ca2+ ions in CMCS/Ca2+ complexes not only provide nucleation sites, but also take part in the nucleation as a reactant. The growth of CaCO3 nanoparticles is inhibited for the adsorption of CMCS molecules on their surfaces. During the growth of CaCO3 nanoparticles, some of the CMCS molecules are imbedded in, which result in the distortion of CaCO3 lattice. The CaCO3 nanoparticles aggregate due to the bridging effect of CMCS molecules.Both larger concentration of CMCS and lower temperature favor the growth of CaCO3 nanoparticles, however, inhibit their aggregation. Smaller concentration of Ca2+ favors both the growth and the aggregation of CaCO3 nanoparticles. Higher temperature (60℃) favors the formation of calcite and aragonite. In CMCS solutions, the addition of Mg2+ ions inhibit the heterogeneous nucleation of calcite through the adsorption on its surfaces, and the inhibition efficiency increases with the increase of Mg2+ content.TopicⅢ. The influence of HBP-SCCHS on the crystallization of CaCO3CaCO3 particles are crystallized in the aqueous solution of HBP-SCCHS by a slow vapor diffusion method. The influences of HBP-SCCHS and Ca2+ concentrations, temperature, [Mg2+]/[Ca2+] ratios, initial pH and aging time, on the crystallization of CaCO3 are investigated. The CaCO3 particles are characterized by SEM, XRD, FTIR, TGA and N2 adsorption-desorption methods. The morphologies, polymorphs, content of HBP-SCCHS and specific surface area are obtained. The results indicate that in acidic solution (pH=4), the HBP-SCCHS/Ca2+ chelates play a key role in the heterogeneous nucleation, growth and aggregation of CaCO3. The HBP-SCCHS/Ca2+ chelates are formed under the chelation between HBP-SCCHS and Ca2+ ions. During the heterogeneous nucleation of amorphous calcium carbonate (ACC), the Ca2+ ions in HBP-SCCHS/Ca2+ chelates not only provide nucleation sites, but also take part in the nucleation as a reactant. The ACC is thermodynamic unstable and transforms into vaterite instantaneous for its tiny volume and high surface energy. In HBP-SCCHS solution with smaller concentration (such as 0.1 g·L-1), vaterite transforms into rhombohedral calcite. The HBP-SCCHS molecules inhibit the growth of calcite through adsorbing on their sides. When the concentration of HBP-SCCHS (2.0 g·L-1) is larger than its critical aggregation concentration (0.6 g·L-1), the core-shell shaped micelles form and the micelles modulate the formation of lens-like vaterite aggregates. The HBP-SCCHS molecules that do not take part in the formation of micelles modulate the formation of rod- and dumbbell-like vaterite aggregates. During the growth of CaCO3 nanoparticles, some of the HBP-SCCHS molecules are imbedded in, which result in the distortion of CaCO3 lattice.With the increase of aging time from 1 d to 4 d, both the particle size distribution of the lens-like aggregates and the average particle size of nanoparticles increase. When the aging time is 30 d, the lens-and dumbbell-like aggregates transform into rhombohedral crystals with surfaces that composed of nanoparticles. With the increase of Ca2- concentration, the particle size distribution of the lens-like aggregates and the average particle size of nanoparticles decreases. The content of vaterite in mixtures of vaterite and calcite also decrease. Higher temperature favors both the formation of rod- and dumbbell-like aggregates and the growth of calcite. The initial pH influences the nucleation and growth of CaCO3 notably, and the rhombohedral calcite is obtained from basic solutions. TopicⅣ. The influence of HPCHS on the crystallization of CaCO3CaCO3 particles are crystallized in the aqueous solution of HPCHS by dropping the Na2CO3 solution directly into HPCHS/Ca2+ mixed solution. The influences of HPCHS, Ca2+ and CO32- concentrations, [Ca2+]/[CO32-] and [Mg2+]/[Ca2+] ratios on the crystallization of CaCO3 are investigated. The CaCO3 particles are characterized by SEM, XRD, FTIR and TGA methods. The morphologies, polymorphs and content of HPCHS are obtained. The results indicate that regardless of the conditions, the HPCHS system is uniformly an adsorption controlled process. At fixed concentrations of Ca2+(and CO32-) ions, both the average particle size and the nucleation degree decrease with the increase of HPCHS concentration, however, the content of HPCHS adsorbed on or included in CaCO3 crystals increases. The concentrations of Ca2+(and CO32-) ions have small influence on the morphologies of CaCO3 at fixed HPCHS concentration. The initial pH of the reactant solutions and the ratios of [Ca2+]/[CO32-] affect the morphologies but not the polymorphs of CaCO3. The addition of Mg2+ influences not only the morphologies but also the polymorphs of CaCO3. The Mg2+ inhibits the heterogeneous nucleation of calcite through the adsorption on their surface at smaller ratios of [Mg2+]/[Ca2+] (such as 1/4 or 1/1), however, at larger ratio of [Mg2+]/[Ca2+] (such as 4/1), Mg2- incorporates into lattice of calcite and result in the formation football-or flower-shaped aragonite.TopicⅤ. The influence of XC on the crystallization of CaCO3CaCO3 particles with stacked rhombohedral morphologies and rough surfaces are crystallized by dropping the Na2CO3 solution directly into XC/Ca2+ mixed solution. The influences of XC, Ca2+ and CO32- concentrations, [Ca2+]/[CO32-] and [Mg2+]/[Ca2+] ratios on the crystallization of CaCO3 are investigated. The CaCO3 particles were characterized by SEM, XRD, FTIR and TGA methods. The morphologies, polymorphs and content of CMCS are obtained. The results indicate that the XC/Ca2+ complexes play a key role in the heterogeneous nucleation and growth of CaCO3. The CMCS/Ca2+ complexes are formed under the electrostatic interaction between XC and Ca2+ ions. During the heterogeneous nucleation of ACC, the Ca2+ ions in XC/Ca2+ complexes not only provide nucleation sites, but also take part in the nucleation as a reactant. The ACC transforms into thermodynamic stable calcite subsequently, and the calcite nanoparticles suspend in solution. With the aging time prolonging, the rhombohedral calcite precipitated when its volume became large enough. According to the simple crystal model, more XC molecules adsorb on the stepped (S) and kinked (K) surfaces than on the flat (F) surface, with the result that the growth rates of the S and K faces are smaller than that of the F face. During the growth of CaCO3, some of the XC molecules were imbedded in, which result in the distortion of CaCO3 lattice. The CaCO3 nanoparticles stack for the bridging effect of CMCS molecules.Smaller CaCO3 crystals with greater stacked degree were obtained in larger concentrations of Ca2+ and CO32-, while the concentration of XC was fixed, and the content of XC in CaCO3 decreases. The larger difference between [Ca2+] and [CO32-] promotes the growth of CaCO3. The larger the ratio of [Ca2+]/[CO32-] or the initial pH, the greater stacked degree of CaCO3. The addition of Mg2+ influences not only the morphologies but also the polymorphs of CaCO3. The Mg2+ inhibits the heterogeneous nucleation of calcite through the adsorption on their surface at smaller ratios of [Mg2+]/[Ca2+] (such as 1/4 or 1/1); however, incorporates into lattice of calcite and results in the formation bundle-shaped aragonite at larger ratios of [Mg2+]/[Ca2+] (such as 4/1).