Study On Synthesis, Characterization Of Different Types Of Hydroxyapatite And Their Adsorption Of Heavy Metal Ions

Hydroxyapatite (HAP) is a kind of very good biocompatibility of biological materials,Carbonated hydroxyapatite is a kind of structural carbonate-containing hydroxyapatite. Because of the entry of the CO₃^2-, the structure of hydroxyapatite obvious distortion , and the crystallinity decreased, particle is small and dispersion well. Carbonated hydroxyapatite have large surface area and effective surface activity, so it is advantage to heavy metals adsorption. So carbonated hydroxyapatite is a new type of environment functional materials.In this study, the ordinary hydroxyapatite and carbonated hydroxyapatite were synthesized by the method of sol-gel,and flower -like and spherical surface of carbonated hydroxyapatite was synthesized by the method of the carbon dioxide bubble-template. X-ray diffraction(XRD), transmission electron microscopy(TEM), Scan electron microscopy, Fourier transform infrared spectroscopy (FT-IR), Surface area measurement(BET) were employed to characterize the different types of prepared hydroxyapatite. The results showed that the surface area of hydroxyapatite synthesized by the method of sol-gel was 61.77m/g, and particle size was 30.12nm . So the hydroxyapatite particles was nano-scale. By adding (NH₄)₂CO₃ as the main source of carbonate, we changed the addition amount of (NH₄)₂CO₃ to get five synthetic hydroxyapatite by the method of Sol-gel. And infrared spectrum showed, in addition to the samples that the group of the least amount of adding (NH₄)₂CO₃, the remaining four had a structural carbonate peak, indicating that thase four were the carbonate hydroxyapatite. The samples were good dispersion. Their specific surface area were greater than 50m²/g, and the pore volume greater than 0.13 cm³/g. Their pore size between 10nm and 20nm, which are belong to medium-size hole. So the obtained samples having hole and large surface area , which was conducive to the adsorption of pollutants. To the Carbonated hydroxyapatite synthesized by the method of the carbon dioxide bubble-template, their SEM showed the surface of it had a flower-shaped samples of branched lamellae structures and irregular spherical. The sample was with a small amount of OCP phase, while the longer reaction time , OCP phase less, the higher the purity. BET showed samples surface area were measured at 20～30 m²/g, which were smaller than other samples and their particle size were micron.Removal toxic heavy metal ions from wastewater pollution is a hot area. Heavy metal pollution could cause water degradation. A large number of metals such as chromium, mercury, lead, copper, cadmium, zinc, nickel, etc, were well known significant toxic substances. Hydroxyapatite as effective adsorbent with high stability had been reported fixed. In this article, we used different types of synthetic hydroxyapatite, sheet-like carbonate hydroxyapatite and flower-like carbonate hydroxyapatite as adsorbent, and hydroxyapatite adsorbed Cu²⁺ and Ni²⁺, and carbonate hydroxyapatite adsorbed Cu²⁺ and Zn²⁺, to research the affect of different times, different metal ion concentration, pH and temperature on the adsorption of metal ions, and to explore the adsorption mechanism. The results showed that: The process of hydroxyapatite and carbonate hydroxyapatite adsorption of three metal ions followed pseudo-second-order kinetic equation, and the adsorption equilibrium could be achieved in 60 min. Little effect of temperature on the adsorption efficiency. As the pH value increased the adsorption capacity increasing too. At low pH, metal ion removal was generally thanks to the adsorption of hydroxyapatite,to its high pH, metal ion removed by chemical precipitation and hydroxyapatite adsorption results of synergy. Adsorption isotherm types were belong to the Langmuir-type adsorption isotherm. The capacity of hydroxyapatite to adsorpt Cu²⁺ and Ni²⁺ was Cu²⁺> Ni²⁺; carbonate hydroxyapatite's adsorption capacity on Cu²⁺ nd Zn²⁺ was Cu²⁺> Zn²⁺; Hydroxyapatite's adsorption capacity of Cu²⁺ was better than carbonate hydroxyapatite, which was due to large surface area of hydroxyapatite, indicating that the surface area was one of the factors affecting the adsorption.