| Nano-hydroxyapatite both is an important inorganic material which is a component of human and animals,bones and teeth, and is an important environmental functional material which is used to control water and soil pollution. Because of its unique crystal structure and large surfase area, small size and high solubility, nano-hydroxyapatite has been become the research hotspot with its potential value of wide attention by the international academic.This study will use a synthetic, large surface area and high puritynano-hydroxyapatite as the experimen tal sample. Nano-hydroxyapatite powders are prepaerd by the sol-gel method with nitrate calcium and phosphorus acid as precursors. And its synthetic conditions are discussed. The results show that the aging time, the calcination temperature and the calcination time of the system all impact the particle size and the crystallinity degree,and we get the optimal condition by comparing. X-ray diffraction(XRD), Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy(TEM), surface area measurement(BET), thermogravimetric and differential thermal analysis and Zeta potential measurement are employed to characterize the powders. The results obtained indicate that with the rising of the calcination temperature the particle size of hydroxyapatite becomes bigger but the surface area getssmaller and the degree of crystallinity becomes better. The charge of the hydroxyapatite surface is always negative, which is conducive to the adsorption for heavy metal ions.Relative to the body phase chemical reaction of hydroxyapatite,people is still lack of understanding the surface chemical reaction of hydroxyapatite. We use automatic potentiometric titration to determine the acid-base equilibrium constant by titrating the preparated powders. The influence of the amount of hydroxyapatite, the concentrations of sodium nitrate and the concentrations of the acid and base are considered. The results show that the hydroxyapatite has a buffer whether in acidic condition or in alkaline condition. The more the amount of hydroxyapatite we used, the stengther buffering capacity the hydroxyapatite has. However, the concentration of the acid-base using in the titration has little impact for the results. The surface complexation constant were calculated by computer program FITEQL.In the modern socity, with the development of industry, the heavy metals in the wastewater are increasing and the issue of water pollution has become a serious environmental problem. The hydroxyapatite is getting more concern because of its unique chemical properties. Synthetic nanohydroxyapatite was used to remove metal ions from solution, respectively. The influence of various parameters on the adsorption, including adsorption time, pH value of the suspensions, initial concentration of metal ions and the temperature is investigated and the adsorption mechanism is discussed. The results show that, the adsorption of metal ions at the surface of nanohydroxyapatite is in agreement with pseudo-second-order kinetic equation, the equilibrium can be achieved in 60min; the adsorbed amount of metal ions increases as the pH value and the initial concentration of metal ions increases. The Langmuir adsorption isotherms can be applied to the experimental results. The adsorption capacity is in the order of Cd2+ > Zn2+ . Computer software MEDUSA is used to simulate speciation in aqueous and then WINSGW is used to obtain the coordination constants between nano-hydroxyapatite and metal ions . |
