The Formation Of Several Common Soil Ca-Ps On The Mineral Surface And In The Bulk Solution And The Influencing Factors

P is one of the necessary nutrition elements for plant growing. In our northern calcareous soils, inorganic phosphorus most exists in the form of Ca-P and its content is over80%in average. The different of the availability between different forms of inorganic phosphorus is vary greatly. Cag-P is the second effective phosphorus source to the crops.Ca10-P is not easy to be absorbed in a short period of time, so it’s existence as the crop potential phosphorus source. Therefore, study at the formation and conversion mechanism of typical calcium phosphate in soil to improve the phosphorus validity has important significance.The experiment studied phosphorus adsorption character on CaCO3and the effect of initial phosphorus concentration, ageing temperature after adsorption and ageing time. And then, study the influence factors of synthesis calcium phosphate in the laboratory to determine the most appropriate conditions to synthesis octacalcium phosphate. We applied X-ray diffraction (XRD), Microscope scanning methods (SEM) analysis to characterize the phase components, morphology of the samples. The main results are shown as follows:1. To use homogeneous precipitation method synthesis octacalcium phosphate with the urea as pH modulators. CaHPO4·2H2O,calcium phosphate and octacalcium phosphate are generated in the system. Increasing the reaction temperature and the concentration of urea, the purity of OCP increases and the OCP fiber become more uniform. When the urea concentraton is0.7mol/L and0.8mol/L, the synthetic products containing CaHPO4·2H2O under the condition of75℃. The octacalcium phosphate product can be more pure at80℃,85℃,90℃.2. When pH is6.5, maximum adsorption capacity is to be58.4795mg/g(calculation in accordance with P), however, when pH changing to be8.5, maximum adsorption capacity is to be6.1237mg/g. therefore phosphorus adsorption on CaCO3decreases with pH increases. When the pH is low, the solubility of CaCO3increases and form a surface precipitate with PO4 3. The diffraction peak hydroxyapatite appear when The characteristic peak of CaC03become weak with the aging time extending. CaHPO4·2H2O(brushite) formed on the surface.Increasing reaction temperature promote CaHPO4·2H2O, which the intermediate product transformation into hydroxyapatite. The higher the temperature is beneficial to the formation of hydroxyapatite.After aging, the diffraction peak of hydroxyapatite enhancement if improve the sdsorption amount of P. The particle size become large and the flaky morphology of hydroxyapatite become more clear.