HYDROLYSIS OF CALCITE IN POTASSIUM PHOSPHATE SOLUTIONS

抄録

Hydrolysis of calcite was investigated in 0.1 mol/L KH₂PO₄/KB₂PO₄ solutions with various pHs between 4.5 and 8.5 at 60°C by means of solution analyses (pH, Ca and P concentrations), X-ray diffraction, Fourier-transformed infrared spectroscopy and scanning electron microscopy. Calcite was mostly hydrolyzed within several days and the final product was octacalcium phosphate (OCP) or apatite phase depending on their initial pHs. OCP was initially formed in the solution with lower pH and it was transformed into apatite phase with increasing in pH. Calcite was directly transformed into apatite in 0.1 mol/L K₂HPO₄ solution with the highest initial pH. These phenomena were probably related to solubility of apatite, OCP and calcite at pH during hydrolysis. FT-IR analysis showed that the apatite phase formed was B-type carbonated apatite, in which CO₃^2- ion substituted for PO₄^3- ion.