EFFECTS OF FLUORIDE ON THE HYDROLYSIS OF CALCITE IN POTASSIUM DIHYDROGEN PHOSPHATE SOLUTION

抄録

Hydrolysis of calcite was investigated in 0.1M KH₂PO₄ solution containing potassium fluoride (0 and 1005 ppm as F) at 37°C by means of solution analyses (pH, Ca, P and F concentrations), X-ray diffraction, ³¹P magic angle spinning nuclear magnetic spectroscopy (MAS NMR), Fourier-transformed infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM). With the non-fluoride solution, octacalcium phosphate (OCP) was a main product of the hydrolysis for 10 days though some amount of calcite still remained. With increasing in fluoride concentration in the solution, OCP formed less and apatite phase formed instead. Remaining calcite was also decreased with fluoride concentration. Fluoride in the solution was completely absorbed in the product after hydrolysis for 10 days except for the highest fluoride concentration of 1000 ppm. FT-IR analysis showed that the apatite phase formed was fluoridated B-type carbonated apatite, in which CO₃^2- ion substituted for PO₄^3- ion. Fluoride ion was found to promote fluoridated carbonated apatite formation directly and/or through OCP transformation.