Formation of apatites in the system: KCl-CaCl_2-Ca_3(PO_4)_2-K_3PO_4-H_2O at 25 deg C

摘要

Apatites from the system, KCl-CaCl_2-Ca_3(PO_4)_2-K_3PO_4-H_2O at 25 deg C were obtained and characterized using x-ray diffraction, infrared absorption spectroscopy and chemical analysis. The crystallinity of the apatite depended on the initial solution composition and on the solution pH at equilibrium. Apatites poor in crystalinity were usually obtained from solutions with high pH. The maximum amount of chloride, Cl~- ion incorporated in the apatite crystals was about 5.0 wtpercent (1.4 M). This amount was higher than that obtained in previous preparations at 100 deg C by hydrolysis of CaHPO_4 or by precipitation method (about 3 wtpercent of 1 M); but lower than the amount for a fully substituted chlor-apatite, Ca_(10)(PO_4)_6Cl_2 which is 7.0 wtpercent (2.0 M). The incorporation of potassium in the apatite was limited to 1.2 wtpercent (0.3 M). Variations in a- and c-axis dimensions (increase and decrease, respectively) indicated a Cl-for-OH substitution: (Ca,K)_(10)(HPO_4,PO_4)_6(Cl,OH)_2. The incorporation of K~+ in these apatites appeared to very limited and not related to the incorporation of Cl~- when the pH effect is neglected.