Crystallization of Calcium and Magnesium Phosphates from Solutions of Medium and Low Concentrations

Abstract Calcium phosphates are precipitated at 25 °C from solutions of medium (Ca = P = 50 mM) and low (Ca = P = 10 mM) concentrations in the presence of magnesium. Experiments are also performed with solutions in which Ca + Mg = P = 50 mM and Ca + Mg = P = 10 mM. An amorphous calcium phosphate, Ca3 (PO4)2 · nH2O, and brushite, CaHPO4 · 2 H2O, are the phases first nucleated. The phases occurring one year later are brushite in the more concentrated solutions, hydroxyapatite (Ca5OH(PO4)3) and whitlockite (Ca9MgH(PO4)7) in the others. Octacalciumphosphate, Ca8H2 (PO4)6 · 5H2O, occurs as transitory phase. The effects of concentration, pH, supersaturation and magnesium on the precipitation and evolution of calcium phosphates, and the conditions for phase stability are discussed.