Modeling of the synthesis conditions impact on the structure of calcium magnesium phosphates

Abstract

Calcium magnesium phosphates are widely used as bioceramics, sorbents, catalysts, cement, etc. Herein, calcium magnesium phosphates were obtained by chemical precipitation from a solution using dolomite as a source of calcium and magnesium, hydroxyethylidene diphosphonic acid as an inhibitor of crystallization. The chemical composition of synthesized samples was characterized with a molar ratio (Ca + Mg)/P of 1.29–1.52 and Mg/(Mg + Ca) of 0.54–0.65. The effect of various parameters (solution temperature, precipitator addition rate, duration of precipitate aging, solution addition sequence, and method of precipitation washing) on the chemical and phase composition, texture, and morphology of calcium magnesium phosphates by X-ray diffraction, Fourier transform infra-red spectroscopy, differential-thermal and thermogravimetric analyses, N2 adsorption-desorption, scanning electron microscopy, and fractional factorial experiments were studied. It was established that (i) the hydroxyethylidene diphosphonic acid addition, (ii) the sequence of adding reaction solutions, and (iii) the method of precipitation washing had the greatest influence on the chemical and phase composition of the obtained samples. The surface area and pore volume of calcium magnesium phosphates were significantly increased by the introduction of hydroxyethylidene diphosphonic acid up to 265 m2/g and 0.568 cm3/g, which makes it possible to obtain materials with a developed mesoporous structure for adsorptions application.